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    BMA400 calibration

    cmorris
    New Poster

    BMA400 calibration

    Hello, 

    we are utilizing the BMA400 in one of our new product designs, and are communicating via SPI to a MSP430 processor. 

    We calibrate the BMA400 to remove any DC offset according to the design guidelines posted here: (https://community.bosch-sensortec.com/t5/Knowledge-base/BMA400-accelerometer-design-guide/ta-p/7397).

    I notice that the Y and Z axes reads just shy of 1g when aligned with gravity; I read about  +/-0.97g on both channels. However, the X  axis outputs the +/- 1g as expected. Our full scale rangle is +/-2g. Since the resolution is 12bit, the bit range is +/- 2048. I should see a count of +/-1024 when aligned with gravity, but I see closer to +/-1000 on both the T and Z axes. Again, this is after calibrating out the DC offset. 

    Do we need to account for this rescaling in software, or is there something I am missing with the sensor? There's no mention of this in the calibration procedure, so I'm confused as to why I don't see a count of +/- 1024 when the sensor is aligned with gravity. 

    Thanks!


    3 REPLIES 3
    BSTRobin
    Community Moderator

    Re: BMA400 calibration

    Hi cmorris,

    As your full scale rangle is +/-2g, BMA400 range should be set to 4g range. You should see +/-512 data when aligned with gravity.
    See it from BMA400 data sheet:

    BMA400 range.png

    cmorris
    New Poster

    Re: BMA400 calibration

    I believe you are incorrect about this. It says multiple times in the datasheet that the ranges are +/-2g,+/-4,+/-8,+/-16,

    BSTRobin
    Community Moderator

    Re: BMA400 calibration

    Hi cmorris,

    You can do the test:
    Set BMA400 range to 4g, place sensor still. Z axis LSB data should be about 512.

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