+ Reply to Thread
Page 4 of 7 FirstFirst 1 2 3 4 5 6 7 LastLast
Results 31 to 40 of 64

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

  1. #31
    New Member
    saveourseas has a brilliant future saveourseas has a brilliant future saveourseas has a brilliant future saveourseas has a brilliant future saveourseas has a brilliant future saveourseas has a brilliant future saveourseas has a brilliant future saveourseas has a brilliant future saveourseas has a brilliant future saveourseas has a brilliant future saveourseas has a brilliant future saveourseas's Avatar
    Join Date
    May 2005
    Location
    New York NY, Los Angeles CA, Dallas TX
    Posts
    712
    Mk15.5, Prism, Prism2

    Ray, Dolphin, Mk15

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

    Quote Originally Posted by nilmol  View Original Post
    Looking at the title of this thread - Am I the only one thinking that in order to make a calibration one needs at least two checkpoints? And to establish linearity one needs a minimum of three checkpoints? Preferably more than three. To me a single checkpoint is just - a checkpoint...

    /nils
    Calibrating in pure O2 then verifying that the cells settle to ambient atmospheric O2 pressure by exposing them to air is a single point calibration with a simple verification using a known gas (ambient air).

    To check linearity, you need to look at the actual millivolts in air, multiply that reading by 4.76 (4.75 if calibrating at 0.98 PPO2), then flushing the loop with O2 and verifying that the cells are outputting the expected millivolts.


    For instance, if my cells were outputting 10.8mV in air, I would expect them to output 51.4mV in pure O2 or 51.3 (10.8 * 4.76/5) if we are looking at a .98ppo2 target calibration (0.02 slop for humidity).

    More checkpoints would be great, especially at higher pressures, but you also have to contend with elevated temperatures and 100% condensing humidity around the cells. So, in essence none of these out of water/off loop methods insure that the cells are not current limited above ambient pressures or non-linear at the higher mV output, or have an issue with the temperature compensating circuit which is why it is so important to verify the cells before and during diving.

    I can't wait for a digital O2 cell!
    "However beautiful the strategy, you should occasionally look at the results." Winston Churchill
    A is A

  2. #32
    Prism 'prentice Mike is a splendid one to behold Mike is a splendid one to behold Mike is a splendid one to behold Mike is a splendid one to behold Mike is a splendid one to behold Mike is a splendid one to behold Mike is a splendid one to behold Mike is a splendid one to behold Mike is a splendid one to behold Mike is a splendid one to behold Mike is a splendid one to behold Mike's Avatar
    Join Date
    Feb 2005
    Location
    Melbourne
    Posts
    458
    Prism

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

    Quote Originally Posted by saveourseas  View Original Post
    To check linearity, you need to look at the actual millivolts in air, multiply that reading by 4.76 (4.75 if calibrating at 0.98 PPO2), then flushing the loop with O2 and verifying that the cells are outputting the expected millivolts.
    As much as I hate to disagree with someone with such impeccable taste in rebreathers...

    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)

  3. #33
    Acme Serpentine Lubricant lizardland has a reputation beyond repute lizardland has a reputation beyond repute lizardland has a reputation beyond repute lizardland has a reputation beyond repute lizardland has a reputation beyond repute lizardland has a reputation beyond repute lizardland has a reputation beyond repute lizardland has a reputation beyond repute lizardland has a reputation beyond repute lizardland has a reputation beyond repute lizardland has a reputation beyond repute lizardland's Avatar
    Join Date
    Mar 2005
    Location
    North...
    Posts
    2,372

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

    Quote Originally Posted by Mike  View Original Post
    As much as I hate to disagree with someone with such impeccable taste in rebreathers...

    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)
    I wonder where they got that idea... One of many reasons I wouldnt trade my 35 yr old Mk15 for a modern rig.

    Too easy to push the cal button to cover up cell problems. Harder to delude yourself turning the screw on a pot.

