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5.8 Nulling Out
Sometimes it is possible for some utilities to be masked
by other utilities and this can happen when one or more
utilities are in close proximity to each other or when
stronger signals may radiate. In certain applications and
congested areas the ‘Nulling’ technique allows operators
to eliminate the induction signal directly beneath the
transmitter but at the same time induces the transmitter
signal onto other nearby utilities that previously have not
been able to be located
Figure 5.6 Nulling Out effect
Two persons Nulling Out technique:
1. Place the transmitter close to the services you
wish to trace (a parallel sweep may be used for
this) and using the locator at a distance of
approximately 10m/30’ from the transmitter,
pinpoint the strongest signal.
2. The sensitivity on the locator is adjusted so that
the bar graph response is approximately 75%
3. Release the side support arm.
4. With the locator over the centre of the signal
the second operator should hold the transmitter
at waist level, with the transmitter on its side –
release support arm pointing down.
5. The transmitter is then moved from side to side
to find the ‘Null’ spot between two detectable
signals; the transmitter should then be lowered
towards the ground keeping it in the ‘Null’ spot.
6. At ground level we are ideally looking for a
‘Null’ no wider than 50mm/2” (Sensitivity on the
locator may need to be adjusted to achieve
this).
7. With the transmitter left on the ground in the
‘Null’ spot. The locator is used to check for
additional signals either side of the ‘Nulled’
signal.
8. Should the ground be uneven the transmitter
may be turned across the line of the service
provided the release support arm remains
facing downwards. (this will improve the
stability of the unit)
One person Nulling Out technique:
Figure 5.6 Nulling Out - Single person sweep
1. Lay the transmitter on its side using the side
support arm.
2. Sweep the area around the transmitter with the
receiver at least 10m/30’ from it.
3. Reposition the transmitter at 5m/15’ intervals
around the area and repeat step 2
4. Stop when there is a response
5. Pinpoint and mark any lines
6. Trace the lines out of the area
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