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RMV vs SAC rate

Discussion in 'Shearwater Research' started by BlueTrin, Oct 10, 2019.

  1. BlueTrin

    BlueTrin DIR Practitioner

    # of Dives: 50 - 99
    Location: London
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    It looks like the Perdix does not allow you to enter the tank size to convert the SAC into RMV.

    Can I check with you guys that my understanding is correct ?

    The SAC is in pressure unit (that would be bar for me), while the RMV is in volume.

    Both are adjusted for ambient pressure.

    So if I use a 2x12liters twinset and have a SAC of 1bar/min, this would translate to 24liters/min, is that correct ?
     
  2. foob

    foob Nassau Grouper

    # of Dives: 100 - 199
    Location: San Francisco
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    Believe so
     
  3. tursiops

    tursiops Marine Scientist and Master Instructor ScubaBoard Supporter

    # of Dives: 2,500 - 4,999
    Location: U.S. East Coast
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    Yes, remembering it is a surface value. At 10m you'll use twice that. Correct, no way to enter tank size in the computer or the app.
     
    BlueTrin likes this.
  4. Manatee Diver

    Manatee Diver Manta Ray

    # of Dives: None - Not Certified
    Location: Tampa Bay, FL
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    Third party apps like Macdive allow you to enter tank size to get the RMV rate.
     
    RayfromTX likes this.
  5. Pavao

    Pavao Manta Ray

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    SAC vs RMV, who cares what’s called? I think people love to complicate things and this just creates confusion.

    I consume x cf3/min at the surface, it’s what matters, from here I can calculate the consumption at any depth, irregardless what name one may assine to it.

    One for pressure and the other for volume just leaves room for error in my opinion.
     
  6. tursiops

    tursiops Marine Scientist and Master Instructor ScubaBoard Supporter

    # of Dives: 2,500 - 4,999
    Location: U.S. East Coast
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    You may be missing the point of the thread. The OP's computer only reports psi or bars per minute. He wants to convert this to cuft or liters per minute, possibly so you will be happy. :)
     
    StefinSB and BlueTrin like this.
  7. Norwegian Cave Diver

    Norwegian Cave Diver Barracuda

    # of Dives: 200 - 499
    Location: Calgary Alberta Canada
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    I use the Shearwater Petral 2 (non AI). In the "Dive Setup - Dive Planner" menus - it requires an RMV value to be entered.
    In the Shearwater Cloud version - I can go in after a dive and enter tank info to create a SAC Rate for that specific dive.
    Seems like Shearwater should automatically create a RMV for me for each specific dive also. Would be much nicer to enter a very accurate number in the "planning" stage of a dive.
     
  8. rsingler

    rsingler Scuba Instructor, Tinkerer in Brass Staff Member ScubaBoard Sponsor

    # of Dives: 500 - 999
    Location: Napa, California
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    See the Shearwater FAQ for their philosophy on why they do not do that...

    Or if it's not there, look thru other threads in this forum. They have responded to this question on more than one occasion.
     
  9. foob

    foob Nassau Grouper

    # of Dives: 100 - 199
    Location: San Francisco
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    I prefer bar/min to liters/min. That's what the gauge goes by.

    Easy to convert to liters just multiply tank volume.
     
  10. BlueTrin

    BlueTrin DIR Practitioner

    # of Dives: 50 - 99
    Location: London
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    I prefer l/min because it does not change when I use:
    • a 12l
    • a 15l
    • a twin 12l
    The bar/min is not adjusted for ambient pressure so I would prefer to use GTR to estimate how much time remaining is in my tanks. This is probably not true if you have to change depth often during the dive.
     
    Centrals, jstrang and racanichou like this.

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