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    BME 680 and BME 280 Not Reading Constant Humidity

    BME 680 and BME 280 Not Reading Constant Humidity


    I am using the BME 680 and the BME 280 in a sealed glass jar. I know the absolute humidity in the jar is constant because it is sealed.

    However, when I get my data from the sensors and calculate the absolute humidty, I am not getting a contant absolute humdity. I have been getting data from the jar being indoors at room temperature and at atmospheric pressure.

    Is this because of how the sensors work? Are they not made for monitoring a small, enclosed space? If it is because of how the sensors work, I need to know why this is happening so I can account for it in my calculations.

    Thank you for your help!

    17 REPLIES 17

    Hi Jet,

    I know that the absolute humidity (water content) should be constant. I do not know what the value should be, but I do know that it should be constant. I know it should be constant because the sensors are in a sealed glass jar. No water vapour can get in or out.

    The problem is that when I calculate the absolute humidiy (water content) using the data given to me by the sensors, I do not get a constant absolute humidity (water content). Over time, the humidity goes up and down far more than I would expect. I expect some variation because the sensors have a margin of error, but what I am seeing is beyond this margin of error. I am not getting a reading of constant humidity even though I know that I should be. (because I am monitoring the humidity in a sealed glass jar.)

    Basically, I know the absolute humidity is constant. However, the sensors are not reading a constant humidity. This is the problem. The temperature and relative humidiy given to me by the sensors does not represent constant humidity over time. Even though I know the humidity should be constant.


    Thank you for your response and please let me now if anything else needs more clarification.

    The BME 280 and BME 680 are connected to an Arduino. I log the data from the sensors every 1 minute using an SD card. The whole setup is sealed in this glass jar.The BME 280 and BME 680 are connected to an Arduino. I log the data from the sensors every 1 minute using an SD card. The whole setup is sealed in this glass jar.


    Occasional Contributor

    Hi Sir:

         I think the absolute humidity is not constant although it is in jar and No water vapour can get in or out.

        In a confined space, internal humidity is affected by temperature, for example, when the temperature is relatively low, the internal humidity (dew point) drops after the saturated water condenses。

        Acturally according to your sensor data we know the temperature data in jar is changed, so it influences the relative humidity and the absolute humidity and the absolute humdity with the temperature change is not constant.



    Hi Jet,

    I considered that possibility as well. I know that relative humidity changes with temperature. However, if water is constant and there is no condensation, the absolute humidity does not change with temperature. I considered that maybe condensation was happening in my case but the relative humidity never approaches 100% (saturation). I also never observed any condensation. There is very little water vapour in the jar. The concentraion of water in the jar is the same as in the air.

    When I did research online to get more answers about the possible condensation, I could not find anything to explain what I was seeing. I do not believe water condensation explains what I am seeing. If it is the case though, it would be very helpful if you could send me some sources that can help me better undersatnd what could be happening.

    I believe it may have to do with what the sensors are designed for. Maybe they aren't made to mointor accurate water content in a small cofnined space? I don't necessarily think it is any flaw in the sensors, I just think I may be using them for something they are not intended for. And if that is the case, I would like to better understand why they don't work perfectly for my application so I can take that into account in my calculations and tests.


    Thank you for your quick responses 

    Occasional Contributor

    Hi Sir:

         I talked to our internal experts, your test environmental condition and the absolute humidity you have known need be confirmed.

         I understand your mind, but I think you should use an precise humidity barometer to know the real humidity, include absolute and relative.

        Maybe the test environmental condition you set up is strict and the absolute humidity was changed like you said, but actually this only is our guess, not accurate, you should have the precise reference device to compare with your test and calculation results.

       Currently maybe our sensor results have a little deviation with the real ambience, which means offset, but it is acceptable, we could fix it by humidity calibration.

        Are you using BME280 api? the latest version?

    Hi Jet,

    Thank you for talking with your experts.

    I would definitely use a precise humidity barometer but I actually do not need an accurate value of absolute humidity. I am only focusing on the change in humidity. The actual value is not important for my applications, I just need to know if the humidity is changing.

    I want to use the sensors to detect water leaks into a container. I am using the jar right now as a control because I know no water can get in or out, but I am not getting constant humidity from the sensors. This is not a big problem if I could predict the innaccuracy of the sensors. I want to understand why they are not giving me constant humidity so I can take it into account in my data analysis so I can understand what an enivronement without constant humidity would look like with these sensors. Right now, I know that an environment with constant humidity gives me data without constant humidity. If I can understand this fluctuation in humidity in the sensors, I can better understand what it would look like if the environment stopped having constant humidity.

    You mentioned the sensors have a deviation with the real ambience and I agree that it is acceptable since I do not need an accurate sarting value for humidity. I only care about if that value increases or not.

    If the only error in the sensors was a deviation in value, than I would not expect the problem I am having and I am unsre if calibration would fix this beacause the humidity read by the sensors would probably still fluctuate. Even if the sensors did not give me an accuarate value of humidity, I would still expect that humidity value to be constant but I am not seeing that.

    The relationship between the RH and temperature from the sensors is not consistent with constant humidity. I expect the temperature and relative humidity to change but I expect them to always correlate with the same absolute humidity.

    I made this graph last year and you can see that at a constnt AH, the temperature and relative humidty values can change but still correlate to that AH value. Therefore, I expected to see a constant humidty in the jar based on the RH and temperature values given to me by the sensors.


    Thank you for your consistent responses. Please let me know if you think I am wrong in anything or if you need any more clarification. I am open to being wrong, but I would like to know where and why I am wrong so I can better understand.