Thermocouple types commonly used thermocouple could be divided into two types: standard thermocouple and non-standard thermocouple. Standard thermocouple 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 China since January 1, 1988, thermocouple and thermocouple were manufactured according to IEC international standard, and specify the S, B, E, K, R, J, T seven standardization thermocouple type thermocouple for China unified design. The working principle of thermocouple when there are two different conductors and semiconductors A and B TO form A loop, its both ends are connected, as long as the temperature of the two nodes is different, one end of the temperature T, called end or hot end work, the other end of the temperature for the TO, known as the free end ( Also known as the reference side) Or cold end, produced in the loop current, which exist in the loop of electromotive force is called thermoelectric emfs. This due to the different temperature and produces electromotive force is called the seebeck effect. Related to the seebeck effect, there are two: one is that when a current flows through the joint of two different conductors here they absorb or release heat, Depending on the direction of the current) , known as the peltier effect; Second, the temperature gradient of the electric current flows through the presence of a conductor, absorb or release heat conductors ( Depending on the direction of the current relative to the temperature gradient) , known as the Thomson effect. The two different conductor or the combination of the semiconductor is called the thermocouple. The thermocouple thermoelectric potential EAB ( T, T0) Was synthesized from potential contact potential and temperature difference. Contact potential refers to two different conductors or semiconductor in the contact potential, this potential with two conductors or the nature of the semiconductor and related to the temperature at the contact point. Thermoelectric potential refers to the same conductor or semiconductor in different temperature at both ends of the electric potential, this potential is only with the temperature at the ends of the conductor or the nature of the semiconductor and related, and the length of the conductor, cross section size, the temperature distribution along the length direction of the business. Whether the contact potential or thermoelectric potential contacts are due to focus on the endpoint of potential, as a result of the different number of electrons in thermoelectric potential is the synthesis of the two thermocouple measurements. When circuit disconnection, at disconnect a, b, there is an electric potential difference between delta V, the polarity and size and the circuits of thermoelectric potential. And regulations in the cold end, when A current flows from A to B, called A positive, B is negative. Experimental results show that when the delta V is very small, and delta V delta T is proportional to the relationship. Definition of delta T delta V differential rate of thermoelectric potential for thermoelectric potential, is also called the seebeck coefficient. Seebeck coefficient of symbols and depends on two conductors of thermocouple thermoelectric properties and the difference in temperature between nodes.