Temp Handbook

Transcript

Numerous practical details provide the user with valuable information about temperature measurement in industrial applications. 03/TEMP-EN Rev. B 06.2008 Industrial Temperature Measurement Practice The most important methods for measuring temperature and their basic principles are described. Industrial Temperature Measurement Practice ABB Instrumentation This document together with all its contents is Copyright Protected. Translating, copying and dissemination in any form – including editing or abstracting – in particular reproductions, photo-mechanical or electronic, or storing in data processing systems or data networks without the written consent of the copyright owner is expressly forbidden and violators will be subject to legal actions. The issuer and the team of authors ask your understanding, because of the large quantity of data presented, that no guarantee for its correctness can be assumed. In cases of doubt, the original documents, regulations and standards apply. © 2008 ABB Automation Products GmbH Practices for Industrial Temperature Measurements Author Team: Karl Ehinger, Dieter Flach, Lothar Gellrich Eberhard Horlebein, Dr. Ralf Huck Henning Ilgner, Thomas Kayser Harald Müller, Helga Schädlich Andreas Schüssler, Ulrich Staab ABB Automation Products GmbH Introduction Automation is a growing, worldwide fundamental technology. The driving force for its growth are the variety of distinct economical and environmental requirements of the basic food and energy supply for an efficient, low emission utilization of natural resources and energy and the increased productivity in all manufacturing and distribution processes. As a result of the enormous growth of the markets in certain regions of the world and the increasing integration between them, new requirements and unexpected opportunities have arisen. The interaction between the actual measurement technology and the processes is continually becoming tighter. The transfer of information and quality evaluations have traditionally been a key requirement and a fundamental strength of the ABB-Engineers for worldwide optimization through automation. Temperature, for many processes in the most varied applications, is the primary measurement value. The wide spectrum of applications in which the measurement locations are usually directly in the fluid medium, often pose difficult requirements on the process technician. With this Handbook for industrial temperature measurements we are attempting to provide the technician with solutions to his wide variety of responsibilities. At the same time, it provides for those new to the field, insight into the basics of the most important measurement principles and their application limits in a clear and descriptive manner. The basic themes include material science and measurement technology, applications, signal processing and fieldbus communication. A practice oriented selection of appropriate temperature sensor designs for the process field is presented as well as the required communication capability of the meter locations. The factory at Alzenau, Germany, a part of ABB, is the Global Center of Competence for Temperature, with numerous local experts on hand in the most important industrial sectors, is responsible for activities worldwide in this sector. 125 years of temperature measurement technology equates to experience and competence. At the same time, it forms an important basis for continued innovation. In close cooperation with our customers and users, our application engineers create concepts to meet the measurement requirements. Our Sector-Teams support the customer, planner and user in the preparation of professional solutions. 5 The most modern developments, supported by a network of globally organized ABBResearch Centers, assure innovative products and solutions. Efficient factories and committed employees manufacture the products using the latest methods and production techniques. Competent and friendly technical advice from Sales and Service round out the ABB offering. We wish you much pleasure when reading this Handbook and that you may find success when applying the principles to practical applications. Thanks also the all the authors who have contributed to the creation of this book. We also look forward to your suggestions and comments, which are appreciated and can be incorporated in new technological solutions. “Power and Productivity for a better world“ Eberhard Horlebein PRU Temperature Director Product Management www.abb.com/instrumentation 6 Formula Symbols p Pressure (Pa, bar) V Volume (l, m3) n Material quantity (mol) R Gas Constant t Temperature (°C, °F, K, °N, °R) t90 Temperature per ITS-90 in °C (°F) T90 Temperature per ITS-90 in K Q Heat energy (J, Nm, Ws) Ll Spectral radiation density (W m-2 l-1) en Elementary thermal voltage (mV) Rt Resistance at the temperature t (Ω) R0 Resistance at the temperature 0 °C (°F) (Ω) α Slope coefficient of a Pt100 between 0 °C (32 °F) and 100 °C (212 °F) (K-1 or °F-1) δ Coefficient from the Callendar equation (K-2) β Coefficient per van Dusen for t < 0 °C (32 °F) (K-4) Abbreviations AISI American Iron and Steel Institute ANSI American National Standards Institute DKD Deutscher Kalibrier Dienst (German Calibration Service) JIS Japanese Industrial Standards NF Normalisation Francaise (French Standards) NAMUR Normungs-Ausschuss the Mess- and Regelungstechnik (Standards Commission for Measurement and Control Technology) NACE National Association of Corrosion Engineers ASME American Society of Mechanical Engineers MIL Military Standard 7 Page 1 125 Years of Competency in Temperature Measurement Technology at ABB . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 2 2.1 2.1.1 2.1.2 2.1.3 2.1.4 2.2 2.2.1 2.2.2 2.2.3 2.2.4 2.3 2.3.1 2.3.2 2.3.3 2.3.4 Introduction to Temperature Measurement Technology . . . . . . . . . . . . . 17 Historic Development . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 Heat and Temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 The Historic Development of the Thermometers . . . . . . . . . . . . . . . . . . . . . . 18 The Thermodynamic Temperature Scale . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 The International Temperature Scale of 1990 (ITS 90) . . . . . . . . . . . . . . . . . 23 Basics of Temperature Measurement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 The Physical Concept of Temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 The Technical Significance of Temperature . . . . . . . . . . . . . . . . . . . . . . . . . 25 The Thermoelectric Effect . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 The Temperature Dependent Ohmic Resistance . . . . . . . . . . . . . . . . . . . . . 29 The Principles of Temperature Measurement . . . . . . . . . . . . . . . . . . . . . . . . 33 Mechanical Contacting Thermometers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35 Electric Contacting Thermometers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36 Additional Contacting Measurement Principles . . . . . . . . . . . . . . . . . . . . . . . 37 Non-contacting Temperature Measurement . . . . . . . . . . . . . . . . . . . . . . . . . 38 3 Industrial Temperature Measurement Using Electrical Contacting Thermometers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40 Sensors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40 Thermocouples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40 Mineral Insulated Thermocouple Cables . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51 Thermocouple Wires and Compensating Cables . . . . . . . . . . . . . . . . . . . . . 55 Older National Standards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58 Measurement Resistors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62 Industrial Temperature Sensor Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76 Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76 Installation Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81 Process Connections Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85 Process Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87 Thermowell Designs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89 Corrosion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96 Material Selections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106 Ceramic Thermowells . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108 Application Specific Temperature Sensor Designs . . . . . . . . . . . . . . . . . . . 111 Dynamic Response of Temperature Sensors . . . . . . . . . . . . . . . . . . . . . . . 127 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 127 Step Response and Transfer Functions, Response Time and and Time Constants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 128 Establishing the Dynamic Values . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129 Influencing Factors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129 3.1 3.1.1 3.1.2 3.1.3 3.1.4 3.1.5 3.2 3.2.1 3.2.2 3.2.3 3.2.4 3.2.5 3.2.6 3.2.7 3.2.8 3.3 3.4 3.4.1 3.4.2 3.4.3 3.4.4 8 3.5 3.5.1 3.5.2 3.6 Aging Mechanisms in Temperature Sensors . . . . . . . . . . . . . . . . . . . . . . . 131 Drift Mechanisms for Thermocouples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131 Drift Mechanisms for Resistance Thermometers . . . . . . . . . . . . . . . . . . . . 143 Possible Errors and Corrective Measures . . . . . . . . . . . . . . . . . . . . . . . . . . 148 4 Non-Contacting Temperature Measurements in Field Usage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 154 Advantages and Uses for Applying Infrared Measuring Technology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 154 Fundamentals and Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 155 Determining the Emissivity Values . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159 Measuring Temperatures of Metals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 160 Measuring Temperatures of Plastics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 161 Measuring Temperatures of Glass . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 162 The Measuring Path . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 163 Stray Radiation and High Ambient Temperatures . . . . . . . . . . . . . . . . . . . . 165 Optic Radiation Input, Protection Glass and Window Materials . . . . . . . . . 166 Indication and Interfaces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 169 Application Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 170 4.1 4.2 4.2.1 4.2.2 4.2.3 4.2.4 4.2.5 4.2.6 4.2.7 4.3 4.4 5 5.1 5.2 5.3 5.4 5.5 5.6 5.7 5.8 5.9 5.10 Measurement Signal Processing and Evaluation . . . . . . . . . . . . . . . . . 171 Application of Transmitters in Temperature Measurements . . . . . . . . . . . . 171 Measurements of Thermal Voltages and Resistances . . . . . . . . . . . . . . . . 174 Power Supply of Temperature Transmitters . . . . . . . . . . . . . . . . . . . . . . . . 177 Design Principles for a Temperature Transmitter . . . . . . . . . . . . . . . . . . . . 178 Programmable Temperature Transmitters . . . . . . . . . . . . . . . . . . . . . . . . . 184 Communication Interfaces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 188 Temperature Transmitters in Explosion Hazardous Areas . . . . . . . . . . . . . 194 Electromagnetic Compatibility (EMC) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 201 Temperature Transmitters using Interface Technology . . . . . . . . . . . . . . . . 203 High Accuracy Temperature Measurements with Programmable Transmitters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 206 6 Accuracy, Calibration, Verification, Quality Assurance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 209 Accuracy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 209 Basic Fundamentals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 209 Determining (Estimating) the Measurement Uncertainties . . . . . . . . . . . . . 210 Measurement Uncertainty Estimations using a Practical Example . . . . . . . 213 Error Effects for Temperature Measurements . . . . . . . . . . . . . . . . . . . . . . . 215 Calibration and Verification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 224 Definitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 224 Calibration Methods for Temperature Sensors . . . . . . . . . . . . . . . . . . . . . . 225 The Traceability of the Calibration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 226 Suitable Standards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 227 The Water Triple Point . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 228 6.1 6.1.1 6.1.2 6.1.3 6.1.4 6.2 6.2.1 6.2.2 6.2.3 6.2.4 6.2.5 9 6.2.6 6.2.7 6.2.8 6.2.9 6.2.10 6.3 Documenting the Calibration Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 229 The German Calibration Service (DKD) . . . . . . . . . . . . . . . . . . . . . . . . . . . 231 DKD-Laboratories at ABB . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 232 Conducting a Calibration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 234 User Advantages offered by the DKD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 235 Quality Assurance Measures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 239 7 7.1 7.2 7.3 7.4 7.5 Explosion Protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 244 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 244 Terms and Definitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 245 Types of Protection in Europe and in North America . . . . . . . . . . . . . . . . . 252 Marking of the Apparatus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 256 Evidence of the Intrinsic Safety . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 259 8 SIL - Functional Safety in Process Automation . . . . . . . . . . . . . . . . . . . 261 9 Standards and Regulations for Temperature Measurements . . . . . . . . 263 10 Appendix 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 267 11 Appendix 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 271 12 Bibliography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 276 13 Basic Values for Thermocouples and Resistance Thermometers . . . . 280 10 1 125 Years of Competency in Temperature Measurement Technology at ABB Significant activities at ABB in industrial temperature measurements date back to 1881. Fig. 1-1: G. Siebert factory Wilhelm Siebert started in his family’s cigar rolling factory G. Siebert in Hanau, Germany, by melting platinum and mechanically working the material into wires. He learned the art of “Assaying“ at the plant of Dr. Richter & Co. in Pforzheim, Germany. In 1905 Degussa became a participant in the G. Siebert company. Later on the treatment of Platinum and Platinum/Rhodium wires for thermocouples was further developed here. Between 1860 and 1900 the development of electrical temperature measurements began. This laid the cornerstone for present day process automation and far distance transfer of measurement signals. During 1883...1891 another branch of the long existing temperature measurement technology resulted from the invention by Prof. Ferdinand Braun (1850...1918/Nobel Prize in Physics 1909) of the Braun Pyrometer. Fig. 1-2: Electrical precision-pyrometer according to Braun 11 A protected Platinum wire was used as sensor which was connected across a Wheatstone Bridge to galvanometer. The measurement value could be read directly from a calibrated scale in °C, without calculations, due to the changing resistance of the bridge. This instrument was used to measure temperatures to 1500 °C (2732 °F) in ovens and boilers. In 1893 the Telethermometer was invented, e.g. “to remote control the heater from an office”. It was used to measure the temperature in rooms, greenhouses, oasts, drying chambers or ovens in the Ceramic industry. Fig. 1-3: Telethermometer Further developments in temperature sensors during the time span 1894…1974: Fig. 1-4: 12 Temperature sensor history up to 1974 Over a span of approximately 50 years, beginning in 1939, transmitters were developed to improve the transmission of the measured temperatures. Development steps for temperature transmitters during the time span 1939…1985: Fig. 1-5: Temperature transmitter history up to 1985 From 1950...1954 the Degussa company developed a high temperature capable thermocouple “PtRh18“ with long term stability, which later, in 1967...1974, was certified by the American Standards Association Committee C96 (ISA) as “PtRh18“ Thermocouple Type B. About 1960 the Degussa company in Hanau, Germany, began series manufacturing of new temperature measurement wire resistors. 1962 Obrowski and Prinz from Degussa defined the reference function and basic value tables for the “PtRh18“ thermocouples. 13 In 1960 Degussa began manufacturing thermocouple wires and mineral insulated cables. By 1970, Degussa had technically improved this process which led to a volume increase. Fig. 1-6: Cross section of a mineral insulated cable 1977 Degussa further expanded their temperature measurement technology activities by acquiring Bush Beach Engineering Ltd. in England, who brought with them vast application experience in the oil and gas industry sector. 1978 one of the first worldwide electronic transmitters for mounting directly in the temperature sensor head was developed. It can be installed in explosion hazardous areas. After intensive tests in the Degussa factory, the transmitter was introduced into the market at leading customers in the process industries. After some initial concerns, the product received enormous acceptance. The new transmitter began replacing existing technologies. Fig. 1-7: First transmitter for mounting in the sensor head (TR01) 1988 saw the introduction of an industrialized version of fiber optic temperature measurement instruments, which, e.g., can make temperature measurements in microwave systems. 14 1989 Degussa founded a new subsidiary and brand, SENSYCON in Hanau, Germany. 1991 Hartmann & Braun acquired SENSYCON. 1994 SENSYCON temperature measurement technology manufacturing was moved from Hanau to Alzenau, Germany, about 15 km (10 mi) away. 1995 the first HART-sensor head transmitter was developed. 1996 Elsag Bailey acquired Hartmann & Braun including the temperature measurement systems from SENSYCON. 1998 the first fieldbus capable temperature transmitter was developed. 1999 ABB acquired Elsag Bailey, whereby SENSYCON temperature measurement technology achieved a worldwide leading role in the instrumentation sector. 2006 new powerful and state of the art temperature transmitters designated TTH300 for sensor head mounting and TTF300 for field mounting were introduced to the market. Fig. 1-8: Transmitters TTH300 and TTF300 15 The temperature sensor series – SensyTemp TSP100 and SensyTemp TSP300 for the process industries represent the present state of the technology. Fig. 1-9: Temperature sensor series SensyTemp TSP “With a Tradition for Innovation“ ABB in the last 125 years has actively lead the way in temperature measurement technology. The goal is to challenge the measurement technology and improving the efficiency to satisfy the global requirements of the customers. 16 2 Introduction to Temperature Measurement Technology 2.1 Historic Development 2.1.1 Heat and Temperature Only in recent times has the heat phenomenon been studied systematically. Previously, man was satisfied with a few qualitative, practice oriented experiences relative to heat. With the invention of the steam engine, the interest of the scientists in the heat phenomenon increased. Joseph Black was the first to realize the difference between heat and temperature. In 1760 he declared that applying the same heat to different materials results in different temperatures. Initially heat was considered to be a material substance, which could be added or removed from a material or, could be transferred from one material to another. This substance was named Caloric. When wood is burned, according to this theory, the Caloric content in the wood is transferred to the flame, from there further on to the boiler set over the flame and then to its contents. When the water in the boiler becomes saturated with caloric, it is converted to steam. Only toward the end of the 18th century did observations lead Benjamin Thompson (Count Rumford) and Humphry Davy to an alternate theory, which described heat as a cyclic phenomenon. The theory that heat is a form of energy is attributed, among others, to the work of the physicist Sadi Carnot, who is considered the father of scientific thermodynamics. He investigated early in the 19th century, the motion of heat from the viewpoint of how the energy stored in the steam is converted to mechanical work. The investigation of the reverse process, namely, how work is converted to heat, led to the basic thought that energy is conserved, i.e., it can neither be created nor destroyed. This approach led to the law of conservation of energy (First Law of Thermodynamics). The prerequisite for a clear understanding of heat requires an exploration of the atomic structure of materials. In the middle of the 18th century, Maxwell and Bolzmann developed the mathematical basics and formulated the kinetic gas theory. In this theory, heat is equated to molecular movement. The thermal motions of a molecule are totally random and independent of each other. Their velocity distribution however can be defined by strict mathematical laws. The question regarding the concept of temperature, however, was still not conclusively answered. 17 Maxwell defined the temperature of a body as a thermal property, which makes it possible to transfer heat (energy) to or from another body. From a measurement viewpoint, temperature is then the physical property which provides information about the energy content of a system and thereby describes the heat energy content (degree of heat, heat status). For Maxwell temperature was the measure of the average kinetic energy of the molecules which constitute the substance, and the measurement of the temperature provides a mean to determine the energy (heat) content of the substance. The term temperature supposedly originated from the Latin word “tempera“, which means "moderate or soften". If one wants to determine the temperature of a system, it follows that the velocity of the molecules should be selected as the value to be measured. Based on this approach, a system will have no heat content when the molecules have lost all their kinetic energy, i.e., are at rest. This condition could be defined as “absolute heatlessness“. Since the observation and measurement of the motion of the molecules is impractical and unrealistic, it is unusable in practice. Therefore to make practical temperature measurements, other methods must be employed. Utilized are the effects that the heat (energy) has on other properties of the system, e.g. geometric expansion when heat is applied. Human senses evaluate the temperature of a body only subjectively. Even so, the terms “hot“, “warm“, “cold“ or “ice cold“ mean something to everyone based on their own experience and are relatively useful for comparison purposes. This also applies to visual terms such as “red hot“ or “white hot“. The exact assignment of a temperature value (quantification) however eludes the subjective possibilities of man. For an objective and reproducible measurement of the temperature of a body, a suitable measurement instrument is required. 2.1.2 The Historic Development of the Thermometers Instruments to measure the temperature generally are called thermometers. What the relationship to temperature was that the old Egyptians had, has not been handed down. No instrument was ever discovered in any of the Egyptian drawings from which one can infer that it was utilized for temperature measurement. But it is quite clear that the old Egyptians understood how to make ice (evaporative cooling). The oldest known instrument for “measuring“ temperature was based on the expansion of air and is attributed to the Greek Heron of Alexandria (about 120 BC). It was not a Thermo “Meter“ in the true sense since it did not have a scale. Thermometers based on the same principle (the so called Thermoscopes) appeared again at the beginning of the 17th century in Europe. 18 Individuals who have been identified as being associated with the continued systematic development of thermometers, are Satorio Santorre, Giovanfrancesco Sagredo, Galileo Galilei, Benedetto Castelli and Vicencio Viviani. That all these names have an Italian heritage can be traced to the fact that the glass blowing art was most developed in Italy at that time. a) Fig. 2-1: b) c) a) Early air thermometer (thermoscope) with compass to measure the changes; b) Early florentine thermometer; c) Typical thermometer around 1750 The step from Thermoscope to liquid filled thermometer is attributed to Grand Duke Ferdinand II of Toscany, a student of Galilei. In 1654 he manufactured liquid alcohol filled thermometers (so called Florentine Thermometer) made with a bulb and capillary (including a scale with 50 units). The scales were aligned by comparing the instruments among each other. Antonio Alemanni around 1660 built a thermometer with a length of 108 cm (42.5“) which was divided into 520 units. The capillary for this thermometer was like a coil. This instrument is still available today. In 1701 Sir Isaac Newton described a liquid oil filled thermometer and a calibration method at the temperature of freezing water, (0 °N), and the temperature of blood (12 °N). At the beginning of the 18th century, the Dutchman Musschenbroek was apparently the first to conceive the thought of using the expansion of metals for measuring temperatures. 19 Around 1703 the Frenchman Amontons designed a gas thermometer with a constant volume and postulated, that heat was a type of movement. He was the first to mention the concept of a zero temperature point in nature, which would be reached if all movement was completely at rest. In 1714 Fahrenheit, a glass blower from Danzig in Poland, appreciably improved the existing liquid filled thermometers and implemented the initial step to a measurement instrument. He initially filled the thermometer with alcohol and later with Mercury, which had the advantage of not wetting the glass capillary and which also could be used up to the boiling point of water. These “Fahrenheit Thermometers“ had a scale which was reproducible because Fahrenheit introduced three fixed values: • 0 for the temperature of an ammonium chloride mixture, • 4 for the temperature of melting ice and • 12 for the temperature of the human body. It was desirable at that time to define the spacing between the fixed values as 12 in accordance with the duodecimal numbering system. Since the individual values were unsuitably large, they were halved a number of times until each of the original degrees corresponded to 8 degrees. The result was that the freezing point of water now occurred at a value of 32 and body temperature at a value of 96. Later Fahrenheit used the boiling point of water as the upper fixed value and established its value as 212 °F by extrapolating the scale from 0 °F to 32 °F. He maintained these values, whose difference is 180 °F, for all later measurements. Closer observation resulted in a body temperature of 98 °F in a healthy individual. This scale can still be found in a number of countries today. Around 1715 the Frenchman Réaumur defined a temperature scale which bears his name. In this scale the ice point is 0 °R and the temperature increase which an alcoholwater mixture (20 % water) experiences as its volume increases by 0.1 % is defined as 1 °R. Transferring this scale to a Mercury thermometer resulted in a value of 80 °R for the boiling point of water. In 1740 the Swede A. Celsius defined a scale with 100 graduations in which the freezing point of water is 0 and its boiling point is 100. Three years later the Celsius scale was established by his student Carl von Linné, which exists to the present day, with the conditions 0 °C for the freezing point and 100 °C for the boiling point. In the middle of the 18th century, the temperature measurement (Thermometry) was commonly introduced to the science as measurement technology. The maximum measurable temperatures at that time were about 300 °C (572 °F). The desire to measure temperatures of molten metals (metallurgy) led to the development of additional measurement methods. 20 The important milestones of the later developments: 1800 Construction of a simple bimetal thermometer by A. L. Brèguet. 1818 Discovery of the relationship between the electrical resistance of an ohmic conductor and temperature by H. Cr. Oersted. 1820 Description of the effect of thermoelectricity by Seebeck. 1821 Construction of the first thermocouple by H. Davy. 1840 Development of a thermocouple made of Nickel-Silver and iron for measuring body temperature by Chr. Poggendorf. 1852 Establishment of a thermodynamic temperature scale, which is independent of all material properties and is based on the 2nd Law of Thermodynamics by William Thompson (later Lord Kelvin). 1871 Construction of a Platinum resistance thermometer by Werner von Siemens 1885 Further development of the Platinum resistance thermometer into a precision thermometer, including higher temperature use by H.L. Callendar 1887-1889 Construction of thermocouples for technical temperature measurements by H. le Chatelier and C. Barus 1892 Development of the first usable spectral pyrometer by H. le Chatelier. The problems which scientists in the 18th century had in using their instruments and the transfer of their measurement results were clarified by statements made by René-Antoine Ferchault de Réaumur in the year 1730: “The thermometers are without a doubt one of the nicest inventions of modern physics, and they have also contributed most to its progress. One likes very much to observe thermometers in order to determine the temperature of the air; namely, one uses the instrument when it is too hot or too cold for comfort. If on the one hand one realizes how amusing and useful this instrument is, one knows on the other hand its imperfections. The action of all thermometers is different. Finally, one understands only the thermometer which one has observed for many years. All others remain incomprehensible.“ 21 2.1.3 The Thermodynamic Temperature Scale The decisive starting point for a general temperature scale is the indispensable requirement for a reproducible scale, independent of the special characteristics of the materials used. In addition, the entire temperature range must be applicable without restrictions, actually, from the lowest to the highest temperatures. This is the only way to ensure the transferability of measurement results. The path to this goal is provided by the basics of thermodynamics and was first followed by Lord Kelvin in the year 1852. Thermodynamics describes the relationship between condition changes of materials and temperature, allowing the temperature to be determined when any of these condition changes can be measured. The definition of the thermodynamic temperature scale is derived from the 2nd Law of Thermodynamics using the Carnot Cycle. The starting point is the fact that the temperature change in a perfect gas under constant volume and pressure conditions is a function only of the heat quantity Q added or removed and is proportional to it. A gas volume which has no heat energy content has reached its lowest thermodynamic energy level. From this viewpoint Kelvin postulated the existence of a lowest possible temperature, the absolute zero, and assigned the value 0 to that condition. By defining the scale in this manner, negative temperatures cannot exist, and therefore, the temperature scale proposed by Kelvin has an absolute character, an absolute temperature scale. Thermodynamic temperature conditions are defined by the absolute temperature value with units of "Kelvin" (K). The Kelvin units are one of the primary units which exist today in the International System of Units (SI). For the practical determination of the temperature, the quantities of heat added or removed during the process cycle must be determined experimentally. The required procedure is technically very difficult to solve. Using the equation of state for a perfect gas as a basis p·V=n·R·T which defines the relationship between the thermodynamic values pressure (p), volume (V), temperature (T) of a quantity (n) of a gas and the ideal gas constant (R), it can easily be shown that the thermodynamic temperature (T) can be calculated from the measurement of one of the other variables (pressure or volume), provided that the other values remain constant. The scientific significance of the thermodynamic temperature scale achieved even greater importance, when L. Bolzmann and M. Planck found a method to include light-radiation of very highly heated substances in the basic equations of thermodynamics. 22 2.1.4 The International Temperature Scale of 1990 (ITS 90) In metrological practice, thermodynamic temperatures are measured with a gas thermometer, or at higher temperatures, using radiation pyrometers. The first valid, generalized definition for a temperature scale, was for normal Hydrogen in the year 1889. It was based on using a gas thermometer as the measuring instrument. The effort for this measurement method can hardly be justified for practical measurements. Therefore at the beginning of the last century the first experiments were conducted to define an easily representable, and thereby practical temperature scale, which would be in essential agreement with the thermodynamic temperature scale. The first version of this scale was the “International Temperature Scale of 1927“ (ITS-27). Based on the scales ITS 48 and IPTS-68, the EPT-76 was published in 1975. Further basic theoretical and experimental investigations of a thermodynamic temperature scale in the subsequent years led to a new and improved formulation which has been valid since 1990, the “International Temperature Scale of 1990“ (ITS-90). Temperatures measured per ITS-90 are designated T90 for temperature values in K and t90 for temperature values in °C. ITS-90 defines a temperature scale in the range from 0.65 K to far above 3000 K. It is divided into ranges, some of which overlap, for which defined temperature points the “Normal Instruments“ (to picture the ranges between the fixed points), and equations are prescribed for extrapolation. In the temperature range to 1357 K (1084 °C/1983 °F), for thermometric measurements 16 fixed points are used for the defining and mathematical relationships are given with which temperature values between two of these fixed points can be determined. The fixed points are the phase equilibrium values for extremely pure substances, at which the phase change (liquid to gas or liquid to solid) occurs at constant temperature values. Numerical values are assigned to these temperatures that best agree with the thermodynamic measurements. The most important fixed point in ITS90 is the triple point of water, at which solid, liquid, and gaseous water coexist in equilibrium and which occurs at T90 = 273.16 K or t90 = +0.01 °C. 23 Equilibrium Conditions T90 / K t90 / °C Vapor pressure of Helium 3...5 -270.15...-268.15 13.8033 -259.3467 ~ 17 ~ 20.3 ~ -256.15 ~ -252.85 Triple point of Neon 24.5561 -248.5939 Triple point of Oxygen 54.3584 -218.7916 Triple point of Argon 83.8058 -189.3442 Triple point of Mercury 234.3156 -38.8344 Triple point of equilibrium Hydrogen Vapor pressure of equilibrium Hydrogen Triple point of Water (329 hPa) (1022 hPa) 273.16 0.01 Melting point of Gallium 302.9146 29.7646 Solidification point of Indium 429.7485 156.5985 Solidification point of Tin 505.078 231.928 Solidification point of Zinc 692.677 419.527 Solidification point of Aluminum 933.473 660.323 Solidification point of Silver 1234.93 961.78 Solidification point of Gold 1337.33 1064.18 Solidification point of Copper 1357.77 1084.62 Tbl. 2-1: Defined fixed points for ITS-90 In the temperature range above 1357 K, ITS-90 is defined using the Planck Radiation Formula (black body radiation). Dependent on the type of normal instrument (interpolation instrument), ITS-90 is divided into three temperature ranges: In the range from 0.65 K to 24.55 K the steam and gas pressure thermometers of various designs are used as the normal instruments. In the range from 13.8 K to 1234.93 K the Platinum resistance thermometer is used as the normal instrument. Platinum normal resistance thermometers (so called ITS-90Thermometers) must satisfy very high technical requirements and are exceptional precise instruments. For practical applications in calibration laboratories there also exist so called secondary thermometers, which are less precise but possess better mechanical stability. In the range above 1234.93 K (solidification point of silver) radiation pyrometers are the normal instrument. 24 2.2 Basics of Temperature Measurement 2.2.1 The Physical Concept of Temperature Temperature can be viewed as a measure of the statistically determined average velocity of the molecules in a body and thereby it is kinetic energy. In order to warm a body from temperature T1 to T2, energy must be added. How much depends to some degree on the number of molecules (the amount of material) and their size. In order to describe the thermodynamic energy level of the body by its temperature, the velocity distribution of its molecules must be determined based on statistical principles. Thus the laws of Thermodynamics only apply when a sufficiently large number of molecules are present. In modern Thermodynamics the temperature of a body is described as a type of heat potential, with the property to add or remove heat (heat sources and heat sinks). So the temperature gradient (the direction of the greatest temperature difference) defines the direction of the greatest heat effect within a body. The direction of the heat effect is always from the higher to the lower temperature. Although this statement may appear trivial, it is of fundamental importance when using contacting thermometers. 2.2.2 The Technical Significance of Temperature Temperature is one of seven basic values in the current SI-System of Units and at the same time, probably the most important parameter in measurement technology. Temperature measurements can be roughly divided in three application categories: • Precision temperature measurements for scientific and basic research • Technical temperature measurements for measurement and control technology • Temperature monitoring using temperature indicators. The goal of the technical temperature measurement is to strive for a practical solution for every application requirement, which should be an optimum for the required measurement accuracy at acceptable costs. Of the many methods used for temperature measurements, and of those described in detail in this handbook, the electrical temperature sensors have a dominant position in the measurement and control technology. They convert the measured value into an electrical signal. 25 2.2.3 The Thermoelectric Effect The Seebeck-Effect together with the Peltier and Thomson Effect belongs to a group of thermoelectrical effects. Its discovery has been attributed to T. J. Seebeck. In the year 1822 he published the observation that a current can be recognized in an electrical circuit comprising two dissimilar metal conductors, when each of the two connection points of the conductors is at a different temperature level. The cause of this thermal current is the generation of a thermal voltage (thermal force) whose magnitude is proportional to the temperature difference between the hot and cold ends and additionally is a function of the applied material combination. As early as 1826 A. Becquerel recommended a Platinum-Palladium thermocouple for temperature measurement. Theory of the Thermoelectric Effect The temperature dependence of the electron potentials, which cause a charge shift in an electrical conductor when it is placed in a nonhomogeneous temperature field, is considered today as the origin of the thermoelectrical effects. Simply stated: the free charge carriers (electrons) in a one side warmed conductor distribute themselves in a nonhomogeneous manner so that a potential difference (thermal voltage) is generated. At the cold end more electrons accumulate while at the hot end, the electron quantity is decreasing. Therefore it is plausible that even in a single electrical conductor in a temperature field a thermal voltage is generated. This thermal voltage can only be measured if a second conductor is added (thermocouple), provided that the temperature dependence of this effect is different in the second conductor from that in the first conductor (see Fig. 2-2). 26 Cu 20 °C 20 °C Uniform electron distribution for a homogeneous temperature distribution in a conductor a) 20 °C 988 °C + b) U - 20 °C Electron depletion at the hot end 988 °C NiCr + 20 °C NiAl - Fig. 2-2: 40.0 m V c) Dissimilar electron concentration in the circuit consisting of two different conductors Generation of a thermal voltage If the thermal voltage effects in both conductors are the same (e.g. for identical conductor materials), then the effects cancel each other and no thermal voltage can be measured. It is important that this thermal voltage effect is the result of a volume diffusion effect of the charge carriers and not a contact voltage phenomenon between the two materials. Therefore it is understandable that the thermal voltage is produced along the entire length of the thermocouple and not only at the “hot“ connection between the two legs. 27 Principles The Law of Linear Superposition (Superposition Principle) applies to thermocouples, if one visualizes a thermocouple as a series circuit consisting of a (infinite) number of individual elements. The thermal voltage generated in the thermocouple is the same as the sum of the thermal voltages generated in the individual elements. An additional hot zone added between the hot and the cold end therefore has no effect on the resultant thermal voltage, since the additional added thermal voltages cancel each other. e 1000 °C (1832 °F) 800 °C (1472 °F) e1 600 °C (1112 °F) 20 °C (68 °F) e2 e3 e = e1 + e2 + e3 Fig. 2-3: Superposition of thermal voltages The Law of Homogeneous Temperature states that the thermal voltage in a conductor in a homogeneous temperature field is equal to zero. Therefore the thermal voltages in a thermal circuit (series circuit) made up of any number of different material combinations is also equal to zero, if all the components are at the same temperature. For practical application this means that even nonhomogeneous thermocouple wires or plug connections of different materials have no effect as long as no temperature difference exists at that location. Therefore design care must be exercised, especially in the area of plug connections. E.g. a massive thermal insulation (isothermal block) may be used to achieve a homogeneous temperature. The Law of a Homogeneous Circuit states, that the temperature of homogeneous conductors between two measurement locations does not have any effect on the resultant thermal voltage. Of greater importance is the reverse conclusion: if the resultant thermal voltage changes through regions of nonhomogeneous temperatures (with constant hot and cold ends) then the conductor material in not homogeneous. Nonhomogeneous conditions can occur during production, or already during use (mechanical or 28 thermal overstressing) of thermocouples. Of course, the nonhomogeneous conditions will have no effect if they are in a homogeneous temperature field. d a c b e Fig. 2-4: Thermal circuit: c = Metering point; a, b = Thermal legs; d, e = Reference junction Derived Fundamental Conclusions for the Use of Thermocouples: • In a homogeneous temperature field no thermal voltage is generated. • In a homogeneous conductor the magnitude of the thermal voltage is only a function of the temperature difference between the ends of the conductor. • The junction of a thermocouple does not generate any thermal voltages. 2.2.4 The Temperature Dependent Ohmic Resistance The electrical conductivity of all metals increases greatly with decreasing temperatures. The electrical conductivity of a metal is based on the movement of its conduction electrons, the so called electron gas. It consists of the outer electrons of the metal atoms. The atoms of the metal form a dense ion lattice structure. The lattice atoms oscillate. As the temperature increases the oscillation amplitude increases. This impedes the motion of the conduction electrons, resulting in a temperature dependent increase of the electrical resistance. This effect is described as a positive temperature coefficient (Tc) of the electrical resistance. It is utilized as the measurement effect. Additionally, flaws in the crystalline structure of the metal interfere with the electron flow. These flaws include foreign or missing lattice electrons, lattice faults at the particle boundaries and atoms in the lattice interstices. Since these interference effects are temperature independent, they result in an additional constant resistance value. 29 Therefore the relationship between temperature and electrical resistance is no longer linear, but can be approximated by a polynomial. Metals, which are suitable for use as resistance thermometers, should have a high Tc, so that the temperature dependent resistance changes are pronounced. There are additional requirements for the materials including high chemical resistance, easy workability, availability in a very pure state and excellent reproducibility of the electrical properties. Also the resistance materials may not change their physical and chemical properties in the temperature range in which they are to be used. Freedom from hysteresis effects and a high degree of pressure insensitivity are further requirements. Platinum, in spite of its high price, has become dominant as the resistance material for industrial applications . Alternative materials such as Nickel, Molybdenum and Copper are also used, but play a subordinate role at this time. 30 Platinum Resistance Thermometer Curves For Platinum the resistance to temperature relationships are especially easy to describe. A polynomial of this form suffices: Rt = R0 (1 + At + Bt2) Rt = R0 (1 + At +Bt2 +C(t-100)t3) for t ≥ 0 °C for t < 0 °C (1) (2) The value R0 is the resistance of the thermometer at 0 °C. The coefficients A, B and C, as well as all the other important properties which the Platinum resistance thermometers must satisfy are contained in Standard EN 60751. Callendar in 1886 had already formulated the relationship as a quadratic equation for temperature ranges > 0 °C. He first defined by using a strictly linear approach similar to that for gas thermometers, a so called Platinum temperature tp using the expression: t p = 100 × 1 R 1 Rt − R0 = × − R100 − R0 α R0 α (3) If one substitutes for α the average temperature coefficient between 0 °C and 100 °C, the equation gives a linear relationship between the resistance Rt and the temperature tp, in which tp not only agrees at 0 °C but also at 100 °C with the actual temperature t. For all other temperatures the calculated value of tp differs from the true temperature t. By introducing a second constant δ, the differences between the true temperature t and the Platinum temperature tp are taken into account: ⎛ ⎛ t ⎞ ⎛ t ⎞⎞ ⎟⎟ ⎟ × ⎜1 − Rt = R0 × ⎜1 + αt + αδ × ⎜ ⎝ 100 ⎠ ⎝ 100 ⎠⎠ ⎝ (4) This gives the “historical“ form as: ⎡⎛ t ⎞2 ⎛ t ⎞⎤ ⎟⎥ ⎟ −⎜ t − t p = δ × ⎢⎜ ⎣⎝ 100 ⎠ ⎝ 100 ⎠⎦ (5) This equation is known as the Callendar-Equation. The basic Callendar-Equation however, leads quickly to appreciably large errors for temperatures < 0 °C. The equation was improved by van Dusen in 1925 by the introduction of an additional correction factor with a constant value β (β is equal to zero for temperatures ≥ 0 °C). This modified equation is known as the Callendar-van Dusen-Equation. 31 From a mathematical standpoint, there are no differences between the curves in the DIN EN standards and Callendar-van Dusen-Equation. In both cases the curves are defined by three or four (at t < 0 °C) coefficients. It is relatively simple to convert the constants A, B, C into a, d and b. For years the formulation of Callendar-van Dusen enjoyed great popularity because of the simplicity by which the constants can be determined directly by calibrating at different temperatures (0 °C, 100 °C etc.). Furthermore, the parameters α and δ can essentially be considered to be material properties. In this case, the α-value provides information about the purity of the used Platinum and the δ-value about the actual mechanical construction of the thermometer (voltage freeness). Since the introduction of ITS-90, the boiling point of water (100 °C) is no longer a defined point in the temperature scale, and since that temperature is essential for determining the α-value in the Callendar-van Dusen equation, this formulation has lost its significance in recent times. Typically, the curves today are defined by equations (1) and (2), with the coefficients published in the Standard EN 60751: A = 3.9083 x 10-3 K-1 B = -5.775 x 10-7 K-2 C = -4.183 x 10-12 K-4 32 2.3 The Principles of Temperature Measurement The development of temperature measurement has and is occurring in parallel with the technological developments. Thereby only a portion of the new measurement methods have replaced the older ones. They have actually expanded their scope allowing temperature measurement to be made in areas where in the past none or only very restricted ones were possible. In the following table a number of measurement methods will be presented in condensed form together with their application ranges and significance. The table below is based on the temperature measurement methods described in VDI/VDE 3511 Sheet1) Measurement Methods Range Error Limits from to °C (°F) Mechanical Thermometers Liquid filled glass thermometer Non-wetting liquid Wetting liquid -38 (-36) -200 (-328) 630 (1166) according to DIN 16178 210 (410) Sheet 1 Indicator Thermometers Bimetal thermometer Rod expansion thermometer Liquid filled spring thermometer Vapor pressure spring thermometer -50 (122) 400 (752) 1...3 % of the indicator range 0 (32) 1000 (1832) 1...2 % of the indicator range -30 (-22) -200 (-328) 500 (932) 1...2 % of the indicator range 700 (1292) 1...2 % of the scale length Thermocouples Cu-CuNi, Type U, T -200 (-328) Fe-CuNi, Type L, J -200 (-328) NiCr-Ni, Type K, NiCrSi-NiSi, Type N PtRh-Pt, Type R, S 10 % Rh (S); 13 % Rh (R) Pt Rh30-PtRh6, Type B 600 (1112) 0.75 % of the reference value 900 (1652) of the temperature, at least according to EN 60584 0 (32) 1300 (2372) 0 (32) 1600 (2912) 0.5 % of the reference value of the temperature, at least 0 (32) 1800 (3272) according to EN 60584 Resistance Thermometers with Metal Resistors Pt-resistance thermometer Ni-resistance thermometer Tbl. 2-2: -200 (-328) 1000 (1832) 0.3...4.6 °C (32.54...40.28 °F) depending on the temperature (EN 60751) -60 (-76) 250 (482) 0.4...2.1 °C (32.72...35.78 °F) depending on the temperature (according to DIN 43760) Measurement methods 33 Measurement Methods Range Error LImits from to °C (°F) Semiconductor Resistance Thermometers Hot wire resistance thermometer, thermistor -40 (-40) -60 (-76) -100 (-148) Cold wire resistance thermometer Silicon measurement resistor 180 (356) 0.1...1 °C (0.2...2 °F); 200 (392) 0.5...2.5 °C (1...5 °F) 400 (752) depending on the temperature 200 (392) 2...10 °C (4...18 °F) -70 (-94) Semiconductor diodes/integrated temperature sensor 175 (347) 0.2...1 °C (0.4...2 °F) 160 (320) 0.1...3 °C (.02...6 °F) depending on the temperature Radiation Thermometers Spectral pyrometer 20 (68) 5000 (9000) 0.5...1.5 % of the temperature, but at least 0.5...2 °C (1...4 °F) in the range from -100...400 °C (-148...752 °F) Infrared radiation pyrometer -100 (-148) 2000 (3600) 0.5...1.5 % of the temperature, but at least 0.5...2 °C (1...4 °F) in the range from -100...400 °C (-148...752 °F) Total radiation pyrometer -100 (-148) 2000 (3600) 0.5...1.5 % of the temperature, but at least 0.5...2 °C (1...4 °F) in the range from -100...400 °C (-148...752 °F) 150 (302) 3000 (5400) 0.5...1.5 % of the temperature, but at least 0.5...2 °C (1...4 °F) in the range from -100...400 °C (-148...752 °F) -50 (-58) 1500 (2900) 0.5...1.5 % of the temperature, but at least 0.5...2 °C (1...4 °F) in the range from -100...400 °C (-148...752 °F) Ratio pyrometer Thermography instrument Quartz thermometer Thermal noise thermometer -80 (-112) -269 (-452) Ultrasonic thermometer Gas thermometer 250 (482) Resolution 0.1 °C (0.2 °F) 970 (1778) 0.1 % 3300 (6000) approx. 1 % -268 (-450) 1130 (2066) depending on design Optical Methods Fiber optic luminescence thermometer Fiber optic measurement system based on Raman-Radiation Tbl. 2-3: 400 (752) 0.5 °C (32.9 °F) 600 (1112) 1 °C (33.8 °F) Continuation – measurement methods A differentiation is made between contacting temperature measurement methods and non-contacting measurement methods. The contacting measurement methods, which are dominant in industrial temperature measurement technology, can be further subdivided into mechanical and electrical contacting thermometers. 34 2.3.1 Mechanical Contacting Thermometers The expansion of gases, liquids and solids as the temperature increases is experienced daily. To use this effect for temperature measurement in practice, the specific properties of the material have to be taken into account. Considering a solid body, the length change (dL) of a bar exposed to a temperature change (dt) as a first approximation is proportional to the bar length (L): dL = a x L x dt The proportionality factor a (linear thermal longitudinal expansion coefficient) is a property of the specific material. The integration of this equation, beginning with the length of the bar at a given temperature, gives the length of the bar at temperature t. Since the proportionality factor a can only be considered as linear over small temperature ranges, higher order terms must be included in the calculation for larger temperature differences. The technical application of this sensor principle leads to bar and bimetal thermometers. They are installed in industrial applications where local indicators are all that is required. The dependence of a liquid volume on temperature can be utilized in an analogous manner. In this case, a cubic expansion coefficient ß applies. This coefficient is also a property of the type fluid being employed. Liquid filled thermometers are encountered as glass thermometers (clinical thermometers, filament thermometers) or as direct indicators for machine glass thermometers. They are used for local temperature monitoring of liquids, gases and steam in pipelines and tanks. A variant is the liquid filled spring-loaded thermometer. In this design a capillary tube completely filled with liquid is placed in a metal housing. Changes in the temperature produce an increase or decrease in the pressure which is transmitted over a membrane to an elastic, deformable spring. Newer designs measure the pressure differences and use a pressure transmitter to display the temperature values. If the liquid is replaced by a gas, then essentially the same design principles can be applied as for the liquid filled spring-loaded thermometers. For gas pressure thermometers the ideal gas equation is used to evaluate the temperature relationships of the gas. It can be considered either at a constant pressure or a constant volume. Gas pressure thermometers can also be used for local measurements and as temperature indicators, e.g., in machines. For both the liquid filled as well as the gas pressure thermometers it is essential that the measurement body is completely surrounded by the medium whose temperature is being measured. 35 2.3.2 Electric Contacting Thermometers Thermocouples If two dissimilar metals are connected together, a voltage is generated. This voltage is a function of the combined metals and the changes in the temperature (Thermal Voltage). Resistance Thermometers Metals as electrical conductors offer a resistance to the current flowing through them as a result of the oscillations of the lattice atoms. The magnitude of the resistance is dependent on the temperature. Semiconductor Sensors Semiconductors also exhibit a characteristic change of their electrical resistance when the temperature changes. A differentiation is made between cold wire (PTC-resistors), and hot wire (NTC-resistors or thermistors). Semiconductor PTC’s are polycrystalline ceramics based on barium titanate. This material combination generates, in addition to the semiconductor effect, ferroelectricity. This leads to a very large increase of the electrical resistance in a narrow temperature range. The ideal application range is between -50 °C (-58 °F) and 150 °C (302 °F). Additionally the PTC's have a leap-temperature at which the increase of the resistance changes dramatically. For this reason they are specially suitable for use as temperature limit switches for machines and systems. The NTC's, made of a mixture of polycrystalline ceramic oxides, with NiO, CaO, Li2O additives, work differently. They are manufactured using a high temperature sinter process. They are normally used in a temperature range from -110 °C (-166 °F) to 300 °C (572 °F). For the NTC's the relationship between the resistance and the temperature is almost exponential. Because of the non-linear curve and the drift when subjected to temperature change stresses, the use of NTC's in industrial measurement technology is limited. Due to their low cost they are primarily used in the appliance and automotive industries and in other mass produced consumer product industries. 36 Silicon Measurement Resistors Silicon also possesses a pronounced positive temperature coefficient and can therefore be used for temperature measurements between -70 °C (-94 °F) and 160 °C (320 °F), over which range the curves deviate only slightly from linear. Silicon measurement resistors have a high temperature coefficient and long term stability. To date they have not found wide acceptance. 2.3.3 Additional Contacting Measurement Principles Oscillating Quartz Temperature Sensors Oscillating quartz, cut at a specific angle, has a high temperature coefficient for its resonant frequency (approx. 100 ppm/K). This quartz can be used for temperature measurement. Its frequency vs. temperature curve is not linear, but is very reproducible. It can be described by a 5th order polynomial. The application range for these sensors is typically between -80 °C (-112 °F) and 300 °C (572 °F). The expected large industrial use of the oscillating quartz thermometers which have been introduced in 1986, has never been realized. Thermal Noise Thermometers For determining thermodynamic temperatures the high accuracy thermal noise thermometer is suitable. In the temperature range 300 °C (572 °F) to 1200 °C (2192 °F) it achieves a measurement uncertainty of 0.1 %. The measurement principle is based on the temperature dependence of the average velocity of the electrons in an unloaded resistor. There are however problems in practical applications, because the thermal noise in amplifier assemblies, connection cables and other components require costly elimination effort. The use of thermal noise thermometers, due to their high cost, is limited to applications where the properties of the other more common thermometers are not stable and cannot readily be removed for recalibration. Thermal noise thermometers for example are not affected by nuclear radiation in a reactor. They are often used in combination with other electrical thermometers. Fiber Optic Temperature Measurement Systems This is a special measurement system, in which the locally temperatures in a glass fiber cable can be measured. It consists of a measurement instrument (laser source, optical module, receiver and evaluation unit) and a quartz glass fiber cable. Thermal molecular oscillations of the quartz glass material cause a Raman-Radiation within the fiber optic cable. The Anti-Stokes portion of the Raman-radiated light is a function of the temperature. The local fiber temperature is determined from its intensity. In this way the temperature distribution in cables, wires, pipes etc., can be measured by using fiber optics. It is used to detect local temperature differences (temperature increases), which indicate errors or damages to cables, wires and pipes. 37 Fiber Optic Thermometers The fiber optic thermometer consists of a glass fiber at the end of which a crystal is mounted, e.g., a Cr-YAG-Crystal. It is excited by a pulsed luminescent radiation. The length of the excitation during the excitation conditions and therefore the decay time of the luminescent radiation decreases with increasing temperature. The application range is between -50 °C (-58 °F) and 400 °C (752 °F). Fiber optic thermometers are advantageous in areas where high electromagnetic fields may be expected as well as in potentially explosive atmospheres. Also included is the use in industrial microwave applications, (e.g., driers). 2.3.4 Non-contacting Temperature Measurement Infrared Measurement Technology, Pyrometry The recognition of radiation heating of a hot body belongs to the basic experiences of mankind. The measurement of temperature radiation (infrared radiation) to determine the temperature of a body is one of the newer temperature measurement methods in the industrial sector. In a pyrometer the thermal radiation emanating from a body is focussed by a lens on a radiation receiver. As receiver, thermocouples, photomultipliers, photoresistors, photodiodes etc. can be used. The “heat radiation“ generates an electrical signal which can be utilized to determine the temperature. A differentiation is made between the various pyrometer types, such as total radiation pyrometer, spectral pyrometer, radiation density pyrometer, distribution pyrometer and disappearing filament pyrometer. Pyrometers can replace contacting thermometers only in a few applications. More often they are used to supplement contacting methods in areas where no or unsatisfactory results occur. Basically, pyrometry, in contrast to contacting methods, can only measure the heat on the surface. The application focus is the temperature measurement on surfaces, on fast moving parts, on objects with minimal heat capacity or heat conductivity, on objects with fast changing temperatures and on objects which are not easily accessible. Also products which cannot be touched due to sterilization or processing constraints (e.g. in the food industry) are suitable for temperature measurements with pyrometers. 38 Thermal Imaging Cameras In principle the thermal imaging camera has the same physical effects as a pyrometer. However, the pyrometers determine the average temperature of the entire surface being measured while the thermal imaging camera produces a thermal picture of the object. Area sensors are used for this. The number of available detector elements defines the quality of the picture. Thermal imaging cameras are primarily used today to monitor and control machinery, electrical and mechanical systems and objects in which localized heating could damage or destroy the item as well as where heat losses are to be determined. Acoustic Measurement Methods The dispersion velocity of sound in various materials is a function of the temperature (the absolute temperature is proportional to the square of the sound velocity). This property can be used as temperature measurement method Two methods are utilized: the resonant method (e.g. quartz resonators) and non-resonant methods, which utilize for example a sound transit time measurement. Measurement sensors for non-resonant solid body sensors consist of a Rhenium wire which operates based on a Pulse-Echo principle. Acoustic measurement methods are especially suitable for high temperatures. They are used to determine the temperature profiles in furnaces such as those used in waste incineration systems. A disadvantage of the acoustic method is its relatively high cost. 39 3 Industrial Temperature Measurement Using Electrical Contacting Thermometers 3.1 Sensors 3.1.1 Thermocouples The simplest thermocouple designs are those made using insulated thermal wires. The usual insulation materials are glass fibers, mineral fibers, PVC, Silicone rubber, Teflon or Ceramic. They must be compatible with the installation requirements, which include chemical resistance, temperature resistance, moisture protection, etc. A special design of insulated thermocouple wires are mineral insulated thermocouple cables. Thermocouples according to EN 60584/IEC 584 The thermocouples described in these standards are generally divided into two groups. The precious metal thermocouples Types S, R and B, and the base metal thermocouples Types E, J, K, N and T. These standardized types are incorporated in many international standards and, relative to their basic thermal voltage values, are compatible. For example, it is possible to use a Type K according to EN 60584 as a Type K according to ANSI-MC 96.1, or even, as a Type K according to JIS C 1602. Only in the deviation limits of the accuracy classes may differences be found. Detailed information for each type is available in the corresponding standard. 40 Thermal Voltage [mV] 80 Type E 75 Type J 70 65 60 Type K 55 50 Type N 45 40 35 30 25 Type T Type R 20 Type S Type B 15 10 5 0 -5 -10 -300 -100 100 300 500 700 900 1100 1300 1500 1700 1900 Temperature [°C] Fig. 3-1: Basic value curves for thermocouples according to EN 60584 41 Type S (Pt10%Rh-Pt): Defined Temperature Range -50...1768 °C (-58...3214 °F). The Type S thermocouple was developed and tested over 100 years ago by H. LeChatelier. These early investigations already indicated that the primary advantages of the Type S were the reproducibility of its measurements, its stability and its applicability to middle high temperatures. This was the primary reason why it has been selected as the standard thermocouple since 1927 (ITS 27) until the introduction on 1st January 1990 of ITS 90. The nominal composition of Type S consists of Platinum-10%Rhodium compared against Platinum. The positive conductor (SP) contains 10.00 ± 0.05 % Rhodium. For the alloy, Rhodium with a purity of ≥ 99.98 %, and Platinum with a purity of ≥ 99.99 % should be used. The negative conductor (SN) is made of Platinum with ≥ 99.99 % purity. The Type S thermocouple can be used in a temperature range from -50 °C (-58 °F) almost to the melting point of Platinum at 1769 °C (3216 °F). It should be noted that the output voltages for continuous operation are only stable to about 1300 °C (2372 °F). The life span of the thermocouple is limited at the higher temperatures due to the physical problem of grain growth in the wires. This reduces the mechanical strength, also impurities can diffuse into the wires and thereby change the thermal voltage. The thermocouple is most stable when it is operated in a clean, oxidizing environment (e.g., air), although short term use in inert, gaseous atmospheres or in a vacuum is possible. Without suitable protection, it should not be used in reducing environments, in metallic or nonmetallic vapors containing, for example, Lead, Zinc, Arsenic, Phosphorous, or Sulphur, or in lightly reducing oxides. Decisive for the stability at higher temperatures is furthermore the quality of the protection tube and insulation material. Ceramic, in particular Aluminum oxide (Al2O3) with a purity of ≥ 99 %, is best suited for this purpose. Metallic protection tubes should never be used at the higher temperatures > 1200 °C (2192 °F). Type R (Pt13%Rh-Pt) Defined Temperature Range -50...1768 °C (-58...3214 °F). At the beginning of the twentieth century it was noticed that the Type S thermocouples used in the USA and in Europe showed large differences in their thermal voltages among each other. In some temperature ranges differences up to 5 °C (9 °F) were noted. The reason was that in Europe the Rhodium used for the alloy was contaminated with 0.34 % iron. Since many instruments were already calibrated with these “contaminated Type S“ thermocouples, the Type R was developed as a compromise, which has comparable thermal voltages. 42 The nominal composition of Type R consists of Platinum-13%Rhodium compared against Platinum. The positive conductor (RP) contains 13.00 ± 0.05 % Rhodium. For the alloy Rhodium with a purity of ≥ 99.98 %, and Platinum with a purity of ≥ 99.99 % should be used. The negative conductor (RN) is made of Platinum with ≥ 99.99 % purity. For the most part of their defined temperature range, Type R thermocouples have a temperature gradient about 12 % higher (Seebeck-Coefficient) than the Type S thermocouples. The remaining material properties are identical to the Type S. Type B (Pt30%Rh-Pt6%Rh) Defined Temperature Range 0...1820 °C (32...3308 °F). The Type B thermocouple was introduced into the market in the fifties by Degussa/Hanau, Germany, and was called PtRh18, a name which is still used in some areas today. It was designed to satisfy the requirements for temperature measurements in the range 1200...1800 °C (2192...3272 °F). The nominal composition for Type B consists of Platinum-30%Rhodium compared against Platinum-6%Rhodium. The positive conductor (BP) contains 29.60 ± 0.2 % and the negative conductor (BN) 6.12 ± 0.2 % Rhodium. For the alloy Rhodium with a purity of ≥ 99.98 %, and Platinum with a purity of ≥ 99.99 % should be used. They also contain a very small amount of Palladium, Iridium, Iron and Silicon impurities. Investigations have shown, that thermocouples, in which both conductors are made of Pt-Rh alloys, are suitable and reliable for measuring high temperatures. They have decided advantages over Types R and S, with regard to improved stability, increased mechanical strength and higher temperature capabilities. The maximum application temperature range for Type B is essentially limited by the melting point of the Pt6%Rh conductor (BN) at approx. 1820 °C (3308 °F). A Type B thermocouple can, if handled properly, be operated for a number of hours at temperatures to 1790 °C (3254 °F), and for a few hundred hours at temperatures to 1700 °C (3092 °F), without an appreciable change in the output thermal voltage values. The thermocouple operates most reliably when operated in clean, oxidizing environment (air), a neutral atmosphere or in a vacuum. Suitable protection is mandatory if it is to be used in reducing environment as well as in environments with destructive vapors or other contaminants which might react with the Platinum materials. The selections of suitable protection tube and insulation materials are the same as for Type S. Type J (Fe-CuNi) Defined Temperature Range -210 ...1200 °C (-346...2192 °F). Because of its relatively steep temperature gradient (Seebeck-Coefficient) and low material costs, Type J, in addition to Type K, is one of the most commonly used industrial thermocouples today. 43 Nominally, Type J consists of Iron compared against a Copper-Nickel alloy. The positive conductor (JP) is made of commercially available Iron with a purity of approx. 99.5 % with approx. 0.25 % Manganese and approx. 0.12 % Copper, as well as smaller quantities of Carbon, Chromium, Nickel, Phosphorous, Silicon and Sulphur. The negative conductor (JN) is made of a Copper-Nickel alloy, which is called Constantan. It should be noted that alloys designated as Constantan which are available commercially, may have a Copper content between 45 % and 60 % . For negative conductor (JN) usually an alloy with approx. 55 % Copper, approx. 45 % Nickel and approx. 0.1 % each of Cobalt, Iron and Manganese is used. It should be stressed, JN conductors cannot generally be exchanged with conductors of Types TN or EN, even though all consist of Constantan. Manufacturers of Type J thermocouples usually combine one particular Iron melt with an appropriate CopperNickel batch in order to achieve the basic thermal voltage values of Type J. Since the composition of both conductors (JP and JN) can vary from manufacturer to manufacturer, it is not advisable to use individual conductors from more than one manufacturer, otherwise the required tolerance classes in some instances may be exceeded. Although the basic values for Type J are defined in the standard for a temperature range from -210...1200 °C (-346...2192 °F), the thermocouples should only be used in a range of 0...750 °C (32...1382 °F) when operating continuously. For temperatures over 750 °C (1382 °F) the oxidation rate for both conductors increases rapidly. Further reasons for the restricted temperature range are to find in the special properties of the positive conductor (JP). Since Iron rusts in damp environments and becomes brittle, it is not advisable to operate Type J thermocouples at temperatures below 0 °C (32 °F) without suitable protection. In addition, Iron experiences a magnetic change at 769 °C (1462 °F) (Curie point) and at approx. 