A sensor is a detection device that can perceive measured information and transform the detected information into electrical signals or other required forms of information output according to certain rules, to meet the requirements of information transmission, processing, storage, display, recording, and control. It is the primary link for achieving automatic detection and automatic control. The national standard GB7665-87 defines a sensor as: "A device or apparatus that can detect specified measured quantities and convert them into usable signals according to certain rules, typically composed of sensitive elements and conversion elements."

Sensors can be classified from different perspectives: their conversion principles (the basic physical or chemical effects underlying sensor operation); their applications; their output signal types; and the materials and processes used to manufacture them.

Based on the operating principle, sensors can be divided into two major categories: physical sensors and chemical sensors.

The classification of sensors by operating principle: Physical sensors utilize physical effects such as piezoelectric effect, magnetostriction, ionization, polarization, thermoelectric, photoelectric, and magnetoelectric effects. Even small changes in the measured signal quantity will be converted into an electrical signal.

Chemical sensors include those based on phenomena such as chemical adsorption and electrochemical reactions. Small changes in the measured signal quantity will also be converted into an electrical signal.

Some sensors cannot be classified as purely physical or purely chemical. Most sensors operate based on physical principles. Chemical sensors face numerous technical issues, such as reliability, feasibility of mass production, and cost. Once these challenges are resolved, the application of chemical sensors will see significant growth.

Classification of Sensors

Classification 1: By Application, Sensors Can Be Categorized

Pressure-sensitive and Force-sensitive Sensors Position Sensors

Level Sensors Energy Consumption Sensors

Velocity Sensors Acceleration Sensors

Radiation Sensors Thermal Sensors

Classification 2: By Principle, Sensors Can Be Categorized

Vibration Sensors Humidity Sensors

Magnetic Sensors Gas Sensors

Vacuum Sensors Biosensors, etc.

Classification 3: By Output Signal, Sensors Can Be Divided Into

Analog Sensors — Convert the measured non-electrical quantity into an analog electrical signal.

Digital Sensors — Convert the measured non-electrical quantity into a digital output signal (including direct and indirect conversion).

 
Quasi-Digital Sensors — Convert the measured signal quantity into a frequency signal or short-period signal output (including direct or indirect conversion).

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

Classification 4: By Material

 
Under the influence of external factors, all materials exhibit corresponding, characteristic reactions. Among them, materials that are more sensitive to external effects, i.e., those with functional properties, are used to manufacture the sensitive elements of sensors. From the perspective of applied materials, sensors can be divided into the following categories:

(1) By the type of material used: Metals, Polymers, Ceramics, Mixtures

 
(2) By the physical properties of the material: Conductors, Insulators, Semiconductors, Magnetic Materials

(3) By the crystal structure of the material: Single Crystal, Polycrystalline, Amorphous Materials

Classification 5: By Manufacturing Process, Sensors Can Be Distinguished Into

Integrated Sensors, Thin-Film Sensors, Thick-Film Sensors, Ceramic Sensors