Troubleshooting and Maintenance
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Caution: The FS system MUST be disconnected from trawl cable during Mega-
Ohmmeter tests to prevent possible damage to the electronics!
If the impedance between the cable’s two conductors is relatively low then the cable should
be inspected for possible problems with splices, water ingress, and moisture in slip-rings (if
connected during test).
If the impedance between the cable’s conductors and the vessel’s hull is relatively low then
inspect the cable for any visible damage to the cable armour/jacket. Other possible causes
are bad splices or bad slip-rings (if connected during test)
5.4.5.2 Closed Loop Resistance, Voltage and Current at Trawl
Unit
As previously mentioned, the closed loop resistance must be less than 100 Ohms for proper
operation of the FS system.
This test should be done with the FS system disconnected but with the winch slip-rings
included. For whatever cable type and length used the following specifications must be met
for operation with the Simrad FS trawl Monitoring system:
Cable Closed Loop Resistance <100 ohms
Signal Attenuation Through Cable:
<40 dB (1/100 signal amplitude) @ 55 kHz
<20 dB (1/10 signal amplitude) @ 12 kHz
The cable closed loop resistance determines the maximum voltage drop along the trawl
cable. For proper operation the FS 70 trawl unit electronics require a supply voltage of 60
to 200 VDC. For typical operation, the current is approximately 195 mA to 250 mA with
peaks to 450 mA. The equations for calculating the voltage drop along the trawl cable are
described in the next paragraph.
There are two methods to check the closed loop resistance of the 3
rd
wire:
Method 1
To do the test the conductors at one end of cable should be shorted together. An ohmmeter
is then used at the other end of cable to measure the resistance between the conductors.
Method 2
An estimate of cable losses and resistance can be done by measuring the voltage and
current at the trawl unit. This measurement requires the trawl unit electronics to be
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