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Thread: Probable failed cell and Cell Checker Question

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    Probable failed cell and Cell Checker Question

    I bought a new Inspo Vision from AP a couple of weeks now, and I now have ten hours on it.

    Whilst diving the Aeolian Skye yesterday I noticed a problem with cell one - previously during the cal all cells raced towards 1.01, but this time cell one lagged a bit and never reached more than 0.97. Anyway, the unit did complete the cal and having dived regularly over the last few days I thought it was probably just a bit of moisture on the cell face.

    During the dive things did not settle and cell one read higher than the other two, which tracked each other to within 0.01. The unit did not give a cell warning, but when the difference reached 0.1 some 25 minutes into the dive I was not happy. Controller 2 showed the same high reading for cell 1. I couldn't satisfactorily verify the readings of the remaining two cells with a dil flush (the O2 solenoid kicked in so quickly I couldn't get the cells to drop to the expected 0.73 so we canned the dive at this point). As none of the three readings was dangerously high or low, and all were changing with my breathing I stayed on the loop. At 6 metres an O2 flush confirmed cells two and three were spot on at 1.58 and 1.60, cell one hit 1.75.

    Checking the head after the dive it was no wetter than normal, but just in case the back of the cell was wet I took the coax plug and blue cover off - in fact, the back of the cell and connector looked fine. A shallower drift dive was planned for the afternoon so I reassembled the unit after an hour or so drying and dived it to 20m having moved the suspect cell to position 2 to see if that made a difference. On the cal cell 2 was now lagging, and although for the first half of the dive it tracked cell 1 and cell 3 it later started to climb again. Unfortunately I wasn't able to do a dil flush as after 2 days diving I was down to 20 bar of O2 - I finished the dive OC rather than empty the cylinder.

    Having read the drifiting cell thread here on RBW I think that the cell is a dud. I recalibrated just now with a copletely dry head and it was still slow. It's only a few weeks old so i'll be talking to AP, but I think my trimix analyser fund has just been changed into a cell checker fund.

    I am happy to post the log files if someone can tell me how to turn the graphs into a PDF file.

    I have just a couple of questions:

    1. Was it reasonable to stay on the loop after my attempt to validate the cells failed (I reasoned that it was as all three were within 0.1 and within a safe range), or would you have bailed OC?

    2. As another Rebreather diver said yesterday "rebreathers are thousands of pounds of high technology which depend on one hundred and fifty pounds of highly unreliable sensor technology" - I can see that a cell checker will be an additional line of defence against my box of death's mission to kill me, but how often should I use it (weekly, monthly, before every dive??) given that some weeks I am in the water four or five times. I don't have a problem checking the cells the night before every dive, but surely there's a trade off here, as every time I remove and replace the cells there will be some wearing of the cells, mountings and coaxial plugs.

    CC
    Last edited by Captain Calamity; 25th May 2009 at 14:31.

  2. #2
    Brent - Narked at 90
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    Re: Probable failed cell and Cell Checker Question

    Quote Originally Posted by Captain Calamity  View Original Post
    2. As another Rebreather diver said yesterday "rebreathers are thousands of pounds of high technology which depend on one hundred and fifty pounds of highly unreliable sensor technology" - I can see that a cell checker will be an additional line of defence against my box of death's mission to kill me, but how often should I use it (weekly, monthly, before every dive??) given that some weeks I am in the water four or five times. I don't have a problem checking the cells the night before every dive, but surely there's a trade off here, as every time I remove and replace the cells there will be some wearing of the cells, mountings and coaxial plugs.

    CC
    Without the mV readings (which you should have taken with the SMB widget you got from APD), it is difficult to state what went wrong but I strongly suspect the cell leaked electrolyte.
    When this happens, the cells output rises when external pressure is applied. It is rare that you will be able to see this on the surface.
    We had a batch of Aii cells which did this. Now, imagine two, or all three had that fault, what would your controller have done?

