sunnyboy
Member
+1 (several times, in fact)
+1 (several times, in fact)
decostanza
New Member
"IMHO, the problem with current limited cells begins with calling this a failure. It's not. Current limiting is what happens when a cell is running out of lead. Anyone calling an empty cylinder a failed cylinder? A car that ran out of gas a failed tank? No? Well then. Same thing. "
Embee,
That is a very profound way of looking at it and I hadn't considered that before. Thank you for sharing that perspective.
Don
Embee,
That is a very profound way of looking at it and I hadn't considered that before. Thank you for sharing that perspective.
Don
Mark Chase
ATB=AlwaysTalkingBollocks
Because before you did the flush cell 2 was reading 2.2
Cell 1 & 3 only red 1.3?
SO the unit was working hard to keep 1 & 3 up to 1.3 set point but the cells are limited at 1.3 so the unit is overcompensating which is why cell 2 (the only working cell) is reading 2.2
And yes you would confirm this with small manual injections of 02 to OVER 1.3. You should see cells 1 2 & 3 hit 1.3 but cell 1 & 3 will stop rising where as cell 2 will carry on reafing higher as you inject. Prooving 1 & 3 are stuck at 1.3 max reading capabuility
Hope that makes sense
matt
Well-Known Member
emmbee said:Imagine two current limited cells, but not quite the same. They read, respectively, 1.22 and 1.15 at 1.3, 1.3 and 1.215 at 1.5, 1.38 and 1.22 at 1.7 (in case you're wondering I sort of picked that off Paul Raymaekers's paper on page 1 of this thread, I'm not completely making this up). Assume the third cell is correct. The average system will inject until the ppO2 is 1.7: (1.38+1.22)/2=1.3. The median will only inject to 1.5: median of 1.5, 1.3 and 1.215 is 1.3. I know people dive 1.5. 1.7, I've never heard anyone say it's a good idea. Not a big help, but some help nonetheless.
I have never understood why we cannot have a warning for potential current limiting. Here we have the unit asking the solenoid to deliver O2 and one cell responding when the other 2 are not. This could be a solenoid/gas-supply issue, but either way something is a miss and the unit could flag #3 as needing confirmation with a flush (say) after the 12th solenoid injection.
Agreed the human is the ultimate computer, but surely adding some simple warning (not an error) to the current limit case would be possible. Are there some cases where this warning would give false-positive?
Matt.
I have never understood why we cannot have a warning for potential current limiting. Here we have the unit asking the solenoid to deliver O2 and one cell responding when the other 2 are not. This could be a solenoid/gas-supply issue, but either way something is a miss and the unit could flag #3 as needing confirmation with a flush (say) after the 12th solenoid injection.Imagine two current limited cells, but not quite the same. They read, respectively, 1.22 and 1.15 at 1.3, 1.3 and 1.215 at 1.5, 1.38 and 1.22 at 1.7 (in case you're wondering I sort of picked that off Paul Raymaekers's paper on page 1 of this thread, I'm not completely making this up
Agreed the human is the ultimate computer, but surely adding some simple warning (not an error) to the current limit case would be possible. Are there some cases where this warning would give false-positive?
Hi Matt,
Bearing in mind that I don't work in the industry, and I don't know what their actual justification is...
I don't think what you're proposing is a good idea.
Because, the way I see it, the real problem with current limitation is not the ceiling on ppO2 reading, it's the non-linearity before that (the ppO2 reading doesn't increase as much as the actual ppO2).
It's not when two cells are stuck below setpoint. Anyone reading 1.2 1.25 2.4, with the solenoid firing constantly, and only the last cell moving, up, will go WTF?
It's when they do reach setpoint, but at an unsafe ppO2. Like in my example. Note that in principle you could very well read 1.32 1.28 2.4.
In other words, your idea would warn of a possible problem when there's no doubt in any one's mind that there is a problem, and probably what the likely cause is. It would do nothing in the much more insidious, and therefore dangerous, scenario: the cells are responding, the machine is reaching setpoint. So not very useful.
