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    BME680 - BSEC: IAQ value is not changing.

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    New Poster

    BME680 - BSEC: IAQ value is not changing.

    Greetings Bosch Community,

    Recently, I have been using the BME680 sensor to detect the quality of the indoor environment. And as per the documentation provided by Bosch, the BSEC converts the output data (resistance-Ohm) of the MOS Gas sensor of the BME680 to an IAQ that ranges between (0) and (500). Also, the software solution helps compensating the output data of temperature, humidity and pressure sensors. After implementing the BSEC in my project, I noticed some problems in the results that I was receiving from the sensor:

    - The resulted data from the temperature, humidity and pressure sensors was changing each and every 3 seconds (the default configuration) and the values were reasonable. Except for the IAQ which was stuck at the value 25 ('iaq_accuracy' = 0, 'static_iaq' = 0) without moving, even when the gas resistance and the other values were changing frequently (the sensor was tested in different conditions and it kept delivering the same IAQ value).

    - The gas resistance and the pressure variables were declared as floats but the received data was always an integer.

    - On the same condition, the gas resistance kept rising each and every 3 seconds without stabilizing at a specific value.

    I am using the STM32F091CC and GCC as a compiler.

    I am looking forward to hearing from you and I appreciate your quick response.

    Best regards. 

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    3 REPLIES 3
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    Community Moderator

    Re: BME680 - BSEC: IAQ value is not changing.

    How long have you been running BSEC during your test? When BSEC was just started, it takes at least 5 minutes in LP mode (or 20 minutes in ULP mode) before the IAQ Accuracy rises and the IAQ output starts changing.

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    Re: BME680 - BSEC: IAQ value is not changing.

    Hi handytech, 

    Acutually, I can't remember for how long I kept it running continuously in LP mode. I mean I am not sure if I left it running for more than 5 mins without interruption.

    But, I will try to leave it running for more than 5 mins and see if it moves or not. 

    Thank you so much for the information and your quick response. 

    Just another question, is it always necessary to leave the BME680 working for more than 5 mins, in LP mode, before having the real readings on the IAQ ?, or is it just needed for the first time when someone uses the BSEC ? 

    And during those 5 mins, how accurate are the other variables (temperature, humidity, pressure. etc.) ? 

    Thank you again and looking forward to hearing from you. 

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    Community Moderator

    Re: BME680 - BSEC: IAQ value is not changing.

    The BME680 needs to run for some time to stabilize to its environment. Generally, the longer a BME680 was turned off, the longer it may take to stabilize, but we estimate these 5 minutes operation in LP mode to be typically sufficient. Without any information, BSEC must assume that it has just been started for the first time and possibly for a sensor that hasn't been running for a long time, therefore BSEC starts all algorithms and processes from scratch, including this 5min period.


    @LeGuépard wrote:

    Just another question, is it always necessary to leave the BME680 working for more than 5 mins, in LP mode, before having the real readings on the IAQ ?, or is it just needed for the first time when someone uses the BSEC ? 


    Yes due to the above, but..

    Optionally, BSEC supports a state file to be saved to some external memory which can be later restored. This feature is handful for example if you must replace the battery of a device without loosing BSEC's self-calibration history. In case you were to reload a valid state file after having replaced the battery, you would see that the IAQ values would already be changing in the first few minutes. But since the sensor is still affected by the behavior described above, there is a low confidence on the data quality whithin this period that is still indicated by an IAQ accuracy of zero as a result.


    @LeGuépard wrote:

    And during those 5 mins, how accurate are the other variables (temperature, humidity, pressure. etc.) ? 


    When a board or device starts running, it may take a bit of time for the pcb and its components to stabilize to new ambient conditions as well, thus slightly affecting the temperature and relative humidity measurements, but the effect is typically not significant for the pressure output.

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