Cis Lunar Mk 6

Barfab · 16th November 2007, 00:53

Quote: (Originally Posted by Tino de Rijk)

Nicolai,

Let’s not fight about definitions. “Calibration” and “validation” are quite broad terms, applicable to many applications and industries.
I just used a liberal interpretation of the terms to fit the difference between calibration in a CCR and the new way of dealing with cell behavior as used my Poseidon which I freely dubbed “validation”.
I have no desire to be scientifically of semantically correct.

As to your four scenario’s: the first three are clear and obvious and are indeed used as such in the MK-VI as far as we can tell from the white paper and Rich’ and Nigel’s explanations.

The fourth one (mixed mode, both solenoids active, creating a predetermined reference mix) however is not simple at all to pull off. The main point is that for the first three (only one solenoid on), the injection does not have to be very precise.
As long as the solenoid opens long enough to fully flush the little calibration chamber of the 1st cell within the MK-VI, it is fine, and you have a KNOWN gas to use as a reference, if combined with the ambient pressure coming from the pressure transducer, which these days are very accurate.

However, to get a reference MIX of two gasses is a whole different ballgame.
Now also both solenoids need to be calibrated, i.e. need to inject a very precise and very small amount of gas in order to get an accurate mix to calibrate (not validate) against. This effectively means it will have to have a very accurate flowrate, regardless of temperature, ambient pressure, intermediate pressure etc. If a solenoid is even just a very little bit off, you get a different mix than expected in the calibration chamber.

It would in fact have to be far more accurate than the mass flow orifices in MCCR’s, where it really doesn’t matter if it injects 0.50 or 0.52 or 0.48 liter per minute: acceptable margins are quite wide.

The only way known to me to do that is by measuring it against a flowmeter, which you can not easily do while diving.
In order to do this in a reliable way, you would have to have an in-dive way of constantly checking the precise flowrate of the solenoid – yet another level of calibration and validation, this time for the solenoids, to add to the equation and complexity.

So, for all practical reasons, I don’t see this as an easy thing to pull off, unless I’m overlooking something obvious and/or the Poseidon boys have come up with something revolutionary to do that.

Ciao,

Tino.

I don'y understand why you think is necessary a precise CMF flow on the cell. I think that the small amount of gas is mainly function of the time when the solenoid is on.
Ciao
Fabio

silent running · 16th November 2007, 01:10

Quote: (Originally Posted by deepreef)

Not true at all -- the diver only needs to know this stuff if the diver wants to *intentionally* dive with oxygen that is not within tolerances of proximity to 100%. The basic sports level diver will simply get a "Do Not Dive" alarm, and will be pissed off, and will send Poseidon a nasty letter -- but will at least be alive.

Now, it may well be that there are parts of the world where sufficiently pure O2 is simply not available -- in which case the diver cannot dive. Period. (At least not safely). But this is true of ALL rebreathers -- the difference is that the MK-VI is capable of *determining* that the O2 is out of tolerance, and is thus capable of alerting an otherwise naive diver of the problem.

Aloha,
Rich

P.S. Back to work for now -- more later....

Hi Rich, why not allow the MK6 to operate with O2 purity down to 94%? I'm guessing that MK6 divers will be discouraged from diving at 1.4 due to the high CNS and OTUs over multiple days of diving. And as Tino said above, the reamaining % is likely N2 or Argon and most of the O2 injects will be during ascent and the PP of these other trace gases will be decreasing.

For me and probably most traveling divers, the unit not being able to function with less than 99% would be a deal breaker as it would rule out most of the Pacific and you more than anybody must know what a crime that would be... -Andy

Tony_Q · 16th November 2007, 01:31

Hi Rich,

Thanks for your response. Very interesting to understand the design emphasis on validation rather than calibration.

My use of the word "conventional" was with respect to use of 3 cells in eCCRs, not the voting logic used to estimate PO2 for oxygen control purposes. Loose wording, sorry.

