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Are AI transmitters as accurate as SPG's?

Discussion in 'New Divers & Those Considering Diving' started by purbeast, Aug 5, 2019.

  1. purbeast

    purbeast Contributor

    # of Dives: 0 - 24
    Location: Rockville, MD
    I got my first AI transmitter this past weekend and tested it out last night.

    I noticed that the PSI reading was about 100 - 150 less than my actual SPG appeared to be showing.

    Is this normal?

    I also as having issues pairing it. It paired perfectly fine as the instructions said the first time, but then I turned the air off of my tank and put it back on, and I could not get it to pair again. I tried like 3 more times and had no luck.

    FWIW it's a Suunto AI transmitter and I have a Vyper Novo. It's also the older model of transmitter (without the green light on it) but it was sent to Suunto to fix whatever it was recalled for, before I purchsased it.
  2. Outbound

    Outbound Contributor

    # of Dives: 200 - 499
    Location: Michigan
    AI transmitters are more accurate than brass n glass SPGs.

    As for your Suunto pairing flaking out, I know several people who have had this same problem. If you can't get it to pair, you can try clearing the pairing code and then try to re-pair it again. Not sure if you have tried that yet.
    kelemvor likes this.
  3. Zef

    Zef Divemaster

    I think the more pertinent question is: are SPGs as accurate as AI transmitters?

    I believe the AI transmitter to be more accurate across its entire range compared to an SPG.

    The advantage with regard to accuracy with an SPG is that it is relatively more reactive to pressure change than an AI transmitter. For instance when you do a buddy check one step is to look at your SPG while breathing off the 2nd stage to see if the needle moves. With an AI transmitter the change in pressure when taking those breaths might not register for a few seconds because the computer must take the pressure change into consideration and calculate the breathing rate along with the pressure drop.

    But in actual use, the accuracy of either is more than good enough.

    I have a Suunto Vyper Air with the old style transmitter. I have only had a problem pairing it once. If you clear the code and re-pair the computer and transmitter, know that the computer needs to be closer to the transmitter than normal use. Also, I believe high power lines and other electronic devices can interfere with the signal when it is trying to pair so look around the next time you are having problems to see if there is anything in the vicinity that might be causing a problem.

    John Bantin likes this.
  4. JackD342

    JackD342 Dive Shop

    # of Dives: 500 - 999
    Location: Highland Park, IL
    I expect an analog gauge to be less accurate than an electronic device, especially at lower pressures. Compare to a few other gauges.
    Once paired the pairing should remain in memory until you reset it. Not sure what is going on there.
    The recall was not a functional issue, it was a concern with the possibility of the transmitter failing to contain the HP upon pressurization.
  5. tbone1004

    tbone1004 Technical Instructor ScubaBoard Supporter

    # of Dives: I'm a Fish!
    Location: Greenville, South Carolina, United States
    they will be both more accurate and more precise than a traditional SPG. Analog gauges are typically only reasonably accurate in the middle of their range. This is why most speedometers have 60mph in the middle of their range. For SPG's, they are most always 5000psi gauges so they are most accurate from 2000-3000psi. They are also only considered accurate to +1 increment, so if it reads 2000psi, it could be anywhere from 1900-2100psi since angle of view can skew your perceived value for precision. This is about 5% which is more than good enough for diving, but they can only realistically be calibrated to about 2% at best. They are highly susceptible to going out of whack since they rely on bending metal, so as they age, are cycled rapidly, etc. they tend to get stiff and are no longer accurate.

    The sensors used in the transmitters are typically calibrated to 1% across the entire range, though some may be .25% *unsure who is using what*, but that is going to be within 50psi on the high end, and within 30psi under normal ranges which is certainly more than good enough. If your SPG reads one value and the transmitter reads another, the only way I would ever trust the analog gauge is if the transmitter is reading erratic values. I.e. put it on an AL80 and it says 6000psi, or you know you just filled it and the SPG says 3000psi but the transmitter says 25psi or something ridiculous like that which is a major failure of the sensor and would be considered exceptionally rare in what is essentially a solid state device. In the real world when we use pressure transducers, those types of issues usually happen when wires aren't making good connections due to vibration or in rare cases the sensors being exposed to something grossly over their working pressures that physically damaged it.
    If the transmitter and SPG are giving stable readings and are giving the same general reading, i.e. within 500psi of each other, then the transmitter is 99.999% the one that has the right value.
    One thing that will frustrate the daylights out of you is if you have two transmitters hooked up to the same source. I.e. I had one transmitter on each post of my doubles regs for use with my CCR that was not manifolded and the pressure was off by like 16psi between transmitters. Well within the accepted calibration, but knowing they were on the same gas supply and having an ever so slightly different value was enough of a nuisance that at the end of the day I became unlazy and plugged the right post.
    eleniel, Kmart921, markmud and 6 others like this.
  6. purbeast

    purbeast Contributor

    # of Dives: 0 - 24
    Location: Rockville, MD
    Okay great thanks for the information. I had no clue the transmitters were more accurate so that is good to know.

    I will try clearing out the code later tonight and trying to repair. I will look into how to clear the code.

    I had the computer right next to the transmitter and it simply wasn't registering. The lightning icon wasn't showing up like it did the first time it paired no problem.

    I think I'm also going to get a small hose to attach the AI transmitter to, like a 6" or something. I wasn't a big fan of it just sticking out of the 1st stage. The transmitter was quite bigger than I expected it to be.
  7. AfterDark

    AfterDark Solo Diver

    # of Dives: 1,000 - 2,499
    Location: Rhode Island, USA
    When they work, yes.
    Bob DBF likes this.
  8. tbone1004

    tbone1004 Technical Instructor ScubaBoard Supporter

    # of Dives: I'm a Fish!
    Location: Greenville, South Carolina, United States
    @purbeast keep in mind that putting the hose on gives you all of the leaking failure modes of an SPG by adding the hose and spool back to the system. The transducer is almost as reliable from a leaking perspective as a port plug. Depending on which regulator you have, you may find some alternate hose routing works better for you by aiming the transducer more down
  9. loosenit2

    loosenit2 si respiratio sub aqua amet

    # of Dives: I'm a Fish!
    Location: Virginia
    have never had one of mine not work
    Lostdiver71 and kelemvor like this.
  10. purbeast

    purbeast Contributor

    # of Dives: 0 - 24
    Location: Rockville, MD
    Yeah I mean it's really aesthetic which probably isn't really a good reason. It just sticks out the side and is kinda bulky. Maybe I should just get a quick disconnect because when I put it in my regulator bag that I got, it's just kind of bulky and if I could just take it off quickly and put it back on quickly, then it would travel a bit better.

    Or maybe I should at least get it wet before I make a decision on what is better lol.

    I have an Atomic Z2 reg and it only has 2 HP ports on it, and the other one on the other side has my SPG connected to it.

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