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| Measure 100% of CO2 inside a chamber |
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| CatalinaWOW:
OK. Assuming you wait long enough for the gases in the cylinder to be well mixed you might do well to measured optical absorbtion. At peak absorbtion around 4.2 micrometers absorbtion at standard pressure will be near total over only a few dozen cm. By picking a narrow band near the peak absorbtion you can get an "easily" measured quantity that should be able to directly measure the CO2 density. Of course this is designing, building and calibrating an instrument, not buying a cheap component. |
| LaserSteve:
The Co2meter folks are probably bombarded by the "recreational pharmaceutical" people about their sensors. I could see them limiting development data for that reason. Based on past experience if you call with a legitimate use, I Think you would get very good integration support. Steve |
| Dave_PT:
Lets assume that the normal air is (only for simplification) only one gas with a specific "n" (number of moles). If the chamber has the same volume and the same temperature, from ideal gas law, I can get: PV=nRT => P=n*(RT/V) => P=n*k And we can assume that the total pressure inside the chamber is equal to the sum of the gases pressures inside. So Ptot = Pa + Pb, "a" and "b" are ideal gases. This is valid for the 2 gases, and if the constant k is equal to both, so I can write: Pa/na = Pb/nb I can put all math into a system of equations. Ptot = Pa + Pb Pa/na = Pb/nb In summary I can control the percentage of the mixture only by looking at the pressures. By now, let's ignore all the specific calculations and assume that (assuming only) we have 2 gases with the same number moles. So if I pressure the chamber with 1bar of gas "a" and add a 1 bar of gas "b", I think that is correct to assume that the mixture have 50% of gas "a" and 50% of gas "b" (with a fan inside to mixture the gases). The next step is decompose the normal air (assuming: 78% nitrogen, 21% oxygen, 1% argon) and solve all the math. Then the MCU will do the smart calculations and control some electrovalves (gas "a", gas "b" and chamber exhaust) and use the feedback of a good pressure sensor. With all of this and the logging I think that is possible to achieve the expected results. Right now, I'm waiting some answers from the university... Thank you all for the support. |
| CatalinaWOW:
Your approach will work if you meet the condition that the exhaust gas is a perfect mixture of the input gases. It is analogous to fluid dilution in beakers. The only way I can see to achieve that is to never have an input valve and exhaust valve open at the same time, and to force a delay between opening the exhaust and input long enough to achieve perfect mixing. Which may work for your situation, though you earlier mention continuous flow. The interval could be reduced with a stirring fan. You may have to compensate for gas absorbed by fixtures and samples in the chamber (can be detected by anomolous pv=nrt results). Will definitely need to measure both pressure and temp, s constant temp assumption will not be valid. |
| ehughes:
I have done something similar (for Hydrogen) acoustically. If you can also measure temperature with a decent amount of accuracy and precision then it is pretty straightforward. Sound speed in C02 is well understood. Since you have some situation awareness (you know what gases are present) it should be pretty easy to do. We used a resonator to extract sound speed but a time of flight could work well. There really isn't much off the shelf but you could cobble something together. |
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