© 2020 Radiodetection Ltd 36
9.2 CD reset
About CD reset
When you trace a signal on very long target lines, the
transmitter signal gradually bleeds into the ground by
capacitance. This means the phase angle of the
remaining signal gradually changes. A CD Reset can be
used to re-establish correct CD operation.
To perform a CD reset, press and hold the key
This is referred to as phase-shift and can occur
whenever an alternating current signal is flowing in a
system of conductors that have a significant capacitance
or inductance. The relative phase angle between the two
frequencies will alter, but only over extended distances.
Figure 9.2: CD reset
Figure 9.2 illustrates a buried line with significant
capacitance to ground. It illustrates the gradual phase-
shift that occurs along the line. The diagram shows a
reference point on each waveform. At first, the reference
point occurs right on the Peak of a positive half cycle (A).
It gradually moves towards the zero crossing point (D)
and ends up on the Peak of a negative half cycle (F).
The direction has shifted from forwards to backwards. At
the intermediate point (D) the current flow cannot be
determined. At this point the CD arrows on the RD8100
locator will flash on and off. In the example shown in the
illustration, by returning to (C) which is the last point at
which a CD reading was achieved, and performing a CD
reset, the response at (C) will be equivalent to that of (A).
In most cases the phase angle shift does not occur until
many kilometers from the transmitter and in some cases
a CD reset may only be required every 20 kilometers (15
miles).
Performing a CD reset
You should perform a CD reset every time you select a
CD frequency. CD reset can only be performed when in
CD mode.
To perform a CD reset:
While using any CD frequency,
1 Press and hold the key
Alternatively
1 Press the key to enter the menu
2 Scroll to the CDR menu using the or keys
3 Press the key to enter the CDR menu
4 Select YES
5 Press the key to reset CD and exit to the main
menu
9.3 CD clamps & stethoscopes
On both the CD / CM clamp and the CD stethoscope
there is an arrow that indicates which way the clamp or
stethoscope is facing in relation to the transmitter. If the
arrow is pointing away from the transmitter when the CD
reset is performed the locator display shows 000 and the
bar graph reads 100%. If the arrow is pointing towards
the transmitter, the locator display shows 111 and there
is no bar graph reading.
When using either of these accessories it is important to
reset the CD at a known point, near the transmitter,
before making any identification measurements
Refer to Section 8 for more information on clamps and
stethoscopes.
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