DMU380ZA Series
User’s Manual
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Doc# 7430-3810 Rev. 02
Page 22
moves in close proximity to a large ferrous object. When the Use Mags switch is
turned from OFF to ON, the AHRS380ZA will reinitialize the yaw/heading angle with
the compass reading provided from the magnetic field sensor readings.
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 for
the AHRS380ZA. Algorithm reset returns the AHRS380ZA to a high gain state, where the
AHRS380ZA rapidly estimates the gyro 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 can not 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 operating range, it is recommended that the
restart on over range setting be turned off. Handling of an inertial rate sensor over-range
is controlled using the restartOnOverRange switch. If this switch is off, the system will
flag the overRange status flag and continue to operate through it. If this switch is on, the
system will flag a masterFail 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-passed rate
sensor fall below 3 deg/sec to begin initialization. The system will then attempt a normal
algorithm start.
Dynamic
Motion
ON
The default setting is ON for the AHRS380ZA. Turning off the dynamic motion setting
results in a higher gain state that uses the accelerometer feedback heavily. During
periods of time when there is known low dynamic acceleration, this switch can be turned
off to allow the attitude estimate to quickly stabilize.
Turn
Switch
threshold
0.5
deg/sec
With respect to centripetal or false gravity forces from turning dynamics (or coordinated
turn), the AHRS380ZA 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.
BIT
See 4.4.3
3.4.3
AHRS380ZA Built-In Test
As with the IMU380ZA and VG380ZA, the Built-In Test capability allows users of the
AHRS380ZA to monitor health, diagnostic, and system status information of the unit in
real-time. The Built-In Test information consists of a BIT word (2 bytes) transmitted in
every measurement packet.
In addition, there is a diagnostic packet ‘T0’ that can be
reque
sted via the Get Packet ‘GP’ command which contains a complete set of status for
each hardware and software subsystem in the AHRS380ZA. See Sections 6 and 7 of the
Progra
mming Guide, for details on the ‘T0’ packet.
The BIT word contained within each measurement packet is detailed below. The LSB
(Least Significant Bit)) is the Error byte, and the MSB (Most Significant Bit) is a Status
byte with programmable alerts. Internal health and status are monitored and
communicated in both hardware and software. The ultimate indication of a fatal problem
is the masterFail flag. The softwareError bit also provides useful information regarding
the status and quality of the AHRS380ZA magnetic alignment. If the AHRS380ZA has
not been properly magnetically calibrated, the AHRS380ZA shall indicate a
softwareError.
The masterStatus flag is a configurable indication that can be modified by the user. This
flag is asserted as a result of any asserted alert signals which has been enabled. See
Section 9 Advanced BIT for details on configuring the masterStatus flags. Table 11
shows the BIT definition and default settings for BIT programmable alerts in the
AHRS380ZA.
