ESDU Engineer

Temperature Measurement – How to select and use the optimum device

Engineers and scientists selecting and using temperature measurement devices have to consider a wide range of issues including measurement uncertainty, sensitivity, life, size, cost, manufacturing constraints, dynamic response, temperature of operation and robustness. The range of techniques for the measurement of temperature is extensive, utilising such diverse phenomena as thermoelectricity, temperature-dependent variation of the resistance of electrical conductors, fluorescence and spectral characteristics.

Recently released are two Data Items that provide detailed information on the two most commonly-used device types, namely thermocouples (ESDU 06018) and the various resistance techniques available, such as thermistors (ESDU 06019). These two new Data Items supplement the comprehensive general guide to temperature measurement in ESDU 02006. They extend and update information in superseded Data Items on thermocouples and resistance thermometry.

The purpose of ESDU 06018 and 06019 is to provide information and practical guidance on selecting and designing temperature measurement systems. For example, ESDU 06018 considers the selection, preparation, and installation of thermocouples, the use of compensating or extension cables, and methods of referencing to a known temperature. The requirements for reliable systems operating to commercial tolerances are also described. Various factors that might impair the accuracy and stability of thermocouples are identified together with methods of reducing their effect. A check list for the design of a thermocouple system is given and a flowchart procedure for selecting appropriate thermocouple materials is provided. The employment of the techniques described will ensure that the temperature of the measuring junction is within known tolerances.

These two new Data Items are available within the Heat Transfer Series and in selected Industry Packages.