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    BME680 rgas clarification

    MassaRoddel
    Member

    BME680 rgas clarification

    Is it correct that the measured gas resistance depends on the interval between measurements? And if so, is there a formula to compensate this?

    example:

    320C+150ms@250ms = 113k

    320C+150ms@1000ms = 62k

    320C+150ms@4000ms =  25k

    320C+150ms@10000ms =  13k

    5 REPLIES 5
    Vincent
    Community Moderator

    Re: BME680 rgas clarification

    No, it is not the case. 

    The gas register will only change when the gas containinate  level changed. 

    But the heat temperature and duration will help gas component to be reflected on the gas register. 

    MassaRoddel
    Member

    Re: BME680 rgas clarification

    Maybe my was explanation was not good enough. Of course, the rgas register value does not change itself over time. But the measured value does change depending on the interval between measurements. It gives different results depending on the interval.

    In our application we want to monitor evaporation processes therefore we measure as fast as possible. Unfortunally this gives results which we cannot compare with others.

    However, the absolute value is not so important to us.

    Vincent
    Community Moderator

    Re: BME680 rgas clarification

    The combination of [duty-cycle & heater temperature] defines a certain equilibrium between the surface state and the ambient air.  Duty-cycle means On-time & off-time, e.g. 200 ms on and 800 ms off.

    One should always operate the sensor with the same mode. Because if you change the mode, you also change the equilibrium, and get other results just due to changing the operation mode.

    Best is to use our BSEC software for most applications. If you need a high data rate, We recommend to use the "high power mode" implemented newly into BSEC 1.4.8.0. With that, you have a data-rate of 1 Hz.

    tschweizer
    New Poster

    Re: BME680 rgas clarification

    I'm facing the same troubles as MassaRoddel described.

    My unserstanding was that the heating plates temperature of the gas sensor is >>controlled<< by measuring the resistance of the heating element which is -by physical law- temperature dependant. If the resulting equilibrium between heater settings and the ambient temperature has to be considered, what's the point in having a control loop as mentioned in 3.3.5 of the datasheet? Is the gas sensors resistance values dependence on ambient temperature canceled out by means of this control loop or does it have to be corrected externally for each fixed duty cycle setting one applies? 

     

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