SonTek/YSI
ADVField/Hydra Operation Manual (September 1, 2001) 67
4.7. Optional Compass/Tilt Sensor for the ADVField
The ADVField can be equipped with a compass/tilt sensor to translate data from the probe’s
XYZ coordinate system to an Earth (East-North-Up or ENU) coordinate system. The sensor used
is the Precision Navigation TCM2 Electric Compass Module.
• Communication with the ADV is through an RS-232 interface. Although direct communica-
tion with the compass is not required under normal conditions, this interface lets you “talk”
directly with the compass (see §4.7.6).
• When properly calibrated, the TCM2 provides accurate heading data (±2.0°) and accurate
pitch/roll data (±0.1° up to 50°).
• There are limitations when using the ADV with a compass. Foremost is the 50° limit on
pitch/roll. Any pitch/roll beyond this will produce unpredictable results.
• It is essential that the compass be correctly mounted relative to probe orientation to ensure
accurate compass data and the correct rotation of XYZ velocity data (see §4.7.2).
• Care should be taken to limit how fast the orientation of the ADV changes because high-
frequency motion can distort compass data. The compass/tilt sensor has a maximum fre-
quency response of about 2 Hz.
• Remember that the ADV measures velocity relative to its own speed – if the ADV is mov-
ing, the recorded velocity is the vector sum of the ADV velocity and the true water motion.
4.7.1. Testing Compass Operation
This section describes a simple procedure to verify basic compass operation performed using a
continuous display of compass data (heading, pitch, and roll). The display can be obtained using
the direct command interface, the DOS-based compass calibration software (
COMPCAL
), or the
Windows-based compass calibration software (Compass, part of SonUtils). If using the direct
command interface, the command
Compass CONT
gives a continuous output of heading, pitch,
and roll.
COMPCAL
and Compass (see ADVField Software Manual) provide continuously updated
graphical and tabular displays of compass data. Guidelines to running this test:
• Be sure the compass is oriented vertically (§4.7.2) and the hardware orientation switches
(§4.2) match the compass installation.
• The area around the ADV should be predominantly free of magnetic material.
• Start the display of compass data.
• Point the probe’s X-axis (if compass is mounted in conditioning module) or the underwater
canister’s X-axis (if the compass is mounted with the processing module) towards each
compass direction (north, south, east, and west).
• Compare the compass output with the expected reading.
• Test the pitch/roll sensors by tilting the ADV about the X-axis (roll) and Y-axis (pitch).
• The compass and tilt data should appear reasonable to within the accuracy of the sensor
(±10° heading, ±5° tilt). Large errors or a lack of response indicates a problem.
• This is not a precise test of compass accuracy, but a means to evaluate basic performance.
• For best results, we recommend performing a compass calibration before every deployment.
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