Hard-iron-only calibration, Accelerometer calibration, 2 accelerometer calibration – PNI TCM User Manual
Page 23: 4 hard-iron-only calibration
PNI Sensor Corporation
DOC#1014688 r06
TCM User Manual
– July 2013
Page 18
Note that a similar and acceptable alternative pattern would be to follow the
recommended 12 point Full-Range Calibration pattern, but substituting the >±45
° of pitch
with whatever pitch can be achieved and the ±10° to ±20° or roll with whatever roll can
be achieved up to these limits.
5.1.4
Hard-Iron-Only Calibration
It is not uncommon for the hard-iron magnetic distortions around the TCM to change.
Some reasons for this include significant temperature change or temperature shock to a
system, as well as gradual aging of components. A Hard-Iron-Only Calibration allows
for quick recalibration of the TCM for hard-iron effects, and generally is effective for
operation and calibration in the tilt range of 3° or more (
≥45° is preferred). The
recommended 6 point calibration pattern given below is a circle of alternately tilted,
evenly spaced points, with as much tilt as expected during use.
Table 5-5: 6 Point Hard-Iron-Only Calibration Pattern
Sample #
Yaw
Pitch
1
Roll
1
1
0°
max. negative
max. negative
2
60°
max. positive
max. positive
3
120°
max. negative
max. negative
4
180°
max. positive
max. positive
5
240°
max. negative
max. negative
6
300°
max. positive
max. positive
Footnote:
1. For best results, the tilt experienced during calibration should match that experienced
in service. For example, if the TCM will be subject to ±45° of pitch and roll when in
service,
then “max negative” should be -45° and “max positive” should be +45°.
5.2 Accelerometer Calibration
The TCM uses a MEMS accelerometer to measure the attitude of the compass. This data is
output as pitch and roll data. Additionally, the accelerometer data is critical for establishing
an accurate heading reading when the TCM is tilted, as discussed in the PNI white paper
“Tilt-Induced Heading Error in a 2-Axis Compass”, which can be found on PNI’s web site
The TCM algorithms assume the accelerometer only measures the gravitational field. If the
TCM is accelerating, this will result in the TCM calculating an inaccurate gravitational