- Some metal detectors are categorized as very low frequency (or VLF) detectors. For these detectors, a transmitting coil gets an electrical current. This current causes a magnetic field to be emitted. Another coil, called the receiving coil, then picks up this magnetic field and transmits it back. However, if there are metal objects in the area below the detector, these objects will generate their own magnetic field in response to the transmitting coil. As a result, the signal from the receiving coil will be delayed, which will cause the machine to detect the presence of metal.
- Another kind of metal detector is the pulse induction (PI) variety. Pulse induction detectors run brief pulses of current through a wire that works as both the transmitter and the receiver. If no metal is near the wire, each electrical pulse will rapidly fade away. However, if there are metallic objects nearby, these objects will store some of the reflected pulse, causing the pulse to linger for longer. The speed with which these pulses are given out will change the type of metal that the detector is sensitive to. Slower pulses will make the detector more sensitive to the presence of silver, but faster pulses will be better for finding nickel and gold.
- Because different types of metal detectors are good for different conditions, the type of detector you want to use may vary. Fortunately, both types are pretty good at detecting gold. An advantage of the VLF type of detector is that it can be set to only signal detection of objects of a certain size. This can be very useful to avoid finding metal pieces of trash, like the tabs on soda cans. On the other hand, if there is a lot of salt in the soil, VLF detectors will not be very effective. In this case, a PI metal detector is recommended, especially with very rapid pulses for maximum gold sensitivity.
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