Calibration of Thermocouples

The calibration of a thermocouple consists of the determination of its electromotive force (emf) at a sufficient number of known temperatures so that, with some accepted means of interpolation, its emf will be known over the entire temperature range in which it is to be used. The process requires a standard thermometer to indicate temperatures on a standard scale, a means for measuring the emf of the thermocouple, and a controlled environment in which the thermocouple and the standard can be brought to the same temperature. Some of the more commonly used techniques for accomplishing such calibrations will be discussed in this chapter. Much of this material is based upon National Bureau of Standards Circular 590, Methods of Testing Thermocouples and Thermocouple Materials, and the calibration methods appearing in Chapter 19, Part 3, Temperature Measurement, of the American Society of Mechanical Engineers Power Test Codes.