I was really trying to make one key point in my post which you expressed very well and more succintly in your response:
"it is about knowing whether or not you can trust those values as being representative of what you're actually breathing."

ASV goes a long way towards addressing this issue but can never solve it completely because of the possibility of gas sampling or contamination problems which testing of an oxygen cell can never detect.

As long as divers understand this point (ASV test is good doesn't always mean breathing gas is good) and are alert to its implications, I fully agree that this technology is a great step forward.

The above raises interesting implications for diver training and skill level required to safely operate this unit as compared to that required for existing eCCRs.

Regards,
Tony

najones · 16th November 2007, 04:23

Quote: (Originally Posted by silent running)

Hi Rich, why not allow the MK6 to operate with O2 purity down to 94%? I'm guessing that MK6 divers will be discouraged from diving at 1.4 due to the high CNS and OTUs over multiple days of diving. And as Tino said above, the reamaining % is likely N2 or Argon and most of the O2 injects will be during ascent and the PP of these other trace gases will be decreasing.

For me and probably most traveling divers, the unit not being able to function with less than 99% would be a deal breaker as it would rule out most of the Pacific and you more than anybody must know what a crime that would be... -Andy

Andy I'm afraid that you have it backwards. The way the MK6 works, it can easily handle say 94% O2. The more interesting question is whether it should allow someone to dive such a mix. This is a marketing issue. As I previously posted, support for diving such a mix is easy to add (and will be added). What is TBD is who gets to use this feature.

silent running · 16th November 2007, 07:07

Quote: (Originally Posted by najones)

Andy I'm afraid that you have it backwards. The way the MK6 works, it can easily handle say 94% O2. The more interesting question is whether it should allow someone to dive such a mix. This is a marketing issue. As I previously posted, support for diving such a mix is easy to add (and will be added). What is TBD is who gets to use this feature.

Hi Nigel, I thought that was the ? I posed:why not allow a diver to dive down to 94%? The most obvious limitation is that one cannot reach a 1.4 SP without a software fix. But why would any CCR diver will want to do multple dives per day at 1.4?

The other issue is the unknown gas%: what is it and what exact fraction is it?

I have no trouble believing that the MK6 can figure out the excact O2% and adapt automatically and I'm pleased/impressed that it can do so. But I think that if the unit is supposed to both simplify CCR diving for the masses make it more safe, dealing effectively with sagging O2 purity in remote dive destinations is not a lot to ask of such a sophisticated device.

The big ? is: what are the trace gasses and what % of these gases are tolerable in the O2 supply for a CCR diver on a multiday CCR trip? -Andy

Tino de Rijk · 16th November 2007, 12:13

Quote: (Originally Posted by Barfab)

I don'y understand why you think is necessary a precise CMF flow on the cell. I think that the small amount of gas is mainly function of the time when the solenoid is on.
Ciao
Fabio

Because you need to have an exact, known mix if you want to use if for calibration (not for "just" validation, using my previous definitions).
If e.g. both the O2 solenoid and the diluent (=air) solenoid would be able to inject EXACTLY the same amount, you will have a predictable mix of EAN60.45 in the loop ((1.00 + 0.209) / 2).
Such a mix would enable you to calibrate till around 20 meter or so (where it gives a PO2 of 3 x .6045 = 1.81 bar, and assuming you can test linearity of the cell till around that value). That is better than 6 meters, but still not that deep.
So, for deeper calibration, you would need to alter the mix, make it more "lean", i.e. inject even smaller amounts of O2 in the mix. Less than a cc or so....

However, if for whatever reason one of the two solenoids is only the slightest bit off, you'll have a different, and unknown mix, to which you cannot calibrate (as it is unknown).
The gas calibration chamber of cell no. 1 that the system uses is most likely quite small (I assume some cubic centimers; certainly not liters, otherwise it would slow down the calibrations as it would take too loong to flush), so it would have to be an injection that should be exact to a level of one cc or less or so in order to be accurate.

