Revision 7.10
2/28/2012
Appendix J: Calibrating the glider Revolution
(TM)
compass
Gliders using the True North Revolution
(TM)
compass require that the compass be
calibrated
to
ensure accurate compass readings. Calibration compensates for any permanent or induced
magnetic fields from the glider, and must be performed after the compass is installed on the
glider. For this reason, Dock Server machines are delivered with a
compass calibrator
application that can be run as
localuser
. The software uses a Freewave transceiver to
communicate with the compass installed on the glider, requiring no physical connection
between the Dock Server machine and the glider. This also enables the compass to be calibrated
without opening the glider on which it is installed.
The compass calibrator application is configured in Linux using file:
/etc/opt/compass/compassCalibrator.conf
which is initially installed with the following XML as content:
<?xml version="1.0" encoding="UTF-8"?>
<compassCalibratorConfiguration>
<port port="/dev/ttyUSB1" baud="115200" dataBits="8"
stopBits="1" parity="none"></port>
<numberOfReadings>3000</numberOfReadings>
<characterDelay>100</characterDelay>
</compassCalibratorConfiguration>
The
port
element attributes are similar to those found in the dockServerState.xml file. For
example, the file above configures the compass calibrator application to communicate using
serial port
/dev/ttyS0
. To use a different serial port (eg.
/dev/ttyUSB0
) simply update
the XML
port
attribute in compassCalibrator.conf. The
numberOfReadings
element
defines how many data points are collected from the compass during calibration. This is initially
set to 3000, which is usually adequate. Finally, the
characterDelay
element defines the
delay (in milliseconds) between each character communicated to the glider from the compass
calibrator application. A delay is required to limit the risk of characters being dropped during
communication, with 100 milliseconds usually being adequate. Typically, the port element
attribute is the only configuration update a user has to make.
Starting the compass calibrator in Linux
The compass calibrator application comes installed with Dock Server version 6.36 and later, and
can be run on a Dock Server machine by using the following steps:
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