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www.xsens.com
2.4
Tips for best practice
2.4.1
Multiple sensors connection
Although there is no connection limit in Xsens DOT app, SDK or BLE services, hardware
and OS constraints of the central devices have a ceiling to the maximum number of sensors
that can be connected simultaneously. For Android, MacOS and Windows, it is possible to
connect up to 7 sensors. In iOS, Linux PC or Raspberry Pi, it is possible to connect up to
11 sensors. The actual connection capability highly depends on the devices you choose.
However, the BLE performance cannot be guaranteed if the connection limit is reached. If
big data loss or connection failure cases is observed, reduce the sensor connection number
or transmission payload.
2.4.2
Magnetic distortion
Ferromagnetic material (iron or steel), magnets or strong currents (several amperes) in
the environment near the sensor will cause disturbance to the magnetic field. The
magnetometer in Xsens DOT sensors is used as a 3D compass to determine the direction
of the Earth true north (heading or yaw), used as an absolute reference in the calculation
of 3D orientation. For detailed information about the influence of magnetic field on
orientation, see the PhD thesis “
Inertial and magnetic sensing of human movement near
tic materials” D. Roetenberg 2006
. For best results when measuring with Xsens
DOT, it is advised to avoid highly magnetized areas when carrying out measurements,
particularly in the beginning.
To check the magnetic distortion, you can use the Xsens DOT App to check the Magnetic
Norm
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in magnetic field data after connecting at least one DOT. Look at the Magnetic Norm
curve while moving in the measurement area.
•
Areas for which the magnetic norm = 1 and the variation remains within ±0.2 are
magnetic homogeneous
and best for carrying out the measurements (see Figure
5). However, if the measurement begins with a magnetic norm of around 2 or 3,
and remains within ±0.2 of this value, the orientation should remain accurate.
•
If the Mag Norm will vary depending on the location and orientation of the device
(see Figure 6), there are magnetic distortions in the environment.
Figure 5: Mag Norm fluctuates when moving
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Magnetic Norm (Mag Norm) is the norm of all magnetic axis vectors (X, Y and Z) combined. It can
be used as an indication of magnetic distortions.
