Metal detector / metal detector working principle and advantages and disadvantages
With the improvement of people's living standards, the quality of life requirements are not satisfied with being able to eat and use, but put forward a higher goal of good food and good use. Only high-quality products can stand on the market and win consumers' Dear. Metal detectors are widely used in various processing and packaging industries such as food, pharmaceutical, and daily chemical industries. As a key control point of HACCP, manufacturers are encouraged to carry out quality control to ensure that the final products that enter the market will not cause harm to consumers.
Usually, the metal detector consists of two parts, a detection coil and an automatic rejection device, wherein the detection coil is a core portion. When the coil is energized, a magnetic field is generated. When a metal enters a magnetic field, it causes a change in the magnetic field, thereby judging that there is a metal impurity.
Some products themselves contain water, salt, etc., and they also cause metal-like interference to the magnetic field. This phenomenon is called product effect. This type of problem can be solved by the product effect compensation function.
After the metal is detected, the sensor activates the signal and drives an automatic reject device, such as a flap, a push rod, etc., to remove the impurities.
Specifically, it is eddy current. The detector produces a periodically varying magnetic field, and a periodically varying magnetic field creates a vortex electric field in space. The eddy electric field, if it encounters metal, forms an eddy current that can be detected.
The eddy current is generated and reacts to the magnetic field to change the voltage and impedance of the coil.
The current from the transmitting coil produces an electromagnetic field just as if the motor would also generate an electromagnetic field. The polarity of the magnetic field is perpendicular to the plane of the coil. Whenever the current changes direction, the polarity of the magnetic field changes. This means that if the coil is parallel to the ground, the direction of the magnetic field will alternate between changes, one to the other, perpendicular to the ground, and then perpendicular to the ground.
As the direction of the magnetic field changes repeatedly in the ground, it will interact with any conductor object encountered, causing the target itself to produce a weak magnetic field. The polarity of the target magnetic field is exactly the opposite of the polarity of the transmitting coil magnetic field. If the direction of the magnetic field generated by the transmitting coil is perpendicular to the ground, the target magnetic field is perpendicular to the ground.
The receiving coil completely shields the magnetic field generated by the transmitting coil. But it does not shield the magnetic field from the underground target. In this way, when the receiving coil is located above the target that is emitting the magnetic field, a weak current is generated on the coil.
This current oscillates at the same frequency as the target's magnetic field. The receiving coil amplifies this frequency and transmits it to the metal detector's console, which in turn analyzes the signal.
advantage:
Easy to operate
2. Economical and reliable
3. Wide range of applications
Disadvantages:
Not sensitive enough
2. Affected by the environment
3. Affected by the test object
The principle of the metal detector is that the magnetic field of the metal entering the detector causes the magnetic field to change, the sensor starts the signal, and drives the automatic rejection device, such as the flap, the push rod, etc., to remove the impurities. However, some products themselves contain water, salt and other components, which also cause metal-like interference to the magnetic field.