What is the thermocouple thermoelectric emf of causes and conditions _ instrument

Thermocouple is to put the two different conductor connection into a closed loop, if they are two contact put in different heat source temperature, respectively, in the circuit can produce thermoelectric emf, this kind of phenomenon called the thermoelectric effect. The device is called thermocouple. Produced by thermocouple thermoelectric potential consists of two parts: contact potential temperature and electric potential. Thermoelectric potential reasons is that the ends of the conductor in the same because of their different temperature and produce a thermoelectric potential, due to the high temperature of the electron energy is larger than the low temperature electronic energy, and ran to the low temperature from high temperature terminal electron number than from the low temperature end ran to more, the high temperature side lose electrons and positive results of high temperature end, low end negatively charged by electron, thus forming a static electric field, at this point, in the ends of the conductor produces a corresponding electrical potential difference of the differential electric potential. The causes of contact potential is, when the two different conductor A and B, when in contact with electron density difference ( Assuming that NA > NB) , the rate of diffusion in two directions is different, the number of the electrons from A to B more than from B to A, A loss of electrons and positive result, negatively charged by electron, B in A and B of the contact surface to form A static electric field from A to B, this potential difference between A and B also form A contact potential. Condition is 1. Of thermocouples must be two different conductors of 2. The temperature of the thermocouple two contact must be different