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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
locator 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.
13.8 Submersible antenna
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 locator sensing antennas
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 (300ft).
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 locator
is used in a surface vessel. It is crucial to have effective
communication between the operator with the locator 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.
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 locator. The locator is used onboard a boat,
which should by positioned directly over the line. The
transmitting signal should be applied by Direct Connection
with the strongest possible signal and at the frequency
that the submersible antenna is calibrated to. Make a
ground connection about 50m (160ft) 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.
Tips for using a submersible antenna:
The user in the boat should be a specialist or have
considerable experience using a locator so that they can
give concise instructions to the diver.
It is prudent for the pair to practice working together on dry
land before attempting to locate underwater. Using the
antenna, the diver should locate and trace a known line
blindfolded receiving directions from the user with the
locator out of sight of the line and the diver.
Because of rapid signal loss and a combination of large
surface area and very conductive soil there may be
problems applying a suitable signal for tracing a large
diameter pipe. It may be necessary to use a high power,
low frequency tracing signal.
It is necessary to define a method of recording target line
position and depth before starting work in the boat or on
the seabed.
Figure 13.14: Using a submersible antenna
WARNING! Only properly licensed and experienced
divers should attempt to use the submersible antenna.
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