Ir detection limit

joshhan2000 · 20th December 2005, 07:27

We have all been hearing about IR detection of CO2. I can personal say I use the technique for many years in the lab. For the past 6 month I have be experimenting with the free radical separation of CO2. But there are limit to IR detection of CO2. One limit that has to be over come is at higher then one ATM gas is no longer following the ideal gas law. I know we have all read about PV=NRT but how many really under stand that this is called ideal gas law. It is name this because it is the way gas behaves in ideal condition. That means 1 ATM or lower and close to 20 deg C. After that we need to Van Der Waals equation which is:

This it the way you must look at gas in the non-ideal state. Now that you understand a little how gases work. I can come back to my point as the gases get more pressurized there are more electro static forces. Hydrogen bonding, Van Der Waals forces, London dispersion forces. These force make the CO2 behave differently then when under ideal condition. So not only do you have to deal with the Moisture content of the systems you also have to deal with Quantum Mechanics of the system. I am sure there has been a lot of very ingenious ways of dealing with the moisture content I would just like to know how they are planning to deal with a gas that is at 10 Atm. The follow are helpful web site.

http://www.licor.com/env/PDF_Files/co2_abs.pdf

http://www.ac.wwu.edu/~vawter/PhysicsNet/Topics/Thermal/vdWaalEquatOfState.html

**nigelh** · 20th December 2005, 11:05

Quote: (Originally Posted by joshhan2000)

But there are limit to IR detection of CO2. One limit that has to be over come is at higher then one ATM gas is no longer following the ideal gas law. I know we have all read about PV=NRT but how many really under stand that this is called ideal gas law. It is name this because it is the way gas behaves in ideal condition. That means 1 ATM or lower and close to 20 deg C. After that we need to Van Der Waals equation

Are you sure? The VdW values for CO2 are, admittedly, quite different from O2/N2/He but up to about 10bar the deviation from ideal is trivial (<5%) in biological terms. I quite like IR systems as they tend to give a bulk measure and with a bit of curve fitting their idiosyncrasies can be ironed out as they are predictable.
I think the big snag is, as you say, 100% condensing humidity.

joshhan2000 · 21st December 2005, 06:45

I was not talking about the deviation of the Pressure. There really is not much difference in that at all. I was talking about how IR work in detection of CO2. IR can only detect molecules that have a dipole moment. You can figure out the module by using symmetry operations theory. But needless to say CO2 has a dipole moment. Were O2 N2 He and H2 do not. This is what makes IR good at detecting CO2. But when you increase the pressure by 10 bars you have also decreased the space the gas occupies by 10 times. This decrease in space leads to formation of CO2 crystal structures. Although these crystal are quick forming and quick to fall apart they are still there. So when you use the 4500 nm wave length of light to activate the CO2 you will get a falsely high reading form the crystals and will not achieve the 97% accurate that we all want. I not saying that IR can not be adjusted using things like Fourier Transform or by doing a calibration scale but in the lab we just simply cut the gas pressure down. I know that last year when using IR to measure CO emission of cars it took 25 know samples to calibrate the IR to read acutely. IR is not a linear scale that we are all use to on the O2 sensors. It is polymeric and will take a lot of work to calibrate the scale properly.

**nigelh** · 21st December 2005, 10:35

Quote: (Originally Posted by joshhan2000)

I was not talking about the deviation of the Pressure. There really is not much difference in that at all.

Sorry. That's how I took VdW.

Quote:

But when you increase the pressure by 10 bars you have also decreased the space the gas occupies by 10 times. This decrease in space leads to formation of CO2 crystal structures. Although these crystal a quick forming and quick to fall apart the still are there.

This is new to me. I clearly need to read up.

Quote:

So when you use the 4500 nm wave length of light to activate the CO2 you will get a falsely high reading form the crystals and will not achieve the 97% accurate that we all want. I not saying that IR can not be adjusted using things like Fourier Transform or by doing a calibration scale but in the lab we just simply cut the gas pressure down. I know that last year when using IR to measure CO emission of cars it took 25 know samples to calibrate the IR to read acutely. IR is not a linear scale that we are all use to on the O2 sensors. It is polymeric and will take a lot of work to calibrate the scale properly.

