Vivax Metrotech vLocDM, User Handbook Manual

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6.2 Pinpointing
Before measurements are taken it is necessary to precisely pinpoint the pipeline.
To do this, follow the following steps:
1. Rotate the locator so that the compass line direction indicator is pointing North/South.
2. Move the locator in the direction indicated by the arrow. Stop when the arrow changes to the opposite
direction.
3. Adjust the gain by pressing the “+” or “-” pushbuttons so that the bar graph reads approximately 50%.
4. Find the largest signal by moving the receiver side to side over the suspected position of the pipeline, see:
(a) Stop at the largest signal. (Note that the left/right arrows will help in this process but the largest bar
graph reading gives a truer indication of the actual pipe position.) Now rotate the receiver again until
the largest signal is found and the line indicator is pointing at North and South position
(b) The receiver is now over and the handle is in line with the pipe.
(a) (b)
6 Using the vLocDM Receiver
NOTE
The largest signal and current reading will probably be generated by the anode bed cable.
Confirm which is which by taking current readings and noting the current direction. The
currents on the pipe will be flowing towards the transmitter. The current on the anode
cable will be flowing away.
NOTE
The sum of the currents on the two pipe locations should be close to the current
displayed on the transmitter. If they are not, it may be that there is a fault at the
connection point or that the current flowing on the anode bed cable is interfering
with the signal from the pipe. To confirm this take readings a good distance from the
connection point. Be aware that the anode bed cable very often runs along the same
trench as the pipe for some distance and will affect the readings.