Thermocouples are widely used in industrial and numerous types, can satisfy diversified customers' needs. The pt100 thermocouple is commonly used in industry, a temperature sensor it with metal platinum resistance with the temperature change, the principle of work. The principle of pt100 thermocouple pt100 thermocouple, it is directly proportional to the change of resistance with temperature. Pt100 resistance and temperature variation relationship is: when pt100 temperature 0 ℃ its resistance of 100 ohms, at 100 ℃ its resistance value is about 138. 5 ohms. Its industrial principle when pt100 at 0 degrees Celsius when his resistance of 100 ohms, pt100 thermocouple its resistance into uniform growth as temperatures rise. Metal thermocouple resistance value and temperature can use the following general approximate relation said, namely the rt = rt0 [ 1 +α( t- t0) ] Type of rt for temperature t resistance; Rt0 for temperature t0 ( Usually t0 = 0 ℃) When the corresponding resistance; Alpha for temperature coefficient. Relationship between resistance and temperature of semiconductor thermistor for rt = aeb in rt for temperature for t/t type of resistance; A and b depends on the structure of the semiconductor material constant.