Although thermocouple and thermocouple in the process of using temperature measuring instrument, but the performance still have difference. Thermocouple main characteristic: the wide measuring range, stable performance, at the same time, simple structure, good dynamic response, more can far eastone - 4 20 ma electrical signals to facilitate automatic control and centralized control. Thermocouple temperature measurement principle: is based on thermoelectric effect. Connect the two different conductor or semiconductor into closed loops, when the two contacts in temperature is not at the same time, the circuit will produce thermoelectric potential, this kind of phenomenon called the thermoelectric effect, also known as the seebeck effect. There are two kinds of closed loop of thermoelectric potential of electric potential; The thermoelectric potential and contact potential. Thermoelectric potential means the same at both ends of the conductor potential because of the different temperature, different conductors with different electron density, so they produce electric potential is not the same, the contact potential as its name implies is refers to the two different conductor in contact, because the electron density of different produce certain electronic diffusion, when they reach a certain potential, which is formed by the balance after the contact potential depends on the size of the two different conductor material properties and their temperature contact point. There are two kinds of structure of the thermocouple type and type. Ordinary thermocouples generally by the hot electrode, insulation tube, to protect casing and junction box and other parts. And type thermocouple is the thermocouple wire, insulation material and metal protective casing combination after assembly, after stretching processing from a combination of a solid. But it takes a special electrical signal of thermocouple wires to pass, this kind of wire we called compensation conductor. Different thermocouples require different compensation conductor, its main function is connected to the thermocouple, away from the power of the reference junction of the thermocouple, so that the reference temperature stability. Compensation wire is divided into compensation type and extended type two kinds, extend the chemical composition of the wire and the compensation of thermocouple is the same, but in practice, to extend the type of wire is not used is the same as the thermocouple material of metal, usually use and thermocouple wires to replace with the same electron density. Compensation and thermocouple wires of the wire are generally not very clear, the positive connection of the thermocouple compensating lead red line, while the cathode connecting the rest of the color. Most of the material compensating lead wires are commonly used copper nickel alloy. Although thermocouple is widely applied in industry, but because of its temperature range makes it application by certain restrictions. Thermocouple temperature measurement principle: is based on the conductor or semiconductor resistance changes with the change in temperature. Its many advantages, can also remote transmission signal, high sensitivity, strong stability, compatibility and accuracy are better, but you need to power, can't instantaneous measured the change in temperature. Industrial thermocouple usually use pt100, pt10, cu50, cu100, platinum thermocouple temperature measurement range is generally 200 - below zero 800 degrees Celsius, copper thermocouple for 40 to 140 degrees Celsius below zero. As to distinguish the type of thermocouple and thermocouple compensation wire, but it does not need and is cheaper than thermocouple.