PNI Prime Pro User Manual page 17

Hard-Iron Effects
Hard-iron distortions are caused by permanent magnets and magnetized objects in close
proximity to the sensors. These distortions add or subtract a fixed component to each
axis of the magnetic field reading. Hard-iron distortions usually are unchanging and in
a constant location relative to the sensors, for all heading orientations.
Soft-Iron Effects
Magnetically "soft" materials effectively bend the magnetic field near them. These
materials have a high magnetic permeability, meaning they easily serve as a path for
magnetic field lines. Unlike hard-iron effects, soft-iron effects do not increase or
decrease the total field in the area. However, the effect of the soft-iron distortion
changes as the host system's orientation changes. Because of this, it is more difficult
to compensate for soft-iron materials.
Temperature Effects
While the hard-iron and soft-iron distortion of a system may remain quite stable over
time, normally the distortion signature will change over temperature. As a general rule,
the hard-iron component will change 1% per 10°C temperature change. Exactly how
this affects heading depends on several factors, most notably the hard-iron component
of the system and the inclination, or dip angle.
Consider the example of a host system with a 100 µT hard-iron component. This is a
fairly large hard-iron component, but not completely uncommon. A 10°C temperature
change will alter the magnetic field by ~1 µT in the direction of the hard-iron
component. Around San Francisco, with an inclination of ~60°, this results in up to a
couple of degrees of heading change over 10°C.
Consequently, no matter how stable a compass is over temperature, it is wise to
recalibrate after significant temperature change since the magnetic signature of the host
system will change with temperature. The Prime Pro helps accommodate this issue by
allowing the user to save up to 8 sets of magnetic calibration coefficient sets, so
different calibration coefficients can be generated and loaded at different temperatures.
Other Considerations
Prime Pro can store up to 8 different sets of magnetic calibration coefficients, hence if
the system magnetic signature will change in different known unique states, perform a
user calibration in these unique states and save each of the calibration coefficients. The
unique calibration coefficients can be recalled when the system is operated in that
specific state again.
PNI Sensor
Prime Pro User Manual Preliminary September 2022
DOC#TBD
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