Manual

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

Roll

0°

max. negative

60°

max. positive

120°

max. negative

180°

max. positive

240°

max. negative

300°

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

(http://www.pnicorp.com/technology/papers).

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