910 °C (1670 °F) an Alpha-Gamma crystal structure change occurs. Both effects, particularly the latter, have a significant influence on the thermoelectric properties of the Iron and therefore on the Type J thermocouple. Should a Type J be operated above 910 °C (1670 °F), the output thermal voltages will change appreciably, especially when cooled quickly to lower temperatures. In the temperature range 0...760 °C (32...1400 °F) the Type J can be used in vacuum, oxidizing, reducing or inert atmospheres. In Sulphur containing environments, suitable protection should be employed at temperatures above 500 °C (932 °F). 44 Type K (NiCr-NiAl) Defined Temperature Range -270...1372 °C (-454...2501 °F). Since this thermocouple type for middle temperatures is more resistant against oxidation than Types J and E, it is used in many applications today for temperatures over 500 °C (932 °F). Nominally, the thermocouple contains a Nickel-Chromium alloy compared against a Nickel-Aluminum alloy. The positive conductor (KP) is identical to the material of Type E positive conductor and consists of 89 to 90 % Nickel, 9 to 9.5 % Chromium, approx. 0.5 % Silicon, approx. 0.5 % Iron and smaller amounts of Carbon, Manganese and Cobalt. The negative conductor (KN) contains 95 to 96 % Nickel, 1 to 2.3 % Aluminum, 1 to 1.5 % Silicon, 1.6 to 3.2 % Magnesium, approx. 0.5 % Cobalt, as well as minimal traces of Iron, Copper and Lead. The basic values for Type K thermocouples are defined for the range from -270... 1372 °C (-454...2501 °F). It should be noted that at temperatures over 750 °C (1382 °F) the oxidation rate in air for both conductors increases sharply. Also, it should not be installed without suitable protection at higher temperatures in Sulphur containing, reducing or alternately oxidizing and reducing atmospheres. There are also effects to be considered here which drastically change the output thermal voltages. If a Type K is exposed for longer periods of time to higher temperatures in a vacuum, then the Chromium volatilizes out of the alloy of the KP conductor (“vacuum sensitivity“). If on the other hand, a smaller, but not negligible amount of oxygen or steam is present at the thermocouple, the KP conductor may be subjected to the so called “green rot“. In these situations, the oxidation attacks only the easier to oxidize Chromium without oxidizing the Nickel. At temperatures between 800 °C and 1050 °C (1472... 1922 °F) this is most severe. “Green rot“ and “vacuum sensitivity“ produce irreversible effects on the composition of the conductor and thereby on the thermal voltage. Erroneous measurements of more than 100 °C (212 °F) are possible! In addition, a magnetic change in the Nickel leg KN occurs at 353 °C (667 °F) (Curie point). The Nickel-Chromium alloy of the KP-conductor in the range from 400...600 °C (752...1112 °F) changes from an ordered to an unordered atomic distribution state, the so called “K-Condition“. If a Type K is operated at temperatures over 600 °C (1112 °F) and subsequently cooled too quickly, these changes may not be reversible and can change the output thermal voltages by up to 5 °C (9 °F). Both effects are reversible, since they can be restored to their original condition by heating to over 600 °C (1112 °F) and then slowly cooling (for additional information see chapter 3.5 "Aging Mechanisms in Temperature Sensors"). 45 Type N (NiCrSi-NiSi) Defined Temperature Range -270...1300 °C (-454...2372 °F). Type N is the newest thermocouple defined in this standard. It was developed at the end of the sixties and offers distinct advantages due to its higher thermoelectric stability at temperatures over 870 °C (1598 °F) and less tendency to oxidize compared against thermocouples Types J, K and E. Nominally, the thermocouple consists of a Nickel-Chromium-Silicon alloy compared against a Nickel-Silicon alloy. The positive conductor (NP) contains approx. 84 % Nickel, 13.7 to 14.7 % Chromium, 1.2 to 1.6 % Silicon, <0.15 % Iron, <0.05 % Carbon, <0.01 % Magnesium, as well as minimal traces of Cobalt. The negative conductor (NN) contains approx. 95 % Nickel, 4.2 to 4.6 % Silicon, 0.05 to 0.2 % Magnesium, <0.15 % Iron, <0.05 % Carbon, as well as small amounts of Manganese and Cobalt. These conductors are also known by their trade names Nicrosil (NP) and Nisil (NN). Of all the base metal thermocouples, Type N is best suited for applications with oxidizing, damp or inert atmospheres. As a result of its relatively high Silicon content, the oxidation occurs on the surface of the conductor. Tightly adhering and protective oxides are formed which minimize further corrosion. In reducing atmospheres or air in the range of 870...1180 °C (1598...2156 °F) the thermocouple exhibits a decidedly higher thermoelectric stability than a Type K thermocouple under the same conditions. Also the “K-State“ which occurs in the Type K is almost completely suppressed due to the Silicon content. At higher temperatures in Sulphur containing, reducing or alternately oxidizing and reducing atmospheres suitable protection is still necessary. The “Green rot“ and “vacuum sensitivity“ phenomena described for the Type K thermocouple do also occur in the Type N, where however, both the Chromium and the Silicon volatilize in vacuum. Attention: Type K and N cannot be exchanged for each other! Type T (Cu-CuNi) Defined Temperature Range -270...400 °C (-454...752 °F). This is one of the oldest thermocouples for low temperature measurements, and is still commonly used in the triple point range for Neon at -248.5939 °C (-415.4690 °F) up to 370 °C (698 °F). Type T nominally contains Copper compared against a Copper-Nickel alloy. The positive conductor (TP) consists of approx. 99.95 % pure Copper with an Oxygen content of 0.02 to 0.07 % dependent on the Sulphur content of the Copper. The remaining impurities amount to approx. 0.01 % in total. The negative conductor (TN) consists of a Copper-Nickel alloy, also called Constantan with approx. 55 % Copper and 45 % Nickel, as well as approx. 0.1 % each of Cobalt, Iron and Manganese. The TN conductor is identical to and can be interchanged with an EN conductor. It is, however, generally not identical to Type JN conductors. 46 The Type T thermocouple exhibits good thermoelectric homogeneity. Due to the good heat conductivity of the conductors, problems can occure when used for precision measurements, resulting from heat abstraction, particularly if the conductor diameter is very large. The Type T can be used in vacuum, oxidizing, reducing or inert atmospheres. It should be noted that above 370 °C (698 °F) the oxidation rate of the TP-conductor increases dramatically. It is not recommended to use the thermocouple in hydrogen containing environments above 370 °C (698 °F) without suitable protection, because the TP-conductor could become brittle. Type E (NiCr-CuNi) Defined Temperature Range -270...1000 °C (-454...1832 °F). The thermocouple has a relatively small heat conductivity, very high resistance in humid atmospheres, good homogeneity, and a relative steep temperature gradient (Seebeck-Coefficient) at extremely low temperatures. For these reasons it has become the most common thermocouple for low temperature measurements. Above 0 °C (32 °F) it has the steepest temperature gradient of all the thermocouples defined in the standard. Type E nominally consists of a Nickel-Chromium alloy compared against a CopperNickel alloy. The materials of the positive conductor (EP) are identical to those already described for the KP-conductor in the Type K, and the negative conductor (EN) is the same as the TN-conductor in the Type T . The Type E thermocouple can be used in a temperature range from -270...1000 °C (-454...1832 °F). For temperatures over 750 °C (1382 °F) the oxidation rate in air for both conductors is high. Since the EP-conductor is identical to the KP-conductor, the same effects of “vacuum sensitivity“, “K-State“ and “Green rot“ already described are also applicable to this thermocouple. The Type E is essentially insensitive to oxidizing or inert atmospheres. In Sulphur containing, reducing or alternately oxidizing and reducing atmospheres suitable protection is still necessary. 47 Type Class 2 Class 3 Type R, Type S Temperature range 0...1100 °C (32...2012 °F) Deviation limits ± 1 °C (1.8 °F) Temperature range 1100...1600 °C (2012...2912 °F) Deviation limits ±[1+0.003 x (t -1100)] °C ±[1+0.0017 x (t -2000)] °F Class 1 0...600 °C (32...1112 °F) ± 1.5 °C (2.7 °F) 600...1600 °C (1112...2912 °F) ± 0.0025 x [t] °C ± 0.0014 x [t] °F – – – Type B Temperature range – – 600...800 °C (1112...1472 °F) ± 4 °C (7.2 °F) 800...1700 °C (1472...3092 °F) ± 0.005 x [t] °C ± 0.0028 x [t] °F Deviation limits – Temperature range – – Deviation limits Type J Temperature range Deviation limits Temperature range Deviation limits -40...375 °C (-40...707 °F) ± 1.5 °C (2.7 °F) 375...750 °C (707...1382 °F) ± 0.004 x [t] °C ± 0.002 x [t] °F Type K, Type N Temperature range -40...375 °C (-40...707 °F) Deviation limits ± 1.5 °C (2.7 °F) Temperature range 375..1000 °C (707...1832 °F) Deviation limits ± 0.004 x [t] °C ± 0.002 x [t] °F Type T Temperature range Deviation limits Temperature range Deviation limits -40...125 °C (-40...257 °F) ± 0.5 °C (0.9 °F) 125...350 °C (257...662 °F) ± 0.005 x [t] °C ± 0.0028 x [t] °F Type E Temperature range -40...375 °C (-40...707 °F) Deviation limits ± 1.5 °C (2.7 °F) Temperature range 375...800 °C (707...1472 °F) Deviation limits ± 0.004 x [t] °C ± 0.002 x [t] °F Tbl. 3-1: – 600...1700 °C (1112...3092 °F) ± 0.0025 x [t] °C ± 0.0014 x [t] °F – -40...333 °C (-40...631 °F) ± 2.5 °C (4.5 °F) 333...700 °C (631...1292 °F) ± 0.0075 x [t] °C ± 0.0042 x [t] °F – – – – -40...333 °C (-40...631 °F) ± 2.5 °C (4.5 °F) 333...1200 °C (631...2192 °F) ± 0.0075 x [t] °C ± 0.0042 x [t] °F -167...40 °C(-269...104 °F) ± 2.5 °C (4.5 °F) -200...-167 °C (-328...-269 °F) ± 0.015 x [t] °C ± 0.0008 x [t] °F -40...133 °C (-40...271 °F) ± 1 °C (1.8 °F) 133...350 °C (271...661 °F) ± 0.0075 x [t] °C ± 0.0042 x [t] °F -67...40 °C(-89...104 °F) ± 1 °C (1.8 °F) -200...-67 °C (-328...-89 °F) ± 0.015 x [t] °C ± 0.0008 x [t] °F -40...333 °C (-40...631 °F) ± 2.5 °C (4.5 °F) 333...900 °C (631...1652 °F) ± 0.0075 x [t] °C ± 0.0042 x [t] °F -167...40 °C (-269...104 °F) ± 2.5 °C (4.5 °F) -200...-167 °C (-328...-269 °F) ± 0.015 x [t] °C ± 0.0008 x [t] °F Classes and deviation limits for thermocouples acc. to EN 60584 (former IEC 584) Thermocouples according to DIN 43710 The thermocouples Type U (Cu-CuNi) and Type L (Fe-CuNi) defined in this standard are no longer included in any current national or international standards. This has not precluded the continued use of these thermocouples in many applications. They were not included in EN 60584 or IEC 584, but replaced by the Types J and T. DIN 43710 recommends that these thermocouples should not be used for any new applications and if existing installations are updated or reworked, the thermocouples should be replaced by Types J and T. Attention: They cannot simply be exchanged for one another! 48 Thermal Voltage [mV] 60 55 Type L 50 45 40 35 Type U 30 25 20 15 10 5 0 -5 -10 -200 -100 0 100 200 300 400 500 600 700 800 900 1000 Temperature [°C] Fig. 3-2: Basic curves for thermocouples according to DIN 43710 Type U Cu-CuNi) Defined Temperature Range -200...600 °C (-328...1112 °F). Type U nominally consists of Copper compared against a Copper-Nickel alloy. The positive conductor (UP) is made of the same Copper composition as the positive conductor described for Type T earlier in this section. The negative conductor (UN) is made of a Copper-Nickel alloy (Constantan) with approx. 55 % Copper, approx. 44 % Nickel and approx. 1 % Manganese. 49 As a result of these very small differences in their compositions, the basic values for the thermal voltages for the Type U are different from those for Type T. The remaining material properties are however essentially the same as those for Type T. Type L (Fe-CuNi) Defined Temperature Range -200...900 °C (-328...1652 °F). Type L nominally consists of Iron compared against a Copper-Nickel alloy. The positive conductor (LP) is made of the same Iron composition as the positive conductor of Type J. The negative conductor (LN) is made of the same Copper-Nickel alloy (Constantan) as the negative conductor of Type U. Therefore the basic values for the thermal voltages for Type L are different from those for Type J. The remaining material properties are however essentially the same as those for Type J. Type Type U Temperature range Deviation limits Temperature range Deviation limits Type L Temperature range Deviation limits Temperature range Deviation limits Tbl. 3-2: DIN 50...400 °C (122...752 °F) ± 3 °C (5.4 °F) 400...600 °C (752...1112 °F) ± 0.0075 x [t] °C ± 0.0028 x [t] °F 50...400 °C (122...752 °F) ± 3 °C (5.4 °F) 400...900 °C (752...1652 °F) ± 0.0075 x [t] °C ± 0.0028 x [t] °F Classes for the deviation limits for thermocouples according to DIN 43710 Non-Standard Thermocouples In addition to the standardized thermocouples, there is a whole set of non-standard thermocouples for special applications, whose basic values are not included in any current standard. The basic values for these thermocouples must be established by the manufacturer using individual calibrations. The most well known include: Iridium-Iridium rhodium (Ir-Ir40%Rh) For laboratory measurements in neutral or weak oxidizing atmospheres at temperatures to 2000 °C (3632 °F). The thermocouple consists of very brittle cold rolled steel wires which may not be bent. They are insulated using capillary tubes made of pure Aluminum oxide (Al2O3). The thermal voltage is approx. 10 mV at 2000 °C (3632 °F). 50 Tungsten-Tungsten Rhenium (W-W26%Rh), Tungsten Rhenium-Tungsten Rhenium (W5%Rh-W26%Rh) and Tungsten Rhenium-Tungsten Rhenium (W3%Rh-W25%Rh) These thermocouples, identified in the USA by the letters “G“, “C“ and “D“, are designed for use in high vacuums and for inert gases to 2320 °C (4200 °F). The thermal voltage is at 2320 °C (4208 °F) for W-W26%Rh approx. 38.6 mV, for W5%Rh-W26%Rh approx. 37.1 mV and for W3%Rh-W25%Rh approx. 39.5 mV. Pallaplath® (Pt5%Rh-Au46%Pd2%Pt) This thermocouple can be used to 1200 °C (2192 °F) in air, but is not suitable for environments containing Silicon or Carbon. It combines the stability of a precious metal with the high thermal voltages of a base metal thermocouple. The thermal voltage is approx. 55.4 mV at 1200 °C (2192 °F). Gold Iron-Chromium (AuFe-Cr) This thermocouple is used primarily for low temperature measurements in a range from -270...-200 °C (-454...-328 °F). At -270 °C (-454 °F) the thermal voltage is approx. 4.7 mV. 3.1.2 Mineral Insulated Thermocouple Cables Mineral insulated thermocouple cables have an outer sheath made of metal and for any one design, 2...6 internal wires made of a thermal material. The insulation consists of highly compressed metal oxide powder, preferably Magnesium oxide MgO, or Aluminum oxide AI2O3. They are used where particularly high mechanical, electrical and chemical stability is required. Because they are readily bendable, these cables are preferred where problematic space requirements exist and a flexible installation is desired, e.g. in machine building, laboratories and experimental test facilities. The minimum bending radius is approx. 3 x outside diameter of the cable. As a result of the development of economical manufacturing processes, sheathed cables are finding more and more applicability as an essential part for the production of standard thermocouples, especially in the industrial measurement and control sector as well as for automotive sensors. Due to the metallic outer sheath, these thermocouples are essentially unaffected by field induced electromagnetic interference (EMI), provided that they are grounded correctly. 51 Insulation and Insulation Resistance The achievable insulation resistance is a function of the purity of ceramic insulation material. Aside from the standard material MgO with a purity of > 97 %, also MgO with a purity of 99.4 % and Al2O3 can be used. Since these oxides are highly hygroscopic, care must be exercised when handling the cable. After removing the sealing or cutting the cable, it has to be dried properly. Afterward the open ends have to be immediately sealed against moisture entry. Storing for any length of time with open ends must be avoided. Since the insulation material of the mineral insulated thermocouple cables and sheathed thermocouples has a low rest conductivity, the insulation resistance decreases as the length of the cable or thermocouple increases. Therefore a length related resistance with the units Ω x m or MΩ x m is specified. For lengths less than 1 m the insulation resistance is specified independent of the length. Based on EN 61515 the insulation resistance must be tested with a voltage of 75 ±25 V DC for outside diameters ≤ 1.5 mm and with 500 ±50 V DC for outside diameters >1.5 mm. Insertion depth at test temperature min. m (ft.) Ambient temperature Test temperature °C (°F) Insulation resistance min. MΩ x m 1 (3) 20 ±15 (68 ±27) 1000 Increased temperature Types J, K, N, E 0.5 (1.5) 500 ±15 (932 ±27) 5 Increased temperature Type T 0.5 (1.5) 300 ±15 (572 ±27) 500 Tbl. 3-3: Minimum insulation resistance of mineral insulated thermocouple cables according to EN 61515 Length of Insertion depth Test Insulation Thermoat test temperature resistance couple temperature min. m (ft.) m (inch) °C (°F) MΩ x m Ambient temperature Ambient temperature ≥ 1 (3) Insulation resistance min. MΩ Total length 20 ±15 (68 ±27) 1000 – – 1000 < 1 (3) Total length 20 ±15 (68 ±27) Increased temperature Types J, K, N, E All lengths 50 % of the total length max. 0.3 (1) 500 ±15 (932 ±27) – 5 Increased temperature Type T All lengths 50 % of the total length max. 0.3 (1) 500 ±15 (932 ±27) – 500 Tbl. 3-4: 52 Minimum insulation resistance of sheathed thermocouples with insulated measurement spot locations according to EN 61515 It should be noted when using sheathed thermocouples that the insulation resistance of the insulating ceramic decreases appreciably with increasing temperatures. When longer lengths of the sheath material are exposed to high temperatures, measurement errors could result due to shunt currents or cross talk between adjacent measurement installations along the length of the cable. Sheath Materials Basically, mineral insulated thermocouple cables could be made of materials sufficiently ductile, preferred however, are those made entirely of austenitic stainless steel. Nickel alloys are also useful for special applications. Though not all sheath material/thermocouple combinations are possible, e. g., for high heat resistant sheath materials the required intermediate annealing temperatures required for processing may, in part, be appreciably above the allowable temperature limits for the thermocouple materials. The most common sheath materials are: 1.4541 (corresponds to AISI 321) Max. operating temperature: 800 °C (1472 °F). Application areas: Nuclear plants and reactor construction, chemical system engineering, heat treating furnaces, heat exchangers, paper and textile industries, petrochemical and petroleum industries, lubricant and soap industries. Material properties: Good intercrystalline corrosion resistance, also after welding. Good resistance against crude oil products, steam and combustion gases. Good oxidation resistance. Good welding properties for all standard welding processes, no subsequent heat treatment required after welding, good ductility. 1.4571 (corresponds to AISI 316 TI) Max. operating temperature: 800 °C (1472 °F) Application areas: Nuclear plants and reactor construction, chemical system engineering, furnace manufacture, chemical and pharmaceutical industries. Material properties: Increased corrosion resistance to specific acids due to the addition of Molybdenum. Resistant against pitting, salt water and aggressive industrial influences. Good welding properties for all standard welding processes, no subsequent heat treatment required after welding, good ductility. 53 1.4749 (corresponds to AISI 446) Max. operating temperature: 1150 °C (2102 °F) Application areas: Petrochemical industries, metallurgy, energy technologies and for recuperators, heat treatment ovens, systems for controlling fluidized bed coatings, waste incineration plants. Material properties: Extremely good resistance against reducing atmospheres containing Sulphur. Very good resistance against oxidation and air. Good resistance against corrosion by combustion products, Copper, Lead- and Tin melting. Good welding properties for applications using arc or WlG welding. Preheating to 200...400 °C (392... 752 °F) is recommended. Subsequent heat treatment is not required. 1.4841 (corresponds to AISI 314) Max. operating temperature: 1150 °C (2102 °F) Application areas: Steam boilers and blast furnaces, cement and tile ovens, glass manufacture, petroleum and petrochemical industries, furnace manufacture, power plants. Material properties: Exceptional corrosion resistance, even at high temperatures. Suitable for Carbon and Sulphur containing atmospheres. Air oxidation resistance to 1000 °C (1832 °F) (batch operation) or 1150 °C (2102 °F) (continuous operation). Very good for higher alternating temperature changes. Long term continuous operation is not recommended for temperature ranges from 425...850 °C (797...1562 °F). Good welding properties for applications using arc welding. Subsequent heat treatment is not required. Good ductility in the as received condition. After longer use some slight brittleness can be expected. 1.4845 (corresponds to AISI 310 S) Max. operating temperature: 1100 °C (2012 °F) Application areas: Steam boilers and blast furnaces, cement and tile ovens, glass manufacture, petroleum and petrochemical industries, furnace manufacture, power plants. Material properties: Good resistance against oxidation and sulfidization. Due to the high Chromium content resistant to oxidizing aqueous solutions as well as good resistance against Chlorine induced stress crack corrosion. Good resistance in Cyanide melters and neutral fused salt at high temperatures. Not sensitive to “Green rot“. Readily weldable. It is recommended that heat be added during welding. When intercrystalline corrosion may occur, solution heat treat after welding. 1.4876 (corresponds to Incolloy 800®) Max. operating temperature: 1100 °C (2012 °F) in air Application areas: power plants, petroleum and petrochemical industries, furnace manufacture. Material properties: Due to the admix of Titanium and Aluminum the material has especially good heat resistance. Suitable for applications, where highest loading is required. Resistant to scale. Exceptionally stable where carburization and nitration can be expected. Good welding properties for applications using arc or TlG welding. Subsequent heat treatment is not required. 54 2.4816 (corresponds to Inconel 600®) Max. operating temperature: 1100 °C (2012 °F) Application areas: Pressurized water reactors, nuclear power plants, furnace manufacture, plastic industry, heat tempering, paper and food industries, steam boilers, airplane engines. Material properties: Good general corrosion resistance, resistant to stress crack corrosion. Exceptional oxidation resistance. Not recommended for CO2 and Sulphur containing gases above 550 °C (1022 °F) and Sodium above 750 °C (1382 °F). Stable in air to 1100 °C (2012 °F). Good welding properties for all welding techniques. The material should be annealed before welding. Subsequent heat treatment is not required. Exceptional ductility even after long term use. Platinum 10% Rhodium Max. operating temperature: 1300 °C (2372 °F) Application areas: Glass, electrochemical and catalytic technology, chemical industry, laboratory applications, melting, annealing and firing ovens. Material properties: High temperature resistance to 1300 °C (2372 °F) under oxidizing conditions. In the absence of Oxygen, Sulphur, Silicon, high heat resistance to 1200 °C (2192 °F). Especially resistant to halogens, acetic acid, NaOCI solutions etc. Embrittlement due to absorption of Silicon from sheath ceramics. Sulphur eutectic formation possible above 1000 °C (1832 °F). Phosphorous sensitivity. 3.1.3 Thermocouple Wires and Compensating Cables It is often necessary to locate the reference junction of the thermocouple at a great distance from the measurement site due to safety concerns or constructional reasons. In other instances the measurement circuit installation is fixed and the actual thermocouple is designed as a measuring inset so that it can easily be exchanged. Also, for cost reasons, especially for precious metal thermocouples it is economical to use another, less costly material for the reference junction. In this case, an interconnection cable is used between the actual thermocouple and the reference junction, which over a restricted temperature range has the same thermoelectrical properties as the corresponding thermocouple. These “connector links“ are the thermocouple and compensating cables. The application range for these cables is limited in most national and international standards to a temperature range of -25 °C (-13 °F) to 200 °C (392 °F), or is dependent on the temperature resistance of the insulation material used. The insulation material itself is to be selected so that the requirements at the “local site“, including chemical and heat resistance, moisture protection etc. are satisfied. 55 Concepts Thermal cables are made of thermal wires or braid conductors, which have the same nominal composition as the corresponding thermocouple. Compensating cables are made of substitute materials (other alloys than those for the thermocouple), but having the same thermoelectrical properties over a limited temperature range. Since the agreement of the thermal voltage of the particular thermocouple is based on the compensating pair and not on its individual wire, there may not be any temperature differences at the transition locations between the legs of the thermocouple. Otherwise parasitic thermal voltages will produce measurement errors. The allowable deviation limits for the thermocouple or compensating cables limit the additional deviations which may be added in the measurement circuit of such a cable in microvolts. Thermocouple Wires and Compensating Cables according to EN 60584-3/DIN 43722 Since 1994 EN 60584-3 has been accepted by all the industrial countries worldwide. DIN 43722 is the minimally modified German version of IEC 584-3: 1989. Short Designation: Thermocouple wires (original material) are identified by the letter X (X stands for eX-tension), which is added after the code letter for the thermocouple, for example: JX. Compensation cables (substitute material) are identified by the letter C (C stands for Compensating), which is added after the code letter for the thermocouple, for example: KC. Since for some thermocouples, additional substitute materials are used, they must be identified by an additional letter for differentiation, for example: KCA and KCB. Color Identification: The color for the negative conductor for all thermocouple types is white, the positive conductor corresponds to specifications in the following table. Type of thermocouple Color of positive conductor and sheath Color of negative conductor Tbl. 3-5: 56 S orange white R orange white B gray white J black white K green white N pink white T brown white E violet white Color code for thermocouple wires and compensating cables according to DIN 43722 The outer sheath, if present, has the same color code as the positive conductor. An exception are the connection wires for Intrinsically Safe circuits, for which the color code is blue for all thermocouple types. If the thermocouple or compensating cables have a plug connector, then it must be identified with the same color code as the positive conductor or sheath. The entire connection plug is to colored, or alternatively, a color dot can be applied to its outer surface. Deviation Limits: The allowable deviations listed in the table below (in microvolts) for thermocouple wires and compensating cables for the allowable temperature ranges. The deviations in brackets are the equivalent deviations expressed in (°C/°F) when the meter location of the entire measurement circuit (thermocouple with connected thermocouple wires or compensating cable) is also at the same temperature. Type of Type thermoof couple cable 1 Deviation limit Class 2 Applicable temperature range Temp. at the measurement location J JX ±85 μV (±1.5 °C/±2.7°F) ±140 μV (±2.5 °C /±4.5 °F) -25...200 °C (-13...392 °F) 500 °C (932 °F) T TX ±30 μV (±1.5 °C/±2.7 °F) ±60 μV (±1.0 °C /±1.8 °F) -25...100 °C (-13...212 °F) 300 °C (572 °F) E EX ±120 μV (±1.5 °C/±2.7 °F) ±200 μV (±2.5 °C /±4.5 °F) -25...200 °C (-13...392 °F) 500 °C (932 °F) K KX ±60 μV (±1.5 °C/±2.7 °F) ±100 μV (±2.5 °C /±4.5 °F) -25...200 °C (-13...392 °F) 900 °C (1652 °F) N NX ±60 μV (±1.5 °C/±2.7 °F) ±100 μV (±2.5 °C /±4.5 °F) -25...200 °C (-13...392 °F) 900 °C (1652 °F) K KCA – ±100 μV (±2.5 °C /±4.5 °F) 0...150 °C (32...302 °F) 900 °C (1652 °F) K KCB – ±100 μV (±2.5 °C /±4.5 °F) 0...100 °C (32...212 °F) 900 °C (1652 °F) N NC – ±100 μV (±2.5 °C /±4.5 °F) 0...150 °C (32...302 °F) 900 °C (1652 °F) R RCA – ±30 μV (±2.5 °C /±4.5 °F) 0...150 °C (32...302 °F) 1000 °C (1832 °F) R RCB – ±60 μV (±5.0 °C /±9 °F) 0...200 °C (32...392 °F) 1000 °C (1832 °F) S SCA – ±30 μV (±2.5 °C /±4.5 °F) 0...100 °C (32...212 °F) 1000 °C (1832 °F) S SCB – ±60 μV (±5.0 °C /±9 °F) 0...200 °C (32...392 °F) 1000 °C (1832 °F) B BC – ±40 μV (±3.5 °C /±6.3 °F) 0...100 °C (32...212 °F) 1400 °C (2552 °F) Tbl. 3-6: Deviation limits for thermocouple wires and compensating cables classes according to DIN 43722 57 3.1.4 Older National Standards For many of the cables described in older standards, national or international basic values do not exist, yet these products are installed in many systems worldwide. For new installations and when updating existing systems, only the thermocouple and compensating cables according to IEC 584-3: 1989 or DIN 43722 described in the previous sections should be used. The best known still being used, but no longer being updated in the national standards are: Compensating Cables according to DIN 43713 / DIN 43714 Short Designation: In DIN 43713 / DIN 43714 a differentiation was not made between compensating and thermocouple wires. All cables are designated as compensating cables and identified by the abbreviation AGL followed by the text “DIN 43714“ and the nominal composition of the corresponding thermocouple, for example: AGL DIN 43714 Fe-CuNi. Color Code: The color code for the insulation of positive conductor for all thermocouple types is red, for the negative conductor the color codes are listed in the table below: Type of thermocouple Color of positive conductor Color of negative conductor and sheath white Tbl. 3-7: S red R red white L red dark blue K red green U red brown Color codes for compensating cables according to DIN 43714 The outer sheath, if present, has the same color code as that listed in the above table. An exception are those cables for Intrinsically Safe circuits, for which the color code is always light blue for all thermocouple types which also includes a stripe or tracer thread with the color for the particular negative conductor. 58 Deviation Limits: The allowable deviations (in °C / °F) are listed in the table below for the compensating cables with the allowable operating temperature ranges. Type of thermocouple Type of cable Allowable deviation limit Operating temperature range Cu-CuNi (U) Cu-CuNi ± 3.0 °C (± 5.4 °F) 0...200 °C (32...392 °F) Fe-CuNi (L) Fe-CuNi ± 3.0 °C (± 5.4 °F) 0...200 °C (32...392 °F) NiCr-Ni (K) NiCr-Ni ± 3.0 °C (± 5.4 °F) 0...200 °C (32...392 °F) NiCr-Ni (K) SoNiCr-SoNi1 ± 3.0 °C (± 5.4 °F) 0...200 °C (32...392 °F) NiCr-Ni (K) SoNiCr-SoNi2 ± 3.0 °C (± 5.4 °F) 0...100 °C (32...212 °F) Pt10%Rh-Pt (S) SoPtRh1-SoPt1 ± 3.0 °C (± 5.4 °F) 0...200 °C (32...392 °F) Pt10%Rh-Pt (S) SoPtRh2-SoPt2 ± 3.0 °C (± 5.4 °F) 0...100 °C (32...212 °F) Pt13%Rh-Pt (R) SoPtRh1-SoPt1 ± 3.0 °C (± 5.4 °F) 0...200 °C (32...392 °F) Pt13%Rh-Pt (R) SoPtRh2-SoPt2 ± 3.0 °C (± 5.4 °F) 0...100 °C (32...212 °F) Tbl. 3-8: Deviation limits according to DIN 43710 for compensating cables acc. to DIN 43713 Thermocouples and Compensating Cables according to ANSI-MC96.1 (USA) Short Designation: In ANSI-MC96.1 a differentiation was not made between compensating and thermocouple cables. All cables were identified the same by the code letter X, added after the code letter for the thermocouple, for example: EX. Color Code: The color code for the insulation of the negative conductor for all thermocouple types is red, for the positive conductor the color codes are listed in the table below: Type of thermocouple Color of sheath Color of positive conductor Color of negative conductor Tbl. 3-9: S green black red R green black red B gray gray red J black white red K yellow yellow red T blue blue red E violet violet red Color codes for thermocouple wires and compensating cables according to ANSI-MC96.1 The outer sheath, if present, has the same color code as those listed in the above table. 59 Deviation Limits: The allowable deviations listed in the table below (in microvolts and °C / °F) for thermocouple and compensating cables for the allowable operating temperature ranges. Type of Type of thermocouple cable Deviation limit Classes Operating temperature range special standard – ±1.7 °C (±3.06 °F) 0...200 °C (32...392 °F) ±1.1 °C (±1.98 °F) ±2.2 °C (±3.96 °F) 0...200 °C (32...392 °F) E EX J JX K KX – ±2.2 °C (±3.96 °F) 0...200 °C (32...392 °F) T TX ±0.5 °C (±0.9 °F) ±1.0 °C (±1.98 °F) 0...100 °C (32...212 °F) R SX – ± 57 μV 0...200 °C (32...392 °F) R SX – ± 57 μV 0...200 °C (32...392 °F) S SX – ± 57 μV 0...200 °C (32...392 °F) S SX – ± 57 μV 0...200 °C (32...392 °F) B BX – + 0 μV/-33 μV 0...100 °C (32...212 °F) Tbl. 3-10: Deviation limits for thermocouple wires and compensating cable classes according to ANSI-MC96.1 Thermocouple Wires and Compensating Cables according to NF C 42-324 (France) Short Designation: In NF C 42-324 a differentiation is made between thermocouple wires and compensating cables (Câble de Extension et Câble de Compensation), but a compensating cable can also be a thermocouple, which may differ from the thermocouple because its composition has a lower thermoelectric quality (tolerance). That means that the compensating cables may or may not be identical to the thermocouple. The thermocouple wires are identified by the code letter X added after the code letter for the thermocouple, for example: JX. Compensating cables are identified by the code letter C added after the code letter for the thermocouple, for example: KC. Color Code: The color code for the insulation of the positive conductor for all thermocouple types is yellow, for the negative conductor the color codes are listed in the table below. The outer sheath, if present, is identified by the color codes listed in the table below. 60 Type of thermocouple Thermo- Compensating Color of positive couple wire cable conductor Color of negative conductor and sheath S – SC yellow green R – SC yellow green B – BC yellow gray J JX JC yellow black K KX KC yellow violet K – VC yellow brown K – WC yellow white T TX TC yellow blue E EX EC yellow orange Tbl. 3-11: Color codes for thermocouple wires and compensating cables according to NF C 42-324 Deviation Limits: The allowable deviations listed in the table below in °C (°F) for thermocouple and compensating cable for the allowable operating temperature ranges. Temperature range -25...250 °C (-13...482 °F) TX JX EX KX ±0.5 °C (±0.9 °F) ±1.5 °C (±2.7 °F) ±1.5 °C (±2.7 °F) ±1.5 °C (±2.7 °F) Tbl. 3-12: Deviation limits for thermocouple wires according to NF C 42-324 Temperature range -25...100 °C (-13...212 °F) TC JC EC KC VC WC SC BC ±1.0 °C ±3.0 °C ±3.0 °C ±3.0 °C ±3.0 °C ±3.0 °C ±7.0 °C ±4.0 °C (±1.8 °F) (±5.4 °F) (±5.4 °F) (±5.4 °F) (±5.4 °F) (±5.4 °F) (±12.6 °F) (±7.2 °F) 100...200 °C (212...392 °F) – ±3.0 °C ±3.0 °C ±3.0 °C (±5.4 °F) (±5.4 °F) (±5.4 °F) – 200...250 °C (392...482 °F) – ±3.0 °C ±3.0 °C (±5.4 °F) (±5.4 °F) – – ±3.0 °C ±7.0 °C ±4.0 °C (±5.4 °F) (±12.6 °F) (±7.2 °F) – – – Tbl. 3-13: Deviation limits for compensating cables according to NF C 42-324 61 3.1.5 Measurement Resistors When making temperature measurements using measurement resistors the electrical resistance of a sensor subjected to the temperature is the variable utilized. The temperature dependence of the electrical resistance of metals, semiconductors and ceramics is used as the measurement value. The materials are divided into two groups based on the slope of the curve: NTC- and PTC-sensors. PTC-sensors are materials whose resistance increases as the temperature increases (positive temperature coefficient) or “cold wire“. Included are the metallic conductors which are used in the manufacture of the measurement resistors described below. NTC-sensors (negative temperature-coefficient) or “hot wire“ are usually semiconductor or ceramic sensors, which are usually installed for specific requirements and temperatures. Materials for Measurement Resistors The are a number of requirements which must be met for the materials used as temperature sensors in order that good and reproducible measurements can be made. • • • • • • Large temperature coefficient, Minimal sensitivity to environmental effects (corrosion, chemical attack), Wide measurement range, Interchangeability, Long term stability, Easily processed. For industrial temperature measurement technology, Platinum is the most used material for the resistors followed by Nickel. It is for this reason that both of these materials will be described in detail in the following. The Platinum measurement resistors with a nominal value of 100 Ω (Pt100) has become established in recent years as the industrial standard. 62 Rt [Ω] Nominal Values The resistors are identified by the resistance at 0 °C (32 °F) (nominal value). Ni100 and Pt100 the most common types have a resistance of 100 Ω at 0 °C (32 °F), Pt500 or Pt1000 have 500 or 1000 Ω respectively at 0 °C (32 °F). Pt2000 2500 Pt1000 2000 Pt500 1500 1000 500 Pt100 Pt20 Pt10 0 -200 -100 0 100 200 300 400 500 600 700 800 900 Temperature [°C] Fig. 3-3: Resistance Rt relationship to temperature for Platinum measurement resistors with different nominal values Temperature Coefficient (Tc) More precisely stated, the temperature coefficient of the electrical resistance. It defines the change in electrical resistance between two temperatures, usually between 0 °C and 100 °C (32 °F and 212 °F) with the units: Ω ---------Ω⋅K which is therefore dimensionless --1K For smaller temperature ranges a linear relationship can be assumed: [ ] R t = R 0 1+ α ( t − t 0 ) with α= R100 − R 0 R 0 ⋅100° C 63 Where: t: Temperature in °C t0: Reference temperature ( e.g. 0°) Rt: Resistance at temperature t in Ω R0: Nominal resistance at 0 °C in Ω α: Average temperature coefficient between 0 °C and 100 °C (32 °F and 212 °F) in K-1 Platinum Material Its advantages include very pure producability, high chemical resistance, easy manufacturability, good reproducibility of the electrical properties and a wide application range between -250 °C and 850 °C (-418 °F and 1562 °F). The temperature coefficient of spectral pure Platinum is 0.003925 K-1 and is different than the value required for Pt-measurement resistors. The Platinum used for industrial Platinum temperature resistors is selectively produced. Specified in EN 60751 for the Platinum sensors, among others, are the temperature relationship to the resistance, the nominal value, the allowable deviation limits and the temperature range. Measurement Characteristics of Platinum Simplified: It the range from 0...100 °C (32...212 °F) Platinum has a temperature coefficient of 0.00385 K-1, i. e. a Pt100 measurement resistor at 0 °C (32 °F) has a resistance of 100 Ω and at 100 °C (212 °F) 138.5 Ω. Expanded: By definition the basic values are divided into two different temperature ranges: For -200...0 °C (-328...32 °F) a third order polynomial applies [ R t = R 0 1+ A ⋅ t + B ⋅ t 2 + C ⋅ ( t −100° C) ⋅ t 3 ] For the range from 0...850 °C (32...1562 °F) a second order polynomial applies [ R t = R 0 1+ A ⋅ t + B ⋅ t 2 ] The coefficients according to EN 60751 are: A = 3.9083 · 10-3 K-1 B = 5.775 · 10-7 K-2 C = 4.183 · 10-12 K-4 64 For temperatures above 0 °C (32 °F) the relationship between the temperature an the resistance can be described by the equation: 2 t=− Rt − R0 A 2⎛ A⎞ − ⎜ ⎟ + ⎝ 2⋅B ⎠ 2⋅B R0 ⋅ B in which the resistance values for the basic value tables in EN 60751 are listed for temperature in steps of 1 K. For the sensitivity, i.e. the resistance change according to K, for temperatures <0 °C (32 °F): ΔR = R 0 A + 2⋅B ⋅ t − 300° C ⋅ t 2 + 4⋅C ⋅ t 3 Δt ( ) For temperatures above 0 °C (32 °F) the following applies: Sensitivity [Ω / K] ΔR = R 0 ( A + 2⋅B ⋅ t) Δt 9 8 Pt2000 7 6 5 4 Pt1000 3 Pt500 2 Ni100 1 Pt100 0 -200 -100 0 100 200 300 400 500 600 700 800 900 Temperature [°C] Fig. 3-4: Sensitivity dR/dT for Ni100 and Platinum measurement resistors with dIfferent nominal values 65 Tolerance Classes for Platinum According to EN 60751 the Platinum resistance thermometers the deviation limits Δt are divided into two tolerance classes: ( ) ( ) Class A: Δt = ± 0.15 °C + 0.002 ⋅ t Class B: Δt = ± 0.30 °C + 0.005 ⋅ t Tolerance designation Temperature range Tolerance in K Deviation limit at 0 °C (32 °F) resistance Temperature R0 = 100 Ω R0 = 500 Ω R0 = 1000 Ω Class A -200...650 °C ±(0.15 K+0.002 · [t]) (-328...1202 °F) ±0.15 K ±0.06 Ω ±0.29 Ω ±0.59 Ω Class B -200...850 °C ±(0.30 K+0.005 · [t]) (-328...1562 °F) ±0.30 K ±0.12 Ω ±0.59 Ω ±1.17 Ω Deviation limit at 100 °C (212 °F) Class A ±0.35 K Class B ±0.80 K Deviation Limit [°C] Tbl. 3-14: Deviation limit according to EN 60751 and expanded deviation limit 6 5 4 3 ss Cla B 2 1 Class A 0 -200 -100 0 100 200 300 400 500 600 700 800 900 Temperature [°C] Fig. 3-5: 66 Deviation limit for Platinum resistance thermometers in °C Nickel Material It is appreciably less expensive than Platinum. Its temperature coefficient is almost twice as high, but it has a decidedly poorer chemical resistance. The measurement range is limited to only -60...250 °C (-76...482 °F) and the allowable deviation limits are greater than for Platinum. The Nickel measurement resistors are standardized in DIN 43760. Measurement Characteristics of Nickel Simplified: In the range from 0...100 °C (32...212 °F) Nickel has a temperature coefficient of 0.00618 K-1 i.e. the measurement resistor Ni100 at 0 °C (32 °F) has a resistance of 100 Ω and at 100 °C (212 °F) 161.85 Ω. Expanded: The relationship between the resistance and temperature for Nickel in a temperature range -60...250 °C (-76...482 °F) is: ( R t = R 0 1+ A ⋅ t + B ⋅ t + C ⋅ t 4 + D ⋅ t 6 ) where A = 0.5485 · 10-2 K-1 B = 0.665 · 10-5 K-2 C = 2.805 · 10-11 K-4 D = -2 · 10-17 K-6 Rt [Ω] According to DIN 43 760 the nominal value is 100.00 Ω (therefore: Ni100). Additionally, resistors with R0 = 10 Ω, 1000 Ω or 5000 Ω are also manufactured. 300 250 200 Ni100 150 100 50 0 -100 -50 0 50 100 150 200 250 Temperature [°C] Fig. 3-6: Relationship of the resistance Rt to the temperature for Ni100 67 In the standard the maximum allowable deviation limits Δt for Nickel resistors are defined by: for 0...250 °C (32...482 °F) Δt = ±(0.4 °C + 0.028 ⋅ t ) for -60...0 °C (-76...32 °F) Deviation Limit [°C] Δt = ±(0.4 °C + 0.007 ⋅ t ) 2.5 2.0 1.5 Ni100 1.0 0.5 0.0 -100 -50 0 50 100 150 200 250 Temperature [°C] Fig. 3-7: Maximum deviation limit in °C for Ni100 Nickel resistors are often found in the heating, ventilating and air conditioning sectors. 68 Measurement Resistor Designs Only Platinum measurement resistors will be discussed in the following. They are divided into two categories, thin film and wire-wounded resistors. Ceramic, glass or plastic are used as the basic carrier materials. Thin Film Resistors The measurement coil is made of Platinum wires with diameters between 10 µm and 50 µm. Wire-wounded Resistors A precisely adjusted Platinum coil with connections leads is located in a ceramic double capillary. Glass frit powder is packed into the holes of the capillaries. Both ends of the ceramic body are sealed with glass frit. After the glass frit is melted the Platinum coil and the connection leads are fixed in place. In another design, the Platinum coil is not placed in the holes of a ceramic cylinder, but is placed in a slot in the ceramic body. The outside dimensions are between 0.9 mm and 4.9 mm (0.035” and 0.20”) with lengths between 7 mm and 32 mm (0.28” and 1.25”). Typical applications: demanding measurement and control requirements in the process industries and laboratory applications. Connection wires Platinum coil Drilling Ceramic double capillary Fig. 3-8: Ceramic wire-wounded resistor 69 Glass Measurement Resistors In this design the measurement coil is wound in a bifilar configuration on a glass rod and melted into the glass and the connection wires attached. After it is adjusted, a thin wall glass tube is placed over measurement coil and both elements fused together. The geometric dimensions of the diameter are between 0.9...5.0 mm (0.035”...0.20”) with lengths varying between 7...60 mm (0.275”...2.35”). Typical applications: chemical system engineering. Connection wires Glass rod Platinum coil Glass tube Fig. 3-9: Glass measurement resistor Slot Resistance Thermometer The Platinum measurement winding is placed stress free in a slot in a plastic band and connection leads attached stress free. The insulation body is surrounded, including the cable exit by shrinkable tubing. The geometric dimensions for the width can vary between 8 mm (0.31”) and 12 mm (0.5”), lengths between 63 mm and 250 mm (2.5” and 10”). The thickness is 2 mm (0.08”). Typical applications: temperature measurements in the winding of electrical machines and on curved surfaces Foil Temperature Sensors The Platinum measurement winding is embedded between two Polyimide foils and the connection leads attached. The thickness is 0.17 mm (0.007”). Typical applications: Measurements on pipes Metal Film Resistors In place of measurement wires thin platinum layers are used as the measurement element. The layers are applied to ceramic carriers. There are a number of methods for depositing thin layers, e.g. vacuum vapor deposition, sputtering or sintering a thick Platinum paste. 70 Platinum Thick Film Measurement Resistors In this design a Platinum paste is applied to a ceramic substrate using a silk screen process and fused. Then the resistance is trimmed to the nominal value, a glass protection layer and connection leads attached and then stress relieved. The thickness of the Platinum layer is between 10 µm and 15 µm. Platinum Thin Film Measurement Resistors Flat types A Platinum layer 1 µm to 2 µm thick is vapor deposited or sputtered onto a ceramic substrate. The desired geometric shape is formed by cutting with a laser or structured using photolithography. The Platinum traces are between 7 µm and 30 µm wide. A laser trimmer is used to adjust the resistance to the nominal value. For protection against mechanical damage (scratches) a 10 µm thick glass ceramic insulation is applied using a silk screen process and fused. After the connection leads are attached by welding the connection spots are covered by a fused glass coating applied in a stress free manner. The geometric dimensions of the flat types vary from 1.4 mm x 1.6 mm (0.05” x 0.06”) to 2 mm x 10 mm (0.08” x 0.40”), the substrate thickness from 0.25 mm to 0.65 mm (0.010” to 0.026”) Typical applications: all application ranges, surface temperature measurements Fig. 3-10: Thin film measurement resistor 71 Thin Film Tubular Types In addition to the flat type thin film measurement resistors a round form is available. In this design the flat measurement resistors are inserted axially in cylindrical ceramic tubes. The ends of the tube are sealed by melting glass frit across them which also seals and positions the ends of the measurement resistor together with the connection leads. The end result is a round shape. The ceramic also provides protection for the thin film measurement resistors. The outside dimensions of the diameter are 2 mm to 4.8 mm (0.080” to 0.20”) and the lengths are 5 mm to 14 mm (0.20” to 0.55”) . Typical applications: process engineering Fig. 3-11: Thin film tube type (Installation principle) 72 Thin Film Platinum Measurement Resistors with Solder Connection Pads In this design the connection pads are coated with a solderable metallization. The design has adjacent connection pads with solder depots suitable for direct connection of insulated cables. Measurement resistors with connection pads at opposite ends are called “Surface Mounted Devices“, SMD, which can be directly soldered to circuit boards or hybrid circuits. Typical application: On circuit boards. Fig. 3-12: Thin film and metal wire measurement resistor designs Selection Criteria and Application Limits The application limits of the sensors are restricted by numerous parameters. The most important, without question, is the temperature. Exactly defined temperature limits are difficult to specify. In addition to the temperature, they are also influenced by the medium to be measured, mechanical factors (different expansion coefficients) and the accuracy and reliability requirements. It is not possible to specify a universally applicable conclusion as to which resistance thermometer design represents the best solution. The best construction solution is in a high way depending on the application conditions. Selection criteria are: – Temperature range It is rare, that for a specific application the entire range specified in the standards is required. For high temperatures (greater than 600 °C (1112 °F)) sensors with special connection leads (NiCr) are used. For applications with temperature shocks wirewounded types are preferred. 73 – Required accuracy and long term stability The accuracies are derived from the tolerance classes of from the actual individual measurement values; for long term stability, specific ambient conditions must be considered. Particularly, for industrial conditions above 400 °C (752 °F) caution should be exercised, carefully weigh versus thermocouples. – Sensitivity and self heating Sensitivity is defined by the resistance changes according to K and for the Pt100 it is 0.385 Ω/K and for the Pt1000 it is 3.85 Ω/K. Since the measurement signal is derived directly from measured current, the resistance to the current (voltage drop at the measurement resistor is U = RxI) in the circuit causes self heating in the measurement resistor, which increases as the square of the current (P = I2 xR). For accurate measurements the self heating must be kept small and therefore the current has to be limited. It can be stated simply that for industrial applications, using the measurement currents of modern transmitters, the following needs not to be considered. Expanded: Iallow = 2 EK ⋅ ΔTallow R0 dU 2 = R 0 ⋅ α ⋅ 2 Tallow ⋅ EK dT where Iallow : EK: ΔTallow: R0: α: Allowable measurement current Self heating coefficient in W/K Allowable temperature increase Nominal resistance Temperature coefficient Typical values for the voltage sensitivity for an allowable temperature increase of 0.1 K for Pt100 film type measurement resistors are approx. 0.1 mV/K and for a Pt1000, approx. 0.4 mV/K for measurements in flowing water. In air, the values for a Pt100 are approx. 0.03 mV/K to 0.09 mV/K. The maximum allowable measurement current for flowing water for a Pt100 is approx. 6 to10 mA and for a Pt1000 approx. 3 mA. In air for a Pt100 it is approx. 2 mA and for a Pt1000 approx. 1 mA. Wire resistors have somewhat lower self heating coefficient than the film resistor types and therefore can be operated with higher allowable measurement currents (for Pt100 Iallow. is approx. 4 mA to 14 mA in water and 2 mA to 3 mA in air). Their nominal value is however limited to 100 mW. 74 – Response time The response time of the bare resistors is usually of little concern because the design of the thermometer into which they are installed is the dominant factor in determining the response time. The following values, however, are of importance in laboratory applications. The small geometric dimensions of the film type measurement resistors and their associated minimal heat capacity results in short response times, at T0.5 approx. 0.1 s in water and approx. 3 s to 6 s in air. For wire type resistors the response time T0.5 is between 0.2 s and 0.5 s in water and between 4 s and 25 s in air. – Geometric dimensions and connection wire resistances The assigned basic values and their allowable deviation limits apply to the measurement resistors including the connection wire resistances (generally 10 mm...30 mm (0.4”...1.2”) long) or for longer connection wires up to a defined sensor point. All additional connection wires and junction resistances must be considered or compensated using special circuits. 75 3.2 Industrial Temperature Sensor Design 3.2.1 Design Temperature sensor (thermocouples or resistance thermometers) designs can be traced back to three basic versions: – Sheathed temperature sensors – Temperature sensors with exchangeable measuring insets – Temperature sensors for high temperatures (straight thermocouples) Sheathed Temperature Sensors They consist of wires embedded in an insulating powder inside a metal tube. At one end the measuring element is capped and the other end contains a connection element, which can be a cable, plug or connection box. During the manufacturing process for mineral insulated cables, the initially large diameter is reduced by stretching which compresses the insulating powder in such a manner that a flexible, vibration tight unit results. Outside Ø of the cable (D) Minimum wall Minimum Ø Minimum nominal thickness of the internal insulation ± deviation limits (S) conductor thickness (I) (C) mm / inch mm / inch mm / inch mm / inch 0.5 ± 0.025/0.020 ± 0.001 1.0 ± 0.025/0.040 ± 0.001 1.5 ± 0.025/0.060 ± 0.001 1.6 ± 0.025/0.063 ± 0.001 2.0 ± 0.025/0.080 ± 0.001 0.05/0.0020 0.10/0.0040 0.15/0.0060 0.16/0.0063 0.20/0.0080 0.08/0.0031 0.15/0.0060 0.23/0.0091 0.24/0.0094 0.30/0.0118 0.04/0.0016 0.08/0.0032 0.12/0.0047 0.13/0.0051 0.16/0.0063 3.0 ± 0.030/0.118 ± 0.001 3.2 ± 0.030/0.125 ± 0.001 4.0 ± 0.045/0.157 ± 0.002 4.5 ± 0.045/0.177 ± 0.002 4.8 ± 0.045/0.187 ± 0.002 0.30/0.0118 0.32/0.0125 0.40/0.0157 0.45/0.0177 0.48/0.0187 0.45/0.0177 0.48/0.0187 0.60/0.0236 0.68/0.0268 0.72/0.0283 0.24/0.0095 0.26/0.0102 0.32/0.0125 0.36/0.0142 0.38/0.0150 6.0 ± 0.060/0.236 ± 0.0025 6.4 ± 0.060/0.252 ± 0.0025 8.0 ± 0.080/0.315 ± 0.0032 10.0 ± 0.100/0.394 ± 0.0039 0.60/0.0236 0.64/0.0252 0.80/0.0315 1.00/0.0395 0.90/0.0354 0.96/0.0378 1.20/0.0472 1.50/0.0590 0.48/0.0187 0.51/0.0200 0.64/0.0252 0.80/0.0315 D = Outside diameter C = Conductor diameter S = Wall thickness I = Insulation thickness Tbl. 3-15: Construction and dimensions of mineral insulated cables with 2 inner conductors 76 The sheathed temperature sensors are used, e.g., where the measurement site is difficult to access. Applications: Bearing temperature measurements, hot gas ducts, open tanks, laboratories, test stands, etc. Fig. 3-13: Sheathed temperature sensor design for direct contact with the medium 77 Temperature Sensors with Exchangeable Measuring Inset The measurement inset is constructed in a manner similar to the sheathed temperature sensors. The connections are usually made using screw terminals on a ceramic socket. To protect this unit from process conditions and to facilitate replacing the unit without shutting down the process, the unit is built into a protection fitting. It consists of a thermowell with process connections (e.g. flanged, threaded) and a connection head, with provisions for installing an appropriate cable connector. These components are defined in the standards: DIN 43729 for connection heads, DIN 43772 for thermowells. L min 30 U Ø 12.5 C Ø 24h7 Ø7 4 Form 4 (D1, D4) S 50 ØD Ø 6.1 ØE Welded flange Fig. 3-14: Standardized thermowell examples: form 4 for hot steam pipelines NAMUR thermowells for short response times The entire sets of design types are defined in the standards: DIN 43770, DIN 43771 for temperature sensors with exchangeable measuring insets and DIN 43733 for straight thermocouples. 78 Manufacturers and users have developed additional designs, based on the standardized ones, in order to accommodate varying operating and installation requirements. Type BUKH Type BUZH Type AGL M20 x 1.5 M20 x 1.5 M24 x 1.5 M24 x 1.5 Fig. 3-15: Additionally developed connection head examples; Type BUZH, BUKH for transmitter installed in the cover Type AGL Flameproof Enclosure / Explosionproof Often direct contact of the measuring sensor with the medium is not possible. In order to increase the life of the inset when oxidation and corrosion effects are present, or to facilitate a fast exchange without interrupting the process, thermowells are utilized. For higher pressures, thermowells are made of drilled solid materials and processed on the outside. They have the advantage that their dimensions, shape and wall thickness can be optimally matched to the requirements (pressure, flow, etc.). Thermowells manufactured using these designs are usually more expensive than those made of tubing and pipes. For this reason the thermowells made from solid materials are only used for medium contacting temperature sensor area. Outside of the medium contact area, they can be extended using extension tubes if required. For processes with lower loads, economical thermowells are used manufactured from tubing material with a welded plug at the outer end. Medium Minimum installation length Gas 15...20 times thermowell diameter at the tip Liquid 5...10 times thermowell diameter at the tip Solid 3...5 times thermowell diameter at the tip Tbl. 3-16: Recommended installation lengths (standard values for stationary media) 79 The installation length includes the length contained in the pipe couplings. In addition, listed in the following are minimum length recommendations for the most common thermowells: Thermowell diameter 9 mm 0.357¨ 11/12 mm 0.433¨/0.472¨ 14/15 mm 0.551¨/0.590¨ 22 mm 0.866¨ 25 mm 0.984¨ Medium Minimum installation length Gas 180 mm 7.09¨ 250 mm 9.84¨ 300 mm 11.81¨ 450 mm 17.72¨ 500 mm 19.69¨ 80 mm 3.15¨ 110 mm 4.33¨ 160 mm 6.30¨ 250 mm 9.84¨ 300 mm 11.81¨ Liquid Tbl. 3-17: Recommended installation lengths for standard thermowell diameters Sensor head (option with transmitter) Measuring inset Extension tube Thermowell Process connection Fig. 3-16: Completely assembled temperature sensor with thermowell and extension tube 80 Temperature Sensors for High Temperatures (Straight Thermocouples) These are also designed with exchangeable measuring insets. Since these applications are predominantly in combustion processes (temperatures to 1800 °C (3272 °F), these sensors incorporate some special design features. Measuring inset: Thermocouple wires with large cross sections in a ceramic insulating rod Thermowell: Made of heat resistant metals or ceramics. Process connections: Since these applications are predominantly pressure free, basic connections (oval flange, threaded bushings) with packing glands can be used. Connection head N K 16 22 24 32 26 32 S ØD H Design ST P-AK D 15 H 22 Thermocouple with ceramic insulation Ceramic thermowell Metal extension Ceramic inner tube Design ST P-AKK tube Process connection M20 x 1.5 Fig. 3-17: Example: Temperature sensor design “Straight Thermocouple“ 3.2.2 Installation Requirements In industry there are a multitude of applications requiring temperature measurement. In many instances a standardized temperature sensor cannot be used. Special designs are required in order to optimize the measurement, e.g. measuring sensors with extremely short sensor lengths or thermowells with minimum mass. Heat Transfer Temperature sensors must always be in good contact with the medium, so that a fast temperature equilibrium condition can be achieved. Thermal measuring errors can be minimized using appropriate measures. 81 With increasing flow velocity the heat transfer increases and installation lengths can be reduced. This is particularly apparent by the D-Sleeves defined in standard DIN 43772 for use in hot steam pipelines. They are only installed to the tapered end and therefore have an appreciably shorter installation length than the previously listed rules of thumb (see Tbl. 3-17 Recommended installation lengths): Fig. 3-18: Temperature sensor in a hot steam pipeline at high flowrate 82 Installation Positions If the designed installation length required for the installation is not available, then design changes to the sensor or to the installation arrangement may be required to assure more advantageous conditions: • A tapered thermowell can reduce the required installation length by approx. 30 %. • In pipelines with smaller diameters (DN 10...DN 20 (3/8”...3/4”)) the thermowell can be made an integral part of the connection adapter. Fig. 3-19: Shorter installation lengths using reduced thermowell tips or exposed measuring inset Fig. 3-20: Temperature sensor installation in small diameter pipelines 83 At the installation site, selection of the connection adaptor orientation for the sensor may also be used to achieve the required length: • By lengthening the connection adaptor for the sensor (see Fig. 3-20), • by increasing the diameter of the pipeline, • by installing at an angle, • by installing in an elbow (this installation method is preferred because it reduces the pipeline cross section the least and imposes the least stress on the thermowell) see Fig. 3-21. Fig. 3-21: Installation orientations in a pipeline Installations without Thermowells Using a directly installed temperature sensor without a thermowell can improve the response time and with the smaller diameter the installation length can be made very short (possibly:1.5; 2; 3; 6 mm (0.060“; 0.080“; 0.125“; 0.250“)). Thermocouples, in comparison to resistance thermometers measure at point locations, allowing very short installation lengths (see Tbl. 3-18). Diameter 1.5 mm (0.060“) 3 mm (0.125“) Medium Minimum installation length Gas 30 mm (1.18“) 6 mm (0.250“) 60 mm (2.37“) 100 mm (4.00“) Liquid 8 mm (0.312“) 30 mm (1.18“) 60 mm (2.37“) Solid 5 mm (0.200“) 20 mm (0.750“) 30 mm (1.18“) Tbl. 3-18: Recommended installation lengths for direct immersion (without thermowell) of the temperature sensors For resistance thermometers the temperature sensitive length of the measurement resistors, type dependent, is approx. 7...30 mm (0.28“...1.18“) long and must be added to the values in the table. 84 3.2.3 Process Connections Types Installations in pipelines are predominantly made using threaded, flanged or welded connections. The selected installation type determines the pressure rating, since the pressure existing in the process pipeline acts on the cross section of the connection fitting. Threaded Connections Cylindrical threads are sealed using gaskets installed in the seal area. Based on the temperature at the seal and the aggressiveness of the medium, gaskets made of Fluorocarbon, Copper or stainless steel can be used. Because of the different elasticities and because the process pressure could cause the gaskets to lift from the seal surface, pressures which can be sealed are relatively low (max. 100 bar (1,450.38 psi)). Tapered threads seals are achieved by the sealing action of the thread design without requiring additional gaskets or the use of teflon tape. Since the seal exists along the entire length of the threads, the process pressures which can be sealed are higher. Dependent on the manufacturing process for the threads in the threaded bushings or nipples and the strength of the material, pressures of 300...400 bar (4,351.13...5,801.51 psi) can be sealed. Flanged Connections For flanged connections the pressure rating of the flange determines the maximum pressure. Pressure ratings up to 160 bar (2,320.60 psi) are available. At the lower pressures, flat gaskets are used while at higher pressure, O-ring gaskets in conjunction with ring joints are used. Note: The smaller the projected area of the seal, the higher the seal pressure because when bolting the mating parts together, a higher compression force between the parts can be achieved. Welded Connections In ranges to 700 bar (10,152.64 psi) welded thermowell connections are often used. Care should be exercised, especially at high flow velocities, to assure that the connection nipples/thermowells are designed to be close fitting, to prevent damage or breakage of the thermowell due to vibrations at resonance. Conical and Lens Type Connections For high pressure applications (up to 4000 bar (58,015.07 psi)) in gas synthesis applications, requiring fast responding and replaceable sensors, conical shaped seal systems are used, in which the mating piece has an approx. 1° larger angle, so that the seal is effectively produced by a line shaped seal area. In this design, extremely high seal forces can be achieved. 85 Fig. 3-22: High pressure temperature sensor with conical seal Pressure Tests Often the manufacturer must provide a test certification showing that the seal is effective under pressure (see chapter 6). Typically, a test pressure 1.5 times the pressure rating of the operating pressure is applied for 3 minute period. 86 3.2.4 Process Requirements When selecting the optimal sensor for a particular application, the required properties must first be defined: – Short response time – Accuracy – Small space requirements The result is a design with small sensors. On the other hand, the process requirements must be considered: – – – – – – Temperature Flow velocity Pressure Vibration Abrasion Aggressive media These require a more substantial design with longer installation lengths, because: – – – – – – The temperature requires a reduction in the strength, the flow velocity causes a bending force and resonance vibrations, the pressure causes a radial force on the sheathed surface, the vibration causes a load on the material, especially at the attachment point, the abrasion causes material loss, an aggressive fluid causes a loss of the wall thickness due to corrosion attack. In addition to the many special designs, there are also thermowells, which are completely defined in the standards (e.g. DIN 43772). The thermowell should provide protection for the measuring inset against chemical and mechanical damage. The selection of the thermowells is on the one hand dependant on the process parameters and on the other on the required measurement parameters. 87 Permitted pressure [bar] The standard DIN 43772 includes the load diagrams for various thermowell designs. 800 *) Form 4 (D2, D5) Protection sleeve c = 125mm (5“): Bending, flow impact lengths = 125 mm (5“) Thermowell diameter = 24 mm (0.95“) Thermowell inside diam. = 7 mm (0.28“) 720 Vapor pressure curve 640 **) 560 480 **) Form 4 (DS) Protection sleeve c = 65 mm (2.6“): Bending, flow impact lengths = 65mm (2.6“) Thermowell diameter = 18 mm (0.7“) Thermowell inside diam. = 3.5 mm (0.14“) *) 400 320 240 160 80 0 0 60 120 180 240 300 360 420 480 540 600 Flow velocity Water = 5 m/s (16 ft./s) Steam = 60 m/s (200 ft./s) Air = 60 m/s (200 ft./s) Temperature [°C] Fig. 3-23: Typical load diagram, material 1.4571 (316 Ti) Fig. 3-24: Pressure/Material dependent selection of thermowells (form 4 with 65 mm (2-1/2”) tapered length/installation length) 88 3.2.5 Thermowell Designs Thermowells must satisfy the following functions: • Position the temperature sensitive sensor tip in the process • Protect the temperature sensor • Seal the process areas from the environment. Failure of any of these components can lead to operation interruptions, release of flammable, explosive or poisonous materials, equipment damage or personnel injury. Therefore a meticulous risk and load analysis is essential. Thermowells, dependent on the application area, are subjected to certain legal requirements. As pressurized parts e.g. materials, design, calculations, manufacture and testing must satisfy the Pressure Equipment Directive. Internationally the rules and regulations in the ASME-Codes have as wide acceptance. In explosion hazardous areas, the thermowells provide a separation between zones of different hazardous levels (see also chapter 7). Thermowells are available in proven and standardized forms with a variety of different process connections. Fig. 3-25: Thermowell designs (schematically) For standardized thermowells, load diagrams are published in the corresponding standard, which specify the maximum allowable pressure in air/steam or water at a specific temperature and a specific maximum flow velocity. Often, however, thermowells deviate in dimensions and/or operating conditions from the standard values. 89 Thermowell Materials In addition to the design and dimensions of the thermowells, the selection of the material is of decisive importance. The material must be compatible with the process conditions and have sufficient stability (see chapter 3.2.4 and chapter 3.2.6). For pressure containing parts, material test certifications are often required for their heat strength and/or notch impact strength. The load limits for the materials in the lower temperature ranges are determined, e.g., from the 1 %- yield point and at higher temperatures from the 100,000 hour creep strength. These values are published as a function of the operating temperature in the material standards or data sheets. The safety factor (e.g. 1.5 for ductile steel) and possible load reductions due to welded connections can be found as a function of the material group in the relevant directives. Thermowells made of brittle materials (e.g. glass, ceramic) require special considerations, since a single impact could lead to sudden and complete destruction. As a rule, considerably higher safety factors and protection measures are required relative to impact stresses. In critical installations a second barrier (compression fittings, solid electric feedthrus, etc.) is necessary, which prevents the escape of hazardous material in case of a thermowell breakage. Selection of the Thermowell Design The medium acts mechanically on the thermowell through pressure, flow velocity and eddy formation. Therefore selection of a thermowell design includes: • The stress due to the external static pressure, • the bending stress due to the flow of the medium, • the stress due to the outside induced flexural vibrations. An example of a installation situation for thermowells is shown in Fig. 3-26. 90 Medium Distributed load Welded seam Vibrationable length Product flow length Bearing point Outer diameter Flange adaptor Inner diameter Temperature θ Pressure ρa Spec. density ρ Velocity ν Process tube Tip Fig. 3-26: Thermowell installation example The pressure strength can be increased by increasing the wall thicknesses. At higher temperatures, the strength values for many materials decrease to the point where acceptable wall thicknesses can only be achieved by using higher heat resistant steel or nickel alloys. The statistical calculations for the thermowell loads yield the stress conditions. The stresses due to external pressure are superimpose on the bending stresses due to the flowing medium. As a function of the outside diameter of the thermowell, the skin-friction coefficient, the velocity of the medium and its density a distributed load is produced on the thermowell. This causes a bending stress whose maximum occurs at the mounting location. The most effective method to reduce high bending stresses is to reduce the length of the thermowell. Additionally increases in the outside diameter at the mounting location or selection of a stronger material are also possible alternatives. In horizontal installations at higher temperatures a bending stresses can be produced by the weight of the thermowell because of the creep processes and lead to appreciable deformations. 91 Vibration Analysis The dynamic loads due to the vibration of the thermowells require a detailed discussion. The vibrations cause alternating stresses in the thermowell, which are superimposed on the stress conditions described above. In addition to the resonant frequency of the thermowells in its installed condition, the excitation frequencies of external periodic forces are important. One of these excitation frequencies are caused by vortex shedding of the flowing medium downstream from the thermowell. At certain flow conditions, a “Karman Vortex Street“ forms which alternately sheds individual vortices from the sides of the thermowell. The frequency of the vortex shedding is a function of the process parameters and the thermowell dimensions. Laminar flow 0 < Re < 4 Stagnation eddy 4 < Re < 40 Kármán Vortex Street 40 < Re < 160 Turbulent flow Re > 160 Fig. 3-27: Flow conditions around thermowells The periodic excitation forces cause the thermowell to vibrate. The stress due to the vibration amplitude increases rapidly in the resonance range, i.e. when the excitation frequency is the same as the resonant frequency of the thermowells. Since the damping in the worst case can be assumed to be small, the amplification factor of the vibrations at resonance approaches infinity. This quickly leads to fatigue and breakage of the thermowell at the mounting location or at any other sharp edge or sudden change in the wall thickness (Notch effects). Periodic excitation forces, which can also be produced by pumps, compressors and other rotating or oscillating masses, are transmitted through the pipeline to the thermowell. Non-critical and aperiodic forces (e.g. individual pressure shocks), do not lead to excessive forces and long term vibrations of the thermowells. 