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A – Operating Theory
Figure A-7: Example with metal present on the seabed during compensation
Figure A-8: Example where the vehicle was not moved smoothly
The "active compensation" window will automatically make a best fit to the vehicle data. This curve will
be overlaid on the scattered points. The resulting parameters in the results section at the bottom of the
screen. The linear parameter, m, should be in the region 10-20, and the quadratic parameter should be
approximately -0.05. A curvature opposite to that shown in
Figure A-5
or an unexpected value of m
indicates that the calibration was not carried out correctly or the subsea electronics have failed in some
way.
A.2.4.3 Checking the Rejection
If desired, the system's rejection of seawater can now be seen. Returning to the run/display screen, the
target voltages are displayed. With the vehicle still 3m above the sea bed, these should be within a few
µV of zero. If the vehicle is now slowly dropped to the seabed, then the target voltages should remain
close to zero. They may deviate slightly in either a positive or negative sense, but should remain much
less than the signal threshold of 15µV.
If the voltages change suddenly when the vehicle lands on the sea bed, then this may be due to either
detection of a metal object, or the coils not being firmly attached to the vehicle. Significant changes will
reduce the accuracy of the survey data when operating close to the ultimate range of the system. The
Teledyne TSS 440 system operates at much greater survey ranges and this places stringent
requirements on the background compensation and the rigidity of the coil mounting frame.
If the voltages vary when the vehicle is some way above the sea bed, then this is most likely due to an
error in the active compensation procedure. It must be repeated, perhaps on a slightly different area of
the seabed.
A-8
© Teledyne TSS
DPN 402196 Issue 4.1
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