Troubleshooting with Spec IAQ 968-008 gas sensor module

  • Dear all,
    I'm using this sensor module for ambient air monitoring. I tested the module by blowing into it to change the gas concentration in order to observe the output's changing. It was very strange that anytime I blew into the module, the Vgas output outputted oscillates in nearly sine waveform (not really sine but it was a kind of) with a frequency of some tens of Hz. The result was observed by an oscilloscope. Vcc = 2.8V. Time scale = 4s/div.


    I'm going to read the analog results using MCU and I'm afraid I can't if the input signal is just like this. I don't know what I did wrong. Could you please help me in this regard? Thank you so much.

  • Mod

    Have you considered the 60 minutes stabilization time?

  • Hi gohan. Thanks for your comment. Yes I did. I've already leave it for stabilization in more than 15 minutes.

    I've just realized in "SPEC Sensor Operation Overview" document, it mentions that "With respect to humidity, a rapid RH change can cause a spike in the baseline/zero current, which then rapidly re-stabilizes near its original level" (page 4). I'm thinking this is the reason why I've got that strange result. It also means that I cannot test Spec sensor by blowing into it because this will rapidly change the humidity. Am I right?

  • Mod

    I guess so

  • Update: After having been left for idle operation in more than half of a day, the sensor finally generated much more stable results 🙂 Now I can blew into it and it does not generate pulses like previously. However the changing was so little that could not be observed clearly by oscilloscope. Because it is IAQ sensor, not C02 gas sensor, maybe the result should be like that.

  • Mod

    CO2 sensors are usually make of a IR emitter and a detector so it can make a direct measurement, while gas sensors are usually much slower as the sensors needs to be "cleaned" with heat and then wait for it to absorb the gas particles

  • @gohan Thank you so much for your clarifying.

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