What is a thermocouple?

When both ends of two types of metal conductors are electrically connected and a temperature difference is applied to both ends. (Seebeck effect)
Since the magnitude of the current flowing varies depending on the difference in temperature, the temperature at one end (on the measuring instrument side) can be kept at a constant temperature (0℃ in principle), and the temperature at the other end (on the measuring instrument side) can be known by measuring the value of the generated current (thermoelectromotive force).
Even if the temperature difference is the same, the current flowing varies depending on the combination of the two metal conductors.
A combination of these two types of metal conductors is called a thermocouple. There are combinations of thermocouples suitable for the temperature, environment, and application to be measured. Therefore, it is important to select an appropriate thermocouple.