© 2014 Radiodetection Ltd
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4.6.1 Passive Sweep
A passive sweep is used to locate any Power, Radio, or
CPS signals that may be radiating from buried
conductors.
To perform a passive sweep:
1 Press the
key to select the passive frequency
you wish to locate. You can select from the
following passive frequencies:
Power
Radio
CPS (DLM model only)
2 Adjust the sensitivity to maximum; reduce the
sensitivity to keep the bar graph on scale when
there is a response.
3 Traverse the area in a grid search (Figure 4.4), at a
steady walk, and hold the locator comfortably with
the antenna in line with the direction of movement
and at right angles to any lines that may be crossed.
Stop when the locator response rises to indicate the
presence of a line. Pinpoint the line and mark its
position. Trace the line out of the area being searched.
Resume grid search in the area.
In some areas there may be a confusing amount of
50/60Hz power signals. Lift the locator 50mm from the
ground and continue the sweep.
Switch the locator to Radio Mode if the locator supports
this feature. Increase sensitivity to maximum and repeat
the above grid search procedure over the area.
Pinpoint, mark, and trace out any lines that are located.
In most, but not all areas, radio mode will locate lines
that do not radiate power signals and a grid search
should be made in both power and radio modes.
4.6.2 Inductive search
An inductive search procedure is a more certain
technique for locating unknown lines. This type of
search requires a transmitter and locator and two
people. This type of search is referred to as a ‘two
person sweep’. Before starting the sweep, define the
area of search and the probable direction of lines
crossing the area. Ensure the transmitter is switched on
and in induction mode.
Figure 4.5: Inductive search
The first person operates the transmitter and the second
person operates the locator. The transmitter induces a
signal onto lines as it passes over them and the lines
are then detected with the locator at a suitable distance
away from the transmitter.
A suitable distance is around 15 meters
– although this
will depend upon the transmitter used and the level of
induction power used.
Hold the transmitter with its length aligned with the
assumed direction of any lines.
The second person holds the locator at the start of the
area to be searched and with the locator antennae at
right angles to the probable direction of the buried lines.
Set the locator sensitivity level as high as possible
without the locator picking up any airborne signals
directly from the transmitter.
When the transmitter and locator are in line both
operators start to move forward in parallel. The operator
with the locator sweeps it backwards and forwards,
keeping the locator vertical, as they proceed in parallel
with the transmitter. This method allows for
misalignment of the transmitter, locator and buried line.
The transmitter applies the strongest signal to the lines
directly below it, which are then located with the locator.
Move the transmitter from side to side to establish the
highest signal which indicates that the transmitter is also
directly above the line(s).
Mark the ground at the point of each peak signal
detected with the locator. Repeat the search along any
other possible paths of lines.
Once the positions of any lines have been marked,
reverse positions, place the transmitter over and along
each line in turn, and trace the line out of the search
area.
Figure 4.4: Passive sweep
Summary of Contents for rd7000+
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