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Thread: Calibration of Cells - Single point - 2 point -Air or O2?

  1. #41
    Nils Möllerström nilmol will become famous soon enough nilmol will become famous soon enough nilmol will become famous soon enough nilmol will become famous soon enough nilmol's Avatar
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    Re: Calibration of Cells - Single point - 2 point -Air or O2?

    Quote Originally Posted by saveourseas  View Original Post
    Hi Nils.
    Wouldn't calibration in O2 with a verification in ambient air (or a known gas) fit your definition of a calibration of a slope using two known gasses (verified O2 and ambient air or a verified diluent? Then diluent flushes while diving should give you checkpoints, albeit at higher mV outputs than your calibration and a totally different environment.
    Cell checkers are great... to a point. They don't mimic the conditions of a rebreather in use which can have great effect on a cell and its circuitry. I use one myself but know that nothing will take the place of in-water checks.

    I thought the Poseidon patent was Bill Stone's, but you mention Arne's company. I don't know the history beyond Bill's involvement.
    I agree, with the slightly difference in viewing it. You have one measurepoint in air and one measurepoint in 100% O2. Together, not as solitairs, they make up for a calibration. It's semantics, I know. But if it's our wish as as diving community to push manufacturers in a certain direction then semantics do count.
    A third (or more) measurepoint may verify or discard linearity in the calibration.

    So if we can agree on the semantics we totally agree.

    Next question is, will it actually help us pushing manufacturers in the right direction? Well why not try and see, it won't cost anything...

    The patent that Poseidon uses carries Arne's name at the bottom line...


    /nils

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    Re: Calibration of Cells - Single point - 2 point -Air or O2?

    Quote Originally Posted by Snusmumrik  View Original Post
    Paul, is that a joke? How we can create zero PPO2 with oxygen-containing mixes? Or you say that we must carry helium/nitrogen bottle for calibration purposes?
    You just ask your old chainsmoking uncle to breathe on the cells for a short while...

    Seriously. never heard of anyone carrying an inert gas for calibration purposes. However, for those who have argon in their suit inflation bottle it's a possibility. Although probably not with the cells in the RB. So I guess it would require a cell checker. And if you have a cell checker you don't really need argon...
    So, possible yes - but useful... I doubt it...

    /nils

  3. #43
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    Re: Calibration of Cells - Single point - 2 point -Air or O2?

    Quote Originally Posted by Mike  View Original Post
    You do realise that 2 points do not imply a line don't you? They could be two points on the most squiggly of curves for all you know if you just look at two points. The sensor might actually be outputting 14 mv in air, 120 mv at 50% and falling away to 66.5 mv at 98%. Just measuring 2 points does not prove linearity.

    Much as my mates deride my prism for being as waterproof as a tea bag, it's simple calibration process is still about as good as it is possible to be. Replace scrubber - unit full of air.
    Check it holds negative.
    Do three full flushes WHILE WATCHING THE SECONDARY. You see the massive PPO2 jump on the first flush, then the logarithmic increase as you approach 100% on the second and third flushes.
    Then you adjust as necessary with a screwdriver individually for each cell. And if you need to turn the screwdriver more than a partial turn for any cell it is blatantly obvious that there is a problem.

    It's a bit fiddly, but it forces any numpty to be very aware of the change in cell voltage overtime - the degree of action you need to take is directly proportional to the drift in the cell output since last calibration. This is markedly different to the 'push button to calibrate' systems where you don't need to notice how screwed everything was before the magic button applied an unknown fudge factor to an unknown millivolt reading.

    It bemuses me that people have been having the same issue with calibration for 15 years, when it is so straight forward.

    Mike
    (it also bemuses me how anal people get about exact readings. If my cells are within a couple of % of each other, and track together, that's plenty accurate enough a calibration for me. My loop stays between about .9 and 1.6 for the entirety of each dive. A variation to .85 or 1.65 is not going affect me one bit)

    All agreed, (aside from the current limiting test to 1.6 underwater, which no mnf does, except possibly the Poseidon, which has some secret proprietary method?) the P1 cal is dead simple, comprehensive and very informative.

    But Mike, all, if we know our cells are good from .21 to 1 to 1.6, how could there be a squiggly line between them? -Andy

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    Calibration of Cells - Single point - 2 point -Air or O2?

    Quote Originally Posted by Snusmumrik  View Original Post
    Paul, is that a joke? How we can create zero PPO2 with oxygen-containing mixes? Or you say that we must carry helium/nitrogen bottle for calibration purposes?
    I think Paul is getting at the fact that you can see a slope with current systems.

    1st point is the computer knowing that 0mV is equal to ppO2 of 0, this isn't checked it is seen as a fact.

    2nd point is the actual calibration - you are telling the computer that a particular mV reading equals a particular ppO2.

    3rd point is the check of diluent - if the 1st 2 points are wrong the diluent will not read correctly as it will assign the wrong mV reading to the diluent.

    4th point is your O2 spike on descent where you are checking the linearity continues past your O2 check.

    Of course if the linearity is off randomly in different directions it may miss it.

    In addition if the biggest concern is when the cells become current limited (change linearity) during the dive as the linearity check is only good for the time it was performed and to the ppO2 level that this occurred.

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    Re: Calibration of Cells - Single point - 2 point -Air or O2?


    But Mike, all, if we know our cells are good from .21 to 1 to 1.6, how could there be a squiggly line between them? -Andy
    You're correct of course, once you add a third point, it does define a line, (if the points are linear of course) or an arc otherwise.


    Paul, I have no trouble accepting that a cell will be putting out zero mv at zero ppO2. The bit I want to confirm is that it is not still at zero mv at .1 PPO2, or .2, or .3 etc. Confirm that there is no offset error. Hence the assumption of zero mv at zero PPO2 is of no value in confirming linearity.

    Mike

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    Re: Calibration of Cells - Single point - 2 point -Air or O2?

    Quote Originally Posted by mdma946552  View Original Post
    ok monkey your the boss
    Boss???? Yes like all men are the heads of the households they live in.
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    Re: Calibration of Cells - Single point - 2 point -Air or O2?

    Quote Originally Posted by paulraymaekers  View Original Post
    don't forget the third point of calibration: zero PPO2

    we know that sensors have zero output at 0 bar PPO2, so with the 2 extra points you are in fact checking linearity

    Easy, put a cell in a small bag, and let it eat all the 02, then it goes to sleep in what is left over Nitrogen.

    There is your 3rd point.
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    Re: Calibration of Cells - Single point - 2 point -Air or O2?

    Quote Originally Posted by mdma946552  View Original Post
    i see that now to thanks paul and monkey and all the others contributing real facts and rebreathers
    ummmmm.... that's a strech..... at best I poke the dragon.
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    Re: Calibration of Cells - Single point - 2 point -Air or O2?

    Quote Originally Posted by snusmumrik  View Original Post
    paul, is that a joke? How we can create zero ppo2 with oxygen-containing mixes? Or you say that we must carry helium/nitrogen bottle for calibration purposes?
    argon?
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    Talking Re: Calibration of Cells - Single point - 2 point -Air or O2?

    [QUOTE=Monkey;460518]Boss???? Yes like all men are the heads of the households they live in.wow your the boss at home to now i am impressed

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