PCM
+
Operation Manual 17
Taking Measurements
– Distribution Systems
Below are some typical results, which can be found from
using the PCM
+
for CP system diagnosis on a distribution
system.
Good local knowledge and a map of the pipe network
are essential to determine suitable positions to connect
the PCM
+
Transmitter and where to take readings. It is
worthwhile taking measurements over the complete site
before concentrating on any particular area.
The following diagram is a typical street involving ‘Tie-ins’
and an ‘L’. The readings from the PCM
+
and distances
to prevent interference have been included. By working
around the map a short was quickly and easily detected.
Figure 5.6: Distributed system
Figure 5.7: Interpreting distributed systems
5.2 Pipelines and Pipeline defects
Interpretation of Readings and Graphs
Pipe coating in good condition is shown as very little
loss of current.
Pipe coating in poor condition is shown as a rapid loss
of in current.
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.
Figure 5.8: Poor coated steel shield
This effect is either a section of perfect coating or
ground conditions that are shielding the signal in dry
or rocky ground.
Figure 5.9: Perfect coating
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