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4205 SIDE SCAN SYSTEM 0021769_REV_D
Most breaks occur around the tow cable termination or where a previous repair has been made. A cable
break may be found or confirmed by laying out the cable and attaching an Ohmmeter across each end of
the open wire. Then, flex the cable first near the termination or repaired section, and then along its entire
length until the break is reached. When flexing, the ends of the broken wire may touch, giving a continuity
reading on the meter.
7.10.1.3 Insulation Resistance Breakdown
Insulation breakdown is the most difficult fault to locate. Cable leakage is not necessarily located near the
end of terminations. However, the area near each termination receives the most abuse and is, therefore,
subject to suspicion. Successive cutting of the cable end until leakage disappears will prove successful in
many cases.
CAUTION! Before cutting the cable for any of the above reasons, a careful
visual examination should be made for any signs of physical damage.
With both ends disconnected, the tow cables should measure between 100 Mega-ohms and infinity
between conductors with a 500 VDC Megohmmeter. When using a Simpson 260 Multi-meter, all cables
wire-to-wire or wire-to-shield should measure infinity.
Any leakage on the multimeter indicates cable leakage.
7.10.1.4 Damaged Tow Cable Connector
The towfish has a trip line that prevents the vehicle from hanging up on a snag. When the line trips, the
cable connection to the towfish disconnects exposing the high voltage pins to seawater. Pin corrosion will
start to occur as long as power is still applied. If the power is not immediately removed, and the cable is
not immediately retrieved, and the connector flushed out with freshwater, there may be permanent
damage to the connector. This will require cable re-termination.
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