In addition, it would give the impression that if there is a possible current limiting, then "the machine will warn me". So possibly downright dangerous.
Cheers,
Matthieu
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matt
Well-Known Member
Not sure that everyone is in no doubt about this problem and actually knows how to deal with it - I'd suggest the the machine will warn me mentality is already out there, but with some common cases omitted.
Matt.
Mark Chase
ATB=AlwaysTalkingBollocks
Its an excelent idea to spend out on an electronic gizmo with obvious life saveing potential
BUT
Without an electronic gizmo to check for current limited cells YOU MUST check them manualy every dive
WIth an electronic gizmo to warn you of potential current limited cells YOU MUST check them every dive to make sure the electronic gizmo is working :moon:
Of course when you dont have a gizmo you are forced into manual checks as you have no other choice. I call this Sharp Stick Dicipline
If you do have a gizmo you will no doubt double check it manualy a few times then ignore it and become complacent till one day it fails when of course you will most likley die. I call this a triumph of Darwin over Tec
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matt
Well-Known Member
I'd bet you 50p that the majority of divers are checking this occasionally and that the number not checking it at all is large.
But we can't have the bet, because we have no way to know.
What would be interesting to know is why people with old cells still trust them, to the point where current-limiting is a killer.
Personally I have not seen a current-limited cell in my unit - for the first 9 years I changed all 3 at once every 12 months and for the last 6 years I have change one every 3-4 months running the oldest to 18 months.
Cheers,
Matt.
But we can't have the bet, because we have no way to know.
What would be interesting to know is why people with old cells still trust them, to the point where current-limiting is a killer.
Personally I have not seen a current-limited cell in my unit - for the first 9 years I changed all 3 at once every 12 months and for the last 6 years I have change one every 3-4 months running the oldest to 18 months.
Cheers,
Matt.
Its an excelent idea to spend out on an electronic gizmo with obvious life saveing potential
BUT
Without an electronic gizmo to check for current limited cells YOU MUST check them manualy every dive
WIth an electronic gizmo to warn you of potential current limited cells YOU MUST check them every dive to make sure the electronic gizmo is working :moon:
Of course when you dont have a gizmo you are forced into manual checks as you have no other choice. I call this Sharp Stick Dicipline
If you do have a gizmo you will no doubt double check it manualy a few times then ignore it and become complacent till one day it fails when of course you will most likley die. I call this a triumph of Darwin over Tec
uwxplorer
rEvo carrier
Once the electronics is present, why not make it the best possible, in particular if it can save the life of someone who may not be complacent but task-loaded or cognitively impaired for reasons unknown and unpredictable?
I can buy the merits of manual versus electronics as far as making you aware of how the unit is supposed to work, etc, but we are talking about an electronic unit.
By definition, the electronic unit will kill you if it fails (and cells are parts of the unit) and you fail to notice it. Ergo, it needs to be designed to fail you the least possible, and I guess it could be argued that in the case we are discussing, an opportunity was missed to provide the user with a warning that something was obviously (I believe) amiss. I am not defending the principle of all-electronic rebreathers, just the fact that when it is so, it needs to be the least unsafe. I am no expert and will not testify in court, but my simple question is why this kind of simple tests is not implemented. I can buy the argument that it makes the code more complex, which may result in bugs, etc., but we are talking about a XXIst century unit, right? OK, bad remark, Airbus lost a jet on the assumption that a pilot would react intelligently to a repeated stall alarm. Stress situation anyone?
As argued before, cells can essentially get limited (or fail) whenever they feel like it (they don't need to be old: a shock, water, etc. can do the trick). Therefore it makes sense for an electronic unit to test whether the readings make any sense. In the accident discussed above, a reading over 2 at the specified depth doesn't make sense unless the pO2 is indeed quite high (hypothesis 1) or the cell is "failing" in a very unusual manner (hypothesis 2).
In hypothesis one, a warning must be displayed that most likely the other two cells (whether or not they agree with each other, but in particular if they BOTH read below the setpoint after a while at max depth and after repeated solenoid injection - potentially with no O2 injected if the O2 cylinder is empty or closed) are now suspicious. The recommended course action can be debated: disregard the two other cells, instruct to bailout, your recommendation here, etc.
