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can be vertical (it can rest on its end cap), or it can be tilted (it could rest on
a transducer face). Whatever its tilt, the tilt must remain constant as you
rotate the WorkHorse. When prompted, rotate the WorkHorse smoothly and
slowly. Pay particular attention to the Overall Error. For example;
HEADING ERROR ESTIMATE FOR THE CURRENT COMPASS CALIBRATION:
OVERALL ERROR:
Peak Double + Single Cycle Error (should be < 5():
DETAILED ERROR SUMMARY:
Single Cycle Error:
Double Cycle Error:
Largest Double plus Single Cycle Error:
RMS of 3rd Order and Higher + Random Error:
If the overall error is less than 5°, the compass does not require alignment.
You can align the compass to reduce the overall error even more (if
desired).
NOTE. WinSC does the compass verification as part of the Deployment
Wizard (see
9.3
Compass Calibration Procedure
The built-in automated compass calibration procedure is similar to the
alignment verification, but requires three rotations instead of one. The
WorkHorse uses the first two rotations to compute a new calibration matrix
and the third to verify the calibration. It will not accept the new matrix
unless the calibration was carried out properly, and it asks you to verify that
you want to use the new calibration if it is not as good as the previous cali-
bration. While you are turning the WorkHorse for the two calibration rota-
tions, the WorkHorse checks the quality of the previous calibration and dis-
plays the results. It compares these results with the results of the third cali-
bration rotation.
There are two compass calibrations to choose from; one only corrects for
hard iron while the other corrects for both hard and soft iron characteristics
for materials rotating with the ADCP. Hard iron effects are related to resid-
ual magnetic fields and cause single cycle errors while soft iron effects are
related to magnetic permeability that distorts the earth's magnetic field and
causes double cycle errors. In general, the hard iron calibration is recom-
mended because the effect of hard iron dominates soft iron. If a large dou-
ble cycle error exists, then use the combined hard and soft iron calibration.
a. Start DumbTerm.
b. Start the test with the AF-command and choose the calibration type.
c. Place the ADCP in the same orientation as it will be deployed.
d. When prompted, rotate the WorkHorse slowly 360 degrees.
P/N 957-6163-00 (January 2001)
"Verify the Compass," page
WorkHorse Sentinel User's Guide
( 1.55(
( 1.54(
( 0.07(
( 1.61(
( 0.31(
30).
page 21
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