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Hypothetical - 2 AI transmitters instead of backup SPG?

Discussion in 'Computers, Gauges, Watches and Analyzers' started by Shafqat Ahmed, Jul 12, 2019.

  1. Shafqat Ahmed

    Shafqat Ahmed Angel Fish

    # of Dives: 50 - 99
    Location: San Francisco
    So this is purely hypothetical - I'm pretty happy with my single transmitter + mini SPG.

    I see some divers on SB prefer not to use a backup SPG, typically because they want fewer hoses, and I'm curious if using 2 transmitters on the same tank (ideally of different transmit frequencies) might be an option for some of them that have a few hundred dollars to spare. Just trying to be helpful :)

    Besides being expensive, I was just wondering if there's any other reason this might be a dumb idea.
  2. -JD-

    -JD- Eclecticist ScubaBoard Supporter

    # of Dives: 25 - 49
    Location: Greater Philadelphia, PA
    A second receiver-computer would also be required for full redundancy, but I otherwise don't see a problem with it.
  3. dmaziuk

    dmaziuk Great White

    Failure on the receiving end would be a problem, but then again, if that's your whole computer going titsup, that won't be the only problem.
  4. DiveTucson

    DiveTucson Angel Fish

    This is one that will get so many opinions.

    When I dive single tank recreational setup I dive with either a transmitter or SPG but not both. If one fails I call the dive and move on. By having both you are adding another failure point and another layer of complexity that is just not necessary.

    How many dives have you had to call because of a transmitter or SPG problem?
    rongoodman likes this.
  5. scubadada

    scubadada Diver Staff Member ScubaBoard Supporter

    # of Dives: 1,000 - 2,499
    Location: Philadelphia and Boynton Beach
    So, now I have one transmitter, two AI computers off the same transmitter, and still have my SPG, I'm covered :) My second computer used to be non-AI, I was still covered...
    caruso likes this.
  6. loosenit2

    loosenit2 Solo Diver

    I frequently dive solo with an al 80 and a 19 cuft pony. When I do I have two transmitters connected to my teric. Never had a problem with the teric displaying tank pressure from both xmiters. As others have mentioned computer going out would be problem,but that is same problem as 1 xmiter and 1 computer. You would also have to have 1st stage with 2 HP ports, and it might, I emphasize might, make your hose routing a little odd.

    Seems kinda over redundant to me in general though. Everyone talks about computer backups, but I never hear anyone talking about multiple SPGs. Modern computers are very reliable.
  7. KWS

    KWS ScubaBoard Supporter ScubaBoard Supporter

    # of Dives: 500 - 999
    Location: SE TEXAS
    would not be a problem with a DC that can monitor multiple xmitters. so long as the backup xmitter is just that a psi backkup sensor. your computer will use the primary for full blown functions and the backup as a buddy tank input for psi only.
  8. caruso

    caruso Solo Diver

    # of Dives: 200 - 499
    Location: Long Island, NY
    I do the same if anyone is taking votes. Although my spg is about the size of a nickel and is next to my LP inflator on a thin hose ziptied to the LP hose. I carry a backup transmitter in my toolkit.

    I find the mini SPG quite useful to check tank pressure pre-dive in addition to the redundancy and therefore see no reason for a second transmitter even though I carry 2 identical receiver computers.
  9. KWS

    KWS ScubaBoard Supporter ScubaBoard Supporter

    # of Dives: 500 - 999
    Location: SE TEXAS
    First let me say i have been on submarines for my military service. the purpose of a backup is to provide a alternate source that does not use the same systems of the system that is being backed up. If you have to go to the backup then you are not in normal operations and you understand you will be operating in less than full processing capability. In the case of doubles psi sensors are off different tanks, different regs and different hoses. a total failure in the psi system on one side can be replaced totally replaced by the other so long as you do not close the isolation valve. 2 sensors on the same system is basically a backup for the readout portion of the functions only. On a single tank system you will never be able to use a alternate gas source. its piping if you only have one HP port. A regulator fault may kill both primary and secondary routes. Next the other aspect of a backup is that it uses different technology than the primary to boot. that is accomplished by an spg and a xmitter. Again if on a single tank system its benefit is fouled by a common source and regulator. There is a lot to be said for having every bit of data regarding the dive. It makes need graphs etc. At the end of the day is it really necessary for the conduct of the dive and are the additional failure points and costs worth it? Since I mentioned doubles a minute ago. if you had a failure on one side and you closed the X-conn valve you no longer have any psi input to go on. That makes a case for redundancy of PSI monitoring. However there are rules of survival involved and one of them is that if you have a failure on one side you isolate the leak and immediately proceed to the surface. at that point the psi reading is of no concern as you do not use a PSI reading to determine how much you can push the clock. rule of 1/3/s and similar ones prevent that need. It would not be unexpected that both xmitter batteries should go dead at close to the same time. NO BATTERIES IN AN SPG and that is why it is a good back up for your question.
  10. dmaziuk

    dmaziuk Great White


    The first problem with having two transmitters is your backup system is poorly designed. The second problem is that if you're OK with continuing your dive on the one backup transmitter, then you should have been OK with diving on one single transmitter in the first place. So it's also overdesigned.
    blake7 likes this.

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