Thermocouples ( in command, it may be used the abbreviation „TC") are temperature transducers which change the temperature variation of the measured environment into the   thermoelectromotive force variation ( t.t.e.m. ), which, afterwards, connected to an indicator or a registering instrument is displayed in temperature measures(units).

Theoretically a thermocouple consists in 2 thermoelectrodes made of metals or different alloys, welded only at one of the two ends. The local heating of the welding ( measurement junction ) determines the bringing about of a thermoelectromotive force at the vacant ends of the thermoelectrodes  ( reference junction ). The value of this force depends upon the difference of  temperature between the measurement junction and the reference one.