3DM
®
-GX5-25
User Manual
5.8
Communications 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. Overrunning the communication
bandwidth will result in dropped data packets. Most computer RS232 ports are limited to 115,200 baud
even though the 3DM-GX5-25 is capable of running at 921,600 baud.
5.9
Platform Frame Transformation
The transformation from the sensor frame to the platform frame (
)
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) is preferred. For complex transformations between the frames, a calibration
should be performed or analysis from a model should be conducted.
5.10
Estimation Filter Operation
The 3DM - GX5 - 25 combines the information from the IMU sensors to calculate an Attitude and
Heading Reference System (AHRS) solution that incorporates the strengths of the individual sensors
while minimizing their weaknesses.
In a conventional system, Attitude and Heading Reference System (AHRS), several sources of error
exist when making attitude estimates. First, the algorithm assumes the acceleration vector is
dominated by Earth’s gravity, with only transient linear accelerations. When long- duration linear
accelerations are experienced, such as when an aircraft performs a sustained 2G turn, the sensor will
report incorrect pitch and roll angles. This error results from the assumption that the accelerometers
are only sensing Earth’s gravity. A second source of error occurs when the device attempts to measure
the Earth’s magnetic field. This field is very weak compared to the numerous magnetic anomalies
typically found on platforms, or naturally occurring close to the Earth’s surface. A third source of error
occurs when attempting to navigate between geographic way- points expressed in latitude and
longitude. This error is due to the difference between detecting magnetic north, which is output by the
sensor, and true north, which is used to define lines of longitude. If the AHRS is always used in one
geographical location, the user can correct for this difference using a constant offset. If the AHRS is
used over a wide range of longitude, the magnetic declination must be calculated from a magnetic
model.
42
Summary of Contents for 6253-4220
Page 1: ...LORD User Manual 3DM GX5 25 Attitude and Heading Reference System AHRS ...
Page 45: ...3DM GX5 25 User Manual Figure 33 Import Export Settings Menu 45 ...
Page 53: ...3DM GX5 25 User Manual 8 Troubleshooting 8 1 Troubleshooting Guide 53 ...
Page 67: ...3DM GX5 25 User Manual Figure 43 Connecter interface cable sold separately PN 6224 0100 67 ...