I make a lot of my living doing measurement systems but mostly these days lumps of metal trailing nasty shock waves so I find this area interesting. Do I assume that the problem here is the CO2 is a sublimating solid? Does it even have a gaseous state at 10 bar? Sheesh. I think I'll go and sit in a darkened room and hold my head.

Thanks for the reply

joshhan2000 · 21st December 2005, 11:10

I was not saying that CO2 is sublimating that will not happen till about 1000 bar. I was saying that the CO2 will emit the IR radiation back out. This is why IR works. If the CO2 is 10 times closer then normal the gas will have a higher thermal conductivity.

paulraymaekers · 21st December 2005, 19:26

Quote: (Originally Posted by joshhan2000)

I was not saying that CO2 is sublimating that will not happen till about 1000 bar. I was saying that the CO2 will emit the IR radiation back out. This is why IR works. If the CO2 is 10 times closer then normal the gas will have a higher thermal conductivity.

?? are we talking about the same PPCO2 or the same FCO2 at 1 and 10 bar

?? is the effect so big when we have the same PPCO2 at 1 and at 10 bar, because this is what we want to mesure

regards
paul

Genesis · 21st December 2005, 23:05

I think the point he's trying to make is that the IR method of determining CO2 levels is disrupted to some degree (e.g. linearity is impacted) by the total pressure of the gas in the system (that is, P(absolute))

Determining absolute pressure though is easy. Indeed, you already have ambient pressure in most units, in that the processor has a depth sensor fitted to it in one form or another. This becomes a matter of computation and thus is solveable.

The larger issue has always seemed to be humidity. There are ways around that (drying the sample is not terribly difficult to accomplish - but it takes a god-awful amount of power, which is at a premium in a Rebreather.)

Taken as a whole they present a problem that so far has resisted a compact, energy-efficient solution.

joshhan2000 · 22nd December 2005, 02:27

No the point I was trying to make that even if you solve the moisture problem you will still have to solve the high pressure problem. CO2 reacts under high pressure. If you do not believe me ask some one that has had the Argon bottle toped of with CO2. Under pressure the CO2 reaction to form Carbonic acid. So even if you get all the moisture out of the loop you will not be able to get an accurate reading. There is a difference between precision and accuracy.

PeteS · 22nd December 2005, 03:16

Quote: (Originally Posted by joshhan2000)

CO2 reacts under high pressure. If you do not believe me ask some one that has had the Argon bottle toped of with CO2. Under pressure the CO2 reaction to form Carbonic acid.

Argon? Carbonic Acid? Small sharks?

I thought it was a reaction between CO2 and water that produced carbonic acid, hence acid rain. And that was all ambient pressure.

Ho hum, something new every day.......

joshhan2000 · 22nd December 2005, 03:34

at higher perssure it will react faster.

