Compass Calibration Procedure - RD Instruments WorkHorse User Manual

WorkHorse Mariner ADCP User's Guide
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. Prepare the ADCP for calibration (see
18).
b. Using BBTalk, send a Break to wake up the ADCP.
c. On the Transfer menu, click Command History. In the Enter a
Command box, enter AF and click OK. When the calibration proce-
dure starts, choose the calibration type.
d. Tilt the ADCP (see
horse with a block under one side of the end-cap. A 35-mm block will
give you an 11-degree tilt. Check the on-screen instructions to see if the
orientation is OK. Adjust as necessary.
NOTE. The tilts must remain constant during the rotations. The
transducer beam is the center point of the rotation.
e. When prompted, rotate the ADCP slowly 360 degrees (approximately 5
degrees per second).
f. The second rotation requires the ADCP to be tilted 15 degrees in another
direction than from the first rotation (see
the on-screen instructions to orient the ADCP correctly. When
prompted, rotate the ADCP slowly 360 degrees (approximately 5 de-
grees per second).
page 20
"Preparing for Calibration," page
Figure 11, page 21). Tilt an upward-looking Work-
Figure 11, page 21). Follow
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