PNI FieldForce Trax - Manual (Page 18)

PNI Sensor Corporation DOC#1016505 r06
TRAX User Manual Page 14
Other Considerations
Unlike a compass, such as PNI’s TCM module, the TRAX is an AHRS and as such it
can compensate for transient changes in the local magnetic field. However, the
TRAX will work best if it is kept away from dynamic magnetic fields. For example,
if there is an electric motor is in the host system that will be turning on and off during
TRAX operation, then mount the TRAX far away from the motor such that the
motor’s state does not affect the heading when TRAX is in Compass Mode.
Alternatively, TRAX can store up to 8 different sets of magnetic calibration
coefficients, so in the case of the motor, generate and use one set of magnetic
calibration coefficients for when the motor is off and another set for when it is on.
The main objective of a magnetic user calibration is to compensate for hard-iron and soft-
iron distortions to the magnetic field caused by components within the user’s host system.
To that end, the TRAX needs to be mounted within the host system and the entire host
system needs to be moved as a single unit during a user calibration. The TRAX allows the
user to perform a calibration only in a 2D plane or with limited tilt, but provides the greatest
accuracy if the user can rotate through 360° of heading and at least ±45°of tilt.
The following subsections provide instructions for performing a magnetic calibration of a
TRAX system. Several calibration mode options exist, as summarized in Table 5-1. To meet
the accuracy specification, the number of samples should be the “Minimum Recommended”
value, or greater. Calibration may be performed using TRAX Studio or using the PNI binary
protocol, and up to 8 sets of magnetic calibration coefficients may be saved. The
recommended calibration patterns described in the following sub-sections provide a good
distribution of sample points. Also, PNI recommends the location of the TRAX remain fairly
constant while only the orientation is changed.
Table 5-1: Magnetic Calibration Mode Summary
Calibration
Mode Static Accuracy in
Compass Mode
Tilt Range
during Cal
Minimum
Recommended
# of Samples
Allowable
Range of #
of Samples
Full-Range 0.3° rms >±45° 12 10
– 18
2D Calibration <2° <±5° 12 10 – 18
Limited-Tilt <2° over 2x tilt range ±5° to ±45° 12 10
– 18
Hard-Iron-Only
Restores prior
accuracy
>±3° 6
4 - 18
Before proceeding with a calibration, ensure the TRAX is properly installed in the host
system. The device should be installed as discussed in Section 4, and the software should be