The 5917/5918 Probe and
Detector System is used either on land, or on the beach.
The 5917D
Divers Probe can also be used in up to 50 meters water to locate
submarine cables.
A tone in the range of 16 Hz to 25 Hz is transmitted
down the submarine cable by an Electroding Generator such as the
Tinsley type 5915 unit. This signal is picked up by a Tinsley 5917 or
5917D Probe connected to the 5918 Detector. The 5818 Detector and 5917
Beach receiving probe would normally be held by a person walking along
the beach, however, as they are portable, the detector may be operated
from any small boat or launch to search over shallow water. The 5917D
would normally be held by a diver and would be connected to the 5918
in a boat/ship via an umbilical cable. It is suitable for use in depth
up to 50 Meters. The received signal is processed and passed to the
analogue front panel meter and headphones audio output.
Normally, the Electroding
Generator, Tinsley type 5915, is located in the submarine cable
Terminal Station nearest to the search area. When the Electroding
Detector System is in the vicinity of the cable, the 5915 Electroding
Generator is powered thus applying the low frequency signal to the
cable under test. At these frequencies, the field of the signal
extends into the land and water surrounding the cable for a
considerable distance.
The person holding the
5917 probe would normally walk/swim a course to cross the cable on the
landward side of any expected cable fault position with the probe in
its horizontal position at right angles to the cable.
The Detector is set (by
thumbwheel switch) to the frequency being transmitted by the
Electroding Generator. A frequency of either 16.7Hz or 25 Hz is
recommended. As the detector crosses the cable, the field from the
signal current in the cable induces a voltage into the probe.
This signal is then processed by the Electroding Detector and a
deflection on the meter is registered.
This may be heard by the operator as a high pitch frequency from the
headphones.
For identification
purposes, the Electroding Generator may be keyed on and off
periodically.
Once the cable signal has been identified and confirmed, the person
then follows the cable on a zigzag course to plot the position of the
cable, or until the signal disappears.
When this happens, a fault or break has been located.
Further tests may be made
for a more precise fix of the cable position by using the probe in a
vertical orientation. In this case a null is registered when the probe
passes exactly above the cable.
