Selection Guide S 1833 X 05 Published by Evaluation International, April 2005 Index classification 2.1 SELECTION GUIDE FOR TEMPERATURE INSTRUMENTATION INTERNATIONAL INSTRUMENT USERS’ ASSOCIATIONS EVALUATION INTERNATIONAL-WIB-EXERA CIRCULATION This report has been prepared for EI, WIB & EXERA members. Because of the general interest shown in it, and because it contains only published information freely provided for the purpose by equipment manufacturers, or objective information derived by independent, impartial research, it is made available to non-member organisations. The normal comprehensive evaluation reports produced by EI-WIB-EXERA remain confidential to members of these organisations. About EI, WIB and EXERA EWE is the acronym for three international instrument users' associations which collaborate in the sponsoring, planning and organisation of instrument evaluation programmes. They have the long term objective of encouraging improvements in the design, construction, performance and reliability of instrumentation and related equipment. The evaluation of the selected instruments is undertaken by approved, independent laboratories with respect to the manufacturers' performance specifications and to relevant international and national standards. Each evaluation report describes the assessment of the instrument concerned and the results of the testing. No approval or certification is intended or given. It is left to the reader to determine whether the instrument is suitable for its intended application. All reports are circulated throughout the entire membership of EWE. Evaluation International - International Instrument Users' Association The Pool House, South Hill, Chislehurst, Kent, England BR7 5EH International Instrument Users' Association WIB Prinsessegracht 26, 2514 AP, The Hague, The Netherlands EXERA Association des Exploitants d'Equipments de Mesure, de Regulation et d'Automatisme, 9 Rue de Rocroy, 75010, Paris, France. International Instrument Users' Associations EWE Membership List January 2005 Acetex Chimie E Heineken Technical Services W Aeroport de Paris E Infraserve/Hoechst W Agence de L'Eau Artois Picardie E Institut National de l'Environment E Industriel at des Risques Air Liquide E Institut National de Recherche & Securite E Akzo Nobel Engineering W Institut de Regulation et Automation E ASM Brescia E Italcimenti/CTG E Atofina Italie E Jacobs Engineering BV W Aventis Pasteur E KEMA Nederland BV W BNFL plc EI Laborelec W BP-Amoco EI Lubrizol France E BP France E MEMC E British Energy plc EI Nancie E CETIAT E Nantes Metropole – Direction de l’Eau E CETIM E Nederlands Meetinstituut W Chiyoda Corporation W Nestec Ltd W COGEMA E Petro SA W DGA/DCE E Polimeri Europa E DOW Benelux W RATP E DSM Technopartners BV W Renault SA E Du Pont de Nemours BV W Rhoditech E EADS LV E Saudi Arabian Oil Company EI Electricite de France (EDF) E Severn Trent Water EI ENEL E Shell France E EniACQUA E Shell Global Solutions International W Environment Agency EI Solvay BV Benelux W ExxonMobil USA W SNCF E Federelettrica E SIP Standardiserad Instrumentprovning EI Fluor Daniel Consultants BV W Suez Environnement E Gaz de France E Technip E GEMCEA E Total France E/W Generale des Eaux E UKAEA EI Health & Safety Executive EI Universite De Genes E CONTENTS 1. INTRODUCTION 1.1 Aims of the study 1.2 Scope 1.3 Limits of the study 1.4 Summary of contents 2. OVERVIEW OF THE CONCEPT OF TEMPERATURE, TERMS & DEFINITIONS 2.1 What is temperature? Definition of 2.2 Thermal equilibrium and the Zeroth Law of Thermodynamics 2.3 What is a thermometer? 2.4 Summary of the five main Temperature Scales 2.5 The International System of Units (SI) 2.6 Definition of the SI Unit of Thermodynamic Temperature - Kelvin 2.7 The Multiplying Prefixes of the SI 2.8 Temperature Conversions 2.9 The Spectrum of Temperature 2.10 The Evolution of Thermometry and Temperature Scales 2.11 Practical Realisation of the Definition of Thermodynamic Temperature & The International Temperature Scale of 1990 (ITS-90) 3. CATEGORIES OF TEMPERATURE INSTRUMENTATION 3.1 Liquid-in-glass thermometers 3.1.1 Introduction 3.1.2 Principles and materials of construction 3.1.3 Common defects 3.1.4 Calibration of liquid-in-glass thermometers 3.1.5 Precautions in use 3.2 Dial-type expansion thermometers 3.2.1 Bulbs, wells, and capillaries 3.2.2 Liquid-Filled Systems 3.2.3 Vapour Systems 3.2.4 Gas-Filled Systems 3.2.5 Mercury-Filled Systems 3.2.6 Ambient temperature compensation 3.2.7 Effects of bulb elevation 3.2.8 Barometric errors 3.3 Resistance temperature detectors (RTDs) 3.3.1 Introduction and Overview 3.3.2 Materials and construction 3.3.3 Sources of error 3.3.4 Measurement of RTD resistance 3.4 Thermistors 3.4.1 Overview 3.4.2 Sensor types 3.4.3 Self-heating effect 3.4.4 Measuring bridges 3.4.5 Thermistors combined with resistors 3.4.6 Specialised applications 3.4.7 Calibration and testing 3.5 Thermocouples 3.5.1 Overview 3.5.2 Thermocouple materials 3.5.3 Hardware and fabrication 3.5.4 Emf measurement 3.5.5 Calibration 3.6 Radiation thermometers or pyrometers 3.6.1 Overview 3.6.2 