Carbon Dioxide Detection
Carbon Dioxide Detection
(OP)
Hi All
I'm doing a project on carbon dioxide detection in the human breath. I'm considereing using infrared source and detector(thermopile) for the detection proces.
Is any any out there who can provide me with some help?
I'm doing a project on carbon dioxide detection in the human breath. I'm considereing using infrared source and detector(thermopile) for the detection proces.
Is any any out there who can provide me with some help?





RE: Carbon Dioxide Detection
The wavelength is 4.25u and you will need to use a dual wavelenth or similar technology to eliminate interference from water vapour in the exhaled breath.
A small lamp bulb will make a good IR source.
Murata make a pyroelectric detector with a built in CO2 band filter, but there are others.
The Murata device is an AC only detector so you will need to use a flashing IR source.
If you need fast response you might have to consider using a mechanical shutter to interrupt the IR source, if speed is not critical then just flash the bulb at about 1 Hz.
CO2 absorbtion of IR is not linear so be prepared to do some curve straightening.
Good luck
RE: Carbon Dioxide Detection
1. Will a Dual Channel Thermopile Detector do?
2. I realise that i need some kind of chopper(mechanical) wheel to modulate the source but i really do not know what are the components required to build the mechanical shutter.
3. Are there any specific light bulb? as in the model number i can get?
RE: Carbon Dioxide Detection
Without some sort of control system, aren't you going to wind up measuring the atmosphere?
TTFN
RE: Carbon Dioxide Detection
So what do i do about quantification. Currently i've having lots of difficulties even getting the correct components for the detection cicuitry.
1. The emitter Source(Incandescent Source).
2. The appropriate Detector. currently i'm using a TPS2534 provided by perkin elemer and i'm not really sure if it is the right way to go about.
So care to advice what components i require? before i hit into the quantification bit...
RE: Carbon Dioxide Detection
Other possibilities:
gas chromatography
infrared spectrometry
chemical precipitation
TTFN
RE: Carbon Dioxide Detection
I am using infrared spectroscopy .....but what components are required for the detection which is what i'm not sure about...
RE: Carbon Dioxide Detection
RE: Carbon Dioxide Detection
I'm not convinced that this is "as would be expected." The net signal of an IR detection is a combination of transmission and emission.
The CO2 absorption band does not imply zero transmission, particularly at short ranges, as might be configured in a lab. MODTRAN shows a 26% transmission at 4.255 microns at a distance of 4 meters.
Therefore, your subject's warm breath against a cold wall will appear somewhat warmer. The same subject's warm breath against a warm body may or may not appear colder.
TTFN
RE: Carbon Dioxide Detection
RE: Carbon Dioxide Detection
How tight is your bandpass filter? Don't forget that if your band pass filter is external to the dewar, it's emitting and reflecting as well and that stuff reaches the detector. Did you move the camera to do the different measurements?
The CO2 spike at short ranges is VERY narrow. The same MODTRAN run shows transmissions higher than 60% at both 4.167 and 4.348 microns at the same range. That means that your measured signal is a weighted average:
~50%*background + ~50%*breath.
But, the radiance of breath or air, for that matter, is considerably lower than that of a solid material at the same temperature. The net effect is a net radiance that's warmer than room temperature, but colder than external body temperature.
TTFN
RE: Carbon Dioxide Detection
RE: Carbon Dioxide Detection