In hypothesis two, the situation is still uncommon in the sense that, as in hypothesis 1, there is no good explanation for why the other two cells can't reach the setpoint after countless injections at constant depth. Maybe the O2 is off? Well, scream at the diver, because continuing to inject will not help him/her!
Just saying. The computer between our ears will soon be (is?) much less powerful than the one on our back (or on our wrist).
I can buy the merits of manual versus electronics as far as making you aware of how the unit is supposed to work, etc, but we are talking about an electronic unit.
By definition, the electronic unit will kill you if it fails (and cells are parts of the unit) and you fail to notice it. Ergo, it needs to be designed to fail you the least possible, and I guess it could be argued that in the case we are discussing, an opportunity was missed to provide the user with a warning that something was obviously (I believe) amiss. I am not defending the principle of all-electronic rebreathers, just the fact that when it is so, it needs to be the least unsafe. I am no expert and will not testify in court, but my simple question is why this kind of simple tests is not implemented. I can buy the argument that it makes the code more complex, which may result in bugs, etc., but we are talking about a XXIst century unit, right? OK, bad remark, Airbus lost a jet on the assumption that a pilot would react intelligently to a repeated stall alarm. Stress situation anyone?
As argued before, cells can essentially get limited (or fail) whenever they feel like it (they don't need to be old: a shock, water, etc. can do the trick). Therefore it makes sense for an electronic unit to test whether the readings make any sense. In the accident discussed above, a reading over 2 at the specified depth doesn't make sense unless the pO2 is indeed quite high (hypothesis 1) or the cell is "failing" in a very unusual manner (hypothesis 2).
In hypothesis one, a warning must be displayed that most likely the other two cells (whether or not they agree with each other, but in particular if they BOTH read below the setpoint after a while at max depth and after repeated solenoid injection - potentially with no O2 injected if the O2 cylinder is empty or closed) are now suspicious. The recommended course action can be debated: disregard the two other cells, instruct to bailout, your recommendation here, etc.
In hypothesis two, the situation is still uncommon in the sense that, as in hypothesis 1, there is no good explanation for why the other two cells can't reach the setpoint after countless injections at constant depth. Maybe the O2 is off? Well, scream at the diver, because continuing to inject will not help him/her!
Just saying. The computer between our ears will soon be (is?) much less powerful than the one on our back (or on our wrist).
Matt, Ever consider that you could quite well have had one/two/three current limited cells yet only not "seen" this behaviour, within (because of) your limited range of observed PPO2!
At what point do you consider a cell is current limited:
8 bar? Achievable... Unmanned testing has proven that certain galvanic oxygen cells are (may still be) linear to 8 bar after 2 years.
2.55 bar? Limit of a lot of eCCR elecs to display PPO2, even if it's actually 4+ bar being breathed
1.6/8 bar? Limit a recreational diver might conduct manned self-testing to.
<1.3? Lower than set points...
For a galvanic oxygen cell current limited at 2.6 bar, it fails the first criteria yet still is not current limited by the remaining three....
matt
Well-Known Member
Hi Brad,
Of course all cells have an upper-limit for their output, so the term current-limited would need some sort of formal definition. I have no clue what the upper-limit for a new cell is, other than I know there is one. I do know it is higher than 1.6, so that's all I need to know.
When I say I have not seen a current-limited cell I mean I have not found one that won't go to 1.6 when I ask it to.
Cheers
Matt.
Mark Chase
ATB=AlwaysTalkingBollocks
I agree totaly that an idiot proof electronicly controled CCR is the best idea yet.
