The metal detector is mainly composed of two parts: a probe and a control device. The principle of the whole machine is that the probe is composed of 3 coils wound on the skeleton, and the center coil is connected to the oscillator. After frequency division and power amplifier, the oscillation generated by the oscillator is fed back to the detection coil to generate an alternating magnetic field.

The alternating magnetic field induces a signal in the detection coils, but since these coils are connected in reverse, the two signals are subtracted from each other. When the composite signal is zero, the probe is in a balanced state. Because metals are both magnetic and conductive, when a metal object passes through the detection area, it will interfere with the original alternating magnetic field. Ferromagnetic materials will locally strengthen the original alternating magnetic field, and non-ferromagnetic materials will locally weaken the original alternating magnetic field. The receiving coil is designed in a differential form. When there is no external metal passing through, its output is in a balanced state; when there is metal passing through, the alternating magnetic field in the detection area is disturbed, destroying the balance of the probe, so that the output end of the detection coil has a weak Varying alternating voltage output, this weak voltage signal will be included in the output signal amplitude and phase after high-amplification, phase-sensitive detection, low-amplification, voltage comparison, short pulse suppression, monostable trigger and other electronic control circuits The “metallic” information is separated out and used as sound and light alarms and control signals for actuators.

The execution signal is sent out by the relay and sent to the automatic actuator to automatically alarm or detect metal objects.