Manual

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GROUND BALANCING
What is Ground Balancing?
Why do I need to Ground Balance?
All soils contain minerals. Signals from ground minerals
are often tens or hundreds of times as strong as the
signal from a buried metal object. The magnetism of
iron minerals, found in nearly all soils, causes one
type of interfering signal. Dissolved mineral salts,
found in some soils, are electrically conductive,
causing another type of interfering signal.
Ground Balancing is the process by which the metal detector cancels
the unwanted signals coming from the ground minerals while still
detecting the signals from buried metal objects. This is accomplished
by matching the detector’s ground balance setting to the phase of
the ground signal.
When the detector is calibrated to the soil, the result will be deeper target
detection, quieter operation, and more accurate target identification.
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Ground Balancing procedure with the “Phase Lock” touchpad.
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Turn the F5 on and select AM (All-Metals) mode.
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Find a clear piece of ground with no metal
present, using All-Metals or Pinpoint mode.
(Note: Pinpoint preferred)
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Set the threshold to a slight background hum.
(Note: default setting of “0” is adequate)
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Press and hold the Phase Lock touch pad, and
pump coil over clean ground.
(Note: pump coil from 1” off ground to 6-8” off ground)
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When the phase value “settles down” to only one or two numbers
in variation, release the Phase Lock touch pad while still pumping
the coil. Note that the Audio Response to the ground changed
and “EVENED OUT” when you released the button. Also note that
the Gnd Bal setting changed to match the Phase Value, giving
you a visual AND audio Ground Balance confirmation. After
balancing, you can hunt in All-Metals... or return to Disc Mode.
To maintain the best ground balance setting for your detector, the GND
BAL setting on the left of the screen should always approximate the
PHASE value on the right of the screen.
The most accurate PHASE value is the value displayed when “pumping”
the coil over the ground in an area free of metal.
F5-manual-SPREADS(24pg).qx 10/2/08 3:11 PM Page 12
GROUND BALANCING – Technical Information
Understanding ground conditions assists the user in setting up the
machine, knowing when to readjust ground balance, and in
understanding the responses of the machine while searching. The
Fisher F5 provides two kinds of ground data:
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the amount of
mineralization (the greater the amount of mineralization, the greater the
loss of detection depth & ID accuracy; this loss is more pronounced in
Discrimination Mode)
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the type of mineralization (which affects mostly
where the ground balance should be set).
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The Fe
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4-segment bar graph indicates the amount of ground
mineralization, independent of type, expressed as an equivalent volume
concentration of magnetite (Fe
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). It updates every second. It is
sensitive to motion and will give the most accurate readings if you
“pump” the search coil up and down several times over the ground. The
presence of metal or “hot rocks” will cause the readings to be inaccurate.
If you stop moving the search coil, the bar graph will go blank.
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H — HIGH 0.4 - 1.6 1,000 - 4,000
M — MEDIUM 0.1 - 0.4 250 - 1,000
L — LOW 0.025 - 0.1 60 - 250
VL — VERY LOW 0.006 - .025 15 - 60
none - - less than .006 less than 15
Magnetic susceptibility is expressed in micro-cgs units. In a salt water
environment in the absence of iron minerals, the bar graph indicates
relative electrical conductivity.
In soils with greater than 4,000 micro-cgs units magnetic susceptibility, the
signal from the soil may saturate (“overload”) the circuits. This will not harm
the detector but the machine will not be usable in that condition. The
solution is to hold the search coil several inches above the soil surface so
it isn’t “seeing as much dirt”. By listening and watching you will know how
high you need to hold the search coil in order to avoid overload.
The highest magnetic susceptibilities are usually found in soils developed
over igneous rocks, in alluvial ‘black sand” streaks on beaches, and in
red clay soils of humid climates.
The lowest magnetic susceptibilities are usually found in white beach sands
of tropical and subtropical regions, and soils developed over limestone.