Importance of RBV Calibration

For the SPAN system to provide the best performance, the rotation offset of the IMU body to the Vehicle frame (RBV) should be known as accurately as possible. Since constraints happen at the vehicle level, any error in the offset will translate into worse performance.

After the SPAN system has been installed and the appropriate translations and rotations have been applied (see SPAN Configuration, SPAN Configuration for PwrPak7 or SPAN Configuration for CPT7), the IMU Body frame is aligned with the Vehicle frame. However, aspects of the mounting platform and vehicle design, such as vehicle tilt, and slight misalignments in installation can cause the IMU Body frame to be slightly out of alignment with the Vehicle frame. The misalignment of the IMU Body frame from the Vehicle frame will add a bias to the SPAN solution.

The following diagrams show examples of a PwrPak7-E1 installed in a vehicle with misalignment issues.

The misalignments shown in the previous figures have been exaggerated for illustration purposes.

In a typical SPAN system installation, the slight misalignments shown in the examples above are hard to detect and difficult to measure. For this reason, it is recommended that a Body to Vehicle Frame rotation calibration routine be used so the SPAN system can determine and compensate for these angles. Refer to Body to Vehicle Frame Rotation Calibration Routine or Multi-Line Body to Vehicle Frame Rotation Calibration Routine for more information.

These parameters are estimated in the background when the system is fully converged, however it is always better to have this measured as precisely as possible before mission critical data is collected.

Since slight variations in alignment can be introduced when the IMU, PwrPak7-E1 or CPT7 is remounted, a Body to Vehicle Frame calibration should be performed each time the device is remounted.

An accurate RBV is especially important if the position is being transferred to a user offset.