The temperature sensor is the earliest and most widely used type of sensor. The market share of temperature sensors exceeds that of other sensors. From the beginning of the 17th century, people began to use temperature for measurement. With the support of semiconductor technology, semiconductor thermocouple sensors, PN junction temperature sensors and integrated temperature sensors have been developed in this century. Correspondingly, acoustic temperature sensors, infrared sensors and microwave sensors have been developed in succession according to the laws of interaction between waves and matter.
Conductors of two different materials, such as being connected to each other at a certain point, heat the connection point, and a potential difference occurs at the point where they are not heated. The value of this potential difference is related to the temperature of the measurement point of the non-heating part and is related to the material of the two conductors. This phenomenon can occur over a wide temperature range. If the potential difference is accurately measured and the ambient temperature of the non-heated part is measured, the temperature of the heating point can be accurately known. Because it must have two different material conductors, it is called a "thermocouple." Thermocouples made of different materials are used in different temperature ranges and their sensitivity varies. The sensitivity of a thermocouple is the amount of change in the output potential difference when the temperature of the heating point changes by 1°C. For most metal-supported thermocouples, this value is approximately between 5 and 40 microvolts/°C.