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 Erstellt: 12.02.23, 13:39 Betreff: Metal Detectors Explained
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Metal detectors are devices specially designed to detect metals that lie deep in the water or ground. When it was invented, it is specifically designed for screening or security purposes and to locate mines. There is a lot of industry which uses metal detectors such as food processing, textiles, pharmaceuticals, chemicals, packaging and plastic industries. It is important to check the foods for metal debris to avoid food poisoning. Those metals debris can be broken down to pieces on the machinery in food processing industry. On the other hand, you may find a lot of people that use metal detectors in hunting for treasures and old coins that are electronically driven. So, you might wonder how this thing work to detect metals that are hidden or how metal detector that is hand held work. So let's take a closer look at these detectors to know how they work.
Metal Detectors: How Do They Work?
Generally, metal detectors work on the fundamental principle that when electric current pass through a loop it will produce a magnetic field. One of the basic parts of a detector is an oscillator; it will produce the alternating current. Magnetic field is produced when an alternating current or electricity pass through the transmittal coil which is present in metal detectors. So, when a metallic object or a conductor is present close to the coil, it will generate a current in the object that will produce another magnetic field on it. There is another coil in the loop that can be found in detectors that is called the receiver coil that can detect magnetic field changes because of the presence of a metal or a metallic object. The latest metal detectors use these technologies; VLF very low frequency PI pulse induction and BFO beat-frequency oscillator. Let us discuss about these technologies:
Very Low Frequency (VLF) Technology
The most common technology used in metal detectors is VLF. There are coils in sets of two which is the receiver and the transmitter coil. The coil where electric current is sent and creates magnetic fields which constantly push down to the ground and pull back is called the transmitter coil. Magnetic field gets generated by the metal detector which reacts in any metallic or conductor that passes on it. When it encounters the object, the electric current and the magnetic field is formed around the conductor.
In reciprocal, the receiver coil is protected from the influence of the magnetic field which the transmitter coil produces and it is only affected by the conductor and /or the metallic object's magnetic field. The electricity that runs on this receiver coil produces a magnetic field that is weak when a conductor gets near the metal detector. In turn the coil will amplify and send the frequency of the electricity that has the same frequency with the magnetic field that comes from the metal to make analysis in the control box. Through this, the metal detector that works on VLF (very low frequency) will be able to determine disparity among the kinds of metals, the depth of the position when being detected.
PI Technology
A single coil is used in the PI technology (pulse induction) that is feasible on both transmitter and receiver. However, it is also possible to use 2 to 3 coils. Metal detector that works in this kind of technology can send a short burst and /or pulse of current in the coil that will generate a shorter magnetic field. In every pulse, the generated magnetic field will reverse the polarity and will eventually collapse. Electrical spike can be created and will last in very short period. When the magnetic field, pulse and spike collapses, a known current called as reflected pulse will occur and into the coil it will run. This reflected pulse can only last in seconds.
The reflected pulse can last in a longer period when a metallic or a conductor will get contact with the metal detector. The reason of this is caused by the opposing magnetic field that is produced by the metal detector. Metal detector is a device that has an integrator which contains a sample circuit that can be monitored closely on every spike. The thing that convert the signal, reads and amplifies will convert the signal into a direct current. The connected audio circuit when getting the right amount of electricity will produce tones that indicate a presence of a metallic object.
BFO Technology
The beat, frequency oscillator is like the VLF (very low frequency) that uses two wire coils. The first coil of the device can be found in the control box, and in the search head lays the second coil. The first coil which can be found in the control box most of the time is smaller compared to the second one in the search head. The two coils on the other hand, stay connected in the oscillator that sends out number of thousand electric pulses per second. When the pulse passes through every coil radio waves can be created and the receiver that can be found in the control box collects them all.
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