Leaders in Pipelin
e Survey Systems
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SYSTEM MANUAL Version 6.03i
23
4.6. Pipeline Voltage message
The Signal Generator will check the existing AC voltage on the
pipeline (the AC component of the pipe to soil potential) when
it is first switched on and again when a current has been
selected. If this is too high (greater than 10v peak voltage)
then a warning will be shown.
If this warning is given,
IT IS ESSENTIAL
that the following procedure is carried out to
avoid damage to the generator.
•
Disconnect all CP stations and cross-bonds to other pipelines within 3000ft (if not
already done)
•
As detailed in 4.3.2, use a multi-meter set to AC current and connect between the
Pipe
and
Ground
leads – disconnect from Signal Generator first. If value is above
100mA RMS then there is a foreign AC signal on the line – DO NOT CONNECT
SIGNAL GENERATOR
•
Use a multi-meter set to DC volts and connect between the
Pipe
and
Ground
leads –
disconnect from generator first. If the DC voltage is greater than +/-10v – DO NOT
CONNECT SIGNAL GENERATOR
•
Re-check Signal Generator (go through switch on procedure again)
•
To proceed with the connection press
AUTO
.
It is the responsibility of the surveyor to check the pipe-to-soil
voltage (AC and DC) and current (AC) before proceeding.
4.7. Automatic level adjustment
To carry out a Current Attenuation Survey it is essential to ensure a constant-current
signal is applied to the pipeline. Once the signal current of the Signal Generator has been
set, the Automatic Level Adjustment will become active after 1 minute. This mode is
indicated by the message ‘OUTPUT LOCKED’ appearing on the display (see flow chart in
4.9 below).
Once the signal current has been set, it will remain constant until the battery is exhausted.
Any changes in operating conditions during the survey, e.g. changes in resistance at the
Earth Spike
due to rain or capillary action, will be automatically compensated for by the
Signal Generator.
If conditions change dramatically such that the Signal Generator is unable to maintain the
correct current, it will set the output to alternate between zero and the maximum attainable
(up to the set value), every 6 seconds. The surveyor (the Detector operator) will notice the
display on the Detector showing an alternating increasing and decreasing signal, indicating
that the current is no longer stable and the Signal Generator and connections need to be
checked.
This usually occurs if the
Earth Spike
contact ‘dries out’ making a higher resistance circuit
for which the Signal Generator is unable to compensate.
Pipeline Voltage
too high!!
Disconnect CP
AUTO to restart