And no, it is not only a function of time the solenoid is open.
There is quite some literature around here on Rebreather World on the fysics of CMF devices and how to get reliable flowrates.
In the case of a solenoid that is even more difficult. E.g. very short injection times (sub-second) will not necesarily yield the same flowrates as longer ones: there is a sort of start/stop effect. This is something specific to solenoids; CMF's in MCCR's are "always on".
You are right that timing is of course the item to ultimately control it with, but the volume injected is "flowrate (in liter/minute) * time (in minutes)" that gives flow (in liters). So both need to be known. Now, time is easy and accurate to control and even (electronically) verify, but flowrate is not. At least not to my knowledge, in the level of accuracy needed here.

Even if you could control the volumes perfectly, the next thing you need to assure is perfect mixing of the two gasses, to avoid having small pockets of one gas in the small chamber. complicates things even further....

But I would be very happy if someone proves me wrong! Never too old to learn...!

Ciao,

Tino.

Davichin · 16th November 2007, 20:03

Quote: (Originally Posted by Ben Field)

Does your depth sensor recalibrate for Fresh and salt water, can it be set to different salinity?

Please correct me because I most likely wrong

, but I think it does not matter the density of the fluid you are diving in because the depth sensors are pressure sensors that then convert to depth.
As long as they are good and linear at measuring pressure (so they are good at calculating your PO2, N2 absorving etc...) you don´t really need to know if you are really geometrically at 30 or 30.5 m, do you?.

najones · 16th November 2007, 22:14

Quote: (Originally Posted by silent running)

Hi Nigel, I thought that was the ? I posed:why not allow a diver to dive down to 94%? The most obvious limitation is that one cannot reach a 1.4 SP without a software fix. But why would any CCR diver will want to do multple dives per day at 1.4?

The other issue is the unknown gas%: what is it and what exact fraction is it?

I have no trouble believing that the MK6 can figure out the excact O2% and adapt automatically and I'm pleased/impressed that it can do so. But I think that if the unit is supposed to both simplify CCR diving for the masses make it more safe, dealing effectively with sagging O2 purity in remote dive destinations is not a lot to ask of such a sophisticated device.

The big ? is: what are the trace gasses and what % of these gases are tolerable in the O2 supply for a CCR diver on a multiday CCR trip? -Andy

The issue is one of weighing risks. If you allow / require someone to set a parameter, then you have to evaluate the probability of them setting it incorrectly and the consequences of them doing so. In this case what are the relative risks / benefits of the rig requiring the O2 to be > than say 98.5% pure versus allowing a user to dive on say 90% O2 by having the diver inform the system that they are intentionally diving on lousy O2? By definition technical divers lean towards control and configuration of their equipment and can mostly be relied upon to correctly set parameters. I'm not sure this is true of sport divers.

To summarize, a technical version of the MKVI would allow you to set the actual FO2 of the O2 supply.

The sport version of the MKVI may or may not allow you to set the actual FO2 of the of the O2 supply, depending upon a decision from the marketing folks.

For both versions of the rig, the control system will be able to detect an O2 supply that differs from the expected FO2 by more than about +/- 2%. In the event that the FO2 is too far out, then the rig will "fail" its initial (surface) calibration. For the technical diver, the remedial action will be trivial - tell the rig what you are really diving. The sport diver will have this capability if the marketing folks concur.

Tino de Rijk · 17th November 2007, 09:15

Quote: (Originally Posted by silent running)

The big ? is: what are the trace gasses and what % of these gases are tolerable in the O2 supply for a CCR diver on a multiday CCR trip? -Andy

Andy, you're right in this of course, but this applies to each & any Rebreather out there (with the exception on SCR's running on Nitrox - and even there, depending on how the Nitrox was produced). Both are not toxic, but Argon might have a slight negative effect on deco.
It usually is N2 and/or Argon, depending on production method.

