Do you know how thermocouples measure temperature?

Thermocouple is a temperature sensing element that converts temperature signal into thermoelectric potential signal, and then converts it into the temperature of the measured medium through electrical instruments. The basic principle of thermocouple temperature measurement is that two homogeneous conductors of different components form a closed loop. When there is a temperature gradient at both ends, current will pass through the loop. At this time, there is an electromotive force thermoelectric potential between the two ends, which is the so-called Seebeck effect. The two homogeneous conductors of different components are thermocouples. The end with higher temperature is the working end, and the end with lower temperature is the free end. The free end is usually at a constant temperature. According to the functional relationship between thermoelectric potential and temperature, a thermocouple scale is made; the scale is obtained when the temperature of the free end is 0℃, and different thermocouples have different scales. When a third metal material is connected to the thermocouple loop, as long as the temperature of the two contacts of the material is the same, the thermoelectric potential generated by the thermocouple will remain unchanged, that is, it will not be affected by the third metal connected to the loop. Therefore, when measuring the temperature of the thermocouple, a measuring instrument can be connected. After measuring the thermoelectric potential, the temperature of the measured medium can be known.
The basic structure of a thermocouple is a hot electrode, insulating material and a protective tube; it is used in conjunction with display instruments, recording instruments or computers. In field use, thermocouples suitable for various environments are developed based on factors such as the environment and the medium being measured.
The basic principle of thermocouple contact temperature measurement is that the temperature measuring element must reach thermal equilibrium with the object being measured. Therefore, a certain period of time is required during temperature measurement to allow the two to reach thermal equilibrium. The length of the holding time is related to the thermal response time of the temperature measuring element. The thermal response time mainly depends on the structure of the sensor and the measurement conditions, which varies greatly. Therefore, in the daily calibration process, it is necessary to select the appropriate heating rate and thermal equilibrium time according to different types of thermocouples.