Ill people have to measure body temperature, weather conditions change, people have to measure the temperature, and in the industry also need to control the temperature and measure various temperatures. Temperature measurement instruments are also used more and more widely. They are industrial automation instruments that measure the degree of hot and cold objects.

Since 1592, Galileo invented the first temperature indicator without scale. The temperature measuring instrument has now undergone several generations of development, and both technology and performance have been greatly developed. Common temperature meters include thermometers, temperature recorders, temperature transmitters, and more. The earliest thermometer was a mercury thermometer (Fahrenheit thermometer), which was later developed into Celsius mercury thermometer. After that, bimetal thermometers, thermocouple thermometers, etc. appeared one after another.

In modern society of science and technology, thermometers have made great progress and types have gradually increased. Gas thermometers, resistance thermometers, thermocouple thermometers, high temperature thermometers (above 500°C), pointer thermometers, semiconductor thermometers, thermocouple thermometers, photopyrometers, colorimetric thermometers, radiation thermometers, liquid crystal thermometers, etc.

According to the measurement method, the temperature measuring instrument can be divided into contact type and non-contact type. The former needs to contact with the measured medium when measuring temperature, and the latter does not need to. According to the principle of work, it includes direct-reading level meters, differential pressure level meters, buoyancy level meters, electromagnetic level meters, nuclear radiation level meters, sonic level meters, optical objects. Position meters and so on. According to the primary instrument and the secondary instrument, the thermocouple, thermal resistance, bimetal thermometer, and local temperature display instrument are classified as a single instrument; temperature recorder, temperature inspection instrument, temperature display instrument, temperature regulator, etc. Temperature transmitters, etc. are classified as secondary instruments.