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    bme 680 seems to change the calibration in different environments in long time measures

    Occasional Visitor

    bme 680 seems to change the calibration in different environments in long time measures

    I use the bme680 Sensor as an IOT Device together with the ESP32 and the esphome firmware. I can read sensor data and can see all measured values. I bought 2 same Sensors and at the start both had the same level in Resistance, Temperature and Humidity. Then i installed the Sensors in different locations for a week. One Sensor in the office and one in a heavy VOC athmosphere in our glasfiber production. I had good values and could see in the office high Resistance and in the VOC atmosphere low Resistance. So i could Test the full range of values. Now i have both Sensors back in the office and the Sensor values are not the same more like at the start. It seems that they adjusted to the environment. The office Sensor and the Sensor from the VOC atmosphere have still the same Resistance from there former environment, but in the office environment now. The Sensor from the glasfibre production is still with low Resistance and the office sensor with high Resistance. That makes no sense for me. There seems to be no absolute zero point in the sensor and so the measurements are worthless. What is wrong here ? Is it possible to reset the bme680 ? I need the same values in same environment. I need to monitor the gas atmosphere reliable and valid. Please help me with this. Thanks

    1 REPLY 1
    Community Moderator

    Re: bme 680 seems to change the calibration in different environments in long time measures


    @BASER wrote:

    There seems to be no absolute zero point in the sensor and so the measurements are worthless. What is wrong here ?


    The BME680 can track tVOC levels, but is not selective to specific compounds, and as other sensors working on a similar MOX sensing technology, such devices cannot output an absolute tVOC level. Therefore this sounds like the expected behavior. Each BME680 needs to stabilize to some equilibrium based on the envrionment it has been operating in.


    @BASER wrote:

    I need the same values in same environment.


    It seems like you are currently using the raw resistance output. I believe it would be good to evaluate the BSEC library. Among other things, BSEC will keep track of this background history to self-calibrate. By using BSEC, two fully stabilized and calibrated sensors sharing the same BSEC history will show the same IAQ outputs in the same environment. Alternatively if the devices are sitting in a fixed location, we would recommend to use the sIAQ (static IAQ) output instead.

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