25
Comprehensive Operating Manual & Guide to Metal Detecting
PRO-TECH
GROUND BALANCING - Technical Info
Fe3O
4
BAR GRAPH
The Fe
3
O
4
7-segment bar graph indicates the amount of ground mineralization,
independent of type, expressed as an equivalent volume concentration of magnetite
(Fe
3
O
4
). It updates every second. It is sensitive to motion and will give the most
accurate readings if you pump the searchcoil 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 searchcoil, the bar graph will go blank.
INDICATION
RELATIVE
% Fe
3
O
4
SUSCEPTIBILITY
MINERALIZATION
7 Bars
High
over 1
over 2500
2 to 6 Bars
Medium
.026 - 1.0
61 - 2,500
1 Bar
Very Low
0.006 - .025
15 - 60
none
--
less than .006
less than 15
Magnetic susceptibility is expressed in micro-cgs units. In a saltwater environment in
the absence of iron minerals, the bar graph indicates relative electrical conductivity.
In soils with greater than 10,000 micro-cgs units magnetic susceptibility, the signal
from the soil may saturate, or overload, the circuitry. This will not harm the detector
but the machine will not be usable in that condition. The solution is to hold the
searchcoil several inches above the soil surface so it is not “seeing as much dirt.” By
listening and watching you will know how high you need to hold the searchcoil 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.
12
PRO-TECH
Comprehensive Operating Manual & Guide to Metal Detecting
THE BASICS OF METAL DETECTING (continued)
2. Trash
Modern trash is prevalent everywhere and you may wish to learn the Target-ID
readings for common items such as pop tops and aluminum cans. Modern trash
is also usually on or near the surface so depth indication may also give you
clues to potential Target-ID.
3. Identifying Buried Objects
Different types of metals are classified along the arc at the top of the screen on
a 0-100 scale from left to right. A 2-digit numerical reading is also provided in
the middle of the display for more precise Target Identification in Discrimination
Mode.
4. Size and Depth of Buried Objects
When using the detector in the motion DISC Mode, the relative depth of an
object is displayed to the left of the display over the SIGNAL strength indicator.
A more accurate depth reading is available using PINPOINT. Pinpoint displays
target depth, in inches. The Pinpoint Mode does not require the searchcoil to be
in motion to detect metals. The ability to hold the searchcoil motionless over the
target also aids in tracing an outline of the buried object, or in pinpointing the
exact location of the object using techniques described in the pinpointing section
of this manual.
5. Electromagnetic Interference (EMI)
Electrical interference (EMI) can cause a metal detector to chatter
spontaneously, to lose sensitivity for no apparent reason or to cause a periodic
wobbly audio sound. Common sources of electrical interference include power
lines, electronic communication equipment such as cellphones, fluorescent
lamps, military electronics such as radar, other metal detectors and computer
equipment.
Your first line of defense against EMI is to reduce the Gain and/or Threshold. In
areas with heavy EMI, operating at reduced sensitivity levels will result in the
loss of some depth, but at least the metal detector will be usable.
See the section on Electrical Interference for a more thorough explanation of
EMI and how to manage it.