Sadly its not been invented yet and due to the lack of proper funding for R&D and the harsh environments we ask the electronics to function in, I doubt if it ever will
CCRs are pretty much designed and built in a shead by enthusiastic people
I am cool with that but I am not so cool with total reliance on the result of their labour
Once a CCR has been built thats had the sort of test to destruction R&D they throw at something like a passanger jet, I might consider trusting it
Even the APOC people with the best intentions of ticking every CE box in existance managed to produce a unit that instantly failed in the real world use due to some silly little fault
Mark Chase
ATB=AlwaysTalkingBollocks
Well sadly I know for a first hand fact the cells can go to 3.0 PP02
I may be wrong but I thought I read somewhere the old Inspo couldn't display over 2.5?
uwxplorer
rEvo carrier
Not mentioning, as I did, that even the R&D put into passenger jet computers did not factor in that a pilot could do the most stupid thing no-one would have ever thought a professional pilot would intentionally do, i.e. hold the nose of a plane up as it fell off the sky blaring "stall, stall" alarms...
matt
Well-Known Member
Well sadly I know for a first hand fact the cells can go to 3.0 PP02
I may be wrong but I thought I read somewhere the old Inspo couldn't display over 2.5?
Correct. Cell reading on Inspo is still maxed at 2.55, which is the max value of the 8-bit numer (11111111 = 255).
Matt, which is as per the openly disclosed manufacturers specification or design of the cell. This is something APD can specify from Teledyne or Aii etc etc when they purchase their cells.
Irrelevant really - except for pushing the boundaries during unmanned testing and when you document the units performance - as it ought to be greater than the eCCR is capable of reading/displaying.
We probably need to talk in terms of a galvanic oxygen cell being functionally current limited.
Mark, At least 2 rebreather design companies have had an R&D spend on their units exceeding multi-millions USD/EUR respectively.
One of those companies, the Biomarine Mk15 series is quite well respected still 30 years later and had a quite idiot proof eCCR controller that I don’t believe anyone has ever died of current limited oxygen cells on…..Despite the Mk15/16/A5800 having arguably the greatest number of manned dive hours of any eCCR to date.
Additionally the electronics themselves that control our PPO2 should be isolated in all regards from the harsh environment we like to dive in. The cells themselves despite being immersed in the loop’s environment have nothing to do with the actual control of the PPO2….
Mark, as your aware there is no CE requirement directing that MAVs don’t and can’t stick! Likely a good thing for the industry…as everyone on the market at the time would have failed but a bad thing for divers as end-users.
Even as a mechanical rather than an electronics issue this can still applied to the topic. Because the money had been spent on R&D by OSEL up front, the design was failsafe as supplied; any diver experiencing a stuck on oxygen injector could survive the dive, safely ascending with manageable PPO2.
On the Apoc you can safely breathe through ascent, staying on the loop, just by holding the O2 injector button down. The constant flow of oxygen at a pre-determined controlled rate continues to provide a breathable loop: even without visibility of the PPO2. Not exactly a recommended SOP but there in your quiver of options, for use in extremis.
The Apoc’s oxygen injector button did exactly what its Functionally Safe design was meant to do. When it failed (only failure option was stuck on), it did so in an identifiable and safe manner and in a manner that the diver was quite aware of: both by feel and audibly. This needs to happen with eCCR’s oxygen control when the galvanic oxygen cells perform as designed; as two of three being functionally current limited (below 1.3/6/8 bar) suddenly, is neither a rare event*** nor a failure of the cells themselves.
***some divers will never see a functionally current limited cell, multiple others have been killed by the occurrence.
matt
Well-Known Member
Do you know any manufacturer of cells used in the popular rebreather market that publish this, Brad? Agree it would be interesting to note.
Which other company has recreational eCCR R&D budget in multi-millions? Can't be OSEL as they don't ship any eCCR.
From a user perspective it doesn't matter. It was released with faults just like all the other have been.
Matt.
sheck
New Member
In principle I get what you are saying, but not many divers are using a setpoint above 1.3
So it's more likely to be controller setpoint of 1.3 with readings of
1.2
2+
1.2
and the solenoid continuing to fire trying to drive those 1.2s up to 1.3 when the true loop is already way too high.
hi bralex
let me correct that for you
some divers will never see a functionally current limited cell inside an apoc, because the electronics don't exist
or am i wrong,
alby