Sensor is a kind of detection device, can feel the measured information, and can detect the perceived information, according to certain rules into electrical signals or other required form of information output, in order to meet the information transmission, processing, storage, display, record and control requirements. It is the first step to realize automatic detection and control. The national standard GB7665-87 defines a sensor as: "A device or device that can feel the specified measured and convert into usable signals according to certain rules, usually consisting of a sensitive element and a conversion element".

Sensors can be classified by different points of view: their conversion principle (the basic physical or chemical effect of the sensor's operation); Their use; Their output signal type and the materials and processes used to make them.

According to the working principle of sensors, sensors can be classified into physical sensors and chemical sensors:

The application of physical sensors is the physical effect, such as piezoelectric effect, magnetostriction phenomenon, ionization, polarization, thermoelectric, photoelectric, magnetoelectric and other effects. Small changes in the measured semaphore are converted into electrical signals.

Chemical sensors include those that take chemisorption, electrochemical reaction and other phenomena as a causal relationship. Small changes in the measured semaphore will also be converted into electrical signals.

Some sensors cannot be classified as either physical or chemical. Most sensors operate on the basis of physical principles. There are many technical problems of chemical sensors, such as reliability problems, the possibility of scale production, price problems and so on. If these problems are solved, the application of chemical sensors will have a huge growth.

Sensor classification

Sensor classification 1: Sensors can be classified according to their purpose

Pressure sensitive and force sensor  position sensor

Liquid level sensor  sensor energy consumption

Speed sensor  acceleration sensors

Gamma ray radiation sensor Heat sensor

Sensor classification 2: According to its principle, the sensor can be classified

Vibration sensor  humidity-sensitive sensors

Magnetic sensor  gas sensors

Vacuum sensor  biosensor, etc. 

Sensor classification 3: According to the output signal as the standard, the sensor can be divided into:

Analog sensor - Converts a measured non-electrical quantity into an analog electrical signal. 

Digital sensor - Converts the measured non-electrical quantity into a digital output signal (both direct and indirect).

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Pseudo digital sensor -- output that converts the measured semaphore into a frequency signal or short period signal (including direct or indirect conversion).

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Switch sensor - When a measured signal reaches a specific threshold, the sensor outputs a set low or high level signal accordingly.

Sensor classification 4: By material classification

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Under the action of external factors, all materials will make corresponding and characteristic responses. Those of them that are more sensitive to external effects, that is, those that have functional properties, are used to make sensors sensitive elements. From the point of view of applied materials, sensors can be divided into the following categories:

(1) According to the category of materials used: metal, polymer, ceramic, mixture

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(2) According to the physical properties of the material: conductor, insulator, semiconductor, magnetic material

(3) According to the crystal structure of the material: single crystal, polycrystal, amorphous material

Sensor classification 5: According to its manufacturing process, sensors can be divided into:

Integrated sensor, film sensor, thick film sensor, ceramic sensor