Comprehensive Operating Manual & Guide to Metal Detecting
Comprehensive Operating Manual & Guide to Metal Detecting
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F75
SE
F75
SE
MANUAL GROUND BALANCING
In most situations, it is preferable to push the trigger switch to activate FASTGRAB™
automatic ground balancing. Generally, it is best to first let the computer automatically cancel
interference from ground minerals. However, for gold prospecting, searching on a wet
saltwater beach, or searching in an area with so much metal trash that there is no
clean
ground for the computer to sample, we recommended that you manually ground balance.
Manual ground balancing requires a bit of skill, acquired with some practice.
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.
Ground Balancing (continued)
G.H. PHASE
90
GC PHASE 90
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.
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