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Thread: Pondering simplicity: analog o2 monitoring?

  1. #41
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    Re: Pondering simplicity: analog o2 monitoring?

    Quote Originally Posted by Sparedone  View Original Post
    Simply a magnificent build! Love seeing a well thought out rig based on an already excellent design. The immaculate condition in the photos speak volumes as well. You wouldn't happen to have it's twin collecting dust by chance?

    With this inspiration I now have encapsulated strontium aluminate on it's way for glow paint to add to my build.
    No I don't have another one like this, but know about 1 unit similar but not nearly in the condition of this one.

    Best regards?
    Chett. L

  2. #42
    Mature mouth breather silent running has a reputation beyond repute silent running has a reputation beyond repute silent running has a reputation beyond repute silent running has a reputation beyond repute silent running has a reputation beyond repute silent running has a reputation beyond repute silent running has a reputation beyond repute silent running has a reputation beyond repute silent running has a reputation beyond repute silent running has a reputation beyond repute silent running has a reputation beyond repute silent running's Avatar
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    Re: Pondering simplicity: analog o2 monitoring?

    Quote Originally Posted by Sparedone  View Original Post
    Welcome to a post where the 1950s meet a youngsters musings as I'm adding a ppo2 monitor to a o2 breather build.

    Concept: Use analog mv readings for ppo2 monitoring.

    Benefit: fewer failure points due to reduced components.

    Design concept: Cell, potentiometer at the cell, cable gland, cable, potted needle gauge.

    Even the most basic digital ppo2 meter adds complexity to the simple process of displaying a calibrated a mv reading off the cell.

    Why not a potted analog needle guage run off a cell directly? No battery to change, flood or fail. No lcd display to burn out, no circuitry to corrode. Sure, you can't expect accuracy from an needle gauge while invertered or after smashing it with a rock. Also they also don't like water, but with no battery to change they could be epoxy entombed.

    What else am I needing to learn before I stick two on my build?

    Thanks for considering a tinkerer's pondering.

    Regards,
    Cameron
    Hello Cameron, your idea is a very good one, the same idea behind the analog secondary on the Prism 1/Topaz and MK's.

    As a Prism diver since 2003, I have travelled all over the Pacific and Caribbean and never broken an analog secondary, nor missed a dive, thanks to the simple architecture of the Prism one, of which the analog gauge is a central feature. Indeed, I have done several dives on my Prism with the electronics/high current side turned off after a battery died or the battery compartment flooded. No big deal, the gauge worked flawlessly as it always does, because it is isolated from the high current side of the unit architecture.

    Another useful feature of the Prism's analog rotary sensor dial is that as you scroll between sensors 1-2-3, you get to see how each sensor reacts when put under the load of the gauge needle. If a sensor comes up fast, you know you have plenty of current, if it is sluggish and seems to get more so as it nears setpoint, you know it's likely on its way out. It seems to me that this system allows you to be the most in touch with your sensors during a dive as there is no conversion or averaging or computer calibration involved above or below the water. A CMF CCR with only analog gauges would probably be the most reliable of all designs, it certainly would be less likely to fail under x number ata of saltwater than one which relies on high current and microprocessors.

    I believe Robert Landreth may still be making his high quality double jeweled gages with Lumberg cables, which are possibly better than the P1 stock version. I have banged my P1 gauges around plenty with no problems, just make sure they are clipped off when not in use and they wear fine. And anyway, life support equipment should always be treated with utmost care no matter how durable a manufacturer claims it to be... -Andy

  3. #43
    RBW Member cstmwrks is a jewel in the rough cstmwrks is a jewel in the rough cstmwrks is a jewel in the rough cstmwrks is a jewel in the rough cstmwrks is a jewel in the rough cstmwrks is a jewel in the rough cstmwrks is a jewel in the rough cstmwrks's Avatar
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    Re: Pondering simplicity: analog o2 monitoring?

    Quote Originally Posted by heyydude  View Original Post
    So, the cool thing about these milliamp gauges is like you said, they don't need batteries.

