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

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

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.