In the temperature measurement, K type thermocouple is widely used, and it has many advantages such as simple structure, convenient manufacture, wide measuring range, high precision, small inertia and easy transmission of output signals. In addition, since the thermocouple is a passive sensor, it does not need an external power supply for measurement. It is very convenient to use, so it is often used to measure the temperature of the gas or liquid in the furnace, the pipe, and the surface temperature of the solid.