Vega AHRS-1 / AHRS-3 / MAG-1 Operating Manual
Page 13
Calibrate
This allows calibration of the magnetic sensor.
In-Flight calibration Procedure
Please see documentation supplied with the SP-6 for more information.
Fly the aircraft in safe area where you can perform random banked turns. Do not exceed the safety limits of the aircraft
during the calibration flight.
Start the calibration in the Compass setup menu by selecting “Calibrate”. The AHRS-1/3 /
MAG-1 will display the compass calibration screen. You should see the compass heading
change to “111” to confirm that calibration has started.
Fly a number of banked 180 or 360 degree turns at different bank angles - i.e. shallow, medium and steep turns. Try to
add many different pitch attitudes in various orientations relative to the field direction. It does not matter in what order you
fly the maneuvers. A typical, good calibration tends to take 5-10 minutes of flight.
Do not activate any electrical equipment that creates large magnetic fields during the calibration process (for example
starter motors, autopilot servos, landing lights etc). The heading starts reading
111
after you start calibration. After 36 ini-
tial samples have been collected this changes to
222
. This should take approximately one turn. Continue the flight
while maneuvering until the heading starts reading normally. This happens once the SP-6 has collected 100 distinctly dif-
ferent magnetic samples. At this point the heading should start showing reasonable numbers. Continue the calibration
flight, settling into straight and level at intervals on different headings and verify the heading readout against an ACCU-
RATE reference. Continue the flight until you find heading errors that are within 1 to 2 degrees, about the limit one can
reasonably expect.
When satisfied, end the calibration by selecting “DONE” in the compass calibration menu. This will save the calibration to
permanent memory in the SP-6. Should you not be able to achieve a good heading readout, please locate the compass to
a better location in the aircraft.
The AHRS-1/3 / MAG-1 displays the calibration sample count and fit percentage during calibration. The sample count will
count up to 150 after which new samples replace the oldest samples stored. The fit percentage is a value from 0% to
100%. The aim is to get to a value as close as possible to 100%. The fit starts displaying other than 0% after the first 36
samples. Fit values of 98% and higher are considered good. If you cannot achieve this you do not have a good installa-
tion location for your compass. You may still get reasonably good heading accuracy despite a lower fit. However, to en-
sure long term accuracy please consider locating the SP-6 in a better area in your aircraft.
If the readout decreases suddenly by a large amount (for example from 85% to 42%), this is typically caused by a
strong time-variant magnetic field such as can be created by electrical equipment (motors, relays, current flow in cables).
In such a case please either end and restart the calibration or continue the calibration flight until the fit error is acceptable
again (the incorrect magnetic sample(s) will eventually be removed). It is advised to locate the interference source and
either move this or the SP-6 to a better location in the aircraft.
Note: should you move the SP-6 to a new location or fit new equipment close to the SP-6 you will have to perform the cal-
ibration again. There is no practical limit as to how many times you can perform and save a new calibration.