92 As a consequence a very conservative design rule requires that the excitation frequency never exceed 80 % of the resonant frequency of the thermowells in applications with a high risk potential. When vibration problems exist, shortening the unsupported length (which also changes the resonant frequency) is the most effective measure to prevent failures due to vibration. The reduction of the effective total length can also be achieved by adding close fitting sleeves or supports at suitable locations. Welded sleeves can be used to reduce the length of the part protruding from the sleeve/thermowell. In those applications where it is not possible to follow the 80 % design rule (e.g. temperature sensors for Diesel motors, turbines, compressors etc.), comprehensive type tests are required. They include, for example, vibration tests at resonant frequency point at the operating temperature, where acceleration amplitudes at the thermowell tips may exceed 150 g (150 times the acceleration of earth gravity). After 10 million load cycles have been successfully passed, long term reliability can be assumed. In spite of this, the resonant frequency point should be passed quickly when starting up or closing down the system, when possible. Optimization Measures Unfortunately many measures to improve the mechanical stability have a negative impact on the measuring characteristics. High load carrying, i.e., relatively thick walled thermowells result in a decidedly longer response times due to their heat capacity. They can be reduced by making the fit between the measuring inset and the opening in thermowell tighter, reducing the thickness at the thermowell tips, as well as reducing the measuring inset diameter as far as this is technically possible. Thermowell with vibration desirable short installation lengths show a relatively large heat loss. Possible improvement measures include reducing the temperature sensitive length of the measuring inset to the end of the temperature sensor and reducing the thickness at the thermowell tip. 93 Problem Corrective measures Thermowell geometry Corrective measures Operating parameters Excitation frequency too close to resonance point – Reduce unsupported length – Increase outside diameter – Reduce flow velocity (Medium density has no effect) Pressure force at tip too high – Increase outside diameter of the tip – Select higher strength thermowell material – Reduce operating pressure Bending stress at the mounting location too high – Reduce flow velocity – Reduce medium density – Reduce operating pressure – Increase outside diameter at the mounting location – Reduce length – Select higher strength thermowell material Tbl. 3-19: Summary of the primary optimization options for thermowells Important for highly stressed thermowells is to avoid stress peaks at step diameter changes, threads, weld seams etc. The so called Notch effect can be reduced by carefully rounding all sharp edges at geometry transitions, selecting less sensitive thread types, move welded seams to less sensitive locations, etc. It is possible to optimize the flow conditions by appropriate thermowell geometries, e.g., a tapered thermowell with its continuously changing outside diameter reduces the formation of a vortex street and thereby the excitation forces. Various operating conditions can be considered together, as long as the selections for the undesirable conditions are defined (e.g. maximum flow velocity at maximum medium density and maximum pressure). It should be noted that the density of the medium may increase if the phase changes or if it is cooled which adds to stresses on the thermowell. 94 Selecting Practical Thermowell Specifications Several special programs are available to assist in selecting thermowell designs. The basis for the selections is the careful specification of the operating conditions and design details (see Tbl. 3-20). The determination of the correct entry parameters, as well as the interpretation the selection results together with optimization measures requires, especially in borderline applications, a fundamental knowledge of the subject and experience. Design and manufacturing quality are in the end, decisive for operating safety of thermowells. Category Required information Useful information General System Design Special hazardous conditions Geometric installation requirements Medium Composition Temperature Pressure Flow velocity Density at operating conditions Material Temperature limits Corrosion resistance Weldablility Available material specifications Problems with corrosion, abrasion Connection materials Geometry Diameter Length Connection dimensions Maximum possible diameter Response time Heat conduction error Test pressure Normal volume, mass flowrate, Pipeline size Tbl. 3-20: Information for selecting thermowell designs Connections of Thermowells For the dimension of the process connections there are standardized calculation methods (e.g. for welded seam thicknesses, flange connections) or corresponding experience values (e.g. nipples with seal rings, self sealing tapered threads). For process connections with gaskets the so called sealing pressure is decisive. It is a function, in addition to the type, of the material and dimensions of the gasket, as well as the operating temperature and proper installation. For threads an appropriate lubricant to reduce the thread friction and prevent galling is recommended. Thereby the stresses on the threaded nipples are reduced and higher sealing pressures at lower tightening torques are achieved. For threads with gaskets, retightening after the first load cycles to equalize the seating processes and maintain the gasket forces is recommended. 95 3.2.6 Corrosion Reasons for the Formation of a Corrosion Element The electrochemical processes, in which the corrosion occurs, are determined by the material, the ambient effects and the composition of the electrolytes. For the formation of a corrosions element, i.e. the generation of a potential difference, certain factors must be present: • Material zones with electrically conductive materials at different potentials, • a connection between these zones for exchanging charge carriers (electrons), • completing the circuit by the electrolyte. Corrosion elements can exist in parts, that appear to be made of “one“ material due to composition differences in the alloy or contamination. Corrosion Types Surface Corrosion Surface corrosion, which can be uniform or nonuniform over the entire surface, produces crater type depressions. This can be countered by properly sizing the thermowells. Or, the material loss due to corrosion can be reduced by increasing the surface quality. Uniform corrosion is easiest to combat through use of suitable materials. Fig. 3-28: Uniform material disintegration corrosion shown schematically A Starting condition B Material thickness disintegration of the part due to uniform corrosion K Grain (crystal) 96 Contact Corrosion Contact corrosion occurs when two dissimilar metals are in contact in the presence of an electrolyte. The less precious of the two metals is subjected to the most corrosion, the material loss is uniform. The problem is design related and can be counteracted, e.g. by selection of similar material type combinations. High Temperature Corrosion The suitability of materials for use at high temperature is primarily due to the build up of a protective oxide layer on the surface. The presence of this oxide layer reduces the direct contact between the metal and the atmosphere, finally preventing it. The oxidation resistance of a material at elevated temperatures depends on the type of oxide which forms. If the oxide is loose and porous, the oxidation process continues until the entire surface is oxidized. The selection of suitable alloys must be made considering the actual operating conditions. The oxidation resistance of Fe-Ni-Cr alloys at isothermal conditions is primarily a function of their chromium content, while the Nickel and Iron components contribute only slightly. Under cyclic temperature conditions the degree of resistance can change appreciably. In this case, alloys with a higher Nickel contact are decidedly better, because it reduces the thermal expansion and thereby the flaking off of the oxide. fehlt Fig. 3-29: High temperature corrosion of CrNi-Steel 1.4841 (AISI 314) for use in waste Incineration systems at temperatures approx. 1300 °C (2372 °F) after 5-days-service 97 Pitting Corrosion The pitting corrosion is a localized, pinpoint shaped, penetrating type of corrosion, which in a relative short time can progress through the entire thickness of the metal. Since it actually eats into the metal and only exhibits point like damage on the surface, it is often difficult to recognize and therefore dangerous. It is greatly accelerated in chloride containing aqueous solutions. The addition of Molybdenum (Mo) and higher chromium contents provides better resistance, e.g. 1.4571 (AISI 316) which contains 2.5 % Mo. The material 1.4539 (Uranus B6) with 5 % Mo appreciably improves the resistance compared to 1.4571 (AISI 316). Fig. 3-30: Pitting corrosion schematically I Passive layer, with small localized breakthroughs at which pinpoint and hole shaped corrosion occurs II Active disintegration of the material Fig. 3-31: Pitting corrosion in a Monel thermowell after usage in a chemical system 98 Crevice Corrosion Crevice corrosion occurs due to potentials in the narrow openings caused by the presence of oxygen, such as may exist under a water surface or in narrow gaps, e.g. at the thermowell/flange connection. As a manufacturing countermeasure, the thermowell should be welded to the flange without gaps. The material disintegration occurs as a groove or surface phenomenon. Since crevice corrosion is not always visually evident, it is one of the most dangerous types of corrosion. Steels with higher pitting resistance are also less susceptible to crevice corrosion. Fig. 3-32: Crevice corrosion schematically III Passive layer, which will no longer be created in the narrowing gap III Active disintegration of the material III Surface contamination, deposits, etc. 99 Intercrystalline Corrosion Intercrystalline corrosion is caused by selective corrosion. This occurs due the existence of differing potentials at the grain boundaries, or due to nonhomogeneous structures, in which the grain boundaries are dissolved. This type of corrosion occurs primarily in stainless steels when exposed to an acidic medium when, due to heating effects (450...850 °C (842...1562 °F)) in austenitic stainless steels and above 900 °C (1652 °F) for ferritic stainless steels the Chromium Carbides precipitate in a combined “critical“ form at the grain boundaries. This causes a localized depletion of Chromium in addition to the precipitated Chromium Carbides. For reducing these effects, steels with reduced Carbon content, so called “Low carbon“ steels such as 1.4404 (316L) or so called stabilized (with Titanium or Niobium) steels such as 1.4571 and 1.4550 (AISI 316Ti and 347) are used. The Titanium or Niobium binds with the Carbon to stabilize the Ti- or Nb-carbides, so that even for critical heat effects, the Chromium Carbides cannot be precipitated. Fig. 3-33: Intercrystalline corrosion schematically III Passive layer formed at grain boundaries where Chromium has not been depleted III Selective attack near the grain boundaries in zones with depleted Chromium III Grain boundaries with Chromium Carbide 100 Transcrystalline corrosion Differing from intercrystalline corrosion the transcrystalline corrosion takes place within the grains in a material structure. It generally occurs along those sliding planes, on which an increased displacement density (the number of displacements which exist which is a measure of previous deformations ) has occurred due to plastic deformations and therefore a higher energy level has resulted. It is a form of corrosion with serious consequences, since it usually becomes apparent only after a breakage has occurred (e.g. after continuous, large tension loads). Fig. 3-34: Transcrystalline corrosion stress cracks schematically; branching cracks II Passive layer II Localized penetration through the passive layer 101 Stress Crack Corrosion Conditions for the occurrence of stress crack corrosion are the presence of tensile and residual stresses (e.g. caused by welding or cold working), the presence of an electrolyte and the existence of a crack. These stresses lead to a movement of the internal displacements in the material. On the surface of the part sliding stages occur. If the surface is covered with a tightly attached blocking oxide layer, it can rupture at the sliding stages and corrosion can attack the material. The interaction between the corrosion and the mechanical loads leads to accelerated crack formation and early failure of the part. The tendency towards stress crack corrosion is particularly evident in austenitic steels. This aided by Halogen ion containing corrosion elements, especially ones containing Chlorides of Alkali or Earth Alkali metals, e.g. solutions which contain Sodium, Calcium or Magnesium chlorides. As the chloride ion concentration increases, so does the susceptibility. For this reason in sour gas applications, e.g. according to NACE, a hardness of 22 HRC should not be exceeded for steels. Cold worked thermowells should be stress relieved after they have been formed. Medium Material - Composition - Electro-chemical - coditions (Redox and - corrosion potential) - pH value - Temperature - Stream ... - Type - Composition - Structure - Precipitation - Grain boundaries - Surface - ... SCC Mechanical stress - Residual stress - Operating stress - (stat./dynam./therm.) - ... Fig. 3-35: Stress crack corrosion as the result of the interaction among of different factors 102 Vibration Crack Corrosion Vibration crack corrosion is the result of the existence of dynamic tensile stresses in the presence of a corrosive medium. Displacement of the sliding stages of the material on the surface of the part, which occurred due to the vibration forces lead to deep cracks. Even weak electrolytes can cause an early failure of the part. Vibration crack corrosion can be counteracted by selecting suitable materials as a function of the attacking medium and by appropriate thermowell design. For critical applications operating near the stress limits, it is essential that design calculations be made. They should consider especially the critical resonance vibrations (see chapter 3.2.5). Fig. 3-36: Vibration crack corrosion example of a flange/thermowell connection. The crack started at the beginning of the threads on the process side. Stress and vibration corrosion can occur in all metallic materials. The corrosion process for stress crack corrosion is a function of the material and occurs as electrolytic interor transcrystalline corrosion. 103 Hydrogen Embrittlement Hydrogen embrittlement is caused by cathodic reactions in an electrolyte. The active hydrogen diffuses into the material and is stored in the tetrahedron and octahedron spaces in the crystal lattice. The crystal lattice is expanded and the hydrogen atoms restrict the elastic movement of the metal atoms (embrittlement). When stressed, cracks are formed eventually leading to failure of the material. As with all crack corrosion the process remains unnoticed initially and only becomes apparent after a failure has occurred. Special materials are used to prevent this type of corrosion. The types of damage caused by hydrogen in an aqueous medium in steels are different from those that occur at high temperatures in gases. The damage in gaseous media is based primarily on the decarburization of the steel, while, dependent on the temperature of the material and the pressure in the medium containing the hydrogen, the decarburization may progress from the surface into the inner sections of the steel. The diffusion effects are forced into the background. In a truer sense, only the damages caused by the inner decarburization are designated as hydrogen attacks. Since the decarburization can be suppressed if the carbon is combined, all carbide building steel alloys are superior to the carbon steels in regard to compressed hydrogen resistance. The resistance increases in general with increasing alloy content. The specially developed steels for use against compressed hydrogen attack contain above all else, Chromium, Molybdenum and Vanadium elements in low alloy steels such as 1.7362 . They are standardized in SEW 590 (Steel Iron Material Sheet). In addition to these materials, other steels can be used dependent on the stress conditions, particularly the material groups “heat resistant and high heat resistant steel“ as well “stainless and acid resistant steel“. Selective Corrosion Differing from the corrosion mechanisms discussed up to this point, selective corrosion only attacks one structure type, while the rest of the structure remains completely intact. For the austenitic CrNi steels it is primarily the Sigma-Phase and the δ-Ferrite which is converted to the Sigma-Phase which is selectively attacked. This type of corrosion occurs predominantly in the welded seams of austenitic CrNi steels. A selective attack occurs for certain mixtures of reducing and oxidizing acids, e.g. hydrofluoric/ nitric acid mixtures and in strong oxidizing sulphuric acid. 104 General Comments Even when the material selection is optimized, an aggressive attack could still occur in certain areas, e.g. at welded seams, because during welding, decomposition of the alloy can occur. Partial material compositions may be formed which have a lower resistance. In order to prevent this possibility, thermowells manufactured from solid materials are used where an aggressive medium is present so that weld seams on the medium side are not required. In addition, sometimes two thermowells are using, one placed inside the other. In general, there are materials suitable for most media, but there is no material that is totally resistant. For the temperature measurements the interaction of aggressive media and high temperatures, disintegration is always a given. The degree depends on the material selection, which may be used to minimize the effects or to maximize the life of the instrument. For selecting the correct material it is advisable, as a minimum, to use at least the same material quality which was used to make the tank/pipeline. If cost or strength is a concern, a material can be used with appropriate properties for the sheath material, e.g. Glass, Teflon, Tantalum, or an abrasion and corrosion resistant coating such as Stellite. 105 3.2.7 Material Selections The following table provides an overview of the many materials used for thermowells. Max. Material No. Temp. in °C (°F) Material properties Application range Unalloyed, Heat and High Heat Resistant Steel 400 (750) 1.0305 (ASTM 105) Unalloyed steel 500 (930) 1.5415 Low alloy heat resistant (AISI A204 Gr.A) with Molybdenum additive Welded and threaded thermowells in steam pipelines Welded and threaded thermowells 540 1.7335 Low alloy heat resistant steel (1000) (AISI A182 F11) with Chromium & Molybdenum additives Welded and threaded thermowells 570 1.7380 Low alloy heat resistant steel (1000) (AISI A182 F22) with Chromium & Molybdenum additives Welded and threaded thermowells 650 1.4961 (1200) Welded and threaded thermowells High heat resistant austenitic Chrome-Nickel steel (Niobium stabilized) Rust and Acid Resistant Steel 550*) 1.4301 (1020) (AISI 304) Good resistance against organic acids at Food and beverage moderate temperatures, salt solutions, e.g. industry, medical sulfates, sulfides, alkaline solutions at system engineering moderate temperatures 550*) 1.4404 (1020) (AISI 316 L) Through the addition of Molybdenum higher corrosion resistance in non-oxidizing acids, such as acetic acid, tartaric acid, phosphoric acid, sulphuric acid and others. Increased resistance against intercrystalline and pitting corrosion due to reduced Carbon content Chemical and paper industries, nuclear technology, textile, dye, fatty acid, soap and pharmaceutical industries as well as dairies and breweries 550*) 1.4435 (1020) (AISI 316 L) Higher corrosion resistance than 1.4404, lower Delta-ferrite content Pharmaceutical industry 550*) 1.4541 (1020) (AISI 321) Good intercrystalline corrosion resistance. Good resistance against heavy oil products, steam and combustion gases. Good oxidation resistance Chemical, nuclear power plants, textile, dye, fatty acid and soap industries 550*) 1.4571 (1020) (AISI 316 Ti) Increased corrosion resistance against cer- Pharmaceutical tain acids due to addition of Molybdenum. industry and dairies Resistant to pitting, salt water and aggres- and breweries sive industrial influences *) As a function of the pressure load and corrosion attack, operating temperatures to 800 °C (1472 °F) are possible. 106 Max. Temp. in °C (°F) Material No. Material properties Application range Heat Resistant Steel 1100 (2012) 1.4749 (AISI 446) Very high resistance to Sulphur conUse in flue and combustion taining gases and salts due to high gases, industrial furnaces Chromium content, very good oxidation resistance not only at constant but also for cyclical temperatures (Minimum resistance to Nitrogen containing gases) 1200 (2192) 1.4762 (AISI 446) High resistance to Sulphur containing gases due to high Chromium content (Minimum resistance to Nitrogen containing gases) Use in flue and combustion gases, industrial furnaces 1150 (2102) 1.4841 (AISI 314) High resistance to Nitrogen containing and Oxygen poor gases. Continuous use not between 700 °C (1292 °F) and 900 °C (1652 °F) due to embrittlement (higher heat resistance than 1.4749 and 1.4762) Poser plant construction, petroleum and petrochemical, industrial furnaces 1100 (2012) 2.4816 (Inconel 600) Good general corrosion resistance, resistant to stress crack corrosion. Exceptional Oxidation resistance. Not recommended for CO2 and Sulphur containing gases above 550 °C (1022 °F) and Sodium above 750 °C (1382 °F) Pressurized water reactor, nuclear power, industrial furnaces, steam boilers, turbines 1100 (2012) 1.4876 (Incoloy 800) Due to addition of Titanium and Aluminum the material has especially good heat resistance. Suitable for applications, where in addition to scale resistance, highest toughness is required. Exceptional resistance to carburizing and nitration Pressurized water reactor, nuclear power construction, petroleum and petrochemical, industrial furnaces Tbl. 3-21: Thermowell materials For applications at low temperatures, austenitic Cr-Ni or Ni alloys are used. They are characterized by especially high toughness at very low temperatures. 107 3.2.8 Ceramic Thermowells Metal thermowells are preferred since they assure an absolute seal against the medium and the pressure. Their use is limited to temperatures below 1150...1200 °C (2102...2192 °F), because their mechanical strength as well as their oxidation resistance above this temperature range can no longer assure a sufficiently long operating life. Ceramic thermowells, because of their comparatively poorer mechanical properties (very brittle) are only used when the operating conditions exclude the use of metal or for chemical resistance or for very high measuring temperatures. In the temperature range 1200...1800 °C (2192...3272 °F) ceramic thermowells must be used. Installation Orientation In order to assure satisfactory operation, a number of special aspects must be considered. Ceramic thermowells break easily and are shock sensitive, and have low mechanical strength at high temperatures. Rules of thumb for using ceramic thermowells: • • • • • • • Keep the length short Install vertically Approach higher temperate zones very slowly Keep away from direct vibrations Protect from added weight due deposits Avoid impact stresses from flying particles Store dry (best in an oven). It is not essential that the measuring location be in the middle of the oven chamber. At a shorter distance from the wall, i.e. a shorter installation length, the temperature profile is practically constant (as long as the wall is not cooled). Since the temperatures at the wall or at the lining in a furnace are usually less than 1200 °C (2192 °F), heat resistant steel materials can be used for such applications. The ceramic thermowell should be inserted in a metal supporting tube in order to keep the unsupported length, which might be subjected to bending forces, short. This design also has the advantage, when the temperature sensor is mounted in the support tube using the usual sliding collar/flanged stop, that it can be introduced slowly stepwise into the process zone. 108 Fig. 3-37: Installation of a straight thermocouple with an adjustable mounting Thermal Shock Resistance The ceramic thermowell materials used have different sensitivities to thermal shock. The ability to withstand temperature changes decreases with increasing purity of the (Al2O3) thermowells (C 530 > 80 % purity, not gas tight; C 610 > 60 % purity, gas tight and C 799 > 99 % purity, gas tight). Even hairline cracks in the ceramic thermowell can allow foreign materials to infiltrate and cause the thermal voltage values to drift. To prevent cracks, care must be exercised when installing or removing the thermowell from the process. It should only be subjected to gradual temperature changes. The use of an internal thermowell made of a gas tight ceramic inside an outer thermowell made of a thermal shock resistant ceramic is advantageous. In this design, the outer thermowell protects the inner thermowell. The air layer between the two thermowells also protects the inner thermowell from a too large temperature shock. This increases the life of the temperature sensor. 109 Installation Information Decisive is the temperature of the process into which the sensor is to be inserted. If the sensor is to be installed under these conditions, then the procedure is to insert the sensor to the middle of the furnace liner, wait 10 minutes, and then continue to insert the sensor in 10 cm (3/8”) steps waiting another 5...10 minutes after each step. Using this procedure, the sensors will be preheated by the radiation from the interior of the furnace to slowly reach the medium temperature. If these precautionary measures are not observed, the ceramic tube can be destroyed by internal heat stresses! Ceramic thermowells Max. operating temperature in °C (°F) Material No. Material properties 1400 (2550) C 530 Temperature change resistant, fine pores, not gas tight, shock sensitive 1500 (2750) C 610 Gas tight, high fire resistance, average temperature change resistance, low AI2O3 purity, shock sensitive 1800 (3250) C 799 Very gas tight, highest fire resistance, minimal temperature change resistance, shock sensitive Tbl. 3-22: Ceramic thermowell materials Furthermore, for special applications, e.g. metal melts, thermowells made of carbides or nitrides may be used. 110 3.3 Application Specific Temperature Sensor Designs Hot Gas Measurements in a Furnace A temperature sensor measures changes in gas temperatures very slowly due to the poor thermal conductivity of gases. In order to reduce large errors due to thermal radiation (cooled walls), which may exist in blast furnaces, vacuum temperature sensors are utilized. The hot process gasses are drawn off using a vacuum created with compressed air. Compressed air Connection for vacuum meter Fig. 3-38: Vacuum temperature sensor in a blast furnace Temperature Measurements in High Pressure / High Temperature Reactors In these applications temperature sensors with in- and outside ceramic thermowells and used. The thermocouple wires are sealed by a pressure tight connector as they exit to the connection box. To protect against aggressive fluids which might influence the thermocouple characteristics (e.g. sulphur in Claus Processes), an inert purge gas is introduced through a fitting. This creates a positive pressure in the thermowell. The purge flow can be regulated or increased using an additional outlet connection. Purge gas will only flow if its pressure is greater than the process pressure. Only a very small purge flow is usually required. Applications include the manufacture of chemical products which require the addition of high pressure/temperature elements for the reaction (synthesis reactors, fertilizer production, etc.). 111 Fig. 3-39: Purged thermocouple in a high pressure reactor Temperature Measurements in Particle Loaded Gases For the pneumatic transport of granulates and powders a temperature measurement is often required in order to monitor the temperature to assure that the ignition limit is not exceeded. The temperature sensor, which is inserted in the flow stream is subjected to a high degree of abrasion. It is possible to counteract abrasion by installing armor coated thermowells (e.g., with Stellite, see Fig. 3-40), low wear tips made of solid materials, eccentrically drilled thermowells or by installing an deflecting impingement rod ahead of the thermowell. This temperature sensor design is used in wood and coal processing, cement and glass industries and in coal fired power plants. Fig. 3-40: Armor coated thermocouple in an abrasive gas stream 112 Temperature Measurements in Flue Gas Channels Filter systems in smoke stacks are very sensitive to overheating. Therefore it is important to recognize a temperature increase very quickly. Since a horizontally installed, thin sheathed temperature sensor is not sturdy enough and a minimum insertion length is required, a special design is required. The temperature sensor in this design has a support pipe upstream of the measuring element and which bent at a right angle to guide the flow. Fig. 3-41: Fast responding temperature sensor in a flow channel 113 Multipoint Temperature Sensors for Temperature Measurements in Large Tanks In chemical processes the temperatures in large volumes are often monitored. Since the temperature distribution in a large tank may not be uniform, multiple measuring locations are necessary, which are distributed in a representative manner throughout the volume. Since most tanks only have a single opening at the top, multipoint sensors are used. They have a number of measuring locations within a single thermowell. Multipoint sensors with lengths up to 20 m (65 ft.) and weighing more that a ton are not uncommon. Good heat coupling is established in thermowells by the contact between the measuring element and its inside wall. Individual designs for explosion and pressure proof applications are possible. They are used for status monitoring in liquid and solids storage tanks. Fig. 3-42: Multipoint temperature sensors in storage tanks and process reactors 114 Temperature Measurements in Metal Melting and Salt Baths Using Angled Thermocouples These temperature sensors are used primarily to measure temperatures in non-iron metal melting furnaces and salt baths for hardening. For vertical installation in open vessels an angled design is used so that the connection head and connection cables can be mounted outside of the radiating surface at the top of the furnace. Suitable materials made of thermal shock resistant ceramic are used for thermowells, as well as metal. Since the thermowell for direct immersion in the molten materials is stressed to the maximum, it is considered to be a consumable part. Its durability can be increased, if in this region, an additional protective sleeve is installed over the thermowell. For waste incineration furnaces, rotary kilns, fluidized bed furnaces and air heater applications, thermowells made of silicon carbide, metal ceramic or porous oxide ceramic are particularly well suited because of their high temperature resistance, hardness and abrasion resistance together with their resistance to acid and alkali vapors. These temperature sensor are then not angled, but are designed as “straight thermocouples“. Fig. 3-43: Angled thermocouple in a crucible 115 Resistance Thermometers with Extremely Short Response Times For applications where control functions require that process temperature changes be recognized very quickly, special designs have been developed. The designs are such that the measurement resistor is sintered into the measuring inset tip with using a high heat conducting material. The measuring tip itself is designed as an adapter sleeve, which fits closely into the thermowell, and becomes part of the exchangeable measuring inset. As a result of the extremely good heat transfer possible with this design, response times τ0.5 of less than 3 seconds can be achieved (measured in flowing water at v = 0.4 m/s (1.3 ft/s). Temperature sensors of this design are predominantly used in the primary circulating loops in nuclear plants, as well as in safety relevant applications for energy balancing in chemical systems, where the highest safety requirements must be satisfied, even during a failure condition. Process parameters include flow velocities up to 15 m/s (50 ft./s), pressures to approx. 175 bar (2,538.16 psi) at a maximum temperature of 330 °C (626 °F). Fig. 3-44: Fast response temperature sensor in a reactor cooling pipeline 116 Temperature Measurements in Plastic Extruders An exact knowledge of the product temperature during the extrusion process is an essential factor to assure the workability of the material and the quality of the end product. The measurement is difficult because a built in sensor • would interfere with the flow of the extrusion stream, • must have a very rugged construction, since the processing pressures are between 300...500 bar (4,351.13...7,251.89 psi), • would be greatly affected by exposure to the external heat jacket. The design for this application is a massive sensor with a short length, in whose tip measuring locations at multiple steps are incorporated. Since it is not possible to prevent the effects due to external heat sources, a measurement of the temperature gradient allows a temperature determination to be made. In this way meaningful values for the temperature of the plastic mass can achieved. Fig. 3-45: Extruder temperature sensor 117 Temperature Sensors for the Food and Pharmaceutical Industries Temperature sensors for these applications must be designed in accordance with strict hygienic requirements. This means that the construction must not have any small gaps or dead spaces, where product or residue could be deposited in the sensor. The temperature sensor must be able to be cleaned and sterilized without being disassembled. This property is classified CIP-Capable (Cleaning In Place) and SIP-Capable (Sterilising In Place). The connection head must incorporate a high level of protection, in order to remain sealed when cleaned with a steam jet. The measuring task requires very fast response times (< 3 s) at a high accuracy, so the product quality can be maintained within tight limits. High alloyed stainless steel materials are used such as 1.4571, 1.4435 and 1.4404 (AISI 316Ti, 316L). Fig. 3-46: Temperature sensor with ball type welded adapter for hygienic applications and installation at various angles 118 Temperature Measurements of the Tank Content with a Flush Thermowell All sided heat contact is not always possible with an insertion thermowell, because it may interfere with the process or cannot withstand some of the forces which may occur, e.g. in tanks with stirrers, the thermowell would interfere with the wall scraping stirrer, so the measurements must be made flush with the wall. Special measures must be considered in the sensor design to assure that: • the sensor is thermally decoupled from the wall, • the contact area with the medium large enough, • the measurement will not be affected by external heat jackets. A suitable sensor design assures that the sensor element is in contact only with the interior of the tank and not with its mechanical mounting arrangement. Fig. 3-47: Flush tank wall installation of a temperature sensor 119 Temperature Sensors for Heat Quantity Measurements Since heat energy is very expensive, cost effective balancing is required with very precise measurements. The requirements relative to the design and allowable measurement deviations for heat quantity sensors are defined in the Standard EN 1434-2. Because the accuracy requirement for the sensor pair is in the range of 0.1 °C (0.18 °F), it is very important, that in addition to the correct selection of the sensor, the relationship of the sensor mass to the installation length be considered in order to prevent any external influences from effecting the measurement. Temperature sensors without thermowells with extremely short measuring resistors are used to allow an exact measurement to be made in the center, as required, of the usually small diameter pipelines while minimizing the heat loss. Fig. 3-48: Temperature sensors for the heat quantity measurements 120 Temperature Measurements on Surfaces The surface temperature measurement has gained increasing importance. For a variety of reasons (measuring location hard to access, sterility of the system, no disturbance in the flow circuit, etc.) the direct insertion of temperature sensors into the process loop is often undesirable. For such applications, the non-contacting infra-red measuring methods are not the only ones used (see chapter 4). Surface temperatures are measured using contacting temperature sensors especially in applications where undefined or changing conditions relative to the emission coefficient ε may exist. A differentiation is made between two basic methods, a portable system (sensors positioned manually, touch sensors) and a system with sensors permanently mounted on the surface. For process systems, only the permanently mounted sensors are of importance. For temperature measurements on the surface of bodies a basic knowledge of the temperature difference between the surface and the enclosed medium must be known. Surface sensors operate within a defined temperature gradient range. Errors may result when making surface temperature measurements due to effect of the sensor (interference) itself on the surface temperature (undisturbed). When applying surface temperature sensors it follows that not only the actual errors in the sensor itself must be determined by a calibration, but also, the magnitude of the effect the temperature sensor has on the surface temperature itself must be determined. The correct application of surface temperature sensors requires extensive experience in the field of temperature measurement technology. Requesting technical, application oriented recommendations from the temperature sensor manufacturer are recommended. To keep the heat removal by the measurement element as small as possible, its mass should be a minimum. For small surfaces, thermocouples, because of their small mass with diameters of 0.5 mm (0.020“) are often used. 121 Sensor mounting methods vary for each installation. They can be mounted using soldering, welding, screwing or held in place by a spring. For larger cross sections, resistance thermometers are also used. They are designed as bottom sensitive types for the specific mounting arrangement (tangential/axial). They are either held in place by a pipe clamp or clamped using a metal plate screwed onto the surface. Fig. 3-49: Measurements on a pipe surface 122 Pipe Wall Temperature Measurements in Heat Exchanger Pipes In heat exchangers e.g., a liquid medium is pumped through a pipe bundle installed within a hot gas filled tank. Due to the large contact area, the medium approaches the temperature of the gas. Since the temperature and pressure in the pipes is usually high, near the material limits, monitoring the wall temperature of the pipes is necessary, in order to prevent over stressing the materials and possibly rupturing the pipes. The design of a suitable sensor must assure good contact with the wall without, due its own mass and its contact with the hot gas, produce erroneous results. Since operating temperatures may reach approx. 560 °C (1040 °F), the use of conventional insulating materials is for all practical purposes excluded. The solution for this problem is a sensor with a mineral insulated cable with a V-shaped knife edge whose measuring section is bent toward the inner wall and welded to assure good contact with the pipe wall. In this design, the welded portion forms a cap over the measurement element and which is at the same temperature as the pipe wall. To compensate for the temperature differences, additional compensating windings are incorporated. Fig. 3-50: Measurements on a pipeline in a heat exchanger 123 Temperature Measurements in Housings and Walls In order to measure the temperature in solid bodies, the measuring element is positioned in a hole drilled into the object to be measured. The hole itself and the measuring element disturb the temperature field, so that measurement errors result. The measurement error increases as the size of the hole increases in relation to size of the object and how different the heat conductivity of the inserted temperature sensor is from that of the object. Guidelines for the ratio diameter/depth of the hole for temperature measurements in objects are: • With good heat conductivity 1:5 • With poor heat conductivity 1:10 to 1:15. The solution is a sensor consisting of two independent, spring loaded sheathed thermocouples, which due to their small mass form point shaped measuring locations which essentially assure an error free measurement. These temperature sensors are used, among others, in high, thermally stressed elements in power plants. Fig. 3-51: Difference temperature measurements within a wall 124 Temperature Measurements in Bearing Shells and Housings To measure the temperature of a housing a small hole is usually added with a minimum depth. This requires temperature sensor designs with very short, temperature sensitive lengths. They are usually pressed against the bottom of the hole by a spring to assure good thermal contact. Silver tips are also used to optimize the heat transfer. Since, e.g., there are enormous vibration forces present in Diesel motors, the measuring sensors must be designed with an extremely rugged internal construction coupled with the use of reinforced springs. These temperature sensors are used to measure bearing temperatures in pumps, turbines, blowers and motors. For use in large Diesel motors in ships, type tests are also required by the Ship Classification Societies such as Lloyds Register of Shipping, German Lloyd and others. Fig. 3-52: Temperature measurements in pump bearings 125 Temperature Measurements in Brakes and Railroad Train Axles To monitor the brakes in high speed trains, temperature sensors with the following characteristics are required: • Small, rugged design, • resistant to high mechanical shocks, • special measuring surfaces, which can be mounted as close to the rubbing surfaces (brake linings) as possible, • fast response. An appropriate design is a small, spring loaded sensor with a conical seat mounted in the brake caliper housing. Fig. 3-53: Temperature measurements in a brake caliper 126 3.4 Dynamic Response of Temperature Sensors 3.4.1 Introduction The dynamic response of a temperature sensor describes the reaction of its output signal to a change in the temperature of the medium being measured. When making contacting temperature measurements, the temperature sensor is in direct contact with the measured medium. The temperature which exists, after a equilibrium state is reached, is a “mixed temperatures“ consisting of the original temperature of the temperature sensor and the temperature of the measured medium. In general, the thermal mass of the measured medium is decidedly greater than that of the temperature sensor, so that this “mixed temperatures“ and the temperature of the measured medium are the same. When the temperature of the measured medium TM(t) changes, the temperature sensor reacts. Its output signal TS(t) approaches the new temperature. Finally when the output signal of temperature sensor no longer indicates any measurable changes, the stationary status is reached. During this time period the time related difference is ΔT(t) = TS(t) – TM(t) which is defined as the dynamic measurement error. The dynamic response of a temperature sensor is almost exclusively a function of the equalization processes occurring between the measured object or medium, the temperature sensor and the ambient conditions. Information about the basic values of the dynamic response of the temperature sensor are required e.g. to estimate the response time after a sensor is inserted into a medium at constant temperature, for the measurement or transmission of fast temperature changes and for use in temperature controlled circuits. 127 3.4.2 Step Response and Transfer Functions, Response Time and and Time Constants If a temperature sensor is at a starting temperature TS0, e.g., the ambient temperature TAmb, at time t = 0 is brought into thermal contact instantaneously with a measured object or medium at a constant temperature TM, e.g., by contact or immersion, a thermal equalization process begins. From a curve of the sensor temperature TS(t) as a function of the time, the so called step response, the value of primary interest is the response time tR which is the time when the dynamic measurement error becomes less than a meaningful, defined portion of the measurement uncertainty δ from the starting temperature difference TS0 – TM: 70 δ = 5% δ = 1% TM 60 ΔT(t) 50 80 TS (t) 60 40 40 30 20 100 20 TS0 0 Transfer function h(t) [%] Temperature T [°C] TS(tR) – TM ≤ δ (TSO – TM) 0 t 50%10 20 t95% 40 t99% Time t [s] Fig. 3-54: Typical response time curve (step response) also called transfer function of a temperature sensor The characteristic value for the temperature sensor is its response time. It is called the time constant: T05 and T09 are the times the temperature sensor requires to detect 50 % (90 %) of a temperature step change. The magnitude of the temperature jump is of lesser importance. Therefore, the response to a temperature change by the temperature sensor is a function of the remaining temperature difference from the temperature of the measured medium. The temperature of the measured medium will only be reached exactly at t = ∞. 128 3.4.3 Establishing the Dynamic Values According to VDI 3522 and EN 60751 the following two measurement conditions are recommended to determine comparable dynamic values: air: TA ≈ 25 °C (77 °F), vA = (3 ± 0.3) m/s (→ αA) water: TW ≈ 25 °C (77 °F), vW = (0.4 ± 0.05) m/s (→ αW) When these values are to be converted to other application conditions, the effective heat transfer coefficient for the measurement conditions must be known. They can be estimated from values listed in the VDI-Heat Atlas. Listed in the following table are the values at the above stated standard measuring conditions. D [mm] 0.2 0.4 0.6 0.8 1 2 4 6 8 10 20 [inch] 0.008 0.016 0.025 0.031 0.039 0.079 0.157 0.236 0.315 0.394 0.787 αA [W/m2K] 414 290 237 205 184 132 95 79 70 64 47 αW [W/m2K] 28910 20540 16890 14700 13260 9670 7190 6100 5460 3990 3260 3.4.4 Influencing Factors The values T05 and T09 are dependent on the installation parameters, the temperature sensor and the measured medium. The Main Factors are For the measured medium: • heat capacity, • heat coefficient, • heat transfer coefficient to the temperature sensor, • flow velocity. For the temperature sensor: • size (generally the diameter), • weight, • materials used, • internal construction. The influence factors for the measured medium are given values. These can hardly be optimized. For the temperature sensor however, there are a number of measures which can be taken to shorten the response time. The most important are: • reduction of the diameter in the region of the sensor, • reduction of the mass in the region of the sensor. These two measures are interrelated. 129 The temperature sensor only reaches a constant condition when its temperature is homogeneous. A total warming of the sensor is reached quicker in smaller sensors than in larger ones. It is important to assure, if such measures are taken, that the mechanical stability is not overloaded. The thermowell geometries are also factors affecting the optimization of the response time, as well as the mechanical requirements. • Position the sensor in the middle of the pipe When laminar flow exists, then the highest flow velocity of the measured medium is in the middle of the pipe. If such measures are employed, assure that the mechanical stability is not jeopardized. Sensor installation examples see chapter 3.2. Another means which can be utilized to achieve faster response is to use thermally conductive coupling materials, e.g. heat conducting paste (for Tmax < 200 °C (392 °F)), or the use of thermowell points made of good heat conducting materials. The multitude of sensor geometries preclude the presentation of a complete listing. Transfer function h(t) [%] The effect that the design and dimensions have on the dynamic response of a temperature sensor as well as its construction and especially the heat transfer conditions is shown in Fig. 3-55. The very different responses to a step change are shown for the same measuring conditions (flowing water) and the same resistance thermometer measuring inset (Ø = 6 mm (0.236”) ), due to the addition of a thermowell and finally, due to addition of a corrosion resistant Teflon coating 0.5 mm (0.020“) thick. 100 90 Measuring inset 80 Measuring inset with thermowell 70 60 50 Measuring inset with thermowell and 0.5 mm coating 40 30 20 10 0 0 10 20 30 40 50 60 70 80 90 100 110 120 130 Time t [s] Fig. 3-55: Transfer function for resistance thermometers of different designs in water vW = 0.4 m/s (16 ft./s), TW = 25 °C (77 °F) 130 3.5 Aging Mechanisms in Temperature Sensors Temperature sensors, during use, are subjected to application related aging effects. These complex processes, which define the long term characteristics of the sensor in an application, are generally categorized as “drift“. They are the result metallurgical, chemical and physical effects. The quantitative effects are primarily due to the temperature itself. The consequences of these effects are seen in a drift resulting from the changes in the thermal voltages or resistance values. The values of the thermal voltages and resistances, continually change from those defined in the Standard Value Tables or the Standard Value Series for the ideal temperature sensor. The causes can be roughly divided into two groups: • drift, due to mechanical damage of the temperature sensor or the sensor element, • drift, due to metallurgical changes in the sensor. It can be stated that mechanical damage is almost always the catalyst for metallurgical changes in the sensor materials. 3.5.1 Drift Mechanisms for Thermocouples K-State (Short Range Ordered State) This effect is not actually drift, because its result can be eliminated by appropriate heat treatment of the sensor. The technical effect is essentially identical to normal drift characteristics. Since Type K (NiCr-Ni) thermocouple is the most commonly used thermocouple, and since many users are unaware of these K-State problems, this problem will be presented in detail. The NiCr-leg of Types K (NiCr-Ni) and E (NiCr-CuNi) are subjected to a special effect, which occurs when the wires are cooled quickly from temperatures in the range of 400...600 °C (752...1112 °F), causing a change in the thermal voltages (essentially undefined). 131 This effect, often called an approximation effect, alters the structure of the individual lattice elements and is usually referred to as K-Effect or K-State. Practically all metals of technical importance, solidify either as face-centered-cubic metals (Nickel), bodycentered-cubic metals (Chromium) or as hexagonal-lattice metals (Zinc). There are also other solidification forms with tetragonal, rhombic lattice structures as well as others. For an ideal, pure metal, all the lattice spaces would be occupied by atoms of the same element during solidification. For the NiCr-alloy, an important thermocouple material, which solidifies as a face-centered-cubic lattice (Fig. 3-56) in which the lattice spaces are occupied by atoms of the individual alloy components (Nickel and Chromium) resulting in a mixed crystal. Viewed submicroscopically, the lattice structure of a melt as it solidifies, has the same proportion of individual atomic elements as the stoichiometry of the composition of the alloy. Atom position Fig. 3-56: The face-centered-cubic crystal lattice Considering the atomic structure of a NiCr-crystal more closely, the resultant lattice occupancy by Ni or Cr atoms is dependent on the rate of cooling of the molten metal. Starting by considering a NiCr-alloy, which is at a temperature above 600 °C (1100 °F), the atoms are diffused into the crystal structure, which corresponds to a face-centeredcubic lattice in which the former atoms of the “crystal“ are formed by Chromium atoms, the central atoms by of the individual faces by Nickel. Observing this structure perpendicular to a face, then the positions of the Ni- and Cr-atoms is as shown in the following figure. 132 Chromium Atom Nickel Atom Large ordered state Fig. 3-57: The large-range-ordered state structure of the Ni and Cr atoms at temperatures > 600 °C (1112 °F) If the NiCr-leg of a Type K thermocouple is used in a large-range-ordered state (UState) always at temperatures > 600 °C (1112 °F), then reproducible thermal voltages will result. If this NiCr-leg is slowly cooled (< 100 K/h) to temperatures < 400 °C (752 °F), then an atom structure will be formed called short-range-ordered state (KState) (Fig. 3-58). In this condition, the typical large-range-ordered state structure (Cr atoms at the corners, Ni atoms in the center of the faces) is found in small sections of the lattice, interspersed with “distorted“ lattice areas. Chromium Atom Nickel Atom Short ordered state Fig. 3-58: The short-range-ordered state structure of Ni and Cr atoms This lattice structure also produces reproducible thermal voltages. However, if the cooling from temperatures > 600 °C (1112 °F) occurs very quickly, then the atoms do not have sufficient time to move from a large-range-ordered state structure into a shortrange-ordered state structure. The result is a mixed structure somewhere between the two regular structures described above, i.e. an arbitrary structure, which is in effect an unordered structure (Fig. 3-59). The positioning of the Ni and Cr atoms in any arbitrary structure to each other is possible, dependent on the starting temperature and the time profiles of the cooling. 133 Chromium Atom Nickel Atom Fig. 3-59: An unordered state If a NiCr-leg, which has an unordered atomic structure due to rapid cooling, is allowed to remain for a longer period of time at temperatures < 400 °C (752 °F), then, as a result of thermal diffusion the atoms will gradually revert to the short-range-ordered state structure. In the unordered condition and in the transition phase to a short-rangeordered state structure, the thermal voltages generated by this leg changes. A thermal voltage change equivalent up to 5 K can occur and cause erroneous measurements. For the accuracy and reproducibility, the generated thermal voltage and therefore the suitability for measurement and control functions, the as received condition of the Type K thermocouple is of decisive importance. The last step in the manufacturing of thermocouples or mineral insulated thermocouple cables is always an annealing above 600 °C (1112 °F), to relieve the stresses which resulted from cold working the material. The NiCr-leg therefore has a large-rangeordered state structure. This is followed by rapid cooling in order not to impair the weldablility of the sheath material of the mineral insulated thermocouple cables. The NiCr leg is then in an undefined transition stage, previously described, between K and U. A new thermocouple delivered in a transition stage will quickly change to the K-State, provided the temperature at the measuring location is > 600 °C (1112 °F). In the temperature gradient region between the hot and cold ends, a slow transition to the U-State occurs. Continually changing thermal voltages are the result, which only stabilize after the transiting phase has been completed. The values can vary appreciably from the thermal voltages of a new, as received, thermocouple. Only thermocouples, that are shipped in the “set“ K-State (this can be accomplished by a second, more complex final annealing and by a slow, defined cooling under an inert gas), provide immediate, stable temperature indications. Also to consider is that in the ordered structure state the NiCr-leg, and thereby the thermal voltages it generates, in the temperature range between 250 °C and 600 °C (482 °F and 1112 °F) is relatively undefined. This makes the use of Type K thermocouples for measuring rapidly changing temperatures of limited applicability, since the thermal voltage changes, that occur during the crystal transition stage, are a type of signal hysteresis. 134 A remedy is to add a small amount of Silicon to the alloy for both legs (in thermocouple Type N, NiCrSi-NiSi), which appreciably reduces the short order effects to the point where they, for all practical purposes, are negligible. It should be noted that the replacement of Type K by Type N thermocouples has proceeded very slowly in technical applications. Selective oxidation of Cr When using NiCr-alloys (typically used in Type K thermocouples) exposed to an oxygen poor, neutral or reducing atmosphere in combination with moisture. Green rot occurs in the temperature range between 800 °C and 1000 °C (1472 °F and 1832 °F) a selective Chromium oxidation of the NiCr-leg occurs. Under the described conditions the stabilizing, continuous coating of Nickel oxide cannot form, similar to the condition when an excess of Oxygen is present. The Chromium in the conductor is depleted, the composition of the alloy changes and the thermal voltages decrease dramatically. The thermal voltage for a thermocouple damaged by Green rot corresponds to the temperature difference between the temperature at the measuring location if no wire damage had occurred and the reference junction. The measuring location has effectively moved from the tip to the “back“. Measuring errors caused by Green rot can be as large as a few 100 °C (212 °F). The Ni-leg is not subjected to Green rot. Radioactive Radiation The α- and β-rays have practically no effect on the output signal of a thermocouple. The γ-rays however heat the measuring location and dependent on the intensity and volume exposed to the radiation, cause errors of several hundreds of degrees. Thermal neutron radiation however, changes the thermal material itself. Neutrons are absorbed as a function of the cross section of the material. The subsequent radioactive decay causes conversion in stages into other elements with different thermal properties. The type and duration of the conversion is a function of the radiation dosage. Materials with a smaller absorption cross section experience only small changes while materials exposed to higher absorptions are quickly and completely converted. 135 The following effects occur in the most important thermal materials: • Rhodium has a high absorption cross section and is converted within a short operating time. Thermocouples Types R, S and B are therefore unsuitable for applications where neutron radiation exists. • Tungsten-Rhenium thermocouples experience changes in both thermocouple legs, measurement errors up to 15 % are possible. • Nickel-Chromium wire is also converted. The Iron and Copper in the structure are enriched and the Cobalt and Manganese depleted. • Nickel- or Platinum wire experiences practically no changes. • The insulation material of sheathed thermocouples experience a reduction of the insulation resistance. A continually increasing error is the result. Impurities in the Alloys of Thermocouple Materials In order for a thermocouple to generate thermal voltages, which are defined in the basic values in the standards, the composition of the alloys in the legs of the thermocouple must conform exactly to the specifications. The thermal voltages generated by the thermocouple are very sensitive to minor changes in the alloy composition and therefore to the presence of any traces of foreign materials. The thermal voltage reacts to the presence of foreign materials to such a degree, that alloys which have been tested using a spectrum analyzer and found to have nominally the same composition (within the resolution of the instrument) can consistently generate different thermal voltages. The following table shows the effect of typical impurities on the thermal voltage of a wire made of pure Platinum (purity > 99.99 %). Element dUth (µV/ppm) Fe 2.30 Ni 0.50 Ir 0.35 Mn 0.32 Rh 0.20 Cu 0.12 Pd 0.07 Ag 0.03 Au -0.07 Pb 3.00 Cr 4.04 Tab. 3-23: Influence of impurities on the thermal voltage (dUth) of Platinum 136 That a material is suitable for use as a thermocouple material is first apparent during its calibration, after it has been used to manufacture a thermocouple. Foreign materials can not only infiltrate during the production of the thermal material from the melt, but also during manufacture or further processing of the thermal wire to the point, where an originally “usable“ material can be turned into an “unusable“ one due to the presence of foreign materials. The greatest changes in the wires of a thermocouple occur during their actual operating period. These changes occur due to the infusion of foreign materials, caused by contact with the materials contained in the ambient atmosphere. The major factor for accelerating the diffusion process is the temperature itself. The combination of unfavorable installation conditions and high temperatures can result in the “poisoning“ of the thermal materials. This is particularly true for precious metal thermocouples made of Platinum. The Most Common Cause of Contamination: • Pure materials, such as Copper, Iron and Platinum, experience aging effects primarily from the diffusion of foreign materials into them. • Typical Platinum poisons are Silicon and Phosphorous, whose diffusion rate accelerates above 1000 °C (1832 °F). It accelerates the effects due to the catalytic action of the Platinum. Silicon quickly alloys with Platinum to form an eutectic, brittle alloy, which begins to melt at 1340 °C (2444 °F) and after a few minutes at the high temperatures can cause the thermocouple to fail. Here it is essential that only high purity Aluminum oxide (Al2O3) be used for the insulation material, because it only contains very small traces of Silicon. • When using Pt-thermocouples the Rhodium slowly wanders over the weld area into the Pt-leg and increases or displaces the measuring point. This leads to measurement errors, as soon as change reaches the area of the temperature gradient. • For alloys such as CuNi, NiCr or PtRh start-up drifts may be observed which can be attributed to the relaxation of the stresses in the structure introduced during manufacture. The drift effect continues to slow down, but it is never completely eliminated. • For NiCr-alloys the diffusion of Sulfur is the most common, which diffuses into the grain boundaries and destroys the material. • NiCr-Ni thermocouples exhibit over longer time periods, relative to impurities, in comparison, a smaller aging effect, because the individual legs drift in the same direction effectively compensating the drift effect of the thermocouple (Fig. 3-60). 137 • Through the use of suitable ceramic and sheath materials for the mineral insulated cables of the thermocouple Type K, a surface oxidation (intentional pre-aging) of the wires can be achieved. These protective oxide coatings can multiply the useful operating period (Fig. 3-61). 0.2 Operating time in hours 0 10 0.2 20 0.4 Ni 0.5 0.8 NiCr-Ni 1.0 NiCr 0.3 Pt 0.2 0.1 Pt 6%Rh Thermoelectr. changes [mV] Thermoelectr. changes [mV] Fig. 3-60: Typical aging of NiCr-Ni thermocouples at 1200 °C (2192 °F) 3 Pt* * brittle 2 Pt 6%Rh* 1 Pt 10%Rh* Pt 10%Rh 0.0 Pt 30%Rh 0 Pt 30%Rh* -0.5 -0.3 0 10 20 30 40 50 Operating time in hours Thermomwell contains reducing Silicon Dioxide 0 5 10 15 20 Operating time in minutes Thermomwell contains oxidizing Silicon Dioxide Fig. 3-61: Aging curves for Platinum thermocouples inside thermomwells containing SiO2 in reducing and oxidizing atmospheres 138 Properties Material Portion AI2O3 in % Alsint 99.71)3) Density TemperaMax. in g/cm3 ture operating change temperature resistance in °C (°F) Electrical resistance in Ω / cm 99.7 3.80...3.93 good 1700 (3092) 1014 Pythagoras 18001)3) 76 3.10 very good 1600 (2912) 1013 Pythagoras1)3) 60 2.60 good 1400 (2552) 1013 73...75 2.35 Silimantin 601) very good 1350 (2462) No specs. Degussit Al232)3) 99.5...99.7 3.7...3.95 good 1950 (3542) 1014 (RT) Degussit Al242) 99.5...99.7 3.4...3.6 very good 1950 (3542) 107 (1000 °C (1832 °F)) Al252) 99.5...99.7 2.8...3.1 very good 1950 (3542) 104 (1500 °C (2732 °F)) Degussit 1) 2) 3) Trade name of the company Haldenwanger Trade name of the company Friatec (previously Friedrichsfeld) Gas tight materials (all others are more or less porous) Tab. 3-24: Properties of ceramic insulation materials Changes in the Thermal Voltages due to Mechanical Deformations of the Wire When processing metallic materials for manufacturing thermocouples, it is important to recognize the effects that forming the materials has on the thermal forces. Many extensive investigations of this subject have been conducted in the past (Borelius, Tamman and Bandel). Thermal force differences exist between the hard drawn and soft annealed conditions of a thermocouple wire in an order of magnitude of approx. 1µV/K. This effect must be considered, especially for precious metal thermocouples, because the thermal forces are by their nature, small. For these thermocouples the effects already described can cause appreciable measurement errors. In other words, twisting the wire may produce comparable effects. If a thermocouple is made of wires in their hard drawn condition, (wires which were not subjected to a recrystallization annealing), then during the operating life of the thermocouple the thermal voltages will not be stable, which can be traced back to the slow transition of the wire from a hard to a soft condition. When manufacturing thermocouples, especially those made of Platinum thermocouple wire, it is imperative that the wire first be stabilized by annealing (soft-annealing). Mechanical stresses in the thermocouple wire can cause disturbances in the crystal lattice structure. Bending the wire over a sharp edge or repeated bending with a very small bending radius can lead to appreciable changes of the thermal voltages. 139 Changing the Thermal Voltages due to Coarse Grain Formation Metallic materials drawn down to fine wire sizes are subjected to accelerated grain boundary growth after longer exposure to higher temperatures. This growth leads to the formation of larger and larger grains, so called coarse grain formation. in certain instances this can result in the entire cross section of a thin wire consisting of only a few grains. This not only decidedly reduces the mechanical strength of the wire, but also changes its thermal forces. This effect can be observed especially in the negative legs of thermocouple Types R and S, which are made of unalloyed Platinum materials. It is for this reason that some manufacturers offer a Platinum thermocouple wire with a fine grain quality. Special elements are alloyed into this material, which appreciably reduce the grain boundary growth without affecting the thermal voltage. Changes in the Insulation Resistance A simplified circuit diagram for a temperature sensor includes a signal source and a network of serial and parallel resistors (Fig. 3-62). The serial resistors in a real temperature sensor are made up of the resistors in the connection leads and the resistance at the connection terminals or plug contacts. The parallel resistors result from the non-ideal behavior of the insulation materials, which are used to electrically insulate the cable and connection wires from each other in the measuring inset. RL1.1 RL1.2 Eth parasitic Uth Eth Rins RL2.2 RL2.1 RL = Connection lead resistance Rins = Insulation resistance Fig. 3-62: Simplified electrical circuit diagram for a thermocouple 140 When using thermocouples the changing series (connection leads) resistances play only a subordinate role in the aging processes, as long as they are not subjected to a continuous mechanical wire connection, which could completely disable the thermocouple due to lead breakage. A decrease in the insulation resistance however can result in appreciable errors in the output signal of the thermocouple. A reduction in the insulation resistance may have a number of causes. • In simple thermocouples, made using insulated thermocouple wires, the insulation properties of the wire insulation can be permanently damaged by a single exposure to an excessive temperature and made useless. • For thermocouples, which are designed as measuring insets using a mineral insulated cable, the insulation capability of the insulating ceramic (Al2O3 or MgO) can be strongly limited by moisture absorbed or bound in the ceramic material. Moisture can enter undetected during the manufacture of the product, e.g. if the mineral insulated cable is exposed for a longer period of time with unprotected ends to the normal humidity in the air. The ceramic materials used are extremely hygroscopic, and bind in the moisture as crystal water. Moisture can also be absorbed by a thermocouple during use if it is mechanically damaged. In addition, the insulation properties decline sharply for these materials at higher temperatures (approx. one order of magnitude /100 K), so that for temperatures in the range from 1000 °C (1832 °F) and above, the actual reason for using the insulation no longer exists. This is caused, at higher temperatures, by the increase in the ionic and electron conductivities of all ceramic insulation materials. A marked decrease in the insulation resistance, will without fail, cause electrical shunt currents to flow between the legs of the thermocouple, loading the signal source and causing erroneous thermal voltage signals. 141 Even more critical are the so called secondary measuring locations. These form when both thermocouple legs, due to a decrease in the insulation resistance, are electrically connected together anywhere within the temperature sensor creating an additional (secondary) measuring location. The output signal of the thermocouple is now a combination of the different thermal voltages which are generated at the various measuring locations. The danger presented by these secondary measuring locations occurs when part of the thermocouple is located in areas where the temperature is higher that at the measuring location itself (steam boiler tubes in large power plants, brick lining at the bottom of industrial ovens). Rins [kOhm] The electric insulation capability is naturally not only a function of the insulation material used but also of the geometry (diameter and length) of the thermocouple itself. Especially for very long thermocouples, e.g. in large power plants, it is difficult to achieve high insulation resistance. For applications with temperatures over 1000 °C (1832 °F) the use of thermocouples made with mineral insulated cables can only be recommended with very limiting restrictions. For these applications, the use of thermocouples designed using conventional technology (pipe designs) are to be recommended. The insulation values of the ceramic bodies used in this design are an order of magnitude higher than those of the softer ceramic of the mineral insulated materials. This is due primarily to the differing degrees of compression of the materials. 