4 or 5 cells. Why?

Steve

Hi all,

Can someone explain to me why people feel there is a need for 4 or 5 cells? I’m really not getting this as I have observed and tested a few things out over the years and I just cant see the need.

1. There is no need for a ‘live’ VR3 feed. I plumbed a VR3 into my Classic KISS and ran my pO2 (normal diving) the same as I manually set a second VR3 that wasn’t plumbed in and the difference between the two was very small. I’d imagine the inspo would keep a better lock on the desired pO2 than me on a KISS.
2. If you loose your electronics then personally I would bailout rather than using a VR3

There must be something I’m just not getting.

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silent running

Uhmm, yeah. Is your ECCR capable of holding SP, or not? There's no point in having an ECCR if it can't keep SP better than you can. Are you diving a KISS and changing your SP frequently, or having a hard time maintaining SP? Why?

You can change SP on all constant PO2 comps I know of, to keep up with dive plan changes. So why do you need an interface/4/5th sensor? Why would anyone want another set of seals and another sensor to calibrate, much less the lag time/sample rate of a 4/5 digi interface sensor? Sounds like that much more 2nd guessing about the real PO2...

As for BO, no need as long as 2 sensors are behaving and you can fly the unit without high current, manually.

Good question Steve, I've wondered the same thing here on RBW myself. -Andy

Mdemon

Hi Steve,

I don't use my VR£ for deco either. However I use it, and the rEvoDream for two things; firstly, the obvious. If my handsets pack up I can still get home using the same profile I had intended using the rebreather and all the advantages over OC therein.

The second is more subtle. As well as the 6m linearity checks, using 4/5th cell monitoring allows checking on the first three. So, if I were to swap three cells out at once for some reason, when I first dive* them I have a reference against which to check.

There is also the fact that you then have 4 or 5 cells - if one dies during a diving holiday, you know you have a replacement and you know how that replacement behaves because you've been looking at it all week.

HTH





("dove" them, if I have a pigeon handy)

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lizardland

I must admit I always found it a bit of a paradox that we distrust one cell enough to need three of them to stop us passing out or convulsing but we have enough faith in one of them to track deco.

And then we trust three of them enough to keep us alive but we have so little faith in them that we need an extra one to track deco.

I'm a neolithic tables user and to my little Cro-Magnon mind you either believe that you are on set point or you don't. I don't get the need for extra cells.

I guess it's like carrying three lights in cave diving, carrying any more is such a minimal increase in safety it's hardly worthwhile (though having had a triple light failure whilst solo I feel like a bit of a hypocrite ).

Cheers,

Stuart

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EBT

I guess the motivation is driven out of levels of trust of the electronics.

Personally Im happy to dive the kiss with 2 functioning displays. If they disagree I flush and validate. 3 displays makes life a little easier.

For those with eCCR's, we all know they NEED 3, to allow the electronics to figure out which is buggered (techy term). Of course there could be other electronics strategies, but they add complexity (ie forcing flush).

Im in agreement with the aussie chair diver though, trusting a single cell to manage your bailout at the expense of putting more crap/seals in the loop doesnt sit well with me.

...ditto the deco point, it makes not a lot of difference if you wobble your set point around a bit.

As for using table stuart... <grins> I seem to recall you used a cheap shit computer to run your ressel bailout

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RichClark

I only see it as valid if you're adding extra functionality into the loop. I agree that trusting one cell for you deco is a bad thing - but i do see value in being able to add a HUD and/or a computer using voting logic to calculate deco.

Cheers

Rich

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lizardland

Well you should be used to it by now

Must've been an Aladin... kept on whining for hours and only shut up when its batteries ran out then was unable to dive the next day...

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Mdemon

Too blinkin' right!

My standpoint is; it's going to go wrong. I know that for sure. Ergo, I want something in reserve. The inverse of Alpine.

Computers/electronics work just long enough to lull us into a false sense of security...

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"small minds talk about people, Average Minds Talk About Events, GREAT MINDS TALK ABOUT IDEAS!"

The WRONG Attitude will get you killed.

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

Dutchy

Next question would be all 5 cells be Teledyne (or Analytical) or would you rather have a spread in Brand, Type and even age?

What if a batch is limited at let's assume 1.3 Bar.... Would you find out? (Assuming you are planning to dive at 1.3 and you only flush @6 on deco (in fact checking the cell for the next dive rather than the current one)

If we can't get the basics right then what help is it to double or triple the number of sensors? I'd rather dive 2 cells checked at 0.2, 1.0 and 1.8 bar than anything redundant that isn't tested.

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Mdemon

If the cells are all limited to 1.3 (I suppose it could happen), and my VR£/other cells showed a different value, then at least I would know to check. And they all get tested throughout the dive (do they read/track the same?) and at the end (1.6 on O2 @ 6m?). If you read around on RBW there are several instances of checked cells not working.

If you are on a Classic and a cell drops out AND to reboot your handsets to clear it, the chances are you will end up with no handset PO2 monitoring. That's when having a backup set of cells comes in useful - been there, done that. Yes, you could bailout, but why bother if the loop's OK?

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www.southwestmafia.com

"small minds talk about people, Average Minds Talk About Events, GREAT MINDS TALK ABOUT IDEAS!"

The WRONG Attitude will get you killed.

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