What is the working principle of thermocouple _ instrument

Thermocouple temperature measurement is the basic principle of two kinds of different ingredients of closed loop conductor material composition, when temperature gradient is at both ends, the loop will have an electric current passes through, existed seebeck electromotive force between two ends - at this time Thermoelectric emf, this is the so-called seebeck effect. Two different components of homogeneous conductor electrode as heat, the temperature is higher for work at the end of the end, one end of the low temperature as the free end, usually free end under a constant temperature. According to the thermoelectric emf as a function of temperature, the thermocouple indexing table; Indexing table is free end temperature at 0 ℃, under the condition of different thermocouples with different indexing table. Access in the thermocouple loop when the third metal material, the two contacts at the same temperature as long as the material, produced by the thermocouple thermoelectric is set to remain the same, which is not affected by the third metal access in the loop. Therefore, when the thermocouple temperature measurement, can be connected to the measuring instrument, measured after the thermoelectric emfs, can know the temperature of the measured medium. Thermocouple principle of two kinds of different ingredients of conductor ( Called the thermocouple wire or hot electrode) Two ends synthesis loop, when the junction temperature is not at the same time, in the circuit will generate electromotive force, this kind of phenomenon called the thermoelectric effect, and the electromotive force called thermoelectric potential. Thermocouple is to use the principle of temperature measurement, which directly used for measuring the medium temperature is called at the end of the working side ( Also known as the measuring end) , on the other side called cold end ( Also known as compensation) ; The cold end connected to the display instrument or meter, display instrument will point out the thermocouple thermoelectric potential. Thermocouple is actually a kind of energy converter, it converts heat into electricity, using thermoelectric potential generated by the measuring temperature, the thermocouple thermoelectric potential, should pay attention to the following questions thermocouple thermoelectric potential is the difference on both ends of the thermocouple temperature function, rather than a function of temperature difference on both ends of the thermocouple. The size of the thermocouple thermoelectric potential produced by, when material is uniform thermocouple, has nothing to do with the length and diameter of thermocouple, only with the thermocouple at both ends of the composition of the material and temperature difference. When the two thermocouple wire thermocouple material component is determined, the size of the thermocouple thermoelectric potential, only related with the thermocouple temperature difference; If the thermocouple cold end temperature keeping, the thermoelectric potential is only the end of the thermocouple temperature of single value function. Commonly used thermocouple materials have s accidentally platinum rhodium - 10 Platinum, r accidentally platinum rhodium - 13 Platinum, accidentally platinum rhodium - 30 b Platinum rhodium, 6 k I nickel chromium nickel silicon, t I pure copper copper nickel, j I iron copper and nickel, n I nickel chrome silicon nickel silicon magnesium nickel chromium copper nickel, e.