Teledyne 440, System Manual, Page: 109 / 256

6 – Operating Procedure
DPN 402196 Issue 4.1 © Teledyne TSS 6- 5
WARNING
There have been reports of pressure building up within the Sub-sea unit if water
has been able to seep into the housing. Take great care when opening the SEP
unit.
6.2.1.2 Coil Installation
❐ Electrical characteristics .
Check the coil continuity and insulation resistance. Do not use coils that fail the insulation test.
See
section 6.3.2.1 "Coil Insulation Test" on page 6-13 .
❐ Coil configuration .
Install the coils so that there is a 5-10mm gap between the port and starboard coils and the
centre coil lies flat on top (see
section Figure 3-6: "Assembly of the coil frame" on page 3-10
and Figure 3-6 ). Align the coils so that their connectors all face towards the ROV.
❐ Coil separation distance .
Allow sufficient distance between the coil array and the vehicle body so that the background
signal (with no target) is less than 1000µV for standard coil values and below 7500µV for early
coil values. Usually this requires a coil separation distance of between 0.75m and 1.0m,
depending on the size of the ROV.
❐ Coil mounting .
Make certain the coils are mounted rigidly on the ROV. If the ROV uses a system that lowers
the coil array to its normal operating position after deployment, make certain this locks into the
correct position before you start the first background compensation procedure. See
section
6.2.2.3 "Background Compensation" on page 6-22 for a description of background compensa-
tion.
CAUTION
Never drill holes in the coils. It will result in the coils be unusable.
You may install the coils either at the front or the rear of the ROV. If you use a rear mounting
position, arrange a subsea camera to check that the umbilical does not drag near the coils and
create a false target.
❐ Coil height .
For a small target – Install the coils low on the ROV to extend the detection range as deeply
as possible into the seabed. Operate the ROV carefully to avoid collisions between the coils
and debris on the seabed.
For a large target – Install the coils higher on the ROV to reduce the likelihood of coil saturation.
This position also provides better protection for the coils.
❐ Cables .
Use plastic cable ties to secure the cables to the ROV frame. Make certain the cables cannot
move providing a false target during survey operations.