The principle of thermocouple temperature measurement is based on the thermoelectric effect. Connecting two different conductors or semiconductors into a closed loop, when the temperatures at the two junctions are different, thermoelectric potential will be generated in the loop. This phenomenon is called the pyroelectric effect, also known as the Seebeck effect.
The thermoelectric potential generated in the closed loop is composed of two kinds of electric potentials; thermoelectric potential and contact potential. Thermoelectric potential refers to the electric potential produced by the two ends of the same conductor due to different temperatures. Different conductors have different electron densities, so they generate different electric potentials. The contact potential means when two different conductors are in contact.
Because their electron densities are different, a certain amount of electron diffusion occurs. When they reach a certain equilibrium, the potential formed by the contact potential depends on the material properties of the two different conductors and the temperature of their contact points. At present, the thermocouples used internationally have a standard. The internationally regulated thermocouples are divided into eight different divisions, namely B, R, S, K, N, E, J and T, which can measure the low temperature. It measures 270 degrees Celsius below zero, and can reach a high of 1800 degrees Celsius.
Among them, B, R, and S belong to the platinum series of thermocouples. Since platinum is a precious metal, they are also called precious metal thermocouples and the remaining ones are called low-priced metal thermocouples. There are two types of thermocouple structures, common type and armored type. Ordinary thermocouples are generally composed of thermode, insulating tube, maintenance sleeve and junction box, while armored thermocouple is a combination of thermocouple wire, insulation material and metal maintenance sleeve after assembly, after pulling A solid combination formed by stretching.