BNO055 calibration reuse

[Morv]

Background:

We use the sensor to measure the angle change around an axis. We are not sure if/how much the environment influences the sensor (metallic components/objects).

Calibration and loading of the offsets:

If a calibration file is available, the software loads the calibrationfile (with the according 22 values) when the device is started and loads them to the BNO055. If no calibration file is available, the software enters a calibration mode and waits until the sensor is calibrated (depending on the operation-mode system, accel, gyro, may have a value of 3) and saves the offsets in a file. After loading the calibration file the values of system, accel, gyro and mag differ from the last measured values while in calibration-but and measurements are inaccurate (sometimes between 5 and 10 degrees). We have tested this procedure in IMU and NDOF mode.

What are we doing wrong? Does it make sense to use IMU-mode or NDOF-mode, despite magical influences?

[Jet]

Hi Sir:

    Do you mean  accel, gyro and mag  raw data  or IMU mode or NDOF with FMC mode data differ from the last measured values while in calibration after loading the calibration file the values of system ?

    Did you check their accuracy, which also have a value of 3?

    If device was not moved, we ensure the environmental magnetic field has not been changed.

    If these are all ok, you should compare the current accel, gyro and mag raw data and the last accel, gyro and mag raw data to know what happened.

[Morv]

Hey Jet, thank you for the answer.

I don't mean the raw-data but the status/accuracy value (integer from 0 to 3) for both modes, IMU and NDOF with FMC.

In IMU-mode we are checking that the accuracy of accel and gyro is 3 and ignore mag, in NDOF_FMC we are checking the accuracy of all 3.

Why does the magenetic field matter when in IMU-mode, we understand it that way, that the magnetic field is not involved in the calculation of the values in IMU-Mode.

The device is moved minimally, ~ about half a meter, without which calibration is not possible.

Thank you, we'll write a short program to check the raw data, like you proposed. 

[Jet]

Hi Sir:

       I am sorry that I didn't show my mind clearly.  Actually, like you said, the magenetic field don't be considered when in IMU-mode.

       In NDOF_FMC mode, not only the hard iron is considered, but soft iron also need to check. Please take attention to it.

      It is a good method to know the enviroment changed or not by observing the raw data at the same positon or different positon.