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Comprehensive Operating Manual & Guide to Metal Detecting
Comprehensive Operating Manual & Guide to Metal Detecting
30 15
F75
F75
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)
STEEL BOTTLE CAPS & FLAT IRON TRASH
Modern motion-type target ID metal detectors usually have difficulty consistently identifying
steel bottle caps and other flat iron trash objects. Double-D searchcoils also have a reputation
for having difficulty distinguishing steel bottle caps from coins, and for being unable to
eliminate steel bottle caps from detection. If you are searching in an area where there are
many steel bottle caps or other flat iron trash targets, minimize the amount of unnecessary
digging with the following methods:
1. SEARCH WITH THE
bc
(BOTTLE CAP) PROCESS using the PROCESS # feature.
This method calculates visual ID differently in order to cause steel bottle caps to read
lower on the scale, and to register less consistently. A desirable object such as a coin
will usually produce numeric values that are fairly consistent in both directions of
sweep. See PROCESS # under the DISCRIMINATION Mode section of this manual.
2. SEARCH WITH THE
dP
PROCESS. This method calculates visual ID differently in
order to cause steel bottle caps to ID lower on the scale and to register less
consistently. It also produces more audio clues to the character of the target.
3. LIFT THE SEARCHCOIL. Within 2 inches of a Bi-Axial searchcoil, the crossed magnetic
fields of the Double-D construction can produce anomalous responses. If the object feels
shallow (strong signal, narrow response, or multiple responses in a single sweep) and is
giving consistent high readings like a coin, raise the searchcoil 2 to 3 inches and try again.
A coin will almost always continue to give consistent readings unless it is right next to an
iron object.
A steel bottle cap that is at least 3 inches away from the searchcoil will
usually produce readings that bounce around from medium to low numbers.
4. SWEEP THE REAR OF THE SEARCHCOIL OVER THE CENTER OF THE TARGET,
OR SWEEP RAPIDLY.
a.
If the ID# is repeatable in the range of 68 to 72, when passing the
center of the searchcoil over the target at a normal speed, then the
target is probably a dime or copper penny.
b.
If the ID# is not in the range of 68 to 72 then:
i. Sweep the back end of the searchcoil over the target. If tones
change from high to low, the target is probably a bottle cap.
ii. Sweep the center of the searchcoil rapidly across the target.
1. If tone and ID# drop, it is probably a bottle cap.
2. If a bottle cap, then the faster you sweep, the
lower the tone.
5. USE THE CONFIDENCE INDICATOR
Coins will usually produce a high
confidence level, whereas steel bottle caps
and other trash will usually indicate a low or
erratic confidence, even if the ID numbers
are consistently in the range of a coin.
Confidence level is useful even if not
using the dP or 3b processes.
Capabilities And Limitations (continued)
Sweep back end
of searchcoil over
suspected bottle cap.
(Low Tone = Bottle Cap)
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