Comprehensive Operating Manual & Guide to Metal Detecting
Comprehensive Operating Manual & Guide to Metal Detecting
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F75
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F75
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The range of ground balance settings indicated on the display range from 0 to 99; however,
each displayed number spans 5 detent steps on the settings knob. The actual internal ground
balance settings change with each step; there are a total of 500 different settings. Under some
ground conditions you may be able to hear the individual steps in the setting.
The Fe
3
O
4
bar graph on the LCD display indicates the amount of magnetic mineralization. The
searchcoil must be in motion to measure Fe
3
O
4
. The most accurate measurement is obtained
by pumping the searchcoil, as in the Ground Balancing procedure.
The two-digit G.B. Setting number displayed on the LCD indicates the type of ground mineralization.
Some typical ground mineralization types are:
0 – 10
Wet salt and alkali
5 – 25
Metallic iron. Very few soils in this range. You are probably over metal.
26–39
Very few soils in this range -- occasionally some saltwater beaches
40–75
Red, yellow, and brown iron-bearing clay minerals
75–95
Magnetite and other black iron minerals
When manually ground balancing, try to “feel out” a spot on the ground to make sure there is
no metal present.
In order to avoid locking onto metal, the computer will not balance to
ground where the GB setting is less than 40. Where the ground reads less than 40, manual
ground balancing is required.
To perform the Manual Ground Balancing operation, do the following:
1. Select the MANUAL G.B. function
The legend G.B. SETTING appears.
The present ground balance setting is displayed
(0-99).
The message PUMP COIL TO G.B. will appear.
2. Physically pump the searchcoil and detector up
and down over the ground.
Lift it about 6 inches above the ground and
lower it to within 1 inch
of the ground, about once or twice a second.
3. Turn the SETTINGS KNOB to adjust the setting.
The goal is to eliminate the sound as the coil is
being pumped over the ground. In some soils,
the sound is not completely eliminated.
If the ground balance adjustment is incorrect, there will be a difference in the sound as the
searchcoil is either moving toward or away from the ground. It sounds like you are either
pulling the sound out of the ground,
or
pushing the sound into the ground.
• If the sound is louder as you raise the searchcoil, increase the ground balance setting.
• If the sound is louder as you lower the searchcoil, reduce the ground balance setting.
NOTE: Experienced users often prefer to adjust the ground balance to get a weak but audible
response when lowering the searchcoil. This is called adjusting for positive response.
Positive and Negative Response
The purpose of ground balancing is to adjust the metal detector to ignore ground minerals. If
the setting is incorrect, ground minerals will give either a positive or a negative response,
Ground Balancing (continued)
Search Techniques (continued)
Position the searchcoil an inch or two (2.5-5cm) above the ground, and to the side of the
target. Then pull the trigger. Now move the searchcoil slowly across the target, and the sound
will indicate the target’s location. As you sweep from side to side, and hear no sound at the
ends of the sweep, the target is located in the middle of that zone, where the sound is loudest
and the audio pitch is highest. If the sound is loud over a wide area, the buried object is large.
Use the PinPoint feature to trace an outline of such large objects.
Estimating Target SIZE, DEPTH, and SHAPE
When the trigger is pulled to activate Pinpoint, the LCD displays estimated depth. The
estimate is based on the presumption that it is a coin-sized target.
But what if it is not a coin-sized target? The most common example is that of an aluminum can.
Flattened aluminum cans are usually identified as quarters. Their large size will produce a
strong signal, tricking the microcomputer into thinking that it is a shallow coin.
The following explains techniques for differentiating buried aluminum cans from coins. Sweep
back and forth to get a feel for the target, keeping the searchcoil close to the ground. Now,
continue to sweep back and forth as you slowly raise the searchcoil higher and higher. If the
response diminishes quickly and never gets very broad, the target is probably a coin. If the
response diminishes slowly as you lift the searchcoil, and you get a broad response, the target
is probably an aluminum can. If you practice this by laying a coin and a flattened aluminum
can on the ground, you will quickly understand how to differentiate the two and you will
probably never have to dig another aluminum can. And, you will know whether it was deep or
shallow. This technique works well in the All Metal Modes, and to a lesser extent in
Discrimination Mode.
Objects which are ring-shaped, or flat and round like coins, tend to give a narrower, crisper
response than objects of similar size with irregular shapes. The easiest way to demonstrate
this is with an aluminum screwcap from a soda bottle. In its normal shape, it occupies a
volume, and gives a somewhat broader response than that of a coin. But if you flatten it, the
response will be crisper and more like that of a coin. Again, these differences are most readily
noticed in the All Metal Modes.
Long skinny iron or steel objects such as nails usually produce a double response when
scanned lengthwise, and a weaker single response when scanned crossways. This is most
noticeable in the Motion All Metal Mode. However, a coin lying on its edge can produce a
similar response, so rely on both the Target-ID as well as target feel to distinguish between
different kinds of objects. Objects within 2 to 3 inches of the searchcoil will often produce
multiple responses as you sweep across them, because the response field close to the
searchcoil is irregular.
F75ltdBLK-MANUAL.qx6_M75MBLK-Manual 10/7/14 4:28 PM Page 15
