PNI FieldForce Trax - Manual (Page 16)

PNI Sensor Corporation DOC#1016505 r06
TRAX User Manual Page 12
5 User Calibration
The magnetic sensor in the TRAX is calibrated at PNI’s factory in a magnetically controlled
environment. However sources of magnetic distortion positioned near the TRAX in the user’s
system will distort Earth’s magnetic field and should be compensated for in the host system with
a user calibration. Examples of such sources include ferrous metals and alloys (ex. iron, nickel,
steel, etc.), batteries, audio speakers, current-carrying wires, and electric motors. Compensation
is accomplished by mounting the TRAX in the host system and performing a user calibration. It
is expected the sources of magnetic distortion remain fixed relative to the TRAX‘s position
within the host system. By performing a calibration, the TRAX identifies the local sources of
magnetic distortion and negates their effects from the overall reading to provide an accurate
heading.
As with the magnetic sensor, the accelerometer in the TRAX is calibrated at PNI’s factory. But
the accelerometer gradually changes over time, and the user either will need to periodically
perform a user accelerometer calibration or return the unit to PNI for recalibration. As a rule-of-
thumb, the accelerometer should be recalibrated every 6 to 12 months. Unlike a magnetic
calibration, the accelerometer may be calibrated outside the host system. Accelerometer
calibration is more sensitive to noise or hand jitter than magnetic calibration, especially for
subsequent use at high tilt angles. Because of this, a stabilized fixture is suggested for
accelerometer calibration, although resting the unit against a stable surface often is sufficient.
Key Points:
Magnetic calibration:
o Requires incorporating the TRAX into the user’s host system such that the
magnetic components of the user’s system can be compensated for.
o Allows for 4 different methods of calibration. Full-Range Calibration provides
the highest heading accuracy, but requires ≥45° of pitch. 2D and Limited-Tilt
Calibration allow for good calibration when the range of allowable motion is
limited. Hard-Iron-Only Calibration updates the hard-iron compensation
coefficients with a relatively easy procedure.
Accelerometer calibration requires rotating the TRAX through a full sphere of coverage,
but it does not need to be incorporated in the user’s system during calibration.
If the TRAX will experience different states during operation, such as operating with a
nearby shutter sometimes closed and sometimes open, or operating over a broad
temperature range, then different sets of calibration coefficients can be saved for the
various states. Up to 8 magnetic calibration coefficient sets and 3 accelerometer
calibration coefficient sets can be saved.