    Sent from my GT-I9300 using Tapatalk

  4. #34
    New Member
    saveourseas has a brilliant future saveourseas has a brilliant future saveourseas has a brilliant future saveourseas has a brilliant future saveourseas has a brilliant future saveourseas has a brilliant future saveourseas has a brilliant future saveourseas has a brilliant future saveourseas has a brilliant future saveourseas has a brilliant future saveourseas has a brilliant future saveourseas's Avatar
    Join Date
    May 2005
    Location
    New York NY, Los Angeles CA, Dallas TX
    Posts
    712
    Mk15.5, Prism, Prism2

    Ray, Dolphin, Mk15

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

    Quote Originally Posted by Mike  View Original Post
    As much as I hate to disagree with someone with such impeccable taste in rebreathers...

    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)
    Hi Mike.
    I agree that it is not even close to a "scientifically valid" method for confirming razor straight linearity between the two points which is why I said "more checkpoints would be great", but it is a whole lot better than doing nothing at all, IMO. The reason I like it so much is it also helps to validate a proper flush. If the math says your cells should read 51mV in .98% O2 but you get 44mV after your flush, then either all your cells are not linear (all 3?), you have O2 with something other than O2 in it (which you already checked, obviously) or your flush was no better than a public toilet.

    Agree on the digits. I refer to anything to the right of the decimal as "blinky lights", there to show that the software hasn't hung and that the rapture isn't upon us where molecules have stopped moving. :)
    Last edited by saveourseas; 7th November 2014 at 12:39.
    "However beautiful the strategy, you should occasionally look at the results." Winston Churchill
    A is A

  5. #35
    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
    Join Date
    May 2007
    Location
    Karlskrona, Sweden
    Posts
    230
    Inspiration Vision

    Inspiration Classic

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

    Quote Originally Posted by saveourseas  View Original Post
    Calibrating in pure O2 then verifying that the cells settle to ambient atmospheric O2 pressure by exposing them to air is a single point calibration with a simple verification using a known gas (ambient air).

    To check linearity, you need to look at the actual millivolts in air, multiply that reading by 4.76 (4.75 if calibrating at 0.98 PPO2), then flushing the loop with O2 and verifying that the cells are outputting the expected millivolts.


    For instance, if my cells were outputting 10.8mV in air, I would expect them to output 51.4mV in pure O2 or 51.3 (10.8 * 4.76/5) if we are looking at a .98ppo2 target calibration (0.02 slop for humidity).

    More checkpoints would be great, especially at higher pressures, but you also have to contend with elevated temperatures and 100% condensing humidity around the cells. So, in essence none of these out of water/off loop methods insure that the cells are not current limited above ambient pressures or non-linear at the higher mV output, or have an issue with the temperature compensating circuit which is why it is so important to verify the cells before and during diving.

    I can't wait for a digital O2 cell!
    What I was trying to say was that - to me - a single measure point is ... a single measure point. It doesn't provide a slope nore any idea of linearity. So with a single point measurement you are left to doing assumptions on slope and linearity. I will therfore refuse to call a single point measurement a calibritation. Because it just isn't. And assumption is the mother of all f...kups, right?
    More than one checkpoint is not just great, it's necessary. All IMHO, of course.

    /nils

  6. #36
    New Member
    saveourseas has a brilliant future saveourseas has a brilliant future saveourseas has a brilliant future saveourseas has a brilliant future saveourseas has a brilliant future saveourseas has a brilliant future saveourseas has a brilliant future saveourseas has a brilliant future saveourseas has a brilliant future saveourseas has a brilliant future saveourseas has a brilliant future saveourseas's Avatar
    Join Date
    May 2005
    Location
    New York NY, Los Angeles CA, Dallas TX
    Posts
    712
    Mk15.5, Prism, Prism2

    Ray, Dolphin, Mk15

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

    Quote Originally Posted by nilmol  View Original Post
    What I was trying to say was that - to me - a single measure point is ... a single measure point. It doesn't provide a slope nore any idea of linearity. So with a single point measurement you are left to doing assumptions on slope and linearity. I will therfore refuse to call a single point measurement a calibritation. Because it just isn't. And assumption is the mother of all f...kups, right?
    More than one checkpoint is not just great, it's necessary. All IMHO, of course.

