PNI TCM 5 - Manual (Page 23)

PNI Sensor Corporation Doc #1007537 r12
TCM3 & TCM5 User Manual – Sept 2012 Page 23
4.2.1 Calibration Theory
The exact calibration method will depend on the actual settings of the calibration parameters. An
example of the various settings and their effect can be seen in the TCM Studio – Evaluation
Software section.
The main object of the calibration is to allow the TCM to calibrate out any distortions to the magnetic
field caused by the host system. To that end the TCM needs to be mounted within the host system
and the entire application needs to be moved as a single unit during the calibration. Movement
should include at least 180 ˚ of horizontal rotation, but to achieve the highest accuracy a full 360˚ of
horizontal rotation with as many different tilt angles as possible during the rotation is required.
To achieve the highest accuracy throughout the TCM ’s entire tilt range, the unit will need to be tilted
through the entire range. For example, if the unit is only tilted through 40 ˚ of pitch and roll, then the
heading information from the TCM will only be accurate through 40 ˚ of pitch and roll. For maximum
performance the TCM should be exposed to tilt angles covering a full 360°, meaning upside down.
Recommended calibration procedure for taking the minimum number of sample points
follows.
4.2.2 Hard and Soft Iron Effects
Hard iron distortions are caused by permanent magnets and magnetized steel or iron object within close
proximity to the sensors. This type of distortion will remain constant and in a fixed location relative to the
sensors for all heading orientations. Hard-iron distortions will add a constant magnitude field component
along each axis of sensor output and can be easily compensated for using a simple saturation method.
Soft-iron distortions are the result of interactions between the Earth’s magnetic field and any
magnetically “soft” material within close proximity to the sensors. In technical terms, soft materials have a
high permeability. The permeability of a given material is a measure of how well it serves as a path for
magnetic lines of force, relative to air, which has an assigned permeability of one.
The TCM 3-axis digital compass features soft-iron and hard-iron correction.