Introduction：

In industrial production processes, temperature is one of the important parameters that need to be measured and controlled. In temperature measurement, thermocouples are widely used. They have many advantages, such as simple structure, convenient manufacture, wide measurement range, high precision, small inertia, and easy remote transmission of output signals. In addition, because the thermocouple is a passive sensor, it does not need an external power supply during measurement, and it is very convenient to use, so it is often used to measure the temperature of gas or liquid in furnaces and pipes and the surface temperature of solids.

Working Principle：

When there are two different conductors or semiconductors A and B to form a loop, and the two ends are connected to each other, as long as the temperatures at the two junctions are different, the temperature of one end is T, which is called the working end or the hot end, and the temperature of the other end is T0 , called the free end (also called the reference end) or the cold end, an electromotive force will be generated in the loop, and the direction and magnitude of the electromotive force are related to the material of the conductor and the temperature of the two junctions. This phenomenon is called “thermoelectric effect”, and the loop composed of two conductors is called “thermocouple”.

The thermoelectromotive force consists of two parts, one part is the contact electromotive force of two conductors, and the other part is the thermoelectric electromotive force of a single conductor.

The size of the thermoelectromotive force in the thermocouple loop is only related to the conductor material that composes the thermocouple and the temperature of the two junctions, and has nothing to do with the shape and size of the thermocouple. When the two electrode materials of the thermocouple are fixed, the thermoelectromotive force is the two junction temperatures t and t0. function is poor.