A thermopile is a component that can convert temperature difference and electric energy. It is composed of two or more thermocouples which connected in series. The thermoelectric potential output by each thermocouple is superimposed on each other. When there is a temperature difference between the two sides of the thermopile, it will produce current which  can be used to measure small temperature differences or average temperatures.

When using a thermopile to measure temperature, it can overcome the shortcomings that the potential difference generated by a single thermocouple which is too small and difficult to measure, and avoid the use of expensive high-precision operational amplifiers.