User Manual
© 2017 Inertial Sense, LLC
24
11/30/2017
8
Magnetometer Calibration
The magnetometer is used to estimate heading when the system is in any of the following conditions:
1.) is in AHRS mode
2.) has no GPS fix
3.) has GPS fix and constant velocity (non-accelerating motion)
To have accurate heading under these conditions, the magnetometer must be calibrated. The system allows for
two types of modes for recalibration, external initiated and automatically initiated re-calibration. Regardless of the
recalibration mode, a slower online background calibration runs that continuously improves the magnetometer
calibration to handle local magnetic environment changes. All magnetometer calibration is stored in flash
memory and available on bootup.
8.1
Magnetometer Recalibration
Occasionally the magnetometer will require a complete recalibration, replacing the old calibration with an entirely
new calibration. This is accomplished either through external or automatic initiated recalibration. Use of the
different modes is generally governed by the particular use case for the end customer and is intended to allow for
the most flexibility in an integrated product design.
8.1.1
External Recalibration
External magnetometer recalibration allows the most flexibility in determining when an end user will need to
recalibrate the system. This control over the timing of the recalibration is critical for many use cases and allows
product designers to implement their desired workflows for customers. Further there are use cases where
automatic recalibration is not possible because the quality of the magnetometer calibration is not observable. Such
use cases would include AHRS operation, extended periods without motion or no GNSS fix. External magnetometer
recalibration, as the name suggests is triggered by an external command from the application managing the uINS
hardware. The uINS provides a set of status messages indicating the quality of the magnetometer calibration and
leaves the timing and implementation of a recalibration up to the product designer. Specifically,
INS_STATUS_MAG_NOT_GOOD is an indication of the quality of the magnetometer calibration (see chapter 6 for
more details on the indicators.
During the calibration process, the system should be clear of steel, iron, magnets, or other ferrous materials (i.e.
steel desks, tables, building structures). The uINS should be attached to the system in which it is operating and
rotated together during the calibration process. The following is the
Force magnetometer recalibration procedure
:
1.
Set DID_MAG_CAL.enMagRecal to either:
a.
“0” for
Multi-Axis which is more accurate and requires 360
⁰
rotation about two different axes.
b.
“1”
for Single-Axis which is less accurate and requires 360
⁰
rotation about one axis.
2.
Rotate the system accordingly.
Recalibration
completion
is indicated by either:
1.
INS_STATUS_MAG_RECALIBRATING bit of the insStatus word set to zero. The insStatus word is found in
standard INS output messages (DID_INS_1, DID_INS_2, DID_INS_3, and DID_INS_4).
2.
DID_MAG_CAL.enMagRecal set to 100.
Recalibration
progress
is indicated as a percentage (0-100%) is indicated can be observed from variable
DID_MAG_CAL.progress.
The
“M
ag
used”
indicator in the EvalTool INS tab will be green when magnetometer data is being fused into the
solution, black when not being fused into the solution, and red during recalibrating.
