Current Measurement; Tilted Magnetic Field Identification - SubSurface Instruments PL-VF10 User Manual

The PL-VF Receiver contains a feature that is very useful in identifying a desired cable in a field of
various conductors and/or utilities. It is not unusual for the target conductor (the conductor connected
to the Transmitter) to induce a signal into nearby conductors in a crowded field. In these instances,
the radiated signal on the conductors close to the surface of the earth, may be stronger than the
Transmitter signal on the target conductor buried deep in the ground. The operator will find two
or more paths and must determine which is the target conductor. By using the current measurement
feature of the PL-VF Receiver, the operator can determine the amount of 815 Hz, 8 kHz, 33kHz or
82 kHz current flowing on the conductors, regardless of the depth. The highest current flow indicates
the target conductor.
Place the Receiver vertically over one of the conductor marks and rest the foot of the locator
on the ground. Holding the Receiver vertical, press and release the Shift Button & Depth button
simultaneously. When the meter changes from a "thermometer" type display to a "bar" type display,
hold the r
the cable (adjusted for depth). Next, move to the second cable and repeat the measurement. The
blinking bar will show the signal level on the conductor. In addition, the previous reading is shown
as a solid bar. The higher of these two readings will show which conductor is carrying the greatest
locating signal.
When adjacent cables or pipes are present, they will sometimes create locating errors. Some of the
Transmitter signal is picked up by the adjacent conductors and is redirected so that it combines
with the original signal. The result is a Tilted Magnetic Field. This is often the reason that numeric
depth readouts are sometimes created in error.
The operator can verify the accuracy of path locate by performing a variety of tests.
The 45º Angle Method locate on both sides of the cable path. If the right and left side depth
readings agree to within 5 inches, the path locate is accurate. If the two depth readings do not
agree, then dig with care. A closer locate would be halfway between the two outside depth locate
marks.
Test for interference in the magnetic field by comparing the PEAK location to the Null location. The
determined cable position by these methods should be within 3 inches of each other. A greater
disparity will indicate interference resulting in inaccurate depth.
NOTE: The Left/Right arrows operate off of the Null reading. By utilizing the Left/Right arrows while
in peak mode the user can simultaneously locate in both modes thus quickly identifying the match
or discrepancy between the Peak and the Null reading.
These are important techniques that should be used to ensure the most accurate location possible.
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