(thermoelectric thermometer). An instrument composed of two wires made of dissimilar metals or semiconducting materials that are joined at one end (the measuring junction), the other end being the reference junction, which is maintained at a known temperature (usually 0C). The difference in temperature between the measuring junction and the reference junction generates an electromotive force that is proportional to the temperature difference. Thermocouples are applicable over a range of −200C to 1800C. The most suitable conducting materials are iron-constantan, platinum-platinum-rhodium, copper-constantan, and Chromel-Alumel; graphite-silicon carbide is used in the metallurgical field. Thermocouples are essential for determinations of extreme temperatures that are beyond the range of liquid-in-glass thermometers. Their industrial applications include molten metals, fuel beds, ceramic kilns, furnaces, etc.; in laboratories they are used for both high-temperature and cryogenic research. They are also applicable to intermediate temperatures in cases where conventional thermometers are impracticable.See Thermoelectricity.
