The In-run Compass Calibration (ICC) parameters are estimated in the sensor fusion algorithm. These parameters are then used to compensate the magnetometer sensor readings (for hard-iron and soft-iron effects) before being fed as input to the VRU/AHRS estimation engine. The compensated magnetometer readings are not shown in the MT Manager graphs unless the parameters are stored (see the diagram below).
Figure 1: Data from the sensors (magnetometer and inertial sensors) is calibrated with the calibration parameters in the eMTS. The initial calibration parameters are a result of the factory calibration by Xsens. If ICC or the Representative Motion feature is on, filter states and compensation parameters are available in the RAM-memory. The magnetic field data (data output) from the sensor are not influenced by parameters in the RAM-memory
Using the Representative Motion feature
An important characteristic of ICC is that it determines the level of external magnetic disturbance present (e.g. a structure or a vehicle to which the MTi is not attached) and decides based on that level to include the relevant magnetometer sensor readings for estimation of parameters in the ICC algorithm. The Representative Motion feature as part of ICC is added to speed up the estimation process. If it is known that the MTi is in a homogeneous magnetic field, it is possible to use the MTi in the Representative Motion settings where typical application related motions can be performed. All relevant magnetometer sensor data will be used for the estimation purposes without any disturbance checks, speeding up the estimation process. Based on the sensor mounting environment and application platform, the accuracies might vary. We encourage users to try this feature if they are aware of typical application dynamics and good knowledge of environment of operation.
The Representative Motion code can be set in Low Level Communication and XDA (FA FF 74 01 00 8C (Start) and FA FF 74 01 01 8B (Stop)). In MT Manager, it is possible to stop and start the Representative Motion mode with this button:
During the Representative Motion mode, the RepMo status bit in the Status Word will be 1.
Storing the ICC parameters
Once the ICC parameters are estimated, either in Representative Motion mode or when ICC is running in the background, the calibration parameters can be stored. This is done by the Store ICC Settings command in Low Level Communication (Store ICC Command: FA FF 74 01 02 8A) or press the button in MT Manager:
Once this button is pressed, the MTi will go to config mode and the ICC parameters and magnetometer calibration parameters will be copied from the RAM memory to the non-volatile memory that contains the magnetometer calibration parameters as indicated/shown in the diagram. Once stored, these calibration parameters are then used in the calibration of the magnetometer sensor readings and can be view with MT manager graphs.
Figure 1: Once the command is given by the user to store the ICC and calibration parameters, the MTi will write the parameters to the eMTS on the non-volatile memory. This way, the magnetometer sensor readings are calibrated with the ICC parameters before they are fed into the sensor fusion algorithm. Also, the magnetic field data will be outputted using the new calibration parameters.
This method is ideal when magnetic field mapping is not possible and magnetometer sensor feedback is needed for compass/AHRS applications.. ICC can continue to run in the background to further improve parameter estimation.