Chapter 4 SPAN Operation
CPT7 and CPT7700 Installation and Operation User Manual v12
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4.4.6 Body to Vehicle Frame Rotation Calibration Routine
Kinematic alignment requires that the rotational offset between the vehicle and IMU Body frame (RBV) is
known. If the angles are simple (that is, a simple rotation about one axis) the values can easily be entered
manually through the
SETINSROTATION RBV
command. If the rotational offset is more complex (that is,
rotation is about 2 or 3 axis), then the calibration routine provides a more accurate estimation of the values.
The steps for the calibration routine are:
1. Apply power to the CPT7.
2. Configure the SPAN system including an approximate IMU Body to Vehicle frame (RBV) rotation. See
3. Ensure that an accurate lever arm has been entered into the system.
4. Perform an initial system alignment using one of the methods described in
on page 84. Ensure the system reaches Solution Good.
5. Enable calibration using the
INSCALIBRATE
command with an optional standard deviation target.
INSCALIBRATE RBV NEW [target_stdev]
6. To monitor the calibration, log INSCALSTATUS using the ONCHANGED trigger.
7. Start to move the system. Movement of the system is required for the observation of the angular offsets.
Drive a straight course on level ground (remember that most roads have a crown resulting in a constant
roll of a few degrees). Avoid driving on a surface with a constant, non-zero, slope to prevent biases in the
computed angles. Vehicle speed must be greater than 5 m/s (18 km/hr) for the calibration to complete.
8. When the calibration is complete, either because the accuracy requirement has been met, or the
calibration been stopped by user command (
INSCALIBRATE
command), the calibrated offset value is
automatically applied can be viewed in either the
INSCALSTATUS
log or the
INSCONFIG
log.
To save a calibrated rotation for subsequent start ups, issue the
SAVECONFIG
command after calibration is
complete. Each time the IMU is re-mounted this calibration should be performed again. See also
on page 85 for details on kinematic alignment.
After the
INSCALIBRATE RBV ENABLE
command is entered, there are no body-vehicle rotation
parameters present and a kinematic alignment is NOT possible. Therefore this command should only
be entered after the system has performed a kinematic alignment and has a valid INS solution.
As with the
SETINSROTATION
command, the minimum standard deviation that will be applied is 0.25
degrees (as viewed in the
INSCONFIG
log), even though the
INSCALSTATUS
log may report lower
standard deviations after a successful calibration.
For information about the logs and commands used in this procedure, refer to the
.
4.4.7 Multi-Line Body to Vehicle Frame Rotation Calibration Routine
The single pass Body to Vehicle frame offset calibration feature assumes flat ground when estimating the roll
offsets between the IMU Body and Vehicle frames, as this component of the rotational offset is difficult to
observe through typical ground vehicle motion. In practice this can result in an outstanding roll offset error as
