Thermocouple thermometer is based on thermoelectric effect. It uses the thermocouple as the sensor to convert the measured temperature signal into the potential signal, and through the connecting wire, it is equipped with the display instrument to measure the millivolt level voltage signal to realize the temperature measurement. Thermocouple thermometer can measure higher temperature; it is convenient for long-distance transmission and multi-point measurement; its performance is stable, accurate and reliable; its structure is simple and easy to maintain; its heat capacity and thermal inertia are small, so it can be used to measure point temperature or surface temperature, so it is widely used in industrial production and scientific research, air conditioning and gas engineering.

Thermocouple is usually composed of hot electrode, insulation material, protection tube and junction box. Common thermocouple structures include common thermocouple, armored thermocouple and thin film thermocouple.

(1) Common (assembled) thermocouple

The structure of common thermocouple is composed of thermocouple measuring end, Thermoelectrode, insulating tube, protective sleeve and junction box. Ordinary thermocouple is mainly used to measure the temperature of medium in pipeline and equipment. According to the range of temperature measurement and environmental atmosphere, the choice of thermocouple and protective tube is also different. When it is installed, there are two types of connection: threaded connection and flange connection.

(2) Sheathed thermocouple

Armored thermocouple is a solid combination made of hot electrode, insulating material and metal tube. It has the advantages of fast dynamic response, small heat capacity of measuring end, high strength and good flexibility.

(3) Thin film thermocouple

Thin film thermocouple is a special structure thermocouple made of two kinds of metal films, which is composed of hot electrode, hot contact, insulating substrate and outgoing line. Its measuring end is small and thin, and its heat capacity is very small. It can be used to measure the temperature of small product and transient surface temperature.