1000 100 10 1 MgO 0,1 Al2O3 0,01 800 900 1000 1100 1200 1300 Temperature t [° C] Fig. 3-63: Relationship of the insulation resistance of mineral insulated cables to the operating temperature 142 3.5.2 Drift Mechanisms for Resistance Thermometers The effect of impurities on the temperature coefficient of Pt-resistor materials As already mentioned, the purity of the mandatory alloy compositions is an essential requirement for the thermal materials. The Platinum resistance wire for the manufacture of Platinum measuring resistors is no exception. A rough differentiation can be made between application categories: • For the manufacture of temperature sensors, in order for the requirements in ITS 90 to be satisfied, Platinum with pure quality is required. Temperature sensors of this type are used as definition and interpolation instruments for determining the International Temperature Scale between the fixed points in the temperature range from -189 °C (-308.2 °F) (N2-Point) to 961 °C (1761.8 °F) (Ag-Point). • For resistance thermometers, as they are defined in EN 60751, physically pure Platinum is used, which, as a result of the addition of specific elements to the alloy, are “set“ to the required temperature coefficient α. For its temperature coefficient (which corresponds to the linearized temperature dependence of the material in the temperature range between 0...100 °C (32...212 °F)) the value 3.8506 x 10-3 K-1 can be calculated from the basic values in EN 60751. Impurities, which may contaminate the Platinum during manufacture or during the operating period of the temperature sensor, can change the chemical composition of the material and thereby its temperature coefficient. The result is a deviation from the basic values in the standard. The Platinum resistance wire will be gradually “poisoned“. The sensor drifts. A typical problem, which also leads to the poisoning of the Platinum resistance wire, is the absorption of foreign materials from the thermomwell material, or from the sheath materials used for the mineral insulated cables. This absorption process is practically nonexistent or extremely slow at lower temperatures, but it accelerates dramatically at higher temperatures. For this reason, metallic thermomwells made of stainless steel should not be used when long term temperature exposure over approx. 420 °C (788 °F) is anticipated. For long term use above that temperature, thermomwell materials such as quartz glass, high purity ceramic or mineral insulated cables with a Platinum sheath should be used. 143 A typical indication that the resistance material is aging, which can be attributed to poisoning, is an increase in the Ro-value, accompanied by a decrease in the α-value. The following table demonstrates the effects of impurities on the α-value for physically pure Platinum. Element dα (ppm-1) Fe -1.28 x 10-6 Ni -0.16 x 10-6 Ir -0.20 x 10-6 Mn -0.21 x 10-6 Rh -0.09 x 10-6 Cu -0.35 x 10-6 Pd -0.10 x 10-6 Ag -0.15 x 10-6 Au -0.07 x 10-6 Pb -0.90 x 10-6 Cr -3.25 x 10-6 Tab. 3-25: Effects of contamination on the temperature coefficient (α) of Platinum Drift effects due to mechanical stresses in the sensor element during operation Not only changes in the chemical composition of the resistor material due to contamination by foreign elements can cause instability in the temperature sensor, but also the presence of mechanical stresses in the sensor element or in the total assembly can lead to changes of the resistance values. Continuous mechanical vibrations, especially when combined with high operating temperatures, affect the temperature sensor significantly. There are two effects which can be initiated by the stresses described in the following. In wire wound resistors, which are not solidly positioned in the carrier body for vibration resistant, short circuits between the individual windings can occur causing step change reductions in the Ro-resistance value. The fine wire in the sensor element can be elongated at the connection point by strong vibration loads causing a reduction in the wire cross section. In an extreme case the fine wire can break off. A comparable effect can occur if the resistance thermometer is exposed to continuous large temperature changes and a temperature change resistant design was not used. In such applications, the sensor element, if the fit is too tight, experiences continuous tension and compression forces (alternating stresses) in the connection wires due to the different thermal expansions of the materials. 144 Changes in the connection lead resistance In resistance thermometers using a 2-wire configuration, the connection lead resistance is a direct component of the measured value. To correct the measured resistance value to its actual temperature dependent value, the connection lead resistance is usually specified so it can utilized by the user to correct the value measured. The connection lead resistance can be accounted by the manufacturer by using a resistor with smaller resistance value (negative actual value deviation from reference value). If during the course of operation of the temperature sensor the resistance of the connection leads change (e.g. due to a cross section reduction of the wires, oxidation at the connection locations, etc.), then the deviation of the measured values appear as a drift, which often goes unnoticed. For resistance thermometers connected in 3- and 4-wire configurations this effect is automatically compensated. Material R20 d = 0.6 mm (0.024”) Rt /Ro at 400 °C (752 °F) in Ω/m Measurement error at 400 °C (752 °F) for d = 0.6 mm (0.024”) length = 1 m (39”) uncompensated compensated Cu 0.06 2.75 0.48 K 0.3 K Ag 0.06 2.70 0.47 K 0.29 K NiCr 2.48 1.086 7.8 K 0.62 K CuNi 1.77 0.996 5.1 K 0.02 K Tab. 3-26: Measurement error due to connection lead resistance Wire material Outside diameter d in mm (inch) Number of conductors R/I in Ω /m Cu 3 (0.118) 2 0.111 Cu 3 (0.118) 4 0.107 Cu 4.5 (0.177) 4 0.045 Cu 6 (0.236) 2 0.027 Cu 6 (0.236) 4 0.027 Cu 6 (0.236) 6 0.052 Tab. 3-27: Wire resistance of Cu-mineral insulated cables at room temperature 145 Changes in the insulation resistances The design of resistance thermometers is essentially comparable to thermocouple designs. Comparable materials are also used. The electric insulation capabilities of the insulation materials can change in the application range of the resistance thermometer for a number of reasons. A change causes parasitic short circuits to be created, which act as resistors in parallel with the actual sensor resistance as shown in the circuit diagram below. Electrically they act as voltage dividers. RL1.1 RL1.2 RS Rins RWth RL2.2 RL2.1 RL = Connection lead resistance Rins = Insulation resistance Rs = Sensor resistance Fig. 3-64: Electrical circuit diagram for a real resistance thermometer The resultant shunt current causes a lower, incorrect measurement signal. The effect of “poor“ insulation resistance increases for higher nominal resistances of the sensor (e.g. Pt1000 Ω). For resistance thermometers, which are to be used at high temperature, in certain instances it is better to avoid using resistance thermometers with Ro-resistance values of 25 Ω or 10 Ω. 146 Relative Negative Measurement Error (%) 1.0E+02 1.0E+01 R0 = 1000 Ohm 1.0E+00 1.0E-01 R0 = 100 Ohm 1.0E-02 1.0E-03 R0 = 10 Ohm 1.0E-04 1.0E-05 1.0E-06 1.0E-02 1.0E+00 1.0E+02 1.0E+04 1.0E+06 Parallel Resistance (kOhm) Fig. 3-65: Relative negative measurement error caused by a parallel resistance, due to non-optimal insulation. At this point it should be stressed, that a regular periodic check of the insulation resistance during the operating life of the resistance thermometer is one of the most important quality assurance measures which can be conducted. Especially since the measurement of Rins requires minimal expense and can be made under actual installation conditions. The requirements according to EN 60751 relative to the insulation resistance limits should, in reality, only be considered as minimal requirements. A decrease in the insulation resistance can also indicate a tear in the insulation, through which not only moisture but also other contaminants could penetrate changing the resistance thermometer curves. 147 3.6 Possible Errors and Corrective Measures General In this Chapter the most common sources of errors and measures for their correction are presented. The list does not claim to be complete. The details relate only to the temperature sensors and their leads. Any instruments connected for processing the signals will only be included if they provide feedback about the operation of the temperature sensor. Quick checks of the thermocouples (TC) and resistance thermometers (RTD) and their measurement circuits in the installed condition • Required test instruments: Portable multimeter with mV and Ω ranges, insulation tester with 60...100 V = voltage; all measurements are made at room temperature. • At room temperature the continuity and insulation are tested; use “knocking“ to detect wire breaks. • A TC, under certain circumstances, can probably be considered to be acceptable if R < 20 Ω (wire > 0.5 mm (0.020”) Ø); the value is a function of the wire diameter and length Rins ≥ 100 MΩ (for an insulated TC). • A RTD is also probably acceptable if R ≈ 110 Ω (for Pt100) Rins ≥ 100 MΩ. Heating a TC or RTD, e.g., with a gas flame to approx. 200...400 °C (392...752 °F) (without a controlled temperature) will provide information regarding breaks, reversed polarity (for a TC), too low insulation resistance, etc. Testing in the installed condition • Additional instruments required: mV-source, resistance decade or a commercially available Pt100-simulator • TC: Disconnect connection leads; use the mV-source to inject voltages into the measuring circuit and check indication. Test determines whether the TC or the connected measuring circuit is in error. • RTD: Disconnect connection leads at thermometer; connect the resistance decade and simulate the measurement resistance and check indication. Test determines whether the RTD or the connected measuring circuit is in error. • Additional tests were described in the previous section. If the TC or RTD has a exchangeable measuring inset, replace the inset with a test measuring inset with known values. Test determines whether the temperatures sensor or another component in the measuring circuit is the cause of the measurement error. 148 Error Table for Thermocouples and Resistance Thermometers Error Probable or possible causes Corrective measures Measured signal disturbances (no stable indication) a) Electrical/magnetic interference – Install galvanically isolated transmitter – Maintain a distance of least 0.5m (20”) between signal and power leads when installed in parallel – Use electrostatic shielding by installing a grounded foil/screen – Use twist lead (pairs) to eliminate magnetic coupling – Cross signal and interfering power leads in right angel b) Ground loops – Only one ground point in measuring circuit or measuring system “floating“ (not grounded) c) Decrease of the insulation resistance – Exchange measuring inset – Dry thermometer/measuring inset, suspect moisture absorption; remove and reseal (only possible by manufacturer) a) Incorrect installation – in flow shadow – affected by an interfering heat source – Select installation site so the medium can transfer its temperature undisturbed to the temperature sensor and eliminate the influence of an interfering heat source b) Incorrect installation – insertion length too short – poor heat coupling – Insertion length of thermal element should be at least + 5 x d (liquids) up to 20 x d (gases) (d = thermowell outside diameter) – Assure good heat contact, especially for surface measurements, by using appropriate contact surfaces and/or heat conductive materials (e.g. heat conductive paste, grind surface) – Reduce effect by suitable insulation Temperature sensor responds too slowly (response time), Indication in error – too high heat loss e.g. through extension tube c) Thermowell too thick – Use the smallest technically capable thermowell; response time is proportional to the first power of the cross section or volume of the temperatur sensor, dependent on the heat transfer coefficient and air gaps in the assembly. Fill the latter with contact materials (oil, grease if possible) d) Deposits on the thermowell (it has a thermally insulating effect) – During inspection, remove – If possible, select a different thermowell, or another installation location 149 Continuation: Error Table for Thermocouples and Resistance Thermometers Error Probable or possible cause Corrective measures Break in the temperature sensor a) Vibrations – – – – b) Thermal shock – Select a temperature change resistant sensor design – Incorrect thermowell material selected – Analyze defective thermowell and select a more suitable material; provide supplementary surface protection (e.g. armoring or eccentrically drilled thermowell, impact rod) Very corroded, abraded or eroded thermowell 150 Stronger springs for measuring inset Shorten insertion length Move measuring location (if possible) Specially designed measuring inset and thermowell Error Table Specifically for Thermocouples Error Probable or possible cause Corrective measures Temperature indication too low with a very thin thermocouple – Instrument with a low input or internal resistance, high lead resistance – Adjust leads – Select an instrument with a higher input resistance Varying temperature indication with otherwise proper operation – Reference junction temperature or electric simulation not constant (thermal/electrical reference junction) – Reference junction temperature or reference junction simulation must be maintained constant Temperature indication error increases with increasing temperatures (indication too low) – Decreasing insulation resistance (acts as a shunt path, decreases EMF of the thermocouple) – – – – Large deviations of the temperature indication from the values in the tables – Parasitic voltages (thermal voltages, galvanic voltages) – Incorrect material combinations – Incorrect linearization applied – Poor electrical contact – Check thermocouple and leads, exchange if necessary Large deviations of the temperature indication from the values in the tables – Incorrect compensating cables or their polarity is reversed – Check if the correct compensating cable has the correct polarity – If a compensating cable is used: Temperature of connection terminals max. 200 °C [392 °F). Same temperature of connection terminals at > 100 °C [212 °F] Indication changes over the course of time – Chemical effects on the thermocouple especially at higher temperatures – Exchange defective thermometer, possibly by a suitable thermocouple (e.g. Green rot in Type K → replace with Type N) – The measuring location wanders with the “healthy“ material into cooler regions, possibly insert thermocouple deeper, install air purge (O2-addition) – Thermal aging of the thermocouple – Select larger wire size in order to slow down the aging process – Generally an aged thermocouple indicates lower temperatures than a new one. – Check critical measuring locations regularly – Regular recalibrations Recommended insulation resistance at 20 °C (68 °F) ≥ 100 MΩ, at 500 °C (930 °F) ≥ 2 MΩ Exchange thermocouple measuring inset, then seal against moisture 151 Continuation: Error Table Specifically for Thermocouples Error Probable or possible cause Corrective measures Indicating instrument – Lead break shows room temperature (reference junction in instrument) – Check continuity Negative temperature indication – Reverse thermocouple polarity – Incorrect polarity at thermocouple Indication in error by – Thermocouple Type L 20...25 °C (68...77 °F) linearized as Type J or reverse Indication even though temperature sensor disconnected 152 – Correct linearization – Pick up on the compen- – Dry compensation cable sation cable due to electromagnetic noise – Parasitic galvanic voltage (adjacent meter location) due to moisture in the compensation cable Error Table Specifically for Resistance Thermometers Error Probable or possible cause Temperature indica– Non-negligible lead tion generally too high resistances too high, Not compensated Corrective measures If still possible: – Install larger wire size cables – Compensate leads – Use sensor head transmitters – Convert to 3- or 4-wire circuits – Reduce connection lead lengths – Self heating by measur- – Use a smaller measuring current ing current too high (recommended 1 mA) Temperature indication changes with changing ambient temperatures – Thermometer in 2-wire circuit; the connection leads are subjected to large a temperature change – Convert to 3-wire circuit, which essentially eliminates the ambient temperature effects – Convert to a 4-wire circuit (Connection lead resistance effects completely eliminated) Temperature indication error increases with increasing temperature (indication too low) – Decreasing insulation resistance, acts as a shunt path for the measured signal – Rins approx. 0.1 MΩ in parallel with 100 Ω gives an error of the same magnitude as Tolerance Class B Recommended: Rins at 20 °C ( 68 °F): ≥ 100 MΩ Rins at 500 °C (930 °F): ≥ 2 MΩ (Minimum requirements per EN 60751) – Exchange defective thermometer Deviations of the tem- – Poor lead material, – Check installation perature indication contamination, – Thermally insulate terminals from the values in the moisture (same temperature) tables (parasitic – Temperature difference and galvanic EMF’s) between the terminals of the connection leads – Corrosion at the connection terminals in the connection head Indication changes over the course of time – Thermal aging (Drift of the measuring resistor) – Select suitable high temperature design – Recalibrate regularly – Exchange if necessary 153 4 Non-Contacting Temperature Measurements in Field Usage 4.1 Advantages and Uses for Applying Infrared Measuring Technology Complementing the classical, contacting temperature measurements using thermocouples and resistance thermometers, more and more applications are making temperature measurements using non-contacting infrared-thermometers. The infrared measuring technology is not a new discovery – it has been utilized in industry and research for decades – but only recently have innovations reduced the costs, increased the reliability and appreciably reduced the size of the sensor. All these factors have aroused the interest of new user groups and application areas. Advantages of the non-contacting temperature measurement • Fast measuring method in the ms-range (saves time) or increases in the number of consecutive measurements which can be made in a given time interval, higher information rate (e.g. temperature field distribution measurements). • Measurements on moving objects possible (conveyer processes, rolling mills, etc.). • Measurements in dangerous or inaccessible locations (objects at high voltage, long distance measurements). • High measuring temperatures above 1300 °C (2372 °F) are not a problem. In such applications, contacting thermometers have a limited life span. • No reaction on the object, i.e. no energy is removed from the measured object. Especially suitable for poor heat conductors such as plastics and wood, a higher measuring accuracy than with contacting thermometers plus elimination of the false measuring values. • No mechanical influences on the surface. Therefore wear free, e.g. painted surfaces are not marred and measurements are possible on soft surfaces (foams, elastomers). Contaminations, especially in hygienic applications, are excluded. 154 Having mentioned a number of advantages, the question remains, what must be considered when applying infrared-thermometers: – The object must by optically visible to theinfrared-thermometer. Large amounts of dust or smoke affect the measurement as well as solid obstructions, e.g. measurements cannot be made inside closed metal reaction vessels. – The optics in the measuring head must be protected from dust and condensing liquids. – Only surface temperature measurements can be made, while the different radiation properties of different material surfaces must be considered. Summary: The main advantages are fast response, no reaction on the measured object and a very large temperature range up to 3000 °C (5432 °F). 4.2 Fundamentals and Operation An infrared-thermometer can be compared to the human eye. The lens of the eye is the optic, through which the radiation from the object reaches the light sensitive layer, the retina. There the signal is converted and conducted to the brain. In an infrared thermometer, the lens is responsible for the thermal radiation from the object reaching the radiation sensitive sensor, where the radiation is converted into a useful electrical voltage. Thermal radiation Lens IR-Detector Electronic board with μ-Processor Reference temperature Microstructure thermocouple IR-Thermal voltage Fig. 4-1: Design principle of an infrared measuring (IR) system 155 4.2.1 Physics of Thermal Radiations Every body with a temperature (T) above absolute zero, emits, as a function of its temperature, infra red radiation, so called self radiation. It is the result of internal molecular movements. The intensity of these movements is a function of the temperature of the body. Since the molecular movement simultaneously produces charge motions, an electromagnetic radiation (Photon particles) is emitted. These Photons move at the speed of light and behave according to the known Laws of Optics. They can be deflected and focused using lenses or reflected using mirrored surfaces. The spectrum of this thermal radiation extends from 0.7 to approx.1000 µm wavelengths. This range is not visible to the human eye, because it is above the red range of visible light. It is know by the Latin, “infra"-red. Light Wavelength (μm) Wavelength in μm Used infrared range: 0.7...14 μm Fig. 4-2: The electromagnetic spectrum, with the usable infrared range As mentioned previously, all bodies emit this radiation. In Fig. 4-3 typical radiation curves for a body at various temperatures are shown. One can see, that hot bodies not only emit radiation in the above described infrared range (> 0.7 µm), but a portion of the spectrum lies in the visible range. This is the reason why people can see very hot objects (over 600 °C (1112 °F)) as red hot to white hot. Experienced steel workers can estimate fairly well the temperature of the hot metal by its color. The classic Disappearing Filament Pyrometer has been used in the steel and iron industry since 1930 as a functional measuring system. In Fig. 4-3 one can also see, that the point of maximum radiation shifts to shorter wavelengths as the temperature of the object increases and that the curves for a body at various temperatures do not cross each other. 156 These relationships were recognized by the physicists Stefan and Boltzmann in 1879 and indicated that a unique temperature determination of the measured object can be made based on its radiation curve. Fig. 4-3: Blackbody radiation curve as a function of the temperature Infrared measuring technology is based on this knowledge. As can be seen in Fig. 4-3, the goal is to design an infrared thermometer so that as much of the energy as possible (corresponds to the area under the curve) or the signal from an object can be used for the evaluations. At higher temperatures this is possible using a narrow wavelength range, at lower ranges the energy of a larger spectrum ranges (e.g. 7...14 µm) is used. An additional reason for using instruments with different wavelength ranges, is due to the radiation characteristics of some materials, e.g., those with so called non-graybody radiation (glass, metals and plastic foils). Fig. 4-3 shows curves for ideal blackbody radiation. Many bodies emit less radiation at the same temperature. The relationship of the real radiation value to blackbody radiation is known as the emissivity e, which has a maximum value of 1 (body corresponds to an ideal blackbody) and a minimum value of 0. Bodies, whose emissivity value is less than 1, are called graybody radiators. Bodies whose emissivity value is also a function of the temperature and wavelength, are called non-graybody radiators. 157 Viewed physically, the Conservation of Energy law applies, and therefore the sum of the radiation made up of the absorption (A), reflection (R) and transmission (T) equals "one" (see Equation 1 and Fig. 4-4). (1) A+R+T = 1 Object Thermal source Thermal source A Fig. 4-4: I R T E I = Incoming radiation R = Reflected radiation T = Transmitted radiation E = Emitted radiation A = Absorbed energy portion Sensor Real graybody radiator Solid bodies do not have any transmission in the infrared range (T = 0). Therefore Equation 1 becomes for the absorption and also for the emission: A ⇔E = 1 –R (2) Ideal blackbody radiators have no reflection (R = 0), so that E = 1. Many non-metallic bodies, e.g. wood, plastic, rubber, organic materials, stone or concrete surfaces only reflect minimally and therefore have high emissivity values between ε 0.8 and ε 0.95. Metals on the other hand, especially polished and shiny surfaces, have emissivity values of approx. ε 0.1. These conditions are taken into account by the infrared thermometers by their ability set a selected emissivity factor, see also Fig. 4-5. 158 ε = 1.0 (Blackbody radiator) Specific Emission ε = 0.9 (Graybody radiator) Fig. 4-5: ε varies with wavelength (Non-graybody radiator) Specific emissions for various emissivity values 4.2.2 Determining the Emissivity Values Whether an object is a solid body, a liquid or a gas, it is individual and specific for an infrared sensor. The reasons are its specific material and surface conditions. There are a variety of methods which can be used to determine their effects on the emissivity value. The emissivity value can be determined from a table listing the emissivity values for commonly used materials. Emissivity value tables are also a help in selecting the correct instrument by listing the appropriate wavelength ranges. The table values, especially for metals, should only be used for orientation, because the surface condition (e.g. polished, oxidized or scaled) can affect the emissivity value more than the type of metal itself. There are also methods for determining the emissivity value for a special material. A pyrometer with an emissivity value setting can be used. 1. A sample of the material is heated to a known temperature, which can be measured very accurately using a contacting thermometer (e. g. thermocouple). The temperature of the object is then measured with an infrared thermometer. The emissivity value is then changed until the temperature value corresponds to the temperature measured using the contacting thermometer. This emissivity value can then be used for all subsequent measurements of objects made from the same material. 2. For relatively low temperatures (up to 260 °C (500 °F)) special plastic labels with an adhesive backing and with a known emissivity values are attached to the object to be measured and the temperature of the label measured using an infrared thermometer set to an emissivity value ε = 0.95. The surface of the object is then measured without the label and the emissivity value changed until the correct temperature value is indicated. The emissivity value determined in this manner can then be used for all subsequent measurements of objects made from the same material. 159 3. A blackbody radiator is manufactured using a test body made of the material to be measured. A hole is drilled into the object. The depth of the hole should be at least 5 times diameter of the hole. The diameter must correspond to the diameter of the target area of the instrument being used. If the emissivity value of the inside walls is greater than 0.5, then the emissivity value of the cavity radiator is approx. 1 and the temperature measured in the hole is the correct temperature for the measured object. If the infrared thermometer is now pointed at the surface of the object, the emissivity value can be changed until the temperature indication agrees with the value previously determined using the blackbody radiator. The emissivity value determined in this manner can then be used for all subsequent measurements of objects made from the same material. 4. If the measured object can be coated, a matte black color is applied, for which an emissivity value of about 0.95 is specified. The temperature of this blackbody radiator is measured, and then subsequently the emissivity value is adjusted as described above for measurements made on the uncoated object. 4.2.3 Measuring Temperatures of Metals Measurement Error [%] The emissivity value of metals is a function of the wavelength and the temperature. Since metals often reflect, they have a tendency to have lower emissivity values, which could result in variable and unreliable measurements. In such applications, select an instrument which measures the infrared radiation at a specific wavelength and over a specific temperature range, at which the metal has the highest emissivity value, if possible. For many metals the measurement error increases with the wavelength, so the shortest possible wavelength for the measurement should be used, see Fig. 4-6. Object temperature [°C] Fig. 4-6: 160 Measurement error for an emissivity value misadjusted by 10 % as a function of the wavelength and object temperature The optimal wavelengths for measuring high temperatures of metals is between approx. 0.8...1.0 µm at the limit of the visible range. Wavelengths of 1.6, 2.2 and 3.9 µm might also be used. 4.2.4 Measuring Temperatures of Plastics Many plastics are by nature clear and transparent to human eyes, as well as to infrared radiation. The transmission ranges for plastic foils varies with the wavelength and is proportional to the thickness. The transmission is higher in thin materials than in thicker materials. For optimal temperature measurements of such foils, it is important to select a wavelength at which the transmission value is near zero. Certain plastics (Polyethylene, Polypropylene, Nylon and Polystyrene) are opaque at 3.43 µm, others (Polyester, Polyurethane, Teflon, FEP and Polyamide) at 7.9 µm. For thicker (> 0.4 mm (0.016“)) or heavily pigmented foils, wavelengths between 8 and 14 µm should be selected. If uncertainty still exists, it is advisable to submit a sample of the plastic to the manufacturer of the infrared-thermometer to determine the optimal spectral bandwidth. The reflection value for practically all plastics is between 5 % and 10 % (ε = 0.9...0.95). Transmissivity [%] Polyethylene 0.03 mm (0.0012“) thick 0.13 mm (0.005”) thick Wavelengths [μm] Transmissivity [%] Polyester 0.03 mm (0.0012“) thick 0.25 mm (0.010“) thick Wavelengths [μm] Fig. 4-7: Spectral transmissivity of Polyethylene and Polyester plastic foils Independent of the thickness, Polyethylene is essentially opaque at a wavelength of 3.43 µm and Polyester is completely opaque at a wavelength of 7.9 µm. 161 4.2.5 Measuring Temperatures of Glass When an infrared thermometer is used to measure the temperature of glass, both the reflection and transmission must be considered. By a careful selection of the wavelengths, it is possible, to not only measure the surface temperature of glass, but also temperatures within the glass. For temperature measurements below the surface, a sensor for wavelengths 1.0, 2.2 or 3.9 µm should be used. For surface temperature measurements a sensor with a wavelength of 5 µm is recommended. For low temperatures, 8...14 µm should be used with the emissivity set to 0.85. Summary: All bodies emit infrared radiation, which is only visible to human eyes above 600 °C (1112 °F) (e. g. glowing iron). The wavelength range extends from 0.7 µm to 1000 µm. Blackbody radiators absorb or emit 100 % of the radiation that corresponds to their temperature. The radiation of all other bodies is ratioed to the blackbody. This ratio is called the emissivity value. 162 4.3 A Typical Infrared Measuring Site 4.3.1 The Measuring Path Measured spot Heat source Measured object Fig. 4-8: Typical infrared measuring site Normally, atmospheric air fills the measuring path between the detector and measured object, whose transmission characteristics must be considered if a reliable measurement is to be assured. Atmospheric components such as water vapor or carbon dioxide absorb infrared radiation of certain wavelengths resulting in transmission losses. If these absorption components are ignored, the temperature which will be indicated, in certain instances, will be lower that the actual temperature of the object. Fortunately there are “windows“ in the infrared spectrum which do not contain these absorption wavelengths. In Fig. 4-9 the transmission curve of a 1 m long air path is shown. Typical measuring windows in which infrared radiation passes essentially unimpeded are 1.1...1.7 µm, 2...2.5 µm, 3...5 µm and 8...14 µm. For this reason, commercially available infrared thermometers utilize these wavelengths for evaluating the signals. 163 Transmissivity [%] Wavelength [μm] Fig. 4-9: Transmissivity of a 1 m (39”) long air path at 32 °C (90 °F) and rel. humidity 75 % Additional effects such as dust, smoke and suspended matter could contaminate the optics and lead to incorrect measurements. To prevent particles from adhering, an air stream accessory is offered. It usually has threaded adaptors and a compressed air connection. The air stream assures a positive pressure in front of the optics preventing particles from reaching the optics. If during the measuring process, large quantities of dust or smoke are present which are affecting the measurements, quotient pyrometers should be used. 164 4.3.2 Stray Radiation and High Ambient Temperatures Also thermal radiation sources in the vicinity of the measured object must be considered. It might be possible that temperature measurements of metal pieces in an industrial furnace might be affected by the higher temperature of the furnace walls. This influence of the ambient temperature on the measured value is taken into account by a special compensation. Otherwise, the temperature value indicated for the measured object would be too high. A correctly set emissivity value in conjunction with an automatic ambient temperature compensation assure an accurate temperature measurement. Ambient radiation Measured object Fig. 4-10: Ambient radiation source effects on the measured temperature Infrared sensors are electronic components with a somewhat sensitive nature. They can only operate within specific operating temperature ranges. For some sensors the upper limit is 85 °C (185 °F). Above the allowable operating temperature air or water cooling must be used and a special cable suitable for high temperature applications must be provided. When using water cooling, it is often desirable to also install the air stream accessory to prevent condensation on the optics. 165 4.3.3 Optic Radiation Input, Protection Glass and Window Materials The optic system of an infrared thermometer catches the infrared radiation energy emitted by a circular measured point area and focuses it on the detector. Care must be exercised to assure that the measured point area is completed filled. Otherwise the infrared-thermometer will also “see“ thermal radiation from the background, causing a measurement error. Very good Good Bad Infrared-sensor Object larger than measured point Object smaller than measured point Object and measured point are the same size Fig. 4-11: Measured point size effects Optical resolution is defined as the ratio of the distance between the measuring instrument and the measured object to the measured point diameter. The larger this value the better the instrument and the smaller the measuring object can be for a specific distance. a) b) Fig. 4-12: a) High performance optics combined with crosslaser sighting for more precision b) Close focus lens with a spot size of 1 mm and laser sighting for measurement of smallest structures The optics can either be a mirror optic or a lens optic. Lenses, dependent on their material, can only be used for certain wavelength ranges, but because of design considerations, are the preferred solution. 166 Latest Trends in Sighting Techniques New principles of measurement and sighting techniques facilitate an improved and precise use of infrared thermometers. Developments field of solid state lasers are adapted for multiple laser arrangements to mark the spot sizes. Thus, the real spot sizes inside the object field are denoted with the help of laser crosshairs techniques. Different products use video camera chips instead of optical sighting systems. Development of High-Performance Optics combined with Laser Crosshairs Techniques Simple, cost-effective portable infrared thermometers use single point laser aimers in order to distinguish the centre of the spot with a parallax default. With that technique the user has to estimate the spot size with the help of the spot size diagram and the likewise estimated measuring distance. If the measuring object takes only a part of the measuring spot, temperature rises are only displayed as average value of hot area and ambient cold area. A higher resistance of an electric connection due to a corroded contact results in an unduly heating. Due to small objects and inappropriate big spot sizes, this rise will be shown as a minor heating, only: Thus, potentially dangerous heatings may not be recognized in time. In order to display spots in their real size, optical sighting systems with a size marking were developed. They allow an exact targeting. As laser pyrometers are significantly easier and safer than contact thermometers, engineers have tried to mark the spot size with laser sighting techniques independently from the distance – according to the distance-spot-sizeratio in the diagram. Two warped laser beams approximately show the narrowing of the measuring beam and its broadening in longer distances. The diameter of the spot size is indicated by two spots on the outer circumference. Due to the design the angle position of these laser points on the circuit alternates which makes an aiming difficult. The Principle of the Crosshairs New laser sighting techniques support to denote measuring spots of infrared thermometers as real-size crosshairs, exactly matching the measuring spot in their dimension. Four laser diodes are arranged in symmetrical order around the infrared optical measuring channel. They are connected to line generators, which create a line of defined length inside the focus distance. The line generators, arranged in pairs, face each other. They overlap the projected laser lines at the focus. That way crosshairs are generated, which exactly display the diameter of the measuring spot. At longer or shorter distances the overlapping is only partly. Thus the user has a changed line length and with this changed measuring crosshairs. With the help of this technology the precise dimensions of a measuring spot can be denoted for the first time. This development improves the practical use of products with good optical performance. 167 Protection Glass and Window Materials For measurements in closed reaction vessels, furnaces or vacuum chambers, it is usually necessary to measure through an appropriate measuring window. When selecting a window material make certain that the transmission value of the window is compatible with the spectral sensitivity of the sensor. At higher temperatures, quartz glass is usually the material of choice. At lower temperatures in the 8...14 µm band the use of special infrared transparent materials such as Germanium, Amtir glass or Zinc selenite are required. In addition to the spectral sensitivity, other parameters should be considered when selecting the window material, such as the diameter of the window, temperature requirements, maximum pressure differential across window, ambient conditions as well as the capability of maintaining both sides clean. Just as important a factor is the transparency in the visual range in order to better aim the instrument at the measured object (e. g. in a vacuum chamber). Window Material/ Properties Sapphire Al2O3 Quartz glass SiO2 CaF2 BaF2 AMTIR ZnS ZnSe KRS5 Recommended infrared wavelength range in µm 1...4 1...2.5 2...8 2...8 3...14 2...14 2...14 1...14 Max. window temperature in °C (°F) 1800 (3272) 900 (1652) 600 500 (1112) (932) 300 (572) 250 (482) 250 (482) no specs. Transmission in visible range yes yes yes yes no yes yes yes Resistance to moisture, acids, ammonia compounds. very good very good good somewhat good good good good yes yes yes yes ·/· yes yes yes Suitable for vacuum applications Tbl. 4-1: Overview of various window materials The transmission of a window is primarily a function of its thickness. For a window with a 25 mm (1”) diameter, the thickness required to withstand a pressure difference of one atmosphere is 1.7 mm (0.070”). Summary: As in a camera, the rating of the optics (e. g. telephoto lens), defines the size of an object which can be resolved, or measured. The distance relationship (measuring distance: target area diameter) defines the rating of the optics in an infrared thermometer. The target area for accurate measurements must be completely filled by the measured object. If protection windows are installed between the measuring instrument and the measured object, the proper selection of a window material is important. The effects of wavelength range and installation conditions play an important role. 168 4.4 Indication and Interfaces For the user, the type of indications and available interfaces are important. For some, especially portable instruments, directly available indicators/operating panel combinations can be considered as the primary outputs for the measuring instrument. Analog or digital outputs can be used for additional indicators in the control room or for control functions. A direct connection to data recorders, printers or computers is also possible. + 0/4...20 mA Controller 250 Ohm Recorder Digital Indicator - PC FSK Modem Printer Fig. 4-13: Connection example for an infrared measuring system Industrial bus systems are gaining importance by providing the user with more flexibility. Sensors can be set from the control room without the need to interrupt the manufacturing process. It is also possible to change parameters, when different products are manufactured on the same production line. Without the ability to make these remote sensor parameter adjustments, e.g., emissivity value, measuring range or alarm limits, the changes would have to be made manually at each sensor itself. Since sensors are often installed in inaccessible locations, the intelligent sensor assures continuous process monitoring and control with minimal personnel expenditures. If a fault occurs – too high an ambient temperature, cable break, failure of a component – an error message is displayed automatically. 169 4.5 Application Examples In the beginning, only high temperatures above the 700 °C (1300 °F) range encountered in glass and metal production were measured. In recent years however, additional application areas, especially in the lower temperature ranges, have opened up. • Metal and alloy production • • • • • • • • • • 170 (melting, casting, rolling, hardening, forging, annealing, welding, drawing, sintering) Cement and lime furnaces, rotary furnaces Fire chamber measurements in power plants and waste incineration furnaces Glass industry (glass crucibles, feeders, float glass line) Food and beverage industry (freezing, baking, frying, sterilizing, filling, packaging) Textile industry (drying, fibers) Paper industry (coating, drying) Plastics (casting, forming, granulating) Automotive industry Maintenance and service Chemical industry 5 Measurement Signal Processing and Evaluation 5.1 Application of Transmitters in Temperature Measurements The function of the transmitter is to amplify the electrical signals from the sensor, to correct and if necessary, galvanically isolate them. The conditioned signal can then be easily transmitted over long distances to the in-/output sections of a process control system or controller. The temperature values differentiate themselves in an essential manner from all other measurement values. Since the electrical signal from the temperature sensors or resistors is relative large, signal amplification in close proximity to the sensors is not required. As a result, three basically different mounting locations for the transmitter have evolved: The Rail Mounted is the oldest known mounting arrangement for the transmitter. The most common designs include the 19" or DIN rail mount designs as well as integration directly at the in-/output connections of regulators, valves or controllers. Transmitters for direct Field Mounting are mounted in their own rugged housings. The field mounted transmitter can also be used in difficult industrial environments without the requirement for special protective measures and can be mounted in the close proximity to the sensor. In Head Mounting the transmitter is integrally mounted in the connection head of the temperature sensor. Transmitters which are used for this mounting design are designated as sensor head transmitters. Head mounted Field mounted Rail mounted/ Panel mounted ➡ Fig. 5-1: The three transmitter mounting designs 171 A temperature sensor is considered to be a complete measuring assembly and consists of the thermowell and an exchangeable measuring inset. Dependent on the selected mounting method for the transmitter, the temperature sensor includes either terminals or an adapter for direct mounting of the sensor head transmitter. The advantage of mounting the transmitter in a control room is easier accessibility should a repair be required. This advantage is becoming less important as the electronic designs are becoming more and more reliable. The trend in modern instrument technology is to install the transmitters near the sensor. The sensitive connection wires are shorter, i.e., the closer the transmitter is to the measuring location, the less the danger that noise pickup could interfere with the temperature signal. Short distances between the temperature sensor and transmitter for thermocouples also reduce the required wiring for the compensation cables (see chapter 5.2). These are definite advantages which are realized when using a head or field mounted temperature transmitter. On the other hand, when the transmitter is installed in the vicinity of the sensor, it may require an internal construction suitable higher requirements and have a more rugged transmitter design due to the harsh ambient conditions which may exist in an industrial environment. Fig. 5-2: 172 Transmitter in a field mount housing with local indication and operating module plus a large terminal section The decision whether a transmitter should be field or head mounted depends on the local conditions of the system. Transmitters for field mounting, e. g. model TTF300, have the advantages of a very rugged design and are service friendly. Since the installation location is usually not at an inaccessible measuring location, all start-up and service tasks are easier to perform. A large terminal section and the integration of the operating module underscore these advantages. The required sturdy design of the transmitter is assured by a number of special measures. First, the electronics assembly is completely potted, and secondly, it is mounted in an integrated chamber separated from the terminal section. The electronics is protected even when the cover is removed. Transmitters for sensor head mounting, e.g. Model TTH300, are integrated directly in the head of the temperature sensor. The electronics in this design is also completely potted and also allows the use of a local indicator. The transmitter, when mounted integrally in the sensor head, does not require the installation of a separate transmitter housing, appreciably reducing planning and installation expenditures. 173 5.2 Measurements of Thermal Voltages and Resistances The thermal voltage resulting from the Seebeck-Effect is utilized in a thermocouple as the measuring principle (see chapter 2.2.3). Measuring the temperature from the thermal voltage is actually a difference measurement between the hot end of the thermocouple and the reference junction temperature. For correct measurements, the electrical connection to the reference junction must always be made of the same material as the thermocouple leg or suitable compensation cables must be used. Copper can be used for the remaining wiring. Because UM = U1 - (U2+U3) an exact determination of the measurement voltage U1 can only be made if the reference junction voltage UV = (U2+U3) is known. To measure absolute temperatures, the temperature at the reference junction TR must always be known. TE 2 U2 TE 1 U1 Thermocouple Fig. 5-3: UM U3 Compensating cable TE 3 Reference junction Copper wire Connection transmitter Thermal voltage measurement When using an external reference junction the connection from the thermocouple or from the compensation cable to the copper wires, is located outside of the temperature transmitter. The temperature of the reference junction TR is controlled at a constant value e.g. by an integrated heater. This value is added to temperature value derived from the voltage UM, to determine the temperature at the hot end of the thermocouple. Modern temperature transmitters incorporate an internal reference junction, which greatly simplifies the measuring system for the user. The thermocouple leg or the compensation cables are wired directly to the transmitter. The reference junction is formed by the terminals of the transmitter. Its temperature TR is measured by an integrated temperature sensor and utilized by the transmitter for the internal corrections. The transmitter, in this manner, can determine the temperature of the hot end of the thermocouple directly. 174 Resistance Measurements The measurement principle utilized in a resistance thermometer is the temperature dependence of the resistance of Platinum (see chapter 2.2.4). The resistance is measured by applying a constant current and measuring the voltage drop across the resistor. Ohm’s Law defines the proportionality between the resistance and the voltage. Therefore the voltage is a direct measure for the resistance and thereby the temperature. Three different circuit configurations are used. In a two-wire circuit a current is applied to the temperature dependent resistor RT from a constant current source. The voltage drop across RT is measured by the temperature transmitter and converted. The resultant value, however, is incorrect because of the series resistances of the connection leads (RL1 + RL2) and the contact resistances at the terminals (RK1 + RK2). The two-wire circuit, even for sensor head mounted transmitters is only of limited applicability. Connection lead lengths and terminal connections can be designed with low resistances, and utilizing statistical correction factors the measured values can be compensated in the transmitter. The temperature dependent portion of the resistance of the connection leads must always be taken into consideration. Especially for thin wires and long measuring sensors or connection leads, errors with a magnitude of a number of degrees can result. Conclusion: The two-wire circuit is not suitable for exact temperature measurements. Two-wire circuit RT Fig. 5-4: RL1 RK1 RL2 RK2 IK1 UM U E UM = (RT+RL1+RK1+RL2+RK2) IK1 Circuit diagram of a two-wire circuit In a three-wire circuit two constant current sources are used, in order to compensate for the disadvantages described above for the two-wire circuits. Similar to the two-wire circuit the current source IK2 is used to measure the temperature dependent resistance RT including the connection lead and terminal contact resistances. The additional current source IK1 together with a third connection lead is used to separately compensate the connection lead and terminal contact resistances. Assuming the exact same connection lead and terminal contact resistances for all three connection leads, the effect on the accuracy of the temperature measurements can be eliminated. Practice has shown that this assumption is not always correct. It is not always possible to assure that the terminal contact resistances are always identical. Oxidation itself, during the course of operation, can cause the contact resistance of the individual ter- 175 minals to vary by differing degrees. This can cause a non-negligible error, even in a three-wire circuit. Three-wire circuit RL1 RK1 RL3 RK3 UM RT RL2 Fig. 5-5: IK1 RK2 U UM = RTIK2+ (RL2+RK2) IK2- (RL3+RK3) IK1 E IK2 Circuit diagram of a three-wire circuit The four-wire circuit eliminates all the previously described disadvantages. In this configuration a constant current source is used to apply a current to the temperature dependent resistance RT. The voltage drop across resistance RT used for the temperature measurement is measured by two high resistance connection leads. In this way the voltage drop due to current flowing during the measurement is negligible and the connection lead and terminal contact resistances RL1, RK1, RL2, RK2 do not impact the measurement result. The four-wire circuit is therefore always used when highly accurate temperature measurements are required. Four-wire circuit RL1 RK1 RL3 RK3 RL4 RK4 RL2 RK2 RT Fig. 5-6: IK1 UM U E UM = RT IK1 Circuit diagram of a four-wire circuit Modern transmitters support the measurement of thermal voltages and resistances using the above described circuit configurations in a single instrument. The user can select the optimal measurement configuration for his application. For thermal voltage measurements in industrial applications, the straight forward option using an internal reference junction is used almost exclusively. Use of an external reference junction makes sense when a highly precise reference junction temperature of less than 0.1 K is required. In view of the errors which could result from using the sum of a temperature measuring chain (see chapter 5.10), this approach is reserved for laboratory applications. For resistance measurements, the four-wire circuit should basically be used because of its indisputable advantages. The three-wire circuit, with its disadvantages, should only come into play for resistance measurements when the use of electrical wiring configurations or system conditions are restrictive. 176 5.3 Power Supply of Temperature Transmitters The transmitter is a measuring instrument, which converts an analog input signal into an analog and/or digital output signal. Transmitters contain active electronic components and therefore require power supply to fulfill their functions. The number of connection wires for the power supply and output signals defines the power supply technology for the transmitter. This is designated as 2-/3-/4-wire power supply technology and should not by confused with the resistance measurement configurations described in chapter 5.2 as 2-/3-/4-wire circuits. Four-wire circuit Three-wire circuit Two-wire circuit Power supply Power supply Input E A Power supply Fig. 5-7: Output signal Input E Output A signal Reference wire (ground) Input E A and Output signal 4...20 mA Power supply technology for transmitters The Four-Wire technology is used exclusively in control cabinets. The typical power supply values available are 230 V AC, 110 V AC, 24 V AC or 24 V DC. For the power supply and output signals, four wires are required. The input circuit, output circuit and power supply for the transmitter are electrically isolated from each other. Typical output signals are 0...5 V, 0...10 V, 0...20 mA and 4...20 mA. Additional digital outputs are often included in transmitters with four- or three-wire power supply, that can be used for error or alarm signals. The Three-Wire technology is also used exclusively in control cabinets. The use of the same reference wire for all the instruments eliminates the need for a fourth connection wire. The typical power supply for this option is 24 V DC. Because a connection wire was eliminated, only the in- and outputs are electrically isolated from each other. Typical output signals are 0...5 V, 0...10 V, 0...20 mA and 4...20 mA. 177 The Two-Wire technology is the standard today for field or sensor head mounted transmitters. In this design the same connection wires are used for the power supply and the output signal, which reduces the wiring expenses in comparison to three-wire technology. Because power supply is required for the operation of the transmitter even when there is no output signal, the lowest output signal value cannot be zero (true zero), but must have a value greater than zero (live zero). For this reason, the standard output current range is 4...20 mA. The live zero signal also allows the connection wires to be easily monitored (see „Error Monitoring“ on page 181). The typical power supply for this design is 24 V DC. 5.4 Design Principles for a Temperature Transmitter The transmitter is a measuring instrument which converts an analog input signal into a scaled, analog or digital output signal. Dependent on the requirements, this signal is then available in the measuring chain for further processing in a controller and/or for indication. Sensor Transmitter Indicator S MU A Measured value Electrical signal Scaled Signal Temperature Thermal voltage 4...20 mA Fig. 5-8: Process interface Controller R The components in an industrial temperature measuring chain Temperature transmitters operate based on the current measuring process (LindeckRohte, better stated as a current cross coupled amplifier) which outputs a load independent current of 4...20 mA DC. The curves for the resistance thermometers or thermocouples are not linear. An additional function of the transmitter is to linearize the input signal in order to output a temperature proportional signal. Additional requirements for a temperature transmitter include selectable measuring ranges, sensor failure monitoring, measuring circuit signal contact and the electrical isolation between input, output and power supply. 178 Temperature Transmitter in Four-Wire Technology The transmitter shown in the following figure is designed to either measure the mV-signals (thermocouples) or make the resistance measurements (Pt100). It converts the input values into a proportional, load independent DC current signal of 0...20 mA or 4...20 mA or into a voltage signal of 0...10 V. The adaptation to the measured value type is accomplished by a selection made at the temperature transmitter or by using exchangeable measuring range modules. The temperature transmitter in four-wire technology consist of a switched controller (1), which rectifies and stabilizes the supply power. A electrically isolated voltage (2) is supplied to the in- and output circuits. Additional circuit sections are the amplifier (3), measuring range module (4), electrical isolation (6), output stage (7) and alarm signalling (8). 9 2 1 7 IK 5 4 3 6 8 V 10 Fig. 5-9: Schematic of a temperature transmitter in four-wire technology Transmitters in explosion proof designs incorporate a circuit limiter (5) for the Intrinsic Safety of the input circuit, a power supply limiting circuit (9) and electrical isolation (6). A different explosion proof design has intrinsically safe in- and outputs as well as electronic current and voltage limiters in the output current circuit. In this design a electrical isolation between the input and output is not required. The input signal is fed through the measuring range module (4) to the amplifier (3) whose output is a load independent DC signal. When a electrical isolation (6) circuit is installed, the DC current signal is chopped, decoupled by an isolating repeater and con- 179 verted back to a load independent DC current in a rectified circuit with a load converter. This signal is unipolar. For conversion to a bipolar current signal or voltage an output stage (7) is required. The reference junction correction (10) for thermocouples, monitors the temperature at the connection terminals of the temperature transmitter and accounts for its value in the measurements. The alarm signal transmitter (8) has an adjustable switching point which can be either normally open or normally closed. For a purely analog operating temperature transmitter, this switch point can be set using a potentiometer. For digital temperature transmitters, the switch point, the temperature measuring ranges, the connected sensor and its connection circuit can be set using programming software. Temperature Transmitter in Two-Wire Technology In regard to their electrical functions, these transmitters, viewed from both connection terminals, can be considered to be passive, equivalent resistance circuits. The transmitter behaves as a variable resistor whose resistance changes until the current in the measuring circuit corresponds to the measured value. As a basic component, the 4 mA current, provides the power supply for the electronic circuits in the transmitter. The current is a load independent current with a signal range of 16 mA, which contains the measured value information. 5 6 UK 7 9 UK 4 B 8 1 2 3 V Fig. 5-10: Schematic of a temperature transmitter in two-wire technology 180 This transmitter is designed for the same input signals as the four-wire transmitter. It converts the input single values into a load independent DC current signal of 4...20 mA. The selection of the measured value type is made at the factory by adjustments made in the temperature transmitter. Slope and zero values are also set at the factory in the temperature transmitter using precision resistors. The elimination of the potentiometer and the complete encapsulation of the electronics with potting material assure an unexcelled, rugged construction with long term stability. Transmitters for resistance thermometers or for thermocouples are built using this design. The input signal is fed from the input circuit (1), configured based on the measuring method and measurement range, to the amplifier (2) and converted in a final stage (3) into a load independent DC current. The constant voltage source provides the circuit components with a stabilized voltage. Error Monitoring Error monitoring is an important function of the transmitter. Sensor failure, sensor short circuit and reacting when measured values are outside of the range setting must be recognized. These error conditions can also be signalled over the 4...20 mA output. Today the power supply required by the transmitters can be provided by a basic current < 3.5 mA. As a result, transmitters can be designed in which information can be transmitted outside of the 4...20 mA range. In the error monitor circuit (4) the output signal during a short circuit or measuring circuit interruption condition can be selected to be signalled at a current value either above or below the 4...20 mA range. Measured values outside of the measuring range end values are error conditions, indicating an undesirable status of the process. Sensor failure or sensor short circuit in comparison are error conditions indicating that the sensor should be checked or repaired to rectify this condition. The NAMUR (International User Association of Automation Technology in Process Industries) has published a recommendation defining current ranges, outside of the 4...20 mA measuring range, which provide an adequate separation, for the indication of a measured range error and for a temperature sensor error (Fig. 5-11). This allows the appropriate corrective measures to be initiated quickly. 181 ➊ = Internal current mA requirements 7 ➋ = Forbidden output ≥ 21 < 20.5 20 2 4 6 4 > 3.8 ≤ 3.6 5 ➌= ➍= ➎= ➏= ➐= current range Overrange value Underrange value Dynamic range Measuring range Selectable error signalling range 3 2 7 1 0 Fig. 5-11: NAMUR limits for error signalling of a transmitter in two-wire technology (NAMUR-Recommendation NE 43) Basically the range > 21 mA, as well as the range < 3.6 mA can be utilized for error signaling. Ideally, the behavior during an error condition should be selected so that during an error condition the alarm monitors connected to the output signal will not be effected. In addition, in programmable transmitters, different error conditions can often be user assigned. For example, an error condition which can turn a system off can be set if the current value is > 21 mA. Error conditions, which should only trigger and alarm, can be set if the current value < 3.6 mA. It should be noted, that during a power outage or a break in the 4...20 mA loop (not to be confused with a sensor failure) the current value is always 0 mA. A signalling of this error condition must be made using the analog input of the monitor. Linearization The curves for thermocouples and resistance thermometers are generally not linear. The linearity error is usually larger than all other errors (hysteresis, amplification, aging etc.). Since the curve shapes are known, the measuring error can be compensated using an inverse function. In practice it has been sufficient to approximate the curve shape using straight segments. How to select the straight segments depends on the particular curve shape. In Fig. 5-12 the curve UA (T) is approximated first using a straight line and then two straight lines between equidistant temperature intervals and lastly with three straight lines between optimized temperature intervals for which the deviations from the curve are minimized. 182 For analog transmitters, the method uses an operational amplifier with a defined amplification for each straight section. It is possible using this approach to reduce the total error of the temperature transmitter to approx. 0.1 % of the range. Two point without linearization Four point optimizes linearization Four point equidistant linearization UA UA UA UME UME UME T UMA TMA TME T UMA TMA TME T UMA TMA TME Fig. 5-12: Linearization of a sensor curve using straight line segments For digital temperature transmitters with a microcontroller, the curve can be linearized using software (Firmware) by calculating an inverse function polynomial directly from the curve of the standard temperature sensor. As a result of this technology, the linearization error for digital transmitters is less than for analog ones. 183 5.5 Programmable Temperature Transmitters Analog transmitters are adjusted and set for sensor type and for one measuring range. If a sensor type or measuring range is changed, the transmitter must also be exchanged. A programmable transmitter on the other hand, can be reprogrammed by entering the new parameters for the changed application. When designing a system, it is possible to select transmitters in which the required measuring range can be set at start-up. This simplifies and reduces the planning and design time and reduces replacement part inventory costs. Programmable transmitters also clearly reduce service and maintenance expenditures thus reducing the cost of ownership. Circuit Block Diagram The following circuit block diagram shows a typical design for a programmable temperature transmitter. The transmitter contains two microcontrollers. In the primary circuit as well as in the secondary circuit the controller operates using the software (Firmware) designed for that circuit. In the primary circuit the multiplexer is controlled, which transfers the values from the sensors, the reference and the reference junction. The signals reach the analog-digital-converter and are read by the microcontroller. Filter functions and sensor failure monitoring is also carried out by the this controller. The digitized signal is fed by a transducer to the microcontroller in the secondary circuit. The transducer also provides the electrical isolation between the primary and secondary circuits. Ref. junction Pt100 µC µC U I Reference D Filter MUX A A Sensor break monitor 4...20 mA FSK D EEPROM Fig. 5-13: Circuit block diagram of a digital temperature transmitter The second microcontroller in the secondary circuit controls the digital-analog-converter and is responsible for the data exchange between the communication and the programming software. The required software (Firmware) is stored in an EEPROM. An I/U-converter powers the transmitter from the 4...20 mA signal. This same 4...20 mA signal is used to provide communication with a supervisory system (PC) using a FSKinterface. 184 As can be recognized in the following figure, two sensors can be connected to the transmitter. The averages and differences between the two sensor signals can be calculated and also transmitted as an output signal. Reference junction Pt100 Input 1 Measurement val. conditioning, wire compensation Linearization average difference Reference junction correction lin T Input 2 1 2 + Scaling Damping 4 Status 3 1 = Sensor signal input 2 = Reference junction temperature 3 = Linearized measured value 4 = Percent of the output span 5 = Output value in mA 6 = FSK programming Analog output FSK 5 6 Fig. 5-14: Software structure of a digital temperature transmitter Programmed Curves In a programmable transmitter are all the curves for the most common measuring applications stored. They include the basic values for the appropriate measurement resistors and thermocouples, which can simply be selected when programming the transmitter. A Pt100-resistance thermometer in accuracy class Type B has a temperature dependent measuring error at 400 °C (752 °F) of several K (see Fig. 3-5). For measurements with resistance thermometers the achievable accuracy after selecting the standard curve can never be better than the allowable measuring deviations of the sensor. Programmable transmitters, such as the TTH300, offer the possibility to use the exact curve of a previously measured temperature sensor by entering the coefficients for the Callendar Vandusen equation (polynomial see chapter 3.1.5). 185 For curves with a monotomic curve shape it is possible to enter a free style curve with using as many as 64 points. In this way a digital transmitter can be matched to any sensor or to the calibration or adjustment of the entire measuring chain. To accomplish this, the sensor to be calibrated, together with the transmitter and its power supply instrument, are calibrated against a “Standard“. The deviations of the output signal are corrected in the transmitter. Deviations from the curve for the entire measuring chain as low as < ± 0.05 K are possible. Diagnosis Programmable transmitters include extensive capabilities to detect and signal error conditions. In order to provide the user with an effective trouble shooting strategy, the error types where classified and prioritized by NAMUR based on their cause and importance to operation. A distinction is made between sensor, transmitter, configuration/calibration and measuring range errors. Based on the priority assigned to each error, the transmitter selects and signals the error with the highest priority. Process control systems utilize a classification system for display and diagnosis based on their operating phase, start-up, operation, monitoring or asset management. In this way the user is provided with the most important information at the correct location at the correct time. Standard • • • • Sensor error (break or short circuit) Instrument error Over/under measuring range Simulation active Expanded • • • • • • • • • Over/under alarm value Sensor backup active (Sensor 1 or Sensor 2 failure) Zero or span adjustment active Low power supply High transmitter ambient temperature (> 85 °C (185 °F)) Memory Indicator Writing protection “Drag indicator“ for sensor temperature and electronics temperature Tbl. 5-1: 186 Diagnosis and error classifications for transmitter TTH300 Drift Warning and Redundancy Circuit Recalibration and recertification are normal procedures for measuring locations which are subject to measuring instrument inspections. Two channel transmitters, such as the TTH300, can provide some relief, by increasing the required recalibration interval. To check for drift, a temperature sensor with two integrated measuring locations can be used. In addition to its actual measuring function, the transmitter continuously compares the difference between the two measuring locations. If the deviation exceeds a specified value, an alarm is signalled. Using this signal, the user is advised by the transmitter that a recalibration is required. The number of manual inspections are appreciably reduced, because a recalibration will only be conducted when it is really necessary. To increase the operational availability, two redundant temperature sensors are installed. For single channel transmitters the connections can be manual switched to the other sensor if one fails. Two independent Pt100 measuring locations can be connected to a two channel transmitter. Using the integrated “hot swap“ function, if a malfunction in one of the measuring locations is recognized by the transmitter, an error is signalled and the input is immediately switched to the redundant element. The ontime of the measuring location is significantly increased, since the repair of the defective element can made during the next, scheduled service shut down. In summary, two channel transmitters appreciably reduce service and maintenance expenditures. 187 5.6 Communication Interfaces Programmable transmitters with a classic 4...20 mA signal transmission are available with a digital communication interface. These interfaces are used primarily for diagnosis or for selecting the required transmitter functions for the application while continuing to use the analog output for fast measured value transmission. There are different programmable transmitters interfaces, suitable for local as well as for remote programming. Transmitters with fieldbus interfaces usually no longer include an analog output. The measured signal, diagnosis and parameters are transmitted digitally over the fieldbus. Local Programming The transmitters with local communication interfaces (LCI) often have, in addition to the connections for the 4...20 mA signal, a separate, manufacturer specific programming connection. An adapter is used to connect the instrument directly to the programming device. A requirement is that the distance between the instrument and the programming device is only a few meters (yards). This type of local programming is found primarily in transmitters designed for installation in control rooms and for the economical sensor head transmitters. The programming is usually a one time event, made prior to the start-up of the transmitter, e. g. in the work shop. Continuous monitoring of the transmitter, because it only has a locally accessible interface, is not possible. Changes to the parameters or inspections of the transmitter by service can only be accomplished using portable programming devices. Field Control room LCI Transmitter LCI Adapter Fig. 5-15: Local Communication Interface Remote Programming When the transmitter is to be programmed or monitored from large distances, transmitters with FSK-communication are used (FSK = Frequency Shift Keying). In this design, a frequency of 1200 Hz or 2200 Hz is superimposed on the analog 4...20 mA signal. This type of data transmission is based on the Bell 202 Communication Standard. 