Home Forum Hardware VOC sensor?

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    Ken Jamrogowicz

    I wonder if the VOC sensor in 82000277 has failed or is near to failing?
    In recent weeks, the only time it seems to give “clean-air” readings is when the weather is warm (10 degrees C) and dry.
    I am pretty sure there are no persistent sources of VOC’s in this area.
    The vendor’s web page says operating temperature should be OK down 0 degrees C.


    Hi Ken,

    I think the problem with this are some short, very high readings which blow up the vertical scale of the diagram too much.
    Zoom in a time range without large peaks and you’ll see nice, plausible looking values.
    It would be better to use logarithmic scaling for VOC and PM… @Radu?


    Ken Jamrogowicz

    Please note the VOC sensor operates in reverse. Detected gas gives the low reading. Clean Air gives a high reading. When the unit was new, it looked like this curve upside down.



    Yes, Wolferl is right, those spikes pushed the diagram too much.

    Ken Jamrogowicz

    You are missing the point. The reason the graph looks like that is because the unit is producing readings of 30Meg to 50Meg for short periods of time – perhaps only 1 or 2 samples. Historically, the “sensible readings” have been in the range of 300K. The ratio of 30M to 300K is 100:1. According the specs the Winsen MP503, the range from quite polluted to quite clean is on the order of 10:1. So such big readings cannot be coming from a healthy sensor.

    see the graph within this document https://www.winsen-sensor.com/d/files/ZP07-MP503.pdf

    This sensor gives lower readings with more VOC. These >10Meg “spikes” would therefor represent sudden spikes of amazingly clean air amongst a background of almost continuous high pollution. This is nonsensical.

    These very big readings of >>10M have only appeared in recent months (coinciding with colder weather) that is why I suspect it is the start of a failure. I see that the device has a small built-in heater, perhaps that is what is failing. I suppose time will tell.


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