+ Reply to Thread
Page 1 of 2 1 2 LastLast
Results 1 to 10 of 14

Thread: Isolation

  1. #1
    RBW Member deedee has a spectacular aura about deedee has a spectacular aura about deedee has a spectacular aura about deedee has a spectacular aura about deedee has a spectacular aura about deedee has a spectacular aura about deedee's Avatar
    Join Date
    Jan 2006
    Location
    Florida
    Posts
    57
    rEvo Micro Titanium

    Sentinel

    Isolation

    After reviewing Paul from rEvo approach to isolation with 10k resistors , and Bruce's Shearwater approach to no isolation. I am a bit confused.
    I would like for the two computers to be isolated, but why would 10k resistors even work ? Why not put a diode that lets current in a single direction ?
    Can anyone explain failure modes that isolation protects us from , and which failure modes this protection does not help with ?
    D

  2. #2
    RBW Member Serge is a splendid one to behold Serge is a splendid one to behold Serge is a splendid one to behold Serge is a splendid one to behold Serge is a splendid one to behold Serge is a splendid one to behold Serge is a splendid one to behold Serge is a splendid one to behold Serge is a splendid one to behold Serge is a splendid one to behold Serge is a splendid one to behold Serge's Avatar
    Join Date
    Dec 2007
    Location
    NY
    Posts
    939
    rEvo II

    Evolution

    Re: Isolation

    Quote Originally Posted by deedee  View Original Post
    After reviewing Paul from rEvo approach to isolation with 10k resistors , and Bruce's Shearwater approach to no isolation. I am a bit confused.
    I would like for the two computers to be isolated, but why would 10k resistors even work ? Why not put a diode that lets current in a single direction ?
    Can anyone explain failure modes that isolation protects us from , and which failure modes this protection does not help with ?
    D
    Good question. I'm only a chem-e, so take this with a grain of salt. The diode does not stop the flow of electric current, but the resistor would preferentially throttle it in case there is a short downstream. If there is a problem or a short downstream of the resistor, the other side of the splitter will still be functional. If the short is on the non-resisted side, i.e., the rEvodream, then the entire circuit will be compromised.

    A diode is like a check valve (unidirectional), and a resistor is more like a partially closed valve (bi-directional). But what do I know? I'm only a chem-e.

  3. #3
    Supporting Member Dsix36 has a reputation beyond repute Dsix36 has a reputation beyond repute Dsix36 has a reputation beyond repute Dsix36 has a reputation beyond repute Dsix36 has a reputation beyond repute Dsix36 has a reputation beyond repute Dsix36 has a reputation beyond repute Dsix36 has a reputation beyond repute Dsix36 has a reputation beyond repute Dsix36 has a reputation beyond repute Dsix36 has a reputation beyond repute Dsix36's Avatar
    Join Date
    Aug 2007
    Location
    Deerfield_Beach, Florida
    Posts
    4,108
    rEvo

    Defender Optima Dolphin

    Re: Isolation

    an isolating system can be as simple as a resistor: if the electronics have a high input resistance, like the shearwater 100k, you can put a lower resistor (say 10k) in the line between the cell output and the input of the electronics:if the elecotrinics get shorted for whatever reason, you still have a 10k resistance between the 2 poles of the oxigen cell, and the output will only be affected minimal
    the rEvodreams have already low input resistance (10k: matched to the R22D need), so you can not put an extra resistor there.
    so this meens: if you use 2 shearwaters using the same cell, you can put an isolater resistor on each line to the shearwater, if you use a rEvodream and a shearwater reading the same cell, you only put the isolator on the shearwater side.

    This came straight from Paul, in response to a similar question from me.
    .
    I guarantee that if you CLICK HERE you will not have your view blocked by clothing





    Quote Originally Posted by kwinter  View Original Post
    I could just be blowing smoke out my butt.
    Quote Originally Posted by kwinter  View Original Post
    And note the wisdom from DSix36
    MY ADVICE AND POSTS ARE WORTH EXACTLY WHAT YOU PAID FOR THEM!!!!!!
    POLITICAL CORRECTNESS IS SO YESTERDAY AND I AM DONE WITH IT!!!!!

