PNI SeaTRAX - Manual (Page 16)

PNI Sensor Corporation DOC#1018154 r02
SeaTRAX User Manual Page 11
5 User Calibration
The magnetic sensor in the SeaTRAX is calibrated at PNI’s factory in a magnetically controlled
environment. However sources of magnetic distortion positioned near the SeaTRAX 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 SeaTRAX in the host system and performing a
user calibration. It is expected the sources of magnetic distortion remain fixed relative to the
SeaTRAX‘s position within the host system. By performing a calibration, the SeaTRAX
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 SeaTRAX 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 SeaTRAX 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 SeaTRAX through a full sphere of
coverage, but it does not need to be incorporated in the user’s system during calibration.
If the SeaTRAX 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.