Instruments can improve, expand or supplement human functions. People use sensory organs to see, listen, taste and touch external things, and instruments such as microscopes, telescopes, sound level meters, acidity meters, pyrometers, vacuum centrifugal concentrators can improve and expand these functions. In addition, some instruments, such as magnetometers, radiometers, can sense and measure physical quantities that human sensory organs can not feel, as well as some instruments. Instruments can be recorded, calculated and counted beyond human capabilities, such as high-speed cameras, computers, etc.

Instruments and meters are comprehensive products of many kinds of science and technology. They are widely used and constantly updated. There are many kinds of classification methods. According to the purpose and purpose of use, there are mainly measuring instruments, automobile instruments, tractor instruments, marine instruments, aviation instruments, navigation instruments, driving instruments, radio testing instruments, carrier microwave testing instruments, geological exploration testing instruments, building materials testing instruments, seismic testing instruments, geodetic surveying and mapping instruments, hydrological instruments, timing instruments, agricultural testing instruments, commercial instruments. Testing instruments, teaching instruments, medical instruments, environmental protection instruments, etc.

According to different characteristics, such as function, detection and control object, structure and principle, all kinds of instruments can be further divided into several subclasses or subclasses. For example, industrial automation instruments can be divided into testing instruments, loop display instruments, regulating instruments and actuators according to their functions; among them, measuring instruments can be further divided into temperature measuring instruments, pressure measuring instruments, flow measuring instruments, level measuring instruments and mechanical measuring instruments according to the measured physical quantities; and temperature measuring instruments can also be divided into contact temperature measuring instruments and non-contact temperature measuring instruments according to the measuring methods. Instrument; Contact thermometer can be divided into thermoelectric type, expansion type, resistance type and so on.