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TVOC Sensor Detect Existing VOCS or needs calibration?

#1

Hi,

Please excuse my lack of knowledge here. My understanding is that the tVOC sensor in the indoor monitor shows a relative reading to the 24 hour baseline.

Let’s say my home already has an ongoing source of potential bad VOCs, but I did not have the sensor before.

If I power it up, I assume it’s going to not really show anything wrong? Unless a newer even more concentrated source of VOCs shows up?

If so, how can I calibrate this? Leave the sensor on outside? Leave it on in a room with the window open for 24 hours?

Thank you.

#2

Also is doing such a calibration going to always make my indoor VOC index be super high? outdoor VOCs should be much lower, vs indoors there will always be something, people breathing, etc… Is it expected indoor VOC should always be around outdoors in a “clean env”?

#3

This note describes how to interpret the index.

If I power it up, I assume it’s going to not really show anything wrong? Unless a newer even more concentrated source of VOCs shows up?

Indeed.

If so, how can I calibrate this? Leave the sensor on outside? Leave it on in a room with the window open for 24 hours?

In short: you cannot really calibrate this sensor or metric. Index of 100 stands for roughly the average of VOCs over an extended period of time (12h by default) so leaving the sensor in an environment will eventually normalize the reading back to 100 to represent that environment’s situation. That said if you would like to see how much “higher” are the VOCs inside compared to outside at a given moment then you can bring the sensor outside without cutting power and observe how sharply the index drops. Or keep the sensor outside for the “extended period” and then bring it inside to measure the environment of interest.

#4

Thanks.

This seems a bit different than what Dyson does, which maybe more useful? I believe they have an automatic baseline correction algorithm which adjusts the baseline upon detecting lower values (At a high level, they havent share more that I could find).

I will try the outside trick, but I wonder if that is just going to make the index in the home super high (I also adjusted to 720 learning offset, so it doesnt just reset every 12 hours), as i would assume outside VOCs are going to be much much lower than inside.

Also follow up question:

  1. Does it recalibrate on each boot? i.e even if I have 720 hours learning index, but power it off and reboot, does it take a new baseline again at that time?
  2. Does changing the learning index need a reboot? or just done from portal and done.
#5

I’m realizing that I didn’t clarify which VOC sensor you have. It would seem like it is most likely sgp41, in which case the answers here are accurate to the best of my knowledge. Otherwise please clarify.

  • Does it recalibrate on each boot? i.e even if I have 720 hours learning index, but power it off and reboot, does it take a new baseline again at that time?

Yes, it starts computing the index from ~scratch on each boot of the firmware as the relevant data structures are computed by the main application firmware, not the sensor.

  • Does changing the learning index need a reboot? or just done from portal and done.

No idea, I’m not using the stock firmware myself. But I would be surprised if changes through portal/dashboard required a reboot and didn’t tell you about it.