© 2021 Radiodetection Ltd 10
assist in the calculation of the 4Hz current mapping
value.
AC signals can leak away from the pipeline either directly
to the soil through coating defects or naturally by what is
known as the capacitive coupling effect – the higher the
frequency, the more leakage via capacitive coupling.
As you walk further along the pipe you may find that at
some point the 4Hz current mapping value becomes
erratic or unstable. This may be an indication that the
higher frequency locate signal has got to a very low level
and will more than likely also effect the depth readings.
If this happens you could increase the current output
level of the PCM transmitter if it is not already at the
maximum value, disconnect the PCM transmitter and
connect further along the pipe or you may have to use a
portable transmitter such as the Tx-10.
Connecting the Tx-10 to the pipe by using either the
direct connect or induction method can be used to apply
a locate signal onto the pipe. It will now be possible to
locate the pipe and if the 4Hz current mapping signal is
present from the PCM transmitter, a 4Hz current mapping
value can be taken.
Note On the TX10, only 512Hz, 640Hz or 8kHz can be
used as the locate frequency. If using 512Hz or
640Hz, set the PCMx to LFCD mode or 8kHz
mode if using 8kHz.
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