Home Forum Support A3: CO2 not adjusting for temp ?

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  • #28847
    Walker Angell
    Participant

    Our A3 is giving what appears to be quite erroneous data. This was on the lowest bench of a sauna that doesn’t get above 60°c and comparing to a GasLab 501. We also had two other CO2 sensors nearby with readings nearly identical to the 501. There appear to be two problems; 1) The A3 is reading high with average room temps and 2) is not adjusting for temp changes.

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    #28851
    Walker Angell
    Participant

    Here’s a cleaner example with humans. Just a warm up and cool down. CO2 should not have changed.

    #28852
    Walker Angell
    Participant

    Let’s try this again… A cleaner example WITHOUT humans.

    #28887
    Walker Angell
    Participant

    A response to this would be appreciated. This is a serious issue that calls in to question the accuracy of all uRAD products.

    #28888
    Wolferl
    Moderator

    Hi Quincy,

    CO2 concentration /is/ dependent on air temperature, have a look at this paper.
    Also, the CO2 sensors used (Winsen MH-Z19) are not very accurate, the datasheet states +/- 50ppm + 5% of reading.
    The datasheet also states that the reading is “temperature compensated”…one never knows how good that works inside a device that generates additional heat.
    It is a cheap sensor after all and one cannot expect laboratory-grade precision from them.
    Additionally, that sensor performs some magic self calibration (that could explain the sudden drop to 450 ppm) and can also be calibrated by the MCU.

    HTH & Cheers,
    Wolferl

    #28889
    Walker Angell
    Participant

    Wolferl, that is not acceptable. Our Gaslab 501, IQ Air Visual Pro ($239) and AWAIR Element ($149) all provide accurate CO2 readings that are in agreement with each other and that properly compensate for temp changes. Your readings are off by multiple 100’s of PPM, not just 50 or 5%. Your device costs 2x to 4x more than these others, it should be better, not worse.

    “…one never knows” – YOU should know. You are the manufacturer.

    “that sensor performs some magic self calibration”. Some magic? You are the manufacturer of a device that you are selling. You should fully understand exactly what your vendors are doing. Others who use this same sensor are getting accurate results from it, why are you not?

    #28890
    Wolferl
    Moderator

    Hi Quincy,

    No need to be rude here, dude. I am /not/ the manufacturer, I’m just a customer like you are. I just wanted to point out how this system works.
    If you are not happy with its performance, talk to Radu.

    Cheers and EOD for me,
    Wolferl

    #28891
    Walker Angell
    Participant

    Apologies @Wolferl. You are listed as Mod and I assumed that you work for Radu.

    “If you are not happy with its performance, talk to Radu.” – Exactly why I posted in the support forum that he normally frequents. This is beyond my individual happiness with this device as it calls in to question the accuracy of every device made by uRAD.

    #28911
    Walker Angell
    Participant

    Radu, a response to this would be appreciated.

    #28935
    Radu
    Keymaster

    Hi,

    I just looked over this . For CO2, your unit uses the MIX6010 from Mixsen, very similar to the MH-Z19B presented by Wolferl. These are both classic NDIR single beam CO2 sensors.

    The results you are getting are strange. I suggest you return the unit and I’ll upgrade it to a different, dual-beam CO2 sensor . See http://www.uradmonitor.com/rma

    #28936
    Wolferl
    Moderator

    Hi Radu,

    May I ask which dual-beam CO2 sensor you are using?
    I’m just thinking about upgrading my sensor as well…

    Thx,
    Wolferl

    #28951
    Walker Angell
    Participant

    Thanks Radu. RMA completed.

    My understanding of dual beam sensors is that they calibrate each other. Calibration doesn’t seem to be the problem here but rather a missing calculation for CO2 as a function of temp?

    #28956
    Radu
    Keymaster

    Ok so apparently we have the conclusion, here’s the input from one of the NDIR CO2 sensor manufacturers:

    in Sauna, high temperatures and high humidity will affect the test result, even worse, will damage the CO2 performance

    I believe replacing the sensor will not help. Simply it will not work ok in high temps.

    #28959
    Walker Angell
    Participant

    Thanks Radu. Neither of those s/b contributors.

    – Humidity in a sauna is low, typically between 5-50% RH. Given that humidity in a sauna is produced by ladling water on the stove rocks I’m not sure it’d even be possible to get it higher. I think they are confusing Sauna with a Turkish Bath or Steam Room.

    – The A3 was placed low in the sauna where the temps never get above 60°c and rarely (or never) even above 50°c.

    You can also see this in the temp and humidity of the image I posted above. Both are within the parameters of the sensor and more so within the parameters of the A3 that states ‘-20°c to +65°c’ (and which should likely be changed if the sensors have tighter parameters).

    As I pointed out in my original post there appear to be two problems of the A3 providing quite erroneous data:

    1) ALL CO2 readings are high. Even outside where the USEPA and my own devices are all giving readings of 390-425, the A3 is indicating over 600.

    2) It is not correcting for temperature as every CO2 measurement device must do. Compare the CO2 and temp lines in the two images I posted. Whether this is supposed to be done by the sensor or in the A3 code it is not being done and my guess is that this affects every A3 device with this same sensor and possibly every A3.

    Thank you,

    #28961
    Walker Angell
    Participant

    Something worth noting is that the original sensor you were using (Winsen MH-Z19) does temperature compensation within the sensor. The sensor you indicate is in my A3 and presumably others (Mixsen MIX6010) does NOT do temperature compensation in the sensor from what I can tell and so relies on this being done in code outboard of the sensor.

    Given the inaccurate CO2 readings we get on our A3 and the unexpected fluctuations w/ temperature this makes sense.

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