Chapter 3 SPAN Operation
OEM7 SPAN Installation and Operation User Manual v14
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system transitions to navigation mode.
9. The solution is refined using updates from GNSS. Once the system is operating within specifications and
after some vehicle movement, the INS Status field changes to INS_SOLUTION_GOOD. This indicates that
the INS filter has successfully converged to within performance specifications.
Coarse Alignment
The coarse alignment is the default alignment routine for SPAN. The alignment starts automatically when a
GNSS solution is available, the receiver has computed fine time, the IMU is connected and configured and initial
bias estimates have been completed. During the coarse alignment, accelerometer and gyro measurements are
averaged over a period of time to measure Earth rotation and gravity. From these averaged measurements, initial
estimates of roll, pitch and heading are computed. Because the coarse alignment uses averaged sensor output,
the vehicle must remain stationary for the duration of the alignment, which is approximately 45 seconds. The atti-
tude estimates solved by the alignment are larger than the system specified attitude accuracy and vary upon the
characteristics of the sensor and the geographic latitude of the system. Attitude accuracy converges with motion
after the coarse alignment is complete (see
The ADIS-16488, IMU-CPT, IMU-IGM, HG1930, HG4930, EG320N, EG370N, STIM300 IMUs,
PwrPak7-E1, PwrPak7D-E1, PwrPak7-E2, PwrPak7D-E2 and SPAN CPT7, cannot perform coarse
alignments, as these IMUs cannot accurately measure Earth rotation. For these IMUs, the default align-
ment routine is the kinematic alignment. Refer to
below. If a stationary alignment
is required, refer to
Kinematic Alignment
An alternate form of aligning the SPAN system is a kinematic alignment. A kinematic alignment can be used for
any SPAN system and is the best alignment alternative for lower performance sensors (ADIS-16488, IMU-IGM,
IMU-CPT, HG1930, HG4930, EG320N, EG370N, STIM300, PwrPak7-E1, PwrPak7D-E1, PwrPak7-E2,
PwrPak7D-E2 and SPAN CPT7). The kinematic or moving alignment is performed by estimating the heading
from the GNSS velocity vector and injecting it into the SPAN filter as the initial system heading.
For the kinematic alignment routine to work optimally, the course-over-ground azimuth must not include any bias
from the defined Vehicle Frame. (For example, a plane being blown in the wind has a large ‘crab angle’ and the
course-over ground trajectory will not match the direction the IMU is pointing.)
The rotation from the IMU Body frame to the Vehicle frame (RBV) must be set to enable kinematic alignment. In
order to simplify this configuration it is strongly suggested that you mount the IMU in parallel to the vehicle
frame. The Y axis marked on the IMU enclosure, should point in the direction of travel.
The kinematic alignment begins when the receiver has a good GNSS position, fine time is solved, the Body to
Vehicle frame rotation is known and a GNSS velocity of at least 5 m/s (~ 18 km/h) is observed. During kinematic
alignment, keep the vehicle roll at less then 10°.
5 m/s is the default alignment velocity. If a different alignment velocity is required, it can be
changed using the
SETALIGNMENTVEL
command. Refer to the
for more information.
While it is possible to lower the minimum speed required for kinematic alignment to take place,
the higher the value, the more closely the course-over-ground estimate will match the vehicle
heading.
