BNO055 North calibration

[DavyV]

Hello,

We are trying to build a system using the BNO055 IMU, it is a statically positioned system which rotates slowly and thus does not auto calibrate. For this we accomplished to retrieve and load the calibration data after a manual calibration (rotating the complete system by hand untill all sensor calibrations were 3.

For rotating the system this works perfectly since it mostly relies on the gyro but we alse need to determine the North. Since it is a static system we cannot use the GPS and thus want to use the BNO055 for this. Loading the calibration data in NDOF mode gave us varying results with the North varying +- 10 degrees when loading the calibration values after a reboot. Loading the calibration values in Compass mode gave more consistent results in determining the North, however it is not consistent while rotating the system (i.e. if the system is not positioned towards the north). Rotating the system relative to North gave the following readings:

0 degree rotation -> 347 degrees reading

90 degree rotation -> 62 degrees reading (75 degrees instead of 90 degrees difference)

180 degree rotation -> 152 degrees reading (90 degrees as expected)

270 degree rotation -> 241 degrees reading (89 degrees as expected)

0 degree rotation -> 345 degrees reading (104 instead of 90 degrees difference)

The BNO055 is positioned in a system which includes metal parts so it could be due to Soft Iron distortions. However, in some spots I read that the BSX sensor fusion (which is integrated) supports the soft iron calibration: https://community.bosch-sensortec.com/t5/MEMS-sensors-forum/BHI160-and-soft-iron-correction/m-p/5912 

While other posts indicate it doesn't: https://community.bosch-sensortec.com/t5/MEMS-sensors-forum/How-to-do-BNO055-soft-iron-calibration/t... 

My questions are:

- Is it indeed possible to save calibration values here and use the system elsewhere on earth while getting accurate heading readings.

- Does the internal algorithm do soft iron calibration or not?

- If not, how can I get this calibrated (I know I can insert a SIC matrix but how do I get/measure this matrix?)

- Do you have alternative/better options to get accurate heading readings in such a stationary positioned system which can be used worldwide.

I hope everything above makes sense, I am looking forward to getting some guidance for this.

[Vincent]

We had white paper talking about the sensor fusion especially the magnetic calibration and compensation. 

SIC (soft iron matrix compensation) is one of the topic inside.  And calibrate the SIC,  need some special test equipment like 3D coil to generate defined magnetic environment.  

Hope you can get more idea from this document. 

In generally, SIC is compensate the soft iron from the device which related to design and material selection.  So you can measure it in the lab and compensate it in the design phase.   Then in the real device geography position,  the sensor need to understand the magnetic environment surrounding, That is the reason user need to do manual calibration.   

The calibration movement can refer to this video.  

https://www.youtube.com/watch?v=Bw0WuAyGsnY