© 2023 Radiodetection Ltd 32
WARNING! The transmitter is capable of outputting
potentially lethal voltages. Take care when handling the
terminals, connection leads and ground stake, notify other
technicians working on the line of the hazard and guard
exposed conductors to prevent accidental contact.
WARNING! Ensure the TX transmitter is switched OFF
before making a connection and before disconnection of the
direct connection lead to a service.
Induction
In this mode of operation, the transmitter is placed on the
ground over or near the survey area. If a Direct
Connection lead or signal clamp is not plugged into the
transmitter, it will automatically go into induction mode. In
this mode, only frequencies applicable for induction mode
will be made available as the key is pressed.
Once activated the transmitter will induce the signal
indiscriminately to any nearby buried conductors.
Please note that these signals will also be airborne and it
is advisable to keep the distance between the transmitter
and locator at least 10m / 30’ – this distance may need to
be increased, particularly if depth measurements are
taken.
Signal clamp
An optional signal clamp can be connected to the
transmitter and clamped around a cable or pipe to apply
the transmitter signal. This method of applying the
transmitter signal is particularly useful on insulated live
wires and removes the need to disconnect the supply to
the cable. Clamps are available up to 8.5” / 215mm in
diameter.
WARNING! Do not clamp around uninsulated live
conductors
WARNING! Before applying or removing the clamp
around a power cable, ensure that the clamp is connected to
the transmitter at all times.
6.2 Choice of frequency for
active location
The choice of signal frequency is an important factor for
effective tracing and identification of buried lines, and
there is no single frequency that covers all conditions. For
simple instruments to be used by relatively non-technical
personnel, there is no option but to make a compromise,
and choose a single frequency high enough to give good
performance in the induction mode, but not so high that it
will couple too easily into unwanted lines. Active signals
between 8kHz and 33kHz are commonly used for these
applications. For more comprehensive equipment for
problem-solving by technically competent technicians, a
range of frequencies may be provided. Typical examples
of these and reasons for their use are illustrated below.
512Hz
Figure 6.2 512Hz active signal
This low frequency is most useful for line tracing and
identification over long distances. It does not couple easily
to unwanted lines however it is too low for induction, and
it falls within the band of power frequency harmonic
interference.
8kHz
Figure 6.3 8kHz active signal
This medium frequency is the most useful general-
purpose signal, high enough for induction, outside the
power frequency interference band, and with limited
coupling to wanted lines however it may not be high
enough to impose a strong signal on small diameter line
like telecom cables.
33kHz
Figure 6.4 33kHz active signal
This higher frequency is easily applied by induction to
most lines, so is very useful for initial search. It travels on
small diameter line however it couples more easily to
unwanted lines, and loses its strength over shorter
distances than lower frequencies.
100kHz and Over
Figure 6.5 100kHz active signal
This very high frequency range deals with the difficult
cases – induction onto small diameter lines in dry sandy
soil, and short lengths of cable. It is very easy to apply by
induction however it couples very easily to unwanted
lines, and does not travel far.
512 Hz operation
Due to mobile phone interference, active frequencies
below 500 Hz can be unsatisfactory or unusable.
The RD8200SG will be perfectly useable at 512 Hz
although an experienced customer might notice that they
need to set a higher power output on the TX.
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