Thermocouple principle of thermocouple temperature measurement principle is based on the conductor or the resistance changes over temperature of the semiconductor this feature to measure temperature and parameters related to the temperature. Thermocouple are mostly made of pure metal materials, the application is more platinum and copper, now have begun to use the materials such as nickel, manganese and rhodium thermocouple. Thermocouple is usually need to get the resistance signal through wire transfer to the computer control device or other secondary instrument. Thermocouple applied widely used thermocouple materials is platinum and copper, platinum resistance is high precision, suitable for neutral and oxidizing medium, good stability, has a certain nonlinear, the higher the temperature the smaller resistance change rate; Copper resistance in the temperature range of a linear relationship between internal resistance value and temperature, temperature line number is big, suitable for corrosive medium, more than 150 susceptible to oxidation. China is more commonly used with R0 = 10 Ω, R0 = 100 Ω and R0 = 1000 Ω to wait for a few kinds, their index number Pt10, Pt100, Pt1000 respectively; Copper resistance with R0 = 50 Ω and R0 = 100 Ω two kinds, their index number for Cu50 and Cu100. Pt100 and Cu50 are more widely application.