Airmar PB200 - Manual (Page 117)

PB200 WeatherStation User Manual revision 1.000
Proprietary and Confidential
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WeatherStation, and so remain programmed even after cycling power. If any of
the fields <3>, <4>, or <5> are null fields, the corresponding stored value will
remain unchanged.
The $PAMTC,ATTOFF,Q command is used to query the values of the attitude
offset angles currently programmed into the WeatherStation. The unit will reply
with
$PAMTR,ATTOFF,a,b,c
where a is the current signed azimuth offset value, b is the current signed pitch
offset value, and c is the current signed roll offset value. All values are reported
to the nearest tenth of a degree.
The factory default value for all three parameters is 0.0 degrees.
The azimuth offset angle is used to adjust the apparent wind angle relative to the
bow of the vessel, and the vessel’s heading when using the internal compass.
These values are further used in calculating the true wind speed and angle.
The azimuth offset angle, along with the pitch and roll offset angles are also used
to adjust the reported pitch and roll values in the transmitted $WIXDR sentence.
A properly set azimuth offset angle will allow the unit to accurately report pitch
and roll of the vessel, even though the orientation mark on the sensor housing
may not be facing precisely toward the bow. The recommended procedure to set
these offsets is as follows:
1. If the unit is mounted on a vessel, this procedure should be performed with
calm water and no wind, and with the vessel at rest.
2. First, zero out all offsets by sending the command
$PAMTC,ATTOFF,SET,0,0,0.
3. Determine the desired azimuth offset angle, and program this into the sensor
using the command $PAMTC,ATTOFF,SET,a where a is the azimuth offset
of the sensor relative to the bow, in degrees. The pitch and roll offset fields
should be omitted for this step (or set to zeroes).
4. Allow the vessel to stabilize to its "level" state, and then read the values of
pitch and roll that are reported by the XDR sentence. If the vessel is rocking
back and forth, then take a number of readings and calculate an average for
both pitch and roll.
5. Program the negated versions of these measured pitch and roll values back
into the unit with the $PAMTC,ATTOFF,SET,,b,c sentence. For example, if
the XDR sentence reports an average pitch angle of 6.2 degrees, and an
average roll angle of -4.3 degrees, then you would send the sentence
$PAMTC,ATTOFF,SET,,-6.2,4.3 to the WeatherStation. Note that the
azimuth offset field in this sentence is a null field, indicating we are not
changing its value at this time.