    The uncool thing about them is that they:

    a) Require a Switch to change from sensor to sensor. That switch then must have a Sealed Shaft, and then a Panel Seal which can handle up to 100m of pressure. The Sealed Shaft isn't so hard (Grayhill still makes them) but they changed the Panel Seal from the old style 150 psi model to a new version (frustratingly with the EXACT same part number) which can only handle 15 psi. You then need a way to transit those three different signals to your Meter, which, in the case of the Mark 15, included a custom PCB with a second right-angle PCB attached in tandem.

    b) Require potentiometers to calibrate each cell individually. That means that whatever water tight seal you may have has to be opened, and you must then tweak each pot to calibrate each sensor.

    c) The meter puts a tiny load on the cells, which can affect (albeit small) each sensor signal to the Primary Electronics (which I'm assuming you'd do digitally, because Analog Controllers is a whole 'nuther can o' beeswax - and trust me, I built these buggers myself, so I know whereof I speak).

    d) The meters are unobtanium - they can be custom ordered from Jewell (or the company that took them over) but I'd hate to see what they cost today, or how many quantities you'd have to buy.

    Kevin.
    Hi Kevin,
    Throwing issue d out the window and if one just had a single meter and sensor, how simple would the wiring be? The cell, trim pot across the leads and the meter? Is the trim pot a small value in line with a larger resistor that loads the cell? Or something entirely different?

    At one point I wanted to try to build a close copy of the Electrolung to include analog electronics and polariographic 02 sensors. Even talked with John Kanwisher and wrote to Walter Starck. Walter was pretty open and helpful. John, not so much.

    Anyhow the thoughts of re creating the analog electronics like the Electrolung died with the difficulty of finding a few key parts. Still it's fun to have a better understanding of how some of this stuff worked.
    Last edited by cstmwrks; 18th July 2016 at 04:29. Reason: typo

  4. #44
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    Re: Pondering simplicity: analog o2 monitoring?

    Quote Originally Posted by cstmwrks  View Original Post
    Hi Kevin,
    Throwing issue d out the window and if one just had a single meter and sensor, how simple would the wiring be? The cell, trim pot across the leads and the meter? Is the trim pot a small value in line with a larger resistor that loads the cell? Or something entirely different?

    At one point I wanted to try to build a close copy of the Electrolung to include analog electronics and polariographic 02 sensors. Even talked with John Kanwisher and wrote to Walter Starck. Walter was pretty open and helpful. John, not so much.

    Anyhow the thoughts of re creating the analog electronics like the Electrolung died with the difficulty of finding a few key parts. Still it's fun to have a better understanding of how some of this stuff worked.

    Hey there,

    If you had one of the meters, you could probably recreate the Secondary Display - I'm not sure if Grayhill still makes the Switches, but I still have a few of those kicking around - once you get one of them, you simply reproduce the circuit, which is very straight forward. There is a 2k Ω potentiometer in line with each of the Sensor outputs, which serves the purpose of calibration (flush the loop with 100%, then adjust the trim of the pot until you read .98 or thereabouts).

    When I get back into the shop, I'll try to post some pictures of the traces on the board so you can see how it goes together.

    The impressive thing to me is that these guys were doing this back in '69, and many of these things still work today. I believe that if BioMarine hadn't imploded after losing the contract for the 2nd batch of Mark 16's to Carleton, everyone would have been diving a BioMarine unit today. They were just way ahead of their time. Of course, guys like Martin, Leon, Me, Paul, etc wouldn't be earning a living off these things either - but that's another story for an alternate reality altogether...

    Kevin.

  5. #45
    RBW Member cstmwrks is a jewel in the rough cstmwrks is a jewel in the rough cstmwrks is a jewel in the rough cstmwrks is a jewel in the rough cstmwrks is a jewel in the rough cstmwrks is a jewel in the rough cstmwrks is a jewel in the rough cstmwrks's Avatar
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    Re: Pondering simplicity: analog o2 monitoring?

