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Overview of metal detectors

Overview of metal detectors

Issue Time:2020-10-27

The metal detectors machine applies the principle of electromagnetic induction to Metal Detection. All metals including iron and non-ferrous have high detection sensitivity. The entry of ferromagnetic metals into the detection area will affect the distribution of magnetic lines of force in the detection area, which in turn affects the magnetic flux in a fixed range. Non-ferromagnetic metals entering the detection area will produce eddy current effects and also change the magnetic field distribution in the detection area.

  

   metal detectors machine detailed explanation:

  

   Usually the metal detector is composed of two parts, namely the metal detector and the automatic rejection device, in which the detector is the core part. There are three sets of coils distributed inside the detector, namely the central transmitting coil and two equivalent receiving coils. The oscillator connected to the transmitting coil in the middle generates a high-frequency variable magnetic field. In the idle state, the induced voltage of the receiving coils on both sides Before the magnetic fields are disturbed, they cancel each other out and reach equilibrium. Once the metal impurities enter the magnetic field and the magnetic field is disturbed, this balance is broken, and the induced voltages of the two receiving coils cannot be cancelled. The un-cancelled induced voltages are amplified and processed by the control system, and an alarm signal is generated (metal impurities are detected ). The system can use the alarm signal to drive an automatic rejection device, etc., so as to exclude metal impurities from the production line.


  Metal detectors machine features and concepts:

  

  The accuracy and reliability of the metal detectors machine depends on the stability of the electromagnetic transmitter frequency, generally use the operating frequency from 80 to 800kHz. The lower the working frequency, the better the detection performance of iron; the higher the working frequency, the better the detection performance of high carbon steel. The sensitivity of the detector decreases with the increase of the detection range, and the size of the induced signal depends on the size of the metal particles and the conductivity.

  

   Due to the current pulsation and current filtering, the metal detector has certain restrictions on the conveying speed of the detected items. If the conveying speed exceeds a reasonable range, the sensitivity of the detector will decrease.

  

  In order to ensure that the sensitivity does not decrease, the appropriate metal detectors machine must be selected to suit the corresponding detected products. Generally speaking, the detection range should be kept as small as possible. For products with good high-frequency inductance, the detector channel size should match the product size. The adjustment of detection sensitivity should be determined with reference to the center of the detection coil, and the center position has the lowest induction. The detection value of the product will change with the change of production conditions, such as changes in temperature, product size, humidity, etc., which can be adjusted and compensated through the control function


  Spherical objects have repeatability, the smallest surface area, and the most difficult to detect for metal detectors machine. Therefore, the ball can be used as a reference sample for detection sensitivity. For non-spherical metals, the detection sensitivity largely depends on the location of the metal. Different locations have different cross-sectional areas, and the detection effect is also different. For example, when passing longitudinally, iron is more sensitive; while high-carbon steel and non-iron are less sensitive. When passing horizontally, iron is less sensitive, while high-carbon steel and non-iron are more sensitive.

  

  In the food industry, systems usually use higher operating frequencies. For food such as cheese, due to its inherent high-frequency induction performance, it will increase the response of high-frequency signals proportionally. Moist fat or salt substances, such as bread, cheese, sausage, etc., have the same conductivity as metals. In this case, in order to prevent the system from giving false signals, the compensation signal must be adjusted to reduce the sensitivity of the induction.

  

  Metal detectors machine purpose:

  

Mainly used for metal detection in small food, chemical products, clothing, shoemaking, marine aquatic products, fisheries, dry and fresh aquatic products, pasta, frozen food, dry and fresh fruits and vegetables, sugar, tea, medicine and other industries, detecting raw materials or products Iron, lead and other metal impurities that are mixed or leaked.

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