Commonly used in low temperature zone thermocouple is a kind of temperature detector. Main characteristics of the thermocouple is high accuracy, stable performance. The platinum thermal resistance measurement accuracy is high, it is not only widely used in industrial temperature measurement, and is made into standard benchmark instrument. Thermocouple temperature measuring thermocouple temperature measurement principle and the material is based on the metal conductor resistance value increases with the increase of the temperature of the properties for temperature measurement. Thermocouple are mostly made of pure metal materials, the application is more platinum and copper, in addition, now have begun to use the materials such as nickel, manganese and rhodium thermocouple. The types of thermocouple type thermocouple from thermocouple temperature measurement principle, the measured temperature change is directly measured by thermocouple resistance change, therefore, of the thermocouple lead wire and other wire resistance change will affect temperature measurement. Thermocouple thermocouple is by thermal components ( The resistor body) , wire, insulation materials, stainless steel casing combination solid body, its diameter is generally from 2 to 8 mm, achieve more xiaoke phi is 0. 25mm。 Compared with conventional type thermocouple, it has the following advantages of small volume, no internal air gap, thermal inertia, the measured value after small; Good mechanical properties, resistance to vibration and impact resistant; Can bend, easy to install and use life is long. Capillary thermocouple ends thermocouple temperature sensing element resistance wire winding by special processing, close to the face in the thermometer. Compared with general axial thermocouple, it can reflect more correctly and quickly end face of the actual temperature being measured, is suitable for measuring temperature bearing and other parts of the face.