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Thread: Which eCCR?

  1. #81
    aka Scotty com1 will become famous soon enough com1 will become famous soon enough com1 will become famous soon enough com1's Avatar
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    Re: Which eCCR?

    Sorry cant follow you:
    Quote Originally Posted by Tastyfish  View Original Post
    As an example; assume that you connect a 100k resistor and get 1mV.
    OK Ohm's law: I=V/R=1mV/100k=0.01A
    Quote Originally Posted by Tastyfish  View Original Post
    If you then attach another on in parallel
    R total = (R1*R2)/(R1+R2)= (100k*100k)/(100k+100k) = 50K
    Quote Originally Posted by Tastyfish  View Original Post
    you will get 2mV but the current will stay the same.
    Ohm's law: V= 0,01A*50K=0,5mV
    Quote Originally Posted by Tastyfish  View Original Post
    If it had been a voltage source the it would have been the other way around; the voltage should have stayed at 1mv but the current should have dropped to half the original value.
    Ohm's law: I=U/R so half of the resistance means double voltage

  2. #82
    So many CCR So little etc Mark Chase has a reputation beyond repute Mark Chase has a reputation beyond repute Mark Chase has a reputation beyond repute Mark Chase has a reputation beyond repute Mark Chase has a reputation beyond repute Mark Chase has a reputation beyond repute Mark Chase has a reputation beyond repute Mark Chase has a reputation beyond repute Mark Chase has a reputation beyond repute Mark Chase has a reputation beyond repute Mark Chase has a reputation beyond repute Mark Chase's Avatar
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    Re: Which eCCR?

    From memory my Uri HUD I had on the Inspo Classic had a 10K resister in line which was to prevent errors in the event of a handset failure causeing reverse current.

    Does that sound correct?

    I know nothing about electronics

    I took APDs comments to Uri Barron who designed the HUD and he said they were talking bollocks. I thaught he might be bias so I took the issue to a freind who was an electrical engener doing R&D and he agreed it was bollocks.


    ATB

    Mark

  3. #83
    Duvet Diver Simon A is a glorious beacon of light Simon A is a glorious beacon of light Simon A is a glorious beacon of light Simon A is a glorious beacon of light Simon A is a glorious beacon of light Simon A is a glorious beacon of light Simon A is a glorious beacon of light Simon A is a glorious beacon of light Simon A is a glorious beacon of light Simon A is a glorious beacon of light Simon A is a glorious beacon of light Simon A's Avatar
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    Re: Which eCCR?

    Quote Originally Posted by Kristen24060  View Original Post

    Does anyone know what kind of isolation system Narked at 90 uses for their splitters?
    Narked@90 use a passive isolation system, you can short all the wires together on one isolated output and the other output maintains enough accuracy to get you home.

    HTH
    Simon A

  4. #84
    RBW Member DopRob is an unknown quantity at this point DopRob's Avatar
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    Re: Which eCCR?

    Private Message sent..

  5. #85
    Dave Tomblin wedivebc has a reputation beyond repute wedivebc has a reputation beyond repute wedivebc has a reputation beyond repute wedivebc has a reputation beyond repute wedivebc has a reputation beyond repute wedivebc has a reputation beyond repute wedivebc has a reputation beyond repute wedivebc has a reputation beyond repute wedivebc has a reputation beyond repute wedivebc has a reputation beyond repute wedivebc has a reputation beyond repute wedivebc's Avatar
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    Re: Which eCCR?

    Quote Originally Posted by Tastyfish  View Original Post
    Honestly I do not know how to respond to that. I am an engineer with a master degree in both applied physics and electrical engineering. To me none of your claims stands up to basic science. I can understand that you believe you know how things work and that your arguments are solid but it does not change the fact that they are based on misconceptions or lack of basic knowledge in basic physics.

    A oxygen sensor is a constant current source. This means that it outputs the same current, which depends on the oxygen level, regardless of the load. Of course there is limits to its maximum capacity and thus it has an upper limit on the current. As cells grow old this limit is lowered and eventually it starts to affect normal operation in a rebreather. That is when divers realise that the cell is "current limited", but from a scientific point of view it always has been. The way a system reads the sensor is to attach it a load and measure the voltage generated by the current. Since both the load resistance and the current is constant it is the voltage that varies depending on the oxygen level.

    You talk about a splitter. There is no splitter as such. You simply wire the cell to a second load in parallell with the first. Rather than splitting the readings you do them twice and independently. Since it is a constant current source it will pump out more current and both loads will measure the exact same result. The second wire and the second load will not be any less reliable than the first and they are completely independent and not depending on anything besides the cell itself.

    That basically settle the discussion and invalidates the rest of your claims too. I hope there are more engineers in here that can back me up in this regard.

    If you where to reverse engineer a Poseidon unit I am pretty sure you would find that this is indeed how they do separate readings for their HUD and their controller.

    I have seen this exact setup on both KISS and Pelagian units and it works just fine. If you want an example of a commercial unit with this setup you should read up on the new JJ-CCR with the new DiveCAN-system from Shearwater. It has two completely independent CAN-buses. On each buss there is a separate analog-to-digital converter wired in parallel to the cells. If the first converter fails you will loose the solenoid controller and the Petrel unit, but the HUD will still work perfectly with all three cells. If the second converter fails it is the other way around. Thinking about it the Poseidon have this level of redundancy with two cells on both HUD/handset. Adding the third cell and a third monitor is actually even better. But I still can't help feeling that it would be nice if the tertiary monitor could rely on all three cells too, even though you probably should start thinking about aborting the dive anyway if things fail to that extent!

    The problem I think is you are incorrectly assuming that the cell monitoring circuitry is what is providing the load when in fact the load for the cell is a built in resistor on the cells circuit board and the input impedance of the hand set cell monitoring hardware has minimal effect on the cells load.
    Cheers,

    Dave....

    www.wedivebc.com

  6. #86
    RBW Member Tastyfish is an unknown quantity at this point Tastyfish's Avatar
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    Re: Which eCCR?

    Quote Originally Posted by wedivebc  View Original Post
    The problem I think is you are incorrectly assuming that the cell monitoring circuitry is what is providing the load when in fact the load for the cell is a built in resistor on the cells circuit board and the input impedance of the hand set cell monitoring hardware has minimal effect on the cells load.
    Strictly speaking both the output impedance of the sensor and the input impedance of the monitor combined is what makes up the load for the fuel cell at the hearth of the sensor. So not so much an incorrect assumption as a pedagogical problem digging to deep into the details. The important part is your last sentence which is how this discussion got started and what has been my point all along; the handset monitoring hardware has minimal effect on the cell load. You are the second person here to agree on that. That means that connecting a second monitoring device to a cell will not screw up its readings nor will it make them dependent on each other.
    Last edited by Tastyfish; 1st June 2014 at 18:15.

  7. #87
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    Re: Which eCCR?

    Quote Originally Posted by com1  View Original Post
    Ohm's law: I=U/R so half of the resistance means double voltage
    Yes. You're right. So I screwed up the example.

  8. #88
    RBW Member Mr_Archie is an unknown quantity at this point Mr_Archie's Avatar
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    Re: Which eCCR?

    Quote Originally Posted by wallen  View Original Post
    I was quoted $12,500 Australian for a 7 W/tech config (8,376 Euro). This is with training, which runs about $800 locally.

    Edit: The quote did not include a Poseidon harness and wing.
    I can only say you haven't talked to the right people but my trainning cost $1800 though. Anyway, get what I pay for.

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