AI question - dive time remaining

[fnfalman]

fnfalman[/B]: Frankly, I don't see the usefulness in making that analogy. An analog SPG is not reliant on a capricious wireless connection. I love using technology. I'm a gadget freak, yet give me the choice between an analog SPG vs. a wireless/hoseless AI wrist computer...and I'll choose the analog SPG every time. In this case, I think older technology is more reliable than newer technology.

Perhaps a better analogy might be choosing between a BMW 3 series 2010 or a Honda Civic 2010. Which car do you think will be in the shop more in the first 10 years of ownership? Which car do you think will cost more in terms of repairs? Which car costs more to begin with?

P.S. I apologize to the OP for getting the conversation a little off-track. Perhaps our discussion, though, has brought up critical issues that a novice diver should consider when making gear choices.

Capricious wireless connection? It broadcasts a signal and the computer receives the signal. The Bourdon tube in the SPG is nowhere as accurate as the pressure transducer in an AI computer. It had been shown that the SPG can vary up to as much as 150-psi.

As far as BMW M3 versus Honda Civic. How's that a comparison between SPG and AI dive computer? Both the M3 and the Civic use the same technology.

For the people that claim SPGs are more reliable because they don't have batteries or electronics, show me some statistics.

 

[Bubbletrubble]

Capricious wireless connection? It broadcasts a signal and the computer receives the signal. The Bourdon tube in the SPG is nowhere as accurate as the pressure transducer in an AI computer. It had been shown that the SPG can vary up to as much as 150-psi.

In my mind, there's a difference between accuracy (comparison to true/absolute) vs. reliability (addresses consistency/precision and likelihood of failure). Ideally, one should get a gauge that is both accurate and reliable. Please re-read my posts. I have never asserted that analog SPGs are more accurate than air-integrated computers (which rely on an electronic pressure tranducer). From what I have read, electronic pressure transducers are more accurate than the Bourdon tube-based design.

As far as BMW M3 versus Honda Civic. How's that a comparison between SPG and AI dive computer? Both the M3 and the Civic use the same technology.

I agree with you. We're talking about SPGs here. The car is a horrible analogy. Let's drop it.
FYI, BMW 3 series ≠ BMW M3.

For the people that claim SPGs are more reliable because they don't have batteries or electronics, show me some statistics.

Sorry, I don't have the time/money to collect such data for you. I would like to point out that the "gold standard," proven technology here is the older technology (analog SPGs).

 

[The Chairman]

You listed several "failures" with an analog SPG. To be fair, the #1 cause of a leaky HP hose is a corroded o-ring spool +/- bad o-rings,

But not the only failures. I have seen them flooded, read full when there is no pressure and I have heard of them exploding (I've even seen the facial scars from this).

which BTW should be one of those things that receives regular maintenance.

You mean like batteries? I change my sender batteries once a year (like my smoke detector batteries) whether they need it or not. Again, I have never had a sender failure. I guess maintenance is key for ALL Scuba equipment.

Air-integrated computers are still dependent on battery power. I'm surprised that you are asserting that an electronic gizmo is more reliable than an analog SPG. :shocked2:

I have never seen a wireless unit transmit pressure that isn't there. However, I have seen three SPGs that showed pressure (and LOTS of it) when there was none.

@vladimir: What happens if your tank valve is shut off and reg de-pressurized? Do you have to re-pair the wireless receiver and transmitter? Just curious.

I haven't had a problem with that. Both my Suunto and Oceanic synch just fine. FWIW, I prefer the Oceanic protocol over the Suunto, but none have left me clueless. The same can't be said for an SPG.

 

[Bubbletrubble]

I have never seen a wireless unit transmit pressure that isn't there. However, I have seen three SPGs that showed pressure (and LOTS of it) when there was none.

@NetDoc: The particular failure that you describe in the vast majority of cases would be detected during a pre-dive check. I conduct a complete pressurize/de-pressurize cycle at least once while setting up my gear and ensure that the behavior of the needle is appropriate. I do the same after the dive during freshwater rinsing. Of course, I'll concede that no SPG is perfect. It remains possible that the SPG could display the correct reading during pre-dive checks and then fail during the dive.

I'm also going to point out that there are far more analog SPGs than wireless AI computers in service. Please consider how this might change the way you reconcile your personal experience with the true percentage of failures (analog SPG vs. wireless AI system).

 

[jhelmuth]

You all won't remember this, but therre used to be arguments against SPGs when they were new...

Now having said that, let's consider some points:

[1] WHEN your gas consumption is no longer your limiting factor (your NDL is), the AI really becomes almost a useless feature. (and yes... this happens frequently with divers who dive often and have lower SAC rates and are in good physical condition - something we all oght to seek out in our own diving)

[2] AI does not add any unnecessary risk due to failure. If the sender stops working, you simply are now diving a more-traditional non-AI computer.