  4. #4
    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
    Join Date
    Feb 2005
    Location
    Vancouver Island BC Canada
    Posts
    3,854
    Hollis Prism 2, Megalodon

    CCR Instructor Trainer

    Re: Isolation

    A diode requires a certain amount of voltage to cause current to flow in the direction it is suppose to. That is called forward bias and is typically 700mv for a silicon diode which is much higher than most O2 cells can provide.
    Last edited by wedivebc; 19th March 2010 at 03:24.
    Cheers,

    Dave....

    www.wedivebc.com

  5. #5
    Shearwater Copis Diver Gill Envy has a reputation beyond repute Gill Envy has a reputation beyond repute Gill Envy has a reputation beyond repute Gill Envy has a reputation beyond repute Gill Envy has a reputation beyond repute Gill Envy has a reputation beyond repute Gill Envy has a reputation beyond repute Gill Envy has a reputation beyond repute Gill Envy has a reputation beyond repute Gill Envy has a reputation beyond repute Gill Envy has a reputation beyond repute Gill Envy's Avatar
    Join Date
    Nov 2005
    Location
    seattle
    Posts
    2,011
    Copis Meg and rEvo III

    Evolution

    Re: Isolation

    ISC has added protection between their stock and Shearwater computers on the Copis II but I've never gotten around to it between my shearwater HUD and Pursuit ... It would be nice if someone (Bruce perhaps ;~) would be willing to flood hooked up shared cells to demonstrate how one computer can effect another if it get's shorted. I've always presumed it would be pretty obvious and be a fairly blatant BO situation but have been cautioned on that. I'd also like to know if such a scenario on two "un-isolated" computers would render both permanently FUBAR-ED even once the fried circuit is removed... as in, in field in a remote location.

  6. #6
    Roland Somodi rolanddiver is a glorious beacon of light rolanddiver is a glorious beacon of light rolanddiver is a glorious beacon of light rolanddiver is a glorious beacon of light rolanddiver is a glorious beacon of light rolanddiver is a glorious beacon of light rolanddiver is a glorious beacon of light rolanddiver is a glorious beacon of light rolanddiver is a glorious beacon of light rolanddiver is a glorious beacon of light rolanddiver is a glorious beacon of light rolanddiver's Avatar
    Join Date
    Aug 2007
    Location
    Kaposvar, Hungary
    Posts
    660
    Homebuilt(s)

    Inspiration Classic

    Re: Isolation

    Another approach is to use OP AMPs. Since you most likely need OP AMPs because of the resolution, the same operational amplifier could act as an isolator. it is easy to set the input impedance to match with the required load of the cells, also their own input impedance is very very high and output impedance is low. Should one of them fail, the output of the others will not ba affected too much, if at all. I hope it helped.


    Very Respectfully

    Roland Somodi

  7. #7
    Supporting Member Dsix36 has a reputation beyond repute Dsix36 has a reputation beyond repute Dsix36 has a reputation beyond repute Dsix36 has a reputation beyond repute Dsix36 has a reputation beyond repute Dsix36 has a reputation beyond repute Dsix36 has a reputation beyond repute Dsix36 has a reputation beyond repute Dsix36 has a reputation beyond repute Dsix36 has a reputation beyond repute Dsix36 has a reputation beyond repute Dsix36's Avatar
    Join Date
    Aug 2007
    Location
    Deerfield_Beach, Florida
    Posts
    4,108
    rEvo

    Defender Optima Dolphin

    Re: Isolation

    It doesn't have to be a computer that fails and gets shorted out. It could be as simple as a cable getting pinched and causing the short. If the system is using isolation, then it would not short out the cell and cause bad readings on the other computer/HUD. You can test this out by just shorting out the wiring at the splitters and checking the electronics to test the isolation.
    .
    I guarantee that if you CLICK HERE you will not have your view blocked by clothing





    Quote Originally Posted by kwinter  View Original Post
    I could just be blowing smoke out my butt.
    Quote Originally Posted by kwinter  View Original Post
    And note the wisdom from DSix36
    MY ADVICE AND POSTS ARE WORTH EXACTLY WHAT YOU PAID FOR THEM!!!!!!
    POLITICAL CORRECTNESS IS SO YESTERDAY AND I AM DONE WITH IT!!!!!

