A sensor is a detection device that can sense the information being measured and convert the sensed information into an electrical signal or other required forms of information output according to a certain rule, to meet the requirements of information transmission, processing, storage, display, recording, and control. It is the primary link in achieving automatic detection and control. The national standard GB7665-87 defines a sensor as: "A device or device that can sense the specified measured quantity and convert it into a usable signal according to a certain rule, usually consisting of sensitive elements and conversion elements."

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

Based on the working principles of sensors, they can be classified into two major categories: physical sensors and chemical sensors.

Physical sensors apply physical effects such as piezoelectric effects, magnetostriction, ionization, polarization, thermoelectricity, photoelectricity, and magnetoelectricity. The slightest change 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, where the slightest change in the measured signal quantity will also be converted into an electrical signal.

Some sensors cannot be categorized as either physical or chemical. Most sensors operate based on physical principles. Chemical sensor technology faces many challenges, such as reliability issues, the possibility of mass production, and price issues. Solving these problems will lead to a significant increase in the application of chemical sensors.

Sensor Classification

Sensor Classification 1: According to their applications, sensors can be classified as:

Pressure and force sensors  Position sensors

Level sensors  Energy consumption sensors

Speed sensors  Acceleration sensors

Radiation sensors  Thermistors

Sensor Classification 2: According to their principles, sensors can be classified as:

Vibration sensors  Humidity sensors

Magnetic sensors  Gas sensors

Vacuum sensors  Biosensors, etc.

Sensor Classification 3: According to their output signals, sensors can be classified as:

Analog sensors – Convert non-electrical quantities of the measured object into analog electrical signals.

Digital sensors – Convert non-electrical quantities of the measured object into digital output signals (direct and indirect conversion).

Pseudo-digital sensors – Convert the signal quantity of the measured object into frequency signals or short-period signals (direct or indirect conversion).

Switch sensors – When the measured signal reaches a specific threshold, the sensor outputs a set low or high signal.

Sensor Classification 4: According to materials

Under the influence of external factors, all materials react accordingly, with characteristic responses. Those that are sensitive to external effects, i.e., those with functional properties, are used to make sensor sensitive elements. From the perspective of the materials used, sensors can be divided into the following categories:

(1) According to the category of materials used: Metals, Polymers, Ceramics, Composites

(2) According to the physical properties of materials: Conductors, Insulators, Semiconductors, Magnetic materials

(3) According to the crystal structure of materials: Single crystal, Polycrystal, Amorphous materials

Sensor Classification 5: According to their manufacturing processes, sensors can be classified as:

Integrated sensors, Thin-film sensors, Thick-film sensors, Ceramic sensors