34 RD8000 Operation Manual
10.5 Stethoscopes
10.5.1 When to use a stethoscope
At times, it may not be possible to put a clamp around a
cable because of congestion or because of inaccessibility.
A stethoscope antenna should be used in the place of the
clamp to identify cables.
10.5.2 How to use a stethoscope
Plug the stethoscope into the receiver accessory socket.
Press the concave head against each cable in turn to
detect a maximum signal.
10.5.3 Types of stethoscope
Large stethoscope antenna
The large stethoscope antenna, which plugs into the
receiver accessory socket, is used for cable identification
in situations where the cable is exposed. It is particularly
useful for identifying heavy cables lying in a tray where
it is not possible to fit a clamp. The concave detector
head on the end of the insulated, flexible gooseneck is
placed firmly against the cable to be identified. If there
are a number of cables, the stethoscope antenna will
give the strongest response from the cable to which the
transmitter signal has been applied.
Small stethoscope antenna
The small stethoscope antenna has a 25mm concave
head at the end of a 2m lead. The small stethoscope
can be screwed into an extension rod or used at the end
of several extension rods joined together for identifying
inaccessible small cables.
Miniature hi
-
gain stethoscope
The miniature stethoscope is similar to the small
stethoscope but has no handle or facility for extension
rods.
The miniature stethoscope can also be used as a
miniature antenna for locations where the bulk of the
receiver makes it inconvenient for use, such as locating
pipes or cables in walls.
CD stethoscope
In restricted areas, the CD stethoscope can be used to
obtain current direction but not current measurement.
10.6 Submersible antenna
10.6.1 When to use a submersible
antenna
Tracing buried pipes and cables across waterways and
estuaries are frequent and critical locating applications.
Less frequent but equally important is tracing and locating
lines between the mainland and offshore islands. When
locating pipes and cables the receiver sensing antennae
should be as close as possible to the target line so it
is not practical to locate lines buried under a river or
seabed from the surface. In most cases, it is necessary to
measure the depth of cover to ensure the line is protected
from dragging anchors or other underwater hazards.
The submersible, double depth antenna is suitable for use
under water for tracing pipes or cables. There is a weight
at the bottom of the antenna for stability and the unit has
been pressure tested to IP68 to a depth of 100m.
The antenna is supplied with 10m of submersible marine
umbilical cable as standard, but lengths of up to 100m
can be supplied. The extra length enables the antenna to
be carried by a diver on a riverbed or seabed while the
receiver is used in a surface vessel. It is crucial to have
effective communication between the operator with the
receiver and the diver with the antenna.
Alternatively the antenna can be fastened to the end of
a non-metallic boom from a barge and lowered to the
riverbed or seabed.
10.6.2 How to use a submersible
antenna
Apply the transmitter signal to the target line at an access
point on the shore. The submersible antenna line for
tracing the line underwater is plugged into the accessory
socket of the receiver. The receiver is used onboard a
boat, which should by positioned directly over the line.
The transmitting signal should be by direct connection
with the strongest possible signal and a low frequency
(less than 1kHz). Make a ground connection about 50m
from the transmitter. Test the quality of signal on the line
before locating on the water.
Note: The submersible antenna is calibrated to work at
one frequency.