But I agree with you: if the O2 content is quite low, and you really don't trust or can't verify the source: don't use it. Determining the O2 fraction is the easy bit.... I'd say this is an education issue, not a technical one. We cannot expect Rebreather's to have a full gas-chromatograph on board for gas analyses (well, maybe the ORB... :-) ).
Applying this to the MK-VI: should IMHO be part of the training to say something like "if O2 purity is below 95% or so, make sure that the gas is officially rated for breathing and diving. If not: don't use it". But again: applies to all Rebreather's.

ciao,

Tino.

najones · 17th November 2007, 11:18

Quote: (Originally Posted by Davichin)

Please correct me because I most likely wrong

, but I think it does not matter the density of the fluid you are diving in because the depth sensors are pressure sensors that then convert to depth.
As long as they are good and linear at measuring pressure (so they are good at calculating your PO2, N2 absorving etc...) you don´t really need to know if you are really geometrically at 30 or 30.5 m, do you?.

Davichin: You are correct. Dive equipment does not use depth sensors per se. They use absolute pressure sensors from which depth is inferred.

16th November 2007, 00:53	#221 (permalink)
Barfab New Member Current Rebreather/s: Inspiration Classic Megalodon Ouroboros Ray Azimuth Other SCR Other Rebreather/s: Ray Azimuth Other SCR Join Date: Feb 2005 Location: Italy Posts: 50	Re: Cis Lunar Mk 6 Quote: (Originally Posted by Tino de Rijk) Nicolai, Let’s not fight about definitions. “Calibration” and “validation” are quite broad terms, applicable to many applications and industries. I just used a liberal interpretation of the terms to fit the difference between calibration in a CCR and the new way of dealing with cell behavior as used my Poseidon which I freely dubbed “validation”. I have no desire to be scientifically of semantically correct. As to your four scenario’s: the first three are clear and obvious and are indeed used as such in the MK-VI as far as we can tell from the white paper and Rich’ and Nigel’s explanations. The fourth one (mixed mode, both solenoids active, creating a predetermined reference mix) however is not simple at all to pull off. The main point is that for the first three (only one solenoid on), the injection does not have to be very precise. As long as the solenoid opens long enough to fully flush the little calibration chamber of the 1st cell within the MK-VI, it is fine, and you have a KNOWN gas to use as a reference, if combined with the ambient pressure coming from the pressure transducer, which these days are very accurate. However, to get a reference MIX of two gasses is a whole different ballgame. Now also both solenoids need to be calibrated, i.e. need to inject a very precise and very small amount of gas in order to get an accurate mix to calibrate (not validate) against. This effectively means it will have to have a very accurate flowrate, regardless of temperature, ambient pressure, intermediate pressure etc. If a solenoid is even just a very little bit off, you get a different mix than expected in the calibration chamber. It would in fact have to be far more accurate than the mass flow orifices in MCCR’s, where it really doesn’t matter if it injects 0.50 or 0.52 or 0.48 liter per minute: acceptable margins are quite wide. The only way known to me to do that is by measuring it against a flowmeter, which you can not easily do while diving. In order to do this in a reliable way, you would have to have an in-dive way of constantly checking the precise flowrate of the solenoid – yet another level of calibration and validation, this time for the solenoids, to add to the equation and complexity. So, for all practical reasons, I don’t see this as an easy thing to pull off, unless I’m overlooking something obvious and/or the Poseidon boys have come up with something revolutionary to do that. Ciao, Tino. I don'y understand why you think is necessary a precise CMF flow on the cell. I think that the small amount of gas is mainly function of the time when the solenoid is on. Ciao Fabio __________________ World is a....Rebreather!
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16th November 2007, 01:10	#222 (permalink)
