General Machine Products RD7000 Traceable Rod Detection - Manual (Page 20)

14 RD7000 Operation Manual
Switch to null response mode and move the receiver to
find the null position. If the position of the peak and the
null pinpoints correspond, it can be assumed that the
pinpoint is precise. The pinpoint is not precise if the marks
do not correspond, but both marks will show an error to
the same side. True line position will be close to
peak position.
The line lies half the distance to the other side of the peak
position as the distance between the peak and the
null positions.
4.4 Sweep and search
There are a number of techniques available for locating
unknown lines in an area. Using these techniques is
particularly important before conducting any excavation
work to ensure that buried lines are not damaged.
4.4.1 Passive Sweep
A passive sweep will locate any Power, Radio or CPS
(RD7000DL only) signals that may radiating from buried
conductors.
To perform a passive sweep:
Press and release the key to switch the
receiver on.
Press the key to select the passive frequency
you wish to locate. You can select from the
following passive frequencies:
Power.
Radio.
CPS.
Adjust the sensitivity to maximum; reduce the
sensitivity to keep the bar graph on scale when
there is a response.
Traverse the area in a grid search (Figure 7.6), at
a steady walk, and hold the receiver comfortably
with the antenna in line with the direction of
movement and at right angles to any lines that
may be crossed.
1.
2.
a.
b.
c.
3.
4.
Stop when the receiver 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 receiver 50mm from the
ground and continue the sweep.
Switch the receiver to Radio Mode if the receiver 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.
4.4.2 Inductive search
An inductive search procedure is the most certain
technique for locating unknown lines. This type of search
requires a transmitter and receiver 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 in induction mode.
Figure 4.4:
Passive sweep
Figure 4.5: Inductive
search