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VLF (very low frequency) ground canceling metal detectors work on the principle of conductivity. These metal detectors will locate any metal with a conductive surface within 45-60 cm (18" to two feet) of the ground surface. A signal is heard because an electromagnetic field is generated and caused to flow out into space away from the search coil. As the lines of the electromagnetic field penetrate the surface of the metal, tiny circulating electrical currents called eddy currents are caused to flow in the surface of the metal. These eddy currents then generate their own electromagnetic fields which radiate in all directions in space. Those currents which radiate directly upwards toward the receiver's search coil windings are picked up. A reduced voltage is then fed into the amplifying wires where it is conditioned to drive a loudspeaker, meter or headphones. The larger the surface, the greater the signal.

Metal detectors do not react to mass but to surface area. In other words, a flat coin will make a larger signal than a coin on its edge.

Most VLF metal detectors are equipped with an alternative mode called a TR discriminator mode. This mode is 90% accurate in being able to discriminate between two classes of non-ferrous and ferrous (iron containing) substances:

  • gold, silver, copper, lead, zinc and nickel. These metals have better conductivity than do those in the second group
  • iron, tin, foil-coated wrappers and bottle tops
 

Pin Pointing the Target

When a signal is heard, and do not ignore the faint ones, immediately swing back over the area to pinpoint it. An accurately pinpointed target will save you hours of digging work.


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