Optical systems 3.6.3 Selecting a radiation thermometer 3.6.4 Calibration 3.6.5 Precautions necessary in the use of radiation thermometers 3.7 Bimetallic thermometers 3.8 Calibrators and simulators 3.9 Integrated circuit (IC) transistors and diodes 3.10 Quartz crystal thermometry 3.11 Ultrasonic thermometers 3.12 Miscellaneous temperature sensors 3.12.1 Self-measuring devices 3.12.2 Acoustic time domain reflectometry 3.12.3 Carbon resistors 3.12.4 Capacitance cable for detecting hot spots 3.12.5 Fluidic sensors 3.12.6 Johnson noise thermometer 3.12.7 Liquid crystals 3.12.8 Paramagnetic salts 3.12.9 Spectroscopic temperature measurement 3.12.10 Thermography 3.12.11 Colour Indicators, Crayons and Pellets 3.12.12 Pyrometric Cones 4. GENERAL SELECTION CRITERIA 4.1 Temperature range 4.2 What is the smallest temperature change you need to record? (required resolution) 4.3 How well the temperature must be known (required accuracy) 4.4 External environment (atmospheric effects) 4.5 Type of use 4.6 Use of thermowells 4.7 Other factors 5. REFERENCES APPENDICES APPENDIX A RELEVANT BRITISH/EUROPEAN STANDARDS APPENDIX B HISTORICAL EVOLUTION OF THE THERMODYNAMIC AND PRACTICAL TEMPERATURE SCALES APPENDIX C THE ROLE OF THE PLATINUM RESISTANCE THERMOMETER IN THE ITS-90 APPENDIX D TOLERANCE CLASSES FOR Pt100 THERMOMETERS (IEC 751: 1983) APPENDIX E Pt100 REFERENCE TABLES (IEC 751: 1983) APPENDIX F TOLERANCE CLASSES FOR THERMOCOUPLES (IEC 584-2: 1982) APPENDIX G THERMOCOUPLE REFERENCE TABLES (IEC 584-1:1995) APPENDIX H DATA TABLES FOR RADIATION THERMOMETERS OR PYROMETERS APPENDIX I EXAMPLE INSTRUMENT SPECIFICATION: LABFACILITY TEMPMASTER 100 DIGITAL THERMOMETER APPENDIX J PARTIAL LIST OF UK MANUFACTURERS AND SUPPLIERS OF TEMPERATURE INSTRUMENTATION LIST OF TABLES LIST OF FIGURES SELECTION GUIDE FOR TEMPERATURE INSTRUMENTATION Author: S Croft MSc MInstMC April 2005 1. INTRODUCTION Sira Test & Certification Ltd (Sira) on behalf of Evaluation International (EI) has compiled this report. It has been compiled from technical and commercial literature in the public domain and from information data sheets available from manufacturers, agents or sales representatives. In addition, it draws upon Sira’s twenty years experience in the realm of independent temperature instrument evaluation and calibration. 1.1 Aims of the study The aim of this study is to produce a document (for use by the EI membership) to assist a prospective purchaser in selecting an appropriate temperature measuring instrument for his/her particular application. It will identify the main categories of temperature measuring instrument widely available in industry, consider known pros and cons with each, and discuss general selection criteria. An example instrument specification is also included. 1.2 Scope This document provides advice for those wishing to select and use instruments for measuring temperature. It introduces the main concepts of temperature measurement, together with terms and definitions. The main categories of measuring instrument are discussed as well as principal selection criteria; general parameters associated with each instrument type are identified, together with known pros and cons. An example instrument specification will be given, and a limited selection of market- leading UK manufacturers will be listed. 1.3 Limits of the study This document does not seek to identify all manufacturers/models of temperature instrumentation as it is estimated that there are many thousands of different models currently available in the UK alone. Instead, this document will steer the user into asking the right questions when selecting an appropriate temperature measuring instrument. The study will be limited to categories of instrument widely used in industry. While this document provides a general overview of temperature measurement, it is not an in-depth scientific treatment of the subject. The document primarily covers temperature measurements made within the range –272°C (cryogenic temperatures) to 3800°C, this being the range most relevant to industrial measurement. Some techniques for making measurements outside this range are covered but only in outline. 1.4 Summary of contents Section 2 discusses concepts, terms and definitions associated with temperature measurement, as well as identifying temperature units and conversions. Section 3 identifies the main categories of industrial temperature instrumentation (together with some lesser known examples), grouped mainly according to operating principle. A detailed description of each type is given; typical parameters such as operating range, resolution and accuracy are included. A summary of known pros and cons is listed for each of the main instrument types. Section 4 briefly outlines principal selection criteria, such as range of temperature being measured, required ‘accuracy’ in use, cost of installation, environmental conditions, and so on. Relevant British/European temperature standards are listed in 1 Appendix A, whilst Appendix B details the historical evolution of the thermodynamic and practical temperature scales.