A brief introduction to the testing principle of metal detectors
Metal detectors are widely used in daily work and life to prevent candidates from bringing mobile phones and other communication tools into the examination room, and to prevent metal objects from causing danger in special occasions. Metal detectors are also widely used in security fields, such as security inspection at airports, detection of residual nails in wood, detection of underground metal pipelines, mine detection, etc., and even grave robbers use it to find underground cultural relics. Here is a brief discussion of the test principle of the metal detector. Metal detectors work on a variety of principles, and here are two of them.
One: Metal detectors are divided into detection coils and detectors
The principle of the whole machine includes: the oscillating circuit generates oscillation, which is fed to the detection coil after frequency division and power amplification to generate an alternating magnetic field. When the material mixed with metal impurities passes through the coil, its alternating magnetic field will be disturbed, so the detection There will be a slight change at the output end of the coil, alternating voltage output, this weak voltage signal is passed through circuits such as high release, phase sensitive detection, low release, voltage comparison, suppression of short pulse interference, and monostable triggering, etc., and finally used The relay actuator operates to alarm with sound and light, and at the same time, it can stop the conveyor, or activate the push-out mechanism, so as to detect objects mixed with metal impurities.
Two: The principle is to adjust the gain potentiometer of the high-frequency oscillator, just to make the oscillator in a critical oscillation state, that is to say, just to make the oscillator start to vibrate. When the detection coil is close to the metal object, due to the electromagnetic induction phenomenon, an eddy current will be generated in the metal conductor, which will increase the energy loss in the oscillation circuit, weaken the positive feedback, weaken the oscillation of the oscillator in the critical state, and even fail to maintain the oscillation. Vibration stops with the lowest energy required. If this change can be detected and converted into a sound signal, it can be determined whether there is a metal object under the detection coil according to the presence or absence of the sound. metal detection.