  8. #8
    Helium Addict O.C.Diver is a glorious beacon of light O.C.Diver is a glorious beacon of light O.C.Diver is a glorious beacon of light O.C.Diver is a glorious beacon of light O.C.Diver is a glorious beacon of light O.C.Diver is a glorious beacon of light O.C.Diver is a glorious beacon of light O.C.Diver is a glorious beacon of light O.C.Diver is a glorious beacon of light O.C.Diver is a glorious beacon of light O.C.Diver is a glorious beacon of light O.C.Diver's Avatar
    Join Date
    Mar 2006
    Posts
    361

    Re: Isolation

    Quote Originally Posted by deedee  View Original Post
    After reviewing Paul from rEvo approach to isolation with 10k resistors , and Bruce's Shearwater approach to no isolation. I am a bit confused.
    I would like for the two computers to be isolated, but why would 10k resistors even work ? Why not put a diode that lets current in a single direction ?
    Can anyone explain failure modes that isolation protects us from , and which failure modes this protection does not help with ?
    D
    Kevin Juergensen would likely be the one to best explain this as he did the testing and brought the technology to Rebreathers over a decade ago.

    Ted

  9. #9
    Brent - Narked at 90
    divetheworld has a reputation beyond repute divetheworld has a reputation beyond repute divetheworld has a reputation beyond repute divetheworld has a reputation beyond repute divetheworld has a reputation beyond repute divetheworld has a reputation beyond repute divetheworld has a reputation beyond repute divetheworld has a reputation beyond repute divetheworld has a reputation beyond repute divetheworld has a reputation beyond repute divetheworld has a reputation beyond repute divetheworld's Avatar
    Join Date
    Mar 2005
    Location
    Prescot, England
    Posts
    2,423
    Deep Pursuit or a Camelion

    and 11 others inc. a UT-240

    Re: Isolation

    We've been harping on about isolation for years. Mind you, we actually developed on that works. All our cable sets come with it as standard.

    The isolation is really simple but you are juggling a lot of balls in the air to get it right.
    The failures we are trying to protect against are;
    1. Cut cable and a direct short
    2. Flooded computer with shorted connections
    3. Disconnected Fischer with seawater signal crossover

    At the same time the system must work accurately with the second cable connected or disconnected.

    A single resistor inline doesnt do everything. Remember that a controller doesnt get unplugged. It's failure modes are not the same as that of a plugged computer.

    The dive computers on the market all have a different internal impedance. So when we connect our dive computers or displays the impedance the cell should see should be approximately 10k (ref. Teledyne). As long as this is the case, all is copasetic.
    If we do our calcs to ohms law then we can introduce a simple impedance network that will balance this adequately. But if we then choose to dive without a second handset, our calcs go wrong as you are missing a load.
    So the impedance matching must be a factor of the computers internal impedance, the impedance of our network and the potential failure mode and the impedance we expect of each of those failure modes.
    So the plan would be to do those calculations with every possible mode of operation, every possible failure and every possible dive computer.

    when you get it right, you dont have the failure modes of an active system that is dependant upon a power supply but we have a little less accuracy than that system under a complete cable failure. The accuracy is within acceptable limits so we call that a success.
    Involved in the design of our circuits were everyone from Teledyne to VR Technology.
    Copying skips understanding. Understanding is how you grow. You have to understand why something works or why something is how it is. When you copy it, you miss that. WWW.NARKEDAT90.COM
    www.puwer.co.uk PUWER and Machinery CE Marking www.ce-eu.com

  10. #10
    CEO-Shearwater
    bgpartri has a brilliant future bgpartri has a brilliant future bgpartri has a brilliant future bgpartri has a brilliant future bgpartri has a brilliant future bgpartri has a brilliant future bgpartri has a brilliant future bgpartri has a brilliant future bgpartri has a brilliant future bgpartri has a brilliant future bgpartri has a brilliant future bgpartri's Avatar
    Join Date
    Apr 2005
    Location
    Vancouver, Canada
    Posts
    721
    rEvo, JJ

    Meg,CCR2000,KISS,Inspo,Dolphin

    Re: Isolation

    Quote Originally Posted by deedee  View Original Post
    After reviewing Paul from rEvo approach to isolation with 10k resistors , and Bruce's Shearwater approach to no isolation. I am a bit confused.
    I would like to clarify this. I did not in any way imply that I am against isolation. Shearwater products fully support isolation and most manufacturers incorporate isolation when they use Shearwater products in their rebreathers.

    What I actually said is that in some situations, choosing not to use isolation is a valid choice. For example, if I was diving a Sport KISS and never went beyond 100 feet and never went into decompression, it is acceptable, in my mind, to just bail out with any problem.

    If I were a mile back in a cave at 300 feet, my recommendation would be quite different.

    Bruce
    The greatest enemy of knowledge is not ignorance. It is the illusion of knowledge.
    http://www.shearwater.com

+ Reply to Thread
Page 1 of 2 1 2 LastLast

Posting Permissions

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