188 The Bell 202 Communication Standard + 0.5 mA 0 Analog Signal (4...20 mA) - 0.5 mA "1" = 1200 Hz "0" = 2200 Hz Fig. 5-16: Bell 202 Communication Standard The two frequencies contain bit information 1 or 0. A real simultaneous communication with a response time of approx. 500 ms per measured value can be achieved. Because the average value of the frequency is zero, the FSK-communication does not affect the analog signal. To program the transmitter a FSK-modem is required. The HART-Protocol The HART-Protocol (Highway Addressable Remote Transducer, i.e. a protocol for bus addressable field instruments) operates using the above named technology. The HART-Protocol is an industry tested digital communication method available for field instruments. There is a worldwide HART-User Group. All well known companies in the measurement and control fields are members. HART conforms to the Open Systems Interconnection basic reference model (OSI) for open system communications, developed by the International Standards Organization (ISO). Point-to-point operation is used for simple programming of HART-instruments. When programming, it is always necessary that the connected HART-instrument is powered. There are suitable programming adapters or transmitter power supplies available for this purpose. The following figure shows the various point-to-point operating modes. 189 Field Control FSK Room Transmitter Configuration Adapter FSK Transmitter Isolator FSK Modem 4...20 mA FSK Modem FSK Transmitter Isolator 4...20 mA FSK Modem Fig. 5-17: FSK-programming The manufacturer specific programming adapters accept the HART-temperature transmitter and provide its power supply. The FSK-modem is used to convert the FSK-information into a PC compatible format. Using this design, the transmitter, prior to start-up in the field, can be programmed from the control room without any large wiring expenses. If the temperature transmitter is already installed in the field, it is possible to program it using a handheld terminal (HHT) without any effect on the 4...20 mA output signal. The FSK-modem is integrated in the HHT. The power supply is provided by the transmitter power supply in the control room. According to the HART-specifications, a load of at least 250 Ω must always be installed in the 4...20 mA loop. This assures that the low internal resistance of the power supply cannot short out the HART-signal. When using older or simple power supply instruments, the connection wire must be opened and a resistor installed. In modern HART transmitter power supply instruments this load is integrated. In addition, they are transparent to the FSK-signals. A simple connection of a handheld terminal or FSK-modem can be made either in the field or in the control room. Many of the transmitter power supplies contain sockets, for connecting terminals or modems so that the current output or supply circuit need not be opened. If power supplies are installed instead, which do not have the ability to transmit FSK-signals, then an FSK-modem must be installed between the transmitter power supply and temperature transmitter. In every HART-interconnection two indicating/operating instruments are allowed. A primary one, usually in the process control system, and a secondary one, e. g. a handheld terminal or a laptop. 190 HART Multi-Drop-Mode In the Multi-Drop-Mode the transmitter with a FSK-interface is also bus capable. The two connection wires for the 4...20 mA signal is also used for the bus communication. This operating mode requires only a single pair of wires and a power supply to communicate with up to 15 field instruments. When the connected instruments are configured for this operating mode, their output current is frozen at 4 mA. The instruments only communicate digitally. Their analog output signal is no longer used to transmit temperature values. The connection of a recorder or an analog indicator is no longer possible. FSK Modem 4 mA Transmitter 1 4 mA 4 mA Transmitter 2 Transmitter 15 Power supply Fig. 5-18: Bus operating mode Multi-Drop In this operating mode the transmission of parameters and diagnosis data is in the foreground. Since only about 2 measured values can be transmitted digitally over the HART-Protocol per second, this communication method is only used for slower processes, e. g. the monitoring of very distant systems such as pipelines or tank farms. HART-Multiplexer It is also possible using a FSK-multiplexer to connect multiple instruments to a single programming instrument. Several hundred HART-field instruments can be accessed from a central location. This simplifies the start-up and maintenance since they can be performed while the system is operational. It is possible to set a HART-transmitter in the simulation-mode, so that the 4...20 mA signal can be set to a fixed, user programmable current value. In this manner, the current loop can be tested without using the measured value. The measuring location parameter values can be stored in the programming instrument. This is a practical function for accessing the diagnosis and asset management data. This allows a quick response when service is required. This functionality can only be viewed as an intermediate step for fieldbus systems with open fieldbus protocols. 191 Fieldbus Systems The art of instrumentation was dramatically changed by the introduction of fieldbus technology. In the past, a two conductor wire had to be connected from each instrument to the control room for the analog 4...20 mA signals. In the fieldbus only a single two connection wire cable is required to connect up to 32 temperature transmitters. 1 Temperature transmitter PROFIBUS PA PROFIBUS DP Segment coupler koppler 2 PROFIBUS PA Profile (Pt100-Temp.) Temperature transmitter 3 850°C Physical Limitation 100°C Measurement Limit Upper Alarm Limit Upper Warning Limit Temperature transmitter Measurement Value 32 0°C Temperature transmitter -200°C Lower Warning Limit Lower Alarm Limit Measurement Limit Physical Limitation Bus connection Fig. 5-19: PROFIBUS PA installation using a PROFIBUS PA-profile This figure shows an example of a PROFIBUS PA installation of 32 temperature transmitters. Since this concerns a fieldbus, it is necessary to install a bus termination at the end of the cable. The transmission medium is a twisted two wire copper cable with a shield. Instruments can be exchanged or added during operation. With a common transfer rate of 31.25 KBaud distances up to 1900 m (6200 ft.) can be spanned. The temperature transmitters can easily be integrated into PROFIBUS DP-Networks using a segment coupler. The segment couplers have a simple baudrate conversion factor of 1:3. Therefore the transmission speed of the PROFIBUS DP when using these segment couplers is fixed at 93.75 kbit per second (93.75 KBaud). If one wants to circumvent this fixed transmission ratio between the PA and DP, a DP/PA-Link can be used instead of the segment coupler. This allows, dependent on the transmission length of the PROFIBUS DP, the total transmission speed to be realized. 192 What has been accomplished in the European markets through the activities of the PNO (Profibus-Nutzer(User)-Organization), is accomplished in the American market place by the FF (Fieldbus Foundation). Each organization supports a non-compatible bus protocol. Only the bus supplied transmission technology per IEC 1158-2 and the data transmission speed of 31.25 kbit per second are identical for PROFIBUS PA and FOUNDATION Fieldbus. Fieldbus Profiles The PROFIBUS PA-Profile enables the exchangeability and interoperability of field instruments from different manufacturers. It is an integral component of PROFIBUS PA and can be obtained from the PROFIBUS-User Organization. The PA-Profile consists of a framework specification, which contains valid definitions for all instrument types, and instrument specification sheets which include the specific agreements which were reached for each instrument type. The profiles use standardized function blocks. The description of the instrument behavior is accomplished by defining the standard variables, which describe the properties of the transmitter in detail. Every instrument must have a GSD (Generic Slave Data) file, which contains the specific instrument data. These files are necessary in order to connect the instrument described therein into the bus. The procedure is supported by the software tools from the different manufacturers. Every instrument must make available the parameters defined in the PROFIBUS PA-Profiles. Measured values are calculated in a Transducer-Block (TR) and transmitted over an AI-Block to the PROFIBUS-Master. The following table lists the most important parameters of an AI-Block. For actuators, AO-Blocks are used. Parameter Read Write Function Out ● PV_SCALE ● ● Scaling of the process variables PV_FTIME ● ● Rise time of the function block- output in s ALARM_HYS ● ● Hysteresis of the alarm function in % or range HI_HI_LIM ● ● Upper alarm limit HI_LIM ● ● Upper warning limit LO_LIM ● ● Lower warning limit LO_LO_LIM ● ● Lower alarm limit HI_HI_ALM ● Status the upper alarm limit with time stamp HI_ALM ● Status the upper warning limit with time stamp LO_ALM ● Status the lower warning limit with time stamp LO_LO_ALM ● Status the lower warning limit with time stamp Tbl. 5-2: Actual measured value of the process variables Defined parameters of an AI-Block in the PROFIBUS PA-profiles 193 For the various parameters it can be seen that not only the measured value, but also the alarm and warning information is transmitted. The digital transmission of the measured values allows a higher accuracy to be achieved, because the conversion of the measuring range to a span of 4...20 mA is no longer necessary. Wider measuring ranges can be defined, without sacrificing any accuracy. Programming Software For the different instruments from the various manufacturers, special programming software is available. A number of firms have developed a common programming software for their entire instrument palette. It can be used, from a common user interface (GMA-Standard), to program the parameters and read the measured values and diagnosis information from different instrument types. 5.7 Temperature Transmitters in Explosion Hazardous Areas The ability to install transmitters in explosion hazardous areas is an important requirement for their use in chemical, petrochemical and process industries. The design, construction and operation must be in accord with the generally accepted regulations. Equipment, which is installed in explosion hazardous areas classified as Zone 0 or 1, as well as hazardous dust areas classified as Zone 20 or 21, must have been issued a test examination certificate by a registered, certification body. This certificate is issued when the design of the equipment has been examined and found to be in accord with the standards for the applicable ignition type. The concept of explosion protection includes not only the design of the instrument installed in the explosion hazardous area, but also the consequences of the designs of all the other components in the measuring chain. Fig. 5-20 and Fig. 5-21 show the structure for typical measuring chains for the installation of temperature transmitters in explosion hazardous areas. 194 Field (explosion hazardous area) Control room (safe area) Power supply 24 ... 230 V UC 1 4 ... 20 mA 4 ... 20 mA 2 Two-wire design, transmitter intrinsic safety e. g. II 2(1)G EEx [ia] ib IIC T6 Active isolator, input intrinsic safety e. g. II (2)G [EEx ib] IIC Intrinsically Safe Installation: Ex-temperature transmitter (Two-wire design) with Ex-input transmitter power supply Field (explosion hazardous area) Control room (safe area) Power supply 24 ... 230 V UC 1 4 ... 20 mA 4 ... 20 mA 4 ... 20 mA 2 Two-wire design, transmitter intrinsic safety e. g. II 2(1)G EEx [ia] ib IIC T6 Ex safety barrier e. g. II (2)G [EEx ib] IIC Active isolator Non-Ex Intrinsically Safe Installation: Ex-temperature transmitter (Two-wire design) with Ex-safety barriers installed between transmitter and power supply Field (explosion hazardous area) Control room (safe area) 1 + 0/4 ... 20 mA 2 3 + - - Power supply 24 V DC Three-wire design, transmitter input intrinsic safety e. g. II (1)G [EEx ia] IIC or II (2)G [EEx ib] IIC Intrinsically Safe Installation: Ex-Temperature transmitter (Three-wire design) Fig. 5-20: Installation of temperature transmitters in explosion hazardous areas 195 Field (explosion hazardous area) Control room (safe area) 1 + 0/4 ... 20 mA - 2 4 3 Power supply 24 ... 230 V UC Four-wire design, transmitter input intrinsic safety e. g. II (1)G [EEx ia] IIC or II (2)G [EEx ib] IIC Intrinsically Safe Installation: Ex-temperature transmitter (Four-wire design) Field (explosion hazardous area) Control room (safe area) Power supply 24 ... 230 V UC 1 0/4 ... 20 mA 2 4 Ex safety barrier e. g. II (1)G [EEx ia] IIC 3 Power supply 24 ... 230 V UC Four-wire design, transmitter Non-Ex Intrinsically Safe Installation: Ex-temperature transmitter (Four-wire design) with Ex-safety barriers installed ahead of the transmitter Field (explosion hazardous area) Control room (safe area) 1 4 ... 20 mA 4 ... 20 mA 2 Two-wire design, transmitter with flameproof enclosure with incidentpower-limitation for temperature sensor, e. g. II 1/2G EEx d IIC T6 Power supply 24 ... 230 V UC Isolator Non-Ex Flameproof enclosure temperature transmitter (Two-wire design) with transmitter power supply Fig. 5-21: Installation of temperature transmitters in explosion hazardous areas 196 If the transmitter is to be installed in an safe area, then all that is required is that an intrinsically safe input circuit be incorporated in the transmitter. If this is not the case, then the required intrinsic safety can be achieved by installing suitable safety barriers, designed specifically for temperature sensors. Transmitters for these applications are often designs using three- or four-wire technology. Since the power supply is integrated, a separate power supply is not required. Transmitters for field or sensor head mounting always use a two-wire design. For the protection type intrinsic safety the power supply is provided either by power supply with integrated electrical isolation or from a network component with barriers installed ahead of it. The function of the power supplies or barriers is to assure that energy limitation required by the intrinsic safety regulations is present. For installations using the flameproof enclosure type of protection, ordinary network components and transmitters without special safety measures can be used, because the explosion protection in this case is provided by the flameproof enclosure in the field. To use this measuring technology, the user must follow the requirements without any qualifications if possible. For example, if exchanging an instrument in the hazardous area while it is powered is a requirement, then the protection type intrinsic safety has been proven to be advantageous. An intrinsically safe handheld terminal can also be connected to the transmitter in the field while powered in the explosion hazardous area. Therefore, the communication described earlier can also be utilized in such environments without limitations. Power Supply for Programmable Transmitters For non-explosion hazardous areas, a two-wire transmitter can be supplied from a normal power supply source with 12...36 V. Often a load with a connection to ground is incorporated across which the signal voltage can be measured. Due to this connection, galvanic coupling could occur between the measuring circuits of two transmitters resulting in erroneous currents. This is especially true when the temperature transmitter does not have electrical isolation between the in- and output circuits. To correct this situation, the use of power supplies is suggested. A modern power supply has four principle functions: • Supplying the intrinsically safe measuring circuits while taking into account the required internal resistances for HART-communication • Decoupling the intrinsically safe field circuits from the non-intrinsically safe control room circuits • Electrical isolation • Load conversion The power supply provides a voltage UM at the input terminals of the transmitter (1) from its output voltage US reduced by the load of lead resistance RL,. The input circuit (3) has a supply input and for explosion proof design includes an Ex-Limiter (2). A correctly sized internal resistance is incorporated in the power supply circuit for the HARTcommunication so the installation of an external 250 Ohm resistor is not required. The 197 next component, a curve module (4) operates per its setting dependent on the application, to provide a proportional or linearized output. In the newer transmitter power supplies this module is not included because the measured signal has already been linearized in the transmitter. This conditioned signal is fed to the output amplifier (6) through the electrical isolation stage (5). The electrical isolation is transparent to the superimposed HART-Signal. The supply voltage is electrically isolated from the input or supply and output circuits by a switching regulator with rectifier (8), Ex-Limiter (9) and the power supply (10). Field (explosion hazardous area) Control room 9 8 10 RL 1 t UM 2 3 4 5 6 US Fig. 5-22: Two-wire transmitter and isolator in an explosion proof design The following conditions must be satisfied when connecting a transmitter to a power supply: UM ≤ US - 22 mA x RL UM US RL 198 = Minimum operating voltage for the transmitter = Minimum supply voltage of the power supply = Connection wire resistance between transmitter and power supply (loop) If additional instruments, e. g. indicators are connected to the 4...20 mA loop, then the internal resistances (load resistance) of these instruments must be added to the connection wire resistance RL. Programmable transmitters, such as the TTH300 or the TTF300, control their integrated indicators over a digital interface. In this case, the required power is supplied by the operating voltage UM. It must not be considered separately. The maximum possible current is assumed to be 22 mA at the minimum voltage, since modern transmitters use the current range above 20 mA to signal error conditions. (see chapter 5.4). The intrinsic safety of the interconnections is assured if the following conditions are satisfied: Intrinsically Safe Equipment plus Cable e.g. ABB-transmitter Ui Ii Pi Li + Lc (cable) Ci + Cc (cable) Associated Equipment e.g. Transmitter power supplies/SPC input ≥ ≥ ≥ ≤ ≤ Uo Io Po Lo Co The power supplies are available as 19"-cards for installation in 19" housings, in a snap design for rail mounting and plug-in designs for card mounting frames. The plug-in designs are moving into the foreground more and more because they reduce the wiring costs. Power Supply of the Fieldbus Transmitters A fieldbus barrier protects the main segment of the fieldbus from improperly connected field instruments and assures continued operation of the fieldbus. It incorporates the following functions and advantages: • Electrical isolation between the main and branch lines to provide protection from problems which might occur due to potential differences and error currents due to potential equalization. • The short circuit current limiters on the outputs prevents errors on the fieldbus segment. The segment continues to operate. • Connections available for up to four intrinsically safe field instruments. • Cascading of up to four fieldbus barriers per fieldbus segment. 199 • No additional distribution boxes required. For the last fieldbus barrier a switchable termination resistor is included that can be activate. • Installation in explosion hazardous areas. • Easy Ex-Loop-Check using the FISCO-Design. Operate Engineer Ethernet Control PROFIBUS DP/DPV1 Linking device PROFIBUS PA PROFIBUS PA EEx ia Field T P F Fig. 5-23: Fieldbus supply using a fieldbus barrier 200 5.8 Electromagnetic Compatibility (EMC) The EU-Directive 2004/108 EC (formerly 89/336/EWG) is controlling for the EMC (Electromagnetic Compatibility) of a temperature transmitter. The EMC requirements are defined in the International Standard IEC 61326 . The standards are defined in IEC 801-1 to IEC 801-6 and IEC 61000-4-1 to IEC 61000-4-17. In addition to the basic generic standards, there are also product standards, which must be observed for the various instruments. In addition to the requirements in the EMCDirective there are additional special requirements for the chemical industries, which are defined in the NAMUR-Guidelines (NE 21) and include or exceed the requirements in the basic generic standards. The most common causes of interference are electric or electromagnetic in origin: • Variations or short term interruptions in the supply voltage • Static electricity discharges • Electromagnetic fields • Transient over voltage pulses (bursts) on the supply or signal connection cables • Transient over voltage, energy rich individual pulses (spikes) The originators of interference signals are often electric and electronic switches, relays, circuit breakers, frequency converters, fluorescent tubes, magnetic valves, motors, wireless equipment, as well as atmospheric disturbances such as lightning. In particular, the discharge of static electricity and the generation of electromagnetic fields often occur in the production process itself. The interference behavior defines the reaction of an instrument to an interference using three evaluation criteria: A. No reduction in function Primarily for analog instruments, recognizable effects within the error limits are permissible. Pure digital instruments may not exhibit any recognizable effects. B. Reduction in function Evaluated is the effect on the function during the period in which the interference effects occur. Reduction of function during this time period is permissible. Subsequently, the function must return to its original status automatically without any permanent changes. C. Loss of function Evaluated is the effect on the loss of function from the start of the interference until it is restored automatically or manually. For operation outside of the tolerance limits the instruments must automatically return to normal operation or switch to a start ready safety setting. 201 For suppression of electromagnetic interferences, appropriate measures should be employed by the user when installing the instrument. Measures Guidelines and Recommendations Current supply – electrically isolated – symmetric – ground free Installation – power and signal cables routed separately – instrument not installed close to electromagnetic interference sources – provide lightning protection if installed outdoors Cable shield – assure sufficient potential equalization – exclude equalizing currents in shields – provide a cable shield preferably on both sides – ground cable shield to housing in the shortest way using large area connections Modern electronic transmitters generally have the best possible disturbance reaction. They comply with the increased NAMUR requirements and guidelines and often actually exceed them. When the potential equalization is poor or the installation has a high degree of electromagnetic noise, it is not always possible to achieve the desired results. In such applications it may help to electrically isolate the low resistance shield from the system potential and only ground the cable shield at one end. 202 5.9 Temperature Transmitters using Interface Technology In many installations the functionality of the in-/output assemblies of Stored Programmable Controllers (SPC) or Process Control Systems (PCS) is not sufficient, requiring an additional signal adapter stage. This might be the case when temperature measurements, transmitter power supply, electrical isolation, load increases or intrinsically safe signal circuits for explosion hazardous areas are required. These functions are performed by suitable interface components. Analog Interface Technology For the analog Interface Technology, 2 connection wires are required for each signal. The supervisory systems often contain 8 or 16 channel input cards. In order to connect to the input cards in these systems, an internal distribution system is required. If the signal connection wires have to be routed over a very long distance, the individual pairs can be connected to a larger cable containing multiple pairs of wires. In order to reduce the wiring and connection expenditures, interface components are installed on the prewired module carriers. The wiring level and the function level are thereby separated from each other. Without a module, a quick check of the wiring is possible. Easy plugin technology allows quick connection to the module carrier or individual socket. Digital Interface Technology In the automation and process technology, the required field signals are often gathered from distant systems. In the classical, analog point-to-point wiring scheme, in which all signals are usually carried over 2 connection wires, long cable runs, many distribution boxes are required. Expenses are appreciably reduced when using a decentralized, digital interface technology (Remote I/O). All in-/output modules are designed to be bus capable, so they can be connected to an open fieldbus over a bus coupler (gateway). In the module carrier the data is exchanged between the bus coupler and the I/O modules over a fast, redundant internal bus. The assignment of the field signals, is done using the software. The plug-in bus coupler allows adaptation to the fieldbus being used. Every bus coupler contains a complete process picture of all the connected field signals. The supervisory process control system or the controller communicate with the external fieldbus over the bus couplers. Expensive wiring in no longer necessary. 203 Fig. 5-24: Digital interface components S900 Bus coupler and the connected in-/output modules constitute one node. Larger numbers of participants are incorporated by adding additional nodes. The cycle time for the internal communication bus is in the range of a few milliseconds. The number of nodes, bus length and cycle time of the external bus structure depend upon the bus system used. Every bus coupler represents one participant. In order to increase the number of participants, the bus is extended from one bus coupler (bus node) to the next bus coupler. In order to increase the availability of the in-/output modules, the fieldbus connections can be designed to be redundant. The analog in-/output components are designed for HART-communication. All important measured values, diagnosis and configuration information from the connected HART field instruments are available over the bus and can be transmitted to the process control system. The programming of the HART-transmitters can be done directly from the process control system over the fieldbus, through the remote-I/O-level to the HART-instruments, without any problems. The temperature or HART-transmitters connected to a remote-I/O-system are therefore comparable to fieldbus transmitters in their function. 204 Fig. 5-25: Decentralized redundancy capable fieldbus interface components (with integrated HART or fieldbus communication) The sensors or actuators to be connected are power supplied directly from the modules. The wiring for separate power supplies is no longer necessary. The highest possible degree of safety and noise insensitivity is assured by an power supply electrically isolated from the bus and short circuit proof in- and outputs. Modern remote-I/O-systems, such as the S900, also incorporate a comprehensive redundancy concept. 205 For applications in explosion hazardous areas an Ex-isolation module can also be used as the decentralized interface component for direct installation in Zone 1 areas. Fig. 5-26: Compact remote I/O-system CB220 for zone 1 installation 5.10 High Accuracy Temperature Measurements with Programmable Transmitters If an absolute accuracy of 0.1 K (± 0.05 K) is required, it is only possible if the entire measuring chain is calibrated as a unit. This will become clear after all the measuring values in the measuring chain are evaluated. 1 2 3 4 5 6 7 A t S AGL L L D Fig. 5-27: Industrial temperature measuring chain from sensor to digitizer In a typical measuring chain the temperature is measured by a sensor (1). The temperature signal is then fed to a transmitter (3) over the compensating cable (2). There the signal is amplified and fed to transmitter power supply (5) over another pair of connection wires (4). The signal is transmitted to an analog/digital converter (7) over more connection wires (6). Only after this conversion is the measured value in digital form 206 and in no longer subject to changes. Tbl. 5-3 shows the typical, statistical errors occurring in the process industry for a 0...400 °C (32..752 °F) measurement with a resistance thermometer in a three-wire circuit. Measurement Uncertainty Cause Typical Error 1 Sensor Tolerance Class A according to EN 60751, at 40 °C (104 °F) 0.95 K 2 Heat loss Ratio insertion depth to diameter = 7 (see chapter 6.1.4, Fig. 6-2) 0.4 K 3 Self heating Measurement current 0.3 mA 0.05 K 4 Signal connection wires Three-wire circuit, noise 0.1 K 5 Transmitter Accuracy 0.1 % 0.4 K 6 4...20 mA loop Noise 0.05 K 7 Transmitter power supplies Accuracy 0.25 % 1K 8 4...20 mA loop Noise 0.05 K 9 input to PCS/SPC Accuracy 0.1 % 0.4 K Total uncertainty Error sum, root mean square 1.55 K Tbl. 5-3: Uncertainty of an industrial temperature measurement 0...400 °C (32...752 °F) Additional errors due to the compensation cable and reference junction, when making measurements with thermocouples, must also be considered. The compensation cables has the same thermal voltage as the element material itself at a specific temperature. Above 100 °C (212 °F) appreciable differences may occur. This is especially true if the materials of the compensation cable are so called special alloys. Even within their allowable ambient temperature range, the compensating cables have a tolerance. In EN 60584 the deviation limits for the individual compensating cables are listed. This list indicates that for each element, and therefore each cable type, the deviation limits are a number of µV and therefore a deviation of number of K is possible. Dependent on the accuracy as well as the achievable thermal coupling of the reference junction an additional measurement error of 0.1 to 0.5 K must be considered. In addition to these statistical errors, there are dynamic errors based on the finite response time of industrial temperature sensors (see chapter 3.4.4) and of the ambient temperature dependent errors due to measurement type used which must also be considered. The largest contribution to the ambient temperature errors can be attributed to the usually high temperature changes in the field at the transmitter. Typical values for the assumed example are 0.02K per 10K ambient temperature change. Sensor head mounted transmitters, because of their proximity to the sensor, have the least interference on the sensitive signal connection wires. Their use, due to their not negligible ambient effects, only comes into play when the temperature variations at the sensor head are expected to be small. Otherwise, field mounted transmitters are preferred for high accuracy measurements. When the digital signal output from a fieldbus 207 transmitter is used, the errors due to the analog signal processing in the transmitter power supplies or in the analog input circuits of the data processing instruments are eliminated. Since the largest contribution to the statistical errors comes from the sensor itself, fieldbus transmitters cannot make any appreciable improvement to the total accuracy. High accuracy measurements can only be achieved with temperature transmitters, if the statistical measurement uncertainty of the entire measuring chain is compensated. Recalibration and recertification are common procedures for measuring locations that are subject to measuring equipment testing. To compensate for the statistical errors the temperature sensor is calibrated at many different temperature reference points. The curve produced by the comparison calibration in a precision temperature measurement system is stored in the non-volatile memory of the sensor head mounted transmitter. The calibration of field mounted transmitters is somewhat more complex, because the sensor and the transmitter must always be calibrated as a matched pair, if all the errors in the measuring chain are to be compensated. Stated more precisely, for analog measuring circuits the input circuit of the data processing system, and the transmitter power supply, if used, must be connected during the calibration, because they make a significant contribution to the total error. In practice this is not done very often because of the complexity it entails. Calibrated fieldbus transmitters have a distinct advantage, because the use of digital signal transmission eliminates the additional signal errors. The remaining measurement uncertainty is then only a function of the calibration equipment and the resolution of the correction curve. The achievable measurement uncertainty of the temperature sensors in the temperature range from 0...400 °C (32...752 °F) is ± 50 mK. This measuring accuracy can be documented by a DKD-Certificate (German Calibration Service) (see chapter 6.2). 208 6 Accuracy, Calibration, Verification, Quality Assurance 6.1 Accuracy 6.1.1 Basic Fundamentals As with the measurements of all variables, temperature measurements cannot be made at any arbitrary accuracy. The result of the measurement is not only dependent on the variable being measured, but also on the measuring process being used, which is affected by very many other factors, which in turn also influence the measurement results. Error effects may include: • errors due to the incompleteness of the measuring instrument used, • errors due to the influence on the (undisturbed) measured value by the measurement instrument (sensor), • errors due to effects caused by deficiencies in the test model (especially during the evaluation), • errors of a random type due to unforeseen factors resulting from predictable interference effects of an “experimental environment“. If an “error free value“ is defined as the measured “true value“ (an unknown which is to be determined by the measurement), then all the measurement values which result from repeated measurements under the same conditions and with a measurement setup of high enough resolution, will lie around the true value within a specific range (variation range). The measurement error of the individual measurements is defined as the difference between the measured value and the (actually unknown) true value. Measuring error = measured value - true value This raises the question, which of the measured values is closest to the true value and can serve as the result of the measurement? The simplest assumption states that the arithmetic average of all the measurements taken is very close to the true value and can be used as measured result. This value is the called the correct value, or sometimes the best estimate and can be calculated by the following equation:. 1 n q = ∑ qi n i =1 n = number of individual measurements qi = result of individual measurements The magnitude of its variation range within which the measured results are found, depends on the quality of the measurements and makes an approximate statement about the inherent uncertainty of the measurement results (measuring uncertainty). 209 The know-how of the technician is used to solve the measurement task in a manner that minimizes the number and scope of the undesirable interference effects on the measurement. In a qualitatively high quality measurement, the variation range measurements will be small as will be the measurement uncertainty. 6.1.2 Determining (Estimating) the Measurement Uncertainties When measuring results are compared, e. g. during a certification test, statements, in addition to the measured value itself, regarding their reliability are also important. The specification of the measurement uncertainty has become established as a measure of the quality of the measurement. The determinations the measurement uncertainty must, in every case, be based on fundamental technical knowledge, i.e. on objective facts. Even then the results are subjective, because they are based on judgments using a number of assumptions and estimates. Such quality judgements will generally be accepted if the method used to make the judgements is clear. To estimate the measurement uncertainty, they are usually divided into two categories: • Random measurement uncertainties (statistical error effects) and • Systematic measurement uncertainties. Systematic measurement uncertainties are predictable and correctable. They always occur under the same measuring conditions with the same magnitude and sign. A typical example of a systematic error is calibrating with uncalibrated test equipment. A digital multimeter, which has an error of 0.1 % in its 0.2 V measuring range, will always indicate a voltage of 199.8 mV when measuring exactly 200 mV; the reading will be low by -0.2 mV. A measurement made with this instrument will produce an incorrect result. This measurement result can, using the specifications in the instrument’s calibration certificate, be corrected eliminating the systematic measuring error. Statistical measurement uncertainties are random measurement uncertainties and therefore their direction and magnitude cannot be predicted or corrected. The magnitude of the effects can be determined from repeated measurements under the same conditions can be defined by calculating a distribution curve from the measured results. If the measurement is subject to multiple random error effects, then this fact will also have an impact on the distribution curve for the measured values. For three or more random error effects it is probable that a normal distribution curve (Gaussian bell curve) will be approached. The descriptor values for a normal distribution curve are its average μ and its standard deviation σ. 210 Fig. 6-1: Normal distribution curve (Gaussian bell curve) Fig. 6-1 shows the typical shape of a normal distribution curve for a constant μ at different σ-values. The distribution function p(x) defines the frequency (probability), with which the individual measured values Xi will occur within the range of the average μ. For all curves, 68.3 % of all the measured values in the range of ±σ are around the average μ; σ therefore makes a qualified statement about the spread of the individual measured results. If the σ-range is extended by a factor k (k > 1, confidence factor), then more measured values can be expected to be within this range about the average. It is customary to use a confidence factor k = 2 for the measurement uncertainty. Using this value, one can expect that 95.4 % of all measured values will be within this range (coverage probability of 95.4 %). Values for the coverage probability P as a function of k k= 1 2 3 4 P(σ) in % 68.3 95.4 99.73 99.994 The measurement uncertainty from the viewpoint of GUM (Guide to the Expression of Uncertainty in Measurement) All previous considerations started from the basis that for every measured value a true value exists. In practical measurements true values do not exist, or at last, are unknown. Around 1980, on the initiative of the CIPM (Comité International des Poids et Mesures = International Bureau of Weights and Measures, in Sevres near Paris, France) an approach was defined (Recommendation INC-1 (1980)), which is based totally on experimentally determined measurements. Therefore, for every measured result, there exists a value for a correction to the systematic measurement uncertainty, 211 always consisting of a value and its associated uncertainty. GUM uses a so-called standard measurement uncertainty and sets it essentially equal to the basic distribution curve for the measured value. To differentiate, the standard measurement uncertainty per GUM is designated by the letter u while for the standard deviation, the normal distribution is usually designated by the symbol σ. The total measurement uncertainty of a measurement, which is composed of a number of factors, is usually calculated as the geometric sum (square root of the sum of the squares) of the individual standard measurement uncertainties. The calculated total measurement uncertainty is usually stated with a confidence interval k, in order to achieve the desired coverage probability. The GUM method differentiates between two categories for calculating the measurement uncertainties: Type A-Uncertainties are all the uncertainty components of a measurement, which result from the repeated measurements method (n independent, observations made under the same measuring conditions) and can be described by specifying a numerical standard deviation (σ-value). Included in the Type A-uncertainties are, e. g. correction specifications contained in the calibration reports, for which the distribution function for the calibration is known or is specified (generally a normal distribution). Type B-Uncertainties are all the uncertainty components of a measurement, which cannot be defined after repeated measurements and analysis from the resultant distribution function, because of the inability to make repeated measurements. Typical Buncertainty specifications include, e. g., the measurement accuracy specifications in a data sheet. Here one only knows, that with such an instrument the maximum deviation of the measured values from the true value will be within the error limits stated in the data sheet. What the probability of a measured value being in the middle or at the limits of the range is unknown to the user. Type B-uncertainties are always assumed when concrete value specifications cannot be made regarding the uncertainties and one therefore has to rely on estimations based on experience. Hereby it is necessary that a realistic distribution function is established by an analysis of the measuring procedure Thus GUM uses not only a measurement uncertainty interval to describe contributions to a measurement uncertainty, but even more probability distributions. 212 6.1.3 Measurement Uncertainty Estimations using a Practical Example A simplified example would be the estimation of the measurement uncertainty for the measurement of the “true“ temperature in a tube furnace. The temperature of the tube furnace is determined using a Type S (Pt10%Rh-Pt) thermocouple. The thermocouple was calibrated and a calibration report is available. The furnace is controlled to a temperature of 1000 °C (1832 °F) by an electronic controller. The thermal voltage generated by the thermocouple is measured using a digital voltmeter using a measuring location selector switch. The thermocouple has a reference junction temperature of 0 °C (32 °F). For the thermal voltage measurements a 7 1/2 digit instrument with a measuring range of 200 mV is used. The voltmeter was calibrated and a calibration report is available. The total measurement uncertainty consists of the following measurement uncertainty components Type B-measurement uncertainty components: 1. The accuracy and stability of the reference junction temperature is estimated at 0 °C (32 °F) to be ± 0.1 K. The distribution function of the uncertainties has a uniform distribution. 2. The uncertainty, consisting of the non-homogeneities of the thermocouple is estimated (results from previous evaluations) to be ± 0.3 K (uniform distribution). 4. The measuring location selector switch produces parasitic thermal voltages (contact resistance), which cause errors in the measured value. From the data sheet for the instrument, maximum parasitic thermal voltage uncertainties of ± 3 μV are used. These correspond to a temperature uncertainty of ± 0.2 K. 5. The uncertainty of the calibration of the thermocouple is specified in the calibration report as ± 0.8 K. For this value, a confidence interval of k = 2 has been specified, which yields a probability of > 95 %. 6. The uncertainty in the calibration of the voltmeter is ± 3 μV (k = 2, standard distribution). 213 Type A-measurement uncertainty components: 7. The thermal voltage is measured 20 times at approximately 1 minute intervals. An average and the standard deviation of the measured values are calculated. The resultant standard deviation is ± 4 μV. This value is used as the standard uncertainty of the measurement value acquisition in determining the total measurement uncertainty. The variation range of ± 4 μV is caused, among other things, by random interferences (electromagnetic interferences, thermal noise, etc.), and also includes time dependent effects due to controller loop variations. From the calculated average, using the specifications in the calibration reports of the thermocouple, the exact oven temperature can be calculated. No. Description Uncertainty (Xi) k Distribution Factor for Standard Sensitivity Uncertainty standard uncertainty Ci contribuuncertainty U(Xi) tion (K) Ui (y) 1 Accuracy and stability of the reference junction 0.1 K 1 Normal 1/1.73 0.06 K 1.0 0.06 2 Non-homogeneity of the thermocouple 0.3 K 1 Normal 1/1.73 0.17 K 1.0 0.17 4 Parasitic thermal voltages of the selector switch 3 μV 1 Normal 1/1.73 1.7 μV 0.05 K/μV 0.09 5 Uncertainty of the thermocouple calibration 0.8 K 2 Standard 1 0.4 K 1.0 0.4 6 Uncertainty of the voltmeter calibration 3 μV 2 Standard 1 1.5 μV 0.1 K/μV 0.15 7 Uncertainty of the measured value acquisition 4 μV 2 Standard 1 4 μV 0.1 K/μV 0.4 1.27 Tbl. 6-1: Uncertainty estimation for tube furnace temperature measurements The measurement uncertainties calculated for the tube furnace from the values specified in the calibration report is ≅ ± 1.3 K. At a confidence factor of k = 2 (coverage range = 95 %), gives a measurement uncertainty of ± 2.6 K. 214 6.1.4 Error Effects for Temperature Measurements Basic Considerations Users always raise the question, what tolerance class is required for a temperature sensor in order to make the temperature measurements within the required accuracy? Every real temperature sensor has a curve, which deviates more or less from the ideal curve, as it is defined in the standards. Since temperature sensors cannot be manufactured to any arteriolar accuracy, the standards define the deviation limits from the standard curves within which the measurements made by a real temperature sensor must lie. Basically two tolerance classes are defined, an expanded tolerance class (Class B or Class 2) and a more restrictive tolerance class (Class A or Class 1). There can also be other tolerance specifications which are agreed to between the user and the manufacturer and defined in the purchase order. Temperature sensors, which meet the requirements for a specific tolerance class, are usually “picked“ from a manufacturing batch. Even the more restrictive tolerance class A (e. g. for measurement resistors Pt100 according to DIN EN 60751) always include some measurement uncertainties (e.g. ± 0.35 K at 100 °C (212 °F) or ± 0.75 K at 300 °C (572 °F)), which could be unacceptable for precision measurements. If a special tolerance classification is defined in the purchase order, which is even more restrictive, it becomes more and more difficult to find a temperature sensor, which can fulfill these requirements. This is especially true if the tolerance limits are to be maintained over a wide temperature range. Sensors with such narrow tolerance limits are therefore very expensive. The accuracy requirements to temperature measurements has increased dramatically in recent times. A few years ago, the measurement uncertainty achieved by a Class A sensor element was still “considered to be the one to beat“. Now these accuracies are no longer satisfactory for many applications. The following requirements have become more important in recent years: • Measuring smaller temperature differences between the in- and outlet temperatures of cooling towers (increasing the efficiency of the cooling tower). At the same time, certain maximum outlet temperatures may not be exceeded. • Measuring the temperature difference between the reactants added in a chemical reactor and the end product of the reaction, for continuous energy balancing as a preventative measures for explosion/process interruption protection. • Measuring more exactly process temperatures in the pharmaceutical industries during the manufacture and processing of temperature sensitive products. • Measuring more exactly process temperatures in the sterilization procedures in the milk and dairy product industries (UHT milk). • Measuring more exactly processing temperatures for sterilization in biochemical systems. 215 A very effective method for satisfying the application requirements described above is offered by the precision calibration of a temperature sensor which initially has some arbitrary tolerance (e. g. Class B). In the calibration report, the relationship between the temperature and the resistances or thermal voltages established during the calibration are documented and can be utilized by the user to correct the measuring results. If the temperature sensor is connected to a programmable transmitter, then the correction factors can be stored in the transmitter. For the user this combination, whose input is the temperature measurement itself and whose transmitter output value in mA, behaves like an ideal temperature sensor in accord with the standard. The remaining error is reduced by an order of magnitude and is only limited by the accuracy of the calibration itself and the digital resolution of the transmitter (typically between 0.05 K and 0.1 K). This method provides a cost effective alternative to the expensive selection of highly precise temperature sensors. Error effects due to “natural“ uncertainty components of yet unused sensors As already mentioned, temperature sensors cannot be manufactured to any arbitrary accuracy. This is in part due to the manufacturing processes and to the purity of the materials used. Particularly for non-precious metal thermocouples, the non-homogeneities in the composition or structure of the alloys can lead to appreciable measurement uncertainties. Non-homogeneities can only have an effect on the measured results when they are in the range of the temperature gradient. Non-homogeneities can be manufacturing related, they can be operation related or they can be first noticed in the application phase. Non-homogeneities can lead to errors of several K, and in some special cases, up to several hundred K. Strong mechanical stresses, e. g. severe bending or kinking of the thermocouple wire, can produce non-homogenous sections by changing the material structure. A suitable annealing procedure for the thermocouple wire, in some instances, can reverse the non-homogeneities to a certain degree. For thermocouples Type K (NiCr-Ni), as well as for all other thermocouples, which have a NiCr-leg, the effect of the so-called K-Condition should be considered. Before applying, assure that the Type K thermocouples are installed only after they have been subjected to a stabilizing annealing (see also chapter 3.5). The measuring error caused by the K-Condition can be in the order of 2 K to 5 K. 216 Error effects, which occur during the operation of the sensor The accuracy of an unused temperature sensor unfortunately does not remain constant during its operating life. The temperature sensor experiences aging (drift) (see chapter 3.5). Measurement uncertainty effects, caused by drift, are very difficult for the user to recognize, because their effects occur very slowly and usually go unnoticed. The start of a drift processes and its effects can only be determined by regularly monitoring the temperature sensor (periodic recalibrations) and quantifying by magnitude and direction (see chapter 6.2.10). Other contributors to the measurement uncertainties when operating thermocouples are the small internal resistances of other connected instruments. Thermocouples are high resistance sources, thermocouple wires may have resistances of several kΩ. Connection lead resistances when using resistance thermometers in a 2-wire circuit must be considered, when they are a non-negligible component of the sensor resistance (see chapter 3.6). The ohmic resistance of the connection leads between the measuring instrument and the measurement resistor add to the actual measured sensor value. The temperature indications will be too high. Compensation measures include adjusting the measuring circuit, or accounting for the connection lead resistance during the signal evaluation. It is for this reason, that for a resistance thermometer in 2-wire circuit, the connection lead resistance from the sensor element to the connection socket are included in the specifications. It is assumed, that the correction value for the connection lead resistance does not vary over the measuring temperature range. The connection leads, however are subjected to certain temperature effects, which could change the resistance value of the connection lead. Therefore this correction may include a certain error component. The order of magnitude of real connection lead resistances is shown in the following table. Listed are the lead resistance for a 1 m (39”) long pair of connection leads (in and out), made of copper, as a function of the wire cross section. Wire cross section (mm2) 0.14 0.22 0.5 0.75 1.5 Resistance (Ohm/dblm) 0.638 0.406 0.179 0.119 0.06 Resultant error for Pt100 (K) +1.7 +1.1 +0.5 +0.3 +0.2 Tbl. 6-2: Ohmic resistance of a Cu-wire (dblm = double meter) and the resultant measuring error 217 If the connection lead resistances are known, they can be considered when the measured signal is evaluated. The hard to estimate temperature effect of the connection lead resistance remains as a measurement uncertainty component. This effect can be essentially eliminated by utilizing resistance thermometers in 3- or 4-wire circuit designs. Parasitic thermal voltages are undesirable voltage components, which are generated by the different metals and alloys in the measuring circuits at the connection points, when these are in a temperature gradient. They cause errors not only in the resistance measurements, but also in the thermal voltage measurements. These metal transitions occur primarily at the connection or extension locations for the connection leads of the temperature sensors. They can introduce an appreciable temperature load and generate parasitic voltages at the connection sockets, especially for short measuring insets. A measurement of the parasitic thermal voltages, or a systematic estimation of the errors they cause for a possible correction, is hardly possible. Dependent on the polarity of the generated voltages, the measuring error will result in indications too high or too low. For resistance measurements a polarity reversal of the measuring current is a simple method to check the effect of parasatic voltages on the measurement. Two measurements are made, one immediately after the other, with the same measuring current, but with a reversed polarity. If there is an appreciable difference between the two measurements, then it is due to parasitic thermal voltage effects. The arithmetic average of the sum of the absolute values of the two measurements is then the error corrected measured value. High precision instruments offer special methods for compensating parasitic thermal voltages occurring during resistance measurements. Parasitic thermal voltage effects for resistance measurement can also be completely eliminated by using an AC voltage bridge. Error components due to “incorrect“ compensating cables Thermocouples with long cable lengths, beyond a certain point (ambient temperatures < 200 °C (392 °F) or < 100 °C (212 °F)), are usually elongated with more economical materials, the compensation cables. The thermal voltages generated by the legs of the thermocouple can differ appreciably from those made of the compensating cable materials. As long as both legs at the connection locations to the compensation cables are at the same temperature, no measuring error is introduced. However, if the connection locations are in a temperature gradient, then errors due the incorrect thermal voltages can result. The extension of thermocouples using compensating cables is only successful, when compensation cables matched to the thermocouple are installed with the correct polarity. 218 Measuring errors, caused by improperly selected or incorrectly connected compensation cables, can lead to errors of several tens of K. For precision thermal voltage measurements, the use of “extended“ thermocouples is generally not recommended. Error effects when evaluating the measuring signal All temperature sensors have a nonlinear curve. When converting the measured signal into a corresponding temperature value, this nonlinearity must be considered. Incorrect or not-considered nonlinearities in the curve can lead to measuring errors of several K. If curves are approximated, linearity errors whose magnitude is a function of the degree of linearization may occur. An incorrect or not-considered reference junction is a classical error when employing thermocouples. The output signal of a thermocouple is always proportional to the temperature difference between the hot and cold ends. Only after the requirement that the temperature at one end is known can the temperature at the other end be determined. The reference junction is the connection location (the one end of the thermocouple), at which a known temperature exists. The reference junction is usually maintained at a temperature of 0 °C (32 °F) by using an ice/water mixture. Other reference junction temperatures (20 °C (68 °F), 50 °C (122 °F)) are also common. For thermocouple measurements with direct indicating measuring instruments, a reference junction is usually integrated in the instrument. The temperature at the connection terminals of the instrument is continually measured and added to the temperature value calculated from the thermal voltage measurements. If the reference junction is not considered, then the measured temperature value is incorrect by the amount equal to the ambient temperature. If an estimated value for the temperature to be measured is not available, then the not considered reference junction temperature often remains completely unknown. If the reference junction is taken into account, but with an incorrect value, then the difference between the true and the assumed reference temperature values causes an error with the same order of magnitude on the measured result. The exact measuring error however, is still dependent on the value of the measured temperature. 219 Error effects due to the practical implementation of the measurement task All considerations to this point have been based on the fact that the temperature of the sensor is the temperature that is to be measured. Thermocouples and resistance thermometers are contacting thermometers and must be in good thermal contact with the medium in order to assume its temperature. Contacting thermometers can only measure their own temperature! This seems to be a trivial observation, but it is an important consideration when selecting the measurement location in the process. If the temperature measurements are made at an unsuitable location, then even though the temperature is measured very precisely, the measured value will be of questionable value. If the measurement is made at the correct (representative) location, this is still not a guarantee that the measurement will be free of systematic error effects. Incorrect sensor temperatures can result from other reasons. If temperatures which are changing with time are to be measured, then the dynamics of the temperature sensor must be capable of following the changes. The time response is generally defined by the response time (τ0) parameter. If the response time is large in comparison to the rate of change of the temperature to be measured, then the result will be a systematic error because the temperature sensor always “lags“ the changing temperature being measured by a certain amount. The problem of excessive heat loss is also an error source that can occur in actual measurements. Behind this occurrence is that fact that contacting temperature sensors continuously remove heat from the measured medium to the temperature sensor (hot measuring location) and from there to the ambient temperature (through the cold end) of the temperature sensor. In other words, energy is constantly being withdrawn at the measuring location: it cools. If temperatures are to be measured that are less than the temperature of the “cold end“, then this process is reversed and energy is added at the measuring location, it warms. The magnitude of this heating or cooling is primarily dependent on: • • • • • 220 the insertion depth of the temperature sensor, the diameter / cross section ratio of the temperature sensor, the heat transfer of the materials used, the heat transfer between the medium and sensor, the temperature difference between the measuring location and the ambient temperature. Measurement error [%] 100% 10% 1% 0.1% 0.01% 0.001% 0.0001% 0 2 4 6 8 10 12 14 n times insertion depth of the thermometer Ø Fig. 6-2: Dependence of the thermal loss errors to the ratio of the insertion depth to the diameter of a temperature sensor for liquids From the curve it can readily be seen that a temperature sensor must have a minimum insertion depth, in order not to exceed a prescribed thermal loss error. In the example, the minimum insertion depth of 5 x the diameter of the inserted temperature sensor is required for thermal loss errors of <1 %. For temperature measurements in gases, the recommended value should be at least doubled because of the poorer heat transfer. Measurement resistors are passive sensors. They must be supplied with a measurement current in order to produce a resistance proportional measuring voltage. The current generates in the measurement resistor a definite power loss with the magnitude Ploss = I2 * R The measurement resistor is actually a small heater element and converts this power loss into heat. The result is an undesirable temperature increase in the sensor, called self heating. Therefore the temperature sensor detects a temperature which is higher than the actual temperature of the medium. 221 The magnitude of the self heating is a function of a number of factors: • the measurement current setting, • the thermal mass of the sensor element, • the removal of the temperature increase by the medium. For typical measurement currents of 1 mA, the power loss in a 100 Ω measurement resistor is 0.1 mW. For sensors well insulated from the ambient, a self heating effect larger than 0.5 K can result. This is particularly true in non-moving gases, because the heat transfer to the medium being measured is very low. In recent times, there is a tendency towards higher standard measurement resistors (Pt200, Pt500, Pt1000), because these, at the same measurement current, produce higher voltages, but also generated more self heating. The errors effects on the measured value increase. Generally the self heating effects can be reduced by lowering the measurement current. Precision measurements (e. g. for quality calibrations) as a rule are conduced at two different measurement currents, which are different by a factor of √2. The measurements are conducted at single and doubled power losses, from which the measured value can be extrapolated to a measurement current of zero. Specifications of the self heating behavior for the more common sensor or measurement resistor designs are given by the manufacturer in the data sheets. The user can then easily estimate the magnitude of the self heating error for a particular measuring current. There are no self heating effects in a thermocouple. Temperature sensors, used for the measurement of flowing media, are subjected to appreciable vibration loads. For continuous vibration excitations, the effects of excessive resonance conditions can lead to destruction of the entire sensor. Even if no external damage is visible on the temperature sensor, vibration loads can prematurely damage the sensor element. A subtle measuring value deviation (drift) is usually the result of sensors exposed to high vibration conditions (e. g. exhaust gas sensors for large Diesel motors indicate such typical behavior). Special vibration resistant designs, in combination with regular recalibrations, provide corrective measures and operational security. The term electromagnetic interferences (EMI) means the presence of undesirable interference voltages in the measuring circuit, generated by time changing external electric or magnetic fields, emanating from electric motors, transformers, power lines or thyristors. Also high frequency radiation can generate electromagnetic interferences. Leak currents, due to damaged electrical heaters, or so-called ground loops can also produce electromagnetic interference in the measuring circuit. The ability to withstand or suppress such interferences is defined as electromagnetic compatibility (EMC). 222 The interference due to electrical AC fields can be reduced by adequately shielding the connection wires. The effects of magnetic induced EMI intervenes on the other hand can hardly be reduced using shielding methods, unless the shield materials are very thick. The only possible solution is to space the measuring circuit and the EMI-sources as far apart as possible. If interference is still present, the measurement connection leads should be routed very close to each other and in parallel if possible. Twisted pairs or coaxial cables provide good protection against AC magnetic fields. Another method to reduce the interference signals is to shorten the interference sensitive signal path and transmit the signal over the remaining distance using the mA output signals from a transmitter. At higher temperatures even the best insulation materials lose their insulation resistance properties. The insulation behavior of an ceramic oxide e. g. is reduced by approx. an order of magnitude for every temperature increase of 100 °C (212 °F). Leakage currents are the result. They are superimposed on the measuring signal and cause errors. Here the use of temperature sensors with grounded metallic protection sheath is recommended. The leakage current then flows through the grounded sheath and not through the sensor element and its measuring circuit. The influence of ground loop effects, which are caused by the compensating currents flowing as a result of the differing ground potentials in a measuring circuit, can also be effectively suppressed by using grounded metallic sheaths for the temperature sensors. Twisted connection leads (twisted pairs) Magnetic field Large induction loop area Shielded connection lead (coaxial cable) Small cross section of the induction loop Reducing the induction loop area reduces the sensitivity to magnetic field interference Leak current flows in the measuring circuit Fig. 6-3: Leak current flows through metallic sheath to earth Use of shields to prevent leakage currents 223 6.2 Calibration and Verification Temperature sensors are prone to a general aging phenomenon which is usually called drift. The magnitude and size of the drift cannot be defined without detailed specifications about the actual installation conditions. Even if these specifications are available, quantifying the drift process is extremely difficult. As a last resort, cyclic measurement tests of the temperature sensor are required to assure, that after long term use, the required specifications relative to the accuracy are still applicable. These measurement tests are usually called calibrations. Calibrations are conducted to assure that the high quality level of the temperature sensor is maintained for the required measurement tasks, even though the sensor itself is subject to a continuous aging process. 6.2.1 Definitions Calibration in the metrology field: Determination of the deviations of a finished product from the defined design values. The design values are either defined in applicable standards, directives or in other specification documents. They can also be defined by separate agreements between the contracting partners. During the calibration no changes are made to the instrument being tested! Calibration of a temperature sensor is understood to mean the determination of their measurement deviation. This is the deviation between the output signal of the temperature sensor at the calibration temperature, and its design value at that temperature. The calibration only provides information about the deviations of the test object at the time of the calibration. Information about the time dependency of the accuracy of the test object during its operating time cannot be provided based on the reasons mentioned earlier. The calibration results are documented in a calibration report. Adjusting a measuring instrument: Making changes in an instrument with the goal of either adjusting the settings so that the measurement deviation found during the calibration: • are as small as possible, or • that their contribution to the measurement deviation after the adjustment no longer exceed the specified error limits. 224 Care must be exercised when changing the settings to protect against unintentional changes (labels, seal marks, seal paint etc.). Documentation of the adjustments in the form of certificate is absolutely necessary. Verification according to national standards is understood to be an accredited calibration. Verifications can only be conducted by approved calibration bodies or by test facilities designated by them. Verifications may only be conducted on products which have been approved under the verification laws and calibration regulations. Products, which are to be verificated, must have been undergone a design type examination (Test Examination Certificate). The intent of such a test is to ascertain whether the measurement stability can be maintained for the duration of the certificate (long term stability) and that protection against manipulation exists. The type tests include tests conducted on a number of representative instruments of the same design (first sample tests). If the test objects satisfy the requirements, the product is issued a type examination certificate. The design is then “frozen“. The actual verification procedure corresponds to a calibration, but only the adherence to the allowable error limits is measured. The verification is identified by a stamp on the instrument. Although verification certificate is usually issued, this is not mandatory for all verifications. The values resulting from the calibration are recorded in the verification certificate. 6.2.2 Calibration Methods for Temperature Sensors There are two basic methods for calibrating temperature sensors. For Fixed Point Calibrations the temperature sensors are exposed to a known temperature. This is produced in high purity materials (e. g. metals) which are heated until they are completely molten and then cooled slowly. A constant temperature exists during the transition stage beginning at the moment of solidification. Under ideal process conditions, this equilibrium status, and thereby a constant temperature, can be maintained for several hours. In the specifications of ITS-90 values are assigned to these fixed points, which are practically identical to the thermodynamic temperatures. For the solidification point of Aluminum e.g. the fixed point temperature t90 = 660.323 °C (1220.5814 °F). Fixed point calibrations are calibration methods with the smallest measurement uncertainties. However, they are very expensive to conduct. For Comparison Calibrations (also called comparison measurements) the test object is exposed to an unknown temperature. This temperature is produced in a so-called calibrator. Calibrators can be stirred liquid baths (to approx. max. 550 °C (1022 °F)) or 225 so-called block calibrators. At higher temperatures (especially for thermocouple calibrations) tube furnaces are usually employed, whose limited thermal properties can be appreciably improved through the use of so-called compensation bodies (metal inserts) or heat pipes. The function of these calibrators is to produce a selectable temperature within a defined calibration volume, stable with time, and spatially homogeneous. A so-called comparison standard is exposed to the temperature together with the test object. The output signal from the comparison standard and the test object are measured over an extended period of time. The output signal from the comparison standard is used as a measure of the existing calibration temperature. Comparison calibrations by nature have higher measurement uncertainties than fixed point calibrations. The calibration expense, however, is appreciably less and calibrations can be conducted at practically any temperature. 