SPG with integrated transmitter. Am I the only one who would like that ?

[dmaziuk]

1) Does it make sense to integrate the AI transmitter into the analog SPG?
2) Can the AI transmitter be passively powered?

Regarding integration, technologically, yes, you can do it as part of one mechanism. It would involve a lot of engineering, but it could be done.

Not really, all you need is a potentiometer: a contact on the needle and a resistive strip (circle) this contact movers along. You can fit it in existing SPGs without any changes to the size.

Passive power depends on larger antenna sizes, shorter distances, and more power from the active device (the computer, in this case). I don't think it works for this application.

As long as you insist on wireless. It all becomes non-issue if you run a thin flexible wire under your wetsuit sleeve and out of the neck opening, like you run the headphones wire under your top coat.

(Of course if you do that, why bother with bourdon tube in the first place: replace it with a plug-sized pressure sensor and save a bunch of money on copper and tin and the rest of it.)

 

[Caveeagle]

I have never been a huge fan of AI, but find the technology interesting. The problem I see with the conversation on this thread is.. Adding any significant size/mass to a typical SPG starts getting you darn close to the size of the 'hosed' AI computers. And, I assume that the size of these computers will be shrinking as technology evolves, so.. If I am determined to keep the long HP hose, why not just go with the hose mounted computer?

Now, making the transmitter the size of a button-gauge and keeping it on the 1st stage really makes sense to me. Get the cost down, and use something like a watch battery that is user replaceable and I can start to see a case for this.

 

[divad]

I can't fathom why you would want anything other than a direct analog connection from the first stage via a hose....if the hose fails, you know. If the bourdon tube fails, you know. If your AI computer and or transmitter fails do they tell you as succinctly or do they just keep trying to communicate?

 

[dmaziuk]

Now, making the transmitter the size of a button-gauge and keeping it on the 1st stage really makes sense to me. Get the cost down, and use something like a watch battery that is user replaceable and I can start to see a case for this.

I suspect antenna is part of the issue: you need a big one, to achieve even the 3' ranges we have now. They use coiled antennas, apparently, to squeeze them into a smaller package, but smaller is a relative term.

I can't fathom why you would want anything other than a direct analog connection from the first stage via a hose....if the hose fails, you know. If the bourdon tube fails, you know. If your AI computer and or transmitter fails do they tell you as succinctly or do they just keep trying to communicate?

Meh. How often do you check your spg? -- Depends on the dive, obviously, but the point is you need the reading when you look at the dial. It can fail anytime between then and your previous look and you won't care. So it's not whether they keep trying or tell you succinctly, it's how long they keep trying before giving up and telling you succinctly.

 

[fnog]

not at 80 bar it isn't going into my lungs.... It's coming in at 10 bar over ambient, so you have to design it to run off of the changing IP with depth

The generator unit would not be at IP, it would be as upwards the first stage as possible, so it would dispose of much more oompf than IP minus ambient. It would be at tank pressure in, eighty bar out. So the generator would dispose at dive begin of 20liters per minute going through a drop of 120bar. If the gas is lighter (Heliox), that is less powerful, but it should still be plenty. I did not calculate the corresponding power but I would be very surprised if this is not enough to power the current tech of ultra low frequency radio transmitter. And it could be enough to power piezzo/ultrasound transmitter, even -but that is yet another question-. What is for sure is that the thing should have zero failure mode where it cuts the flow completely, and should not ever start a grease fire.

@Charles , thanks, it is warming to hear that at least someone likes the prospective scuba technology debate attitude. I can also understand the attitudes of conservatism. If the new is meant to really replace the old, it should have all the good features of the old, or at least a really fat majority of them, so that the net result is actual progress. And aside from features, there are all the safety aspects, and price. For example, I like to check that the needle on the SPG doesnt drop with a heavy breath or short freeflow. A digital replacement should be capable of that, meaning very short response time, no delay, almost realtime reading.

 

[stuartv]

I really don't see the point in trying to generate electricity on the fly. To me, it goes against the principle of prepare what you can before you get in the water. If I can prepare a power source (e.g. a battery) ahead of time, so I get in the water with that "task" already done, I would prefer that. What I hope we'll see is big strides in making that kind of thing much more efficient. Smaller "batteries" that last longer and recharge much more quickly. A coin-sized battery that would power a computer like a Petrel for 60 hours of diving and recharge in 5 minutes. A really small coin-sized battery that would power an AI transmitter for a year or more.

