Commonly used in low temperature zone thermocouple is a kind of temperature detector. Its main characteristic is high accuracy, stable performance. The platinum thermocouple measuring accuracy is high, it is not only widely used in industrial temperature measurement, and is made into standard benchmark instrument. 1, thermocouple temperature measurement principle and material of thermocouple temperature measurement is based on the metal conductor resistance value increases with the increase of the temperature of the properties for temperature measurement. Thermocouples are mostly made of pure metal materials, the application is a lot of platinum and copper, in addition, now began to use the materials such as nickel, manganese and rhodium thermocouple. Pt100: used for thermocouple, thermocouple, temperature meter, temperature transmitter, pressure differential pressure transmitter, hot runner heater, compensation cable, control cable, etc. Cu50: used for thermocouple, thermocouple thermometer, thermocouple checking instrument, thermocouple simulator - Thermocouple simulators, copper thermocouple, thermocouple, etc. Pt100 and cu50 measuring temperature is different, pt100 measurement of high temperature, cu50 measuring the temperature of the low. Thermocouple is one of the industry commonly used temperature detecting element, the working principle of the thermocouple is based on baker ( seeback) Effect, that is, two different components of conductor ends connected into a circuit, such as two different connection end temperature, then to produce the physical phenomenon of thermal current in the circuit. Advantages are: high measuring accuracy. Because of thermocouple direct contact with the object being measured, not affected by intermediate medium. Wide measuring range. The commonly used thermocouple from - 50 ~ + 1600 ℃ can renew edge measurement, some special thermocouple low measurable to - 269℃（ Such as gold iron nickel chrome) High, up to + 2800 ℃ ( Such as tungsten - Rhenium) 。 Simple structure, easy to use. Thermocouple is usually composed of two different kinds of metal wire, but is not limited by the size and the beginning, has protective casing.