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PM en TVOC sensors value

Sensors
#1

Hi

I’ve a smarticitzen kit 2.1 (https://smartcitizen.me/kits/9580) running for more than 48h and it seems to me that some sensors values are a little weird. (residential indoor measurements)

From PM sensor, I’ve reading from 0 to 12 ppm, that seems to very low particularly with a given external PM2.5 value around 50ppm (and about 20ppm for PM10)

From TVOC sensor, I’ve some values that goes above 13000ppb which is really huge !

Looking on other similar kit, this sensorkit seems have the same weird values than me:
https://smartcitizen.me/kits/9551

Whereas this kit has much more consistent measurements:
https://smartcitizen.me/kits/9497

Am I missing something ?

#2

Hi Guillaume,

Thanks for your post!

I have checked your sensor readings. I’ll try to respond for each sensor:

  • PM: I think the sensor is behaving OK. One very simple test you could perform is to light a candle, incense or similar nearby and see if the readings change accordingly. If you don’t want to wait for too long, you can use the console interface.

  • CCS811: This sensor, on the other hand, looks unstable. For reference, some documentation can be found about the specifics of the sensor in this section of the docs. From looking at the comparison between the eCO2 sensor and the temperature, it looks like most of the unstable phases occur after high temperature transients (maybe normal from opening windows or something). Temperature and humidity are used internally to compensate the readings, as the sensor compares it’s actual resistance with the clean air one (baseline), and inputs the ambient conditions in the correction. What I would suggest is to leave the sensor for some more time (1-2 days) in a stable area, without interrupting the power during that time. Let’s review the data after then (ping us here if we miss it).

Let us know!

1 Like
#3

Thank you for your answer !

The first candle test for the PM sensor was unsuccessful only a small spique at 20ppm and then nothing with the candle very close below. The second test with multiple lighting and blow of the candle I manage to have a spike at more than 100ppm so I guest it’s OK.

For CCS811, indeed it’s very correlated with temperature change. It’s still unstable today despite of some tries but I haven’t a very stable temperature place for the moment (the days are hot and some fresh air are required at night ^^). I’m sure I’ll find a way to improve it.

Thank you a lot again !

#4

Just as a curiosity. Yesterday evening I did a small BBQ in my balcony…and this morning when checked the PM values got a surprise (around 500 ppm):

image

2 Likes
#5

Coming back to this, some more insights of what could happen with the CCS811:

  • If it’s in an outdoor environment, some other pollutants (like O3) could be causing the sensor reading to be so high. In your area, O3 levels seem to have been rising substantially in the past months due to the summer (car’s NO2 and more sun radiation = more O3)

imagen
imagen.png1037×454 57.2 KB

(Full info here: http://aqicn.org/city/france/paris/gennevilliers/)

In a previous version of this post (below) I mentioned we could make a hardware reset of the kit. This won’t delete the saved baseline from the CCS811. We’ll work on this and make a release in the future to reset it via the shell interface:

  • One thing you could try, is to make a full hardware reset of the sensor. Before doing so, follow these steps so that it’s easy to reconfigure:
    • Set the kit in Setup mode (RED LED) and connect to the SmartCitizen[…] network with your phone
    • Tap on Start and write down the token of your device
    • Once that’s done, you can go press the Button for 15s until the device turns itself off and comes back to life again
    • You can then reconfigure the kit by putting the kit in Setup mode again and connecting with your phone, using the token you just wrote down
#6

Nice bbq then! :partying_face: