28 RD8000 Operation Manual
9.3 Double-ended connections
Large diameter water pipes and gas distribution pipes
that are laid in sections sometimes have insulated joints
between the sections and can be difcult to locate using
a single ended connect. This is because when using a
single ended connection ground return, signals can often
cause confusion by returning to the transmitter along
other lines. The problem sometimes occurs when return
signals appear stronger than on the target line, usually
because the target line is deeper than the line carrying the
return signal, or the return path may be a better electrical
conductor than the target line.
Applying a double-ended transmitter connection is a
useful technique for positively tracing and identifying
a target line in a situation such as a heavily congested
industrial site, provided there are access points at each
end of the line.
9.3.1 Making a double-ended
connection
Connect the transmitter to an access point on the target
line. The transmitter ground is connected with a long
cable to another access point further along the line. A
complete circuit is achieved without using ground as
a current return path. The long cable should be kept
as far away as possible from the expected route of the
line. Radiodetection supplies 50 meter and 200 meter
extension cables for this purpose.
This method of applying the transmitter signal is ideal for
positive identication of a target line. When a connection
has been made to two points on the same line, the same
level of current should be detectable all round the circuit.
The receiver display should remain constant if the depth
of the line does not change.
Figure 9.5: Making double-
ended connections
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