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. The advantage is; 1) high precision measurement. Because of thermocouple direct contact with the object being measured, not affected by intermediate medium. (2) the measurement range. The commonly used thermocouple from - 50 ~ + 1600 ℃ can renew edge measurement, some special thermocouple with low temperature to - 269℃（ Such as gold iron nickel chrome) And high up to + 2800 ℃ ( Such as tungsten - Rhenium) 。 3. 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 of, outside has protective casing, which are very convenient. 1. Basic principle of thermocouple temperature measurement will be two different welding material A conductor or semi-conductor A and B to form A closed loop, when the conductor A and B two persistent point temperature difference between 1 and 2, occurs between the electromotive force, and thus form the size of A current in the circuit, this kind of phenomenon called the thermoelectric effect. Thermocouple is in using this effect to work. 2. Thermocouple type and structure formation ( 1) Thermocouple types commonly used thermocouple could be divided into two types: standard thermocouple and non-standard thermocouple. Invokes standard thermocouple is refers to the national standard specifies its thermoelectric potential and the relationship between temperature, permissible error, and a unified standard score table of thermocouple, it has with matching display instrument to choose from. Non-standard thermocouple or on the order of magnitude less than the range using standardized thermocouple, generally no unified indexing table, mainly used for the measurement of some special occasions. Standardized thermocouple since January 1, 1988 in our country, the thermocouple and thermocouple were manufactured according to IEC international standard, and the set S, B, E, K, R, J, T seven standardization thermocouple type thermocouple for our country unified design. （ 2) The structure of thermocouple in order to keep the thermocouple is reliable, steady work, the structure of its requirement is as follows: (1) of the two thermocouple hot electrode welding must be strong; (2) two hot electrode should be well insulated between each other, in case of short circuit; (3) compensation conductor should be connected to the free cod of a thermocouple to be convenient and reliable; (4) protect casing thermal electrodes should be able to make sufficient isolation and harmful medium. 3. The thermocouple cold end temperature compensation due to the thermocouple materials are generally more expensive ( Especially when using precious metals) And temperature measuring points are far away the distance to the instrument, in order to save thermocouple materials, reduce cost, usually adopt the compensating conductor (of the cold junction of the thermocouple The free end) Reaches to the relatively stable control indoor temperature and connected to the meter terminals. It must be pointed out that the role of the thermocouple compensation wire only extend thermal electrode, make moves to the control room of the cold junction of the thermocouple meter terminal, it itself does not eliminate the cold end temperature change on the influence of temperature, no compensation. So, still need to take some of the other correction method to compensate of the cold end temperature t0 indicates influence on measuring temperature 0 ℃. Must pay attention to when using thermocouple compensating conductor model match, cannot be wrong polarity, compensation conductor should be connected to the thermocouple temperature should not exceed 100 ℃. Commonly used in low temperature zone thermocouple thermocouple is a kind of temperature detector. Its main characteristic is high accuracy, stable performance. Among them is platinum thermal resistance measurement accuracy is the highest, 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.