The principle of metal detector and the influencing factors of its accuracy

Working principle of metal detector: a central transmitting coil and two equal receiving coils, which are installed in a probe head The oscillator emits a high frequency magnetic field through the middle transmitting coil, which is connected with the two receiving coils, but the polarity is opposite When the magnetic field is free from external interference, the voltage output signals generated by them cancel each other Once the metal impurity enters the magnetic field area, the signals output by the two output coils cannot be cancelled, and the metal detector can detect the existence of metal A small piece of metal in candy or other foods can seriously harm consumers Therefore, the primary purpose of using metal detector is to protect the interests of consumers and establish a good corporate image In addition, a small piece of metal on the production line will also cause serious wear on the production equipment of the enterprise, and the maintenance cost of the equipment is very expensive, which will greatly increase the production cost of the enterprise Several factors that affect the metal detector (1) the frequency of conversion coil, the transmission frequency of conversion coil and the size of metal sheet will directly affect the test results (2) the phase angle of the conversion coil causes the phase relation of various metals Each different metal can produce different detection signals Therefore, the detection signal can be regarded as a vector, the phase angle represents the metal class, and the vector length represents the size of the metal sheet (3) product effect: if a product can conduct electricity, the product usually has certain moisture, so it can be said that it has product effect From the technical point of view of metal detection, this conductive product is the same as metal The sensitivity of metal detector varies with the distribution of magnetic field The closer to the center line, the lower the sensitivity The sensitivity Zui at the center line is low, so when testing, the test sample should pass through the center line Metal detection is a complex technology, and its results are affected by many factors
１。 Inspection port size 2 Working frequency: 3 Metal type 4 Sheet shape 5 External environmental impact 6 Product effect 7 Way: since a period of continuous / intermittent time, food, candy, tobacco and other industries have taken a series of measures to improve product quality However, even in the highly automated and well managed food enterprises, the possibility of metal contamination in the production process cannot be completely ruled out Therefore, if the product is polluted by metal, the enterprise must use the metal detector to remove the unqualified product from the production line.