silent running Mature mouth breather Current Rebreather/s: Prism Topaz Other Rebreather/s: Join Date: Jun 2005 Location: U.S.A. Brooklyn, New York Posts: 1,813	Re: Cis Lunar Mk 6 Quote: (Originally Posted by deepreef) Not true at all -- the diver only needs to know this stuff if the diver wants to intentionally dive with oxygen that is not within tolerances of proximity to 100%. The basic sports level diver will simply get a "Do Not Dive" alarm, and will be pissed off, and will send Poseidon a nasty letter -- but will at least be alive. Now, it may well be that there are parts of the world where sufficiently pure O2 is simply not available -- in which case the diver cannot dive. Period. (At least not safely). But this is true of ALL rebreathers -- the difference is that the MK-VI is capable of determining that the O2 is out of tolerance, and is thus capable of alerting an otherwise naive diver of the problem. Aloha, Rich P.S. Back to work for now -- more later.... Hi Rich, why not allow the MK6 to operate with O2 purity down to 94%? I'm guessing that MK6 divers will be discouraged from diving at 1.4 due to the high CNS and OTUs over multiple days of diving. And as Tino said above, the reamaining % is likely N2 or Argon and most of the O2 injects will be during ascent and the PP of these other trace gases will be decreasing. For me and probably most traveling divers, the unit not being able to function with less than 99% would be a deal breaker as it would rule out most of the Pacific and you more than anybody must know what a crime that would be... -Andy
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16th November 2007, 01:31	#223 (permalink)
Tony_Q New Member Current Rebreather/s: Optima Other Rebreather/s: Join Date: May 2005 Location: Australia Posts: 44	Re: Cis Lunar Mk 6 Hi Rich, Thanks for your response. Very interesting to understand the design emphasis on validation rather than calibration. My use of the word "conventional" was with respect to use of 3 cells in eCCRs, not the voting logic used to estimate PO2 for oxygen control purposes. Loose wording, sorry. I was really trying to make one key point in my post which you expressed very well and more succintly in your response: "it is about knowing whether or not you can trust those values as being representative of what you're actually breathing." ASV goes a long way towards addressing this issue but can never solve it completely because of the possibility of gas sampling or contamination problems which testing of an oxygen cell can never detect. As long as divers understand this point (ASV test is good doesn't always mean breathing gas is good) and are alert to its implications, I fully agree that this technology is a great step forward. The above raises interesting implications for diver training and skill level required to safely operate this unit as compared to that required for existing eCCRs. Regards, Tony
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16th November 2007, 04:23	#224 (permalink)
najones New Member Current Rebreather/s: Not Bought Yet Other Rebreather/s: Not Bought Yet Join Date: Nov 2007 Location: maryland Posts: 17	Re: Cis Lunar Mk 6 Quote: (Originally Posted by silent running) Hi Rich, why not allow the MK6 to operate with O2 purity down to 94%? I'm guessing that MK6 divers will be discouraged from diving at 1.4 due to the high CNS and OTUs over multiple days of diving. And as Tino said above, the reamaining % is likely N2 or Argon and most of the O2 injects will be during ascent and the PP of these other trace gases will be decreasing. For me and probably most traveling divers, the unit not being able to function with less than 99% would be a deal breaker as it would rule out most of the Pacific and you more than anybody must know what a crime that would be... -Andy Andy I'm afraid that you have it backwards. The way the MK6 works, it can easily handle say 94% O2. The more interesting question is whether it should allow someone to dive such a mix. This is a marketing issue. As I previously posted, support for diving such a mix is easy to add (and will be added). What is TBD is who gets to use this feature.
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16th November 2007, 07:07	#225 (permalink)
