6 Using the vLoc-5000
Page 44 of 57
WARNING
NEVER mechanically dig over the path of a buried pipe or cable. ALWAYS dig
carefully.
6.3.9
Cable Tracing using Signal Select or Signal Direction Signals
Energizing cables or pipe with a known signal enables them to be traced with a certain degree of confidence.
However, it is quite common for signals to bleed off onto other lines. This can result in confusion especially in
congested sites or where services run in parallel for some distance.
Signal Select and Signal Direction are well tried and tested methods of identifying which line the transmitter is
connected to. The systems considerably increase the confidence of identification but it should always be kept
in mind that there is no method that can give 100% reliability.
Both Signal Select and Signal Direction rely on the fact that signals that have bled from the target line travel
back towards the transmitter and very often use adjacent lines as easy paths. Hence the return signals tend
to be flowing in the opposite direction than that of the connected line. As we are using signals that are
alternating in nature it can also be considered that the return signals are in the opposite phase than the
applied signal.
Signal select and Signal Direction can only be applied to a target line using the Direct Connection method or
using a low frequency signal clamp. SiS and SD cannot be applied using the Induction method.
Signal Select does not require phase setting to the transmitter but is generally better for short distance
applications.
Signal Direction (SD) is used for both short and long distance applications but does need referencing to the
transmitter.
Signal Select
Apply the transmitter SiS tone using the Loc-10TxSIS Not all frequencies are available with Signal select.
Ones that are available are idendified with “SiS” Ensure the receiver and transmitter sre set to the same
frequency.
The direction of the signal in the targeted line is determined by analyzing the sign of the demodulated Signal
Select signal. When the receiver is positioned over a signal that carries an inverted field (i.e., one in which
the phase is –180° from the expected, the Guidance Compass points down, as shown below for a line that is
bonded to the target line and carries return current.
Signal Select Sample Scenario
An example of how the Distortion Alert feature acts as a warning about situations that (using traditional
methods) appear to be quite ordinary can be seen below. In this case, there is significant bleed over from the
target line to a shallower line, with the current running in the same direction forward in both lines. Since the
bleed over line is shallower, its effect diminishes as the receiver is positioned farther to the right or left. Thus
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