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3DM-GX4
™
-45
™
Inertial Navigation System
User Manual
Performance Optimization
40
5.4
Angular Rate and Acceleration Limits
The 3DM-GX4-45
™
angular rate and acceleration range depend on the sensors installed in the
device. Exceeding the specified range for either sensor will result in high uncertainty values
from the Estimation Filter until the over-range event is corrected.
5.5
Bandwidth
When selecting sensor and estimation outputs to be recorded, communication bandwidth
considerations should be taken into account, especially when using RS232 serial
communications. Lower baud rates equate to lower communication bandwidth which can be
consumed quickly by selecting a large number of measurements at high sample rates. Severely
overrunning the communication bandwidth can have adverse effects on the sensor
performance due to excessive processor usage. Most computer RS232 ports are limited to
115,200 baud even though the 3DM-GX4-45
™
is capable of running at 921,600 baud (such as
when using a USB connection).
5.6
Platform Frame Transformation
The transformation from the sensor frame to the platform frame (
see Platform Frame on page
33
) should be defined to the highest angular accuracy possible. The easiest way to accomplish
this is to co-align the frames. If this is not possible, using a simple transformation, such as 90 or
180 degree rotations on a single axis are preferred. For complex transformations between the
frames, a calibration should be performed or analysis from a model should be conducted.
5.7
GPS Parameters
The GPS receiver used in the 3DM-GX4-45
™
has an altitude limitation of 50 kilometers and a
speed limitation of 500 meters/second in accordance with the United States International
Treaty in Arms Regulation (ITAR) restrictions.
To use the 3DM -GX4 - 45
™
GPS receiver, the external antenna must be connected, and
position with unobstructed light of sight to the sky in order to achieve satellite lock. Operating
environment can also effect GPS operation and it must be operated within operating
specifications.
GPS outages should be kept to a minimum. As the outage period extends above 30 seconds,
errors in the integration of the inertial sensors compound causing the solution to quickly