True. The cheap ones are trying to guess CO2. Those are called "indoor air quality sensors".
Small CO2 sensors have been available for years, for about $50. Compare [1].
Life of this new device is only 10 years, which is short for HVAC systems. A hotel might have a thousand of these.
Older devices say "15+" years.
All these devices have a calibration problem. They drift. They try to correct by treating the lowest value they ever see as "normal" (that's about 400 ppm CO2 today, vs 300 PPM in 1950) and recalibrating. So they're not useful for observing a general increase in CO2. They're also not useful for greenhouses, where CO2 levels may drop below ambient CO2 due to photosynthesis.
Manual recalibration is possible but requires feeding in pure nitrogen and a known nitrogen/CO2 mixture.[2]
Devices which don't need that re-calibration exist.[3] They're more complicated. Also don't seem to be stocked by the usual distributors.
Murata announced this in 2019, and there's a part number (IMG-CA0011-00/
IMG-CA0012-00/IMG-CA0023-00) and a full data sheet.[1] But no distributor has it. Not DigiKey, Mouser, Arrow, or Newark. Even Octopart doesn't list it. It's on Murata's list of recommended products, not the discontinued list. Try contacting Murata.
Small CO2 sensors have been available for years, for about $50. Compare [1].
Life of this new device is only 10 years, which is short for HVAC systems. A hotel might have a thousand of these. Older devices say "15+" years.
All these devices have a calibration problem. They drift. They try to correct by treating the lowest value they ever see as "normal" (that's about 400 ppm CO2 today, vs 300 PPM in 1950) and recalibrating. So they're not useful for observing a general increase in CO2. They're also not useful for greenhouses, where CO2 levels may drop below ambient CO2 due to photosynthesis. Manual recalibration is possible but requires feeding in pure nitrogen and a known nitrogen/CO2 mixture.[2]
Devices which don't need that re-calibration exist.[3] They're more complicated. Also don't seem to be stocked by the usual distributors.
[1] https://rmtplusstoragesenseair.blob.core.windows.net/docs/pu...
[2] https://www.co2meter.com/blogs/news/7512282-co2-sensor-calib...
[3] https://www.murata.com/en-us/products/sensor/co2/overview/te...