Re: [115attendees] My CO2 complete measurement sets so far

[Alexandre Petrescu <[e-mail]>]

Le 11/11/2022 à 20:50, Carsten Bormann a écrit :
>> With Carsten’s device below the difference was 20%+.
[...]
> The really cheap “CO2” measurement devices measure VOC (volatile 
> organic compounds) and guess the CO2 value from there.  This is 
> garbage.  Anything that says “VOC” is probably this garbage. 
> (Anything that shows 385 ppm surely is, unless somebody brought 
> Gandalf to COP27.) > CO2 is measured using non-dispersive infrared
> sensing, NDIR [1], which is what you should be looking for.

I am not an expert of sensors.  But I agree that it is said so:
traditional infra-red based detection is more precise than newer
MEMS-based on-silicium detectors of 'VOC'.

Still, another criterion to think of is that in this case one looks to
identify the risk of covid transmissions, not necessarily the effects of
CO2 breathing like brain intoxication or muscle non-function, etc.  So
the precision of CO2 detection (IR vs MEMS) is probably ambiguous with
respect to covid.

The covid virus might sit on other particles or molecules than CO2,
which might be correlated to other gases than CO2.

In that sense, a detector that detects other gases than CO2 (a VOC
detector) might lead to better chances to correlate to covid viruses.

Even a simple humidity detector might be good at correlating with the
presence of the covid virus, because it is said that the covid virus
might sit on 'air droplets'.  Further, since humidity might relate to
pressure, maybe a pressure detector might help too.

Ideally, one would have a machine that detects some virus in the air,
then sequences its genome and then turns on a red LED.  There were some
efforts in that direction, but efforts stalled.

That said, if I googled today 'covid detector' I could find something
like it, https://opteev.com/ "The World’s First COVID-19 Detector
for Personal Spaces".  Whether that simple google hit is something to
trust, remains to be seen.


Alex

  (If you can go to a very
> dark room and see a small light bulb (!) in the device light up 
> briefly every five seconds, you are witnessing an inexpensive CO2 
> NDIR sensor.)
> 
> Another cheap way to get a high quality NDIR sensor is to buy a 
> (used?) netatmo.  Not very portable, but you get graphs.
> 
>> The reason for buying these was to get some idea if there is a 
>> problem with CO2 that we need to consider in our venue management 
>> processes
> 
> And that was good thinking. I sure hope we don’t have an actual 
> problem with CO2 concentration at our venues (although I did 
> encounter values as high as 4000+ ppm in the university, which is 
> high enough to slow down thinking). The main use of CO2
> concentration here is as an indicator of the pre-breathed air
> content, which is indicative of the danger of aerosol infection
> unless air cleaning is in effect (HEPA, UV-C).
> 
> I’d sure like to see a COVID-19 dashboard for this meeting, after
> 0.5 % was reported by mid-week...
> 
> Grüße, Carsten
> 
> (*) Affiliate link provided on request, if you really want to buy 
> these [1]: 
> https://en.wikipedia.org/wiki/Nondispersive_infrared_sensor
>