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Thread: Cell Question

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    Cell Question

    Ok so I replaced one of my cells a couple of weeks ago and have found that the new one is not lining up with the other two when diving. I have redone the calibration an few times and still last weekend the new cell was reading out from the other two, it was anywhere from 0.05-0.1 difference. I have a cell checker and ran all three through a test last night just to find that they all passed and were reading very close to each other. The only thing I can think of is moisture affecting the one cell more than the others but the last few dives I have done were not much more than an hour in duration. I think the next thing I will do is move the cell to a new position in the RB to see if that may be the culprit, for now I am doing very shallow dives with a buddy who is getting into sidemount so I am not too worried about having the PPO2 rock solid on all three cells. I will also do an 02 flush at the end of the dive to see the reaction then as well. If anyone has any other suggestions I would be glad to hear them, thanks

    Oh yea all three cells are Vandergraph (ISC) and the cell in question is sitting in slot #3 in the head.

    Rob

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    Re: Cell Question

    Quote Originally Posted by diverrob  View Original Post
    Ok so I replaced one of my cells a couple of weeks ago and have found that the new one is not lining up with the other two when diving. I have redone the calibration an few times and still last weekend the new cell was reading out from the other two, it was anywhere from 0.05-0.1 difference. I have a cell checker and ran all three through a test last night just to find that they all passed and were reading very close to each other. The only thing I can think of is moisture affecting the one cell more than the others but the last few dives I have done were not much more than an hour in duration. I think the next thing I will do is move the cell to a new position in the Rebreather to see if that may be the culprit, for now I am doing very shallow dives with a buddy who is getting into sidemount so I am not too worried about having the PPO2 rock solid on all three cells. I will also do an 02 flush at the end of the dive to see the reaction then as well. If anyone has any other suggestions I would be glad to hear them, thanks

    Oh yea all three cells are Vandergraph (ISC) and the cell in question is sitting in slot #3 in the head.

    Rob
    Are you saying it was .05 to .1 atm difference or mv difference. Does the variation go back to normal when the cells dry out after the dive? Why are you so concerrned about such a small variation, what does it really affect?
    Cheers,

    Dave....

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    Re: Cell Question

    The 0.05-0.1 is PPO2 and the reason I seem concerned is that over the past few years this brand of cell has been rock solid and now this one is drifting off so I want to ensure it is not something else other than the cell I suppose. The cells do all line up after they dry out so I am leaning towards the moisture issue but I still want to make sure.


    Rob

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    Cell Question

    Not to make light of the difference that shouldn't be there, but a slight difference of one unit at the smallest measurement should not be of concern. The problem here is that your smallest measurement is 0.01. It always bothered me that Shearwater displays 2 decimal places of pO2. It is not necessary and can lead to this kind of concern. Other displays (including Shearwater HUD) only show one decimal place. So a difference of 0.1 between cells is expected at times and doesn't even raise an eyebrow. I really doubt whether the chemical reaction of the cells is accurate to 0.01 in the first place.


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    Re: Cell Question

    Quote Originally Posted by kwinter  View Original Post
    Not to make light of the difference that shouldn't be there, but a slight difference of one unit at the smallest measurement should not be of concern. The problem here is that your smallest measurement is 0.01. It always bothered me that Shearwater displays 2 decimal places of pO2. It is not necessary and can lead to this kind of concern. Other displays (including Shearwater HUD) only show one decimal place. So a difference of 0.1 between cells is expected at times and doesn't even raise an eyebrow. I really doubt whether the chemical reaction of the cells is accurate to 0.01 in the first place.


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    Put that way I can see your point, I guess I was just so used to the Vangergraph cells lining up all the same it got me thinking this time

    Rob

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    Re: Cell Question

    Does anyone have any info on whether cell positions in the head makes one cell more likely to have moisture issues?

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    Re: Cell Question

    Quote Originally Posted by diverrob  View Original Post
    Put that way I can see your point, I guess I was just so used to the Vangergraph cells lining up all the same it got me thinking this time

    Rob
    Rob, how old are your 2 older sensors?
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    Re: Cell Question

    Quote Originally Posted by diverrob  View Original Post

    Oh yea all three cells are Vandergraph (ISC) and the cell in question is sitting in slot #3 in the head.

    Rob
    Rob, I am experiencing the exact same Thing on my HammeredInspiration..
    I also see a 0.05-0.1 Deviation on my new Vandergraph (N90) vs. my two "older" Vandergraph (N90) cells.. It also tends to vary during different phases of the dive (i.e. towards the end of the dive in most of thedives they are much closer toghether).
    I also checked all of them in a cell checker and all are linear up to 2 ATA PO2 and stable over 30-60 Min which is my usual testing pattern.

    My take out of especially the Change of behaviour thorughout the dive is that they did some further adjustments at the temp circuits causing this.
    Maybe John or Brent can confirm/disconfirm..

    Nevertheless a Deviation in that Region is not giving me a headache at all.. My Overall deco strategy and Approach has a mcuh higher fuzzy factor and I pad it gently because of that, that it really means nothing to me if on over the other cell is "correct"..

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    Re: Cell Question

    Quote Originally Posted by paulraymaekers  View Original Post
    Rob, how old are your 2 older sensors?
    The other two are 4 and 8 months old

  10. #10
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    Re: Cell Question

    Quote Originally Posted by Nitrogenius  View Original Post
    Rob, I am experiencing the exact same Thing on my HammeredInspiration..
    I also see a 0.05-0.1 Deviation on my new Vandergraph (N90) vs. my two "older" Vandergraph (N90) cells.. It also tends to vary during different phases of the dive (i.e. towards the end of the dive in most of thedives they are much closer toghether).
    I also checked all of them in a cell checker and all are linear up to 2 ATA PO2 and stable over 30-60 Min which is my usual testing pattern.

    My take out of especially the Change of behaviour thorughout the dive is that they did some further adjustments at the temp circuits causing this.
    Maybe John or Brent can confirm/disconfirm..

    Nevertheless a Deviation in that Region is not giving me a headache at all.. My Overall deco strategy and Approach has a mcuh higher fuzzy factor and I pad it gently because of that, that it really means nothing to me if on over the other cell is "correct"..
    Yea none of this is stressing me out either but it did get me thinking. I will play around with a few things here over the next couple of dives as I stated above.

    Rob

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