Thermocouple

A thermocouple is a temperature sensor made of two dissimilar metal wires joined at one end, which generates a small voltage that varies with temperature. Thermocouples are rugged, inexpensive, and cover very wide temperature ranges, making them common in industrial heat and process applications.

The voltage arises from the thermoelectric effect at the junction between two different metals, with standardised types such as K, J, and T chosen for their range and environment. Thermocouples respond quickly and tolerate high temperatures but are less precise than RTDs and require cold-junction compensation. They matter in industry because measuring temperature in furnaces, kilns, exhausts, and high-heat equipment demands sensors that survive harsh conditions while spanning a broad temperature range affordably.