Moog Crossbow VG700MB Series - Manual (Page 27)

VG700M User’s Manual
Doc.# 7430-0280-01 Rev. F Page 21
4.3 Mounting the DMU
The DMU should be mounted as close to the center of gravity (CG) of your
system as possible. This will minimize any “lever effect”. If it is not
mounted at the center of gravity, then rotations around the center of gravity
will cause the DMU accelerometers to measure acceleration proportional to
the product of the angular rate squared and the distance between the DMU
and the CG.
The DMU will measure rotations around the axes of its sensors. The DMU
sensors are aligned with the DMU case. You should align the DMU case as
closely as possible with the axes you define in your system. Errors in
alignment will contribute directly into errors in measured acceleration and
rotation relative to your system axes. The sides of the DMU case are used
as reference surfaces for aligning the DMU sensor axes with your system.
The DMU should be isolated from vibration if possible. Vibration will
make the accelerometer readings noisy, and can therefore affect the angle
calculations. In addition, if the magnitude of the vibration exceeds the
range of the accelerometer, the accelerometer output can saturate. This can
cause errors in the accelerometer output.
The DMU case is weather proof.
0 WARNING
Although the DMU is rated and tested for operating temperatures from
–40ºC to +71ºC, the temperature ramp rate must be limited to within
5ºC/minute. The higher ramp rate could potentially result in permanent
damage to the sensors.
; EXAMPLE
4.4 DMU Start Up Procedure
As an example, let’s look at how the DMU might be used on an airplane.
Assume a VG700M is mounted on a small twin-prop plane and will be used
to record the plane's attitude during flight. The VG700M is mounted near
the CG of the plane, and is connected to a laptop serial port during flight.
1. Turn on power to the DMU and let it warm up 5 – 10 minutes.
Power can be on to all electronics, but the engines should be
off.
2. Zero the rate sensors if you haven’t already done previously.
Engines are off, so there is no vibration.
3. Start the engines.
4. Start data collection.
5. Proceed with flight.