6.2.3 The Traceability of the Calibration Looking at the comparison calibration it can be recognized, that in a certain sense it is the transfer of the “accuracy“ (measurement uncertainty) of the comparison standard to the test object. Of course, other measurement uncertainty components also come into play. They result e. g. from the measured data acquisition during the calibration or from non-homogeneous calibration bath temperatures. The resulting measurement uncertainties of the test object must by necessity be larger than those of the comparison standard used. It should be possible to use this test object at another location as a comparison standard. Each step entails an increase in the measurement uncertainty. The comparison standards with the least measurement uncertainties, the national comparison standards, are maintained and made available in Germany by PTB, the National Institute of Technology and Science (Physikalisch-Technische Bundesanstalt). PTB calibrates to customer order the so-called reference comparison standard against the national comparison standard. The reference comparison standards are comparison standards of the highest order e. g. used in DKD (German Calibration Service) certified calibration laboratories. The factory comparison standards, i.e., the comparison standards used to continuously conduct the calibrations, are calibrated against the reference comparison standards. The factory comparison standards are used, as a rule, to calibrate the production test equipment used for the manufacturing inspections. A calibration hierarchy exists made up of a definite number of calibration levels. This calibration hierarchy assures that the results measured by the production test calibration equipment can be traced back, over a complete set of links, to the national comparison standards. The comparability of all the calibration results is thereby assured. This concept is called “traceability“. The traceability of the measured results is a fundamental requirement of QA Systems according to EN ISO 9000. 226 Nat. Institute for metrological national standards Accredited calibration laboratory Reference comparison standard Calibration center Reference comparison standard Inner company calibration laboratory Working comparison standard or factory comparison standard Test euqipment of the company Fig. 6-4: Calibration hierarchy 6.2.4 Suitable Standards For the test instruments in the various levels of the hierarchy, there are specific requirements relative to their technical specifications. This is particularly true relative to their long term stability and freedom from hysteresis. Towards the peak of the triangle the requirements always become more stringent. Therefore the resistance thermometers, to be used as standard thermometers for representing ITS-90 (the highest level of the pyramid), may only be made of spectral pure Platinum material. Thermometers in this design, are usually used as reference comparison standards in laboratories. If thermocouples are used as reference comparison standards, only precious metal thermocouples (preferably Type S (Pt10%Rh-Pt)) come into consideration. These thermocouples must have an especially homogeneous alloy composition, so that any nonhomogeneous temperature distributions which may exist in the calibration oven outside of the actual calibration area, cannot affect the measured result. For use as a factory comparison standard resistance thermometers according to EN 60751 are completely acceptable. Even so, they should be selected after an intensive preliminary test from the best samples, relative to their stability, freedom from hysteresis and high insulation resistance, from the spread of normal production runs. Especially in regard to their insulation resistance, the requirements of EN 60751 should only be considered as minimum requirements. A usable thermometer, which should provide good service as a comparison standard, must definitely exceed these requirements. The industry offers for such applications special designs. 227 6.2.5 The Water Triple Point Fixed point calibrations are calibrations with the smallest measurement uncertainties. Typical for such measurements are measurement uncertainties in the range from 0.5 mK to 5 mK (in temperature ranges: 0.01...660 °C (32.02...1220 °F)). They are also calibrations requiring the highest expenditures in equipment and time. Fixed point calibrations are only used in a few calibration laboratories. The triple point of water is the only fixed point that can be found in practically all high quality calibration laboratories. It is the most important definition point in the ITS-90 scale and is used for regular testing of the comparison standard thermometers (reference comparison standards) in the laboratory. The triple point of water has a defined temperature t90 = 0.01 °C (32.02 °F) at a high precision (measurement uncertainty < 5 mK) and is therefore especially suited for finding the smallest deviations of the resistance of the comparison standard from its design value. Based on the magnitude of such a deviation, a decision can be made if the comparison standard should be recalibrated or if it can continue to remain in service. To produce the water triple point a triple point cell is used. Inner tube for thermometer insertion Glass body Water steam Water Ice Fig. 6-5: Triple point cell Since its introduction, ITS-90, has replaced the previously used value for the freezing point of water (0 °C (32 °F)) by the water triple point. 228 6.2.6 Documenting the Calibration Results A calibration without documentation is practically worthless. A report or certificate should be used to document the results of the calibration and its traceability to the National standards and be in agreement with the International System of Units (SI). It is the proof of the quality of the calibration object. In the industrial sector, it also provides quality assurance in a variety of forms. The best known is the certificate according to EN 10204 (formerly DIN 50049), which is the recognized form for material configuration and material testing. In addition, quality certificates according to DIN 55350 Part 18, form the certification basis when special quality requirements of any type were agreed upon in the purchase order. The named standards regulate which results are to be included in a particular certificate and who has the authority to issue such a certificate, but they make no statements regarding its format or any additional contents of the certificate. The contents and formats for the Calibration Certificates of the German Calibration Service DKD however are regulated in script “DKD-5“. DKD calibration certificates consist of a cover page, with general specifications for the item being calibrated, information about the customer and the laboratory performing the tests. In addition, there are statements relative to the international acceptance of the DKD calibration certificates within the framework of the EA (European Cooperation for Accreditation), which is based on multilateral agreements. The following pages of the calibration certificate document the type and calibration method, names the standards used and their traceability, descriptions of the ambient conditions and the results of the calibrations. A complete description of the calibration results includes the measured variable, the measured value and the measured uncertainty and the total measurement uncertainty. Supplementary statements about the conformity (maintaining the tolerances) can be included. 229 A DKD calibration can be recognized by: DKD-Logo (blue or black) German Eagle (black) DKD - Calibration Mark (red) 5092 DKD-K05701 06-01 Laboratory Seal The DKD calibration mark is also affixed to the calibrated object. 230 6.2.7 The German Calibration Service (DKD) The German Calibration Service (DKD) is an association of calibration laboratories of industrial companies, research institutes, technical authorities, inspection and testing institutes. These laboratories are accredited and supervised by the Accreditation Body of the German Calibration Service (DKD). They calibrate measuring instruments and material measures for measurands and measurement ranges specified within the framework of accreditation. The DKD calibration certificates issued by these laboratories prove traceability to national standards as required by the “standards family” ISO 9000 and by ISO/IEC 17025. The reason for the formation of the DKD in 1977 was an increased demand for traceable calibrations, which PTB could no longer satisfy, particularly in a timely manner. The functions are distributed as follows: Functions of the Accreditation Body: • Accreditation and monitoring of calibration laboratories: Processing and decisions regarding accreditation requests; monitoring the accredited calibration laboratories; planning, conducting and evaluating round robin comparisons. • Representing the German Calibration Service (DKD): Cooperation with board, technical committees and expert panels. Cooperation with committees of the German Accreditation Council (DAR), the European Cooperation for Accreditation (EA) and the International Laboratory Accreditation Cooperation (ILAC). Cooperation with national and international standards and control committees for measurement metrology. • Implementation of new developments: Cooperation in the development of progressive, new monitoring instrumentation (virtual laboratory control; measuring and test equipment); Unified presentation of measurement uncertainties. Functions of the DKD-Laboratories: • The calibration laboratories calibrate order based measurement and test equipments. • They prepare calibration certificates, which numerically document the results of the calibration. • The calibration laboratories assume responsibility for any resultant damages which can be traced back the errors in the calibration. 231 6.2.8 DKD-Laboratories at ABB The ABB factory in Alzenau, Germany has a DKD calibration laboratory, that was established for the calibration of temperature sensors and is registered under the approval number DKD-K-05701. Fig. 6-6: View into the DKD calibration laboratory DKD calibrations in a temperature range from -35...1200 °C (-31...2192 °F) can be conducted. Included are stirred liquid baths as well as tube ovens with compensation blocks. Naturally, water triple point cells are available. For low temperature requirements, the possibility of a DKD calibration using liquid Nitrogen (approx. -196 °C (-320.8 °F)) exists. The most important capital is the experience of the technicians in the laboratory, who have access to many years of company know how in the field of temperature measurement technology. The laboratory is accredited for calibrations of the following equipment: • Measurement resistors with suitable extensions (Pt100 and other Ro nominal values according to DIN EN 60751) • Resistance thermometers according to DIN EN 60751 • Thermocouples according to EN 60584 and DIN 43710 (or comparable international standards) • Temperature sensor with connected transmitter • Temperature sensor with direct indicator • Entire measuring chain (sensors + transmitter + transmitter power supply + indicator). 232 The following table provides information regarding the smallest, achievable measurement uncertainties, with which the calibrations can be conducted. Measured variable or calibration equipment Measuring range °C (°F) Measuring conditions Temperature resistance thermometers 0.010 (32.018) Water triple point cell 5 mK Triple point of water -196 (-320.8) Boiling point of liquid Nitrogen (LN2) 100 mK -35...180 (-31...356) Stirred thermostatic liquid bath 20 mK Comparison against standard resistance thermometer 180...350 (356...662) MeasureComments ment uncertainty 20 mK 350...500 (662...932) 50 mK Precious metal thermocouples -35...500 (-31...932) 0.5 K Base metal thermocouples 400...500 (752...932) 200...400 (392...752) 0...200 (32...392) 1.0 K 0.4 K 0.2 K Resistance thermometers 500...850 (932...1562) Precious metal thermocouples 500...1000 (932...1832) Measurement in tube 1.0 K oven (calibration in Na-heat tube in a 1.0 K range 550...1000 °C (1022...1832 °F)) 1.5 K Comparison measurement against thermocouple Type S Measurement in tube 2.0 K oven (calibration in Na-heat tube in a 3.0 range 550...1000 °C (1022...18320 °F)) Comparison measurement against thermocouple Type S Precious metal 1554 (2829) thermocouples with a wire design (dmax ≤ 1 mm) Fixed point calibration 2.5 K at the temperature of molten Palladium Melting method Contacting surface 50...500 thermometers (122...932) (resistance thermometers and thermocouples) Calibration fixture for surface thermometers 0.008 K· t/°C Method of the Ilmenau Inst. with individual test body t = temp. in °C Transmitter with connected resistance thermometer -35...850 (-31...1562) Such as resistance thermometers Transmitter with connected thermocouple -35...1200 (-31...2192) Such as thermocouples Uprt + 0.1 K Uprt and UTe are the expanded measurement uncertainties for UTe + 0.1 K resistance thermometers or thermocouples 1000...1200 (1832...2192) Base metal thermocouples 500...1000 (932...1832) 1000...1200 (1832...2192) Tbl. 6-3: Accreditation scope 233 6.2.9 Conducting a Calibration A resistance thermometer calibration will be used as an example to describe the actual steps required by the calibration specifications. If the aging characteristic of the test object are unknown, then it is checked first. The resistance of the test object is measured at the water triple point. The test object is held at a temperature 10...20 K above the highest calibration temperature for several hours. After it is cooled in air, the resistance at the water triple point is measured again. If differences are observed, which are below a specific stability limit (max. 1 mK for comparison standard resistance thermometers, approx. 20-30 mK for industrial resistance thermometers), then the actual calibration may be conducted on the test object. If the differences are greater than the specified limits, the complete cycle, heating, cooling and measuring of the resistance at the water triple point are repeated a number of times (approx. 3...5 times). The differences of the resistance value must tend towards zero. Thermometers, that do not meet the stability criteria after the aging procedures have been conducted, are not, or are only calibrated for a reduced accuracy classification. For the actual calibration, the test object is installed in the calibration thermostats together with the appropriate comparison standard, so that their measuring tips (temperature sensitive lengths) are as close together as possible in the middle of the calibration area. After a temperature equilibrium has become established between the test objects and the bath, the measured values are recorded. For precision calibrations, the measurements are made using an AC bridge. This method is advantageous because it operates by matching the resistances to those of the external comparison standards, where the best resolution of the instrument occurs, and also because the parasitic thermal voltages in the measuring circuit are compensated when using an AC current. The measured values of the test objects and the comparison standards are measured cyclically. The switching between the measuring channels is made using a low thermal voltage meter location selector switch. For each measuring channel, a continuos average value is calculated over a defined number of measurements and a standard deviation calculated. If the standard deviations for all the measured channels is less than a defined stability criterion, then the measurements values are accepted as the calibration values. This procedure is repeated at each of the calibration temperatures. For onsite calibrations (inspections) an additional comparison standard resistance thermometer with know resistance values can be incorporated into the complete measurement setup. 234 6.2.10 User Advantages offered by the DKD DKD calibration certificates are recognized by all important industrial countries. This fact, from the viewpoint of a global market place, is gaining in importance for exporting countries. Also, the DKD certificates are recognized as unconditional evidence that the calibrations were conducted with instrumentation subject to quality audit monitoring. This applies not only to the audits based on the standard family DIN EN ISO 9000 but also to the audits specified in other standards, for example, KTA 1401, AQAP 4a, MILStandard, ASME VDA, QS9000 etc. With accreditation by the Accreditation Body of the DKD the correctness of the calibration results is assured. DKD calibration certificates provide completely recognized evidence for legal relief in cases of product liability. The allowed measurement uncertainties ascribed to the laboratory must have been certified by measurements (calibrations of unknown thermometers) within the framework of the accreditation by the Accreditation Body. The systematic measurement instrumentation calibrations in conjunction with an accredited DKD calibration laboratory assures the user, among others: • higher measurement accuracies, • better reproducibility, • possibility for precise setting of the process parameters (higher process output, reduction of defective product), • preventing process down time, • reducing interruptions. The calibration of measuring equipment by an approved DKD calibration laboratory is not a luxury, which one utilizes in conjunction with Quality-Management-System, but provides the user with tangible financial advantages. Summary: Use of a correctly calibrated temperature sensor means reducing defects! Every lot, every batch, every oven charge can only be used in a restricted manner if the calibrations are conducted using faulty measuring equipment. This costs money and increases losses. 235 Recommendations for Recalibration Intervals for Temperature Sensors TemperaAmbient at- Tempeture sensor mospheric rature type conditions changes Resistance Reducing, thermoinert or meter oxidizing according to EN 60751 (wire wound measuring resistors) Special Design conditions No No extreme vibration temperature stresses change stresses Vibration stresses Strong or No extreme vibration temperature stresses change stresses (temperature-shock) Vibration stresses Maximum operating temperature °C (°F) Guidelines for recalibration intervals (months) Metallic or 200 (392) 24 ceramic thermowell 420 (788) 12 In metallic thermowell 660 (1220) 6 850 (1562) 3 In ceramic thermowell 660 (1220) 9 850 (1562) 6 Metallic or 200 (392) 12...15 ceramic thermowell 420 (788) 12 In metallic thermowell 660 (1220) 9 850 (1562) 3 In ceramic thermowell 660 (1220) 6...9 850 (1562) 6 metallic or 200 (392) 18 ceramic thermowell 420 (788) 12 In metallic thermowell 660 (1220) 6 850 (1562) 3 In ceramic thermowell 660 (1220) 6 850 (1562) 3 Metallic or 200 (392) 12 ceramic thermowell 420 (788) 9...12 In metallic thermowell 660 (1220) 6 850 (1562) 3 In ceramic thermowell 660 (1220) 6 850 (1562) 3 Important Information: The listed time intervals are only recommendations. Dependent on the installation conditions (temperature changes, vibration stresses etc.) and the design of the temperature sensor, recalibrations may be required at other time intervals. 236 Temperature sensor type Ambient at- Tempemospheric rature conditions changes Resistance Reducing, thermoinert or meters oxidizing according to EN 60751 (film measuring resistors) Special Design conditions Maximum operating temperature °C (°F) Guidelines for recalibration intervals (months) Metallic or 200 (392) 18 ceramic thermowell 420 (788) 9 In metallic thermowell 660 (1220) 3...6 In ceramic thermowell 660 (1220) 6 Metallic or 200 (392) 12 ceramic thermowell 420 (788) 9 In metallic thermowell 660 (1220) 6 In ceramic thermowell 660 (1220) 6 Strong or No extreme vibration temperature stresses change stresses (temperature-shock) Metallic or 200 (392) 15 ceramic thermowell 420 (788) 9...12 In metallic thermowell 660 (1220) 3...6 In ceramic thermowell 660 (1220) 3...6 Vibration stresses Metallic or 200 (392) 12 ceramic thermowell 420 (788) 9 In metallic thermowell 660 (1220) 6 In ceramic thermowell 660 (1220) 3...6 No No extreme vibration temperature stresses change stresses Vibration stresses Important Information: The listed time intervals are only recommendations. Dependent on the installation conditions (temperature changes, vibration stresses etc.) and the design of the temperature sensor, recalibrations may be required at other time intervals. 237 Temperature sensor type Ambient atmospheric conditions Design Precious metal thermocouples according to EN 60584 (Type S (Pt10%Rh-Pt) Type R (Pt13%Rh-Pt)) Reducing, inert or oxidizing Metallic or Base metal thermocouples according to EN 60584 (Type K (NiCr-Ni) Type N (NiCrSi-NiSi)) Base metal thermocouples according to EN 60584 (Type J (Fe-CuNi)) Maximum operating temperature °C (°F) Guidelines for recalibration intervals (months) ceramic thermowell 800 (1472) 24 In metallic 1000 (1832) 12 thermowell 1250 (2282) 6...8 In ceramic 1000 (1832) 18 thermowell 1250 (2282) 12 ceramic thermowell 700 (1292) 24 In metallic 1000 (1832) 12 thermowell 1150 (2102) 6 In ceramic 1000 (1832) 18 thermowell 1150 (2102) 9...12 ceramic thermowell 700 (1292) 12...15 In metallic 1000 (1832) 6 thermowell 1150 (2102) 1) In ceramic 1000 (1832) 9...12 thermowell 1150 (2102) 1) Metallic or Metallic or Important Information: The listed time intervals are only recommendations. Dependent on the installation conditions (temperature changes, vibration stresses etc.) and the design of the temperature sensor, recalibrations may be required at other time intervals. 238 6.3 Quality Assurance Measures Temperature sensors cannot always be brought into contact with the objects to be measured without special precautions. Generally, special measures are required to prevent exposure of the sensor to excessive mechanical forces, pressure, impact, erosion or vibration and to protect it from chemical attack. In addition, errors due to shunt currents or external voltages must be avoided. The temperature sensor is enclosed by protective materials (connection head, extension tube, thermowell with threaded or flanged connections), that more or less resist the impact of chemical and mechanical forces. The medium contacting parts, such as the thermowells, must especially be considered. In the following, the important measures are described. Detailed measures and requirements should be discussed with the suppliers of the temperature sensors. Leading manufacturers have experts available and approvals for quality assuring measures. Confirmation Steps for Special Applications The applicable German and European regulations, the user and the design specification require an evaluation of the components. The goal of these evaluations and tests is to prove the quality of the instrument, the safety of its materials and connection joints, and to detect weak spots in the welds of the components. Requirements and designs for temperature sensors are defined by the specifications in the regulations. At the very top of the hierarchy are the regulations in the European Pressure Equipment Directive 97/23/EC (AD2000). It has been mandatory since May 2002. Thermowells with threaded and flanged connections or welded thermowells etc. must meet the requirements in the Pressure Equipment Directive 97/23/EC (AD2000). For these components the directive requires a Certificate of Compliance, see also NAMURRecommendation NE80. 239 Regulations – System Based Qualifications AD Specification Sheet HP 0/TRD201 details the general fundamentals for the design, manufacture and testing of pressure vessels and pressure vessel parts (e. g. thermowells). The manufacturer of pressure vessels or pressure vessel parts must have a HP 0/TRD 201 approval. EN 10 204:20004 Metallic products, types of test certificates DIN 55 350-18 Concepts for certifying the results of quality tests, quality test certificates ZFP – Personnel Qualification and continued training of ZFP-Personnel relative to test technology for non-destructive testing and radiation protection Welder tests according to EN 287-1, DGRL 97/23/EG and TRD 201 / AD 2000 HP3 Welding procedure tests according to AD2000-HP 5/2 Specifications – Product Based Qualifications In addition to the general regulations in the national and international standards a number of institutions have issued regulations applicable for special sectors and application conditions relative to product and design approvals. Some examples: PTB German Institute of Technology and Science Type test examinations (Ex-Protection) and official monitoring of the measurements (comparison standards) DKD German Calibration Service is the accreditation body for inspecting the DKD laboratories EXAM Mine Experimental Test Section Dortmund-Derne, Germany type test examinations for explosion protection VDA German Association of the automotive industry KTA 1401 Nuclear plants 240 Maritime Approval Associations GL Germanic Lloyd LRS Lloyds Register of Shipping DNV Norske Veritas (Norwegian) BV Bureau Veritas NK Nippon Kaiji Kyokai (Japanese) ABS American Bureau of Shipping Special Tests (Non-Destructive and Metrological Tests) Mechanical Tests: • Vibration tests according to customer and design specifications e. g. for type test examinations with simulated earthquakes and airplane crashes for installations in nuclear power plants, determination of the resonance points for installation in flows with vortex shedding, type tests at the resonance points within prescribed frequency ranges for shipboard sensor approvals. • Radiographic testing with max. 200 KV output according to DIN 54111 Part 1, Testing Metallic Materials with Roentgen and Gamma Rays. The Roentgen tests are designed to detect porosities, voids, cracks, etc. in the basic material and/or the weld seam. The evaluation of the test results for fusion welds in pressure vessels and pressure containing parts is made according to the AD-Specification Sheets HP 5/3 and/or EN 25817. The regulations define the criteria for acceptance of defects. • Pressure tests using gas (up to 200 bar) and water (up to 3000 bar). The external and internal pressure tests are used to confirm the strength and impermeability of the thermowells and process connections. • Seal tests using Helium leak test with a leak rate of 1 x 10-9 mbar x 1 x s –1, e. g. for ceramic feedthrus. Defects are detected using a leak detector, sniffer probe, measuring the pressure drop or drop formation. • Surface crack detection using fluorescent or dye penetrants according to AD-Specification Sheet HP 5/3 • Hardness test according to Vickers (HV) and Rockwell (HRC) as well as Shore A for elastomers 241 Electrical Tests: • DKD-calibrations from -40...1200 °C (-40...2192 °F), plus the ability to calibrate using liquid Nitrogen (-195.8 °C (-320.44 °F)) or Palladium at its melting point (1554 °C (2829.2 °F)). • Factory calibrations from -195.806 (N2) °C (-320.451 °F) to 1554 (Pd) °C (2829.2 °F) • Response time measurements in water at v = 0.6 m/s and in air at v = 3.0 m/s • Insulation test to max. 3000 V AC Test Certifications • According to DIN EN 10 204 Certificates specified in this standard, as a rule, define the material traceability for chemical and physical properties, but can also confirm the properties through tests (e. g. impermeability of pressure strength, temperature tests). • Test Report 2.1 Certification by the manufacturer, that the delivered products are in accord with the specifications in the order, without information regarding the test results. • Test Report 2.2 Certification by the manufacture of the non-specific (not specified in the order) test results. Tests can be conducted by production personnel (non-specific tests). • Inspection Certificate 3.1 Certification of the materials and their testing per the customer specifications or legal regulations by factory specialists, who are designated by the malefactors and are independent of the production department. • Inspection Certificate 3.2 Certification by an inspector, who is independent of the production department, designated by the manufacturer and an inspector commissioned by the customer or an inspector named in the legal regulations of the results from the specific tests. • According to DIN 55350 Part 18 Quality test certificates in accord with this standard confirm all possible quality criteria based on the tests and measurements conducted. Only the most common certificates are described below. • Quality Test Certificate DIN 55350-18-4.1.1 Manufacturer certificate O, without information regarding the test results for nonspecific (not specified in the order) tests, e. g. batch values or spot tests, prepared by test personnel designated by the manufacturer (factory specialists). 242 • Quality Test Certificate DIN 55350-18-4.1.2 Manufacturer certificate O, without information regarding the test results for specific (specified in the order) tests, e. g. batch values or spot tests, prepared by test personnel designated by the manufacturer (factory specialists). • Quality Test Certificate DIN 55350-18-4.2.1 Manufacturer certificate O without information regarding the test results for specific (specified in the order) tests, prepared by test personnel designated by the manufacturer (factory specialists). • Quality Test Certificate DIN 55350-18-4.2.2 Manufacturer certificate M with information regarding the test results for specific (specified in the order) tests, prepared by test personnel designated by the manufacturer (factory specialists). Information: For all test certificates according to DIN 55350 Part 18 the scope of the test is to defined ahead of time. Additional Certifications • Manufacturer Declaration Certificate of Compliance by the manufacturer for simple electrical equipment according to EN 50020 Par. 5.4 for intrinsically safe measuring circuits including specifications for the corresponding conditions. • DKD-Certificate Calibration certificate for temperature sensors, which can only be prepared by designated personnel in accredited DKD-Laboratories (Calibration Laboratories according to DIN EN ISO/IEC 17025). Tests may only be conducted within the accredited range for the specific instruments and comparison standards. Materials and Procedures They correspond to the specific, valid international standards, such as e. g. DIN, BS, ASTM, etc. They are also delivered to the customer based on special test and inspection specifications (DIN EN 10204:2005). The inspections can be conducted by the customer, by an independent inspection organization (TÜV, LRS, DNV etc.) or by an independent factory specialist. A very comprehensive quality assurance system exists to assure compliance with the international standards. 243 7 Explosion Protection 7.1 Introduction The explosion protection is regulated worldwide by country specific standards. The global ABB sales products satisfy these requirements with minor product variations, which are necessary to satisfy the particular national requirements for explosion protection. This means: the same basic design with approvals for various countries. Using this approach, minor product variations for worldwide marketing, the user can install the same product worldwide. This strategy leads to cost reductions on the customer’s part, e.g. training, planning and maintenance of these products. European Union USA Canada Russia Ukraine Australia Regulations/ Standard/ Approval Agency ATEX – PTB – EXAM BBG – KEMA – TÜV North – ZELM – IBExU... FM EX Approval UL EX Approval CSA Certificate GOST Russia GOST Ukraine IECEX Validity No restrictions No No Approx. 5 restrictions restrictions years Approx. 5 years No restrictions Production Monitoring/ Audits Yes Yes No Yes Tbl. 7-1: Yes No Overview of the more important country specific standards, approvals and approval agencies At their core, the requirements for the approvals are very similar and have a common goal, that, based on the present state of the technology, an explosion cannot occur in a system, in which instrumentation was used which was designed in accord with the national requirements for explosion protection. 244 7.2 Terms and Definitions Explosion Explosion means an exothermic reaction of a material which occurs at a high reaction rate. This requires the presence of an explosive mixture/atmosphere and an ignition source, as well as external impetus to initiate the explosion. Explosion hazard Explosion hazard means the presence of an explosive mixture/atmosphere, without ignition occurring from an ignition source from an external impetus. Explosive gas atmosphere Mixture with air, under atmospheric conditions, of flammable substances in the form of gas or vapour, in which, after ignition, permits self-sustaining flame propagation. Explosion limits The lower (LEL) and upper (UEL) explosion limit defines the range of a mixture in which it is explosive. The limits can be found in the appropriate literature for the particular materials. Explosion groups according to EN-standards The ignition and ignition penetration characteristics of an explosive mixture are typical material properties. These specifications are especially important in the design of equipments. For Intrinsic Safety electrical equipments the ignition energy is the criterion for the ignitability. The smaller the required ignition energy, the more dangerous is the mixture. The ignition penetration characteristics provides information relative to the flame path width and length limits for the equipments with flameproof enclosure. Explosion Group Ignition Energy Test Gas Area I < 200 μJ1) Methane in air Firedamp protection (Mining) II A II B II C < 160 μJ1) < 60 μJ1) < 20 μJ1) Propane in air Ethylene in air Hydrogen in air 1) Tbl. 7-2: Explosion protection Doubling of the energy values is permissible, when the charging voltage < 200 V. Explosion groups according to the EN-standards 245 Gases and vapors are classified by the criteria listed below. The table ranks a number of materials. The equipment to be used for these materials must be qualified accordingly. Explosion Group Ignition Temperature T1 T2 T3 T4 I Methane II A Acetone Ethane Ethyl acetate Ammonia Benzine (pure) Acetic acid Methanol Propane Toluene Ethyl alcohol i-Amylacetate n-Butane n-Butyl alcohol Benzine Acetaldehyde Diesel fuel Ethyl ether Aircraft fuel Heating oil n-Hexane II B Carbon monoxide Ethylene SulphurdiHydrogen II C Hydrogen Acetylene Tbl. 7-3: T5 T6 Ethyl ether Butyl ether Carbon disulphide Material rankings according to explosion group Flash Point Is the lowest temperature at which the liquid under test, under defined conditions, produces vapors in a quantity sufficient to form a flammable mixture above the liquid surface when combined with air. Ignition Energy The minimum ignition energy is the energy contained in a spark which is sufficient to ignite the surrounding explosive atmosphere. Ignition Temperature according to EN-standards The ignition temperature of a flammable material is the lowest temperature, determined in a test instrument with a heated wall, at which the mixture of a flammable material mixed with just ignites. The ignition temperatures of liquids and gases are determined by the procedures described in DIN 51794. For determining the ignition temperature of flammable dust, no standardized procedures exist at this time. There are a number of procedures listed in In the relevant literature. 246 The flammable gases and vapors of flammable liquids are classified in Temperature Classes by their ignition temperatures, and equipment by its surface temperature. Temperature Class Maximum allowable surface temperature of the equipment in °C (°F) T1 T2 T3 T4 T5 T6 Tbl. 7-4: 450 (842) 300 (572) 200 (392) 135 (275) 100 (212) 85 (185) Ignition temperatures of the flammable materials in °C (°F) > 450 (842) ... > 300 (572) ≤ 450 (842) > 200 (392) ≤ 300 (572) > 135 (275) ≤ 200 (392) > 100 (212) ≤ 135 (275) > 85 (185) ≤ 100 (212) Temperature classes Ignition Sources The following list showes some of the common ignition sources found in applications: • • • • • • • • • • hot surfaces (heaters, hot equipment, etc.), flames and hot gases (from fires), mechanically produced sparks (by rubbing, impact and grinding processes), arcs from electrical equipment, compensation currents, static electricity, lightning, ultrasonic, optic ignition sources, electric fields from radio waves, ... Primary and Secondary Explosion Protection When preventing explosions the terms primary and secondary explosions are used. The primary explosion protection is based on preventing the formation of a dangerous explosive atmosphere, i.e.: • • • • • avoiding flammable liquids and gases, increasing the flash point, prevention of an explosive mixture by concentration limitations, ventilation or open area installations, concentration monitoring with emergency shut down procedures. 247 The secondary explosion protection encompasses all measures which prevent or avoid the ignition of a hazardous atmosphere, i.e.: • No active ignition source - Intrinsically safe equipment - Encapsulating the ignition source to prevent external ignition Powder filled Flameproof Pressurized Area/zones categories according to IEC standard (EN 60079-10) Hazardous areas are classified into zones based upon the frequency of the occurrence and duration of an explosive gas atmosphere, as follows: For Gases, Vapors and Mists Zone 0: place in which an explosive atmosphere consisting of a mixture with air of flammable substances in the form of gas, vapour or mist is present continuously or for long periods or frequently. Category: 1 G Zone 1: place in which an explosive atmosphere consisting of a mixture with air of flammable substances in the form of gas, vapour or mist is likely to occur in normal operation occasionally. Category: 2 G Zone 2: place in which an explosive atmosphere consisting of a mixture with air of flammable substances in the form of gas, vapour or mist is not likely to occur in normal operation but, if it does occur, will persist for a short period only. Category: 3 G For Dust Zone 20: area in which an explosive atmosphere consisting of a flammable dust and air in the form of a cloud is always present, over long periods of time, or is often present. Category: 1 D Zone 21: area in which during normal operation an explosive atmosphere consisting of a flammable dust and air in the form of a cloud can form. Category: 2 D 248 Zone 22: area in which during normal operation an explosive atmosphere consisting of a flammable dust and air in the form of a cloud generally does not form and if it does, then only for a short time. Category: 3 D Comments: Coatings, deposits and settling of flammable dust, as well as every other cause, must be considered because they can lead to the formation of a hazardous, explosive atmosphere. The status for normal operation is defined as operation within the design parameters for the system. Apparatus for Category 1G/1D, Instrument Group II Categories 1G (gas) and 1D (dust) include apparatus, that is designed so that it can be operated to correctly measure the variables required by the user and provide a very high degree of safety. Apparatus for these categories are suitable for use in Zone 0 (1G apparatus) and in Zone 20 (1D apparatus). Apparatus in these categories must, even for rarely occurring instrument faults, assure that the required degree of safety exists and therefore must include explosion protection measures so that • even if one type of protection fails, at least the other type of protection assure the required safety, or • if two types of protection fails the required safety is assured. The apparatus in this category must also comply with the extensive requirements in Annex II, Number 2.1 of the EU-Directive 94/9/EG. Apparatus for Category 2G/2D, Instrument Group II Categories 2G (gas) and 2D (dust) include apparatus, that is designed so that it can be operated to correctly measure the variables required by the user and provide basic degree of safety. Apparatus for these categories is suitable for use in Zone 1 (2G apparatus) and in Zone 21 (2D apparatus). The explosion protection measures for this category assures that even during frequent instrument failures or fault conditions, which can usually be expected, the required degree of safety is assured. 249 Apparatus for Category 3G/3D, Instrument Group II Categories 3G and/or 3D include apparatus, that is designed so that it can be operated to correctly measure the variables required by the user and provide basic degree of safety. Apparatus for these categories is suitable for use in Zone 2 (3G apparatus) and in Zone 22 (3D apparatus) for a short period of time. Apparatus for the category assures the required degree of safety during normal operation. DIV Categories according to NEC500 (USA) and CEC Annex J (Canada) In addition to the categories Zone 0 and Zone 1 for European instrumentation for explosion hazardous areas, there are Division categories defined in NEC500 and CEC Annex J. The following table provides an overview of the Zones and Divisions. IEC / EU Zone 0 Zone 1 US NEC505 Zone 0 Zone 1 US NEC500 Zone 2 Division 1 CA CEC Section 18 Zone 0 CA CEC Annex J Tbl. 7-5: Zone 2 Division 2 Zone 1 Zone 2 Division 1 Division 2 Comparison of Zone and Division Classifications IEC Classifications according to IEC 60079-10 EU Classifications according to EN60079-10 US Classifications according to ANSI/NF PA70 National Electrical Code Article 500 and/or 505 CA Classifications according to CSA C22.1 Canadian Electrical Code (CEC) Section 18 and/or Annex J Explosion Groups according to NEC500 (USA) and CEC Annex J (Canada) Explosion groups US NEC500 CA CEC Annex J Explosion groups US NEC505 CA CEC section 18 EU IEC Mining Class I Group D Class I Group C Class I Group A Class I Group B Tbl. 7-6: 250 Test gas Area I Methane Firedamp protection (Mining) II A II B II C II B + Hydrogen Propane Ethylene Acetylene Hydrogen Explosion groups according to US/CA-standards Explosion protection Temperature Classes according to NEC500 (USA) and CEC Annex J (Canada) Max. surface temperatures 450 °C (842 °F) 300 °C (572 °F) 280 °C (536 °F) 260 °C (500 °F) 230 °C (466 °F) 215 °C (419 °F) 200 °C (392 °F) 180 °C (356 °F) 165 °C (329 °F) 160 °C (320 °F) 135 °C (275 °F) 120 °C (248 °F) 100 °C (212 °F) 85 °C (185 °F) Tbl. 7-7: US NEC505 CA CEC section 18 EU IEC T1 T2 T3 T4 T5 T6 US NEC 500 CA CEC Annex J T1 T2 T2A T2B T2C T2D T3 T3A T3B T3C T4 T4A T5 T6 Temperature classes according to US/CA-standards 251 7.3 Types of Protection in Europe and in North America Ignition Type “Intrinsic Safety - Ex i“ according to EN 50020 or EN 60079-11 Type of protection based on the restriction of electrical energy within apparatus and of interconnecting wiring exposed to the potentially explosive atmosphere to a level below that which can cause ignition by either sparking or heating effects. Explosion hazardous atmosphere R U Fig. 7-1: L C Intrinsic safety schematic There are two categories of Intrinsic Safety. Category "ia" for installations in Zone 0: The instruments must be designed so that during a fault condition or during all possible combinations of two fault conditions, ignition is impossible. Category "ib" for installations in Zone 1: The instruments must be designed so that during one fault condition ignition is impossible. 252 Ignition Protection Type “Flameproof Enclosure Ex - d“ according to EN 50018 or EN 60079-1 Enclosure in which the parts which can ignite an explosive atmosphere are placed and which can withstand the pressure developed during an internal explosion of an explosive mixture, and which prevents the transmission of the explosion to the explosive atmosphere surrounding the enclosure. Explosion hazardous atmosphere Chink s w s l Fig. 7-2: Flameproof enclosure schematic Ignition Protection Type “Increased Safety Ex e“ according to EN 50019 or EN 60079-7 Type of protection applied to electrical apparatus in which additional measures are applied so as to give increased security against the possibility of excessive temperatures and of the occurrence of arcs and sparks in normal service or under specified abnormal conditions. Explosion hazardous atmosphere Fig. 7-3: Increased safety schematic 253 Ignition Protection Type “Potted Encapsulation Ex m“ according to EN 50028 or EN 60079-18 Type of protection whereby parts that are capable of igniting an explosive atmosphere by either sparking or heating are enclosed in a compound in such a way that the explosive atmosphere cannot be ignited under operating or installation conditions. Explosion hazardous atmosphere Fig. 7-4: Potted encapsulation schematic Ignition Protection Type “Non-Sparking Equipment – n“ according to EN 50021 or EN 60079-15 Type of protection applied to electrical apparatus such that, in normal operation and in certain specified abnormal conditions, it is not capable of igniting a surrounding explosive gas atmosphere. n Fig. 7-5: 254 Non-sparking electrical equipment schematic Zone 2 Approvals according to FM Approval Standard Class Number 3610, 3611 and 3615 Temperature products from ABB satisfy, dependent on the specific certification and application area, one or more of the following FM standards: • Intrinsically Safe Apparatus and Associated Apparatus for use in Class I, II, and III, Division 1, and Class I, Zone 0 and 1. Hazardous (Classified) Locations. Approval Standard Class Number 3610. • Non-incendive Electrical Equipment for use in Class I and II, Division 2, and Class III, Divisions 1 and 2. Hazardous (Classified) Locations. Approval Standard Class Number 3611. • Explosion proof Electrical Equipment General Requirements. Approval Standard Class Number 3615. The corresponding operating instructions and control drawings are to be considered when installing the instrument. In addition, the requirements of the National Electrical Code (NEC) must be observed. Approvals according to CSA-standards Temperature products from ABB satisfy, dependent on the specific certification and application area, one or more of the following CSA standards. • CAN/CSA-E60079-11:02 Electrical apparatus for explosive gas atmospheres Part 11: Intrinsic safety "i" C22.2 No.213-M1987 (Reaffirmed 1999) Non-incendive Electrical Equipment for use in Class I, Division 2. Hazardous Locations. • C22.2 No. 30-M1986 (Reaffirmed 1999) Explosion-proof Enclosures for use in Class I. Hazardous Locations. The corresponding operating instructions and control drawings are to be considered when installing the instrument. In addition the requirements of the Canadian Electrical Code (CEC) Part I (Safety Standard for Electrical Installation) must be observed. Approvals according to GOST and other Approvals The certifications according to these national standards are based on the EC-Type Examination Certificates and their associated test reports. Generally, additional tests are not required. The different agencies and institutes recognize the test reports. Some certificates however, have expiration limits, requiring increased efforts to maintain the certifications current for the products. 255 7.4 Marking of the Apparatus Apparatus for use in explosion hazardous areas must be clearly marked by the manufacturer. The following marking according to EN 50014 or EN 60079-0/EN 50020 or EN 60079-11 are to be used: • • • • • • Name and address of the manufacturer CE-Mark Identification of the series and the type If applicable, the serial number Year of manufacture Special mark for preventing explosions, in conjunction with the mark which identifies the category • For the Group II the letter “G“ (for explosive gas atmosphere) and/or the letter “D“ (for explosive dust atmosphere). Up to three nameplates are used on the temperature products from ABB for identifying the required marks: • Typeplate with the important information for the product • Approval typeplate with all the applicable explosion marks • Optional label for additional information. 256 Design and Content of Typeplates for Temperature Products from ABB [Company Logo, Manufacturer] [Product name] [Country of manufacture] [Year of manufacture] [Product name + Order Code] [Order No.+ Item No.] [Serial No.] [Technical Specifications U, I, P ] [Transmitter CFG] [Sensor CFG] [Ambient temperature range, standard] [Instr. Man. Logo] [CE Logo] [HW-Revision] [SW-Revision] [Protection Class] Information: The temperature specifications are only listed on the typeplate for non-Ex-versions. Automation Products GmbH O-Code: TTH300-Y0/OPT Ser.-No: 3452345673 TTH300 Made in Germany 2008 8323455672 US= +11...42 V, I a= 4...20 mA, HART CFG: 2 x TC; Type K; 0°C...300°C Tamb = -40°C...+85°C HW-Rev: 1.05 SW-Rev: 01.00.00 www.abb.com/temperature Example: Temperature transmitter type TTH300 2008 Example: Temperature sensor type TSP121 257 Design and Content of an Approval Typeplate for Temperature Products from ABB • • • • Company Logo Manufacturer information Product name (+ Approval name, if different than product name) Approval specifications incl. Approval Logo – ATEX EEx i; Approval specifications according to EC-Type Examination Certificate – ATEX EEx d; Approval specifications according to EC-Type Examination Certificate – ATEX EEx D; Dust Ex, Approval specifications according to EC-Type Examination Certificate – FM; Approval specifications according to Certificate of compliance – CSA; Approval specifications according to Certificate of compliance – GOST; Approval specifications according to Certificate of compliance • CE 0102 Logo with No. of the Test Agency for ATEX typeplates • Allowed ambient temperatures Automation Products GmbH TTH300 Made in Germany 2008 PTB 05 ATEX 2017 X II 1 G EEx ia IIC T6 II 2(1) G EEx [ia]ib IIC T6 II 2G (1D) Ex [iaD] ib IIC T6 T1...T4 Tamb. = -40°C ... +84°C (Zone0) ... +85°C (Zone1) T5 Tamb. = -40°C ... +56°C (Zone0) ... +71°C (Zone1) T6 Tamb. = -40°C ... +44°C (Zone0) ... +56°C (Zone1) 0102 Example: Temperature transmitter TTH300 in design EEX "i" 2008 Example: Temperature sensor TSP121 in design Dust-EX 258 7.5 Evidence of the Intrinsic Safety When interconnecting intrinsically safe circuits according to EN60079-14 an evidence of the Intrinsic Safety is to be maintained. There are two categories: 1. Simple intrinsically safe circuit with only one active, associated and one passive intrinsically safe apparatus without additional power supply. 2. Multiple active apparatus, which during normal operation or during a fault condition can supply electric energy to the intrinsically safe circuit. Simple Intrinsically Safe Circuits They can be checked by an authorized person by comparing the electrical connection values from the respective EC-Type Examination Certificate. The Intrinsic Safety of the connections is maintained, when the following conditions are satisfied: Intrinsically safe equipment plus cable e.g. ABB-transmitter Ui Ii Pi Li + Lc (cable) Ci + Cc (cable) Associated equipment e.g. transmitter power supplies/SPC input ≥ ≥ ≥ ≤ ≤ Field (explosion hazardous area) Transmitter Fig. 7-6: Uo Io Po Lo Co Control room (safe area) Isolated transmitter power supply/SPC-Input Schematic of a simple intrinsically safe circuit 259 The verification should be clearly documented. In addition to the date and name of the tester, system specific documentation should be included, i.e., circuit description, terminal strips, cable routing, switch and terminal housings, etc. Interconnection of Multiple Active Apparatus This differs fundamentally from the previous case. For example, if the interconnection of multiple active, category “ia“ intrinsically safe circuits results in the combined circuit being classified as a category “ib“ circuit, then operation in Zone 0 is no longer possible. A detailed explanation of this type of connection can be found in Annexes A and B of EN60079-14. Additionally, the ignition limit curves in EN 60079-11 or EN50020 will be required. See also EN 60079-25. The advanced handling of this subject is usually the responsibility of qualified personnel and is not included in this handbook. Connection of Intrinsically Safe Circuits with Non-Linear Curves Here special procedures must be followed. They are described in detail in EN 60079-25. The advanced handling of this subject is usually the responsibility of qualified personnel and is not included in this handbook. 260 8 SIL - Functional Safety in Process Automation The standards IEC 61508 and IEC 61511 provide risk assessment methods for the design of safety loops. They define four safety levels, which describe the measures for risk assessment for the system elements. In order to determine the SIL-Level (Safety Integrity Level) of an instrument, all field instruments are subjected to rigorous test requirements and analysis by IEC. The European Union sets the EU-Directive 96/82/EU (Sevesco II-Directive) as the legal basis for the operation of systems with hazard potentials. The implementation of the Directive 96/82/EU follows from the Incident Regulation in the Federal Imission Control Law (12.BlmSchV) dated 26 April 2000. The Incident Regulation required reference, prior to the issuance of the safety relevant equipment, to DIN 19250 and 19251 until 31 July 2004, in which the requirement classes AK 1-8 are described. After 1 August, the Incident Regulation references DIN EN 61508 as well as DIN EN 61511, whose content corresponds to the Standards (IEC 61508/IEC 61511). They define four Safely Levels (SIL1 to SIL4), which define the risk assessment of system elements and from which the field instruments and actuators must be designed. In order to estimate, if an instrument is satisfactory for a specific SIL-Level in the safety chain, the field instruments are tested and analyzed by an independent Institution. In the FMEDA-Test (Failure Mode, Effect and Diagnosis) the hardware structure of the electronics is investigated. Together with the considerations of the (electro) mechanical components, the failure rate for the instrument, e.g. temperature transmitter can be determined. Essentially, the basic characteristics are utilized, which are calculated from the FMEDA: the Hardware Fault Tolerance (HFT), the percentage of safe failures (SFF Safe Failure Fraction) and the Probability of Failure on Demand (PFD). The software development process of SIL certified temperature transmitters is defined in IEC 61508 which, in addition, utilizes the requirements in ICE 61511. Additional general safety considerations for the field instruments are evaluated. In the SIL-Certificate of Compliance, which is issued by the manufacturer, in order to support the customers in the selection of suitable instruments for the safety circuits, the classifications are always based on the lowest SIL level. 261 To safely operate a system, an additional step is required by the IEC regulations which takes into account the entire safety circuit, consisting of the sensor/transmitter, controller and actuators, and assigns a SIL level. Before a safety circuit is designed and calculated, a SIL assessment is carried out, which is used to determine the required safety level for the safety circuit (e. g. SIL2). ABB offers a software program which can be used for all aspects of the system certification from a SIL assessment up to the design and calculation of the safety circuit according to IEC 61508. It also records and stores all decisions and basic calculations. For operation, the safety circuits must also be regularly checked relative to their safety functions and the results recorded. For these checks, it is required that the test routines are defined, conducted and recorded. An expensive process, but which in the end is beneficial to humans and the environment. In addition to an extensive portfolio of instruments, ABB offers a software program, which manages and processes the data for statistical analysis for all the test routines and test results prescribed in IEC 61508. 262 9 Standards and Regulations for Temperature Measurements The standardization of electrical thermometers is difficult because of their wide spread use in process measurement technology and the large variety of design types, but extremely important. The standardization of electrical thermometers is therefore primarily limited to the specification of: • • • • Basic values Electrical interfaces Mechanical interfaces (process connections) Special characteristics For the process measurement sector, the creation of national standards for temperature sensors is the responsibility (in Germany) of Subcommittee 961.1 “Electrical Transmitters“ of the Committee 9.61 “Sensors and Devices“ in Department 9 “Control Technology“ associated with the German Electrical Commission (DKE). For very special applications other bodies are in part responsible. Standards are prepared at the European (CENELEC) or international (IEC) level as well at other comparable bodies (see Tbl. 9-1). International European National (Germany) International Electrical Commission (IEC) Technical Bureau (BT) CENELEC German Electrical Commission (DKE) Technical Committee (TC) 65: “Industrial Process Measurement and Control“ Reporting Secretariat For IEC TC 65 Department (FB) 9: “Process Control“ Subcommittee (SC) 65B: “Devices“ Working Group (BTWG) or Task Force (BTTF) (Project based) Committee (K) 961: “Sensors and Devices“ Working Group (WG) 5: “Temperature Sensors“ Tbl. 9-1: Subcommittee (UK) 961.1: “Electr. Measuring Primaries“ Classification of national and international standards activities for temperature sensors 263 The most important national standard bodies for other countries: USA Canada France Gr. Britain Japan Russia Italy ANSI CSA NF BSI JIS GOST UNI American National Standards Institute Canadian Standards Association Normalisation Francaise British Standards Institution Japanese Industrial Standards National Standards of the Russian Federation Uniticazione Nazionale Italiano Standards Temperature Measurements: EN 50112 EN 50212 Measurement, control, regulation – Electrical temperature sensors – Metal Thermowells for Thermocouples Assemblies Connectors for Thermoelectric Sensors New draft: Draft proposal for DIN EN 50466 Straight Thermocouples with Metal or Ceramic Thermowells and Accessories To replace the following standards: DIN 43729 , DIN 43733, DIN 43734 EN 60751 Industrial Platinum Resistance Thermometers and Platinum Resistance Wires New draft: Draft proposal for DIN IEC 60751 2005, being voted on EN 60584-1 Thermocouples Part 1: Reference Tables: Basic values for the thermal voltages Thermocouples Part 2: Tolerances EN 60584-2 New draft: Draft proposal for DIN IEC 60584-3 Thermocouple Wires and Compensating Cables EN 61152 EN 61515 Dimensions of Metal-Sheathed Thermometer Elements Mineral Insulated Thermocouple Cables and sheathed Thermocouples DIN 16160 DIN 43710 DIN 43712 DIN 43713 Thermometers; Concepts Thermal Voltage and Materials for Thermocouples Thermal Wires for Thermocouples Wires and Stranded Wires for Compensation and Extension CabIes Compensating Cables for Thermocouples Metal Thermowells for Thermocouples Thermocouples; Part 3: Thermocouple Wires and Compensating Cables; Tolerances and Identification System DIN 43714 DIN 43720 DIN 43722 264 DIN 43724 DIN 43725 DIN 43729 DIN 43732 DIN 43733 DIN 43734 DIN 43735 DIN 43762 DIN 43764 DIN 43765 DIN 43766 DIN 43767 DIN 43769 DIN 43771 DIN 43772 DIN 43772 Supplement 1 VDI/VDE 3511-1 VDI/VDE 3511-2 VDI/VDE 3511-3 Measurement and Control; Electrical Temperature Sensors; Ceramic Thermowells and Holding Rings for Thermocouples Electrical Temperature Sensors; Thermocouple Insulating Tubes Measurement and Control; Electrical Temperature Sensors; Connection Heads for Thermocouples and Resistance Thermometers Measurement and Control; Electrical Temperature Sensors; Thermocouple Wires for Thermocouples Measurement and Control; Electrical Temperature Sensors; Straight Thermocouple without Exchangeable Measurement Insets Measurement and Control; Electrical Temperature Sensors; Stop Flanges for Thermocouples and Resistance Thermometers Measurement and Control; Electrical Temperature Sensors; Measurement Insets for Thermocouple Sensors Measurement and Control; Electrical Temperature Sensors; Measurement Insets for Resistance Thermometers Measurement and Control; Electrical Temperature Sensors; Straight Thermometers with Interchangeable Measurement Inset Measurement and Control; Electrical Temperature Sensors; Threaded Stem Thermometers with G 1/2 Mounting Threads Measurement and Control; Electrical Temperature Sensors; Threaded Stem Thermometers with G 1 Mounting Threads Measurement and Control; Electrical Temperature Sensors; Welded-Stem Thermometers Measurement and Control; Electrical Temperature Sensors; Thermometers not Fitted with Thermowells Measurement and Control; Electrical Temperature Sensors; Thermometers with Fast Response Control Technology - Thermowells and Extension Tubes for Liquid-in-Glass Thermometers, Dial Thermometers, Thermocouples and Resistance Thermometers - Dimensions, Materials, Testing Control Technology - Thermowells and Extension Tubes for Liquid-in-Glass Thermometers, Dial Thermometers, Thermocouples and Resistance Thermometers - General Review - Assignment Thermowell/Temperatur Sensor Technical Temperature Measurements - Basics and Overview for Special Temperature Measurement Procedures Technical Temperature Measurements - Contacting Temperature Sensors Technical Temperature Measurements - Measuring Procedures and Measurement Processing for Electric Contacting Temperature Sensors 265 VDI/VDE 3511-4 VDI/VDE 3511-5 VDI/VDE 3522 Technical Temperature Measurements - Radiation Thermometry Technical Temperature Measurements - Installation of Temperature Sensors Time Performance of Contacting Temperature Sensors Explosion Protection Standards, Safety Standards for Combustion Plants, Heat Quantity Measurements EN 60079-10 EN 60079-14 EN 60079-17 EN 1434-1 EN 1434-2 EN 1434-3 EN 1434-4 EN 1434-5 EN 1434-6 EN 14597 DIN 3440 Electrical Apparatus for Explosive Gas Atmospheres Part 10: Classification of Hazardous Areas Electrical Apparatus for Explosive Gas Atmospheres Part 14: Electrical Installations in Hazardous Areas (Other than Mines) Electrical Apparatus for Explosive Gas Atmospheres Part 17: Inspection and Maintenance of Electrical Installations in Hazardous Areas (other than mines) Heat Meters - Part 1: General Requirements Heat Meters - Part 2: Construction Requirements Heat Meters - Part 3: Data Exchange and Interfaces Heat Meters - Part 4: Type Approval Tests Heat Meters - Part 5: Initial Verification Tests Heat Meters - Part 6: Installation, Commissioning, Operational Monitoring and Maintenance Temperature Control Devices and Temperature Limiters for Heat Generating Systems Replaces DIN 3440 Temperature Control and Limiting Devices for Heat Generating Systems; Safety Requirements and Testing International Standards IEC 60584-1 IEC 60584-2 IEC 60584-3 IEC 60751 IEC 61152 IEC 61515 266 Thermocouples - Part 1: Reference tables Thermocouples - Part 2: Tolerances Thermocouples - Part 3: Extension and Compensating Cables Tolerances and identification system Industrial Platinum Resistance Thermometer Sensors Dimensions of Metal Sheathed Thermometer Elements Mineral Insulated Thermocouple Cables and Thermocouples 10 Appendix 1 Application conditions for thermowell materials Material Max. Temp. no pressure °C (°F) Advantages Disadvantages 1.0305 550 (1022) Good resistance to reducing gases Minimum resistance to oxidizers and acids 1.4301 (304) 800 (1472) Heat and corrosion resistant Minimum resistance to reducing flames and Sulphur 1.4306 (304L) 800 (1472) Good resistance to grain boundary corrosion 1.4401 (316) 800 (1472) Good resistance to acids and alkalis 1.4404 (316L) 800 (1472) Good resistance to grain boundary corrosion 1.4435 (316L) 800 (1472) Good resistance to grain boundary corrosion 1.4541 (321) 800 (1472) Good resistance to grain boundary corrosion after welding 1.4571 (316Ti) 800 (1472) Good resistance especially to grain boundary corrosion 1.4762 (446) 1200 (2192) Good resistance to oxidizing and reducing flames, Sulphur containing gases 1.4749 (446) 1150 (2102) Good resistance to oxidizing and Minimum resistance reducing flames, Sulphur to Nitrogen containing containing gases, applications in gases salt baths and metal smelting 1.4772 1250 (2282) Use for Copper - brass smelting 1.4821 1350 (2462) Use for Salt Peter, Chloride and Cyanide containing salt baths 1.4841 (314) 1150 (2102) Good resistance to Nitrogen and Minimum resistance Oxygen poor gases to Sulphur containing gases 1.4845 (310S) 1050 (1922) Higher NiCr content, resistant to high temperature corrosion 1.4876 (Incoloy) 1100 (2012) Resistant to high temperature corrosion and thermal shock 2.4360 (Monel) 600 (1112) Good resistance to steam, high pressure and corrosion Metal thermowells 2.4665 (Hastelloy X) 1100 (2012) Minimum resistance to Nitrogen containing gases Good resistance to oxidizing and carburizing atmospheres at high temperatures 267 Application conditions for thermowell materials Material Max. Temp. no pressure °C (°F) Advantages Disadvantages 2.4810 (Hastelloy B) 1100 (2012) Good resistance to heat and corrosion, especially to HCI and H2SO4 attack 2.4811 (Hastelloy C-276) 1100 (2012) Good resistance to oxidizing and reducing atmospheres and to CI2 gas 2.4816 (Inconel) 1150 (2102) Good resistance to oxidizing and reducing atmospheres at high temperatures Inconel MA 754 1250 (2282) Good mechanical resistance and corrosion resistance at high temperatures in oxidizing atmospheres 3.7035 (Titanium) 600 (1112) Good low temperature corrosion At high temperatures resistance light oxidation and embrittlement Stellite 6 1200 (2192) Good resistance to heat, corrosion, abrasion Tantalum 250 (482) Good resistance to heat and acids Light oxidation and tendency toward embrittlement at high temperatures in air Molybdenum 2100 (3812) Good mechanical resistance to inert, reducing and vacuum conditions, resistant to metal vapors at high temperatures Reacts with Carbon in air and oxidizing gases Cast iron 700 (1292) Babbitt, Lead, Aluminum, Zinc melts Sulphur containing atmospheres must be avoided Metal ceramic thermowells 1.4765 Kanthal 1300 (2372) Good resistance to high temperature oxidation Tends toward embrittlement through recrystallization Kanthal Super (MoSi2) 1700 (3092) Resistance to abrasion, thermal shock, surface vitrifies, chemical resistant, well suited for waste incinerators and fluidized bed ovens Brittle at lower temperatures, ductile above 1400 °C (2552 °F) UCAR LT1 (CrAI2O2 77/23) 1400 (2552) Resistant to abrasion, thermal shock, oxidation, recommended for iron and non-ferrous metal smelting, cement kilns, resistant Sulphur compounds and acids 600 (1112) Corrosive applications in the Impact and bend dew point range for smokestack susceptible gases Coated thermowells 1.0305 enameled 268 Application conditions for thermowell materials Material Max. Temp. no pressure °C (°F) Advantages Disadvantages 1.0305 Glass coated 450 (842) Good oxidation and gas protection Thermal shock susceptible 1.0305 Teflon coated 200 (392) Applications in concentrated hydrochloric, sulphuric and nitric acids Ceramic thermowells AI2O3 80% (C530) 1500 (2732) Temperature change resistant, applications in industrial ovens Fine porosity, not gas tight, shock susceptible AI2O3 60% (C610) 1600 (2912) Average temperature change resistance, gas tight, high fire resistance, applications in industrial ovens Lower purity, shock susceptible AI2O3 99% (C799) 1800 (3272) Gas tight, fire resistant, applications in steel, scoriaceous and glass smelting AI2O3 99.7% (AL23) 1950 (3542) Fine grain, absolutely gas tight, high purity and strength at high temperatures, resistant to hydrofluoric acid, alkalis, metal oxide vapors AI2O3 99.7% (AL24) 1950 (3542) Porous, thermal shock resistant, high temperature strength; waste incinerators and fluidized bed ovens Recrystallized SiC 99% 1600 (2912) Good resistance to acids and alkalis, Applications in neutral atmospheres to 1500 °C (2732 °F); applications in nonferrous metal smelting Self-bound SiC 99% 1350 (2462) Minimum porosity, good resistance to thermal shock, corrosion, abrasion and high temperatures; recommended for applications for oxidizing and reducing atmospheres to 1500 °C (2732 °F) SiSiC (Protect, Silit SK) 1320 (2408) Gas tight, high thermal shock resistance, hard, abrasion resistant; recommended for applications for regenerative air heaters, coal pulverizers, smokestack gases, Zinc, Tin and lead smelting Average thermal shock resistance Porous Average deflections at higher temperatures, not for AI, Cu, Ni, Fe smelting 269 Application conditions for thermowell materials Material Max. Temp. no pressure °C (°F) Advantages Disadvantages SiC62 (TCS) 1100 (2012) High thermal shock resistance, Porous hard, abrasion resistant; recommended for applications for cement kilns, waste incinerators, Zinc, Copper, Aluminum, brass and bronze smelting Si3N4 (Ekatherm) 1000 (1832) Thermal shock resistant, not wetted during smelting, recommended for brass and bronze smelting Shock susceptible Si3N4+AI2O3 (Syalon) 1300 (2372) Thermal shock resistant, recommended for Copper and Aluminum smelting Graphite Oxygen free Copper, brass and High oxidation in air Aluminum smelting 270 1250 (2282) 11 Appendix 2 Materials, Resistance Table The selection of the materials to be used for the temperature sensor is a component of the selection process. Of primary interest are the materials which will be in contact with the medium whose temperature is to be measured. The ambient atmospheres may not be neglected, in which, the humidity is usually the most common factor. In general, the user knows the medium he wants to measure well enough that the material selection is routine. The following table can be used as an aid for the material selection. The specifications are taken from manufacturer’s corrosion resistance lists. A guarantee for the completeness and correctness cannot be assumed. Additional information is available from our application engineers. L + 50 80 (176) + + + + + + + + + - - + + + Acetic anhydride L + 100 20 (68) Acetone L - 100 40 (104) + + + + + + + + + - - + + + - - - - + + Acetylene G - 100 20 (68) Alum. chloride solution L + 30 70 (158) - - - - + - - + + + + + + + + + Alum. chloride solution L + 80 70 (158) - - - - + - - + + + + + + + Alum. sulfate solution L + 20 50 (122) - - - + - + + + + + + + + + + Alum. sulfate solution L + 50 50 (122) - - - + - + + + + - - + + + + Ammonia G - 100 50 (122) + + + + + + + - + - - + + + + - - - + + Ammonia solution L + Aniline L - 100 25 (77) Argon G - 100 100 (212) + + + + + + + + + + + + + + + + + + + + Beer L + Benzine L - 100 20 (68) Benzol L - 100 50 (122) + + + + + + + + + - - + + - - - - + + Blood L + + + + + + Brine L + Bromine Butane G - 100 50 (122) + + + + + + + + + + + - + + - - + + Butyl acetate L + + + 1.4301 (3304) 1.4539 1.4541 (321) 1.4571 (316Ti) Hastelloy B Hastelloy C Titanium Tantalum Platinum Hard Rubber Soft Rubber PFA PTFE EPDM Buna N Viton A PVDF PVC Glass AI2O3 Acetic acid Temperature °C (°F) Concentration (%) Non-Metals Gas/Liquid Electrical conductivity Metals + + + + + + + + + + + + + + + + + + + + + - + + + + + + + + + + + + 25 50 (122) + + + + + + + - + - - + + + + 10 (50) + + + + - + + + + - - + + + + + + + + + + + + + + + + + + + + + + - - + + - + + + + + + - + + + + + + + - + + + + + + + + + + + + + + 20 (68) - - - - - + - + + + + + - + + + + L - 100 20 (68) - - - - - + - + + + + - + + 100 50 (122) + + + + + + + + + + - + - + + 271 Non-Metals 1.4301 (3304) 1.4539 1.4541 (321) 1.4571 (316Ti) Hastelloy B Hastelloy C Titanium Tantalum Platinum Hard Rubber Soft Rubber PFA PTFE EPDM Buna N Viton A PVDF PVC Glass AI2O3 Temperature °C (°F) Concentration (%) Gas/Liquid Electrical conductivity Metals Butyl alcohol L - 100 20 (68) + + + + + + + + + + + + + + + + Butylene G - 100 20 (68) + + + + + + + + + + + + + + + + + Calcium chloride soln. L + 100 20 (68) + Calcium hydroxide soln. L + + + + + + + + + + + + + + + + + + 50 50 (122) + + + + + + + - - + + + + + + + + + Calcium hypochloride sol L + 20 50 (122) - - - - - + + + + Caprolactam L - 50 50 (122) Carbolic acid L - 90 50 (122) - + + + + + + + + - - + + - - - + - + + Carbon dioxide G - 100 50 (122) + + + + Carbon tetrachloride L - 100 50 (122) + + + + + + + + Carbonic acid L + 50 (122) + + + + + + + + + + + + + + + + + - + + Carboxylic acid, diluted L - 50 (122) Chlorine dioxide, dry G - 100 20 (68) + Chlorine hydrogen G - 100 20 (68) Chlorine water L + 100 20 (68) Chlorine, damp