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    BME680 Compensation not working on sIAQ output

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    Community Moderator
    Community Moderator

    Re: BME680 Compensation not working on sIAQ output

    In default mode I believe it is the "4d" config string. 4 days or 28 days is really just a time constant, the algorithm does not work using a fixed time window, rather a single state blob, and new data. No matter how long the sensor has been on, or the time constant, the state file is always the same size.

    Indeed the baseline tracking (25 ~ best air so far) speed is dictated by this time constant. Let's say the sensor is static in an office building, then there is a long weekend, let's say Easter. A longer time constant will prevent the sensitivity increasing due to the lack of stimuli.

     

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    Established Member

    Re: BME680 Compensation not working on sIAQ output

    " A longer time constant will prevent the sensitivity increasing due to the lack of stimuli."

    But sensitivity is fixed for sIAQ. Then, can we ignore this time constant when using sIAQ output?

     

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    Community Moderator
    Community Moderator

    Re: BME680 Compensation not working on sIAQ output

    "But sensitivity is fixed for sIAQ." Yes.
    "Then, can we ignore this time constant when using sIAQ output?" No.

    The time constant will equally affect the baseline tracking, or offset. Therefore if the sensor stays in relatively bad air for multiple days, then this "bad air" will become the new zero sIAQ over time.

    The recommendation stays the same, for static applications, you usually want the 28d time constant and sIAQ together. But for your characterization, feel free to log the raw data instead, compute BSEC in your host from the log file.

    handytech shared a nifty little application some time ago.
    https://community.bosch-sensortec.com/t5/MEMS-sensors-forum/BME680-Using-BSEC-in-backend/m-p/7549/hi...

    o_o
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    Established Member

    Re: BME680 Compensation not working on sIAQ output

    Thank you for the very clear explanation.

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