© 2023 Radiodetection Ltd 41
Locating techniques
8.1 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 8.1 – 8.4: Nulling utilities & interference from services
8.2 Signal & ground connection
Manhole covers
Sometimes when locating, it is not possible to insert the
ground stake into the earth, for example, when locating on
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