Thermocouple has been developed in order to measure the tremperature by making use of Seebeck effect. 2 types of metal are connected, one to become as a hot junction tip and the other as a reference junction tip (output terminal side). If the temperature at these 2 tips are made different, a thermo-electromotive force having a constant relationship with that temperature difference is generated. Here, if you keep the reference junction tip at a constant temperature, you will kknow the temperature at hot junction tip.
Thermocouple is a sensor in which this principle has been incorporated. It is the best sensor among all contact type temperature sensors and can measurein the range of highest temperature.

・For engine exhaust gas systems
・wire type