The sensor is a detecting device that can sense the measured information and can transform the detected information into an electrical signal or other required form of information output according to a certain law to meet the information transmission, processing, storage, Requirements for display, recording and control. It is the first step in achieving automatic detection and automatic control. The national standard GB7665-87 defines the sensor as: "A device or device that can be measured and converted into a usable signal according to a certain rule, usually composed of a sensitive component and a conversion component."

Sensors can be categorized from different perspectives: their conversion principles (the basic physical or chemical effects of sensor operation); their use; their output signal types and the materials and processes used to make them.

According to the working principle of the sensor, the sensor classification can be divided into two categories: physical sensor and chemical sensor:

Classification of sensor operating principles Physical sensors use physical effects such as piezoelectric effects, magnetostriction, ionization, polarization, thermoelectric, optoelectronic, magnetoelectric and other effects. Minor changes in the measured semaphore will be converted into electrical signals.

Chemical sensors include those that cause causal relationships such as chemisorption and electrochemical reactions. Small changes in the measured signal volume are also converted into electrical signals.

Some sensors can neither be classified into physical classes nor classified as chemical. Most sensors operate on the basis of physical principles. There are many technical problems in chemical sensors, such as reliability problems, the possibility of mass production, and price issues. These problems have been solved, and the application of chemical sensors will grow tremendously.