The principle of thermocouple _ instrument

Two different metals welded into a closed circuit is called a thermocouple. Due to the air tightness of different metal free electrons, free electrons in the two kinds of metal in welding place mutual diffusion differed, caused two metal contact point in an electric potential difference, this is contact electromotive force. Contact electromotive force except related to two kinds of metal properties but also related with temperature, under the same temperature, two emf equal, joint in the opposite direction, the total electromotive force is zero. If two different junction temperature, two different electromotive force numerical value, the total electromotive force is not zero, closed circuit current will occur and the current caused by temperature difference is called differential current. Temperature is measured with a thermocouple method is: make a joint temperature is known, the other joints in the temperature of the object under test, measure current, some of the thermocouple temperature difference can infer the temperature being measured. 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 through compensation conductor should be connected to the digital display table 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, we should pay attention to the following questions: 1: thermocouple thermoelectric potential is thermocouple temperature on both ends of the work on the function of the poor, rather than the thermocouple cold end function with the work on both ends of the temperature difference; 2: 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, 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. Thermocouple is in using this effect to work.