Temperature is a basic physical quantity, and all processes in nature are closely related to temperature. Temperature sensors are the earliest developed and most widely used sensors. The market share of temperature sensors greatly exceeds other sensors. Since the beginning of the 17th century, people have used temperature to measure. With the support of semiconductor technology, semiconductor thermocouple sensors, PN junction temperature sensors and integrated temperature sensors have been successively developed this century. Correspondingly, acoustic temperature sensors, infrared sensors, and microwave sensors have been successively developed according to the interaction rules between waves and matter.
If two kinds of conductors of different materials are connected to each other at a certain point, if the connection point is heated, a potential difference will appear at the parts where they are not heated. The value of this potential difference is related to the temperature of the measuring point in the unheated part, and to the material of these two conductors. This phenomenon can occur in a wide temperature range. If this potential difference is accurately measured, and then the ambient temperature of the unheated 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 is also different. The sensitivity of the thermocouple refers to the change in the output potential difference when the heating point temperature changes by 1 ° C. For most thermocouples supported by metallic materials, this value is about 5 to 40 microvolts / ° C.
Thermocouple sensors have their own advantages and disadvantages. They have low sensitivity, are easily affected by environmental interference signals, and are also easily affected by temperature drift of the preamplifier, so they are not suitable for measuring small temperature changes. Since the sensitivity of the thermocouple temperature sensor has nothing to do with the thickness of the material, a very thin material can also be used to make the temperature sensor. Also because the metal material used to make the thermocouple has good ductility, this fine temperature measuring element has a very high response speed and can measure fast-changing processes.
