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  1. #1
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    Possible Cell Issue

    So got to, or just past the anniversary of of my first cells (insertion date, not manufacture) and exchanged them for new. On the last dive before the exchange 1 cell had started to behave erratically, never far enough to drop out on voting logic (SW GF) but certainly not stable.

    Changed them out after leaving them out of packs for 72 hours min and calibrated. At that point though they were reading slightly high in air 0.22-0.23 with around 11.3-11.8 mv before calibration in o2.

    Calibrated them in o2 on SW and HUD.

    I didn't then check them again against dil or air in fairness.

    Dived them yesterday and were fine at 6m on 2 separate 02 flushes on 2 dives despite moisture content on second dive.

    I did perform a dil flush and got an average of 0.3 against a target of 0.3 so this was fine.

    Last night though the cells at rest in air were still reading 0.22-0.23 n air, so let the head dry out and same again today.

    I have checked the SW against the old cells (2 that were still OK) and they also read 0.23/0.23.

    Before I break out the venerable KISS triples and check whether the SW is at fault is there an obvious, logical explanation I am missing.

    At the practical level at the high side a 0.02 discrepancy doesn't worry me so long as it is still only 0.02 at higher ppo2's/pressures.

    At the other end of the spectrum though which is more scary IMHO is that 0.18 would actually be 0.16, and although I don't allow the unit to drop this low its still a concern.

    The inconsistency is common across all 3 so less likely to be wiring but always keep the M/F sections of the Fischer lubed with Fischer oil and was replaced around January anyway.

    Could be the SW and can check against the Triples if necessary.

    We are at circa 175m above SL but thought this would impact in the opposite direction, we are at circa 993 hpa atmosheric according to my altimeter.

  2. #2
    Old but keen Mark Chase's Avatar
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    A: The error 0f 0.02 is not worth worrying about


    B: define erratic behaviour?


    Usualy if the cell is erratic its a connection issue rather than a cell issue

    IMHO cells that are becoming current limited usualy results in the reading hot and fast in the hours before cell death


    I'd have cleaned all the connections and soaked the cell in a bag of pure 02 overnight. That will usualy kill it if its near current limited.

    If not then replace cell in a different position and see if the issue stays in the same place or follows the cell.

    Personally I never found cells linear so If I got them right at 100% 02 they would usualy be a bit out in air or even lower trimix. As I say 0.02 wouldn't give me pause on air / trimix if they were spot on in 02.


    the 0.16 - 0.18 argument is mute You should never be below 0.70 for ANY reason except cell checks

  3. #3
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    Erratic in that it wouldn't hold a stable reading but I didn't test further because I knew it was the cells last dive, having said that I did have the SW off the unit to download the days dives before the dive when the cell acted up and can't remember if I re-applied oil before re-fitting it so may have been a dry joint in fairness.

    No such behaviour yesterday so could have been either cause.

    I also took your advice and "dived round it", probably need to list your quotes that I follow in case my missus needs to hunt you down.
    Last edited by JonG; 25-11-2018 at 12:50 PM.

  4. #4
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    Mine do that as well. I've given up worrying about it.

    There's obviously some sort of non linear behavior going on with them.

    Have you checked them in pure inert gas to see if zero really is zero?



    Measure with a micrometer mark with chalk cut with an axe comes to mind (think it is someone's signature on here)

  5. #5
    Established TDF Member MikeF's Avatar
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    What was the air pressure when you calibrated them and what is it now?

  6. #6
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    993 mb yesterday didn't check on day of calibration

  7. #7
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    What is your height above sea level ? If I calibrate my SW at home I get a slightly different reading than if I do it at sea level
    I trust my rebreather implicitly I just don't trust the owner

    Onwards & downwards.

  8. #8
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    About 180m above, but last cells were .21/.22

  9. #9
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    If you calibrated at sea level then go home to higher altitude you will get different reading & from memory if it reads 0.21 at sea level then I get plus .1 or .2 difference.
    I trust my rebreather implicitly I just don't trust the owner

    Onwards & downwards.


 

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