How Metal Detectors Work - Fisher Labs F 75 User Manual

How Metal Detectors Work

Most hobby metal detectors use VLF Induction Balance technology. Here's how they work.
The search coil (also called search head or loop) contains two electrical induction coils which
are like antennas. One coil transmits a rapidly alternating magnetic field, illuminating the
region surrounding the search coil. If metal is present, its electrical conductivity distorts the
magnetic field. If iron metal is present, its magnetism also distorts the magnetic field, but in a
different way, allowing the metal detector to distinguish between ferrous and nonferrous
metals.
The other coil is a receiving antenna which detects changes in the magnetic field caused by
the presence of metal. Electronic circuits amplify this weak signal, analyze it to determine the
changes which occur as the search coil sweeps over the target, and then convey the
information to the user in the form of a visual display or audio tones. Most modern metal
detectors perform many of these tasks in software running on an internal microcomputer.
The iron minerals which are present in most soils also distort the magnetic field, obscuring the
weak signals of small or deep objects. This can cause the object to go undetected, or to be
misidentified when it is detected. Much of the technology that goes into modern metal
detectors is devoted to the task of eliminating the unwanted signals from iron minerals in the
soil, while not losing the signals from metal objects.
Treasure Hunter's Code of Ethics:
• Always check Federal, State, County and local laws before searching.
• Respect private property and do not enter private property without the owner's permission.
• Take care to refill all holes and try not to leave any damage.
• Remove and dispose of any and all trash and litter found.
• Appreciate and protect our inheritance of natural resources, wildlife and private property.
• Act as an ambassador for the hobby, use thoughtfulness, consideration and courtesy at all
times.
• Never destroy historical or archaeological treasures.
• All treasure hunters may be judged by the example you set; always conduct yourself with
courtesy and consideration of others
Comprehensive Operating Manual & Guide to Metal Detecting
Copyright Fisher Research Labs, Inc. April 22, 2009
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