[3] There is no substantial benefit in reliability to computers vs gauges (either way). Proper dive practice demands that your equipment be properly maintained and checked for good function (incl. battery level in the case of Dive Computers) prior to every dive. If you do the right thing, your possiblity of equipment failure is radically reduced to nearly inconsequential. If you dont do the right thing, re-think your dive practices and/or stop diving. But yes - there is a small degree of risk in having a dive computer fail durring a dive. If so, simply abort the dive immediately and follw appropraite dive practices before getting back in the water with gauges or a replacement computer.


Myself.... I'd rather spend my money on other dive gear and/or dives than an AI computer. But I don't think someone is silly for deciding it's for them. As long as we are reaosnable in our expectations and have some knowledge, we can make good choices. Let's lose the attitudes and help our fellow divers make good decissions without imposing our own prejudices and portraying them as "facts"...

 

[FritzCat66]

WHEN your gas consumption is no longer your limiting factor (your NDL is), the AI really becomes almost a useless feature.

I presume you mean the DTR feature is what becomes useless; the basic air-integration is obviously useful all the time at least for the pressure gauge.

But even if you're referring to DTR becoming "almost useless": How so? Mine keeps calculating an accurate remaining dive time for my depth whether the current limiting factor is gas, N2 saturation, or even O2 - indeed, it makes it very clear on the display which is the limiting factor. I presume most others do the same. It's just as useful a calculation under those circumstances as when gas is the limiting factor.

Now, as some have argued here, that DTR time itself one might or might not find useful, but I don't understand how it could suddenly become less useful just because the dive becomes N2-limited as opposed to gas-limited.

 

[Bubbletrubble]

@jhelmuth: Assuming reasonable operation and maintenance, choice of SPG should not affect safety at all. When an SPG fails, the dive is aborted...unless a backup gauge is in use. The issue that Netdoc and I have a difference of opinion on is whether the wireless system or an analog SPG fails more frequently.

I appreciate that you brought up the issue of economics. Perhaps if I were a dive instructor or DM with access to keyman discounts (60-70% off MSRP), I would be willing to splurge on a wireless AI system...out of sheer curiosity.

 

[jhelmuth]

I presume you mean the DTR feature is what becomes useless; the basic air-integration is obviously useful all the time at least for the pressure gauge.

But even if you're referring to DTR becoming "almost useless": How so? Mine keeps calculating an accurate remaining dive time for my depth whether the current limiting factor is gas, N2 saturation, or even O2 - indeed, it makes it very clear on the display which is the limiting factor. I presume most others do the same. It's just as useful a calculation under those circumstances as when gas is the limiting factor.

Now, as some have argued here, that DTR time itself one might or might not find useful, but I don't understand how it could suddenly become less useful just because the dive becomes N2-limited as opposed to gas-limited.

No... think about what I'm saying.

DTR is one of the two limiting factors - always the minimum time factor - NDL vs gas consumption. If gas consumption is not the limiting time, the the AI computer becomes a "normal" dive computer for purposes of the dive.

So DTR is a necessary feature - it's just reduced to a "comomn" feature when your SAC makes NDL the limiting factor.


All the best,

Jim

 

[FritzCat66]

You know, I rarely say anything like this, but the picture I get here is someone wanting to swim along rather oblivious to the process of their dive, looking at their wrist from time to time to see how much longer they can do that.

I've never found it difficult to figure out how much longer I could be in the water, just going on my pressure alone.

But it seems you kind of answer your own question here: you say you're looking at the pressure alone (but I presume also knowing your depth and your general plan), and thus figuring out how much longer you can be in the water. An AI DTR calculation is just doing that same thing for you (albeit without the benefit of knowing your future plan).

Point being, whether you're making the calculation in your head or letting the computer do it for you, the end goal is the same - determining how much time the diver has. And since the pressure is also being displayed right there along with it, you're free to verify or override the DTR as you please.

Although it can't anticipate drastic changes in depth, of course, nevertheless many of us find that figure relatively accurate and very useful, and generally dive-simplifying.

I imagine there are some folks who have to pre-plan nearly every minute of a highly technical dive, where an AI computer's DTR would be utterly useless. But I doubt that describes most of us, and those folks are probably using far more sophisticated systems anyway.

My personal view is that having my pressure on my wrist would be a small convenience with a big price tag, which would include periodic major annoyance.

Now that is a criticism that can't be much argued against. If you don't find DTR useful, then the only other advantage an AI system might have is just having one unit displaying everything for you... and also logging it all if you're the kind who likes to save and analyze your dive profile later, with depths and cylinder pressures together.

 

[FritzCat66]

So DTR is a necessary feature - it's just reduced to a "common" feature when your SAC makes NDL the limiting factor.

OK, I see what you mean - But in that case I wouldn't call it becoming "almost useless" as you originally said, just maybe "nothing special", or nothing worth paying extra money for.