    Quote Originally Posted by heyydude  View Original Post
    When I get back into the shop, I'll try to post some pictures of the traces on the board so you can see how it goes together.

    They were just way ahead of their time. Of course, guys like Martin, Leon, Me, Paul, etc wouldn't be earning a living off these things either - but that's another story for an alternate reality altogether...

    Kevin.
    Thanks Kevin.. I'm sure plenty of people would be interested to see the circuit. Also I like your fast track method to 1 million dollars... start out with 2. Kept me chuckling for awhile.

    Bill

  6. #46
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    Re: Pondering simplicity: analog o2 monitoring?

    Quote Originally Posted by heyydude  View Original Post
    Hey there,

    There is a 2k Ω potentiometer in line with each of the Sensor outputs, which serves the purpose of calibration (flush the loop with 100%, then adjust the trim of the pot until you read .98 or thereabouts).

    Kevin.
    Some thing this simple? :
    analog.jpg

    I pondered this for awhile. The meter is a magnetic coil and the cell is a power source. Cell sees more 02 and increases it's voltage, voltage increase changes the magnetic field at the meter and moves the needle.


    Did the MK 15 have a 10K resistor across the outputs from the cell like is used when connected to a digital panel meter? or was it pretty much as bare bones as my drawing?

  7. #47
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    Re: Pondering simplicity: analog o2 monitoring?

    Thanks for the diagram, made me laugh.

    I am an idiot when it comes to electronics (well, most things actually) but I would modify the circuit so that the potentiometer is on one lead to the cell, the other cell lead would go to ground ("earth" for everyone not in the US). One lead of the meter would also go to the common ground.

    As I read Kevin's statement each _cell_ would have it's own potentiometer that would allow calibration for each cell, in O2. Then you can use the same meter to read all cells by using a multi position switch.
    Last edited by 4ster; 19th July 2016 at 19:10.

  8. #48
    RBW Member cstmwrks is a jewel in the rough cstmwrks is a jewel in the rough cstmwrks is a jewel in the rough cstmwrks is a jewel in the rough cstmwrks is a jewel in the rough cstmwrks is a jewel in the rough cstmwrks is a jewel in the rough cstmwrks's Avatar
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    Re: Pondering simplicity: analog o2 monitoring?

    Quote Originally Posted by 4ster  View Original Post

    As I read Kevin's statement each _cell_ would have it's own potentiometer that would allow calibration for each cell, in O2. Then you can use the same meter to read all cells by using a multi position switch.
    OK.. that makes much more sense now. When I was asking about the circuit it was for a single cell / meter. Kevin's answer was based on the three cells and a single meter. As I was reading it my mind was still thinking in term of singe cell / meter. Hence the WTF on what ( at the time ) sounded like a pot on both leads.

    Either I should drink less or drink more before posting. Not sure what way to go on that one either.

  9. #49
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    Re: Pondering simplicity: analog o2 monitoring?

    In the Horseshoe Board of the Mark 15, there is a 530 Ω Resistor in-line with each sensor (the Mark 15 was designed to use BioMarine Sensors, which were made individually out of stainless steel, plastic, and other parts). Later, the Mark 16 was modified to have a 2k Ω resistor in line with the sensors (R-10 types made by Teledyne and AI).

    Kevin.

  10. #50
    Thinker n Tinkerer Sparedone is an unknown quantity at this point Sparedone's Avatar
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    Re: Pondering simplicity: analog o2 monitoring?

    Dropping in again with an update. I appreciate the ongoing discussion in the thread. Great tip on watching the needle climb which switching to clarify which cell may be wonky. Learning lots I hope. Looking forward to the mk15 pics as well.

    My cells ended up lost in Florida and the second set are on their way. Turns out my 10kohm meters are just 2.5kohm with an added resistor to total 10kohm. I intend to have this illconceived project isolated from my primary including separate cells so the mv drop from the resistance I presume won't be a problem? Come on good old Canada postal service!

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