20
GROUND BALANCING -Technical Info
Fe
3
O
4
BAR GRAPH
The Fe
3
O
4
4-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 % Fe
3
O
4
SUSCEPTIBILITY
4 Bars -High 0.4 - 1.6 1,000 - 4,000
3 Bars -Medium 0.1 - 0.4 250 - 1,000
2 Bars -Low 0.025 - 0.1 60 - 250
1 Bars -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 searchcoil 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 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.
Ground Error
The bottom left-hand corner of the display contains a graphic which indicates
if your detector’s ground balance setting needs to be adjusted.
The Omega has a tracking system which continually analyzes the phase of the
ground you are scanning. It then compares this
ground phase
value with the in-
ternal Ground Setting established at the time the detector was ground balanced
using GND GRAB or the manual ground balance method.
* If the detector’s internal Ground Setting is equal to the actual phase of
the ground, the detector is properly ground balanced and the Ground
Error window is clear.
* When the detector’s internal Ground Setting is higher than the actual
phase of the ground, the bars on the
top
of the graph will be illuminated.
The bigger the error is, the more bars will show up.
Ground Error continued on next page