silent running Mature mouth breather Current Rebreather/s: Prism Topaz Other Rebreather/s: Join Date: Jun 2005 Location: U.S.A. Brooklyn, New York Posts: 1,813	Re: Cis Lunar Mk 6 Quote: (Originally Posted by najones) Andy I'm afraid that you have it backwards. The way the MK6 works, it can easily handle say 94% O2. The more interesting question is whether it should allow someone to dive such a mix. This is a marketing issue. As I previously posted, support for diving such a mix is easy to add (and will be added). What is TBD is who gets to use this feature. Hi Nigel, I thought that was the ? I posed:why not allow a diver to dive down to 94%? The most obvious limitation is that one cannot reach a 1.4 SP without a software fix. But why would any CCR diver will want to do multple dives per day at 1.4? The other issue is the unknown gas%: what is it and what exact fraction is it? I have no trouble believing that the MK6 can figure out the excact O2% and adapt automatically and I'm pleased/impressed that it can do so. But I think that if the unit is supposed to both simplify CCR diving for the masses make it more safe, dealing effectively with sagging O2 purity in remote dive destinations is not a lot to ask of such a sophisticated device. The big ? is: what are the trace gasses and what % of these gases are tolerable in the O2 supply for a CCR diver on a multiday CCR trip? -Andy
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16th November 2007, 12:13	#226 (permalink)
Tino de Rijk Old, maybe one day wise Current Rebreather/s: Inspiration Vision Other Rebreather/s: Inspiration Classic Evolution Join Date: Mar 2006 Location: Amsterdam Posts: 325	Re: Cis Lunar Mk 6 Quote: (Originally Posted by Barfab) I don'y understand why you think is necessary a precise CMF flow on the cell. I think that the small amount of gas is mainly function of the time when the solenoid is on. Ciao Fabio Because you need to have an exact, known mix if you want to use if for calibration (not for "just" validation, using my previous definitions). If e.g. both the O2 solenoid and the diluent (=air) solenoid would be able to inject EXACTLY the same amount, you will have a predictable mix of EAN60.45 in the loop ((1.00 + 0.209) / 2). Such a mix would enable you to calibrate till around 20 meter or so (where it gives a PO2 of 3 x .6045 = 1.81 bar, and assuming you can test linearity of the cell till around that value). That is better than 6 meters, but still not that deep. So, for deeper calibration, you would need to alter the mix, make it more "lean", i.e. inject even smaller amounts of O2 in the mix. Less than a cc or so.... However, if for whatever reason one of the two solenoids is only the slightest bit off, you'll have a different, and unknown mix, to which you cannot calibrate (as it is unknown). The gas calibration chamber of cell no. 1 that the system uses is most likely quite small (I assume some cubic centimers; certainly not liters, otherwise it would slow down the calibrations as it would take too loong to flush), so it would have to be an injection that should be exact to a level of one cc or less or so in order to be accurate. And no, it is not only a function of time the solenoid is open. There is quite some literature around here on Rebreather World on the fysics of CMF devices and how to get reliable flowrates. In the case of a solenoid that is even more difficult. E.g. very short injection times (sub-second) will not necesarily yield the same flowrates as longer ones: there is a sort of start/stop effect. This is something specific to solenoids; CMF's in MCCR's are "always on". You are right that timing is of course the item to ultimately control it with, but the volume injected is "flowrate (in liter/minute) * time (in minutes)" that gives flow (in liters). So both need to be known. Now, time is easy and accurate to control and even (electronically) verify, but flowrate is not. At least not to my knowledge, in the level of accuracy needed here. Even if you could control the volumes perfectly, the next thing you need to assure is perfect mixing of the two gasses, to avoid having small pockets of one gas in the small chamber. complicates things even further.... But I would be very happy if someone proves me wrong! Never too old to learn...! Ciao, Tino.
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16th November 2007, 20:03	#227 (permalink)
Davichin New Member Current Rebreather/s: Not Bought Yet Other Rebreather/s: Not Bought Yet Join Date: May 2006 Location: Canary Islands Posts: 2	Re: Cis Lunar Mk 6 Quote: (Originally Posted by Ben Field) Does your depth sensor recalibrate for Fresh and salt water, can it be set to different salinity? Please correct me because I most likely wrong , but I think it does not matter the density of the fluid you are diving in because the depth sensors are pressure sensors that then convert to depth. As long as they are good and linear at measuring pressure (so they are good at calculating your PO2, N2 absorving etc...) you don´t really need to know if you are really geometrically at 30 or 30.5 m, do you?.
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16th November 2007, 22:14	#228 (permalink)
