Industrial temperature measurement Basics and practice This document together with all its contents is Copyright Protected. Translating, copying and dissemination in any form – including editing or abstracting – in particular reproduc- tions, 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 ba- sic food and energy supply for an efficient, low emission utilization of natural resources and energy and the increased productivity in all manufacturing and distribution pro- cesses. 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 opportu- nities 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 pro- vide 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 appro- priate 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 compe- tence. 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 ABB- Research Centers, assure innovative products and solutions. Efficient factories and committed employees manufacture the products using the latest methods and produc- tion 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 Introduction to Temperature Measurement Technology . 17 2.1 Historic Development . 17 2.1.1 Heat and Temperature . 17 2.1.2 The Historic Development of the Thermometers . 18 2.1.3 The Thermodynamic Temperature Scale . 22 2.1.4 The International Temperature Scale of 1990 (ITS 90) . 23 2.2 Basics of Temperature Measurement . 25 2.2.1 The Physical Concept of Temperature . 25 2.2.2 The Technical Significance of Temperature . 25 2.2.3 The Thermoelectric Effect . 26 2.2.4 The Temperature Dependent Ohmic Resistance . 29 2.3 The Principles of Temperature Measurement . 33 2.3.1 Mechanical Contacting Thermometers . 35 2.3.2 Electric Contacting Thermometers . 36 2.3.3 Additional Contacting Measurement Principles . 37 2.3.4 Non-contacting Temperature Measurement . 38 3 Industrial Temperature Measurement Using Electrical Contacting Thermometers . 40 3.1 Sensors . 40 3.1.1 Thermocouples . 40 3.1.2 Mineral Insulated Thermocouple Cables . 51 3.1.3 Thermocouple Wires and Compensating Cables . 55 3.1.4 Older National Standards . 58 3.1.5 Measurement Resistors . 62 3.2 Industrial Temperature Sensor Design . 76 3.2.1 Design . 76 3.2.2 Installation Requirements . 81 3.2.3 Process Connections Types . 85 3.2.4 Process Requirements . 87 3.2.5 Thermowell Designs . 89 3.2.6 Corrosion . 96 3.2.7 Material Selections . 106 3.2.8 Ceramic Thermowells . 108 3.3 Application Specific Temperature Sensor Designs . 111 3.4 Dynamic Response of Temperature Sensors . 127 3.4.1 Introduction . 127 3.4.2 Step Response and Transfer Functions, Response Time and and Time Constants . 128 3.4.3 Establishing the Dynamic Values . 129 3.4.4 Influencing Factors . 129 8 3.5 Aging Mechanisms in Temperature Sensors . 131 3.5.1 Drift Mechanisms for Thermocouples . 131 3.5.2 Drift Mechanisms for Resistance Thermometers . 143 3.6 Possible Errors and Corrective Measures . 148 4 Non-Contacting Temperature Measurements in Field Usage . 154 4.1 Advantages and Uses for Applying Infrared Measuring Technology . 154 4.2 Fundamentals and Operation . 155 4.2.1 Determining the Emissivity Values . 159 4.2.2 Measuring Temperatures of Metals . 160 4.2.3 Measuring Temperatures of Plastics . 161 4.2.4 Measuring Temperatures of Glass . 162 4.2.5 The Measuring Path . 163 4.2.6 Stray Radiation and High Ambient Temperatures . 165 4.2.7 Optic Radiation Input, Protection Glass and Window Materials . 166 4.3 Indication and Interfaces . 169 4.4 Application Examples . 170 5 Measurement Signal Processing and Evaluation . 171 5.1 Application of Transmitters in Temperature Measurements . 171 5.2 Measurements of Thermal Voltages and Resistances . 174 5.3 Power Supply of Temperature Transmitters . 177 5.4 Design Principles for a Temperature Transmitter . 178 5.5 Programmable Temperature Transmitters . 184 5.6 Communication Interfaces . 188 5.7 Temperature Transmitters in Explosion Hazardous Areas . 194 5.8 Electromagnetic Compatibility (EMC) . 201 5.9 Temperature Transmitters using Interface Technology . 203 5.10 High Accuracy Temperature Measurements with Programmable Transmitters . 206 6 Accuracy, Calibration, Verification, Quality Assurance . 209 6.1 Accuracy . 209 6.1.1 Basic Fundamentals . 209 6.1.2 Determining (Estimating) the Measurement Uncertainties . 210 6.1.3 Measurement Uncertainty Estimations using a Practical Example . 213 6.1.4 Error Effects for Temperature Measurements . 215 6.2 Calibration and Verification . 224 6.2.1 Definitions . 224 6.2.2 Calibration Methods for Temperature Sensors . 225 6.2.3 The Traceability of the Calibration . ..