20th December 2005, 07:27	#1 (permalink)
joshhan2000 New Member Current Rebreather/s: Not Bought Yet Other Rebreather/s: Not Bought Yet Join Date: Dec 2005 Location: olympia wa usa Posts: 46	Ir detection limit We have all been hearing about IR detection of CO2. I can personal say I use the technique for many years in the lab. For the past 6 month I have be experimenting with the free radical separation of CO2. But there are limit to IR detection of CO2. One limit that has to be over come is at higher then one ATM gas is no longer following the ideal gas law. I know we have all read about PV=NRT but how many really under stand that this is called ideal gas law. It is name this because it is the way gas behaves in ideal condition. That means 1 ATM or lower and close to 20 deg C. After that we need to Van Der Waals equation which is: This it the way you must look at gas in the non-ideal state. Now that you understand a little how gases work. I can come back to my point as the gases get more pressurized there are more electro static forces. Hydrogen bonding, Van Der Waals forces, London dispersion forces. These force make the CO2 behave differently then when under ideal condition. So not only do you have to deal with the Moisture content of the systems you also have to deal with Quantum Mechanics of the system. I am sure there has been a lot of very ingenious ways of dealing with the moisture content I would just like to know how they are planning to deal with a gas that is at 10 Atm. The follow are helpful web site. http://www.licor.com/env/PDF_Files/co2_abs.pdf http://www.ac.wwu.edu/~vawter/PhysicsNet/Topics/Thermal/vdWaalEquatOfState.html
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20th December 2005, 11:05	#2 (permalink)
nigelh New Member Current Rebreather/s: Inspiration Vision Other CCR Other Rebreather/s: Inspiration Classic Other CCR Join Date: Mar 2005 Location: Brighton, Sussex, UK Posts: 792	Re: Ir detection limit Quote: (Originally Posted by joshhan2000) But there are limit to IR detection of CO2. One limit that has to be over come is at higher then one ATM gas is no longer following the ideal gas law. I know we have all read about PV=NRT but how many really under stand that this is called ideal gas law. It is name this because it is the way gas behaves in ideal condition. That means 1 ATM or lower and close to 20 deg C. After that we need to Van Der Waals equation Are you sure? The VdW values for CO2 are, admittedly, quite different from O2/N2/He but up to about 10bar the deviation from ideal is trivial (<5%) in biological terms. I quite like IR systems as they tend to give a bulk measure and with a bit of curve fitting their idiosyncrasies can be ironed out as they are predictable. I think the big snag is, as you say, 100% condensing humidity. __________________ nigelh
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21st December 2005, 06:45	#3 (permalink)
joshhan2000 New Member Current Rebreather/s: Not Bought Yet Other Rebreather/s: Not Bought Yet Join Date: Dec 2005 Location: olympia wa usa Posts: 46	Re: Ir detection limit I was not talking about the deviation of the Pressure. There really is not much difference in that at all. I was talking about how IR work in detection of CO2. IR can only detect molecules that have a dipole moment. You can figure out the module by using symmetry operations theory. But needless to say CO2 has a dipole moment. Were O2 N2 He and H2 do not. This is what makes IR good at detecting CO2. But when you increase the pressure by 10 bars you have also decreased the space the gas occupies by 10 times. This decrease in space leads to formation of CO2 crystal structures. Although these crystal are quick forming and quick to fall apart they are still there. So when you use the 4500 nm wave length of light to activate the CO2 you will get a falsely high reading form the crystals and will not achieve the 97% accurate that we all want. I not saying that IR can not be adjusted using things like Fourier Transform or by doing a calibration scale but in the lab we just simply cut the gas pressure down. I know that last year when using IR to measure CO emission of cars it took 25 know samples to calibrate the IR to read acutely. IR is not a linear scale that we are all use to on the O2 sensors. It is polymeric and will take a lot of work to calibrate the scale properly. Last edited by joshhan2000 : 21st December 2005 at 11:12.
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21st December 2005, 10:35	#4 (permalink)