najones New Member Current Rebreather/s: Not Bought Yet Other Rebreather/s: Not Bought Yet Join Date: Nov 2007 Location: maryland Posts: 17	Re: Cis Lunar Mk 6 Quote: (Originally Posted by silent running) Hi Nigel, I thought that was the ? I posed:why not allow a diver to dive down to 94%? The most obvious limitation is that one cannot reach a 1.4 SP without a software fix. But why would any CCR diver will want to do multple dives per day at 1.4? The other issue is the unknown gas%: what is it and what exact fraction is it? I have no trouble believing that the MK6 can figure out the excact O2% and adapt automatically and I'm pleased/impressed that it can do so. But I think that if the unit is supposed to both simplify CCR diving for the masses make it more safe, dealing effectively with sagging O2 purity in remote dive destinations is not a lot to ask of such a sophisticated device. The big ? is: what are the trace gasses and what % of these gases are tolerable in the O2 supply for a CCR diver on a multiday CCR trip? -Andy The issue is one of weighing risks. If you allow / require someone to set a parameter, then you have to evaluate the probability of them setting it incorrectly and the consequences of them doing so. In this case what are the relative risks / benefits of the rig requiring the O2 to be > than say 98.5% pure versus allowing a user to dive on say 90% O2 by having the diver inform the system that they are intentionally diving on lousy O2? By definition technical divers lean towards control and configuration of their equipment and can mostly be relied upon to correctly set parameters. I'm not sure this is true of sport divers. To summarize, a technical version of the MKVI would allow you to set the actual FO2 of the O2 supply. The sport version of the MKVI may or may not allow you to set the actual FO2 of the of the O2 supply, depending upon a decision from the marketing folks. For both versions of the rig, the control system will be able to detect an O2 supply that differs from the expected FO2 by more than about +/- 2%. In the event that the FO2 is too far out, then the rig will "fail" its initial (surface) calibration. For the technical diver, the remedial action will be trivial - tell the rig what you are really diving. The sport diver will have this capability if the marketing folks concur.
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17th November 2007, 09:15	#229 (permalink)
Tino de Rijk Old, maybe one day wise Current Rebreather/s: Inspiration Vision Other Rebreather/s: Inspiration Classic Evolution Join Date: Mar 2006 Location: Amsterdam Posts: 325	Re: Cis Lunar Mk 6 Quote: (Originally Posted by silent running) The big ? is: what are the trace gasses and what % of these gases are tolerable in the O2 supply for a CCR diver on a multiday CCR trip? -Andy Andy, you're right in this of course, but this applies to each & any Rebreather out there (with the exception on SCR's running on Nitrox - and even there, depending on how the Nitrox was produced). Both are not toxic, but Argon might have a slight negative effect on deco. It usually is N2 and/or Argon, depending on production method. But I agree with you: if the O2 content is quite low, and you really don't trust or can't verify the source: don't use it. Determining the O2 fraction is the easy bit.... I'd say this is an education issue, not a technical one. We cannot expect Rebreather's to have a full gas-chromatograph on board for gas analyses (well, maybe the ORB... :-) ). Applying this to the MK-VI: should IMHO be part of the training to say something like "if O2 purity is below 95% or so, make sure that the gas is officially rated for breathing and diving. If not: don't use it". But again: applies to all Rebreather's. ciao, Tino.
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17th November 2007, 11:18	#230 (permalink)
najones New Member Current Rebreather/s: Not Bought Yet Other Rebreather/s: Not Bought Yet Join Date: Nov 2007 Location: maryland Posts: 17	Re: Cis Lunar Mk 6 Quote: (Originally Posted by Davichin) Please correct me because I most likely wrong , but I think it does not matter the density of the fluid you are diving in because the depth sensors are pressure sensors that then convert to depth. As long as they are good and linear at measuring pressure (so they are good at calculating your PO2, N2 absorving etc...) you don´t really need to know if you are really geometrically at 30 or 30.5 m, do you?. Davichin: You are correct. Dive equipment does not use depth sensors per se. They use absolute pressure sensors from which depth is inferred. Last edited by najones : 17th November 2007 at 14:07.
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