3 ms·

Agreed, the difference between "real" CO2 meters and consumer CO2 meters is really stark. Given that you can get nitrogen and CO2 in tanks, I expect one could b

Agreed, the difference between "real" CO2 meters and consumer CO2 meters is really stark. Given that you can get nitrogen and CO2 in tanks, I expect one could build a calibration setup with a fixed volume tank, two metered gas ports, and some software. Start by purging the tank with nitrogen, then add CO2 for the 400ppm baseline. Calibrate there, then add increments of 100ppm (or 50ppm) CO2 and record the readings up to say 1500ppm total. Then you have a calibration table for that meter that will let you translate from its indicated ppm to the real ppm.

DoofusOfDeath 6y ago
That's roughly my understanding about how these devices are actually tested in labs. Probably not something I'd tackle on my own, but it would be awesome if Consumer Reports or a major newspaper hired a lab to do this. With so many people working from home now, I would think it's an increasingly relevant issue.
nickff 6y ago
That won't necessarily make the meters match. The sensors can be perfectly calibrated for CO2, but still read differently because most of the sensors are sensitive to a variety of other carbon-containing gasses. Most consumer CO2 detectors use a sensor which measures the IR absorption of its surroundings. These sensors have varying cross-sensitivities to a bunch of other gasses including carbon monoxide, propane, alcohol, etc. Calibrating them for CO2 will not compensate for different responses to CO, which is much more IR-absorbent in many of the same frequency bands.
GrumpyYoungMan 6y ago
That's unnecessary since there's pre-calibrated mixtures referred to, unsurprisingly, as "calibration gas" readily available. Googling for "carbon dioxide calibration gas" will find you what you need as well as the appropriate pressure regulators. Note that even the professional meters require calibration on a regular basis; for example the calibration schedule for the Fluke 975 for CO2 is yearly and for carbon monoxide is monthly.

DoofusOfDeath 6y ago

That's roughly my understanding about how these devices are actually tested in labs. Probably not something I'd tackle on my own, but it would be awesome if Consumer Reports or a major newspaper hired a lab to do this. With so many people working from home now, I would think it's an increasingly relevant issue.

nickff 6y ago

That won't necessarily make the meters match. The sensors can be perfectly calibrated for CO2, but still read differently because most of the sensors are sensitive to a variety of other carbon-containing gasses. Most consumer CO2 detectors use a sensor which measures the IR absorption of its surroundings. These sensors have varying cross-sensitivities to a bunch of other gasses including carbon monoxide, propane, alcohol, etc. Calibrating them for CO2 will not compensate for different responses to CO, which is much more IR-absorbent in many of the same frequency bands.

GrumpyYoungMan 6y ago

That's unnecessary since there's pre-calibrated mixtures referred to, unsurprisingly, as "calibration gas" readily available. Googling for "carbon dioxide calibration gas" will find you what you need as well as the appropriate pressure regulators. Note that even the professional meters require calibration on a regular basis; for example the calibration schedule for the Fluke 975 for CO2 is yearly and for carbon monoxide is monthly.