End of the thermocouple thermoelectric potential in the thermocouple temperature on both ends of the work of the function is poor, rather than face thermocouple cold end with the job, temperature difference on both ends of the function; End of thermocouple thermoelectric potential produced by size, when the end of the thermocouple material is uniform, has nothing to do with the length and diameter of end face thermocouple, only to face at the ends of the thermocouple material composition and temperature difference; When facing the two surfaces of the thermocouple thermocouple wire material component is determined, the size of the end surface thermocouple thermoelectric potential, only related with the thermocouple temperature difference; If the thermocouple cold end temperature keeping, this into the thermocouple thermoelectric potential is only the end of the single value function of temperature. Two different welding material A conductor or semi-conductor A and B, form A closed loop, as shown. When the conductor A and B two persistent point temperature difference between 1 and 2, occurs between the electromotive force, thus forming the size of A current in the circuit, this kind of phenomenon called the thermoelectric effect. End thermocouple is in using this effect to work.