The Pelagian Way

Rebreatherlab

Steve,

Before going commerical with the Pelagian I dove a converted IDA-71 using only one cell with the possibility to ad dil straight accross the cell membrane sucessfully for eight years and over 700 hours. It had lots of issues, but none regarding breathing one Po2 and believing it was something else. The reason for two cells is simply that it is quite common a cell dies during a dive. With staggered change outs the risk of two dying on the same dive is less likely. The core point is the ability to validate the cells easily. While loop purging a few times acomplish the same, it is quite common divers dont validate, in my opinion, frequently enough. Maybe because three loop flushes at 90 m uses quite a lot of diluent.

Andy

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Steve

I'm still not seeing how you are able to validate your loop composition with 2 sensors. If the displays are different you do a dil flush and presumably they agree given the lower pO2 (current limited cell being the most likely failure). When you try to bring them back up to your required pO2 how do you know which one is safe? The bad cell may have failed High or failed Low. With only 2 sensors you don't know which way. You still have 2 different outputs and no way of knowing which one is correct as far as I can tell.

A simple question. You are at 50m and your displays read 1.333 and 1.666. You flush with dil and the displays agree and both display 1.222. Which cell is the bad one?

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wedivebc

The one that was reading 1.333 because it is obviously current limited

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Cheers,

Dave....

Man is the only animal burdened with the knowledge he will eventually die

gbmay

Steve, there is a third cell you can add. I use the third cell to run my VR3.

Regards,

George

DeepBlueInnovation

Not necessarily, I believe cells can read high just as easily as they can low when they fail.

Steve

Exactly. Many, many people on these boards have seen sensors do this.

2 just doesn't cut it; having said that, you will get away with it right up until the day you dont. Neither does leaving it up to people to work out how to fit a 3rd sensor themselves. Poor form IMO

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WARNING: I contain occasional coarse language, extreme sexual references, nudity, and adult themes, which may offend some people - Usually churchy types.

Mdemon

(Whilst I agree that 3 is best,) a linearity check on O2 at 6m at the beginning of the dive and another at depth would be helpful if you only have 2.

I don't know how often the linearity fails (especially high) during a dive but I've tended to get cells just completely die, rather than have linearity problems.

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www.southwestmafia.com

It's as easy as abc;

a) "Carry adequate bailout"

b) "If in doubt, bail out"

c) "Always know your PO2"

If you find that hard, stick to crochet.

"Once the agenda-monkeys and perfect-worlders have moved on, perhaps we can do some diving?"

dantheman

Steve,

What is the failure mode of a sensor that causes it to read high?
Can you explain it, or do you have a reference for any investigation of this?

--dan

jradomski

not necessarily one failure modes that cells go into has the output go high (very high in alot of case) right before failing.. (more likely there would be a much larger spread)

I have seen r22d cells read >50mv in AIR

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Joe Radomski
CCR Trimix Instructor Trainer
ANDI Instructor Trainer Director #10

All posts are personal opinions and DO NOT reflect any affiliated agency unless specifically stated.

decoweenie

I too have seen sensors failed reading high on surface, but don't know the mechanic behind it.

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