© 2020 Radiodetection Ltd
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Section 7 - Locating techniques
7.1 Identifying target utilities
Induction
If several conductors are running in parallel, and it is not
possible to connect a transmitter, each line may be
located separately. Proceed as follows:
1 Perform a sweep of the area to find the position and
number of conductors in the area.
2 Map the direction in which the conductors are going.
To trace the lines:
1 Select induction mode on the transmitter.
2 Select the same frequency as on the locator.
3 Place the transmitter on its side and in line with a
conductor
4 Ensure the conductor is directly below the
transmitter
5 This will
‘null out’ the signal directly below the
transmitter, placing no signal on that conductor, and
enable the other conductors to be located
6 Locate each conductor and mark its position
7 Move the transmitter down the route and continue
locating and marking.
8 Trace each conductor out of the search area until the
target can be accurately located.
Unwanted signal coupling
Unwanted coupling of the signal from the target line to
another nearby line is one of the most common location
problems. It leads either to an error in the marked
position and depth of the target line or to marking the
wrong line. A certain degree of coupling is unavoidable
in many situations but there are ways in which a careful
user can reduce coupling and increase location
reliability.
Avoid applying the signal by induction. The signal
may be coupling to more than one line directly from
the transmitter. Use the signal clamp where
possible.
Identify points where lines may be bonded or in
close proximity to each other. Work toward these
points rather than away from them. For example, if
gas and water pipes are bonded within a building,
apply the signal at the valves or access points in the
road rather than in the building.
Reduce coupling to a parallel line by using a low
signal frequency where available
Return signal flowing on another line. Use a double-
ended connection to by-pass the ground return if
possible
Choose a signal application point where the line is
furthest from other lines and not in a congested
area
When using single-ended connection, site the
ground stake as far from the target line as possible
and away from other buried lines
Avoid using existing structures for ground
connections; other buried lines may be bonded to
them
A bad ground connection or just laying the ground
lead on the surface at right angles to the line may
result in less coupling than a good ground provided
long distance tracing is not required.
Figures 7.1
– 7.4: Nulling utilities & interference from services