nigelh New Member Current Rebreather/s: Inspiration Vision Other CCR Other Rebreather/s: Inspiration Classic Other CCR Join Date: Mar 2005 Location: Brighton, Sussex, UK Posts: 792	Re: Ir detection limit Quote: (Originally Posted by joshhan2000) I was not talking about the deviation of the Pressure. There really is not much difference in that at all. Sorry. That's how I took VdW. Quote: But when you increase the pressure by 10 bars you have also decreased the space the gas occupies by 10 times. This decrease in space leads to formation of CO2 crystal structures. Although these crystal a quick forming and quick to fall apart the still are there. This is new to me. I clearly need to read up. Quote: So when you use the 4500 nm wave length of light to activate the CO2 you will get a falsely high reading form the crystals and will not achieve the 97% accurate that we all want. I not saying that IR can not be adjusted using things like Fourier Transform or by doing a calibration scale but in the lab we just simply cut the gas pressure down. I know that last year when using IR to measure CO emission of cars it took 25 know samples to calibrate the IR to read acutely. IR is not a linear scale that we are all use to on the O2 sensors. It is polymeric and will take a lot of work to calibrate the scale properly. I make a lot of my living doing measurement systems but mostly these days lumps of metal trailing nasty shock waves so I find this area interesting. Do I assume that the problem here is the CO2 is a sublimating solid? Does it even have a gaseous state at 10 bar? Sheesh. I think I'll go and sit in a darkened room and hold my head. Thanks for the reply __________________ nigelh
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21st December 2005, 11:10	#5 (permalink)
joshhan2000 New Member Current Rebreather/s: Not Bought Yet Other Rebreather/s: Not Bought Yet Join Date: Dec 2005 Location: olympia wa usa Posts: 46	Re: Ir detection limit I was not saying that CO2 is sublimating that will not happen till about 1000 bar. I was saying that the CO2 will emit the IR radiation back out. This is why IR works. If the CO2 is 10 times closer then normal the gas will have a higher thermal conductivity.
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21st December 2005, 19:26	#6 (permalink)
paulraymaekers rEvo's daddy Current Rebreather/s: rEvo Other CCR Home Build Other Rebreather/s: rEvo Other CCR Home Build Join Date: May 2005 Location: belgium Posts: 1,384	Re: Ir detection limit Quote: (Originally Posted by joshhan2000) I was not saying that CO2 is sublimating that will not happen till about 1000 bar. I was saying that the CO2 will emit the IR radiation back out. This is why IR works. If the CO2 is 10 times closer then normal the gas will have a higher thermal conductivity. ?? are we talking about the same PPCO2 or the same FCO2 at 1 and 10 bar ?? is the effect so big when we have the same PPCO2 at 1 and at 10 bar, because this is what we want to mesure regards paul __________________ www.rEvo-rebreathers.com .... the earth is flat, Elvis is alive, and radial scrubbers give longer dwell time than axials...
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21st December 2005, 23:05	#7 (permalink)
Genesis Bubbless Box of Death Current Rebreather/s: Home Build Other Rebreather/s: Home Build Join Date: Oct 2005 Location: Sunny Florida Posts: 1,394	Re: Ir detection limit I think the point he's trying to make is that the IR method of determining CO2 levels is disrupted to some degree (e.g. linearity is impacted) by the total pressure of the gas in the system (that is, P(absolute)) Determining absolute pressure though is easy. Indeed, you already have ambient pressure in most units, in that the processor has a depth sensor fitted to it in one form or another. This becomes a matter of computation and thus is solveable. The larger issue has always seemed to be humidity. There are ways around that (drying the sample is not terribly difficult to accomplish - but it takes a god-awful amount of power, which is at a premium in a Rebreather.) Taken as a whole they present a problem that so far has resisted a compact, energy-efficient solution.
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22nd December 2005, 02:27	#8 (permalink)
joshhan2000 New Member Current Rebreather/s: Not Bought Yet Other Rebreather/s: Not Bought Yet Join Date: Dec 2005 Location: olympia wa usa Posts: 46	Re: Ir detection limit No the point I was trying to make that even if you solve the moisture problem you will still have to solve the high pressure problem. CO2 reacts under high pressure. If you do not believe me ask some one that has had the Argon bottle toped of with CO2. Under pressure the CO2 reaction to form Carbonic acid. So even if you get all the moisture out of the loop you will not be able to get an accurate reading. There is a difference between precision and accuracy.
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22nd December 2005, 03:16	#9 (permalink)
PeteS Consent Issued! Current Rebreather/s: Inspiration Classic Inspiration Vision Other Rebreather/s: Join Date: Jun 2005 Location: New Zealand Posts: 511	Re: Ir detection limit Quote: (Originally Posted by joshhan2000) CO2 reacts under high pressure. If you do not believe me ask some one that has had the Argon bottle toped of with CO2. Under pressure the CO2 reaction to form Carbonic acid. Argon? Carbonic Acid? Small sharks? I thought it was a reaction between CO2 and water that produced carbonic acid, hence acid rain. And that was all ambient pressure. Ho hum, something new every day....... __________________ Pete S. http://www.steggle.co.nz Every silver lining has a cloud
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22nd December 2005, 03:34	#10 (permalink)
joshhan2000 New Member Current Rebreather/s: Not Bought Yet Other Rebreather/s: Not Bought Yet Join Date: Dec 2005 Location: olympia wa usa Posts: 46	Re: Ir detection limit at higher perssure it will react faster.
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