    /nils
    Fair enough and you are right. Everything about rebreathers are old technology repurposed to go under water, and all the limitations that implies. We have always known the limitations of analog cells, and every method we employ are simply attempts to work with what we have and dodge the known bullets. At some point the only other option is to hang up our spurs and go back to blowing bubbles.
    "However beautiful the strategy, you should occasionally look at the results." Winston Churchill
    A is A

  7. #37
    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
    Join Date
    May 2007
    Location
    Karlskrona, Sweden
    Posts
    230
    Inspiration Vision

    Inspiration Classic

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

    Quote Originally Posted by saveourseas  View Original Post
    At some point the only other option is to hang up our spurs and go back to blowing bubbles.
    It's one option, not the only one.

    A startingpoint could be to get the semantics right, (Calling a spade for a spade);

    Single point measurement - checkpoint
    Two point measurement - calibration of slope
    Three+ point measurement - calibration of slope and linearity.

    If we do, the industry will have difficulty selling us VW while calling them Ferrari.

    And there are systems available that have adressed the cell and calibration problem better than most - the Poseidon. Sadly enough protected by patent. But one other option would be for Poseidon to market their solution as a third party add on for other brands.
    Changing semantics is probably easier and definatly faster than having Poseidon (SeaBear) selling their patent.

    With a cell checker you can have as many checkpoints as you like, but only prior to the dive.

    One option used as of today is the diver adding checkpoints during the dive.

    Me, I use both the above. If and when I "hang up my spurs" it will be for other reasons.



    /nils

  8. #38
    New Member
    saveourseas has a brilliant future saveourseas has a brilliant future saveourseas has a brilliant future saveourseas has a brilliant future saveourseas has a brilliant future saveourseas has a brilliant future saveourseas has a brilliant future saveourseas has a brilliant future saveourseas has a brilliant future saveourseas has a brilliant future saveourseas has a brilliant future saveourseas's Avatar
    Join Date
    May 2005
    Location
    New York NY, Los Angeles CA, Dallas TX
    Posts
    712
    Mk15.5, Prism, Prism2

    Ray, Dolphin, Mk15

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

    Quote Originally Posted by nilmol  View Original Post
    It's one option, not the only one.

    A startingpoint could be to get the semantics right, (Calling a spade for a spade);

    Single point measurement - checkpoint
    Two point measurement - calibration of slope
    Three+ point measurement - calibration of slope and linearity.

    If we do, the industry will have difficulty selling us VW while calling them Ferrari.

    And there are systems available that have adressed the cell and calibration problem better than most - the Poseidon. Sadly enough protected by patent. But one other option would be for Poseidon to market their solution as a third party add on for other brands.
    Changing semantics is probably easier and definatly faster than having Poseidon (SeaBear) selling their patent.

    With a cell checker you can have as many checkpoints as you like, but only prior to the dive.

    One option used as of today is the diver adding checkpoints during the dive.

    Me, I use both the above. If and when I "hang up my spurs" it will be for other reasons.



    /nils
    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.
    "However beautiful the strategy, you should occasionally look at the results." Winston Churchill
    A is A

  9. #39
    rEvo's daddy
    paulraymaekers has a reputation beyond repute paulraymaekers has a reputation beyond repute paulraymaekers has a reputation beyond repute paulraymaekers has a reputation beyond repute paulraymaekers has a reputation beyond repute paulraymaekers has a reputation beyond repute paulraymaekers has a reputation beyond repute paulraymaekers has a reputation beyond repute paulraymaekers has a reputation beyond repute paulraymaekers has a reputation beyond repute paulraymaekers has a reputation beyond repute paulraymaekers's Avatar
    Join Date
    May 2005
    Location
    belgium
    Posts
    4,073
    rEvo

    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? ....
    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
    www.rEvo-rebreathers.com
    ...."Yes you have to pre-breathe to activate the scrubber sorb, anyone who says different doesn't know what they are talking about!"...
    .... to get more accurate CO2 injection in the breathing machine we put 2 mass flow controllers in series ...
    .... The noise is a few tens of nano-volts, so DL were able to reduce the output voltage ...
    .... radial scrubbers give longer dwell time than axials...
    .... the earth is flat and ...

  10. #40
    RBW Member Snusmumrik will become famous soon enough Snusmumrik will become famous soon enough Snusmumrik will become famous soon enough Snusmumrik's Avatar
    Join Date
    Nov 2008
    Location
    St.Petersburg, Russia
    Posts
    207
    IDA-71(KISS Mod)

    IDA-59 O2 Mod & KISS, IDA-72

    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
    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?

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts