Airmar LB150 - Manual (Page 41)

LB150 WeatherStation Technical Manual revision 0.013
Proprietary and Confidential
PRELIMINARY - DRAFT 38
within the 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
front of the vehicle, and the vehicle’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 vehicle, even though the orientation mark on the sensor housing
may not be facing precisely toward the front of the vehicle. The recommended
procedure to set these offsets is as follows:
1. If the unit is mounted on a vehicle, this procedure should be performed with
the vehicle at rest on level ground.
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 front of the vehicle, in degrees. The pitch and roll
offset fields should be omitted for this step (or set to zeroes).
4. Allow the vehicle to come to rest in a "level" state, and then read the values of
pitch and roll that are reported by the XDR sentence.
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.
6. At this point the transmitted XDR sentences should be producing values that
are centered around 0.0 degrees for both pitch and roll.