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7. Finally, ensure that all nylon studs have washers fitted. Tighten the nuts fully. Check that the
outriggers and tie-bars are secure and that there is minimal free movement in the completed
coil assembly.
3.1.4 Altimeter
The Altimeter needs to be mounted such that it has a free view of the seabed and avoids acoustic
interference. If possible the altimeter should also be aligned with the centre of the search coil array.
You should also consider its minimum range measurement specification.
Any horizontal offset between the altimeter and the coil will cause errors in depth of cover
measurements made by the 440 System. The example in
and 'B' will supply totally different readings at the ROV location. When used by the SDC, these
readings would show entirely different measurements for target cover. The magnitude of these errors
will vary according to the seabed topography and the relative positions of the altimeter and the coil
array.
Note that it is the position of the altimeter that causes these errors. Measurements of vertical range
made by the 440 System will retain their accuracy under all normal conditions.
Do not place the altimeter at the opposite end of the ROV to the coils. If you do not
follow this advice, it is possible that the survey data might contain errors caused
by pitch of the ROV or uneven seabed topography.
Figure 3-8: Effects of altimeter horizontal offset
When you select a position for the altimeter, make allowance for its minimum measurement range
capability.
The altimeter provides information valid only for a point directly below its trans-
ducer face but parallel to its axis. When you operate the ROV over uneven sea-
bed, or where the target is in a trench, Teledyne TSS strongly recommends that
DPN 402196 Issue 4.1
Figure 3-8
NOTE
IMPORTANT
© Teledyne TSS
3 – Physical Installation
shows how the two altimeters 'A'
3- 13
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