Teledyne 440, System Manual, Page: 113 / 256

6 – Operating Procedure
DPN 402196 Issue 4.1 © Teledyne TSS 6- 9
13. With the ROV in the water, check again for correct waveforms from the SEP using the SDC
oscilloscope function, and for correct data strings from the altimeter.
Background and Seawater (Active) Compensation Monitoring
14. Perform a background compensation procedure at the start of the dive with the ROV on the
seabed. It is common for the background characteristics of the ROV to change during the first
20 minutes of deployment, possibly due to thermal effects. Survey measurements made during
this period may include errors caused by such changes in ROV characteristics. Repeat the
background compensation procedure 30 minutes after you deploy the ROV. Create a hard
copy of the results and attach it to the survey records.
15. Perform regular background and seawater compensation checks during the survey to ensure
that no changes or shifts have occurred. Use the internal logging facility to record these
checks.
16. Perform a Background Noise Profile check. To perform a Noise Profile of the surveying vicinity,
steer the ROV away from the target to a distance of approximately 10 metres. At this position
check that all the signal voltages fall to zero ±5µV. If any signal voltage is greater than 5µV at a
distance of 10 metres from the target, repeat the full background compensation procedure.
Use the Noise Profile logging facility to record the signals present during the test. If all signals
are close to zero, return to the target and continue the survey.
17. Check the Seawater compensation. Lift the vehicle to 3m off the seabed. The target voltages
should be less than 10µV. If they vary, check the water temperature is set correctly. If good
rejection cannot be obtained then consider using Manual Compensation.
NOTE
A “Flick” in the target voltages occurs at approx. 4m above the seabed, this is not
a fault in the 440 System or its configuration.
Data Logging
18. Log all survey data including the regular background compensation, seawater compensation
checks and Background Noise Profile check.
19. Maintain a written record of any events that occur during the survey (for example a collision
between the ROV and debris, etc.). Describe any corrective actions taken.
20. To assist post-survey analysis a Background Noise Profile should be carried out after a Back-
ground Compensation. This facility allows a log to be generated of background noise in the
surveying vicinity that could affect the quality of the survey data obtained. See section 7.3.5
Background Noise Profile.
End of Survey
21. Print another copy of the System configuration and retain it with the survey records.
22. Wash the sub-sea installation carefully using a fresh-water hose to remove all deposits of salt
and debris. Check the sub-sea installation visually for signs of damage or corrosion. Repair
any damage to the equipment before you stow the ROV.