Document MT0605P.E
© Xsens Technologies B.V.
MTi User Manual
9
2.5.3
Magnetic materials and magnets
When an MTi is placed close to or on an object that is either magnetic or contains ferromagnetic
materials, the measured magnetic field is distorted (warped) and causes an error in measured yaw.
The earth magnetic field is altered by ferromagnetic materials, permanent magnets or very strong
currents (several amperes). In practice, the distance to the object and the amount of ferromagnetic
material determines the amount of disturbance. Errors in yaw (MTi-30, MTi-300 and MTi-G-700 only)
due to such distortions can become quite large, since the earth magnetic field is very weak in
comparison to the magnitude of many sources of distortion.
Whether or not an object is ferromagnetic should preferably be checked by using the MTi’s
magnetometers. It can also be checked with a small magnet, but be careful, you can easily magnetize
hard 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
1
” the object.
In most cases when the disturbance of the magnetic field caused by placement of the MTi on a
ferromagnetic object can be corrected for using a specialized calibration procedure commonly known
as a “hard- and soft iron calibration”. The calibration procedure (MTi-30, MTi-300 and MTi-G-700 only)
can be executed in a few minutes and yields a new set of calibration parameters that can be written to
the MTi non-volatile memory. This calibration procedure is implemented in the software module
“Magnetic Field Mapper” (MFM) that comes with the Software Suite.
Disturbance caused by objects in the environment near the MTi, like file cabinets or vehicles, that
move independently, with respect to the device cause a type of distortion that cannot be accounted
for
2
. With the MTi-300 and MTi-G-700, the effect of magnetic distortions will be lower than in the MTi-
30. Also, the choice for a filter profile greatly influences the total error amount because of the magnetic
distortion.
1
Degaussing is a procedure to apply strong alternating magnetic fields with decreasing magnitude in random
direction to an object that has been magnetized. The effect of the strong alternating fields is to remove any
magnetized (aligned) domains in the object. When degaussing, make sure the MTi is not attached to the object.
2
This type of disturbance is non-deterministic.
