Magnetic Calibration Manual
Xsens MTi User Manual Repository
Magnetic Calibration Manual
Copyright © 2021 Xsens Page 4
Magnetic Distortion Theory
Background
The direction of the measured Earth's magnetic field relative to the orientation of the device
is used as a (3D) compass. This direction is used as an absolute reference in the MT's
orientation estimation algorithms (heading or yaw).
A locally disturbed (warped) magnetic field causes an error in orientation that can be quite
substantial. Ferromagnetic materials, permanent magnets or very strong currents (several
amperes) alter the local Earth's magnetic field. Whether an object is ferromagnetic should
preferably be checked by using the MT's magnetometers. It can also be checked with a small
magnet, but be careful, you can easily magnetize some ferromagnetic materials,
causing even larger errors. If you find that some object is magnetized (hard iron effect, this is
often the case with, for example, stainless steels that are normally not magnetic), it may be
possible to 'degauss' the object.
NOTE:
NOTE:
Never expose the MT to strong magnetic fields.
Never expose the MT to strong magnetic fields.
The MT contains the absolute possible minimum of ferromagnetic materials ('hard' and
'soft' magnetic materials). Nonetheless, some minor components can be magnetized
permanently by exposure to strong magnetic fields. This will not damage the unit but will
render the calibration of the magnetometers useless, typically observed as a (large)
deviation in heading. For mild magnetization, it may be possible to compensate for the
magnetization of the device by a re-calibration (magnetic field mapping). Taking care not to
expose the MT to strong magnetic fields, such as close proximity of permanent magnets,
speakers, electromotors, etc. will prevent magnetization.
In practice, the distance to the object and the amount of ferromagnetic material determines
the magnitude of disturbance.
Distortions of the Earth's magnetic field can be divided into two kinds of effects:
Temporal or Spatial disturbances. These disturbances can be caused by objects in1.
the environment of the motion tracker, like file cabinets or vehicles that
move independently with respect to the MT. This type of disturbance is non-
deterministic, and cannot be fully compensated for. However, the error caused by the
disturbance can be reduced by optimally using the available sensor information and valid
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