Line and probe location in “Ferrolux” mode
57
The filling of the outer ring reflects the quality of the SignalSelect detection. The
following applies:
The clearer the SignalSelect detection, the higher the fill level.
The SignalSelect signal can be very easily identified, and there is only
very little distortion (forward phase shift).
Though the SignalSelect signal can be identified, the determination of
the current flow direction is less reliable due to the high level of
distortion (phase shift). The causes of this can be a distance-related
phase shift or even a significant capacitive coupling in a line that is laid
shallower (see below).
The located line is either not carrying a SignalSelect signal, or the
signal-to-noise ratio is too low to clearly identify the signal and the
current flow direction.
As the distance to the connection point increases, the phase shift against the injected
signal can very slowly but steadily increase due to the capacitive outflow, which is
reflected in a reduction in the quality fill level. To counteract this and compensate for the
phase shift internally, another SignalSelect reset should be carried out, provided that the
line and the current flow direction can still be clearly determined. The procedure is the
same as the one for carrying out an initial reset at the connection point (see page 52).
However, another adjustment should normally only be necessary a few kilometres away
from the fault location.
The quality fill level can also drop relatively abruptly regardless of the distance to the
connection point if a strong coupling takes place in another line which is running parallel
to the line carrying the signal at a shallower laying depth or crosses it, for example. In
this case, the current direction is the same in both lines, which results in a high level of
distortion directly above the lines. As shown in the following example, this can lead to
the quality being very low at this location, but increasing significantly to the left and right
of the lines.
This is due to the fact that the influence of the weaker, overcoupled signal decreases as
the lateral distance increases, and the actual signal on the line on which it is being
transmitted can be clearly determined again accordingly.
Quality of the
SignalSelect detection
Line connected
to the transmitter
Interfering line
