What is the influence of metals and magnetic fields on the orientation measurement?

Xsens' orientation algorithm (XKF) uses the earth's magnetic field as a global reference for North / heading (just like a compass). A local disturbance of the static earth magnetic field may influence the orientation estimate. Xsens provides robust algorithms that can compensate for the effects of magnetic disturbances. Note that only ferromagnetic material, such as iron or nickel, will distort the earth magnetic field. Most metals do not influence the earth magnetic field (e.g. most stainless steels, aluminum).

The effect of a distortion in the earth magnetic field on the magnetic field sensors depends on the amount (mass) of ferromagnetic material present or the level of permanent magnetization and the distance between the disturbing object and the magnetic field sensor. Small amounts of iron, e.g. present in most office furniture, will cause the MTx / MTi to sense a disturbed magnetic field typically within a distance of 20-30 cm. Larger masses such as e.g. a car or boat will cause a stronger disturbance within greater range.

Xsens' XKF orientation filter is near-immune to temporary magnetic distortions, allowing the motion tracker to be moved through a local distortion without effecting the orientation output. This is realized by weighting the available sensory input according to plausibility. In some applications, the motion tracker must be mounted on a device containing ferro-magnetic components, causing a distortion that is rigidly connected to the motion tracker and maintains the same spatial relationship to the motion tracker. For such cases, the MT SDK comprises the Magnetic Field Mapping tool, which is able to completely compensate for the static distortion. This is also often referred to as a soft and hard iron calibration. The calibration can both be performed in a full 3D mode (e.g. for very small vehicles, hand-held devices, cameras etc.) as well as a 2D mode (cars, marine vessels, aerial vehicles, etc.). If magnetic distortions are expected to be long term and variable with respect to the sensor, a filter scenario can be chosen that excludes information of the magnetometers completely.

If your application exposes the motion tracker to oscillating EM-fields, contact Xsens for further information.