Temperature is a basic physical quantity, and all processes in nature are closely related to temperature. The temperature sensor is the earliest developed and most widely used type of sensor. According to a survey by the American Institute of Instrumentation, in 1990, the market share of temperature sensors greatly exceeded that of other sensors. Since the invention of the thermometer by Galileo in the early 17th century, people began to use temperature to measure. The sensor that really converts temperature into an electrical signal was invented by German physicist Sebe in 1821, which is the later thermocouple sensor. 50 years later, another German, Siemens, invented the platinum resistance thermometer. With the support of semiconductor technology, semiconductor thermocouple sensors, PN junction temperature sensors, and integrated temperature sensors have been developed successively in this century. Correspondingly, according to the law of interaction between waves and matter, acoustic temperature sensors, infrared sensors, and microwave sensors have been developed successively.
The following mainly introduces the commonly used thermocouple temperature sensors. For example, if two conductors of different materials are connected to each other at a certain point, if this connection point is heated, a potential difference will appear at the part where they are not heated. The value of this potential difference is related to the temperature of the measurement point in the unheated part, and the material of the two conductors. This phenomenon can occur in a wide temperature range. If the 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 conductors of different materials, it is called a "thermocouple". Thermocouples made of different materials are used in different temperature ranges and their sensitivities vary. The sensitivity of the thermocouple refers to the 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 about 5 to 40 microvolts/°C.
Since the metal materials constituting the thermocouple can withstand very high temperatures, for example, tungsten-rhenium thermocouples can work at high temperatures above 2000 °C and are often used to detect thermophysical parameters in high-temperature environments, and some materials can work at low temperatures. A gold-iron thermocouple, for example, can work around the temperature of liquid nitrogen. It can be seen that the thermocouple sensor can work in a wide temperature range.
Learn more about the temperature sensor.
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