Teledyne 440, System Manual, Page: 138 / 256

6 – Operating Procedure
6-34 © Teledyne TSS DPN 402196 Issue 4.1
If the vertical ranges shown by the 440 System are greater than the actual vertical range, reduce the
value for target scaling factor, and vice versa. Repeat the tests using the new value for target scaling
factor – enter the new value using the option ‘Key in known Target Scaling Factor’ in the target scaling
menu.
Continue repeating the measurements and adjusting the value for target scaling factor until you obtain
a satisfactory set of results.
At each stage, complete the Target Scaling Results form (Form D2).
Defining the performance envelope of the System
If you require a full assessment of the vertical and lateral range performance, follow the procedure
detailed below using the nominal value for target scaling factor determined previously. Note that you
must check the background compensation before you continue.
With the target placed under the centre of the coil array, establish the System with a vertical range
measured to be 0.2m above the target. Record the results on the 440 Accuracy Results form (Form D3
in
Appendix D "Reference" ).
Move the target to a lateral offset of 0.2m and record the vertical range. Note that you may make
measurements on the target to either port or to starboard of the centre-line since experiments have
confirmed that the performance of the 440 System is symmetrical.
Repeat the measurement, increasing the lateral offset in 0.2m increments until a ‘Target Out of Range’
warning occurs. Record each measurement.
Return the target to the centre of the coil array and increase the vertical range by 0.2m. If practicable,
perform a background compensation.
Repeat the measurements of vertical range moving the target laterally every 0.2m. Record each
measurement.
Increase the vertical height by 0.2m and, if practicable, perform a background compensation.
Repeat the above procedure until ‘Target Out of Range’ occurs with the target placed centrally under
the coil array.
The effects of roll, pitch, and skew
Generally, where roll, pitch and skew are less than 15°, the measurements of vertical range delivered
by the 440 System will not degrade by more than ±50mm.
Under some conditions, it may be possible to perform a survey only with some angle of skew between
the target and the ROV. If this is a possibility, repeat the target scaling process described above with an
equivalent skew applied to the coil-array. You may then measure any deviation in accuracy and make
appropriate allowance at a later stage.
You may calculate the effects of roll on measurement accuracy: