PCMx Operation Manual
© 2021 Radiodetection Ltd 29
Mixture of good and poor coating, which is shown as
greater current loss over the section of pipe with poor
coating.
The effect of a short or contact with another service is a
sudden current loss.
The effect of a poorly coated steel shield in contact with the
pipeline is to show reduced current in one measurement
section.
This effect is either a section of perfect coating or ground
conditions that are shielding the signal in dry or rocky
ground.
7.3
Parallel Pipes
Consider a new distribution pipe with the old pipe running
parallel and about 30cm (12 inches) away with a 1 Amp
signal applied.
To make the explanation easier the pipe has been divided
into section A & B. This is demonstrated in Figure 7.8.
Example
1
Fig. 7.8: Parallel Pipes
Section A Good peak and null locate, with peak and null
locates in the same position. Results indicate
a good coating on the pipe (600 and 550mA).
Section B Poor peak and null locate shifted to one side
from the previous alignment. Readings start to
decrease rapidly.
In this case the old pipe had been shorted to the new
pipe. The poor coating on the old pipe provided a good
path for the PCM Transmitter current.
This is indicated by the locate being offset to one side and
the rapid decrease in current reading.
When plotted the graph illustrated this effect with the bend
indicating the position of the short or contact. Figure 7.9.
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