4 hard-iron-only calibration, 2 accelerometer calibration, Hard-iron-only calibration – PNI FieldForce Trax User Manual
Page 22: Accelerometer calibration
PNI Sensor Corporation
DOC#1016505 r06
TRAX User Manual
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° of roll with whatever roll can
be achieved up to these limits. See Section 5.1.1 for more information.
5.1.4
Hard-Iron-Only Calibration
It is not uncommon for the hard-iron magnetic distortions around the TRAX 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 TRAX 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 TRAX 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 TRAX uses a MEMS accelerometer to measure attitude. This data is output as pitch and
roll data. Additionally, the accelerometer data is critical for establishing an accurate heading
reading when the TRAX 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 TRAX algorithms assume the accelerometer only measures the gravitational field. If the
TRAX is accelerating, this will result in the TRAX calculating an inaccurate gravitational