Chlorine, dry + + + + + + + + + + + - + + + + + + + + + + + + + + + + + - - + + + - + + - + + + + + + + + + + + + + - + + + + - - + + + + + - + + + + + + + - - + + + + + + + - - - + + - - + + + + + - + + G - 100 20 (68) - + - - - + + - - + + - + + + + + L - 100 20 (68) + + + + - + + + - - + + - + + - + + Chlorine, dry G - 100 20 (68) + + + + - + + + + + + + Citric acid L + 60 50 (122) Copper chloride soln L + 50 20 (68) Copper sulfate solution L + 50 80 (176) + + + + - + + + + + - + + + + + + - + + Copper sulfate solution L + 100 80 (176) + + + + - + + + + + - + + + + + + - + + Deionized water L - Diesel L - 100 50 (122) + + + + + + + + + - - + + - + + - + + Ethane G - 100 50 (122) + + + + + + + + + + + + + - + - - + + Ethanol L - Ethyl acetate L - 100 50 (122) + + + + + + + + + - - + + - - + - Ethyl alcohol L - 100 78 (172) + + + + + + + + + + + + + + - + + + - + + - + + + - - - + - + + + + + + + + + + - + + + + + + + + + + + + + + + + - - + + + + + + + + + 96 50 (122) + + + + + + + + + + + + + + + + + + + + + - + + Ethyl ether L - 100 20 (68) + + + + + + + + + - - + + - + + - + + Ethylene G - 100 50 (122) + + + + + + + + + + + + + - + + + + + Ethylene chloride L - 100 50 (122) - + - + + + + + + - - + + - + - - + + Ethylene glycol L + 100 50 (122) + + + + + + + + + - - + + + + + Fatty acid L - 100 50 (122) + + + + + + + + + - - + + Fluorine G - 100 20 (68) 272 + + + + - + - + + - + + + + + + - - L + 40 50 (122) + + + + + + + + + - - + + - Formic acid L + 100 80 (176) - + - + - + - + + - - + + - + Gelatin L + Glycerine L - 100 100 (212) + + + + Glycol L - 100 50 (122) 1.4301 (3304) 1.4539 1.4541 (321) 1.4571 (316Ti) Hastelloy B Hastelloy C Titanium Tantalum Platinum Hard Rubber Soft Rubber PFA PTFE EPDM Buna N Viton A PVDF PVC Glass AI2O3 Formaldehyde solution Temperature °C (°F) Concentration (%) Non-Metals Gas/Liquid Electrical conductivity Metals + + + + + + - + + 50 (122) + + + + + + + + + + + + + + + + + + + + + + + + + - + + - + + + + + + + - - + + + + + + + + + Heating oil L - 100 80 (176) + + + + Helium G - 100 80 (176) + + + + + + + + Heptane L - 100 50 (122) + + + + + + + + - - + + - - + + - + + Hexane L - 100 50 (122) + + + + + + + + Hydrazine solution L + 25 20 (68) Hydrobromic acid L + 48 50 (122) - - - - + - - + + + + + + - Hydrochloric acid L + 10 50 (122) - - - - + - + + + + - + + - - + + + + + Hydrochloric acid L + 37 20 (68) Hydrocyanic acid L + 100 20 (68) + + + + + + + + + - - + + Hydrofluoric acid L + 40 20 (68) - - - - - + - - + + - + + - - - + + - - Hydrofluoric acid L + 70 20 (68) - - - - - + - - + - - + + - - - + - - - Hydrogen G - 100 50 (122) + + + + + + Hydrogen peroxide soln. L + 40 20 (68) + + + + - + - + + - + + + + + + - + + + + - + + - + + + - - + + + - + + - + + + + - - - - + + - + + + - + + - - + + + + + + + + + + + + + + + + + + + + + + + + + - + - - - + + + + + - + Hydrogen sulphide dry. G - 100 20 (68) + + + + - + + + + + + + + + Iron-III chloride soln. L + 3 20 (68) - + - - - + + + + Iron-III chloride soln. L + 10 20 (68) - - - - - + + + + + - + + + + + + + + + Iron-III sulfate soln. L + 10 20 (68) + + + + + + + + + + + + + + + + + + + + + + + + + - + + + + + + + + + + + Kerosine L - 100 20 (68) Krypton G - 100 50 (122) + + + + + + + + + + + + + - + + + + - - + + Magnesium chloride soln. L + 50 20 (68) Magnesium sulfate soln. L + 20 50 (122) + + + + + - - - - - + + + + + + + + + + + + + + + + Malic acid L + 50 50 (122) + + + + + + + + + + + + + + Methane G - 100 50 (122) + + + + + + + + + + + + + - + + - - + + Methyl alcohol L - 100 50 (122) + + + + + + + + + + + + + + + - + - + + Methyl benzol = Toluol L - 100 50 (122) + + + + + + Methylene chloride G - 100 20 (68) Mono chlorine acetic acid L + 70 50 (122) + + + + + + + + + + + + + + + + + + - - + + - - + + - + + + + + + + + + + + - - + + - - - - - + + + + + + + + - - + + + - - - + + 273 Non-Metals 1.4301 (3304) 1.4539 1.4541 (321) 1.4571 (316Ti) Hastelloy B Hastelloy C Titanium Tantalum Platinum Hard Rubber Soft Rubber PFA PTFE EPDM Buna N Viton A PVDF PVC Glass AI2O3 Temperature °C (°F) Concentration (%) Gas/Liquid Electrical conductivity Metals Natural gas, dry G - 100 40 (104) + + + + + + + + + - - + + - + Neon G - 100 100 (212) + + + + + + + + + Nitric acid L + 20 40 (104) + + + + - + + + + - - + + - - - + + + + Nitric acid L + 70 50 (122) - + + + - - + + + - - + + - - - + - + + Nitrogen G - 100 50 (122) + + + + + + + + + Oleum L + 10 50 (122) - - - - + - - - + - - + - - + - - + + Oleum L + 20 20 (68) + - - + - - + + Olive oil L - Oxalic acid solution L + Oxygen G - 100 50 (122) + + + + + + Ozone G - Perchloroethylene L - 100 50 (122) + + + + + + + + + - - + + - - + + - + + Petroleum L - 100 20 (68) Phenol L - Phosgene L - 100 20 (68) Phosphoric acid L + 30 50 (122) - + - + + + - + + - - + + + - + + - + + Phosphoric acid L + 80 20 (68) Photo emulsion L + 20 (68) + + + + + + + + Phthalic acid anhydride L - 20 (68) - - - - + + + + + + - + + - + + + + + Potassium chloride soln. L + 30 20 (68) - - - + + + + + + + + + + + + + + + + + Potassium hydroxide sol L + 50 20 (68) + + + + + + - - + Potassium permang. L. L + 50 20 (68) + + + + Potassium sulfate soln L + 20 50 (122) + + + + + Propane G - 100 50 (122) + + + + + + Sea water L + + + - - - - + - - + + - - + + + - + + 10 50 (122) - + - + + + - + + + - + + + + + + + + + + + + + + - - + + 50 (122) + + + + + + + + + + - + + 10 20 (68) + + + + + + + + + - + + + + + + - - + + + + + + - - + + + - + + + + + + + + + + + + - - + + - + + + + + + 90 50 (122) - + + + + + + + + - - + + - - - + - + + + + + + + + + + + - - + + + - - + + - + - + + + - + + + + + + - - + + + + + + + + + + + + + - - + + + + + - + + + + + + + - + + + + + + + + + + - - + + - - + - - + + 50 (122) - + - - - + + + + + + + + + + + + - + + Sodium bicarbonate soln. L + 20 50 (122) Sodium bisulfate soln. L + 10 50 (122) - - - + + + + + + + + + + + + + + + + Sodium bisulfate soln. L + 50 50 (122) + + + + + Sodium carbonate soln. L + 50 50 (122) - - - - + + + + + + + + + + + + Sodium chloride soln. L + 10 20 (68) - + - - - + + + + - - + + + + + + + + + Sodium chloride soln. L + 20 20 (68) - - - - - + + + + - - + + + + + + + + + Sodium hydroxide soln. L + 20 50 (122) + + + + + + + - + - + + + - - + + - + Sodium hydroxide soln. L + 50 50 (122) + + + + + + - - + + + + - - - + + - - 274 + + + + + + + + + + + + + + + + + + + + + + + + + + + + Non-Metals 1.4301 (3304) 1.4539 1.4541 (321) 1.4571 (316Ti) Hastelloy B Hastelloy C Titanium Tantalum Platinum Hard Rubber Soft Rubber PFA PTFE EPDM Buna N Viton A PVDF PVC Glass AI2O3 Temperature °C (°F) Concentration (%) Gas/Liquid Electrical conductivity Metals Sodium hypo chloride sol L + 20 50 (122) - - - - + + - + - - + + + + + - + + Sodium nitrate solution L + 30 50 (122) + + + + + + + + + + + + + + + - + + Sodium silicate solution L + 30 50 (122) + + + + + + + + + + + + + + + + + + Sodium sulfate solution L + 20 50 (122) + + + + + + + + + + + + + + + + - + + Sodium vanadate soln. L + 10 50 (122) + + + + + + Spin bath L + Sulphur dioxide, dry G - 100 50 (122) + + + + - + + + + + + + + + + - + + Sulphuric acid L + 10 50 (122) - + - - + + - + + + + + + + + + + + + Sulphuric acid L + 50 20 (68) - + - - + + - + + + + + + - + + - + + Sulphuric acid L + 96 20 (68) - + - + + + - + + - - + + - + + - + + Sulphurous acid L + 10 20 (68) + + - + - + + + + Tannic acid L + 50 50 (122) + + Tartaric acid L + 20 50 (122) - - - - + + + + Toluol L - 100 50 (122) + + + + + + Trichlorethylene L - 100 50 (122) + + + + + + + + + - - + + - - + + - + + Tricresyl phosphate L Urea L + Vinyl acetate L 100 20 (68) Vinyl chloride L 100 20 (68) Wort (beer) L + Xylene L - 100 50 (122) + + + + + + Yeast L + 20 (68) Zinc chloride solution L + 60 20 (68) 50 (122) + + + + + + + + - - + + + 5 (41) + + + + + + + + + + + + + - + + + + + + + - - + + - - + + - + + - - + + + - - - + + + + + + + + + + + + - + + + - + + + - + + + + + + + + - 100 50 (122) + + + + + + 30 50 (122) - - + + - - - + + + + + - - + + + + + + + + + + + + + + - - + + - + + + + - + + + + + - + - + + + + + + + + + + + + + + + + + + - - - - + + + + + + + + + + + + + + + + + + + Symbols in resistance table: + means usable material - means unsuitable material blank cells indicate unknown resistance 275 12 Bibliography W.W. Wendlandt Thermochimica acta Volume 73, Amsterdam, 1984 Nicholas, White Traceable Temperatures J. Wiley, Sussex, 1994 Asimov Exakte Geheimnisse unserer Welt Droemer Knaur, 1984 (Exact Secrets of Our World) Paul H. Dyke Thermoelectric Thermometry Leeds & Northrup Company, 1955 F. Henning Temperaturmessung J.A. Barth Verlag, Leipzig, 1951 (Temperature Measurements) F. Lieneweg Temperaturmessung akademische Verlagsgesellschaft, Leipzig, 1950 (Temperature Measurements) M.K. Juchheim Elektrische Temperaturmessung 5. Auflage, Fulda, 1996 (Electrical Temperature Measurements) Körtvélyessy Thermoelement Praxis 2. Ausgabe, Vulkan-Verlag, Essen, 1987 (Thermocouple Practice) J. W. Murdock Power Test Code Thermometer Wells Journal of Engineering Power, Oct. 1959 AD-Merkblätter, Taschenbuch-Ausgabe 1998 Carl Heymanns Verlag, Beuth Verlag, 1998 (AD Data Sheets, Pocket Book edition) TRD Technische Regeln für Dampfkessel, Taschenbuch-Ausgabe 1997 Carl Heymanns Verlag, Beuth Verlag, 1998 (TRD Technical Regulations for Steam Boilers Pocket Book Edition) F. Lieneweg (Hrsg./Editor) 276 Handbuch der technischen Temperaturmessung, Abschnitt 6.3 Die mechanische Beanspruchung von Thermometern (Autor: P. Dittrich) Vieweg Verlag, 1976) (Handbook for Temperature Measurements, Chapter 6.3 The Mechanical Forces on Thermometers) O. Uhrig Beitrag zur Berechnung und Gestaltung von hochbeanspruchten Schutzrohren. VDI-Fortschrittsberichte, VDI-Verlag, 1981 (Article for Calculations and Designs for Highly Stressed Thermowells) Hütte Die Grundlagen der Ingenieurwissenschaften Springer-Verlag, 1996 (Basics for Engineering Sciences) S. Schwaigerer Festigkeitsberechnung im Dampfkessel-, Behälter- und Rohrleitungsbau. Springer-Verlag, 1978 (Manufacturing Calculations for Steam Boilers, Tanks and Pipeline Designs Temperatursensoren – Prinzipien und Applikationen Expert Verlag, ISBN 3-8169-1261, 1995 (Temperature Sensors – Principles and Applications) Temperaturmessung in der Technik Expert Verlag, ISBN 3-8169-0200-6 (Temperature Measurements in Technology) Temperatursensoren Firmenpublication, Hartmann & Braun, 8123 D/E (Temperature Sensors - Company Publication) Metall Forschung und Entwicklung Degussa, Frankfurt 1991 (Metal Research and Development) Harald Jacques Industrielle Messtechnik mit Pt-Schichtmesswiderständen (Industrial Measurements with Pt Film Resistors) Joachim Scholz Temperatusensoren für den industriellen Einsatz Degussa-Sonderdruck Nr.8206 aus industrie-elektik + elektronik 29.Jahrgang 1984, Nr.11 Dr. Alfred Hüthig-Verlag / Heidelberg (Temperature Sensors for Industrial Applications) Dr. Harald Jacques Hochstabile Temperatursensoren für vielfältige Anwendungen Degussa-Sonderdruck Nr.8215 (High Stability Temperature Sensors for Multiple Applications) VDI/VDE 2600: Metrologie (Messtechnik), Blatt 1 bis 6 (Sheets 1 to 6) (Metrology) DIN IEC 381: Analoge Signale für Regel- und Steueranlagen (Analog Signals for Control Systems) 277 J.Sturm, B.Winkler MSR in der Chemischen Technik, Band 1 Springer Verlag (Measuring and Control in Chemical Technology, Vol. 1) Bell System Technical Reference: PUB 41212 Data Sets 202S and 202T HART-Nutzerorganisation HART Feld-Kommunikations-Protokoll, Stand 09/92 (HART-User Organization Field Communication Protocol) VDI Berichte 982, Temperatur 92 VDI-Verlag, Stand 1992 (VDI Reports 982, Temperature 92) Mess-, Analysen- und Prozessleittechnik DECHEMA e.V/ACHEMA, Stand 1994 (Measuring, Analyzing and Process Control Technology) PROFIBUS, Technische Kurzbeschreibung PNO, Stand 97 (PROFIBUS, Condensed Technical Description) Fieldbus FOUNDATION, Application Guide Fieldbus FOUNDATION AG-163 Rev. 1.0 DKD-3 Angabe der Messunsicherheiten bei Kalibrierungen Verlag für neue Wissenschaften GmbH, Bremerhaven (Tolerance Specifications for Calibrations) DKD-3-E1 Angabe der Messunsicherheit bei Kalibrierungen, Beispiele Verlag für neue Wissenschaften GmbH, Bremerhaven (Specifications for Measuring Uncertainties for Calibrations, Examples) Dr. W. Kessel Messunsicherheitsanalyse – fundamentaler Bestandteil der Prüfmittelüberwachung (Measurement Uncertainty Analysis, Fundamental Component of Test Equipment Monitoring) Franz Adunka Messunsicherheiten: Theorie und Praxis Vulkan Verlag, Essen, 1998 (Measurement Uncertainities, Theory and Practice) Bernhard, F. (Hrsg..Editor): Handbuch der technischen Temperaturmessung, Springer-Verlag Berlin (Handbook for Temperature Measurements) VDI-Wärmeatlas, 8. Auflage, Springer-Verlag Berlin, 1998 (VDI-Heat Atlas, 8th Edition) 278 Weichert, Lother Temperaturmessung in der Technik VAE Kontakt & Studium Band 9; Expert Verlag (Temperature Measurements in Technology) H. E. Bennett Noble Metal Thermocouples Johnson, Matthey & Co, 1958 Horst Böhm Einführung in die Metallkunde BI Hochschultaschenbücher (Introduction to Metal Science) Dr. A. Schulz Metallische Werkstoffe für Thermoelemente N.E.M.-Verlag Berlin, Heft 10 (Metal Materials for Thermocouples) PTB-Texte, Band 7, 20 Jahre Deutscher Kalibrierdienst, Wirtschaftsverlag NW, 1998 (PTB Texts, Vol. 7, 20 Years German Calibration Service) Ch. Diedrich PROFIBUS PA Verlag Oldenbourg, ISBN 3-8350-3056-3 P. Westerfeld Die Entwicklung der betrieblichen Temperaturmesstechnik in der Prozessautomatisierung in: Elektrotechnik – Signale, Aufbruch, Perspektiven; Geschichte der Elektrotechnik 7 VDE-Verlag Offenbach, 1988 (The Development of Industrial Temperature Measurement Technology in Process Automation) Optris GmbH Basics of Non-contact Infrared Temperature Measurement, 2006 279 13 Basic Values for Thermocouples and Resistance Thermometers Based on the International Temperature Scale ITS-90 According to EN 60584/IEC 584: Thermocouples Types T, E, J, K, N, S, R, B According to EN 60751/IEC 751: Resistance Thermometers Pt100 Based on the Temperature Scale IPTS-68 According to DIN 43710 (repealed since 1994. No new editions): Thermocouples Types U and L According to DIN 43760: Resistance Thermometers Ni100 Resistance thermometers with special measurement resistors Pt50, Pt200, Pt500, Pt1000 The standardized measurement resistor Pt100 according to EN 60751/IEC 751 has a nominal resistance of 100 Ω at 0 °C (32 °F). Based on these standards, measurement resistors with fractional or whole number multiples of these nominal resistance values are commercially available. Based on the statements from the manufacturer the following conversion factors apply. Designation Nominal Resistance 0 °C (32 °F) Factor Resistance Value Pt50 50 Ω 0.5 0.5 x Pt100 EN 60751 / IEC 751 Pt200 200 Ω 2 2 x Pt100 EN 60751 / IEC 751 Pt500 500 Ω 5 5 x Pt100 EN 60751 / IEC 751 Pt1000 1000 Ω 10 10 x Pt100 EN 60751 / IEC 751 For Ni-resistance thermometers, a similar procedure applies. 280 °C Type T Type E Type J Type K Type N Type S Type R Type B Type U Type L Pt100 Ni100 FeCuNi mV NiCrNi mV NiCrSi- Pt10Rh- Pt13Rh- Pt30RhNiSi Pt Pt Pt6Rh mV mV mV mV CuCuNi mV FeCuNi mV °F t90 CuCuNi mV NiCrCuNi mV -270 -269 -268 -267 -266 -6.258 -6.256 -6.255 -6.253 -6.251 -9.835 -9.833 -9.831 -9.828 -9.825 -6.458 -6.457 -6.456 -6.455 -6.453 -4.345 -4.345 -4.344 -4.344 -4.343 -454.0 -452.2 -450.4 -448.6 -446.8 -265 -264 -263 -262 -261 -6.248 -6.245 -6.242 -6.239 -6.236 -9.821 -9.817 -9.813 -9.808 -9.802 -6.452 -6.450 -6.448 -6.446 -6.444 -4.342 -4.341 -4.340 -4.339 -4.337 -445.0 -443.2 -441.4 -439.6 -437.8 -260 -259 -258 -257 -256 -6.232 -6.228 -6.223 -6.219 -6.214 -9.797 -9.790 -9.784 -9.777 -9.770 -6.441 -6.438 -6.435 -6.432 -6.429 -4.336 -4.334 -4.332 -4.330 -4.328 -436.0 -434.2 -432.4 -430.6 -428.8 -255 -254 -253 -252 -251 -6.209 -6.204 -6.198 -6.193 -6.187 -9.762 -9.754 -9.746 -9.737 -9.728 -6.425 -6.421 -6.417 -6.413 -6.408 -4.326 -4.324 -4.321 -4.319 -4.316 -427.0 -425.2 -423.4 -421.6 -419.8 -250 -249 -248 -247 -246 -6.180 -6.174 -6.167 -6.160 -6.153 -9.718 -9.709 -9.698 -9.688 -9.677 -6.404 -6.399 -6.393 -6.388 -6.382 -4.313 -4.310 -4.307 -4.304 -4.300 -418.0 -416.2 -414.4 -412.6 -410.8 -245 -244 -243 -242 -241 -6.146 -6.138 -6.130 -6.122 -6.114 -9.666 -9.654 -9.642 -9.630 -9.617 -6.377 -6.370 -6.364 -6.358 -6.351 -4.297 -4.293 -4.289 -4.285 -4.281 -409.0 -407.2 -405.4 -403.6 -401.8 -240 -239 -238 -237 -236 -6.105 -6.096 -6.087 -6.078 -6.068 -9.604 -9.591 -9.577 -9.563 -9.548 -6.344 -6.337 -6.329 -6.322 -6.314 -4.277 -4.273 -4.268 -4.263 -4.258 -400.0 -398.2 -396.4 -394.6 -392.8 -235 -234 -233 -232 -231 -6.059 -6.049 -6.038 -6.028 -6.017 -9.534 -9.519 -9.503 -9.487 -9.471 -6.306 -6.297 -6.289 -6.280 -6.271 -4.254 -4.248 -4.243 -4.238 -4.232 -391.0 -389.2 -387.4 -385.6 -383.8 -230 -229 -228 -227 -226 -6.007 -5.996 -5.985 -5.973 -5.962 -9.455 -9.438 -9.421 -9.404 -9.386 -6.262 -6.252 -6.243 -6.233 -6.223 -4.226 -4.221 -4.215 -4.209 -4.202 -382.0 -380.2 -378.4 -376.6 -374.8 -225 -224 -223 -222 -221 -5.950 -5.938 -5.926 -5.914 -5.901 -9.368 -9.350 -9.331 -9.313 -9.293 -6.213 -6.202 -6.192 -6.181 -6.170 -4.196 -4.189 -4.183 -4.176 -4.169 -373.0 -371.2 -369.4 -367.6 -365.8 Ω Ω t90 281 °C Type T Type E Type J Type K Type N Type S Type R Type B Type U Type L Pt100 Ni100 t90 NiCrCuNi mV -220 -219 -218 -217 -216 -5.888 -5.876 -5.863 -5.850 -5.836 -9.274 -9.254 -9.234 -9.214 -9.193 -6.158 -6.147 -6.135 -6.123 -6.111 -4.162 -4.154 -4.147 -4.140 -4.132 -364.0 -362.2 -360.4 -358.6 -356.8 -215 -214 -213 -212 -211 -5.823 -5.809 -5.795 -5.782 -5.767 -9.172 -9.151 -9.129 -9.107 -9.085 -6.099 -6.087 -6.074 -6.061 -6.048 -4.124 -4.116 -4.108 -4.100 -4.091 -355.0 -353.2 -351.4 -349.6 -347.8 -210 -209 -208 -207 -206 -5.753 -5.739 -5.724 -5.710 -5.695 -9.063 -9.040 -9.017 -8.994 -8.971 -8.095 -8.076 -8.057 -8.037 -8.017 -6.035 -6.021 -6.007 -5.994 -5.980 -4.083 -4.074 -4.066 -4.057 -4.048 -346.0 -344.2 -342.4 -340.6 -338.8 -205 -204 -203 -202 -201 -5.680 -5.665 -5.650 -5.634 -5.619 -8.947 -8.923 -8.899 -8.874 -8.850 -7.996 -7.976 -7.955 -7.934 -7.912 -5.965 -5.951 -5.936 -5.922 -5.907 -4.038 -4.029 -4.020 -4.010 -4.000 -337.0 -335.2 -333.4 -331.6 -329.8 -200 -199 -198 -197 -196 -5.603 -5.587 -5.571 -5.555 -5.539 -8.825 -8.799 -8.774 -8.748 -8.722 -7.890 -7.868 -7.846 -7.824 -7.801 -5.891 -5.876 -5.861 -5.845 -5.829 -3.990 -3.980 -3.970 -3.960 -3.950 -5.70 -5.68 -5.66 -5.64 -5.62 -8.15 -8.12 -8.09 -8.06 -8.03 18.52 18.95 19.38 19.82 20.25 -328.0 -326.2 -324.4 -322.6 -320.8 -195 -194 -193 -192 -191 -5.523 -5.506 -5.489 -5.473 -5.456 -8.696 -8.669 -8.643 -8.616 -8.588 -7.778 -7.755 -7.731 -7.707 -7.683 -5.813 -5.797 -5.780 -5.763 -5.747 -3.939 -3.928 -3.918 -3.907 -3.896 -5.60 -5.59 -5.57 -5.55 -5.53 -8.00 -7.98 -7.95 -7.92 -7.89 20.68 21.11 21.54 21.97 22.40 -319.0 -317.2 -315.4 -313.6 -311.8 -190 -189 -188 -187 -186 -5.439 -5.421 -5.404 -5.387 -5.369 -8.561 -8.533 -8.505 -8.477 -8.449 -7.659 -7.634 -7.610 -7.585 -7.559 -5.730 -5.713 -5.695 -5.678 -5.660 -3.884 -3.873 -3.862 -3.850 -3.838 -5.51 -5.49 -5.47 -5.45 -5.43 -7.86 -7.83 -7.80 -7.77 -7.74 22.83 23.25 23.68 24.11 24.54 -310.0 -308.2 -306.4 -304.6 -302.8 -185 -184 -183 -182 -181 -5.351 -5.334 -5.316 -5.297 -5.279 -8.420 -8.391 -8.362 -8.333 -8.303 -7.534 -7.508 -7.482 -7.456 -7.429 -5.642 -5.624 -5.606 -5.588 -5.569 -3.827 -3.815 -3.803 -3.790 -3.778 -5.41 -5.40 -5.38 -5.36 -5.34 -7.71 -7.68 -7.65 -7.62 -7.59 24.97 25.39 25.82 26.25 26.67 -301.0 -299.2 -297.4 -295.6 -293.8 -180 -179 -178 -177 -176 -5.261 -5.242 -5.224 -5.205 -5.186 -8.273 -8.243 -8.213 -8.183 -8.152 -7.403 -7.376 -7.348 -7.321 -7.293 -5.550 -5.531 -5.512 -5.493 -5.474 -3.766 -3.753 -3.740 -3.728 -3.715 -5.32 -5.30 -5.28 -5.26 -5.24 -7.56 -7.53 -7.50 -7.47 -7.44 27.10 27.52 27.95 28.37 28.80 -292.0 -290.2 -288.4 -286.6 -284.8 -175 -174 -173 -172 -171 -5.167 -5.148 -5.128 -5.109 -5.089 -8.121 -8.090 -8.059 -8.027 -7.995 -7.265 -7.237 -7.209 -7.181 -7.152 -5.454 -5.435 -5.415 -5.395 -5.374 -3.702 -3.688 -3.675 -3.662 -3.648 -5.22 -5.20 -5.18 -5.16 -5.14 -7.40 -7.37 -7.34 -7.31 -7.28 29.22 29.64 30.07 30.49 30.91 -283.0 -281.2 -279.4 -277.6 -275.8 282 FeCuNi mV NiCrNi mV NiCrSi- Pt10Rh- Pt13Rh- Pt30RhNiSi Pt Pt Pt6Rh mV mV mV mV CuCuNi mV FeCuNi mV °F CuCuNi mV Ω Ω t90 °C Type T Type E Type J Type K Type N Type S Type R Type B Type U Type L Pt100 Ni100 NiCrSi- Pt10Rh- Pt13Rh- Pt30RhNiSi Pt Pt Pt6Rh mV mV mV mV CuCuNi mV FeCuNi mV °F t90 CuCuNi mV NiCrCuNi mV FeCuNi mV NiCrNi mV -170 -169 -168 -167 -166 -5.070 -5.050 -5.030 -5.010 -4.989 -7.963 -7.931 -7.899 -7.866 -7.833 -7.123 -7.094 -7.064 -7.035 -7.005 -5.354 -5.333 -5.313 -5.292 -5.271 -3.634 -3.621 -3.607 -3.593 -3.578 -5.12 -5.10 -5.08 -5.06 -5.04 -7.25 -7.22 -7.19 -7.15 -7.12 31.34 31.76 32.18 32.60 33.02 -274.0 -272.2 -270.4 -268.6 -266.8 -165 -164 -163 -162 -161 -4.969 -4.949 -4.928 -4.907 -4.886 -7.800 -7.767 -7.733 -7.700 -7.666 -6.975 -6.944 -6.914 -6.883 -6.853 -5.250 -5.228 -5.207 -5.185 -5.163 -3.564 -3.550 -3.535 -3.521 -3.506 -5.02 -4.99 -4.97 -4.95 -4.93 -7.09 -7.06 -7.03 -6.99 -6.96 33.44 33.86 34.28 34.70 35.12 -265.0 -263.2 -261.4 -259.6 -257.8 -160 -159 -158 -157 -156 -4.865 -4.844 -4.823 -4.802 -4.780 -7.632 -7.597 -7.563 -7.528 -7.493 -6.821 -6.790 -6.759 -6.727 -6.695 -5.141 -5.119 -5.097 -5.074 -5.052 -3.491 -3.476 -3.461 -3.446 -3.431 -4.91 -4.89 -4.87 -4.84 -4.82 -6.93 -6.90 -6.86 -6.83 -6.80 35.54 35.96 36.38 36.80 37.22 -256.0 -254.2 -252.4 -250.6 -248.8 -155 -154 -153 -152 -151 -4.759 -4.737 -4.715 -4.693 -4.671 -7.458 -7.423 -7.387 -7.351 -7.315 -6.663 -6.631 -6.598 -6.566 -6.533 -5.029 -5.006 -4.983 -4.960 -4.936 -3.415 -3.400 -3.384 -3.368 -3.352 -4.80 -4.78 -4.76 -4.73 -4.71 -6.76 -6.73 -6.70 -6.66 -6.63 37.64 38.06 38.47 38.89 39.31 -247.0 -245.2 -243.4 -241.6 -239.8 -150 -149 -148 -147 -146 -4.648 -4.626 -4.604 -4.581 -4.558 -7.279 -7.243 -7.206 -7.170 -7.133 -6.500 -6.467 -6.433 -6.400 -6.366 -4.913 -4.889 -4.865 -4.841 -4.817 -3.336 -3.320 -3.304 -3.288 -3.271 -4.69 -4.67 -4.64 -4.62 -4.60 -6.60 -6.56 -6.53 -6.50 -6.46 39.72 40.14 40.56 40.97 41.39 -238.0 -236.2 -234.4 -232.6 -230.8 -145 -144 -143 -142 -141 -4.535 -4.512 -4.489 -4.466 -4.443 -7.096 -7.058 -7.021 -6.983 -6.945 -6.332 -6.298 -6.263 -6.229 -6.194 -4.793 -4.768 -4.744 -4.719 -4.694 -3.255 -3.238 -3.221 -3.205 -3.188 -4.58 -4.55 -4.53 -4.51 -4.48 -6.43 -6.39 -6.36 -6.33 -6.29 41.80 42.22 42.63 43.05 43.46 -229.0 -227.2 -225.4 -223.6 -221.8 -140 -139 -138 -137 -136 -4.419 -4.395 -4.372 -4.348 -4.324 -6.907 -6.869 -6.831 -6.792 -6.753 -6.159 -6.124 -6.089 -6.054 -6.018 -4.669 -4.644 -4.618 -4.593 -4.567 -3.171 -3.153 -3.136 -3.119 -3.101 -4.46 -4.43 -4.41 -4.38 -4.36 -6.26 -6.22 -6.19 -6.15 -6.11 43.88 44.29 44.70 45.12 45.53 -220.0 -218.2 -216.4 -214.6 -212.8 -135 -134 -133 -132 -131 -4.300 -4.275 -4.251 -4.226 -4.202 -6.714 -6.675 -6.636 -6.596 -6.556 -5.982 -5.946 -5.910 -5.874 -5.838 -4.542 -4.516 -4.490 -4.463 -4.437 -3.084 -3.066 -3.048 -3.030 -3.012 -4.33 -4.31 -4.28 -4.26 -4.23 -6.08 -6.04 -6.01 -5.97 -5.93 45.94 46.36 46.77 47.18 47.59 -211.0 -209.2 -207.4 -205.6 -203.8 -130 -129 -128 -127 -126 -4.177 -4.152 -4.127 -4.102 -4.077 -6.516 -6.476 -6.436 -6.396 -6.355 -5.801 -5.764 -5.727 -5.690 -5.653 -4.411 -4.384 -4.357 -4.330 -4.303 -2.994 -2.976 -2.958 -2.939 -2.921 -4.21 -4.18 -4.16 -4.13 -4.11 -5.90 -5.86 -5.82 -5.79 -5.75 48.01 48.42 48.83 49.24 49.65 -202.0 -200.2 -198.4 -196.6 -194.8 -125 -124 -123 -122 -121 -4.052 -4.026 -4.000 -3.975 -3.949 -6.314 -6.273 -6.232 -6.191 -6.149 -5.616 -5.578 -5.541 -5.503 -5.465 -4.276 -4.249 -4.221 -4.194 -4.166 -2.902 -2.883 -2.865 -2.846 -2.827 -4.08 -4.05 -4.03 -4.00 -3.98 -5.71 -5.68 -5.64 -5.60 -5.57 50.06 50.47 50.88 51.29 51.70 -193.0 -191.2 -189.4 -187.6 -185.8 Ω Ω t90 283 °C Type T Type E Type J Type K Type N Type S Type R Type B Type U Type L Pt100 Ni100 t90 NiCrCuNi mV FeCuNi mV NiCrNi mV -120 -119 -118 -117 -116 -3.923 -3.897 -3.871 -3.844 -3.818 -6.107 -6.065 -6.023 -5.981 -5.939 -5.426 -5.388 -5.350 -5.311 -5.272 -4.138 -4.110 -4.082 -4.054 -4.025 -2.808 -2.789 -2.769 -2.750 -2.730 -3.95 -3.92 -3.90 -3.87 -3.84 -5.53 -5.49 -5.45 -5.41 -5.38 52.11 52.52 52.93 53.34 53.75 -184.0 -182.2 -180.4 -178.6 -176.8 -115 -114 -113 -112 -111 -3.791 -3.765 -3.738 -3.711 -3.684 -5.896 -5.853 -5.810 -5.767 -5.724 -5.233 -5.194 -5.155 -5.116 -5.076 -3.997 -3.968 -3.939 -3.911 -3.882 -2.711 -2.691 -2.672 -2.652 -2.632 -3.81 -3.79 -3.76 -3.73 -3.71 -5.34 -5.30 -5.26 -5.22 -5.19 54.15 54.56 54.97 55.38 55.79 -175.0 -173.2 -171.4 -169.6 -167.8 -110 -109 -108 -107 -106 -3.657 -3.629 -3.602 -3.574 -3.547 -5.681 -5.637 -5.593 -5.549 -5.505 -5.037 -4.997 -4.957 -4.917 -4.877 -3.852 -3.823 -3.794 -3.764 -3.734 -2.612 -2.592 -2.571 -2.551 -2.531 -3.68 -3.65 -3.62 -3.60 -3.57 -5.15 -5.11 -5.07 -5.03 -4.99 56.19 56.60 57.01 57.41 57.82 -166.0 -164.2 -162.4 -160.6 -158.8 -105 -104 -103 -102 -101 -3.519 -3.491 -3.463 -3.435 -3.407 -5.461 -5.417 -5.372 -5.327 -5.282 -4.836 -4.796 -4.755 -4.714 -4.674 -3.705 -3.675 -3.645 -3.614 -3.584 -2.510 -2.490 -2.469 -2.448 -2.428 -3.54 -3.51 -3.48 -3.46 -3.43 -4.95 -4.91 -4.87 -4.83 -4.79 58.23 58.63 59.04 59.44 59.85 -157.0 -155.2 -153.4 -151.6 -149.8 -100 - 99 - 98 - 97 - 96 -3.379 -3.350 -3.322 -3.293 -3.264 -5.237 -5.192 -5.147 -5.101 -5.055 -4.633 -4.591 -4.550 -4.509 -4.467 -3.554 -3.523 -3.492 -3.462 -3.431 -2.407 -2.386 -2.365 -2.344 -2.322 -3.40 -3.37 -3.34 -3.31 -3.28 -4.75 -4.71 -4.66 -4.62 -4.58 60.26 60.66 61.07 61.47 61.88 -148.0 -146.2 -144.4 -142.6 -140.8 - 95 94 93 92 91 -3.235 -3.206 -3.177 -3.148 -3.118 -5.009 -4.963 -4.917 -4.871 -4.824 -4.425 -4.384 -4.342 -4.300 -4.257 -3.400 -3.368 -3.337 -3.306 -3.274 -2.301 -2.280 -2.258 -2.237 -2.215 -3.25 -3.23 -3.20 -3.17 -3.14 -4.54 -4.50 -4.45 -4.41 -4.37 62.28 62.68 63.09 63.49 63.90 -139.0 -137.2 -135.4 -133.6 -131.8 - 90 89 88 87 86 -3.089 -3.059 -3.030 -3.000 -2.970 -4.777 -4.731 -4.684 -4.636 -4.589 -4.215 -4.173 -4.130 -4.088 -4.045 -3.243 -3.211 -3.179 -3.147 -3.115 -2.193 -2.172 -2.150 -2.128 -2.106 -3.11 -3.08 -3.05 -3.02 -2.99 -4.33 -4.28 -4.24 -4.20 -4.15 64.30 64.70 65.11 65.51 65.91 -130.0 -128.2 -126.4 -124.6 -122.8 - 85 84 83 82 81 -2.940 -2.910 -2.879 -2.849 -2.818 -4.542 -4.494 -4.446 -4.398 -4.350 -4.002 -3.959 -3.916 -3.872 -3.829 -3.083 -3.050 -3.018 -2.986 -2.953 -2.084 -2.062 -2.039 -2.017 -1.995 -2.96 -2.93 -2.90 -2.87 -2.84 -4.11 -4.06 -4.02 -3.98 -3.93 66.31 66.72 67.12 67.52 67.92 -121.0 -119.2 -117.4 -115.6 -113.8 - 80 79 78 77 76 -2.788 -2.757 -2.726 -2.695 -2.664 -4.302 -4.254 -4.205 -4.156 -4.107 -3.786 -3.742 -3.698 -3.654 -3.610 -2.920 -2.887 -2.854 -2.821 -2.788 -1.972 -1.950 -1.927 -1.905 -1.882 -2.81 -2.78 -2.75 -2.72 -2.69 -3.89 -3.84 -3.80 -3.75 -3.71 68.33 68.73 69.13 69.53 69.93 -112.0 -110.2 -108.4 -106.6 -104.8 - 75 74 73 72 71 -2.633 -2.602 -2.571 -2.539 -2.507 -4.058 -4.009 -3.960 -3.911 -3.861 -3.566 -3.522 -3.478 -3.434 -3.389 -2.755 -2.721 -2.688 -2.654 -2.620 -1.859 -1.836 -1.813 -1.790 -1.767 -2.66 -2.62 -2.59 -2.56 -2.53 -3.66 -3.62 -3.57 -3.53 -3.48 70.33 70.73 71.13 71.53 71.93 -103.0 -101.2 -99.4 -97.6 -95.8 284 NiCrSi- Pt10Rh- Pt13Rh- Pt30RhNiSi Pt Pt Pt6Rh mV mV mV mV CuCuNi mV FeCuNi mV °F CuCuNi mV Ω Ω t90 °C Type T Type E Type J Type K Type N Type S Type R Type B Type U Type L Pt100 Ni100 NiCrSi- Pt10Rh- Pt13Rh- Pt30RhNiSi Pt Pt Pt6Rh mV mV mV mV CuCuNi mV FeCuNi mV °F t90 CuCuNi mV NiCrCuNi mV FeCuNi mV NiCrNi mV - 70 69 68 67 66 -2.476 -2.444 -2.412 -2.380 -2.348 -3.811 -3.761 -3.711 -3.661 -3.611 -3.344 -3.300 -3.255 -3.210 -3.165 -2.587 -2.553 -2.519 -2.485 -2.450 -1.744 -1.721 -1.698 -1.674 -1.651 -2.50 -2.47 -2.44 -2.40 -2.37 -3.44 -3.39 -3.35 -3.30 -3.25 72.33 72.73 73.13 73.53 73.93 -94.0 -92.2 -90.4 -88.6 -86.8 - 65 64 63 62 61 -2.316 -2.283 -2.251 -2.218 -2.186 -3.561 -3.510 -3.459 -3.408 -3.357 -3.120 -3.075 -3.029 -2.984 -2.938 -2.416 -2.382 -2.347 -2.312 -2.278 -1.627 -1.604 -1.580 -1.557 -1.533 -2.34 -2.31 -2.28 -2.24 -2.21 -3.21 -3.16 -3.12 -3.07 -3.02 74.33 74.73 75.13 75.53 75.93 -85.0 -83.2 -81.4 -79.6 -77.8 - 60 59 58 57 56 -2.153 -2.120 -2.087 -2.054 -2.021 -3.306 -3.255 -3.204 -3.152 -3.100 -2.893 -2.847 -2.801 -2.755 -2.709 -2.243 -2.208 -2.173 -2.138 -2.103 -1.509 -1.485 -1.462 -1.438 -1.414 -2.18 -2.15 -2.11 -2.08 -2.05 -2.98 -2.93 -2.88 -2.84 -2.79 76.33 76.73 77.12 77.52 77.92 69.5 70.0 70.5 70.9 71.4 -76.0 -74.2 -72.4 -70.6 -68.8 - 55 54 53 52 51 -1.987 -1.954 -1.920 -1.887 -1.853 -3.048 -2.996 -2.944 -2.892 -2.840 -2.663 -2.617 -2.571 -2.524 -2.478 -2.067 -2.032 -1.996 -1.961 -1.925 -1.390 -1.366 -1.341 -1.317 -1.293 -2.02 -1.98 -1.95 -1.92 -1.88 -2.74 -2.70 -2.65 -2.60 -2.56 78.32 78.72 79.11 79.51 79.91 71.9 72.3 72.8 73.3 73.8 -67.0 -65.2 -63.4 -61.6 -59.8 - 50 49 48 47 46 -1.819 -1.785 -1.751 -1.717 -1.683 -2.787 -2.735 -2.682 -2.629 -2.576 -2.431 -2.385 -2.338 -2.291 -2.244 -1.889 -1.854 -1.818 -1.782 -1.745 -1.269 -1.244 -1.220 -1.195 -1.171 -0.236 -0.232 -0.228 -0.224 -0.219 -0.226 -0.223 -0.219 -0.215 -0.211 -1.85 -1.81 -1.78 -1.74 -1.71 -2.51 -2.46 -2.41 -2.36 -2.32 80.31 80.70 81.10 81.50 81.89 74.3 74.7 75.2 75.7 76.2 -58.0 -56.2 -54.4 -52.6 -50.8 - 45 44 43 42 41 -1.648 -1.614 -1.579 -1.545 -1.510 -2.523 -2.469 -2.416 -2.362 -2.309 -2.197 -2.150 -2.103 -2.055 -2.008 -1.709 -1.673 -1.637 -1.600 -1.564 -1.146 -1.122 -1.097 -1.072 -1.048 -0.215 -0.211 -0.207 -0.203 -0.199 -0.208 -0.204 -0.200 -0.196 -0.192 -1.67 -1.64 -1.60 -1.57 -1.53 -2.27 -2.22 -2.17 -2.12 -2.08 82.29 82.69 83.08 83.48 83.87 76.7 77.2 77.7 78.1 78.6 -49.0 -47.2 -45.4 -43.6 -41.8 - 40 39 38 37 36 -1.475 -1.440 -1.405 -1.370 -1.335 -2.255 -2.201 -2.147 -2.093 -2.038 -1.961 -1.913 -1.865 -1.818 -1.770 -1.527 -1.490 -1.453 -1.417 -1.380 -1.023 -0.998 -0.973 -0.948 -0.923 -0.194 -0.190 -0.186 -0.181 -0.177 -0.188 -0.184 -0.180 -0.175 -0.171 -1.50 -1.46 -1.43 -1.39 -1.36 -2.03 -1.98 -1.93 -1.88 -1.83 84.27 84.67 85.06 85.46 85.85 79.1 79.6 80.1 80.6 81.1 -40.0 -38.2 -36.4 -34.6 -32.8 - 35 34 33 32 31 -1.299 -1.264 -1.228 -1.192 -1.157 -1.984 -1.929 -1.874 -1.820 -1.765 -1.722 -1.674 -1.626 -1.578 -1.530 -1.343 -1.305 -1.268 -1.231 -1.194 -0.898 -0.873 -0.848 -0.823 -0.798 -0.173 -0.168 -0.164 -0.159 -0.155 -0.167 -0.163 -0.158 -0.154 -0.150 -1.32 -1.28 -1.25 -1.21 -1.18 -1.78 -1.73 -1.68 -1.63 -1.58 86.25 86.64 87.04 87.43 87.83 81.6 82.1 82.6 83.1 83.6 -31.0 -29.2 -27.4 -25.6 -23.8 - 30 29 28 27 26 -1.121 -1.085 -1.049 -1.013 -0.976 -1.709 -1.654 -1.599 -1.543 -1.488 -1.482 -1.433 -1.385 -1.336 -1.288 -1.156 -1.119 -1.081 -1.043 -1.006 -0.772 -0.747 -0.722 -0.696 -0.671 -0.150 -0.146 -0.141 -0.136 -0.132 -0.145 -0.141 -0.137 -0.132 -0.128 -1.14 -1.10 -1.07 -1.03 -0.99 -1.53 -1.48 -1.43 -1.38 -1.32 88.22 88.62 89.01 89.40 89.80 84.1 84.7 85.2 85.7 86.2 -22.0 -20.2 -18.4 -16.6 -14.8 - 25 24 23 22 21 -0.940 -0.904 -0.867 -0.830 -0.794 -1.432 -1.376 -1.320 -1.264 -1.208 -1.239 -1.190 -1.142 -1.093 -1.044 -0.968 -0.930 -0.892 -0.854 -0.816 -0.646 -0.620 -0.595 -0.569 -0.544 -0.127 -0.122 -0.117 -0.113 -0.108 -0.123 -0.119 -0.114 -0.109 -0.105 -0.95 -0.92 -0.88 -0.84 -0.81 -1.27 -1.22 -1.17 -1.12 -1.07 90.19 90.59 90.98 91.37 91.77 86.7 87.2 87.7 88.3 88.8 -13.0 -11.2 -9.4 -7.6 -5.8 Ω Ω t90 285 °C Type T Type E Type J Type K Type N Type S Type R Type B Type U Type L Pt100 Ni100 t90 NiCrCuNi mV FeCuNi mV NiCrNi mV - 20 19 18 17 16 -0.757 -0.720 -0.683 -0.646 -0.608 -1.152 -1.095 -1.039 -0.982 -0.925 -0.995 -0.946 -0.896 -0.847 -0.798 -0.778 -0.739 -0.701 -0.663 -0.624 -0.518 -0.492 -0.467 -0.441 -0.415 -0.103 -0.098 -0.093 -0.088 -0.083 -0.100 -0.095 -0.091 -0.086 -0.081 -0.77 -0.73 -0.69 -0.66 -0.62 -1.02 -0.97 -0.92 -0.87 -0.81 92.16 92.55 92.95 93.34 93.73 89.3 89.8 90.3 90.9 91.4 -4.0 -2.2 -0.4 1.4 3.2 - 15 14 13 12 11 -0.571 -0.534 -0.496 -0.459 -0.421 -0.868 -0.811 -0.754 -0.697 -0.639 -0.749 -0.699 -0.650 -0.600 -0.550 -0.586 -0.547 -0.508 -0.470 -0.431 -0.390 -0.364 -0.338 -0.312 -0.286 -0.078 -0.073 -0.068 -0.063 -0.058 -0.076 -0.071 -0.066 -0.061 -0.056 -0.58 -0.54 -0.50 -0.47 -0.43 -0.76 -0.71 -0.66 -0.61 -0.56 94.12 94.52 94.91 95.30 95.69 91.9 92.5 93.0 93.5 94.0 5.0 6.8 8.6 10.4 12.2 - 10 9 8 7 6 -0.383 -0.345 -0.307 -0.269 -0.231 -0.582 -0.524 -0.466 -0.408 -0.350 -0.501 -0.451 -0.401 -0.351 -0.301 -0.392 -0.353 -0.314 -0.275 -0.236 -0.260 -0.234 -0.209 -0.183 -0.157 -0.053 -0.048 -0.042 -0.037 -0.032 -0.051 -0.046 -0.041 -0.036 -0.031 -0.39 -0.35 -0.31 -0.27 -0.23 -0.51 -0.46 -0.41 -0.36 -0.31 96.09 96.48 96.87 97.26 97.65 94.6 95.1 95.7 96.2 96.7 14.0 15.8 17.6 19.4 21.2 - 5 4 3 2 1 -0.193 -0.154 -0.116 -0.077 -0.039 -0.292 -0.234 -0.176 -0.117 -0.059 -0.251 -0.201 -0.151 -0.101 -0.050 -0.197 -0.157 -0.118 -0.079 -0.039 -0.131 -0.104 -0.078 -0.052 -0.026 -0.027 -0.021 -0.016 -0.011 -0.005 -0.026 -0.021 -0.016 -0.011 -0.005 -0.19 -0.16 -0.12 -0.08 -0.04 -0.25 -0.20 -0.15 -0.10 -0.05 98.04 98.44 98.83 99.22 99.61 97.3 97.8 98.4 98.9 99.5 23.0 24.8 26.6 28.4 30.2 0 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.00 0.00 100.00 100.0 32.0 1 2 3 4 5 0.039 0.078 0.117 0.156 0.195 0.059 0.118 0.176 0.235 0.294 0.050 0.101 0.151 0.202 0.253 0.039 0.079 0.119 0.158 0.198 0.026 0.052 0.078 0.104 0.130 0.005 0.011 0.016 0.022 0.027 0.005 0.011 0.016 0.021 0.027 0.000 0.000 -0.001 -0.001 -0.001 0.04 0.08 0.12 0.16 0.20 0.05 0.10 0.16 0.21 0.26 100.39 100.78 101.17 101.56 101.95 100.5 101.1 101.7 102.2 102.8 33.8 35.6 37.4 39.2 41.0 6 7 8 9 10 0.234 0.273 0.312 0.352 0.391 0.354 0.413 0.472 0.532 0.591 0.303 0.354 0.405 0.456 0.507 0.238 0.277 0.317 0.357 0.397 0.156 0.182 0.208 0.235 0.261 0.033 0.038 0.044 0.050 0.055 0.032 0.038 0.043 0.049 0.054 -0.001 -0.001 -0.002 -0.002 -0.002 0.24 0.28 0.32 0.36 0.40 0.31 0.36 0.42 0.47 0.52 102.34 102.73 103.12 103.51 103.90 103.3 103.9 104.4 105.0 105.6 42.8 44.6 46.4 48.2 50.0 11 12 13 14 15 0.431 0.470 0.510 0.549 0.589 0.651 0.711 0.770 0.830 0.890 0.558 0.609 0.660 0.711 0.762 0.437 0.477 0.517 0.557 0.597 0.287 0.313 0.340 0.366 0.393 0.061 0.067 0.072 0.078 0.084 0.060 0.065 0.071 0.077 0.082 -0.002 -0.002 -0.002 -0.002 -0.002 0.44 0.48 0.52 0.56 0.60 0.57 0.63 0.68 0.73 0.78 104.29 104.68 105.07 105.46 105.85 106.1 106.7 107.2 107.8 108.4 51.8 53.6 55.4 57.2 59.0 16 17 18 19 20 0.629 0.669 0.709 0.749 0.790 0.950 1.010 1.071 1.131 1.192 0.814 0.865 0.916 0.968 1.019 0.637 0.677 0.718 0.758 0.798 0.419 0.446 0.472 0.499 0.525 0.090 0.095 0.101 0.107 0.113 0.088 0.094 0.100 0.105 0.111 -0.002 -0.002 -0.003 -0.003 -0.003 0.64 0.68 0.72 0.76 0.80 0.84 0.89 0.94 1.00 1.05 106.24 106.63 107.02 107.41 107.79 109.0 109.5 110.1 110.7 111.2 60.8 62.6 64.4 66.2 68.0 21 22 23 24 25 0.830 0.870 0.911 0.951 0.992 1.252 1.313 1.373 1.434 1.495 1.071 1.122 1.174 1.226 1.277 0.838 0.879 0.919 0.960 1.000 0.552 0.578 0.605 0.632 0.659 0.119 0.125 0.131 0.137 0.143 0.117 0.123 0.129 0.135 0.141 -0.003 -0.003 -0.003 -0.003 -0.002 0.84 0.88 0.92 0.96 1.00 1.10 1.16 1.21 1.26 1.31 108.18 108.57 108.96 109.35 109.73 111.8 112.4 113.0 113.5 114.1 69.8 71.6 73.4 75.2 77.0 26 27 28 29 30 1.033 1.074 1.114 1.155 1.196 1.556 1.617 1.678 1.740 1.801 1.329 1.381 1.433 1.485 1.537 1.041 1.081 1.122 1.163 1.203 0.685 0.712 0.739 0.766 0.793 0.149 0.155 0.161 0.167 0.173 0.147 0.153 0.159 0.165 0.171 -0.002 -0.002 -0.002 -0.002 -0.002 1.05 1.09 1.13 1.17 1.21 1.37 1.42 1.47 1.53 1.58 110.12 110.51 110.90 111.29 111.67 114.7 115.3 115.9 116.5 117.1 78.8 80.6 82.4 84.2 86.0 286 NiCrSi- Pt10Rh- Pt13Rh- Pt30RhNiSi Pt Pt Pt6Rh mV mV mV mV CuCuNi mV FeCuNi mV °F CuCuNi mV Ω Ω t90 °C Type T Type E Type J Type K Type N Type S Type R Type B Type U Type L Pt100 Ni100 t90 CuCuNi mV NiCrCuNi mV FeCuNi mV NiCrNi mV NiCrSi- Pt10Rh- Pt13Rh- Pt30RhNiSi Pt Pt Pt6Rh mV mV mV mV CuCuNi mV FeCuNi mV Ω Ω °F t90 31 32 33 34 35 1.238 1.279 1.320 1.362 1.403 1.862 1.924 1.986 2.047 2.109 1.589 1.641 1.693 1.745 1.797 1.244 1.285 1.326 1.366 1.407 0.820 0.847 0.874 0.901 0.928 0.179 0.185 0.191 0.197 0.204 0.177 0.183 0.189 0.195 0.201 -0.002 -0.002 -0.002 -0.002 -0.001 1.25 1.29 1.34 1.38 1.42 1.63 1.69 1.74 1.79 1.84 112.06 112.45 112.83 113.22 113.61 117.6 118.2 118.8 119.4 120.0 87.8 89.6 91.4 93.2 95.0 36 37 38 39 40 1.445 1.486 1.528 1.570 1.612 2.171 2.233 2.295 2.357 2.420 1.849 1.902 1.954 2.006 2.059 1.448 1.489 1.530 1.571 1.612 0.955 0.983 1.010 1.037 1.065 0.210 0.216 0.222 0.229 0.235 0.207 0.214 0.220 0.226 0.232 -0.001 -0.001 -0.001 -0.001 0.000 1.46 1.50 1.55 1.59 1.63 1.90 1.95 2.00 2.06 2.11 114.00 114.38 114.77 115.15 115.54 120.6 121.2 121.8 122.4 123.0 96.8 98.6 100.4 102.2 104.0 41 42 43 44 45 1.654 1.696 1.738 1.780 1.823 2.482 2.545 2.607 2.670 2.733 2.111 2.164 2.216 2.269 2.322 1.653 1.694 1.735 1.776 1.817 1.092 1.119 1.147 1.174 1.202 0.241 0.248 0.254 0.260 0.267 0.239 0.245 0.251 0.258 0.264 0.000 0.000 0.000 0.000 0.001 1.67 1.71 1.76 1.80 1.84 2.16 2.22 2.27 2.33 2.38 115.93 116.31 116.70 117.08 117.47 123.6 124.2 124.8 125.4 126.0 105.8 107.6 109.4 111.2 113.0 46 47 48 49 50 1.865 1.908 1.950 1.993 2.036 2.795 2.858 2.921 2.984 3.048 2.374 2.427 2.480 2.532 2.585 1.858 1.899 1.941 1.982 2.023 1.229 1.257 1.284 1.312 1.340 0.273 0.280 0.286 0.292 0.299 0.271 0.277 0.284 0.290 0.296 0.001 0.001 0.002 0.002 0.002 1.88 1.92 1.97 2.01 2.05 2.43 2.49 2.54 2.60 2.65 117.86 118.24 118.63 119.01 119.40 126.7 127.3 127.9 128.5 129.1 114.8 116.6 118.4 120.2 122.0 51 52 53 54 55 2.079 2.122 2.165 2.208 2.251 3.111 3.174 3.238 3.301 3.365 2.638 2.691 2.744 2.797 2.850 2.064 2.106 2.147 2.188 2.230 1.368 1.395 1.423 1.451 1.479 0.305 0.312 0.319 0.325 0.332 0.303 0.310 0.316 0.323 0.329 0.003 0.003 0.003 0.004 0.004 2.09 2.14 2.18 2.22 2.26 2.70 2.76 2.81 2.87 2.92 119.78 120.17 120.55 120.94 121.32 129.7 130.3 131.0 131.6 132.2 123.8 125.6 127.4 129.2 131.0 56 57 58 59 60 2.294 2.338 2.381 2.425 2.468 3.429 3.492 3.556 3.620 3.685 2.903 2.956 3.009 3.062 3.116 2.271 2.312 2.354 2.395 2.436 1.507 1.535 1.563 1.591 1.619 0.338 0.345 0.352 0.358 0.365 0.336 0.343 0.349 0.356 0.363 0.004 0.005 0.005 0.006 0.006 2.31 2.35 2.39 2.44 2.48 2.97 3.03 3.08 3.14 3.19 121.71 122.09 122.47 122.86 123.24 132.8 133.5 134.1 134.7 135.3 132.8 134.6 136.4 138.2 140.0 61 62 63 64 65 2.512 2.556 2.600 2.643 2.687 3.749 3.813 3.877 3.942 4.006 3.169 3.222 3.275 3.329 3.382 2.478 2.519 2.561 2.602 2.644 1.647 1.675 1.703 1.732 1.760 0.372 0.378 0.385 0.392 0.399 0.369 0.376 0.383 0.390 0.397 0.007 0.007 0.008 0.008 0.009 2.52 2.57 2.61 2.65 2.69 3.24 3.30 3.35 3.41 3.46 123.63 124.01 124.39 124.78 125.16 136.0 136.6 137.2 137.9 138.5 141.8 143.6 145.4 147.2 149.0 66 67 68 69 70 2.732 2.776 2.820 2.864 2.909 4.071 4.136 4.200 4.265 4.330 3.436 3.489 3.543 3.596 3.650 2.685 2.727 2.768 2.810 2.851 1.788 1.817 1.845 1.873 1.902 0.405 0.412 0.419 0.426 0.433 0.403 0.410 0.417 0.424 0.431 0.009 0.010 0.010 0.011 0.011 2.74 2.78 2.82 2.87 2.91 3.51 3.57 3.62 3.68 3.73 125.54 125.93 126.31 126.69 127.08 139.2 139.8 140.4 141.1 141.7 150.8 152.6 154.4 156.2 158.0 71 72 73 74 75 2.953 2.998 3.043 3.087 3.132 4.395 4.460 4.526 4.591 4.656 3.703 3.757 3.810 3.864 3.918 2.893 2.934 2.976 3.017 3.059 1.930 1.959 1.988 2.016 2.045 0.440 0.446 0.453 0.460 0.467 0.438 0.445 0.452 0.459 0.466 0.012 0.012 0.013 0.014 0.014 2.95 3.00 3.04 3.09 3.13 3.78 3.84 3.89 3.95 4.00 127.46 127.84 128.22 128.61 128.99 142.4 143.0 143.7 144.3 145.0 159.8 161.6 163.4 165.2 167.0 76 77 78 79 80 3.177 3.222 3.267 3.312 3.358 4.722 4.788 4.853 4.919 4.985 3.971 4.025 4.079 4.133 4.187 3.100 3.142 3.184 3.225 3.267 2.074 2.102 2.131 2.160 2.189 0.474 0.481 0.488 0.495 0.502 0.473 0.480 0.487 0.494 0.501 0.015 0.015 0.016 0.017 0.017 3.17 3.22 3.26 3.31 3.35 4.05 4.11 4.16 4.22 4.27 129.37 129.75 130.13 130.52 130.90 145.6 146.3 146.9 147.6 148.3 168.8 170.6 172.4 174.2 176.0 287 °C Type T Type E Type J Type K Type N Type S Type R Type B Type U Type L Pt100 Ni100 t90 CuCuNi mV NiCrCuNi mV FeCuNi mV NiCrNi mV NiCrSi- Pt10Rh- Pt13Rh- Pt30RhNiSi Pt Pt Pt6Rh mV mV mV mV CuCuNi mV FeCuNi mV Ω °F Ω t90 81 82 83 84 85 3.403 3.448 3.494 3.539 3.585 5.051 5.117 5.183 5.249 5.315 4.240 4.294 4.348 4.402 4.456 3.308 3.350 3.391 3.433 3.474 2.218 2.247 2.276 2.305 2.334 0.509 0.516 0.523 0.530 0.538 0.508 0.516 0.523 0.530 0.537 0.018 0.019 0.020 0.020 0.021 3.39 3.44 3.48 3.53 3.57 4.32 4.38 4.43 4.49 4.54 131.28 131.66 132.04 132.42 132.80 148.9 149.6 150.2 150.9 151.6 177.8 179.6 181.4 183.2 185.0 86 87 88 89 90 3.631 3.677 3.722 3.768 3.814 5.382 5.448 5.514 5.581 5.648 4.510 4.564 4.618 4.672 4.726 3.516 3.557 3.599 3.640 3.682 2.363 2.392 2.421 2.450 2.480 0.545 0.552 0.559 0.566 0.573 0.544 0.552 0.559 0.566 0.573 0.022 0.022 0.023 0.024 0.025 3.62 3.66 3.71 3.75 3.80 4.60 4.65 4.71 4.77 4.82 133.18 133.57 133.95 134.33 134.71 152.2 152.9 153.6 154.3 154.9 186.8 188.6 190.4 192.2 194.0 91 92 93 94 95 3.860 3.907 3.953 3.999 4.046 5.714 5.781 5.848 5.915 5.982 4.781 4.835 4.889 4.943 4.997 3.723 3.765 3.806 3.848 3.889 2.509 2.538 2.568 2.597 2.626 0.580 0.588 0.595 0.602 0.609 0.581 0.588 0.595 0.603 0.610 0.026 0.026 0.027 0.028 0.029 3.84 3.89 3.93 3.98 4.02 4.87 4.93 4.98 5.04 5.09 135.09 135.47 135.85 136.23 136.61 155.6 156.3 157.0 157.7 158.3 195.8 197.6 199.4 201.2 203.0 96 97 98 99 100 4.092 4.138 4.185 4.232 4.279 6.049 6.117 6.184 6.251 6.319 5.052 5.106 5.160 5.215 5.269 3.931 3.972 4.013 4.055 4.096 2.656 2.685 2.715 2.744 2.774 0.617 0.624 0.631 0.639 0.646 0.618 0.625 0.632 0.640 0.647 0.030 0.031 0.031 0.032 0.033 4.07 4.11 4.16 4.20 4.25 5.15 5.20 5.26 5.32 5.37 136.99 137.37 137.75 138.13 138.51 159.0 159.7 160.4 161.1 161.8 204.8 206.6 208.4 210.2 212.0 101 102 103 104 105 4.325 4.372 4.419 4.466 4.513 6.386 6.454 6.522 6.590 6.658 5.323 5.378 5.432 5.487 5.541 4.138 4.179 4.220 4.262 4.303 2.804 2.833 2.863 2.893 2.923 0.653 0.661 0.668 0.675 0.683 0.655 0.662 0.670 0.677 0.685 0.034 0.035 0.036 0.037 0.038 4.30 4.34 4.39 4.43 4.48 5.42 5.48 5.53 5.59 5.64 138.88 139.26 139.64 140.02 140.40 162.5 163.2 163.9 164.6 165.3 213.8 215.6 217.4 219.2 221.0 106 107 108 109 110 4.561 4.608 4.655 4.702 4.750 6.725 6.794 6.862 6.930 6.998 5.595 5.650 5.705 5.759 5.814 4.344 4.385 4.427 4.468 4.509 2.953 2.983 3.012 3.042 3.072 0.690 0.698 0.705 0.713 0.720 0.693 0.700 0.708 0.715 0.723 0.039 0.040 0.041 0.042 0.043 4.53 4.57 4.62 4.66 4.71 5.70 5.75 5.81 5.87 5.92 140.78 141.16 141.54 141.91 142.29 166.0 166.7 167.4 168.1 168.8 222.8 224.6 226.4 228.2 230.0 111 112 113 114 115 4.798 4.845 4.893 4.941 4.988 7.066 7.135 7.203 7.272 7.341 5.868 5.923 5.977 6.032 6.087 4.550 4.591 4.633 4.674 4.715 3.102 3.133 3.163 3.193 3.223 0.727 0.735 0.743 0.750 0.758 0.731 0.738 0.746 0.754 0.761 0.044 0.045 0.046 0.047 0.048 4.76 4.80 4.85 4.90 4.94 5.97 6.03 6.08 6.14 6.19 142.67 143.05 143.43 143.80 144.18 169.5 170.2 170.9 171.6 172.4 231.8 233.6 235.4 237.2 239.0 116 117 118 119 120 5.036 5.084 5.132 5.180 5.228 7.409 7.478 7.547 7.616 7.685 6.141 6.196 6.251 6.306 6.360 4.756 4.797 4.838 4.879 4.920 3.253 3.283 3.314 3.344 3.374 0.765 0.773 0.780 0.788 0.795 0.769 0.777 0.785 0.792 0.800 0.049 0.050 0.051 0.052 0.053 4.99 5.04 5.09 5.13 5.18 6.25 6.30 6.36 6.42 6.47 144.56 144.94 145.31 145.69 146.07 173.1 173.8 174.5 175.2 176.0 240.8 242.6 244.4 246.2 248.0 121 122 123 124 125 5.277 5.325 5.373 5.422 5.470 7.754 7.823 7.892 7.962 8.031 6.415 6.470 6.525 6.579 6.634 4.961 5.002 5.043 5.084 5.124 3.405 3.435 3.466 3.496 3.527 0.803 0.811 0.818 0.826 0.834 0.808 0.816 0.824 0.832 0.839 0.055 0.056 0.057 0.058 0.059 5.23 5.27 5.32 5.37 5.41 6.53 6.58 6.64 6.69 6.75 146.44 146.82 147.20 147.57 147.95 176.7 177.4 178.2 178.9 179.6 249.8 251.6 253.4 255.2 257.0 126 127 128 129 130 5.519 5.567 5.616 5.665 5.714 8.101 8.170 8.240 8.309 8.379 6.689 6.744 6.799 6.854 6.909 5.165 5.206 5.247 5.288 5.328 3.557 3.588 3.619 3.649 3.680 0.841 0.849 0.857 0.865 0.872 0.847 0.855 0.863 0.871 0.879 0.060 0.062 0.063 0.064 0.065 5.46 5.51 5.56 5.60 5.65 6.81 6.86 6.92 6.97 7.03 148.33 148.70 149.08 149.46 149.83 180.4 181.1 181.8 182.6 183.3 258.8 260.6 262.4 264.2 266.0 288 °C Type T Type E Type J Type K Type N Type S Type R Type B Type U Type L Pt100 Ni100 t90 CuCuNi mV NiCrCuNi mV FeCuNi mV NiCrNi mV NiCrSi- Pt10Rh- Pt13Rh- Pt30RhNiSi Pt Pt Pt6Rh mV mV mV mV CuCuNi mV FeCuNi mV Ω °F Ω t90 131 132 133 134 135 5.763 5.812 5.861 5.910 5.959 8.449 8.519 8.589 8.659 8.729 6.964 7.019 7.074 7.129 7.184 5.369 5.410 5.450 5.491 5.532 3.711 3.742 3.772 3.803 3.834 0.880 0.888 0.896 0.903 0.911 0.887 0.895 0.903 0.911 0.919 0.066 0.068 0.069 0.070 0.072 5.70 5.75 5.79 5.84 5.89 7.09 7.14 7.20 7.25 7.31 150.21 150.58 150.96 151.33 151.71 184.1 184.8 185.6 186.3 187.1 267.8 269.6 271.4 273.2 275.0 136 137 138 139 140 6.008 6.057 6.107 6.156 6.206 8.799 8.869 8.940 9.010 9.081 7.239 7.294 7.349 7.404 7.459 5.572 5.613 5.653 5.694 5.735 3.865 3.896 3.927 3.958 3.989 0.919 0.927 0.935 0.942 0.950 0.927 0.935 0.943 0.951 0.959 0.073 0.074 0.075 0.077 0.078 5.94 5.99 6.03 6.08 6.13 7.37 7.42 7.48 7.53 7.59 152.08 152.46 152.83 153.21 153.58 187.8 188.6 189.4 190.1 190.9 276.8 278.6 280.4 282.2 284.0 141 142 143 144 145 6.255 6.305 6.355 6.404 6.454 9.151 9.222 9.292 9.363 9.434 7.514 7.569 7.624 7.679 7.734 5.775 5.815 5.856 5.896 5.937 4.020 4.051 4.083 4.114 4.145 0.958 0.966 0.974 0.982 0.990 0.967 0.976 0.984 0.992 1.000 0.079 0.081 0.082 0.084 0.085 6.18 6.23 6.28 6.33 6.37 7.65 7.70 7.76 7.81 7.87 153.96 154.33 154.71 155.08 155.46 191.7 192.4 193.2 194.0 194.7 285.8 287.6 289.4 291.2 293.0 146 147 148 149 150 6.504 6.554 6.604 6.654 6.704 9.505 9.576 9.647 9.718 9.789 7.789 7.844 7.900 7.955 8.010 5.977 6.017 6.058 6.098 6.138 4.176 4.208 4.239 4.270 4.302 0.998 1.006 1.013 1.021 1.029 1.008 1.016 1.025 1.033 1.041 0.086 0.088 0.089 0.091 0.092 6.42 6.47 6.52 6.57 6.62 7.93 7.98 8.04 8.09 8.15 155.83 156.20 156.58 156.95 157.33 195.5 196.3 197.1 197.9 198.6 294.8 296.6 298.4 300.2 302.0 151 152 153 154 155 6.754 6.805 6.855 6.905 6.956 9.860 9.931 10.003 10.074 10.145 8.065 8.120 8.175 8.231 8.286 6.179 6.219 6.259 6.299 6.339 4.333 4.365 4.396 4.428 4.459 1.037 1.045 1.053 1.061 1.069 1.049 1.058 1.066 1.074 1.082 0.094 0.095 0.096 0.098 0.099 6.67 6.72 6.77 6.82 6.87 8.21 8.26 8.32 8.37 8.43 157.70 158.07 158.45 158.82 159.19 199.4 200.2 201.0 201.8 202.6 303.8 305.6 307.4 309.2 311.0 156 157 158 159 160 7.006 7.057 7.107 7.158 7.209 10.217 10.288 10.360 10.432 10.503 8.341 8.396 8.452 8.507 8.562 6.380 6.420 6.460 6.500 6.540 4.491 4.523 4.554 4.586 4.618 1.077 1.085 1.094 1.102 1.110 1.091 1.099 1.107 1.116 1.124 0.101 0.102 0.104 0.106 0.107 6.92 6.97 7.02 7.07 7.12 8.49 8.54 8.60 8.65 8.71 159.56 159.94 160.31 160.68 161.05 203.4 204.2 205.0 205.8 206.6 312.8 314.6 316.4 318.2 320.0 161 162 163 164 165 7.260 7.310 7.361 7.412 7.463 10.575 10.647 10.719 10.791 10.863 8.618 8.673 8.728 8.783 8.839 6.580 6.620 6.660 6.701 6.741 4.650 4.681 4.713 4.745 4.777 1.118 1.126 1.134 1.142 1.150 1.132 1.141 1.149 1.158 1.166 0.109 0.110 0.112 0.113 0.115 7.17 7.22 7.27 7.33 7.37 8.77 8.82 8.88 8.93 8.99 161.43 161.80 162.17 162.54 162.91 207.4 208.2 209.0 209.8 210.6 321.8 323.6 325.4 327.2 329.0 166 167 168 169 170 7.515 7.566 7.617 7.668 7.720 10.935 11.007 11.080 11.152 11.224 8.894 8.949 9.005 9.060 9.115 6.781 6.821 6.861 6.901 6.941 4.809 4.841 4.873 4.905 4.937 1.158 1.167 1.175 1.183 1.191 1.175 1.183 1.191 1.200 1.208 0.117 0.118 0.120 0.122 0.123 7.43 7.48 7.53 7.58 7.63 9.05 9.10 9.16 9.21 9.27 163.29 163.66 164.03 164.40 164.77 211.5 212.3 213.1 213.9 214.8 330.8 332.6 334.4 336.2 338.0 171 172 173 174 175 7.771 7.823 7.874 7.926 7.977 11.297 11.369 11.442 11.514 11.587 9.171 9.226 9.282 9.337 9.392 6.981 7.021 7.060 7.100 7.140 4.969 5.001 5.033 5.066 5.098 1.199 1.207 1.216 1.224 1.232 1.217 1.225 1.234 1.242 1.251 0.125 0.127 0.128 0.130 0.132 7.68 7.73 7.79 7.84 7.89 9.33 9.38 9.44 9.49 9.55 165.14 165.51 165.89 166.26 166.63 215.6 216.4 217.3 218.1 218.9 339.8 341.6 343.4 345.2 347.0 176 177 178 179 180 8.029 8.081 8.133 8.185 8.237 11.660 11.733 11.805 11.878 11.951 9.448 9.503 9.559 9.614 9.669 7.180 7.220 7.260 7.300 7.340 5.130 5.162 5.195 5.227 5.259 1.240 1.249 1.257 1.265 1.273 1.260 1.268 1.277 1.285 1.294 0.134 0.135 0.137 0.139 0.141 7.94 7.99 8.05 8.10 8.15 9.61 9.66 9.72 9.77 9.83 167.00 167.37 167.74 168.11 168.48 219.8 220.6 221.5 222.3 223.2 348.8 350.6 352.4 354.2 356.0 289 °C Type T Type E Type J Type K Type N Type S Type R Type B Type U Type L Pt100 Ni100 t90 CuCuNi mV NiCrCuNi mV FeCuNi mV NiCrNi mV NiCrSi- Pt10Rh- Pt13Rh- Pt30RhNiSi Pt Pt Pt6Rh mV mV mV mV CuCuNi mV FeCuNi mV Ω °F Ω t90 181 182 183 184 185 8.289 8.341 8.393 8.445 8.497 12.024 12.097 12.170 12.243 12.317 9.725 9.780 9.836 9.891 9.947 7.380 7.420 7.460 7.500 7.540 5.292 5.324 5.357 5.389 5.422 1.282 1.290 1.298 1.307 1.315 1.303 1.311 1.320 1.329 1.337 0.142 0.144 0.146 0.148 0.150 8.20 8.25 8.31 8.36 8.41 9.89 9.94 10.00 10.05 10.11 168.85 169.22 169.59 169.96 170.33 224.0 224.9 225.7 226.6 227.4 357.8 359.6 361.4 363.2 365.0 186 187 188 189 190 8.550 8.602 8.654 8.707 8.759 12.390 12.463 12.537 12.610 12.684 10.002 10.057 10.113 10.168 10.224 7.579 7.619 7.659 7.699 7.739 5.454 5.487 5.520 5.552 5.585 1.323 1.332 1.340 1.348 1.357 1.346 1.355 1.363 1.372 1.381 0.151 0.153 0.155 0.157 0.159 8.46 8.51 8.57 8.62 8.67 10.17 10.22 10.28 10.33 10.39 170.70 171.07 171.43 171.80 172.17 228.3 229.2 230.0 230.9 231.8 366.8 368.6 370.4 372.2 374.0 191 192 193 194 195 8.812 8.865 8.917 8.970 9.023 12.757 12.831 12.904 12.978 13.052 10.279 10.335 10.390 10.446 10.501 7.779 7.819 7.859 7.899 7.939 5.618 5.650 5.683 5.716 5.749 1.365 1.373 1.382 1.390 1.399 1.389 1.398 1.407 1.416 1.425 0.161 0.163 0.165 0.166 0.168 8.72 8.78 8.83 8.88 8.93 10.45 10.50 10.56 10.61 10.67 172.54 172.91 173.28 173.65 174.02 232.7 233.5 234.4 235.3 236.2 375.8 377.6 379.4 381.2 383.0 196 197 198 199 200 9.076 9.129 9.182 9.235 9.288 13.126 13.199 13.273 13.347 13.421 10.557 10.612 10.668 10.723 10.779 7.979 8.019 8.059 8.099 8.138 5.782 5.815 5.847 5.880 5.913 1.407 1.415 1.424 1.432 1.441 1.433 1.442 1.451 1.460 1.469 0.170 0.172 0.174 0.176 0.178 8.99 9.04 9.09 9.15 9.20 10.73 10.78 10.84 10.89 10.95 174.38 174.75 175.12 175.49 175.86 237.1 238.0 238.9 239.8 240.7 384.8 386.6 388.4 390.2 392.0 201 202 203 204 205 9.341 9.395 9.448 9.501 9.555 13.495 13.569 13.644 13.718 13.792 10.834 10.890 10.945 11.001 11.056 8.178 8.218 8.258 8.298 8.338 5.946 5.979 6.013 6.046 6.079 1.449 1.458 1.466 1.475 1.483 1.477 1.486 1.495 1.504 1.513 0.180 0.182 0.184 0.186 0.188 9.25 9.31 9.36 9.42 9.47 11.01 11.06 11.12 11.17 11.23 176.22 176.59 176.96 177.33 177.69 241.6 242.5 243.4 244.3 245.2 393.8 395.6 397.4 399.2 401.0 206 207 208 209 210 9.608 9.662 9.715 9.769 9.822 13.866 13.941 14.015 14.090 14.164 11.112 11.167 11.223 11.278 11.334 8.378 8.418 8.458 8.499 8.539 6.112 6.145 6.178 6.211 6.245 1.492 1.500 1.509 1.517 1.526 1.522 1.531 1.540 1.549 1.558 0.190 0.192 0.195 0.197 0.199 9.52 9.58 9.63 9.69 9.74 11.29 11.34 11.40 11.45 11.51 178.06 178.43 178.79 179.16 179.53 246.1 247.0 247.9 248.9 249.8 402.8 404.6 406.4 408.2 410.0 211 212 213 214 215 9.876 9.930 9.984 10.038 10.092 14.239 14.313 14.388 14.463 14.537 11.389 11.445 11.501 11.556 11.612 8.579 8.619 8.659 8.699 8.739 6.278 6.311 6.345 6.378 6.411 1.534 1.543 1.551 1.560 1.569 1.567 1.575 1.584 1.593 1.602 0.201 0.203 0.205 0.207 0.209 9.79 9.85 9.90 9.96 10.01 11.57 11.62 11.68 11.73 11.79 179.89 180.26 180.63 180.99 181.36 250.7 251.7 252.6 253.5 254.5 411.8 413.6 415.4 417.2 419.0 216 217 218 219 220 10.146 10.200 10.254 10.308 10.362 14.612 14.687 14.762 14.837 14.912 11.667 11.723 11.778 11.834 11.889 8.779 8.819 8.860 8.900 8.940 6.445 6.478 6.512 6.545 6.579 1.577 1.586 1.594 1.603 1.612 1.611 1.620 1.629 1.639 1.648 0.212 0.214 0.216 0.218 0.220 10.07 10.12 10.18 10.23 10.29 11.85 11.90 11.96 12.01 12.07 181.72 182.09 182.46 182.82 183.19 255.4 256.3 257.3 258.2 259.2 420.8 422.6 424.4 426.2 428.0 221 222 223 224 225 10.417 10.471 10.525 10.580 10.634 14.987 15.062 15.137 15.212 15.287 11.945 12.000 12.056 12.111 12.167 8.980 9.020 9.061 9.101 9.141 6.612 6.646 6.680 6.713 6.747 1.620 1.629 1.638 1.646 1.655 1.657 1.666 1.675 1.684 1.693 0.222 0.225 0.227 0.229 0.231 10.35 10.40 10.46 10.51 10.57 12.13 12.18 12.24 12.29 12.35 183.55 183.92 184.28 184.65 185.01 260.2 261.1 262.1 263.0 264.0 429.8 431.6 433.4 435.2 437.0 226 227 228 229 230 10.689 10.743 10.798 10.853 10.907 15.362 15.438 15.513 15.588 15.664 12.222 12.278 12.334 12.389 12.445 9.181 9.222 9.262 9.302 9.343 6.781 6.814 6.848 6.882 6.916 1.663 1.672 1.681 1.690 1.698 1.702 1.711 1.720 1.729 1.739 0.234 0.236 0.238 0.241 0.243 10.62 10.68 10.74 10.79 10.85 12.41 12.46 12.52 12.57 12.63 185.38 185.74 186.11 186.47 186.84 265.0 266.0 266.9 267.9 268.9 438.8 440.6 442.4 444.2 446.0 290 °C Type T Type E Type J Type K Type N Type S Type R Type B Type U Type L Pt100 Ni100 t90 CuCuNi mV NiCrCuNi mV FeCuNi mV NiCrNi mV NiCrSi- Pt10Rh- Pt13Rh- Pt30RhNiSi Pt Pt Pt6Rh mV mV mV mV CuCuNi mV FeCuNi mV 231 232 233 234 235 10.962 11.017 11.072 11.127 11.182 15.739 15.815 15.890 15.966 16.041 12.500 12.556 12.611 12.667 12.722 9.383 9.423 9.464 9.504 9.545 6.949 6.983 7.017 7.051 7.085 1.707 1.716 1.724 1.733 1.742 1.748 1.757 1.766 1.775 1.784 0.245 0.248 0.250 0.252 0.255 10.91 10.96 11.02 11.07 11.13 12.69 12.74 12.80 12.85 12.91 236 237 238 239 240 11.237 11.292 11.347 11.403 11.458 16.117 16.193 16.269 16.344 16.420 12.778 12.833 12.889 12.944 13.000 9.585 9.626 9.666 9.707 9.747 7.119 7.153 7.187 7.221 7.255 1.751 1.759 1.768 1.777 1.786 1.794 1.803 1.812 1.821 1.831 0.257 0.259 0.262 0.264 0.267 11.19 11.24 11.30 11.35 11.41 241 242 243 244 245 11.513 11.569 11.624 11.680 11.735 16.496 16.572 16.648 16.724 16.800 13.056 13.111 13.167 13.222 13.278 9.788 9.828 9.869 9.909 9.950 7.289 7.323 7.357 7.392 7.426 1.794 1.803 1.812 1.821 1.829 1.840 1.849 1.858 1.868 1.877 0.269 0.271 0.274 0.276 0.279 246 247 248 249 250 11.791 11.846 11.902 11.958 12.013 16.876 16.952 17.028 17.104 17.181 13.333 13.389 13.444 13.500 13.555 9.991 10.031 10.072 10.113 10.153 7.460 7.494 7.528 7.563 7.597 1.838 1.847 1.856 1.865 1.874 1.886 1.895 1.905 1.914 1.923 251 252 253 254 255 12.069 12.125 12.181 12.237 12.293 17.257 17.333 17.409 17.486 17.562 13.611 13.666 13.722 13.777 13.833 10.194 10.235 10.276 10.316 10.357 7.631 7.666 7.700 7.734 7.769 1.882 1.891 1.900 1.909 1.918 256 257 258 259 260 12.349 12.405 12.461 12.518 12.574 17.639 17.715 17.792 17.868 17.945 13.888 13.944 13.999 14.055 14.110 10.398 10.439 10.480 10.520 10.561 7.803 7.838 7.872 7.907 7.941 261 262 263 364 265 12.630 12.687 12.743 12.799 12.856 18.021 18.098 18.175 18.252 18.328 14.166 14.221 14.277 14.332 14.388 10.602 10.643 10.684 10.725 10.766 266 267 268 269 270 12.912 12.969 13.026 13.082 13.139 18.405 18.482 18.559 18.636 18.713 14.443 14.499 14.554 14.609 14.665 271 272 273 274 275 13.196 13.253 13.310 13.366 13.423 18.790 18.867 18.944 19.021 19.098 276 277 278 279 280 13.480 13.537 13.595 13.652 13.709 19.175 19.252 19.330 19.407 19.484 Ω °F Ω t90 187.20 187.56 187.93 188.29 188.66 269.9 270.9 271.8 272.8 273.8 447.8 449.6 451.4 453.2 455.0 12.97 13.02 13.08 13.13 13.19 189.02 189.38 189.75 190.11 190.47 274.8 275.8 276.8 277.9 278.9 456.8 458.6 460.4 462.2 464.0 11.47 11.52 11.58 11.64 11.69 13.25 13.30 13.36 13.41 13.47 190.84 191.20 191.56 191.92 192.29 279.9 280.9 281.9 282.9 284.0 465.8 467.6 469.4 471.2 473.0 0.281 0.284 0.286 0.289 0.291 11.75 11.81 11.87 11.92 11.98 13.53 13.58 13.64 13.69 13.75 192.65 193.01 193.37 193.74 194.10 285.0 286.0 287.1 288.1 289.2 474.8 476.6 478.4 480.2 482.0 1.933 1.942 1.951 1.961 1.970 0.294 0.296 0.299 0.301 0.304 12.04 12.09 12.15 12.21 12.26 13.81 13.86 13.92 13.97 14.03 194.46 194.82 195.18 195.55 195.91 483.8 485.6 487.4 489.2 491.0 1.927 1.936 1.944 1.953 1.962 1.980 1.989 1.998 2.008 2.017 0.307 0.309 0.312 0.314 0.317 12.32 12.38 12.44 12.49 12.55 14.09 14.14 14.20 14.25 14.31 196.27 196.63 196.99 197.35 197.71 492.8 494.6 496.4 498.2 500.0 7.976 8.010 8.045 8.080 8.114 1.971 1.980 1.989 1.998 2.007 2.027 2.036 2.046 2.055 2.064 0.320 0.322 0.325 0.328 0.330 12.61 12.67 12.72 12.78 12.84 14.37 14.42 14.48 14.54 14.59 198.07 198.43 198.79 199.15 199.51 501.8 503.6 505.4 507.2 509.0 10.807 10.848 10.889 10.930 10.971 8.149 8.184 8.218 8.253 8.288 2.016 2.025 2.034 2.043 2.052 2.074 2.083 2.093 2.102 2.112 0.333 0.336 0.338 0.341 0.344 12.90 12.96 13.01 13.07 13.13 14.65 14.71 14.76 14.82 14.88 199.87 200.23 200.59 200.95 201.31 510.8 512.6 514.4 516.2 518.0 14.720 14.776 14.831 14.887 14.942 11.012 11.053 11.094 11.135 11.176 8.323 8.358 8.392 8.427 8.462 2.061 2.070 2.078 2.087 2.096 2.121 2.131 2.140 2.150 2.159 0.347 0.349 0.352 0.355 0.358 13.19 13.25 13.30 13.36 13.42 14.94 14.99 15.05 15.10 15.16 201.67 202.03 202.39 202.75 203.11 519.8 521.6 523.4 525.2 527.0 14.998 15.053 15.109 15.164 15.219 11.217 11.259 11.300 11.341 11.382 8.497 8.532 8.567 8.602 8.637 2.105 2.114 2.123 2.132 2.141 2.169 2.179 2.188 2.198 2.207 0.360 0.363 0.366 0.369 0.372 13.48 13.54 13.59 13.65 13.71 15.22 15.27 15.33 15.38 15.44 203.47 203.83 204.19 204.55 204.90 528.8 530.6 532.4 534.2 536.0 291 °C Type T Type E Type J Type K Type N Type S Type R Type B Type U Type L Pt100 Ni100 t90 NiCrCuNi mV FeCuNi mV NiCrNi mV 281 282 283 284 285 13.766 13.823 13.881 13.938 13.995 19.561 19.639 19.716 19.794 19.871 15.275 15.330 15.386 15.441 15.496 11.423 11.465 11.506 11.547 11.588 8.672 8.707 8.742 8.777 8.812 2.151 2.160 2.169 2.178 2.187 2.217 2.226 2.236 2.246 2.255 0.375 0.377 0.380 0.383 0.386 13.77 13.83 13.89 13.95 14.00 15.50 15.55 15.61 15.66 15.72 205.26 205.62 205.98 206.34 206.70 537.8 539.6 541.4 543.2 545.0 286 287 288 289 290 14.053 14.110 14.168 14.226 14.283 19.948 20.026 20.103 20.181 20.259 15.552 15.607 15.663 15.718 15.773 11.630 11.671 11.712 11.753 11.795 8.847 8.882 8.918 8.953 8.988 2.196 2.205 2.214 2.223 2.232 2.265 2.275 2.284 2.294 2.304 0.389 0.392 0.395 0.398 0.401 14.06 14.12 14.18 14.24 14.30 15.78 15.83 15.89 15.94 16.00 207.05 207.41 207.77 208.13 208.48 546.8 548.6 550.4 552.2 554.0 291 292 293 294 295 14.341 14.399 14.456 14.514 14.572 20.336 20.414 20.492 20.569 20.647 15.829 15.884 15.940 15.995 16.050 11.836 11.877 11.919 11.960 12.001 9.023 9.058 9.094 9.129 9.164 2.241 2.250 2.259 2.268 2.277 2.313 2.323 2.333 2.342 2.352 0.404 0.407 0.410 0.413 0.416 14.36 14.42 14.48 14.54 14.60 16.06 16.11 16.17 16.22 16.28 208.84 209.20 209.56 209.91 210.27 555.8 557.6 559.4 561.2 563.0 296 297 298 299 300 14.630 14.688 14.746 14.804 14.862 20.725 20.803 20.880 20.958 21.036 16.106 16.161 16.216 16.272 16.327 12.043 12.084 12.126 12.167 12.209 9.200 9.235 9.270 9.306 9.341 2.287 2.296 2.305 2.314 2.323 2.362 2.371 2.381 2.391 2.401 0.419 0.422 0.425 0.428 0.431 14.66 14.72 14.78 14.84 14.90 16.34 16.39 16.45 16.50 16.56 210.63 210.98 211.34 211.70 212.05 564.8 566.6 568.4 570.2 572.0 301 302 303 304 305 14.920 14.978 15.036 15.095 15.153 21.114 21.192 21.270 21.348 21.426 16.383 16.438 16.493 16.549 16.604 12.250 12.291 12.333 12.374 12.416 9.377 9.412 9.448 9.483 9.519 2.332 2.341 2.350 2.360 2.369 2.410 2.420 2.430 2.440 2.449 0.434 0.437 0.440 0.443 0.446 14.96 15.02 15.08 15.14 15.20 16.62 16.67 16.73 16.78 16.84 212.41 212.76 213.12 213.48 213.83 573.8 575.6 577.4 579.2 581.0 306 307 308 309 310 15.211 15.270 15.328 15.386 15.445 21.504 21.582 21.660 21.739 21.817 16.659 16.715 16.770 16.825 16.881 12.457 12.499 12.540 12.582 12.624 9.554 9.590 9.625 9.661 9.696 2.378 2.387 2.396 2.405 2.415 2.459 2.469 2.479 2.488 2.498 0.449 0.452 0.455 0.458 0.462 15.26 15.32 15.38 15.44 15.50 16.90 16.95 17.01 17.06 17.12 214.19 214.54 214.90 215.25 215.61 582.8 584.6 586.4 588.2 590.0 311 312 313 314 315 15.503 15.562 15.621 15.679 15.738 21.895 21.973 22.051 22.130 22.208 16.936 16.991 17.046 17.102 17.157 12.665 12.707 12.748 12.790 12.831 9.732 9.768 9.803 9.839 9.875 2.424 2.433 2.442 2.451 2.461 2.508 2.518 2.528 2.538 2.547 0.465 0.468 0.471 0.474 0.478 15.56 15.62 15.68 15.74 15.80 17.18 17.23 17.29 17.34 17.40 215.96 216.32 216.67 217.03 217.38 591.8 593.6 595.4 597.2 599.0 316 317 318 319 320 15.797 15.856 15.914 15.973 16.032 22.286 22.365 22.443 22.522 22.600 17.212 17.268 17.323 17.378 17.434 12.873 12.915 12.956 12.998 13.040 9.910 9.946 9.982 10.018 10.054 2.470 2.479 2.488 2.497 2.507 2.557 2.567 2.577 2.587 2.597 0.481 0.484 0.487 0.490 0.494 15.86 15.92 15.98 16.04 16.10 17.46 17.51 17.57 17.62 17.68 217.74 218.09 218.44 218.80 219.15 600.8 602.6 604.4 606.2 608.0 321 322 323 324 325 16.091 16.150 16.209 16.268 16.327 22.678 22.757 22.835 22.914 22.993 17.489 17.544 17.599 17.655 17.710 13.081 13.123 13.165 13.206 13.248 10.089 10.125 10.161 10.197 10.233 2.516 2.525 2.534 2.544 2.553 2.607 2.617 2.626 2.636 2.646 0.497 0.500 0.503 0.507 0.510 16.16 16.22 16.28 16.34 16.40 17.74 17.79 17.85 17.90 17.96 219.51 219.86 220.21 220.57 220.92 609.8 611.6 613.4 615.2 617.0 326 327 328 329 330 16.387 16.446 16.505 16.564 16.624 23.071 23.150 23.228 23.307 23.386 17.765 17.820 17.876 17.931 17.986 13.290 13.331 13.373 13.415 13.457 10.269 10.305 10.341 10.377 10.413 2.562 2.571 2.581 2.590 2.599 2.656 2.666 2.676 2.686 2.696 0.513 0.517 0.520 0.523 0.527 16.46 16.52 16.58 16.64 16.70 18.02 18.07 18.13 18.18 18.24 221.27 221.63 221.98 222.33 222.68 618.8 620.6 622.4 624.2 626.0 292 NiCrSi- Pt10Rh- Pt13Rh- Pt30RhNiSi Pt Pt Pt6Rh mV mV mV mV CuCuNi mV FeCuNi mV °F CuCuNi mV Ω Ω t90 °C Type T Type E Type J Type K Type N Type S Type R Type B Type U Type L Pt100 Ni100 NiCrSi- Pt10Rh- Pt13Rh- Pt30RhNiSi Pt Pt Pt6Rh mV mV mV mV CuCuNi mV FeCuNi mV °F t90 CuCuNi mV NiCrCuNi mV FeCuNi mV NiCrNi mV 331 332 333 334 335 16.683 16.742 16.802 16.861 16.921 23.464 23.543 23.622 23.701 23.780 18.041 18.097 18.152 18.207 18.262 13.498 13.540 13.582 13.624 13.665 10.449 10.485 10.521 10.557 10.593 2.609 2.618 2.627 2.636 2.646 2.706 2.716 2.726 2.736 2.746 0.530 0.533 0.537 0.540 0.544 16.76 16.82 16.88 16.94 17.00 18.30 18.35 18.41 18.46 18.52 223.04 223.39 223.74 224.09 224.45 627.8 629.6 631.4 633.2 635.0 336 337 338 339 340 16.980 17.040 17.100 17.159 17.219 23.858 23.937 24.016 24.095 24.174 18.318 18.373 18.428 18.483 18.538 13.707 13.749 13.791 13.833 13.874 10.629 10.665 10.701 10.737 10.774 2.655 2.664 2.674 2.683 2.692 2.756 2.766 2.776 2.786 2.796 0.547 0.550 0.554 0.557 0.561 17.07 17.13 17.19 17.24 17.31 18.58 18.63 18.69 18.74 18.80 224.80 225.15 225.50 225.85 226.21 636.8 638.6 640.4 642.2 644.0 341 342 343 344 345 17.279 17.339 17.399 17.458 17.518 24.253 24.332 24.411 24.490 24.569 18.594 18.649 18.704 18.759 18.814 13.916 13.958 14.000 14.042 14.084 10.810 10.846 10.882 10.918 10.955 2.702 2.711 2.720 2.730 2.739 2.806 2.816 2.826 2.836 2.846 0.564 0.568 0.571 0.575 0.578 17.37 17.43 17.49 17.55 17.61 18.86 18.91 18.97 19.02 19.08 226.56 226.91 227.26 227.61 227.96 645.8 647.6 649.4 651.2 653.0 346 347 348 349 350 17.578 17.638 17.698 17.759 17.819 24.648 24.727 24.806 24.885 24.964 18.870 18.925 18.980 19.035 19.090 14.126 14.167 14.209 14.251 14.293 10.991 11.027 11.064 11.100 11.136 2.748 2.758 2.767 2.776 2.786 2.856 2.866 2.876 2.886 2.896 0.582 0.585 0.589 0.592 0.596 17.68 17.74 17.80 17.86 17.92 19.14 19.19 19.25 19.30 19.36 228.31 228.66 229.02 229.37 229.72 654.8 656.6 658.4 660.2 662.0 351 352 353 354 355 17.879 17.939 17.999 18.060 18.120 25.044 25.123 25.202 25.281 25.360 19.146 19.201 19.256 19.311 19.366 14.335 14.377 14.419 14.461 14.503 11.173 11.209 11.245 11.282 11.318 2.795 2.805 2.814 2.823 2.833 2.906 2.916 2.926 2.937 2.947 0.599 0.603 0.607 0.610 0.614 17.98 18.04 18.10 18.16 18.22 19.42 19.47 19.53 19.58 19.64 230.07 230.42 230.77 231.12 231.47 663.8 665.6 667.4 669.2 671.0 356 357 358 359 360 18.180 18.241 18.301 18.362 18.422 25.440 25.519 25.598 25.678 25.757 19.422 19.477 19.532 19.587 19.642 14.545 14.587 14.629 14.671 14.713 11.355 11.391 11.428 11.464 11.501 2.842 2.851 2.861 2.870 2.880 2.957 2.967 2.977 2.987 2.997 0.617 0.621 0.625 0.628 0.632 18.29 18.35 18.41 18.47 18.53 19.70 19.75 19.81 19.86 19.92 231.82 232.17 232.52 232.87 233.21 672.8 674.6 676.4 678.2 680.0 361 362 363 364 365 18.483 18.543 18.604 18.665 18.725 25.836 25.916 25.995 26.075 26.154 19.697 19.753 19.808 19.863 19.918 14.755 14.797 14.839 14.881 14.923 11.537 11.574 11.610 11.647 11.683 2.889 2.899 2.908 2.917 2.927 3.007 3.018 3.028 3.038 3.048 0.636 0.639 0.643 0.647 0.650 18.59 18.65 18.71 18.77 18.83 19.98 20.03 20.09 20.14 20.20 233.56 233.91 234.26 234.61 234.96 681.8 683.6 685.4 687.2 689.0 366 367 368 369 370 18.786 18.847 18.908 18.969 19.030 26.233 26.313 26.392 26.472 26.552 19.973 20.028 20.083 20.139 20.194 14.965 15.007 15.049 15.091 15.133 11.720 11.757 11.793 11.830 11.867 2.936 2.946 2.955 2.965 2.974 3.058 3.068 3.079 3.089 3.099 0.654 0.658 0.662 0.665 0.669 18.89 18.96 19.02 19.08 19.14 20.26 20.31 20.37 20.42 20.48 235.31 235.66 236.00 236.35 236.70 690.8 692.6 694.4 696.2 698.0 371 372 373 374 375 19.091 19.152 19.213 19.274 19.335 26.631 26.711 26.790 26.870 26.950 20.249 20.304 20.359 20.414 20.469 15.175 15.217 15.259 15.301 15.343 11.903 11.940 11.977 12.013 12.050 2.983 2.993 3.002 3.012 3.021 3.109 3.119 3.130 3.140 3.150 0.673 0.677 0.680 0.684 0.688 19.20 19.26 19.33 19.39 19.45 20.54 20.59 20.65 20.70 20.76 237.05 237.40 237.74 238.09 238.44 699.8 701.6 703.4 705.2 707.0 376 377 378 379 380 19.396 19.457 19.518 19.579 19.641 27.029 27.109 27.189 27.268 27.348 20.525 20.580 20.635 20.690 20.745 15.385 15.427 15.469 15.511 15.554 12.087 12.124 12.160 12.197 12.234 3.031 3.040 3.050 3.059 3.069 3.160 3.171 3.181 3.191 3.201 0.692 0.696 0.700 0.703 0.707 19.51 19.57 19.64 19.70 19.76 20.82 20.87 20.93 20.98 21.04 238.79 239.13 239.48 239.83 240.18 708.8 710.6 712.4 714.2 716.0 Ω Ω t90 293 °C Type T Type E Type J Type K Type N Type S Type R Type B Type U Type L Pt100 Ni100 t90 NiCrCuNi mV FeCuNi mV NiCrNi mV 381 382 383 384 385 19.702 19.763 19.825 19.886 19.947 27.428 27.507 27.587 27.667 27.747 20.800 20.855 20.911 20.966 21.021 15.596 15.638 15.680 15.722 15.764 12.271 12.308 12.345 12.382 12.418 3.078 3.088 3.097 3.107 3.116 3.212 3.222 3.232 3.242 3.253 0.711 0.715 0.719 0.723 0.727 19.82 19.89 19.95 20.01 20.07 21.10 21.15 21.21 21.26 21.32 240.52 240.87 241.22 241.56 241.91 717.8 719.6 721.4 723.2 725.0 386 387 388 389 390 20.009 20.070 20.132 20.193 20.255 27.827 27.907 27.986 28.066 28.146 21.076 21.131 21.186 21.241 21.297 15.806 15.849 15.891 15.933 15.975 12.455 12.492 12.529 12.566 12.603 3.126 3.135 3.145 3.154 3.164 3.263 3.273 3.284 3.294 3.304 0.731 0.735 0.738 0.742 0.746 20.13 20.19 20.26 20.32 20.38 21.38 21.43 21.49 21.54 21.60 242.26 242.60 242.95 243.29 243.64 726.8 728.6 730.4 732.2 734.0 391 392 393 394 395 20.317 20.378 20.440 20.502 20.563 28.226 28.306 28.386 28.466 28.546 21.352 21.407 21.462 21.517 21.572 16.017 16.059 16.102 16.144 16.186 12.640 12.677 12.714 12.751 12.788 3.173 3.183 3.192 3.202 3.212 3.315 3.325 3.335 3.346 3.356 0.750 0.754 0.758 0.762 0.766 20.44 20.50 20.57 20.63 20.69 21.66 21.71 21.77 21.82 21.88 243.99 244.33 244.68 245.02 245.37 735.8 737.6 739.4 741.2 743.0 396 397 398 399 400 20.625 20.687 20.748 20.810 20.872 28.626 28.706 28.786 28.866 28.946 21.627 21.683 21.738 21.793 21.848 16.228 16.270 16.313 16.355 16.397 12.825 12.862 12.899 12.937 12.974 3.221 3.231 3.240 3.250 3.259 3.366 3.377 3.387 3.397 3.408 0.770 0.774 0.778 0.782 0.787 20.75 20.81 20.88 20.94 21.00 21.94 21.99 22.05 22.10 22.16 245.71 246.06 246.40 246.75 247.09 744.8 746.6 748.4 750.2 752.0 401 402 403 404 405 29.026 29.106 29.186 29.266 29.346 21.903 21.958 22.014 22.069 22.124 16.439 16.482 16.524 16.566 16.608 13.011 13.048 13.085 13.122 13.159 3.269 3.278 3.288 3.298 3.307 3.418 3.428 3.439 3.449 3.460 0.791 0.795 0.799 0.803 0.807 21.06 21.12 21.19 21.25 21.31 22.22 22.27 22.33 22.38 22.44 247.44 247.78 248.13 248.47 248.81 753.8 755.6 757.4 759.2 761.0 406 407 408 409 410 29.427 29.507 29.587 29.667 29.747 22.179 22.234 22.289 22.345 22.400 16.651 16.693 16.735 16.778 16.820 13.197 13.234 13.271 13.308 13.346 3.317 3.326 3.336 3.346 3.355 3.470 3.480 3.491 3.501 3.512 0.811 0.815 0.819 0.824 0.828 21.37 21.43 21.50 21.56 21.62 22.50 22.55 22.61 22.66 22.72 249.16 249.50 249.85 250.19 250.53 762.8 764.6 766.4 768.2 770.0 411 412 413 414 415 29.827 29.908 29.988 30.068 30.148 22.455 22.510 22.565 22.620 22.676 16.862 16.904 16.947 16.989 17.031 13.383 13.420 13.457 13.495 13.532 3.365 3.374 3.384 3.394 3.403 3.522 3.533 3.543 3.553 3.564 0.832 0.836 0.840 0.844 0.849 21.68 21.75 21.81 21.87 21.93 22.78 22.83 22.89 22.95 23.00 250.88 251.22 251.56 251.91 252.25 771.8 773.6 775.4 777.2 779.0 416 417 418 419 420 30.229 30.309 30.389 30.470 30.550 22.731 22.786 22.841 22.896 22.952 17.074 17.116 17.158 17.201 17.243 13.569 13.607 13.644 13.682 13.719 3.413 3.423 3.432 3.442 3.451 3.574 3.585 3.595 3.606 3.616 0.853 0.857 0.861 0.866 0.870 22.00 22.06 22.12 22.19 22.25 23.06 23.12 23.18 23.23 23.29 252.59 252.93 253.28 253.62 253.96 780.8 782.6 784.4 786.2 788.0 421 422 423 424 425 30.630 30.711 30.791 30.871 30.952 23.007 23.062 23.117 23.172 23.228 17.285 17.328 17.370 17.413 17.455 13.756 13.794 13.831 13.869 13.906 3.461 3.471 3.480 3.490 3.500 3.627 3.637 3.648 3.658 3.669 0.874 0.878 0.883 0.887 0.891 22.31 22.38 22.44 22.50 22.56 23.35 23.40 23.46 23.52 23.57 254.30 254.65 254.99 255.33 255.67 789.8 791.6 793.4 795.2 797.0 426 427 428 429 430 31.032 31.112 31.193 31.273 31.354 23.283 23.338 23.393 23.449 23.504 17.497 17.540 17.582 17.624 17.667 13.944 13.981 14.019 14.056 14.094 3.509 3.519 3.529 3.538 3.548 3.679 3.690 3.700 3.711 3.721 0.896 0.900 0.904 0.909 0.913 22.63 22.69 22.75 22.82 22.88 23.63 23.69 23.74 23.80 23.86 256.01 256.35 256.70 257.04 257.38 798.8 800.6 802.4 804.2 806.0 294 NiCrSi- Pt10Rh- Pt13Rh- Pt30RhNiSi Pt Pt Pt6Rh mV mV mV mV CuCuNi mV FeCuNi mV °F CuCuNi mV Ω Ω t90 °C Type T Type E Type J Type K Type N Type S Type R Type B Type U Type L Pt100 Ni100 NiCrSi- Pt10Rh- Pt13Rh- Pt30RhNiSi Pt Pt Pt6Rh mV mV mV mV CuCuNi mV FeCuNi mV °F NiCrCuNi mV FeCuNi mV NiCrNi mV 431 432 433 434 435 31.434 31.515 31.595 31.676 31.756 23.559 23.614 23.670 23.725 23.780 17.709 17.752 17.794 17.837 17.879 14.131 14.169 14.206 14.244 14.281 3.558 3.567 3.577 3.587 3.596 3.732 3.742 3.753 3.764 3.774 0.917 0.922 0.926 0.930 0.935 22.94 23.01 23.07 23.13 23.19 23.92 23.97 24.03 24.09 24.14 257.72 258.06 258.40 258.74 259.08 807.8 809.6 811.4 813.2 815.0 436 437 438 439 440 31.837 31.917 31.998 32.078 32.159 23.835 23.891 23.946 24.001 24.057 17.921 17.964 18.006 18.049 18.091 14.319 14.356 14.394 14.432 14.469 3.606 3.616 3.626 3.635 3.645 3.785 3.795 3.806 3.816 3.827 0.939 0.944 0.948 0.953 0.957 23.26 23.32 23.38 23.45 23.51 24.20 24.26 24.32 24.37 24.43 259.42 259.76 260.10 260.44 260.78 816.8 818.6 820.4 822.2 824.0 441 442 443 444 445 32.239 32.320 32.400 32.481 32.562 24.112 24.167 24.223 24.278 24.333 18.134 18.176 18.218 18.261 18.303 14.507 14.545 14.582 14.620 14.658 3.655 3.664 3.674 3.684 3.694 3.838 3.848 3.859 3.869 3.880 0.961 0.966 0.970 0.975 0.979 23.57 23.64 23.70 23.77 23.83 24.49 24.54 24.60 24.66 24.71 261.12 261.46 261.80 262.14 262.48 825.8 827.6 829.4 831.2 833.0 446 447 448 449 450 32.642 32.723 32.803 32.884 32.965 24.389 24.444 24.499 24.555 24.610 18.346 18.388 18.431 18.473 18.516 14.695 14.733 14.771 14.809 14.846 3.703 3.713 3.723 3.732 3.742 3.891 3.901 3.912 3.922 3.933 0.984 0.988 0.993 0.997 1.002 23.89 23.96 24.02 24.09 24.15 24.77 24.83 24.89 24.94 25.00 262.82 263.16 263.50 263.84 264.18 834.8 836.6 838.4 840.2 842.0 451 452 453 454 455 33.045 33.126 33.207 33.287 33.368 24.665 24.721 24.776 24.832 24.887 18.558 18.601 18.643 18.686 18.728 14.884 14.922 14.960 14.998 15.035 3.752 3.762 3.771 3.781 3.791 3.944 3.954 3.965 3.976 3.986 1.007 1.011 1.016 1.020 1.025 24.21 24.28 24.34 24.41 24.47 25.06 25.11 25.17 25.23 25.28 264.52 264.86 265.20 265.53 265.87 843.8 845.6 847.4 849.2 851.0 456 457 458 459 460 33.449 33.529 33.610 33.691 33.772 24.943 24.998 25.053 25.109 25.164 18.771 18.813 18.856 18.898 18.941 15.073 15.111 15.149 15.187 15.225 3.801 3.810 3.820 3.830 3.840 3.997 4.008 4.018 4.029 4.040 1.030 1.034 1.039 1.043 1.048 24.53 24.60 24.66 24.73 24.79 25.34 25.40 25.46 25.51 25.57 266.21 266.55 266.89 267.22 267.56 852.8 854.6 856.4 858.2 860.0 461 462 463 464 465 33.852 33.933 34.014 34.095 34.175 25.220 25.275 25.331 25.386 25.442 18.983 19.026 19.068 19.111 19.154 15.262 15.300 15.338 15.376 15.414 3.850 3.859 3.869 3.879 3.889 4.050 4.061 4.072 4.083 4.093 1.053 1.057 1.062 1.067 1.071 24.85 24.92 24.98 25.05 25.11 25.63 25.68 25.74 25.80 25.85 267.90 268.24 268.57 268.91 269.25 861.8 863.6 865.4 867.2 869.0 466 467 468 469 470 34.256 34.337 34.418 34.498 34.579 25.497 25.553 25.608 25.664 25.720 19.196 19.239 19.281 19.324 19.366 15.452 15.490 15.528 15.566 15.604 3.898 3.908 3.918 3.928 3.938 4.104 4.115 4.125 4.136 4.147 1.076 1.081 1.086 1.090 1.095 25.18 25.24 25.31 25.37 25.44 25.91 25.97 26.03 26.08 26.14 269.59 269.92 270.26 270.60 270.93 870.8 872.6 874.4 876.2 878.0 471 472 473 474 475 34.660 34.741 34.822 34.902 34.983 25.775 25.831 25.886 25.942 25.998 19.409 19.451 19.494 19.537 19.579 15.642 15.680 15.718 15.756 15.794 3.947 3.957 3.967 3.977 3.987 4.158 4.168 4.179 4.190 4.201 1.100 1.105 1.109 1.114 1.119 25.50 25.57 25.63 25.70 25.76 26.20 26.25 26.31 26.37 26.42 271.27 271.61 271.94 272.28 272.61 879.8 881.6 883.4 885.2 887.0 476 477 478 479 480 35.064 35.145 35.226 35.307 35.387 26.053 26.109 26.165 26.220 26.276 19.622 19.664 19.707 19.750 19.792 15.832 15.870 15.908 15.946 15.984 3.997 4.006 4.016 4.026 4.036 4.211 4.222 4.233 4.244 4.255 1.124 1.129 1.133 1.138 1.143 25.83 25.89 25.95 26.02 26.09 26.48 26.54 26.60 26.65 26.71 272.95 273.29 273.62 273.96 274.29 888.8 890.6 892.4 894.2 896.0 t90 CuCuNi mV Ω Ω t90 295 °C Type T Type E Type J Type K Type N