Food metal detectors generally use the principles of electromagnetic radiation and electromagnetic detection, using the difference in phase characteristics of the material signal and metal signal at different frequencies, using phase discrimination technology to eliminate the material signal, and only amplify, transform and identify the metal signal, etc. Process, drive relay action, manipulate execution system work.

Radiation coil: It is a coil winding made of copper wire. When an alternating current is applied to the food metal detector coil, an alternating magnetic field will be generated in the coil and radiated to the surroundings.

Receiving coil: The receiving coil is actually two coils with the same external dimensions and the same material, which are symmetrically placed in the alternating magnetic field generated by the radiating coil. It is the spatial configuration of the receiving coil of the food metal detector. In order to ensure that the instrument maintains "0" level output when no metal foreign matter enters the probe, the two coils are connected in reverse series.

Shielding cover: In order to prevent the space or surrounding electromagnetic interference from entering the probe and causing the food metal detector to malfunction, a metal box is required to seal the receiving coil and the radiating coil, while leaving a window through which the tested material can pass, and A magnetic channel must be maintained between the radiation and the receiving coil, and this metal box is the shield. In order to prevent deformation and displacement of the shielding cover and the coil, the shielding cover is filled with filler materials.

The working principle of the system: The signal source provides a high-power AC signal to the radiation coil of the food metal detector probe, so that the probe generates a cross magnetic field in the detection area. In the absence of external interference, the receiving coil maintains a "0" level output. When a metal body passes through the detection area, it will disturb the balanced alternating magnetic field. At this time, the receiving coil outputs an interference signal. This interference signal is amplified, phase-sensitive detection, and then compared and identified with the reference voltage set by the sensitivity adjustment potentiometer. If it is judged as "metal", this signal will trigger the output relay after a delay to control the action of the execution device. There is also a static test system in the food metal detector system, which is used to inspect certain electrical appliances.