RE: Carbon dioxide sensor

e14 Contributor — Thu, 17 May 2012 09:35:39 GMT

Assuming you are using NDIR methodology to measure CO2 it is very difficult to measure exhaled breath concentration with that technology. A number of commercial operations have tried.

CO2 diffuses, so response will be as you expected, in fact you are probably not seeing the true peak as the sensor response will lag slightly, which you are seeing as the value decays.

Using a light source generates heat, which affects density, which effects the reading as you are in effect 'counting molecules' when measuring cocentration. If they are all more widely spaced because the gas is less dense, they'll be less in the way of the measured source, so it'll mis-read the concentration. The other area in exhaled breath is the high humidity, not in itself an issue - until it condenses. This then can effect the internal volume of the gas measuring chamber, any reflectivity that it may be dependent upon, and long term may corrode components.

Be interested to hear more about what you are doing though.