Comment by dfex 21 hours ago
More concerning - can anyone explain why there is such a variation in the results from the DC powered unit vs. the TENG-powered one? The graph at the bottom of the report shows a difference of 30-50ppm between both units when they are sitting side by side on the bench.
Actually the real accuracy is much better, especially with optical NDIR sensors.
We do a lot of testing against reference grade sensors and typically see very good performance and reproducibility [1].
[1] https://www.airgradient.com/blog/performance-of-low-cost-co2...
That’s if the voltage supply was stable and within electrical specs for a sufficient period of time. We can see this is a snippet 2 hours into the discontinous collection.
3.6V is the maximum value that the nrf52832 SoC can handle. I would suspect the VDD is variable.
I skimmed the original article and it only mentions the graph and says that it's "comparable to DC powered unit". I'm guessing < 100ppm difference is somewhat acceptable?
You might be right - it's just odd that it's always showing "more" rather than similar amounts.
Also, according to Claude[1] a 50ppm difference is equivalent to around 25 years current atmospheric carbon increase.
* Pre-industrial (1700s): ~280 ppm
* 1958 (when systematic measurements began): ~315 ppm
* 2000: ~370 ppm
* 2015: ~400 ppm (milestone crossed)
* Current: ~420-425 ppm
[1] "What is the normal range for background CO2 concentrations in the air?"
It’s crazy to think that many people alive today experienced a 30% increase in ambient atmospheric carbon dioxide concentration within their lifetimes.
Not odd at all that it’s always showing more — sensor error is often biased. This is within the listed range though.
I have to know, what's the the rise of people like you chiming in with AI sourced tidbits? It's like the people with no knowledge on a subject that use google as a quick catch up tool so they can participate in a conversation, but somehow even worse. Are they the same people, but now lazier or just true believers in the non-sense engines?
You’re missing some deeply important context there, which is that those measurements are for outdoor atmospheric CO2 only.
Average indoor air quality ranges from 400-1000 ppm CO2, with adverse mental effects starting to appear close to 2000 ppm.
In that context, you can see why a 50 ppm difference is marginal. This is why asking an LLM is not generally a great idea for understanding something - you need to follow it up with more research.
> adverse mental effects starting to appear close to 2000 ppm.
cognition is harmed starting at 1000ppm (https://pmc.ncbi.nlm.nih.gov/articles/PMC3548274/)
That's in the normal range of accuracy of modern CO2 sensors, for example SCD40 from Sensirion is described with an accuracy of ±50.0 ppm ±5.0 %m.v.