
350 Cable Survey System
DPN 402197 © TSS (International) Ltd Page 8 of 18
The altimeter housing is hard anodised to protect from corrosion in sea water and for
limited protection from mishandling. The anodised surface must not be damaged as
this will cause corrosion to develop leading to eventual failure of the pressure hous-
ing.
The altimeter can be affected by transmission of sound through the supporting struc-
ture leading to an erroneous range value that is less than the correct range therefore
to ensure this does not happen make sure the altimeter is de-coupled mechanically
from the structure by using rubber inserts or similar.
The range of the unit is limited; however, it is possible to pick up reflections which are
called “multiples”. These multiple reflections give the impression of a good range
being received by the altimeter but are, in fact, pulses received from the previous
transmission that have travelled to the bottom or sea surface and been reflected in
time for the reception time of the latest transmission. The result is a range that should
be outside the range of the altimeter appearing as a good range.
The ships echo sounder should be checked to determine if ranges from the altimeter
are multiples from an over range water column.
Mount the altimeter at least 0.8m from the bottom of the sub sea vehicle; any range
less than 0.8m will show as an error; however multiples can still be received.
D.3.2 Technical Description
The altimeter circuitry is divided into several sub systems to enable a clearer under-
standing of the system. The sub systems are all manufactured on one printed circuit
board.
Test points are available to aid faultfinding and commissioning. The circuitry uses
miniature surface mount components therefore great care must be taken to avoid
damaging the circuitry. Do not short connections as probes are inserted. The follow-
ing points are present:.
D.3.2.1 Power Supply
Input voltage can range between 8-24VDC providing the SHDN signal is high; (S1/5
is off). If the power supply is known to be constantly above 17VDC switch S1/5 can be
switched on thus disabling the dc-dc converter to conserve power.
Table D–4: Testpoints
TP 1 Spare connection for MONO8 interface.
TP 2 Timer input to micro from sensor/ sonar receiver MUX.
TP 3 Raw sonar signal before bandpass but after sonar receiver.
TP 4 Sonar receiver output signal (positive pulse).
TP 5 Detected sonar signal (negative pulse).
TP 6 High voltage Tx signal across acoustic transducer.
TP 7 Transmitter Tx pulse TTL drive.
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