The basic principle of the thermocouple spot welding head is that the material conductors of two different compositions form a closed loop. When there is a temperature gradient at both ends, a current will flow through the loop, and there is an electromotive force between the two ends - the thermoelectromotive force. This is the so-called Seebeck effect. The homogeneous conductor of two different compositions is a hot electrode, the higher temperature end is the working end, the lower temperature end is the free end, and the free end is usually at a constant temperature.
When a third metal material is connected to the thermocouple loop, as long as the temperature of the two contacts of the material is the same, the thermoelectric potential generated by the thermocouple will remain unchanged, that is, not affected by the third metal access loop. Therefore, when measuring temperature with a thermocouple spot welding head , the measuring instrument can be connected, and after measuring the thermoelectromotive force, the temperature of the measured medium can be known. When the thermocouple measures the temperature, the temperature of the cold end (the measuring end is the hot end, the end connected to the measuring circuit through the lead wire is called the cold end) is kept constant, and the thermoelectric potential is proportional to the measured temperature. If the temperature of the cold end (environment) changes during the measurement, the accuracy of the measurement will be seriously affected. In the cold end, certain measures are taken to compensate for the effect of the cold junction temperature change, which is called the cold junction compensation of the thermocouple. A dedicated compensation wire for connection to the measuring instrument.
