Commonly used in low temperature zone thermocouple is a kind of temperature detector. Thermocouple temperature measurement is based on the metal conductor resistance value increases with the increase of the temperature of the properties for temperature measurement. Its main characteristic is high accuracy, stable performance. Platinum thermocouple measuring accuracy is high, it is not only widely used in industrial temperature measurement, and is made into standard benchmark instrument. 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. Metal thermocouple commonly used thermal material sort is more, more commonly used is a platinum wire. Industrial measurement with metal material in addition to the platinum wire, thermocouple as well as copper, nickel, iron, iron - Nickel, etc. Thermocouple temperature measurement principle is based on a conductor or resistance changes over temperature of semiconductor thermoelectric this feature to measure temperature and parameters related to the temperature. Thermocouple is usually need to get the resistance signal through wire transfer to the computer control device or other secondary instrument. Main kinds of ordinary thermocouples from the thermocouple temperature measurement principle, the measured the change in temperature is directly measured by thermocouple resistance change, therefore, the wires of a thermocouple body such as a variety of wire resistance change will affect temperature measurement. Thermocouple is by thermal components ( The resistor body) , wire, insulation materials, stainless steel casing combination solid body, its diameter is commonly phi - 2 Phi is 8 mm, xiaoke reaches 0. 25φmm。 Compared with conventional type thermocouple, it has the following advantages: 1, small volume, no internal air gap, thermal inertia, the measured value after small; 2, good mechanical properties and resistance to vibration and impact resistant; 3, can bend, easy to install; 4, long service life. End 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. Junction box flameproof thermocouple with special structure, its shell internal explosive mixed gas by sparks or electric arc affected explosion limit within the junction box, that wouldn't make production field explosion. Flameproof thermocouple can be used in the bla B3c level zone with explosion danger place temperature measurement.