The working principle of detectors can vary depending on their type and application field. The following is a detailed introduction to the working principles of several common detectors:


Metal detectors:
Principle: Utilizing electromagnetic induction. The metal detector has a coil through which alternating current passes, generating a rapidly changing magnetic field. When a metal object approaches this magnetic field, eddy currents will be generated inside the metal object, which in turn will generate a magnetic field opposite to the direction of the original magnetic field, thereby changing the strength of the original magnetic field.
Application: Commonly used for food safety testing, such as detecting metal impurities in foods such as meat, candy, and beverages; It is also used for metal impurity detection in industrial raw materials, rubber, plastics, etc.



Infrared detector:
Active infrared detector: composed of an infrared transmitter and an infrared receiver. The transmitting end actively emits infrared radiation, while the receiving end receives infrared radiation, forming a network of infrared radiation. When there is no obstruction between the transmitter and receiver, the detector will not alarm; When an object obstructs, the output signal of the receiver changes and the detector alarms.
Passive infrared detector: mainly composed of optical system, thermal sensor (also known as infrared sensor), and alarm controller. Its core component is an infrared detection device, which can detect changes in thermal radiation within a three-dimensional defense space through the coordination of optical systems.




Microwave detector:
Principle: Applying the Doppler effect principle. Microwave detectors emit microwave signals to the detection area. When people or other objects enter the detection area, they will reflect the microwave signal. By measuring the frequency difference between the reflected signal and the transmitted signal, it can be determined whether there is an intruder.




Radiation detectors (such as pulse type radiation detectors):
Principle: Radiation particles are detected one by one through a pulse detector, and the measured signal corresponds to each incident particle. The number of pulse counts corresponds to the number of incident particles, and the amplitude of a single output signal reflects the energy of the incident particles.
Application: Mainly used for measuring the energy and intensity of heavy charged particles, such as radiation measurement in hospitals, disease control and health, research institutes, industries, and other fields.




Vibration detector:
Principle: Determine whether an intruder is present by detecting the displacement, velocity, or acceleration of object vibration. The commonly used vibration detectors include displacement sensors (mechanical type), velocity sensors (electric type), acceleration sensors (piezoelectric crystal type), etc.