Teledyne 440, System Manual, Page: 118 / 256

6 – Operating Procedure
6-14 © Teledyne TSS DPN 402196 Issue 4.1
6.3.3 Background Compensation and Monitoring
To ensure that information acquired by the 440 System is accurate, you must perform the full
background compensation 20 minutes after you immerse the System in water and turn on the for the
dive. Do not use the measurements made by the System until you have performed the background
compensation.
NOTE
The 440 system has much more stringent requirements than its predecessor, the
340, in terms of background compensation stability. If good quality survey informa-
tion is to be obtained, then the background compensation levels must be abso-
lutely stable and repeatable. Variation in the compensation levels indicates that
the system is not performing correctly. This can be monitored and logged using
the Background Noise Profile facility (see section 6.2.2.5 "Background Noise Pro-
file" on page 6-25). Any problems must be rectified before the survey is per-
formed.
The full background compensation procedure is different from the background
compensation check described in section 6.3.3 "Background Compensation and
Monitoring" on page 6-14. You must perform the background compensation check
at regular intervals throughout the survey operation.
These procedures and checks should not introduce significant delays into the sur-
vey operation, yet will allow greater confidence in the accuracy of survey meas-
urements.
You should consider them an important part of the survey operation.
What Is Background Compensation?
The ‘Background Compensation’ process starts and proceeds after you enter the ‘Background
Compensation’ Menu and click on ‘start’ from the Configuration Menu. It allows the 440 System to
measure any constant signal level caused by the proximity of the ROV, and by the conductive effects of
sea water.
The System measures the background signal on each channel and calculates the average value
during a 10 second period. The average values derived for each channel then represent a ‘zero
reference’ against which signals supplied by the search-coils will be compared. The System considers
any received signals that are greater than this reference as originating from a target.
A sudden and significant change in the results of a background compensation check affecting one
channel could indicate a partial failure of coil insulation. See
section 9.3.1 "Fault on Single Channel
Only" on page 9-11 for details.
Background Compensation Procedure
Place the ROV on the seabed so that the search-coils are at least 10 metres from the target and are
located in an area that is clear of conductive debris.
The ‘Background Compensation’ process starts and proceeds after you enter the ‘Background
Compensation’ Menu and click on ‘start’ from the Configuration Menu.If a printer is on-line and
connected to the SDC, it will print a header that includes the date and time.