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.

Nulling utilities & interference from services