Philips KMZ51 Application Note page 29

Philips Semiconductors
Electronic Compass Design using
KMZ51 and KMZ52
Once the interference field components have been measured, their effect can be compensated by generating
opposite field components -Hix and -Hiy at the respective sensors. Using Philips magnetoresistive sensors
KMZ51 or KMZ52, this task can be fulfilled straight forward by applying appropriate currents to the
compensation coils of the respective sensors. In systems using a microcontroller, the compensation can be
done by subtraction of the interference field components from the respective sensor output signals.
The bidirectional calibration method can principally be implemented in an analog compass system. In that case,
analog storage elements are required and a hardware implementation of equation (13). Using a microcontroller,
the implementation of calibration procedures is generally simpler.
In applications, where not only hard iron effects, but also soft iron effects have to be compensated, more
sophisticated calibration schemes have to be applied. These will not be covered by this application note,
however a range of publications is available on that subject.
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Application Note
AN00022