    Check them when it is reasonable to do so.
    • When they are new
    • Before a trip where a failure would suck big time
    • When the cells exhibit unusual behaviour
    • On a regular basis (not usually more than monthly)
    Brent

    http://www.rebreatherworld.com/showthread.php?t=26408
    http://www.rebreatherworld.com/showthread.php?t=14416
    etc.
    Last edited by divetheworld; 25th May 2009 at 17:15.
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  3. #3
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    Re: Probable failed cell and Cell Checker Question

    Thanks.

    Mini cell checker ordered.

    Providing the three cells read 2.0 at 2 bar and are linear to 1.0 at 1 bar using the mini cell checker is there any need to look at the mV readings routinely, or should I only check these if the cell fails the test using the AP handset readings?

    CC

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    Brent - Narked at 90
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    Re: Probable failed cell and Cell Checker Question

    Quote Originally Posted by Captain Calamity  View Original Post
    Thanks.

    Mini cell checker ordered.

    Providing the three cells read 2.0 at 2 bar and are linear to 1.0 at 1 bar using the mini cell checker is there any need to look at the mV readings routinely, or should I only check these if the cell fails the test using the AP handset readings?

    CC
    The PO2 displayed on your handsets are an extrapolation of the mV. You take readings in air, O2 and 0.1 steps to 2 bar and hold it at 2bar to check.
    There is software with your Mini-Check that will record and graph your results. This will indicate current limitation, linearity and electrolyte leak.
    The only check it doesnt do is checking that they are in specification (8-13mV) in air. Use a voltmeter for this.
    If you still have the mV checking widget (male SMB) that came with your unit from APD, you can use a cheap voltmeter on the Mini-Check and do the full test aswell.

    Brent
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  5. #5
    John Routley
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    Re: Probable failed cell and Cell Checker Question

    This seems to be the second cell to show this behaver in the last 2 weeks and i assume they are apd10 cells your using? the age of the other cell that we have here is H8. whats the date on yours?
    kind regards john routley
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  6. #6
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    Re: Probable failed cell and Cell Checker Question

    Quote Originally Posted by divetheworld  View Original Post
    The PO2 displayed on your handsets are an extrapolation of the mV. You take readings in air, O2 and 0.1 steps to 2 bar and hold it at 2bar to check.
    There is software with your Mini-Check that will record and graph your results. This will indicate current limitation, linearity and electrolyte leak.
    The only check it doesnt do is checking that they are in specification (8-13mV) in air. Use a voltmeter for this.
    If you still have the mV checking widget (male SMB) that came with your unit from APD, you can use a cheap voltmeter on the Mini-Check and do the full test aswell.

    Brent
    Excellent. Just as I had hoped.

    CC

  7. #7
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    Re: Probable failed cell and Cell Checker Question

    Quote Originally Posted by narked at 90  View Original Post
    This seems to be the second cell to show this behaver in the last 2 weeks and i assume they are apd10 cells your using? the age of the other cell that we have here is H8. whats the date on yours?
    kind regards john routley
    I'm answering from work so i'll have to double check, but I think D9. Cetainly they are all 2009 cells as it is a brand new unit.

    I've emailed AP and I am sure they will replace the cell, hopefully they will let me send the old cell back after I run it through the checker so i'll be able to post the values here.

    CC

  8. #8
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    Re: Probable failed cell and Cell Checker Question

    Were these new cells - I had a similar problem this week with 1 cell reading 1.5 bar low - wondering if there is a cell issue? - (Mine were newly replaced cells)

  9. #9
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    Re: Probable failed cell and Cell Checker Question

    Quote Originally Posted by Wol  View Original Post
    Were these new cells - I had a similar problem this week with 1 cell reading 1.5 bar low - wondering if there is a cell issue? - (Mine were newly replaced cells)
    Yes, very new. Only a few weeks old.

    CC

  10. #10
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    Re: Probable failed cell and Cell Checker Question

    Here's the graph from dive two:

    Cells 1,2 and 3 track each other nicely until halfway through the dive when C2 starts to creep away...


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