Type S Type R Type B Type U Type L Pt100 Ni100 FeCuNi mV NiCrNi mV 481 482 483 484 485 35.468 35.549 35.630 35.711 35.792 26.332 26.387 26.443 26.499 26.555 19.835 19.877 19.920 19.962 20.005 16.022 16.060 16.099 16.137 16.175 4.046 4.056 4.065 4.075 4.085 4.265 4.276 4.287 4.298 4.309 1.148 1.153 1.158 1.163 1.167 26.16 26.22 26.29 26.35 26.42 26.77 26.82 26.88 26.94 26.99 274.63 274.96 275.30 275.63 275.97 897.8 899.6 901.4 903.2 905.0 486 487 488 489 490 35.873 35.954 36.034 36.115 36.196 26.610 26.666 26.722 26.778 26.834 20.048 20.090 20.133 20.175 20.218 16.213 16.251 16.289 16.327 16.366 4.095 4.105 4.115 4.125 4.134 4.319 4.330 4.341 4.352 4.363 1.172 1.177 1.182 1.187 1.192 26.49 26.55 26.62 26.68 26.75 27.05 27.11 27.17 27.22 27.28 276.30 276.64 276.97 277.31 277.64 906.8 908.6 910.4 912.2 914.0 491 492 493 494 495 36.277 36.358 36.439 36.520 36.601 26.889 26.945 27.001 27.057 27.113 20.261 20.303 20.346 20.389 20.431 16.404 16.442 16.480 16.518 16.557 4.144 4.154 4.164 4.174 4.184 4.373 4.384 4.395 4.406 4.417 1.197 1.202 1.207 1.212 1.217 26.82 26.88 26.95 27.01 27.08 27.34 27.39 27.45 27.51 27.56 277.98 278.31 278.64 278.98 279.31 915.8 917.6 919.4 921.2 923.0 496 497 498 499 500 36.682 36.763 36.843 36.924 37.005 27.169 27.225 27.281 27.337 27.393 20.474 20.516 20.559 20.602 20.644 16.595 16.633 16.671 16.710 16.748 4.194 4.204 4.213 4.223 4.233 4.428 4.439 4.449 4.460 4.471 1.222 1.227 1.232 1.237 1.242 27.15 27.21 27.28 27.34 27.41 27.62 27.68 27.74 27.79 27.85 279.64 279.98 280.31 280.64 280.98 924.8 926.6 928.4 930.2 932.0 501 502 503 504 505 37.086 37.167 37.248 37.329 37.410 27.449 27.505 27.561 27.617 27.673 20.687 20.730 20.772 20.815 20.857 16.786 16.824 16.863 16.901 16.939 4.243 4.253 4.263 4.273 4.283 4.482 4.493 4.504 4.515 4.526 1.247 1.252 1.257 1.262 1.267 27.48 27.54 27.61 27.68 27.74 27.91 27.97 28.02 28.08 28.14 281.31 281.64 281.98 282.31 282.64 933.8 935.6 937.4 939.2 941.0 506 507 508 509 510 37.491 37.572 37.653 37.734 37.815 27.729 27.785 27.841 27.897 27.953 20.900 20.943 20.985 21.028 21.071 16.978 17.016 17.054 17.093 17.131 4.293 4.303 4.313 4.323 4.332 4.537 4.548 4.558 4.569 4.580 1.272 1.277 1.282 1.288 1.293 27.81 27.88 27.95 28.01 28.08 28.20 28.26 28.31 28.37 28.43 282.97 283.31 283.64 283.97 284.30 942.8 944.6 946.4 948.2 950.0 511 512 513 514 515 37.896 37.977 38.058 38.139 38.220 28.010 28.066 28.122 28.178 28.234 21.113 21.156 21.199 21.241 21.284 17.169 17.208 17.246 17.285 17.323 4.342 4.352 4.362 4.372 4.382 4.591 4.602 4.613 4.624 4.635 1.298 1.303 1.308 1.313 1.318 28.15 28.21 28.28 28.35 28.41 28.49 28.55 28.60 28.66 28.72 284.63 284.97 285.30 285.63 285.96 951.8 953.6 955.4 957.2 959.0 516 517 518 519 520 38.300 38.381 38.462 38.543 38.624 28.291 28.347 28.403 28.460 28.516 21.326 21.369 21.412 21.454 21.497 17.361 17.400 17.438 17.477 17.515 4.392 4.402 4.412 4.422 4.432 4.646 4.657 4.668 4.679 4.690 1.324 1.329 1.334 1.339 1.344 28.48 28.55 28.62 28.68 28.75 28.78 28.84 28.89 28.95 29.01 286.29 286.62 286.95 287.29 287.62 960.8 962.6 964.4 966.2 968.0 521 522 523 524 525 38.705 38.786 38.867 38.948 39.029 28.572 28.629 28.685 28.741 28.798 21.540 21.582 21.625 21.668 21.710 17.554 17.592 17.630 17.669 17.707 4.442 4.452 4.462 4.472 4.482 4.701 4.712 4.723 4.734 4.745 1.350 1.355 1.360 1.365 1.371 28.82 28.89 28.95 29.02 29.09 29.07 29.13 29.18 29.24 29.30 287.95 288.28 288.61 288.94 289.27 969.8 971.6 973.4 975.2 977.0 526 527 528 529 530 39.110 39.191 39.272 39.353 39.434 28.854 28.911 28.967 29.024 29.080 21.753 21.796 21.838 21.881 21.924 17.746 17.784 17.823 17.861 17.900 4.492 4.502 4.512 4.522 4.532 4.756 4.767 4.778 4.789 4.800 1.376 1.381 1.387 1.392 1.397 29.16 29.23 29.29 29.36 29.43 29.36 29.42 29.47 29.53 29.59 289.60 289.93 290.26 290.59 290.92 978.8 980.6 982.4 984.2 986.0 296 NiCrSi- Pt10Rh- Pt13Rh- Pt30RhNiSi Pt Pt Pt6Rh mV mV mV mV CuCuNi mV FeCuNi mV °F NiCrCuNi mV t90 CuCuNi mV Ω Ω t90 °C Type T Type E Type J Type K Type N Type S Type R Type B Type U Type L Pt100 Ni100 NiCrSi- Pt10Rh- Pt13Rh- Pt30RhNiSi Pt Pt Pt6Rh mV mV mV mV CuCuNi mV FeCuNi mV °F NiCrCuNi mV FeCuNi mV NiCrNi mV 531 532 533 534 535 39.515 39.596 39.677 39.758 39.839 29.137 29.194 29.250 29.307 29.363 21.966 22.009 22.052 22.094 22.137 17.938 17.977 18.016 18.054 18.093 4.542 4.552 4.562 4.572 4.582 4.811 4.822 4.833 4.844 4.855 1.402 1.408 1.413 1.418 1.424 29.50 29.57 29.63 29.70 29.77 29.65 29.71 29.76 29.82 29.88 291.25 291.58 291.91 292.24 292.56 987.8 989.6 991.4 993.2 995.0 536 537 538 539 540 39.920 40.001 40.082 40.163 40.243 29.420 29.477 29.534 29.590 29.647 22.179 22.222 22.265 22.307 22.350 18.131 18.170 18.208 18.247 18.286 4.592 4.602 4.612 4.622 4.632 4.866 4.877 4.888 4.899 4.910 1.429 1.435 1.440 1.445 1.451 29.84 29.91 29.97 30.04 30.11 29.94 30.00 30.05 30.11 30.17 292.89 293.22 293.55 293.88 294.21 996.8 998.6 1000.4 1002.2 1004.0 541 542 543 544 545 40.324 40.405 40.486 40.567 40.648 29.704 29.761 29.818 29.874 29.931 22.393 22.435 22.478 22.521 22.563 18.324 18.363 18.401 18.440 18.479 4.642 4.652 4.662 4.672 4.682 4.922 4.933 4.944 4.955 4.966 1.456 1.462 1.467 1.472 1.478 30.18 30.25 30.32 30.39 30.45 30.23 30.29 30.34 30.40 30.46 294.54 294.86 295.19 295.52 295.85 1005.8 1007.6 1009.4 1011.2 1013.0 546 547 548 549 550 40.729 40.810 40.891 40.972 41.053 29.988 30.045 30.102 30.159 30.216 22.606 22.649 22.691 22.734 22.776 18.517 18.556 18.595 18.633 18.672 4.692 4.702 4.712 4.722 4.732 4.977 4.988 4.999 5.010 5.021 1.483 1.489 1.494 1.500 1.505 30.52 30.59 30.66 30.73 30.80 30.52 30.58 30.63 30.69 30.75 296.18 296.50 296.83 297.16 297.49 1014.8 1016.6 1018.4 1020.2 1022.0 551 552 553 554 555 41.134 41.215 41.296 41.377 41.457 30.273 30.330 30.387 30.444 30.502 22.819 22.862 22.904 22.947 22.990 18.711 18.749 18.788 18.827 18.865 4.742 4.752 4.762 4.772 4.782 5.033 5.044 5.055 5.066 5.077 1.511 1.516 1.522 1.527 1.533 30.87 30.94 31.01 31.08 31.14 30.81 30.87 30.92 30.98 31.04 297.81 298.14 298.47 298.80 299.12 1023.8 1025.6 1027.4 1029.2 1031.0 556 557 558 559 560 41.538 41.619 41.700 41.781 41.862 30.559 30.616 30.673 30.730 30.788 23.032 23.075 23.117 23.160 23.203 18.904 18.943 18.982 19.020 19.059 4.793 4.803 4.813 4.823 4.833 5.088 5.099 5.111 5.122 5.133 1.539 1.544 1.550 1.555 1.561 31.21 31.28 31.35 31.42 31.49 31.10 31.16 31.21 31.27 31.33 299.45 299.78 300.10 300.43 300.75 1032.8 1034.6 1036.4 1038.2 1040.0 561 562 563 564 565 41.943 42.024 42.105 42.185 42.266 30.845 30.902 30.960 31.017 31.074 23.245 23.288 23.331 23.373 23.416 19.098 19.136 19.175 19.214 19.253 4.843 4.853 4.863 4.873 4.883 5.144 5.155 5.166 5.178 5.189 1.566 1.572 1.578 1.583 1.589 31.56 31.63 31.70 31.77 31.84 31.39 31.45 31.50 31.56 31.62 301.08 301.41 301.73 302.06 302.38 1041.8 1043.6 1045.4 1047.2 1049.0 566 567 568 569 570 42.347 42.428 42.509 42.590 42.671 31.132 31.189 31.247 31.304 31.362 23.458 23.501 23.544 23.586 23.629 19.292 19.330 19.369 19.408 19.447 4.893 4.904 4.914 4.924 4.934 5.200 5.211 5.222 5.234 5.245 1.595 1.600 1.606 1.612 1.617 31.91 31.98 32.05 32.12 32.19 31.68 31.74 31.79 31.85 31.91 302.71 303.03 303.36 303.69 304.01 1050.8 1052.6 1054.4 1056.2 1058.0 571 572 573 574 575 42.751 42.832 42.913 42.994 43.075 31.419 31.477 31.535 31.592 31.650 23.671 23.714 23.757 23.799 23.842 19.485 19.524 19.563 19.602 19.641 4.944 4.954 4.964 4.974 4.984 5.256 5.267 5.279 5.290 5.301 1.623 1.629 1.634 1.640 1.646 32.26 32.33 32.40 32.47 32.54 31.97 32.03 32.08 32.14 32.20 304.34 304.66 304.98 305.31 305.63 1059.8 1061.6 1063.4 1065.2 1067.0 576 577 578 579 580 43.156 43.236 43.317 43.398 43.479 31.708 31.766 31.823 31.881 31.939 23.884 23.927 23.970 24.012 24.055 19.680 19.718 19.757 19.796 19.835 4.995 5.005 5.015 5.025 5.035 5.312 5.323 5.335 5.346 5.357 1.652 1.657 1.663 1.669 1.675 32.61 32.68 32.75 32.82 32.89 32.26 32.32 32.37 32.43 32.49 305.96 306.28 306.61 306.93 307.25 1068.8 1070.6 1072.4 1074.2 1076.0 t90 CuCuNi mV Ω Ω t90 297 °C Type T Type E Type J Type K Type N Type S Type R Type B Type U Type L Pt100 Ni100 FeCuNi mV NiCrNi mV 581 582 583 584 585 43.560 43.640 43.721 43.802 43.883 31.997 32.055 32.113 32.171 32.229 24.097 24.140 24.182 24.225 24.267 19.874 19.913 19.952 19.990 20.029 5.045 5.055 5.066 5.076 5.086 5.369 5.380 5.391 5.402 5.414 1.680 1.686 1.692 1.698 1.704 32.96 33.03 33.10 33.17 33.24 32.55 32.61 32.66 32.72 32.78 307.58 307.90 308.23 308.55 308.87 1077.8 1079.6 1081.4 1083.2 1085.0 586 587 588 589 590 43.963 44.044 44.125 44.206 44.286 32.287 32.345 32.403 32.461 32.519 24.310 24.353 24.395 24.438 24.480 20.068 20.107 20.146 20.185 20.224 5.096 5.106 5.116 5.127 5.137 5.425 5.436 5.448 5.459 5.470 1.709 1.715 1.721 1.727 1.733 33.32 33.39 33.46 33.53 33.60 32.84 32.90 32.96 33.02 33.08 309.20 309.52 309.84 310.16 310.49 1086.8 1088.6 1090.4 1092.2 1094.0 591 592 593 594 595 44.367 44.448 44.529 44.609 44.690 32.577 32.636 32.694 32.752 32.810 24.523 24.565 24.608 24.650 24.693 20.263 20.302 20.341 20.379 20.418 5.147 5.157 5.167 5.177 5.188 5.481 5.493 5.504 5.515 5.527 1.739 1.745 1.750 1.756 1.762 33.67 33.74 33.81 33.88 33.95 33.14 33.20 33.26 33.32 33.38 310.81 311.13 311.45 311.78 312.10 1095.8 1097.6 1099.4 1101.2 1103.0 596 597 598 599 600 44.771 44.851 44.932 45.013 45.093 32.869 32.927 32.985 33.044 33.102 24.735 24.778 24.820 24.863 24.905 20.457 20.496 20.535 20.574 20.613 5.198 5.208 5.218 5.228 5.239 5.538 5.549 5.561 5.572 5.583 1.768 1.774 1.780 1.786 1.792 34.03 34.10 34.17 34.24 34.31 33.43 33.49 33.55 33.61 33.67 312.42 312.74 313.06 313.39 313.71 1104.8 1106.6 1108.4 1110.2 1112.0 601 602 603 604 605 45.174 45.255 45.335 45.416 45.497 33.161 33.219 33.278 33.337 33.395 24.948 24.990 25.033 25.075 25.118 20.652 20.691 20.730 20.769 20.808 5.249 5.259 5.269 5.280 5.290 5.595 5.606 5.618 5.629 5.640 1.798 1.804 1.810 1.816 1.822 33.73 33.79 33.85 33.91 33.97 314.03 314.35 314.67 314.99 315.31 1113.8 1115.6 1117.4 1119.2 1121.0 606 607 608 609 610 45.577 45.658 45.738 45.819 45.900 33.454 33.513 33.571 33.630 33.689 25.160 25.203 25.245 25.288 25.330 20.847 20.886 20.925 20.964 21.003 5.300 5.310 5.320 5.331 5.341 5.652 5.663 5.674 5.686 5.697 1.828 1.834 1.840 1.846 1.852 34.02 34.08 34.14 34.20 34.26 315.64 315.96 316.28 316.60 316.92 1122.8 1124.6 1126.4 1128.2 1130.0 611 612 613 614 615 45.980 46.061 46.141 46.222 46.302 33.748 33.807 33.866 33.925 33.984 25.373 25.415 25.458 25.500 25.543 21.042 21.081 21.120 21.159 21.198 5.351 5.361 5.372 5.382 5.392 5.709 5.720 5.731 5.743 5.754 1.858 1.864 1.870 1.876 1.882 34.32 34.38 34.44 34.50 34.56 317.24 317.56 317.88 318.20 318.52 1131.8 1133.6 1135.4 1137.2 1139.0 616 617 618 619 620 46.383 46.463 46.544 46.624 46.705 34.043 34.102 34.161 34.220 34.279 25.585 25.627 25.670 25.712 25.755 21.237 21.276 21.315 21.354 21.393 5.402 5.413 5.423 5.433 5.443 5.766 5.777 5.789 5.800 5.812 1.888 1.894 1.901 1.907 1.913 34.61 34.67 34.73 34.79 34.85 318.84 319.16 319.48 319.80 320.12 1140.8 1142.6 1144.4 1146.2 1148.0 621 622 623 624 625 46.785 46.866 46.946 47.027 47.107 34.338 34.397 34.457 34.516 34.575 25.797 25.840 25.882 25.924 25.967 21.432 21.471 21.510 21.549 21.588 5.454 5.464 5.474 5.485 5.495 5.823 5.834 5.846 5.857 5.869 1.919 1.925 1.931 1.937 1.944 34.91 34.97 35.03 35.09 35.15 320.43 320.75 321.07 321.39 321.71 1149.8 1151.6 1153.4 1155.2 1157.0 626 627 628 629 630 47.188 47.268 47.349 47.429 47.509 34.635 34.694 34.754 34.813 34.873 26.009 26.052 26.094 26.136 26.179 21.628 21.667 21.706 21.745 21.784 5.505 5.515 5.526 5.536 5.546 5.880 5.892 5.903 5.915 5.926 1.950 1.956 1.962 1.968 1.975 35.20 35.26 35.32 35.38 35.44 322.03 322.35 322.67 322.98 323.30 1158.8 1160.6 1162.4 1164.2 1166.0 298 NiCrSi- Pt10Rh- Pt13Rh- Pt30RhNiSi Pt Pt Pt6Rh mV mV mV mV CuCuNi mV FeCuNi mV °F NiCrCuNi mV t90 CuCuNi mV Ω Ω t90 °C Type T Type E Type J Type K Type N Type S Type R Type B Type U Type L Pt100 Ni100 NiCrSi- Pt10Rh- Pt13Rh- Pt30RhNiSi Pt Pt Pt6Rh mV mV mV mV CuCuNi mV FeCuNi mV °F NiCrCuNi mV FeCuNi mV NiCrNi mV 631 632 633 634 635 47.590 47.670 47.751 47.831 47.911 34.932 34.992 35.051 35.111 35.171 26.221 26.263 26.306 26.348 26.390 21.823 21.862 21.901 21.940 21.979 5.557 5.567 5.577 5.588 5.598 5.938 5.949 5.961 5.972 5.984 1.981 1.987 1.993 1.999 2.006 35.50 35.56 35.62 35.68 35.74 323.62 323.94 324.26 324.57 324.89 1167.8 1169.6 1171.4 1173.2 1175.0 636 637 638 639 640 47.992 48.072 48.152 48.233 48.313 35.230 35.290 35.350 35.410 35.470 26.433 26.475 26.517 26.560 26.602 22.018 22.058 22.097 22.136 22.175 5.608 5.618 5.629 5.639 5.649 5.995 6.007 6.018 6.030 6.041 2.012 2.018 2.025 2.031 2.037 35.80 35.86 35.92 35.98 36.04 325.21 325.53 325.84 326.16 326.48 1176.8 1178.6 1180.4 1182.2 1184.0 641 642 643 644 645 48.393 48.474 48.554 48.634 48.715 35.530 35.590 35.650 35.710 35.770 26.644 26.687 26.729 26.771 26.814 22.214 22.253 22.292 22.331 22.370 5.660 5.670 5.680 5.691 5.701 6.053 6.065 6.076 6.088 6.099 2.043 2.050 2.056 2.062 2.069 36.10 36.16 36.22 36.28 36.34 326.79 327.11 327.43 327.74 328.06 1185.8 1187.6 1189.4 1191.2 1193.0 646 647 648 649 650 48.795 48.875 48.955 49.035 49.116 35.830 35.890 35.950 36.010 36.071 26.856 26.898 26.940 26.983 27.025 22.410 22.449 22.488 22.527 22.566 5.712 5.722 5.732 5.743 5.753 6.111 6.122 6.134 6.146 6.157 2.075 2.082 2.088 2.094 2.101 36.40 36.46 36.52 36.58 36.64 328.38 328.69 329.01 329.32 329.64 1194.8 1196.6 1198.4 1200.2 1202.0 651 652 653 654 655 49.196 49.276 49.356 49.436 49.517 36.131 36.191 36.252 36.312 36.373 27.067 27.109 27.152 27.194 27.236 22.605 22.644 22.684 22.723 22.762 5.763 5.774 5.784 5.794 5.805 6.169 6.180 6.192 6.204 6.215 2.107 2.113 2.120 2.126 2.133 36.70 36.76 36.82 36.88 36.95 329.96 330.27 330.59 330.90 331.22 1203.8 1205.6 1207.4 1209.2 1211.0 656 657 658 659 660 49.597 49.677 49.757 49.837 49.917 36.433 36.494 36.554 36.615 36.675 27.278 27.320 27.363 27.405 27.447 22.801 22.840 22.879 22.919 22.958 5.815 5.826 5.836 5.846 5.857 6.227 6.238 6.250 6.262 6.273 2.139 2.146 2.152 2.158 2.165 37.01 37.07 37.13 37.19 37.25 331.53 331.85 332.16 332.48 332.79 1212.8 1214.6 1216.4 1218.2 1220.0 661 662 663 664 665 49.997 50.077 50.157 50.238 50.318 36.736 36.797 36.858 36.918 36.979 27.489 27.531 27.574 27.616 27.658 22.997 23.036 23.075 23.115 23.154 5.867 5.878 5.888 5.898 5.909 6.285 6.297 6.308 6.320 6.332 2.171 2.178 2.184 2.191 2.197 37.30 37.36 37.42 37.48 37.55 333.11 333.42 333.74 334.05 334.36 1221.8 1223.6 1225.4 1227.2 1229.0 666 667 668 669 670 50.398 50.478 50.558 50.638 50.718 37.040 37.101 37.162 37.223 37.284 27.700 27.742 27.784 27.826 27.869 23.193 23.232 23.271 23.311 23.350 5.919 5.930 5.940 5.950 5.961 6.343 6.355 6.367 6.378 6.390 2.204 2.210 2.217 2.224 2.230 37.61 37.67 37.73 37.79 37.85 334.68 334.99 335.31 335.62 335.93 1230.8 1232.6 1234.4 1236.2 1238.0 671 672 673 674 675 50.798 50.878 50.958 51.038 51.118 37.345 37.406 37.467 37.528 37.590 27.911 27.953 27.995 28.037 28.079 23.389 23.428 23.467 23.507 23.546 5.971 5.982 5.992 6.003 6.013 6.402 6.413 6.425 6.437 6.448 2.237 2.243 2.250 2.256 2.263 37.91 37.97 38.04 38.10 38.16 336.25 336.56 336.87 337.18 337.50 1239.8 1241.6 1243.4 1245.2 1247.0 676 677 678 679 680 51.197 51.277 51.357 51.437 51.517 37.651 37.712 37.773 37.835 37.896 28.121 28.163 28.205 28.247 28.289 23.585 23.624 23.663 23.703 23.742 6.024 6.034 6.044 6.055 6.065 6.460 6.472 6.484 6.495 6.507 2.270 2.276 2.283 2.289 2.296 38.22 38.28 38.35 38.41 38.47 337.81 338.12 338.44 338.75 339.06 1248.8 1250.6 1252.4 1254.2 1256.0 t90 CuCuNi mV Ω Ω t90 299 °C Type T Type E Type J Type K Type N Type S Type R Type B Type U Type L Pt100 Ni100 FeCuNi mV NiCrNi mV 681 682 683 684 685 51.597 51.677 51.757 51.837 51.916 37.958 38.019 38.081 38.142 38.204 28.332 28.374 28.416 28.458 28.500 23.781 23.820 23.860 23.899 23.938 6.076 6.086 6.097 6.107 6.118 6.519 6.531 6.542 6.554 6.566 2.303 2.309 2.316 2.323 2.329 38.53 38.59 38.66 38.72 38.78 339.37 339.69 340.00 340.31 340.62 1257.8 1259.6 1261.4 1263.2 1265.0 686 687 688 689 690 51.996 52.076 52.156 52.236 52.315 38.265 38.327 38.389 38.450 38.512 28.542 28.584 28.626 28.668 28.710 23.977 24.016 24.056 24.095 24.134 6.128 6.139 6.149 6.160 6.170 6.578 6.589 6.601 6.613 6.625 2.336 2.343 2.350 2.356 2.363 38.84 38.90 38.97 39.03 39.09 340.93 341.24 341.56 341.87 342.18 1266.8 1268.6 1270.4 1272.2 1274.0 691 692 693 694 695 52.395 52.475 52.555 52.634 52.714 38.574 38.636 38.698 38.760 38.822 28.752 28.794 28.835 28.877 28.919 24.173 24.213 24.252 24.291 24.330 6.181 6.191 6.202 6.212 6.223 6.636 6.648 6.660 6.672 6.684 2.370 2.376 2.383 2.390 2.397 39.15 39.22 39.28 39.34 39.41 342.49 342.80 343.11 343.42 343.73 1275.8 1277.6 1279.4 1281.2 1283.0 696 697 698 699 700 52.794 52.873 52.953 53.033 53.112 38.884 38.946 39.008 39.070 39.132 28.961 29.003 29.045 29.087 29.129 24.370 24.409 24.448 24.487 24.527 6.233 6.244 6.254 6.265 6.275 6.695 6.707 6.719 6.731 6.743 2.403 2.410 2.417 2.424 2.431 39.47 39.53 39.59 39.66 39.72 344.04 344.35 344.66 344.97 345.28 1284.8 1286.6 1288.4 1290.2 1292.0 701 702 703 704 705 53.192 53.272 53.351 53.431 53.510 39.194 39.256 39.318 39.381 39.443 29.171 29.213 29.255 29.297 29.338 24.566 24.605 24.644 24.684 24.723 6.286 6.296 6.307 6.317 6.328 6.755 6.766 6.778 6.790 6.802 2.437 2.444 2.451 2.458 2.465 39.78 39.85 39.91 39.97 40.04 345.59 345.90 346.21 346.52 346.83 1293.8 1295.6 1297.4 1299.2 1301.0 706 707 708 709 710 53.590 53.670 53.749 53.829 53.908 39.505 39.568 39.630 39.693 39.755 29.380 29.422 29.464 29.506 29.548 24.762 24.801 24.841 24.880 24.919 6.338 6.349 6.360 6.370 6.381 6.814 6.826 6.838 6.849 6.861 2.472 2.479 2.485 2.492 2.499 40.10 40.16 40.22 40.29 40.35 347.14 347.45 347.76 348.07 348.38 1302.8 1304.6 1306.4 1308.2 1310.0 711 712 713 714 715 53.988 54.067 54.147 54.226 54.306 39.818 39.880 39.943 40.005 40.068 29.589 29.631 29.673 29.715 29.757 24.959 24.998 25.037 25.076 25.116 6.391 6.402 6.412 6.423 6.434 6.873 6.885 6.897 6.909 6.921 2.506 2.513 2.520 2.527 2.534 40.41 40.48 40.54 40.60 40.67 348.69 348.99 349.30 349.61 349.92 1311.8 1313.6 1315.4 1317.2 1319.0 716 717 718 719 720 54.385 54.465 54.544 54.624 54.703 40.131 40.193 40.256 40.319 40.382 29.798 29.840 29.882 29.924 29.965 25.155 25.194 25.233 25.273 25.312 6.444 6.455 6.465 6.476 6.486 6.933 6.945 6.956 6.968 6.980 2.541 2.548 2.555 2.562 2.569 40.73 40.80 40.86 40.93 40.98 350.23 350.54 350.84 351.15 351.46 1320.8 1322.6 1324.4 1326.2 1328.0 721 722 723 724 725 54.782 54.862 54.941 55.021 55.100 40.445 40.508 40.570 40.633 40.696 30.007 30.049 30.090 30.132 30.174 25.351 25.391 25.430 25.469 25.508 6.497 6.508 6.518 6.529 6.539 6.992 7.004 7.016 7.028 7.040 2.576 2.583 2.590 2.597 2.604 41.04 41.11 41.17 41.23 41.30 351.77 352.08 352.38 352.69 353.00 1329.8 1331.6 1333.4 1335.2 1337.0 726 727 728 729 730 55.179 55.259 55.338 55.417 55.497 40.759 40.822 40.886 40.949 41.012 30.216 30.257 30.299 30.341 30.382 25.548 25.587 25.626 25.666 25.705 6.550 6.561 6.571 6.582 6.593 7.052 7.064 7.076 7.088 7.100 2.611 2.618 2.625 2.632 2.639 41.36 41.43 41.49 41.56 41.62 353.30 353.61 353.92 354.22 354.53 1338.8 1340.6 1342.4 1344.2 1346.0 300 NiCrSi- Pt10Rh- Pt13Rh- Pt30RhNiSi Pt Pt Pt6Rh mV mV mV mV CuCuNi mV FeCuNi mV °F NiCrCuNi mV t90 CuCuNi mV Ω Ω t90 °C Type T Type E Type J Type K Type N Type S Type R Type B Type U Type L Pt100 Ni100 NiCrSi- Pt10Rh- Pt13Rh- Pt30RhNiSi Pt Pt Pt6Rh mV mV mV mV CuCuNi mV FeCuNi mV °F NiCrCuNi mV FeCuNi mV NiCrNi mV 731 732 733 734 735 55.576 55.655 55.734 55.814 55.893 41.075 41.138 41.201 41.265 41.328 30.424 30.466 30.507 30.549 30.590 25.744 25.783 25.823 25.862 25.901 6.603 6.614 6.624 6.635 6.646 7.112 7.124 7.136 7.148 7.160 2.646 2.653 2.660 2.667 2.674 41.69 41.75 41.82 41.88 41.95 354.84 355.14 355.45 355.76 356.06 1347.8 1349.6 1351.4 1353.2 1355.0 736 737 738 739 740 55.972 56.051 56.131 56.210 56.289 41.391 41.455 41.518 41.581 41.645 30.632 30.674 30.715 30.757 30.798 25.941 25.980 26.019 26.058 26.098 6.656 6.667 6.678 6.688 6.699 7.172 7.184 7.196 7.208 7.220 2.681 2.688 2.696 2.703 2.710 42.01 42.08 42.14 42.21 42.27 356.37 356.67 356.98 357.28 357.59 1356.8 1358.6 1360.4 1362.2 1364.0 741 742 743 744 745 56.368 56.447 56.526 56.606 56.685 41.708 41.772 41.835 41.899 41.962 30.840 30.881 30.923 30.964 31.006 26.137 26.176 26.216 26.255 26.294 6.710 6.720 6.731 6.742 6.752 7.232 7.244 7.256 7.268 7.280 2.717 2.724 2.731 2.738 2.746 42.34 42.40 42.47 42.53 42.60 357.90 358.20 358.51 358.81 359.12 1365.8 1367.6 1369.4 1371.2 1373.0 746 747 748 749 750 56.764 56.843 56.922 57.001 57.080 42.026 42.090 42.153 42.217 42.281 31.047 31.089 31.130 31.172 31.213 26.333 26.373 26.412 26.451 26.491 6.763 6.774 6.784 6.795 6.806 7.292 7.304 7.316 7.328 7.340 2.753 2.760 2.767 2.775 2.782 42.66 42.73 42.79 42.86 42.92 359.42 359.72 360.03 360.33 360.64 1374.8 1376.6 1378.4 1380.2 1382.0 751 752 753 754 755 57.159 57.238 57.317 57.396 57.475 42.344 42.408 42.472 42.536 42.599 31.255 31.296 31.338 31.379 31.421 26.530 26.569 26.608 26.648 26.687 6.817 6.827 6.838 6.849 6.859 7.352 7.364 7.376 7.389 7.401 2.789 2.796 2.803 2.811 2.818 42.99 43.05 43.12 43.18 43.25 360.94 361.25 361.55 361.85 362.16 1383.8 1385.6 1387.4 1389.2 1391.0 756 757 758 759 760 57.554 57.633 57.712 57.791 57.870 42.663 42.727 42.791 42.855 42.919 31.462 31.504 31.545 31.586 31.628 26.726 26.766 26.805 26.844 26.883 6.870 6.881 6.892 6.902 6.913 7.413 7.425 7.437 7.449 7.461 2.825 2.833 2.840 2.847 2.854 43.31 43.38 43.44 43.51 43.57 362.46 362.76 363.07 363.37 363.67 1392.8 1394.6 1396.4 1398.2 1400.0 761 762 763 764 765 57.949 58.028 58.107 58.186 58.265 42.983 43.047 43.111 43.175 43.239 31.669 31.710 31.752 31.793 31.834 26.923 26.962 27.001 27.041 27.080 6.924 6.934 6.945 6.956 6.967 7.473 7.485 7.498 7.510 7.522 2.862 2.869 2.876 2.884 2.891 43.64 43.70 43.77 43.83 43.90 363.98 364.28 364.58 364.89 365.19 1401.8 1403.6 1405.4 1407.2 1409.0 766 767 768 769 770 58.343 58.422 58.501 58.580 58.659 43.303 43.367 43.431 43.495 43.559 31.876 31.917 31.958 32.000 32.041 27.119 27.158 27.198 27.237 27.276 6.977 6.988 6.999 7.010 7.020 7.534 7.546 7.558 7.570 7.583 2.898 2.906 2.913 2.921 2.928 43.97 44.03 44.10 44.16 44.23 365.49 365.79 366.10 366.40 366.70 1410.8 1412.6 1414.4 1416.2 1418.0 771 772 773 774 775 58.738 58.816 58.895 58.974 59.053 43.624 43.688 43.752 43.817 43.881 32.082 32.124 32.165 32.206 32.247 27.316 27.355 27.394 27.433 27.473 7.031 7.042 7.053 7.064 7.074 7.595 7.607 7.619 7.631 7.644 2.935 2.943 2.950 2.958 2.965 44.30 44.36 44.43 44.49 44.56 367.00 367.30 367.60 367.91 368.21 1419.8 1421.6 1423.4 1425.2 1427.0 776 777 778 779 780 59.131 59.210 59.289 59.367 59.446 43.945 44.010 44.074 44.139 44.203 32.289 32.330 32.371 32.412 32.453 27.512 27.551 27.591 27.630 27.669 7.085 7.096 7.107 7.117 7.128 7.656 7.668 7.680 7.692 7.705 2.973 2.980 2.987 2.995 3.002 44.63 44.69 44.76 44.82 44.89 368.51 368.81 369.11 369.41 369.71 1428.8 1430.6 1432.4 1434.2 1436.0 t90 CuCuNi mV Ω Ω t90 301 °C Type T Type E Type J Type K Type N Type S Type R Type B Type U Type L Pt100 Ni100 FeCuNi mV NiCrNi mV 781 782 783 784 785 59.525 59.604 59.682 59.761 59.839 44.267 44.332 44.396 44.461 44.525 32.495 32.536 32.577 32.618 32.659 27.708 27.748 27.787 27.826 27.866 7.139 7.150 7.161 7.171 7.182 7.717 7.729 7.741 7.753 7.766 3.010 3.017 3.025 3.032 3.040 44.96 45.02 45.09 45.15 45.22 370.01 370.31 370.61 370.91 371.21 1437.8 1439.6 1441.4 1443.2 1445.0 786 787 788 789 790 59.918 59.997 60.075 60.154 60.232 44.590 44.655 44.719 44.784 44.848 32.700 32.742 32.783 32.824 32.865 27.905 27.944 27.983 28.023 28.062 7.193 7.204 7.215 7.226 7.236 7.778 7.790 7.802 7.815 7.827 3.047 3.055 3.062 3.070 3.078 45.29 45.35 45.42 45.48 45.55 371.51 371.81 372.11 372.41 372.71 1446.8 1448.6 1450.4 1452.2 1454.0 791 792 793 794 795 60.311 60.390 60.468 60.547 60.625 44.913 44.977 45.042 45.107 45.171 32.906 32.947 32.988 33.029 33.070 28.101 28.140 28.180 28.219 28.258 7.247 7.258 7.269 7.280 7.291 7.839 7.852 7.864 7.876 7.888 3.085 3.093 3.100 3.108 3.116 45.62 45.68 45.75 45.82 45.89 373.01 373.31 373.61 373.91 374.21 1455.8 1457.6 1459.4 1461.2 1463.0 796 797 798 799 800 60.704 60.782 60.860 60.939 61.017 45.236 45.301 45.365 45.430 45.494 33.111 33.152 33.193 33.234 33.275 28.297 28.337 28.376 28.415 28.455 7.302 7.312 7.323 7.334 7.345 7.901 7.913 7.925 7.938 7.950 3.123 3.131 3.138 3.146 3.154 45.95 46.02 46.09 46.15 46.22 374.51 374.81 375.11 375.41 375.70 1464.8 1466.6 1468.4 1470.2 1472.0 801 802 803 804 805 61.096 61.174 61.253 61.331 61.409 45.559 45.624 45.688 45.753 45.818 33.316 33.357 33.398 33.439 33.480 28.494 28.533 28.572 28.612 28.651 7.356 7.367 7.378 7.388 7.399 7.962 7.974 7.987 7.999 8.011 3.161 3.169 3.177 3.184 3.192 46.29 46.35 46.42 46.49 46.56 376.00 376.30 376.60 376.90 377.19 1473.8 1475.6 1477.4 1479.2 1481.0 806 807 808 809 810 61.488 61.566 61.644 61.723 61.801 45.882 45.947 46.011 46.076 46.141 33.521 33.562 33.603 33.644 33.685 28.690 28.729 28.769 28.808 28.847 7.410 7.421 7.432 7.443 7.454 8.024 8.036 8.048 8.061 8.073 3.200 3.207 3.215 3.223 3.230 46.62 46.69 46.76 46.82 46.89 377.49 377.79 378.09 378.39 378.68 1482.8 1484.6 1486.4 1488.2 1490.0 811 812 813 814 815 61.879 61.958 62.036 62.114 62.192 46.205 46.270 46.334 46.399 46.464 33.726 33.767 33.808 33.848 33.889 28.886 28.926 28.965 29.004 29.043 7.465 7.476 7.487 7.497 7.508 8.086 8.098 8.110 8.123 8.135 3.238 3.246 3.254 3.261 3.269 46.96 47.03 47.09 47.16 47.23 378.98 379.28 379.57 379.87 380.17 1491.8 1493.6 1495.4 1497.2 1499.0 816 817 818 819 820 62.271 62.349 62.427 62.505 62.583 46.528 46.593 46.657 46.722 46.786 33.930 33.971 34.012 34.053 34.093 29.083 29.122 29.161 29.200 29.239 7.519 7.530 7.541 7.552 7.563 8.147 8.160 8.172 8.185 8.197 3.277 3.285 3.292 3.300 3.308 47.30 47.37 47.43 47.50 47.57 380.46 380.76 381.06 381.35 381.65 1500.8 1502.6 1504.4 1506.2 1508.0 821 822 823 824 825 62.662 62.740 62.818 62.896 62.974 46.851 46.915 46.980 47.044 47.109 34.134 34.175 34.216 34.257 34.297 29.279 29.318 29.357 29.396 29.436 7.574 7.585 7.596 7.607 7.618 8.209 8.222 8.234 8.247 8.259 3.316 3.324 3.331 3.339 3.347 47.64 47.71 47.77 47.84 47.91 381.95 382.24 382.54 382.83 383.13 1509.8 1511.6 1513.4 1515.2 1517.0 826 827 828 829 830 63.052 63.130 63.208 63.286 63.364 47.173 47.238 47.302 47.367 47.431 34.338 34.379 34.420 34.460 34.501 29.475 29.514 29.553 29.592 29.632 7.629 7.640 7.651 7.662 7.673 8.272 8.284 8.296 8.309 8.321 3.355 3.363 3.371 3.379 3.386 47.98 48.05 48.11 48.18 48.25 383.42 383.72 384.01 384.31 384.60 1518.8 1520.6 1522.4 1524.2 1526.0 302 NiCrSi- Pt10Rh- Pt13Rh- Pt30RhNiSi Pt Pt Pt6Rh mV mV mV mV CuCuNi mV FeCuNi mV °F NiCrCuNi mV t90 CuCuNi mV Ω Ω t90 °C Type T Type E Type J Type K Type N Type S Type R Type B Type U Type L Pt100 Ni100 NiCrSi- Pt10Rh- Pt13Rh- Pt30RhNiSi Pt Pt Pt6Rh mV mV mV mV CuCuNi mV FeCuNi mV °F NiCrCuNi mV FeCuNi mV NiCrNi mV 831 832 833 834 835 63.442 63.520 63.598 63.676 63.754 47.495 47.560 47.624 47.688 47.753 34.542 34.582 34.623 34.664 34.704 29.671 29.710 29.749 29.789 29.828 7.684 7.695 7.706 7.717 7.728 8.334 8.346 8.359 8.371 8.384 3.394 3.402 3.410 3.418 3.426 48.32 48.39 48.46 48.53 48.60 384.90 385.19 385.49 385.78 386.08 1527.8 1529.6 1531.4 1533.2 1535.0 836 837 838 839 840 63.832 63.910 63.988 64.066 64.144 47.817 47.881 47.946 48.010 48.074 34.745 34.786 34.826 34.867 34.908 29.867 29.906 29.945 29.985 30.024 7.739 7.750 7.761 7.772 7.783 8.396 8.409 8.421 8.434 8.446 3.434 3.442 3.450 3.458 3.466 48.66 48.73 48.80 48.87 48.94 386.37 386.67 386.96 387.25 387.55 1536.8 1538.6 1540.4 1542.2 1544.0 841 842 843 844 845 64.222 64.300 64.377 64.455 64.533 48.138 48.202 48.267 48.331 48.395 34.948 34.989 35.029 35.070 35.110 30.063 30.102 30.141 30.181 30.220 7.794 7.805 7.816 7.827 7.838 8.459 8.471 8.484 8.496 8.509 3.474 3.482 3.490 3.498 3.506 49.01 49.08 49.15 49.22 49.29 387.84 388.14 388.43 388.72 389.02 1545.8 1547.6 1549.4 1551.2 1553.0 846 847 848 849 850 64.611 64.689 64.766 64.844 64.922 48.459 48.523 48.587 48.651 48.715 35.151 35.192 35.232 35.273 35.313 30.259 30.298 30.337 30.376 30.416 7.849 7.860 7.871 7.882 7.893 8.521 8.534 8.546 8.559 8.571 3.514 3.522 3.530 3.538 3.546 49.35 49.42 49.49 49.56 49.63 389.31 389.60 389.90 390.19 390.48 1554.8 1556.6 1558.4 1560.2 1562.0 851 852 853 854 855 65.000 65.077 65.155 65.233 65.310 48.779 48.843 48.907 48.971 49.034 35.354 35.394 35.435 35.475 35.516 30.455 30.494 30.533 30.572 30.611 7.904 7.915 7.926 7.937 7.948 8.584 8.597 8.609 8.622 8.634 3.554 3.562 3.570 3.578 3.586 49.70 49.77 49.84 49.91 49.98 1563.8 1565.6 1567.4 1569.2 1571.0 856 857 858 859 860 65.388 65.465 65.543 65.621 65.698 49.098 49.162 49.226 49.290 49.353 35.556 35.596 35.637 35.677 35.718 30.651 30.690 30.729 30.768 30.807 7.959 7.970 7.981 7.992 8.003 8.647 8.659 8.672 8.685 8.697 3.594 3.602 3.610 3.618 3.626 50.04 50.11 50.18 50.25 50.32 1572.8 1574.6 1576.4 1578.2 1580.0 861 862 863 864 865 65.776 65.853 65.931 66.008 66.086 49.417 49.481 49.544 49.608 49.672 35.758 35.798 35.839 35.879 35.920 30.846 30.886 30.925 30.964 31.003 8.014 8.026 8.037 8.048 8.059 8.710 8.722 8.735 8.748 8.760 3.634 3.643 3.651 3.659 3.667 50.39 50.46 50.53 50.60 50.67 1581.8 1583.6 1585.4 1587.2 1589.0 866 867 868 869 870 66.163 66.241 66.318 66.396 66.473 49.735 49.799 49.862 49.926 49.989 35.960 36.000 36.041 36.081 36.121 31.042 31.081 31.120 31.160 31.199 8.070 8.081 8.092 8.103 8.114 8.773 8.785 8.798 8.811 8.823 3.675 3.683 3.692 3.700 3.708 50.74 50.81 50.88 50.95 51.02 1590.8 1592.6 1594.4 1596.2 1598.0 871 872 873 874 875 66.550 66.628 66.705 66.782 66.860 50.052 50.116 50.179 50.243 50.306 36.162 36.202 36.242 36.282 36.323 31.238 31.277 31.316 31.355 31.394 8.125 8.137 8.148 8.159 8.170 8.836 8.849 8.861 8.874 8.887 3.716 3.724 3.732 3.741 3.749 51.09 51.16 51.23 51.30 51.37 1599.8 1601.6 1603.4 1605.2 1607.0 876 877 878 879 880 66.937 67.014 67.092 67.169 67.246 50.369 50.432 50.495 50.559 50.622 36.363 36.403 36.443 36.484 36.524 31.433 31.473 31.512 31.551 31.590 8.181 8.192 8.203 8.214 8.226 8.899 8.912 8.925 8.937 8.950 3.757 3.765 3.774 3.782 3.790 51.44 51.51 51.58 51.65 51.72 1608.8 1610.6 1612.4 1614.2 1616.0 t90 CuCuNi mV Ω Ω t90 303 °C Type T Type E Type J Type K Type N Type S Type R Type B Type U Type L Pt100 Ni100 FeCuNi mV NiCrNi mV 881 882 883 884 885 67.323 67.400 67.478 67.555 67.632 50.685 50.748 50.811 50.874 50.937 36.564 36.604 36.644 36.685 36.725 31.629 31.668 31.707 31.746 31.785 8.237 8.248 8.259 8.270 8.281 8.963 8.975 8.988 9.001 9.014 3.798 3.807 3.815 3.823 3.832 51.79 51.86 51.93 52.00 52.08 1617.8 1619.6 1621.4 1623.2 1625.0 886 887 888 889 890 67.709 67.786 67.863 67.940 68.017 51.000 51.063 51.126 51.188 51.251 36.765 36.805 36.845 36.885 36.925 31.824 31.863 31.903 31.942 31.981 8.293 8.304 8.315 8.326 8.337 9.026 9.039 9.052 9.065 9.077 3.840 3.848 3.857 3.865 3.873 52.15 52.22 52.29 52.36 52.43 1626.8 1628.6 1630.4 1632.2 1634.0 891 892 893 894 895 68.094 68.171 68.248 68.325 68.402 51.314 51.377 51.439 51.502 51.565 36.965 37.006 37.046 37.086 37.126 32.020 32.059 32.098 32.137 32.176 8.348 8.360 8.371 8.382 8.393 9.090 9.103 9.115 9.128 9.141 3.882 3.890 3.898 3.907 3.915 52.50 52.57 52.64 52.71 52.79 1635.8 1637.6 1639.4 1641.2 1643.0 896 897 898 899 900 68.479 68.556 68.633 68.710 68.787 51.627 51.690 51.752 51.815 51.877 37.166 37.206 37.246 37.286 37.326 32.215 32.254 32.293 32.332 32.371 8.404 8.416 8.427 8.438 8.449 9.154 9.167 9.179 9.192 9.205 3.923 3.932 3.940 3.949 3.957 52.86 52.93 53.00 53.07 53.14 1644.8 1646.6 1648.4 1650.2 1652.0 901 902 903 904 905 68.863 68.940 69.017 69.094 69.171 51.940 52.002 52.064 52.127 52.189 37.366 37.406 37.446 37.486 37.526 32.410 32.449 32.488 32.527 32.566 8.460 8.472 8.483 8.494 8.505 9.218 9.230 9.243 9.256 9.269 3.965 3.974 3.982 3.991 3.999 1653.8 1655.6 1657.4 1659.2 1661.0 906 907 908 909 910 69.247 69.324 69.401 69.477 69.554 52.251 52.314 52.376 52.438 52.500 37.566 37.606 37.646 37.686 37.725 32.605 32.644 32.683 32.722 32.761 8.517 8.528 8.539 8.550 8.562 9.282 9.294 9.307 9.320 9.333 4.008 4.016 4.024 4.033 4.041 1662.8 1664.6 1666.4 1668.2 1670.0 911 912 913 914 915 69.631 69.707 69.784 69.860 69.937 52.562 52.624 52.686 52.748 52.810 37.765 37.805 37.845 37.885 37.925 32.800 32.839 32.878 32.917 32.956 8.573 8.584 8.595 8.607 8.618 9.346 9.359 9.371 9.384 9.397 4.050 4.058 4.067 4.075 4.084 1671.8 1673.6 1675.4 1677.2 1679.0 916 917 918 919 920 70.013 70.090 70.166 70.243 70.319 52.872 52.934 52.996 53.057 53.119 37.965 38.005 38.044 38.084 38.124 32.995 33.034 33.073 33.112 33.151 8.629 8.640 8.652 8.663 8.674 9.410 9.423 9.436 9.449 9.462 4.093 4.101 4.110 4.118 4.127 1680.8 1682.6 1684.4 1686.2 1688.0 921 922 923 924 925 70.396 70.472 70.548 70.625 70.701 53.181 53.243 53.304 53.366 53.427 38.164 38.204 38.243 38.283 38.323 33.190 33.229 33.268 33.307 33.346 8.685 8.697 8.708 8.719 8.731 9.474 9.487 9.500 9.513 9.526 4.135 4.144 4.152 4.161 4.170 1689.8 1691.6 1693.4 1695.2 1697.0 926 927 928 929 930 70.777 70.854 70.930 71.006 71.082 53.489 53.550 53.612 53.673 53.735 38.363 38.402 38.442 38.482 38.522 33.385 33.424 33.463 33.502 33.541 8.742 8.753 8.765 8.776 8.787 9.539 9.552 9.565 9.578 9.591 4.178 4.187 4.195 4.204 4.213 1698.8 1700.6 1702.4 1704.2 1706.0 304 NiCrSi- Pt10Rh- Pt13Rh- Pt30RhNiSi Pt Pt Pt6Rh mV mV mV mV CuCuNi mV FeCuNi mV °F NiCrCuNi mV t90 CuCuNi mV Ω Ω t90 °C Type T Type E Type J Type K Type N Type S Type R Type B Type U Type L Pt100 Ni100 NiCrSi- Pt10Rh- Pt13Rh- Pt30RhNiSi Pt Pt Pt6Rh mV mV mV mV CuCuNi mV FeCuNi mV °F NiCrCuNi mV FeCuNi mV NiCrNi mV 931 932 933 934 935 71.159 71.235 71.311 71.387 71.463 53.796 53.857 53.919 53.980 54.041 38.561 38.601 38.641 38.680 38.720 33.580 33.619 33.658 33.697 33.736 8.798 8.810 8.821 8.832 8.844 9.603 9.616 9.629 9.642 9.655 4.221 4.230 4.239 4.247 4.256 1707.8 1709.6 1711.4 1713.2 1715.0 936 937 938 939 940 71.539 71.615 71.692 71.768 71.844 54.102 54.164 54.225 54.286 54.347 38.760 38.799 38.839 38.878 38.918 33.774 33.813 33.852 33.891 33.930 8.855 8.866 8.878 8.889 8.900 9.668 9.681 9.694 9.707 9.720 4.265 4.273 4.282 4.291 4.299 1716.8 1718.6 1720.4 1722.2 1724.0 941 942 943 944 945 71.920 71.996 72.072 72.147 72.223 54.408 54.469 54.530 54.591 54.652 38.958 38.997 39.037 39.076 39.116 33.969 34.008 34.047 34.086 34.124 8.912 8.923 8.935 8.946 8.957 9.733 9.746 9.759 9.772 9.785 4.308 4.317 4.326 4.334 4.343 1725.8 1727.6 1729.4 1731.2 1733.0 946 947 948 949 950 72.299 72.375 72.451 72.527 72.603 54.713 54.773 54.834 54.895 54.956 39.155 39.195 39.235 39.274 39.314 34.163 34.202 34.241 34.280 34.319 8.969 8.980 8.991 9.003 9.014 9.798 9.811 9.824 9.837 9.850 4.352 4.360 4.369 4.378 4.387 1734.8 1736.6 1738.4 1740.2 1742.0 951 952 953 954 955 72.678 72.754 72.830 72.906 72.981 55.016 55.077 55.138 55.198 55.259 39.353 39.393 39.432 39.471 39.511 34.358 34.396 34.435 34.474 34.513 9.025 9.037 9.048 9.060 9.071 9.863 9.876 9.889 9.902 9.915 4.396 4.404 4.413 4.422 4.431 1743.8 1745.6 1747.4 1749.2 1751.0 956 957 958 959 960 73.057 73.133 73.208 73.284 73.360 55.319 55.380 55.440 55.501 55.561 39.550 39.590 39.629 39.669 39.708 34.552 34.591 34.629 34.668 34.707 9.082 9.094 9.105 9.117 9.128 9.928 9.941 9.954 9.967 9.980 4.440 4.448 4.457 4.466 4.475 1752.8 1754.6 1756.4 1758.2 1760.0 961 962 963 964 965 73.435 73.511 73.586 73.662 73.738 55.622 55.682 55.742 55.803 55.863 39.747 39.787 39.826 39.866 39.905 34.746 34.785 34.823 34.862 34.901 9.139 9.151 9.162 9.174 9.185 9.993 10.006 10.019 10.032 10.046 4.484 4.493 4.501 4.510 4.519 1761.8 1763.6 1765.4 1767.2 1769.0 966 967 968 969 970 73.813 73.889 73.964 74.040 74.115 55.923 55.983 56.043 56.104 56.164 39.944 39.984 40.023 40.062 40.101 34.940 34.979 35.017 35.056 35.095 9.197 9.208 9.219 9.231 9.242 10.059 10.072 10.085 10.098 10.111 4.528 4.537 4.546 4.555 4.564 1770.8 1772.6 1774.4 1776.2 1778.0 971 972 973 974 975 74.190 74.266 74.341 74.417 74.492 56.224 56.284 56.344 56.404 56.464 40.141 40.180 40.219 40.259 40.298 35.134 35.172 35.211 35.250 35.289 9.254 9.265 9.277 9.288 9.300 10.124 10.137 10.150 10.163 10.177 4.573 4.582 4.591 4.599 4.608 1779.8 1781.6 1783.4 1785.2 1787.0 976 977 978 979 980 74.567 74.643 74.718 74.793 74.869 56.524 56.584 56.643 56.703 56.763 40.337 40.376 40.415 40.455 40.494 35.327 35.366 35.405 35.444 35.482 9.311 9.323 9.334 9.345 9.357 10.190 10.203 10.216 10.229 10.242 4.617 4.626 4.635 4.644 4.653 1788.8 1790.6 1792.4 1794.2 1796.0 t90 CuCuNi mV Ω Ω t90 305 °C Type T Type E Type J Type K Type N Type S Type R Type B Type U Type L Pt100 Ni100 FeCuNi mV NiCrNi mV 981 982 983 984 985 74.944 75.019 75.095 75.170 75.245 56.823 56.883 56.942 57.002 57.062 40.533 40.572 40.611 40.651 40.690 35.521 35.560 35.598 35.637 35.676 9.368 9.380 9.391 9.403 9.414 10.255 10.269 10.282 10.295 10.308 4.662 4.671 4.680 4.689 4.698 1797.8 1799.6 1801.4 1803.2 1805.0 986 987 988 989 990 75.320 75.395 75.471 75.546 75.621 57.121 57.181 57.240 57.300 57.360 40.729 40.768 40.807 40.846 40.885 35.714 35.753 35.792 35.831 35.869 9.426 9.437 9.449 9.460 9.472 10.321 10.334 10.348 10.361 10.374 4.707 4.716 4.725 4.734 4.743 1806.8 1808.6 1810.4 1812.2 1814.0 991 992 993 994 995 75.696 75.771 75.847 75.922 75.997 57.419 57.479 57.538 57.597 57.657 40.924 40.963 41.002 41.042 41.081 35.908 35.946 35.985 36.024 36.062 9.483 9.495 9.506 9.518 9.529 10.387 10.400 10.413 10.427 10.440 4.753 4.762 4.771 4.780 4.789 1815.8 1817.6 1819.4 1821.2 1823.0 996 997 998 999 1000 76.072 76.147 76.223 76.298 76.373 57.716 57.776 57.835 57.894 57.953 41.120 41.159 41.198 41.237 41.276 36.101 36.140 36.178 36.217 36.256 9.541 9.552 9.564 9.576 9.587 10.453 10.466 10.480 10.493 10.506 4.798 4.807 4.816 4.825 4.834 1824.8 1826.6 1828.4 1830.2 1832.0 1001 1002 1003 1004 1005 58.013 58.072 58.131 58.190 58.249 41.315 41.354 41.393 41.431 41.470 36.294 36.333 36.371 36.410 36.449 9.599 9.610 9.622 9.633 9.645 10.519 10.532 10.546 10.559 10.572 4.843 4.853 4.862 4.871 4.880 1833.8 1835.6 1837.4 1839.2 1841.0 1006 1007 1008 1009 1010 58.309 58.368 58.427 58.486 58.545 41.509 41.548 41.587 41.626 41.665 36.487 36.526 36.564 36.603 36.641 9.656 9.668 9.679 9.691 9.703 10.585 10.599 10.612 10.625 10.639 4.889 4.898 4.908 4.917 4.926 1842.8 1844.6 1846.4 1848.2 1850.0 1011 1012 1013 1014 1015 58.604 58.663 58.722 58.781 58.840 41.704 41.743 41.781 41.820 41.859 36.680 36.718 36.757 36.796 36.834 9.714 9.726 9.737 9.749 9.761 10.652 10.665 10.678 10.692 10.705 4.935 4.944 4.954 4.963 4.972 1851.8 1853.6 1855.4 1857.2 1859.0 1016 1017 1018 1019 1020 58.899 58.957 59.016 59.075 59.134 41.898 41.937 41.976 42.014 42.053 36.873 36.911 36.950 36.988 37.027 9.772 9.784 9.795 9.807 9.818 10.718 10.732 10.745 10.758 10.771 4.981 4.990 5.000 5.009 5.018 1860.8 1862.6 1864.4 1866.2 1868.0 1021 1022 1023 1024 1025 59.193 59.252 59.310 59.369 59.428 42.092 42.131 42.169 42.208 42.247 37.065 37.104 37.142 37.181 37.219 9.830 9.842 9.853 9.865 9.877 10.785 10.798 10.811 10.825 10.838 5.027 5.037 5.046 5.055 5.065 1869.8 1871.6 1873.4 1875.2 1877.0 1026 1027 1028 1029 1030 59.487 59.545 59.604 59.663 59.721 42.286 42.324 42.363 42.402 42.440 37.258 37.296 37.334 37.373 37.411 9.888 9.900 9.911 9.923 9.935 10.851 10.865 10.878 10.891 10.905 5.074 5.083 5.092 5.102 5.111 1878.8 1880.6 1882.4 1884.2 1886.0 306 NiCrSi- Pt10Rh- Pt13Rh- Pt30RhNiSi Pt Pt Pt6Rh mV mV mV mV CuCuNi mV FeCuNi mV °F NiCrCuNi mV t90 CuCuNi mV Ω Ω t90 °C Type T Type E Type J Type K Type N Type S Type R Type B Type U Type L Pt100 Ni100 NiCrCuNi mV NiCrSi- Pt10Rh- Pt13Rh- Pt30RhNiSi Pt Pt Pt6Rh mV mV mV mV CuCuNi mV FeCuNi mV °F FeCuNi mV NiCrNi mV 1031 1032 1033 1034 1035 59.780 59.838 59.897 59.956 60.014 42.479 42.518 42.556 42.595 42.633 37.450 37.488 37.527 37.565 37.603 9.946 9.958 9.970 9.981 9.993 10.918 10.932 10.945 10.958 10.972 5.120 5.130 5.139 5.148 5.158 1887.8 1889.6 1891.4 1893.2 1895.0 1036 1037 1038 1039 1040 60.073 60.131 60.190 60.248 60.307 42.672 42.711 42.749 42.788 42.826 37.642 37.680 37.719 37.757 37.795 10.005 10.016 10.028 10.040 10.051 10.985 10.998 11.012 11.025 11.039 5.167 5.176 5.186 5.195 5.205 1896.8 1898.6 1900.4 1902.2 1904.0 1041 1042 1043 1044 1045 60.365 60.423 60.482 60.540 60.599 42.865 42.903 42.942 42.980 43.019 37.834 37.872 37.911 37.949 37.987 10.063 10.075 10.086 10.098 10.110 11.052 11.065 11.079 11.092 11.106 5.214 5.223 5.233 5.242 5.252 1905.8 1907.6 1909.4 1911.2 1913.0 1046 1047 1048 1049 1050 60.657 60.715 60.774 60.832 60.890 43.057 43.096 43.134 43.173 43.211 38.026 38.064 38.102 38.141 38.179 10.121 10.133 10.145 10.156 10.168 11.119 11.133 11.146 11.159 11.173 5.261 5.270 5.280 5.289 5.299 1914.8 1916.6 1918.4 1920.2 1922.0 1051 1052 1053 1054 1055 60.949 61.007 61.065 61.123 61.182 43.250 43.288 43.327 43.365 43.403 38.217 38.256 38.294 38.332 38.370 10.180 10.191 10.203 10.215 10.227 11.186 11.200 11.213 11.227 11.240 5.308 5.318 5.327 5.337 5.346 1923.8 1925.6 1927.4 1929.2 1931.0 1056 1057 1058 1059 1060 61.240 61.298 61.356 61.415 61.473 43.442 43.480 43.518 43.557 43.595 38.409 38.447 38.485 38.524 38.562 10.238 10.250 10.262 10.273 10.285 11.254 11.267 11.280 11.294 11.307 5.356 5.365 5.375 5.384 5.394 1932.8 1934.6 1936.4 1938.2 1940.0 1061 1062 1063 1064 1065 61.531 61.589 61.647 61.705 61.763 43.633 43.672 43.710 43.748 43.787 38.600 38.638 38.677 38.715 38.753 10.297 10.309 10.320 10.332 10.344 11.321 11.334 11.348 11.361 11.375 5.403 5.413 5.422 5.432 5.441 1941.8 1943.6 1945.4 1947.2 1949.0 1066 1067 1068 1069 1070 61.822 61.880 61.938 61.996 62.054 43.825 43.863 43.901 43.940 43.978 38.791 38.829 38.868 38.906 38.944 10.356 10.367 10.379 10.391 10.403 11.388 11.402 11.415 11.429 11.442 5.451 5.460 5.470 5.480 5.489 1950.8 1952.6 1954.4 1956.2 1958.0 1071 1072 1073 1074 1075 62.112 62.170 62.228 62.286 62.344 44.016 44.054 44.092 44.130 44.169 38.982 39.020 39.059 39.097 39.135 10.414 10.426 10.438 10.450 10.461 11.456 11.469 11.483 11.496 11.510 5.499 5.508 5.518 5.528 5.537 1959.8 1961.6 1963.4 1965.2 1967.0 1076 1077 1078 1079 1080 62.402 62.460 62.518 62.576 62.634 44.207 44.245 44.283 44.321 44.359 39.173 39.211 39.249 39.287 39.326 10.473 10.485 10.497 10.509 10.520 11.524 11.537 11.551 11.564 11.578 5.547 5.556 5.566 5.576 5.585 1968.8 1970.6 1972.4 1974.2 1976.0 t90 CuCuNi mV Ω Ω t90 307 °C Type T Type E Type J Type K Type N Type S Type R Type B Type U Type L Pt100 Ni100 NiCrNi mV 1081 1082 1083 1084 1085 62.692 62.750 62.808 62.866 62.924 44.397 44.435 44.473 44.512 44.550 39.364 39.402 39.440 39.478 39.516 10.532 10.544 10.556 10.567 10.579 11.591 11.605 11.618 11.632 11.646 5.595 5.605 5.614 5.624 5.634 1977.8 1979.6 1981.4 1983.2 1985.0 1086 1087 1088 1089 1090 62.982 63.040 63.098 63.156 63.214 44.588 44.626 44.664 44.702 44.740 39.554 39.592 39.630 39.668 39.706 10.591 10.603 10.615 10.626 10.638 11.659 11.673 11.686 11.700 11.714 5.643 5.653 5.663 5.672 5.682 1986.8 1988.6 1990.4 1992.2 1994.0 1091 1092 1093 1094 1095 63.271 63.329 63.387 63.445 63.503 44.778 44.816 44.853 44.891 44.929 39.744 39.783 39.821 39.859 39.897 10.650 10.662 10.674 10.686 10.697 11.727 11.741 11.754 11.768 11.782 5.692 5.702 5.711 5.721 5.731 1995.8 1997.6 1999.4 2001.2 2003.0 1096 1097 1098 1099 1100 63.561 63.619 63.677 63.734 63.792 44.967 45.005 45.043 45.081 45.119 39.935 39.973 40.011 40.049 40.087 10.709 10.721 10.733 10.745 10.757 11.795 11.809 11.822 11.836 11.850 5.740 5.750 5.760 5.770 5.780 2004.8 2006.6 2008.4 2010.2 2012.0 1101 1102 1103 1104 1105 63.850 63.908 63.966 64.024 64.081 45.157 45.194 45.232 45.270 45.308 40.125 40.163 40.201 40.238 40.276 10.768 10.780 10.792 10.804 10.816 11.863 11.877 11.891 11.904 11.918 5.789 5.799 5.809 5.819 5.828 2013.8 2015.6 2017.4 2019.2 2021.0 1106 1107 1108 1109 1110 64.139 64.197 64.255 64.313 64.370 45.346 45.383 45.421 45.459 45.497 40.314 40.352 40.390 40.428 40.466 10.828 10.839 10.851 10.863 10.875 11.931 11.945 11.959 11.972 11.986 5.838 5.848 5.858 5.868 5.878 2022.8 2024.6 2026.4 2028.2 2030.0 1111 1112 1113 1114 1115 64.428 64.486 64.544 64.602 64.659 45.534 45.572 45.610 45.647 45.685 40.504 40.542 40.580 40.618 40.655 10.887 10.899 10.911 10.922 10.934 12.000 12.013 12.027 12.041 12.054 5.887 5.897 5.907 5.917 5.927 2031.8 2033.6 2035.4 2037.2 2039.0 1116 1117 1118 1119 1120 64.717 64.775 64.833 64.890 64.948 45.723 45.760 45.798 45.836 45.873 40.693 40.731 40.769 40.807 40.845 10.946 10.958 10.970 10.982 10.994 12.068 12.082 12.096 12.109 12.123 5.937 5.947 5.956 5.966 5.976 2040.8 2042.6 2044.4 2046.2 2048.0 1121 1122 1123 1124 1125 65.006 65.064 65.121 65.179 65.237 45.911 45.948 45.986 46.024 46.061 40.883 40.920 40.958 40.996 41.034 11.006 11.017 11.029 11.041 11.053 12.137 12.150 12.164 12.178 12.191 5.986 5.996 6.006 6.016 6.026 2049.8 2051.6 2053.4 2055.2 2057.0 1126 1127 1128 1129 1130 65.295 65.352 65.410 65.468 65.525 46.099 46.136 46.174 46.211 46.249 41.072 41.109 41.147 41.185 41.223 11.065 11.077 11.089 11.101 11.113 12.205 12.219 12.233 12.246 12.260 6.036 6.046 6.055 6.065 6.075 2058.8 2060.6 2062.4 2064.2 2066.0 308 NiCrCuNi mV NiCrSi- Pt10Rh- Pt13Rh- Pt30RhNiSi Pt Pt Pt6Rh mV mV mV mV CuCuNi mV FeCuNi mV °F FeCuNi mV t90 CuCuNi mV Ω Ω t90 °C Type T Type E Type J Type K Type N Type S Type R Type B Type U Type L Pt100 Ni100 NiCrCuNi mV NiCrSi- Pt10Rh- Pt13Rh- Pt30RhNiSi Pt Pt Pt6Rh mV mV mV mV CuCuNi mV FeCuNi mV °F FeCuNi mV NiCrNi mV 1131 1132 1133 1134 1135 65.583 65.641 65.699 65.756 65.814 46.286 46.324 46.361 46.398 46.436 41.260 41.298 41.336 41.374 41.411 11.125 11.136 11.148 11.160 11.172 12.274 12.288 12.301 12.315 12.329 6.085 6.095 6.105 6.115 6.125 2067.8 2069.6 2071.4 2073.2 2075.0 1136 1137 1138 1139 1140 65.872 65.929 65.987 66.045 66.102 46.473 46.511 46.548 46.585 46.623 41.449 41.487 41.525 41.562 41.600 11.184 11.196 11.208 11.220 11.232 12.342 12.356 12.370 12.384 12.397 6.135 6.145 6.155 6.165 6.175 2076.8 2078.6 2080.4 2082.2 2084.0 1141 1142 1143 1144 1145 66.160 66.218 66.275 66.333 66.391 46.660 46.697 46.735 46.772 46.809 41.638 41.675 41.713 41.751 41.788 11.244 11.256 11.268 11.280 11.291 12.411 12.425 12.439 12.453 12.466 6.185 6.195 6.205 6.215 6.225 2085.8 2087.6 2089.4 2091.2 2093.0 1146 1147 1148 1149 1150 66.448 66.506 66.564 66.621 66.679 46.847 46.884 46.921 46.958 46.995 41.826 41.864 41.901 41.939 41.976 11.303 11.315 11.327 11.339 11.351 12.480 12.494 12.508 12.521 12.535 6.235 6.245 6.256 6.266 6.276 2094.8 2096.6 2098.4 2100.2 2102.0 1151 1152 1153 1154 1155 66.737 66.794 66.852 66.910 66.967 47.033 47.070 47.107 47.144 47.181 42.014 42.052 42.089 42.127 42.164 11.363 11.375 11.387 11.399 11.411 12.549 12.563 12.577 12.590 12.604 6.286 6.296 6.306 6.316 6.326 2103.8 2105.6 2107.4 2109.2 2111.0 1156 1157 1158 1159 1160 67.025 67.082 67.140 67.198 67.255 47.218 47.256 47.293 47.330 47.367 42.202 42.239 42.277 42.314 42.352 11.423 11.435 11.447 11.459 11.471 12.618 12.632 12.646 12.659 12.673 6.336 6.346 6.356 6.367 6.377 2112.8 2114.6 2116.4 2118.2 2120.0 1161 1162 1163 1164 1165 67.313 67.370 67.428 67.486 67.543 47.404 47.441 47.478 47.515 47.552 42.390 42.427 42.465 42.502 42.540 11.483 11.495 11.507 11.519 11.531 12.687 12.701 12.715 12.729 12.742 6.387 6.397 6.407 6.417 6.427 2121.8 2123.6 2125.4 2127.2 2129.0 1166 1167 1168 1169 1170 67.601 67.658 67.716 67.773 67.831 47.589 47.626 47.663 47.700 47.737 42.577 42.614 42.652 42.689 42.727 11.542 11.554 11.566 11.578 11.590 12.756 12.770 12.784 12.798 12.812 6.438 6.448 6.458 6.468 6.478 2130.8 2132.6 2134.4 2136.2 2138.0 1171 1172 1173 1174 1175 67.888 67.946 68.003 68.061 68.119 47.774 47.811 47.848 47.884 47.921 42.764 42.802 42.839 42.877 42.914 11.602 11.614 11.626 11.638 11.650 12.825 12.839 12.853 12.867 12.881 6.488 6.499 6.509 6.519 6.529 2139.8 2141.6 2143.4 2145.2 2147.0 1176 1177 1178 1179 1180 68.176 68.234 68.291 68.348 68.406 47.958 47.995 48.032 48.069 48.105 42.951 42.989 43.026 43.064 43.101 11.662 11.674 11.686 11.698 11.710 12.895 12.909 12.922 12.936 12.950 6.539 6.550 6.560 6.570 6.580 2148.8 2150.6 2152.4 2154.2 2156.0 t90 CuCuNi mV Ω Ω t90 309 °C Type T Type E Type J Type K Type N Type S Type R Type B Type U Type L Pt100 Ni100 NiCrNi mV 1181 1182 1183 1184 1185 68.463 68.521 68.578 68.636 68.693 48.142 48.179 48.216 48.252 48.289 43.138 43.176 43.213 43.250 43.288 11.722 11.734 11.746 11.758 11.770 12.964 12.978 12.992 13.006 13.019 6.591 6.601 6.611 6.621 6.632 2157.8 2159.6 2161.4 2163.2 2165.0 1186 1187 1188 1189 1190 68.751 68.808 68.865 68.923 68.980 48.326 48.363 48.399 48.436 48.473 43.325 43.362 43.399 43.437 43.474 11.782 11.794 11.806 11.818 11.830 13.033 13.047 13.061 13.075 13.089 6.642 6.652 6.663 6.673 6.683 2166.8 2168.6 2170.4 2172.2 2174.0 1191 1192 1193 1194 1195 69.037 69.095 69.152 69.209 69.267 48.509 48.546 48.582 48.619 48.656 43.511 43.549 43.586 43.623 43.660 11.842 11.854 11.866 11.878 11.890 13.103 13.117 13.131 13.145 13.158 6.693 6.704 6.714 6.724 6.735 2175.8 2177.6 2179.4 2181.2 2183.0 1196 1197 1198 1199 1200 69.324 69.381 69.439 69.496 69.553 48.692 48.729 48.765 48.802 48.838 43.698 43.735 43.772 43.809 43.846 11.902 11.914 11.926 11.939 11.951 13.172 13.186 13.200 13.214 13.228 6.745 6.755 6.766 6.776 6.786 2184.8 2186.6 2188.4 2190.2 2192.0 1201 1202 1203 1204 1205 48.875 48.911 48.948 48.984 49.021 43.884 43.921 43.958 43.995 44.032 11.963 11.975 11.987 11.999 12.011 13.242 13.256 13.270 13.284 13.298 6.797 6.807 6.818 6.828 6.838 2193.8 2195.6 2197.4 2199.2 2201.0 1206 1207 1208 1209 1210 49.057 49.093 49.130 49.166 49.202 44.069 44.106 44.144 44.181 44.218 12.023 12.035 12.047 12.059 12.071 13.311 13.325 13.339 13.353 13.367 6.849 6.859 6.869 6.880 6.890 2202.8 2204.6 2206.4 2208.2 2210.0 1211 1212 1213 1214 1215 49.239 49.275 49.311 49.348 49.384 44.255 44.292 44.329 44.366 44.403 12.083 12.095 12.107 12.119 12.131 13.381 13.395 13.409 13.423 13.437 6.901 6.911 6.922 6.932 6.942 2211.8 2213.6 2215.4 2217.2 2219.0 1216 1217 1218 1219 1220 49.420 49.456 49.493 49.529 49.565 44.440 44.477 44.514 44.551 44.588 12.143 12.155 12.167 12.179 12.191 13.451 13.465 13.479 13.493 13.507 6.953 6.963 6.974 6.984 6.995 2220.8 2222.6 2224.4 2226.2 2228.0 1221 1222 1223 1224 1225 49.601 49.637 49.674 49.710 49.746 44.625 44.662 44.699 44.736 44.773 12.203 12.216 12.228 12.240 12.252 13.521 13.535 13.549 13.563 13.577 7.005 7.016 7.026 7.037 7.047 2229.8 2231.6 2233.4 2235.2 2237.0 1226 1227 1228 1229 1230 49.782 49.818 49.854 49.890 49.926 44.810 44.847 44.884 44.921 44.958 12.264 12.276 12.288 12.300 12.312 13.590 13.604 13.618 13.632 13.646 7.058 7.068 7.079 7.089 7.100 2238.8 2240.6 2242.4 2244.2 2246.0 310 NiCrCuNi mV NiCrSi- Pt10Rh- Pt13Rh- Pt30RhNiSi Pt Pt Pt6Rh mV mV mV mV CuCuNi mV FeCuNi mV °F FeCuNi mV t90 CuCuNi mV Ω Ω t90 °C Type T Type E Type J Type K Type N Type S Type R Type B Type U Type L Pt100 Ni100 t90 CuCuNi mV NiCrCuNi mV FeCuNi mV NiCrNi mV NiCrSi- Pt10Rh- Pt13Rh- Pt30RhNiSi Pt Pt Pt6Rh mV mV mV mV CuCuNi mV FeCuNi mV Ω Ω °F t90 1231 1232 1233 1234 1235 49.962 49.998 50.034 50.070 50.106 44.995 45.032 45.069 45.105 45.142 12.324 12.336 12.348 12.360 12.372 13.660 13.674 13.688 13.702 13.716 7.110 7.121 7.131 7.142 7.152 2247.8 2249.6 2251.4 2253.2 2255.0 1236 1237 1238 1239 1240 50.142 50.178 50.214 50.250 50.286 45.179 45.216 45.253 45.290 45.326 12.384 12.397 12.409 12.421 12.433 13.730 13.744 13.758 13.772 13.786 7.163 7.173 7.184 7.194 7.205 2256.8 2258.6 2260.4 2262.2 2264.0 1241 1242 1243 1244 1245 50.322 50.358 50.393 50.429 50.465 45.363 45.400 45.437 45.474 45.510 12.445 12.457 12.469 12.481 12.493 13.800 13.814 13.828 13.842 13.856 7.216 7.226 7.237 7.247 7.258 2265.8 2267.6 2269.4 2271.2 2273.0 1246 1247 1248 1249 1250 50.501 50.537 50.572 50.608 50.644 45.547 45.584 45.621 45.657 45.694 12.505 12.517 12.529 12.542 12.554 13.870 13.884 13.898 13.912 13.926 7.269 7.279 7.290 7.300 7.311 2274.8 2276.6 2278.4 2280.2 2282.0 1251 1252 1253 1254 1255 50.680 50.715 50.751 50.787 50.822 45.731 45.767 45.804 45.841 45.877 12.566 12.578 12.590 12.602 12.614 13.940 13.954 13.968 13.982 13.996 7.322 7.332 7.343 7.353 7.364 2283.8 2285.6 2287.4 2289.2 2291.0 1256 1257 1258 1259 1260 50.858 50.894 50.929 50.965 51.000 45.914 45.951 45.987 46.024 46.060 12.626 12.638 12.650 12.662 12.675 14.010 14.024 14.038 14.052 14.066 7.375 7.385 7.396 7.407 7.417 2292.8 2294.6 2296.4 2298.2 2300.0 1261 1262 1263 1264 1265 51.036 51.071 51.107 51.142 51.178 46.097 46.133 46.170 46.207 46.243 12.687 12.699 12.711 12.723 12.735 14.081 14.095 14.109 14.123 14.137 7.428 7.439 7.449 7.460 7.471 2301.8 2303.6 2305.4 2307.2 2309.0 1266 1267 1268 1269 1270 51.213 51.249 51.284 51.320 51.355 46.280 46.316 46.353 46.389 46.425 12.747 12.759 12.771 12.783 12.796 14.151 14.165 14.179 14.193 14.207 7.482 7.492 7.503 7.514 7.524 2310.8 2312.6 2314.4 2316.2 2318.0 1271 1272 1273 1274 1275 51.391 51.426 51.461 51.497 51.532 46.462 46.498 46.535 46.571 46.608 12.808 12.820 12.832 12.844 12.856 14.221 14.235 14.249 14.263 14.277 7.535 7.546 7.557 7.567 7.578 2319.8 2321.6 2323.4 2325.2 2327.0 1276 1277 1278 1279 1280 51.567 51.603 51.638 51.673 51.708 46.644 46.680 46.717 46.753 46.789 12.868 12.880 12.892 12.905 12.917 14.291 14.305 14.319 14.333 14.347 7.589 7.600 7.610 7.621 7.632 2328.8 2330.6 2332.4 2334.2 2336.0 311 °C Type T Type E Type J Type K Type N Type S Type R Type B Type U Type L Pt100 Ni100 t90 CuCuNi mV NiCrCuNi mV FeCuNi mV NiCrNi mV NiCrSi- Pt10Rh- Pt13Rh- Pt30RhNiSi Pt Pt Pt6Rh mV mV mV mV CuCuNi mV FeCuNi mV Ω Ω °F t90 1281 1282 1283 1284 1285 51.744 51.779 51.814 51.849 51.885 46.826 46.862 46.898 46.935 46.971 12.929 12.941 12.953 12.965 12.977 14.361 14.375 14.390 14.404 14.418 7.643 7.653 7.664 7.675 7.686 2337.8 2339.6 2341.4 2343.2 2345.0 1286 1287 1288 1289 1290 51.920 51.955 51.990 52.025 52.060 47.007 47.043 47.079 47.116 47.152 12.989 13.001 13.014 13.026 13.038 14.432 14.446 14.460 14.474 14.488 7.697 7.707 7.718 7.729 7.740 2346.8 2348.6 2350.4 2352.2 2354.0 1291 1292 1293 1294 1295 52.095 52.130 52.165 52.200 52.235 47.188 47.224 47.260 47.296 47.333 13.050 13.062 13.074 13.086 13.098 14.502 14.516 14.530 14.544 14.558 7.751 7.761 7.772 7.783 7.794 2355.8 2357.6 2359.4 2361.2 2363.0 1296 1297 1298 1299 1300 52.270 52.305 52.340 52.375 52.410 47.369 47.405 47.441 47.477 47.513 13.111 13.123 13.135 13.147 13.159 14.572 14.586 14.601 14.615 14.629 7.805 7.816 7.827 7.837 7.848 2364.8 2366.6 2368.4 2370.2 2372.0 1301 1302 1303 1304 1305 52.445 52.480 52.515 52.550 52.585 13.171 13.183 13.195 13.208 13.220 14.643 14.657 14.671 14.685 14.699 7.859 7.870 7.881 7.892 7.903 2373.8 2375.6 2377.4 2379.2 2381.0 1306 1397 1308 1309 1310 52.620 52.654 52.689 52.724 52.759 13.232 13.244 13.256 13.268 13.280 14.713 14.727 14.741 14.755 14.770 7.914 7.924 7.935 7.946 7.957 2382.8 2384.6 2386.4 2388.2 2390.0 1311 1312 1313 1314 1315 52.794 52.828 52.863 52.898 52.932 13.292 13.305 13.317 13.329 13.341 14.784 14.798 14.812 14.826 14.840 7.968 7.979 7.990 8.001 8.012 2391.8 2393.6 2395.4 2397.2 2399.0 1316 1317 1318 1319 1320 52.967 53.002 53.037 53.071 53.106 13.353 13.365 13.377 13.390 13.402 14.854 14.868 14.882 14.896 14.911 8.023 8.034 8.045 8.056 8.066 2400.8 2402.6 2404.4 2406.2 2408.0 1321 1322 1323 1324 1325 53.140 53.175 53.210 53.244 53.279 13.414 13.426 13.438 13.450 13.462 14.925 14.939 14.953 14.967 14.981 8.077 8.088 8.099 8.110 8.121 2409.8 2411.6 2413.4 2415.2 2417.0 1326 1327 1328 1329 1330 53.313 53.348 53.382 53.417 53.451 13.474 13.487 13.499 13.511 13.523 14.995 15.009 15.023 15.037 15.052 8.132 8.143 8.154 8.165 8.176 2418.8 2420.6 2422.4 2424.2 2426.0 312 °C Type T Type E Type J Type K Type N Type S Type R Type B Type U Type L Pt100 Ni100 t90 CuCuNi mV NiCrCuNi mV FeCuNi mV NiCrNi mV NiCrSi- Pt10Rh- Pt13Rh- Pt30RhNiSi Pt Pt Pt6Rh mV mV mV mV CuCuNi mV FeCuNi mV Ω Ω °F t90 1331 1332 1333 1334 1335 53.486 53.520 53.555 53.589 53.623 13.535 13.547 13.559 13.572 13.584 15.066 15.080 15.094 15.108 15.122 8.187 8.198 8.209 8.220 8.231 2427.8 2429.6 2431.4 2433.2 2435.0 1336 1337 1338 1339 1340 53.658 53.692 53.727 53.761 53.795 13.596 13.608 13.620 13.632 13.644 15.136 15.150 15.164 15.179 15.193 8.242 8.253 8.264 8.275 8.286 2436.8 2438.6 2440.4 2442.2 2444.0 1341 1342 1343 1344 1345 53.830 53.864 53.898 53.932 53.967 13.657 13.669 13.681 13.693 13.705 15.207 15.221 15.235 15.249 15.263 8.298 8.309 8.320 8.331 8.342 2445.8 2447.6 2449.4 2451.2 2453.0 1346 1347 1348 1349 1350 54.001 54.035 54.069 54.104 54.138 13.717 13.729 13.742 13.754 13.766 15.277 15.291 15.306 15.320 15.334 8.353 8.364 8.375 8.386 8.397 2454.8 2456.6 2458.4 2460.2 2462.0 1351 1352 1353 1354 1355 54.172 54.206 54.240 54.274 54.308 13.778 13.790 13.802 13.814 13.826 15.348 15.362 15.376 15.390 15.404 8.408 8.419 8.430 8.441 8.453 2463.8 2465.6 2467.4 2469.2 2471.0 1356 1357 1358 1359 1360 54.343 54.377 54.411 54.445 54.479 13.839 13.851 13.863 13.875 13.887 15.419 15.433 15.447 15.461 15.475 8.464 8.475 8.486 8.497 8.508 2472.8 2474.6 2476.4 2478.2 2480.0 1361 1362 1363 1364 1365 54.513 54.547 54.581 54.615 54.649 13.899 13.911 13.924 13.936 13.948 15.489 15.503 15.517 15.531 15.546 8.519 8.530 8.542 8.553 8.564 2481.8 2483.6 2485.4 2487.2 2489.0 1366 1367 1368 1369 1370 54.683 54.717 54.751 54.785 54.819 13.960 13.972 13.984 13.996 14.009 15.560 15.574 15.588 15.602 15.616 8.575 8.586 8.597 8.608 8.620 2490.8 2492.6 2494.4 2496.2 2498.0 1371 1372 1373 1374 1375 54.852 54.886 14.021 14.033 14.045 14.057 14.069 15.630 15.645 15.659 15.673 15.687 8.631 8.642 8.653 8.664 8.675 2499.8 2501.6 2503.4 2505.2 2507.0 14.081 14.094 14.106 14.118 14.130 15.701 15.715 15.729 15.743 15.758 8.687 8.698 8.709 8.720 8.731 2508.8 2510.6 2512.4 2514.2 2516.0 1376 1377 1378 1379 1380 313 °C Type T Type E Type J Type K Type N Type S Type R Type B Type U Type L Pt100 Ni100 t90 CuCuNi mV NiCrCuNi mV FeCuNi mV NiCrNi mV NiCrSi- Pt10Rh- Pt13Rh- Pt30RhNiSi Pt Pt Pt6Rh mV mV mV mV CuCuNi mV FeCuNi mV Ω Ω °F t90 1381 1382 1383 1384 1385 14.142 14.154 14.166 14.178 14.191 15.772 15.786 15.800 15.814 15.828 8.743 8.754 8.765 8.776 8.787 2517.8 2519.6 2521.4 2523.2 2525.0 1386 1387 1388 1389 1390 14.203 14.215 14.227 14.239 14.251 15.842 15.856 15.871 15.885 15.899 8.799 8.810 8.821 8.832 8.844 2526.8 2528.6 2530.4 2532.2 2534.0 1391 1392 1393 1394 1395 14.263 14.276 14.288 14.300 14.312 15.913 15.927 15.941 15.955 15.969 8.855 8.866 8.877 8.889 8.900 2535.8 2537.6 2539.4 2541.2 2543.0 1396 1397 1398 1399 1400 14.324 14.336 14.348 14.360 14.373 15.984 15.998 16.012 16.026 16.040 8.911 8.922 8.934 8.945 8.956 2544.8 2546.6 2548.4 2550.2 2552.0 1401 1402 1403 1404 1405 14.385 14.397 14.409 14.421 14.433 16.054 16.068 16.082 16.097 16.111 8.967 8.979 8.990 9.001 9.013 2553.8 2555.6 2557.4 2559.2 2561.0 1406 1407 1408 1409 1410 14.445 14.457 14.470 14.482 14.494 16.125 16.139 16.153 16.167 16.181 9.024 9.035 9.047 9.058 9.069 2562.8 2564.6 2566.4 2568.2 2570.0 1411 1412 1413 1414 1415 14.506 14.518 14.530 14.542 14.554 16.196 16.210 16.224 16.238 16.252 9.080 9.092 9.103 9.114 9.126 2571.8 2573.6 2575.4 2577.2 2579.0 1416 1417 1418 1419 1420 14.567 14.579 14.591 14.603 14.615 16.266 16.280 16.294 16.309 16.323 9.137 9.148 9.160 9.171 9.182 2580.8 2582.6 2584.4 2586.2 2588.0 1421 1422 1423 1424 1425 14.627 14.639 14.651 14.664 14.676 16.337 16.351 16.365 16.379 16.393 9.194 9.205 9.216 9.228 9.239 2589.8 2591.6 2593.4 2595.2 2597.0 1426 1427 1428 1429 1430 14.688 14.700 14.712 14.724 14.736 16.407 16.422 16.436 16.450 16.464 9.251 9.262 9.273 9.285 9.296 2598.8 2600.6 2602.4 2604.2 2606.0 314 °C Type T Type E Type J Type K Type N Type S Type R Type B Type U Type L Pt100 Ni100 t90 CuCuNi mV NiCrCuNi mV FeCuNi mV NiCrNi mV NiCrSi- Pt10Rh- Pt13Rh- Pt30RhNiSi Pt Pt Pt6Rh mV mV mV mV CuCuNi mV FeCuNi mV Ω Ω °F t90 1431 1432 1433 1434 1435 14.748 14.760 14.773 14.785 14.797 16.478 16.492 16.506 16.520 16.534 9.307 9.319 9.330 9.342 9.353 2607.8 2609.6 2611.4 2613.2 2615.0 1436 1437 1438 1439 1440 14.809 14.821 14.833 14.845 14.857 16.549 16.563 16.577 16.591 16.605 9.364 9.376 9.387 9.398 9.410 2616.8 2618.6 2620.4 2622.2 2624.0 1441 1442 1443 1444 1445 14.869 14.881 14.894 14.906 14.918 16.619 16.633 16.647 16.662 16.676 9.421 9.433 9.444 9.456 9.467 2625.8 2627.6 2629.4 2631.2 2633.0 1446 1447 1448 1449 1450 14.930 14.942 14.954 14.966 14.978 16.690 16.704 16.718 16.732 16.746 9.478 9.490 9.501 9.513 9.524 2634.8 2636.6 2638.4 2640.2 2642.0 1451 1452 1453 1454 1455 14.990 15.002 15.015 15.027 15.039 16.760 16.774 16.789 16.803 16.817 9.536 9.547 9.558 9.570 9.581 2643.8 2645.6 2647.4 2649.2 2651.0 1456 1457 1458 1459 1460 15.051 15.063 15.075 15.087 15.099 16.831 16.845 16.859 16.873 16.887 9.593 9.604 9.616 9.627 9.639 2652.8 2654.6 2656.4 2658.2 2660.0 1461 1462 1463 1464 1465 15.111 15.123 15.135 15.148 15.160 16.901 16.915 16.930 16.944 16.958 9.650 9.662 9.673 9.684 9.696 2661.8 2663.6 2665.4 2667.2 2669.0 1466 1467 1468 1469 1470 15.172 15.184 15.196 15.208 15.220 16.972 16.986 17.000 17.014 17.028 9.707 9.719 9.730 9.742 9.753 2670.8 2672.6 2674.4 2676.2 2678.0 1471 1472 1473 1474 1475 15.232 15.244 15.256 15.268 15.280 17.042 17.056 17.071 17.085 17.099 9.765 9.776 9.788 9.799 9.811 2679.8 2681.6 2683.4 2685.2 2687.0 1476 1477 1478 1479 1480 15.292 15.304 15.317 15.329 15.341 17.113 17.127 17.141 17.155 17.169 9.822 9.834 9.845 9.857 9.868 2688.8 2690.6 2692.4 2694.2 2696.0 315 °C Type T Type E Type J Type K Type N Type S Type R Type B Type U Type L Pt100 Ni100 t90 CuCuNi mV NiCrCuNi mV FeCuNi mV NiCrNi mV NiCrSi- Pt10Rh- Pt13Rh- Pt30RhNiSi Pt Pt Pt6Rh mV mV mV mV CuCuNi mV FeCuNi mV Ω Ω °F t90 1481 1482 1483 1484 1485 15.353 15.365 15.377 15.389 15.401 17.183 17.197 17.211 17.225 17.240 9.880 9.891 9.903 9.914 9.926 2697.8 2699.6 2701.4 2703.2 2705.0 1486 1487 1488 1489 1490 15.413 15.425 15.437 15.449 15.461 17.254 17.268 17.282 17.296 17.310 9.937 9.949 9.961 9.972 9.984 2706.8 2708.6 2710.4 2712.2 2714.0 1491 1492 1493 1494 1495 15.473 15.485 15.497 15.509 15.521 17.324 17.338 17.352 17.366 17.380 9.995 10.007 10.018 10.030 10.041 2715.8 2717.6 2719.4 2721.2 2723.0 1496 1497 1498 1499 1500 15.534 15.546 15.558 15.570 15.582 17.394 17.408 17.423 17.437 17.451 10.053 10.064 10.076 10.088 10.099 2724.8 2726.6 2728.4 2730.2 2732.0 1501 1502 1503 1504 1505 15.594 15.606 15.618 15.630 15.642 17.465 17.479 17.493 17.507 17.521 10.111 10.122 10.134 10.145 10.157 2733.8 2735.6 2737.4 2739.2 2741.0 1506 1507 1508 1509 1510 15.654 15.666 15.678 15.690 15.702 17.535 17.549 17.563 17.577 17.591 10.168 10.180 10.192 10.203 10.215 2742.8 2744.6 2746.4 2748.2 2750.0 1511 1512 1513 1514 1515 15.714 15.726 15.738 15.750 15.762 17.605 17.619 17.633 17.647 17.661 10.226 10.238 10.249 10.261 10.273 2751.8 2753.6 2755.4 2757.2 2759.0 1516 1517 1518 1519 1520 15.774 15.786 15.798 15.810 15.822 17.676 17.690 17.704 17.718 17.732 10.284 10.296 10.307 10.319 10.331 2760.8 2762.6 2764.4 2766.2 2768.0 1521 1522 1523 1524 1525 15.834 15.846 15.858 15.870 15.882 17.746 17.760 17.774 17.788 17.802 10.342 10.354 10.365 10.377 10.389 2769.8 2771.6 2773.4 2775.2 2777.0 1526 1527 1528 1529 1530 15.894 15.906 15.918 15.930 15.942 17.816 17.830 17.844 17.858 17.872 10.400 10.412 10.423 10.435 10.447 2778.8 2780.6 2782.4 2784.2 2786.0 316 °C Type T Type E Type J Type K Type N Type S Type R Type B Type U Type L Pt100 Ni100 t90 CuCuNi mV NiCrCuNi mV FeCuNi mV NiCrNi mV NiCrSi- Pt10Rh- Pt13Rh- Pt30RhNiSi Pt Pt Pt6Rh mV mV mV mV CuCuNi mV FeCuNi mV Ω Ω °F t90 1531 1532 1533 1534 1535 15.954 15.966 15.978 15.990 16.002 17.886 17.900 17.914 17.928 17.942 10.458 10.470 10.482 10.493 10.505 2787.8 2789.6 2791.4 2793.2 2795.0 1536 1537 1538 1539 1540 16.014 16.026 16.038 16.050 16.062 17.956 17.970 17.984 17.998 18.012 10.516 10.528 10.540 10.551 10.563 2796.8 2798.6 2800.4 2802.2 2804.0 1541 1542 1543 1544 1545 16.074 16.086 16.098 16.110 16.122 18.026 18.040 18.054 18.068 18.082 10.575 10.586 10.598 10.609 10.621 2805.8 2807.6 2809.4 2811.2 2813.0 1546 1547 1548 1549 1550 16.134 16.146 16.158 16.170 16.182 18.096 18.110 18.124 18.138 18.152 10.633 10.644 10.656 10.668 10.679 2814.8 2816.6 2818.4 2820.2 2822.0 1551 1552 1553 1554 1555 16.194 16.205 16.217 16.229 16.241 18.166 18.180 18.194 18.208 18.222 10.691 10.703 10.714 10.726 10.738 2823.8 2825.6 2827.4 2829.2 2831.0 1556 1557 1558 1559 1560 16.253 16.265 16.277 16.289 16.301 18.236 18.250 18.264 18.278 18.292 10.749 10.761 10.773 10.784 10.796 2832.8 2834.6 2836.4 2838.2 2840.0 1561 1562 1563 1564 1565 16.313 16.325 16.337 16.349 16.361 18.306 18.320 18.334 18.348 18.362 10.808 10.819 10.831 10.843 10.854 2841.8 2843.6 2845.4 2847.2 2849.0 1566 1567 1568 1569 1570 16.373 16.385 16.396 16.408 16.420 18.376 18.390 18.404 18.417 18.431 10.866 10.877 10.889 10.901 10.913 2850.8 2852.6 2854.4 2856.2 2858.0 1571 1572 1573 1574 1575 16.432 16.444 16.456 16.468 16.480 18.445 18.459 18.473 18.487 18.501 10.924 10.936 10.948 10.959 10.971 2859.8 2861.6 2863.4 2865.2 2867.0 1576 1577 1578 1579 1580 16.492 16.504 16.516 16.527 16.539 18.515 18.529 18.543 18.557 18.571 10.983 10.994 11.006 11.018 11.029 2868.8 2870.6 2872.4 2874.2 2876.0 317 °C Type T Type E Type J Type K Type N Type S Type R Type B Type U Type L Pt100 Ni100 t90 CuCuNi mV NiCrCuNi mV FeCuNi mV NiCrNi mV NiCrSi- Pt10Rh- Pt13Rh- Pt30RhNiSi Pt Pt Pt6Rh mV mV mV mV CuCuNi mV FeCuNi mV Ω Ω °F t90 1581 1582 1583 1584 1585 16.551 16.563 16.575 16.587 16.599 18.585 18.599 18.613 18.627 18.640 11.041 11.053 11.064 11.076 11.088 2877.8 2879.6 2881.4 2883.2 2885.0 1586 1587 1588 1589 1590 16.611 16.623 16.634 16.646 16.658 18.654 18.668 18.682 18.696 18.710 11.099 11.111 11.123 11.134 11.146 2886.8 2888.6 2890.4 2892.2 2894.0 1591 1592 1593 1594 1595 16.670 16.682 16.694 16.706 16.718 18.724 18.738 18.752 18.766 18.779 11.158 11.169 11.181 11.193 11.205 2895.8 2897.6 2899.4 2901.2 2903.0 1596 1597 1598 1599 1600 16.729 16.741 16.753 16.765 16.777 18.793 18.807 18.821 18.835 18.849 11.216 11.228 11.240 11.251 11.263 2904.8 2906.6 2908.4 2910.2 2912.0 1601 1602 1603 1604 1605 16.789 16.801 16.812 16.824 16.836 18.863 18.877 18.891 18.904 18.918 11.275 11.286 11.298 11.310 11.321 2913.8 2915.6 2917.4 2919.2 2921.0 1606 1607 1608 1609 1610 16.848 16.860 16.872 16.883 16.895 18.932 18.946 18.960 18.974 18.988 11.333 11.345 11.357 11.368 11.380 2922.8 2924.6 2926.4 2928.2 2930.0 1611 1612 1613 1614 1615 16.907 16.919 16.931 16.943 16.954 19.002 19.015 19.029 19.043 19.057 11.392 11.403 11.415 11.427 11.438 2931.8 2933.6 2935.4 2937.2 2939.0 1616 1617 1618 1619 1620 16.966 16.978 16.990 17.002 17.013 19.071 19.085 19.098 19.112 19.126 11.450 11.462 11.474 11.485 11.497 2940.8 2942.6 2944.4 2946.2 2948.0 1621 1622 1623 1624 1625 17.025 17.037 17.049 17.061 17.072 19.140 19.154 19.168 19.181 19.195 11.509 11.520 11.532 11.544 11.555 2949.8 2951.6 2953.4 2955.2 2957.0 1626 1627 1628 1629 1630 17.084 17.096 17.108 17.120 17.131 19.209 19.223 19.237 19.250 19.264 11.567 11.579 11.591 11.602 11.614 2958.8 2960.6 2962.4 2964.2 2966.0 318 °C Type T Type E Type J Type K Type N Type S Type R Type B Type U Type L Pt100 Ni100 t90 CuCuNi mV NiCrCuNi mV FeCuNi mV NiCrNi mV NiCrSi- Pt10Rh- Pt13Rh- Pt30RhNiSi Pt Pt Pt6Rh mV mV mV mV CuCuNi mV FeCuNi mV Ω Ω °F t90 1631 1632 1633 1634 1635 17.143 17.155 17.167 17.178 17.190 19.278 19.292 19.306 19.319 19.333 11.626 11.637 11.649 11.661 11.673 2967.8 2969.6 2971.4 2973.2 2975.0 1636 1637 1638 1639 1640 17.202 17.214 17.225 17.237 17.249 19.347 19.361 19.375 19.388 19.402 11.684 11.696 11.708 11.719 11.731 2976.8 2978.6 2980.4 2982.2 2984.0 1641 1642 1643 1644 1645 17.261 17.272 17.284 17.296 17.308 19.416 19.430 19.444 19.457 19.471 11.743 11.754 11.766 11.778 11.790 2985.8 2987.6 2989.4 2991.2 2993.0 1646 1647 1648 1649 1650 17.319 17.331 17.343 17.355 17.366 19.485 19.499 19.512 19.526 19.540 11.801 11.813 11.825 11.836 11.848 2994.8 2996.6 2998.4 3000.2 3002.0 1651 1652 1653 1654 1655 17.378 17.390 17.401 17.413 17.425 19.554 19.567 19.581 19.595 19.609 11.860 11.871 11.883 11.895 11.907 3003.8 3005.6 3007.4 3009.2 3011.0 1656 1657 1658 1659 1660 17.437 17.448 17.460 17.472 17.483 19.622 19.636 19.650 19.663 19.677 11.918 11.930 11.942 11.953 11.965 3012.8 3014.6 3016.4 3018.2 3020.0 1661 1662 1663 1664 1665 17.495 17.507 17.518 17.530 17.542 19.691 19.705 19.718 19.732 19.746 11.977 11.988 12.000 12.012 12.024 3021.8 3023.6 3025.4 3027.2 3029.0 1666 1667 1668 1669 1670 17.553 17.565 17.577 17.588 17.600 19.759 19.773 19.787 19.800 19.814 12.035 12.047 12.059 12.070 12.082 3030.8 3032.6 3034.4 3036.2 3038.0 1671 1672 1673 1674 1675 17.612 17.623 17.635 17.647 17.658 19.828 19.841 19.855 19.869 19.882 12.094 12.105 12.117 12.129 12.141 3039.8 3041.6 3043.4 3045.2 3047.0 1676 1677 1678 1679 1680 17.670 17.682 17.693 17.705 17.717 19.896 19.910 19.923 19.937 19.951 12.152 12.164 12.176 12.187 12.199 3048.8 3050.6 3052.4 3054.2 3056.0 319 °C Type T Type E Type J Type K Type N Type S Type R Type B Type U Type L Pt100 Ni100 t90 CuCuNi mV NiCrCuNi mV FeCuNi mV NiCrNi mV NiCrSi- Pt10Rh- Pt13Rh- Pt30RhNiSi Pt Pt Pt6Rh mV mV mV mV CuCuNi mV FeCuNi mV Ω Ω °F t90 1681 1682 1683 1684 1685 17.728 17.740 17.751 17.763 17.775 19.964 19.978 19.992 20.005 20.019 12.211 12.222 12.234 12.246 12.257 3057.8 3059.6 3061.4 3063.2 3065.0 1686 1687 1688 1689 1690 17.786 17.798 17.809 17.821 17.832 20.032 20.046 20.060 20.073 20.087 12.269 12.281 12.292 12.304 12.316 3066.8 3068.6 3070.4 3072.2 3074.0 1691 1692 1693 1694 1695 17.844 17.855 17.867 17.878 17.890 20.100 20.114 20.127 20.141 20.154 12.327 12.339 12.351 12.363 12.374 3075.8 3077.6 3079.4 3081.2 3083.0 1696 1697 1698 1699 1700 17.901 17.913 17.924 17.936 17.947 20.168 20.181 20.195 20.208 20.222 12.386 12.398 12.409 12.421 12.433 3084.8 3086.6 3088.4 3090.2 3092.0 1701 1702 1703 1704 1705 17.959 17.970 17.982 17.993 18.004 20.235 20.249 20.262 20.275 20.289 12.444 12.456 12.468 12.479 12.491 3093.8 3095.6 3097.4 3099.2 3101.0 1706 1707 1708 1709 1710 18.016 18.027 18.039 18.050 18.061 20.302 20.316 20.329 20.342 20.356 12.503 12.514 12.526 12.538 12.549 3102.8 3104.6 3106.4 3108.2 3110.0 1711 1712 1713 1714 1715 18.073 18.084 18.095 18.107 18.118 20.369 20.382 20.396 20.409 20.422 12.561 12.572 12.584 12.596 12.607 3111.8 3113.6 3115.4 3117.2 3119.0 1716 1717 1718 1719 1720 18.129 18.140 18.152 18.163 18.174 20.436 20.449 20.462 20.475 20.488 12.619 12.631 12.642 12.654 12.666 3120.8 3122.6 3124.4 3126.2 3128.0 1721 1722 1723 1724 1725 18.185 18.196 18.208 18.219 18.230 20.502 20.515 20.528 20.541 20.554 12.677 12.689 12.701 12.712 12.724 3129.8 3131.6 3133.4 3135.2 3137.0 1726 1727 1728 1729 1730 18.241 18.252 18.263 18.274 18.285 20.567 20.581 20.594 20.607 20.620 12.736 12.747 12.759 12.770 12.782 3138.8 3140.6 3142.4 3144.2 3146.0 320 °C Type T Type E Type J Type K Type N Type S Type R Type B Type U Type L Pt100 Ni100 t90 CuCuNi mV NiCrCuNi mV FeCuNi mV NiCrNi mV NiCrSi- Pt10Rh- Pt13Rh- Pt30RhNiSi Pt Pt Pt6Rh mV mV mV mV CuCuNi mV FeCuNi mV Ω Ω °F t90 1731 1732 1733 1734 1735 18.297 18.308 18.319 18.330 18.341 20.633 20.646 20.659 20.672 20.685 12.794 12.805 12.817 12.829 12.840 3147.8 3149.6 3151.4 3153.2 3155.0 1736 1737 1738 1739 1740 18.352 18.362 18.373 18.384 18.395 20.698 20.711 20.724 20.736 20.749 12.852 12.863 12.875 12.887 12.898 3156.8 3158.6 3160.4 3162.2 3164.0 1741 1742 1743 1744 1745 18.406 18.417 18.428 18.439 18.449 20.762 20.775 20.788 20.801 20.813 12.910 12.921 12.933 12.945 12.956 3165.8 3167.6 3169.4 3171.2 3173.0 1746 1747 1748 1749 1750 18.460 18.471 18.482 18.493 18.503 20.826 20.839 20.852 20.864 20.877 12.968 12.980 12.991 13.003 13.014 3174.8 3176.6 3178.4 3180.2 3182.0 1751 1752 1753 1754 1755 18.514 18.525 18.535 18.546 18.557 20.890 20.902 20.915 20.928 20.940 13.026 13.037 13.049 13.061 13.072 3183.8 3185.6 3187.4 3189.2 3191.0 1756 1757 1758 1759 1760 18.567 18.578 18.588 18.599 18.609 20.953 20.965 20.978 20.990 21.003 13.084 13.095 13.107 13.119 13.130 3192.8 3194.6 3196.4 3198.2 3200.0 1761 1762 1763 1764 1765 18.620 18.630 18.641 18.651 18.661 21.015 21.027 21.040 21.052 21.065 13.142 13.153 13.165 13.176 13.188 3201.8 3203.6 3205.4 3207.2 3209.0 1766 1767 1768 1769 1770 18.672 18.682 18.693 21.077 21.089 21.101 13.200 13.211 13.223 13.234 13.246 3210.8 3212.6 3214.4 3216.2 3218.0 1771 1772 1773 1774 1775 13.257 13.269 13.280 13.292 13.304 3219.8 3221.6 3223.4 3225.2 3227.0 1776 1777 1778 1779 1780 13.315 13.327 13.338 13.350 13.361 3228.8 3230.6 3232.4 3234.2 3236.0 321 °C Type T Type E Type J Type K Type N Type S Type R Type B Type U Type L Pt100 Ni100 t90 CuCuNi mV NiCrCuNi mV FeCuNi mV NiCrNi mV NiCrSi- Pt10Rh- Pt13Rh- Pt30RhNiSi Pt Pt Pt6Rh mV mV mV mV CuCuNi mV FeCuNi mV Ω Ω °F t90 1781 1782 1783 1784 1785 13.373 13.384 13.396 13.407 13.419 3237.8 3239.6 3241.4 3243.2 3245.0 1786 1787 1788 1789 1790 13.430 13.442 13.453 13.465 13.476 3246.8 3248.6 3250.4 3252.2 3254.0 1791 1792 1793 1794 1795 13.488 13.499 13.511 13.522 13.534 3255.8 3257.6 3259.4 3261.2 3263.0 1796 1797 1798 1799 1800 13.545 13.557 13.568 13.580 13.591 3264.8 3266.6 3268.4 3270.2 3272.0 1801 1802 1803 1804 1805 13.603 13.614 13.626 13.637 13.649 3273.8 3275.6 3277.4 3279.2 3281.0 1806 1807 1808 1809 1810 13.660 13.672 13.683 13.694 13.706 3282.8 3284.6 3286.4 3288.2 3290.0 1811 1812 1813 1814 1815 13.717 13.729 13.740 13.752 13.763 3291.8 3293.6 3295.4 3297.2 3299.0 1816 1817 1818 1819 1820 13.775 13.786 13.797 13.809 13.820 3300.8 3302.6 3304.4 3306.2 3308.0 322 Numerous practical details provide the user with valuable information about temperature measurement in industrial applications. 03/TEMP-EN Rev. B 06.2008 Industrial Temperature Measurement Practice The most important methods for measuring temperature and their basic principles are described. Industrial Temperature Measurement Practice ABB Instrumentation