Moog Crossbow NAV440 Series - Manual (Page 27)

7430‐0131‐01 Rev. F
Page 27 NAV440 User Manual
Setting Default Value Comments
Restart On
Over Range OFF This setting forces an algorithm reset when a sensor over range occurs i.e., a
rotational rate on any of the three axes exceeds the maximum range. The default
setting is OFF. Algorithm reset returns the unit to a high gain state, where the
unit rapidly estimates the gyroscope bias and uses the accelerometer feedback
heavily. This setting is recommended when the source of over‐range is likely to
be sustained and potentially much greater than the rate sensor operating limit.
Large and sustained angular rate over‐ranges result in unrecoverable errors in
roll and pitch outputs. An unrecoverable error is one where the EKF cannot
stabilize the resulting roll and pitch reading. If the over‐ranges are expected to
be of short duration (<1 sec) and a modest percentage over the maximum
setting be operating range, it is recommended that the restart on over range
turned off.
Han ng an inertial rate s
dli ensor over‐range is controlled with the
rtOnOverRange resta switch.
• tOnOverRange If restar is off, the system will flag the overRange status flag and
continue to operate through it.
• If restartOnOverRangeis on, the system will flag a master Fail error during an
over‐range condition and continue to operate with this flag until a quasi‐
static condition is met to allow for an algorithm restart.
The quasi‐static condition required is that the absolute value of each low‐pass
rate sensor falls below 3 deg/sec to begin initialization. The system will then
attempt a normal algorithm start.
Dynamic
Motion ON The default setting is ON. Turning off the dynamic motion setting results in a
higher gain state that uses the accelerometer feedback heavily. During periods of
d off time when there is known low dynamic acceleration, this switch can be turne
to allow the attitude estimate to quickly stabilize.
Turn Switch
threshold 10.0 deg/sec With respect to centripetal or false gravity forces from turning dynamics (or
coordinated turn), the unit monitors the yaw‐rate. If the yaw rate exceeds a given
turnSwitch threshold, the feedback gains from the accelerometer signals for
attitude correction are reduced because they are likely corrupted.
AHRS440 Function
The AHRS440 (Attitude Heading Reference System) unit includes an additional internal 3‐axis magnetometer and
associated software running on the DSP processor. This enables the computation of dynamic heading, as well as
dynamic roll and pitch. AHRS440 data provides dynamic heading, roll, and pitch measurements, in addition to the
VG440 and IMU440 data. The dynamic heading measurement is stabilized using the 3‐axis magnetometer as a
magnetic north reference. The dynamic roll and pitch measurements are stabilized using the accelerometers as a
fined long‐term gravity reference. The unit can be configured to turn on and off the magnetic reference for user de
periods of time.
This function utilizes data from calibrated sensors, the gyroscopes, the accelerometers and a magnetometer
(internal or external). For details of the IMU functions, refer to IMU440 Function on page 23. For details of the VG
functions, refer to VG440 (Vertical Gyroscope) Function), on page 25.In addition to those features, the AHRS440
algorithm has two major phases of operation.