I would much rather have that than have any part of my dive depend on a generator that is built into my 1st stage. I want my 1st stage to continue to be as stone simple and reliable as possible.

Also, as I've predicted before, I think CCR tech is only a few years away from a new wave that will see it become ubiquitous. So, rather than think about revolutionizing OC by adding generators to 1st stages, maybe you should think about what great new things could come out of advancing CCR tech.

One example idea, off the top of my head: Somebody invents a new process for scrubbing CO2. Maybe a solid state device that uses some electrochemical process. So, no more lime cartridges and no more limits on bottom time that come from limited scrubber capacity. That means the unit itself also potentially gets way smaller. Maybe even 1/10th the size. For recreational stuff, you could then possibly dive with 2 x AL13s on your CCR and stay down for 5 or 6 hours (wild-ass guess). Or maybe the unit it so small that you can easily use 2 x AL40s and the dil bottle is also your bail-out, so you don't have to carry any extra cylinders. Just a very small twinset with a double hose primary "reg" and an OC "octo" coming off the dil bottle.

Now, once the CCR is small enough, maybe you have room to carry a decent-sized battery pack in it and some new technology lets you use that battery pack to power everything you are carrying - your computers, your AI transmitters, the CCR itself, of course, your lights, and your heated suit liner. Maybe new suits come with a built-in wiring harness that lets you connect everything together or maybe some egghead figures out how to make it work wirelessly. And all the devices that need power have some built-in buffer (a capacitor, maybe?), so that if they lose power from the main cell on your back, they can still run long enough on their own to finish a dive.

Of course, if suits had a built-in wiring harness to connect devices, then you wouldn't need wireless AI. The computer could receive a signal over the wire from the CCR to tell it the current tank pressure.

Or maybe HUD tech improves a lot, too, so you could have 2 computers, both mounted in/on the CCR and HUD units that work with any mask. One computer displays, visually on the left and the other on the right. If you're into 2-button interfaces, then 2 buttons mounted somewhere easy to reach with either hand to let you control the computers. Or maybe virtual buttons. The computers "display" on the inside of your mask and you touch your mask lens on either side to operate the virtual buttons.

 

[kelemvor]

Passive wireless power transfer wouldn't work over that distance. http://www.jpier.org/PIERB/pierb49/06.12120512.pdf this paper explains it in great detail if you care to read. You'd need a massive power source and large antennae to get more than a few centimeters in air.
http://users.tpg.com.au/users/ldbutler/Underwater_Communication.pdf this paper that explains the rf attenuation of water in great detail if you care to read. An ARRL friend of mine send that to me some time ago when I was looking at playing with a transmitter. The paper focuses on radio communication as it applies to amateur radio, but the principles are all the same.

Transmitters are actually using VLF or LF because of the effects explained in the latter PDF.

There's a good quality discussion of some of the details around hoseless AI transmitters from 2010 here: Tank Pressure Transmitters

 

[fnog]

@kelemvor thanks for the references. That confirms with proper electromagnetics what I guessed a few days ago in my 3rd post : transmitting power in seawater is a nogo, unless the transmitter and receiver cases are touching. I had actually found the Lloyd Butler paper by googling.

@stuartv why shun an onboard generator ? If you would trust a rebreather to use in the future an electrochemical process to scrub CO2, would you not rather that it is self powered by the gas fluxes, instead of relying on iffy lithium ion battery life? Regarding progress in batteries and power consumption of PDCs, is there such great margin for improvement ? Li-ion tech already has energy densities close to that of explosives, and electronics may consume a bit less in the future but your LED screen needs to make light (wild guessing again: I don t know whether LEDs in PDC are in top efficiency).

Then again, I can very well imagine that a reliable onboard generator would be not feasible, since many tanks are full of mud or debris, plus it would have to run with thermal stress on moving parts. And it would have to have a bleedthrough safety in case of any failure. I am primarily entertaining myself here, and hopefully others, with the hope that we do indeed see advances in scuba technology soon.

 

[dmaziuk]

Then again, I can very well imagine that a reliable onboard generator would be not feasible, since many tanks are full of mud or debris, plus it would have to run with thermal stress on moving parts. And it would have to have a bleedthrough safety in case of any failure.

It's actually very simple: you need a little electric motor with a little fan and a flashlight bulb with a socket. (Do lego kits come with those? -- I know when I was a kid I had those in my toy box.) Connect motor to the bulb, put fan on the motor, stick the motor+fan assembly in a vaccum cleaner hose, breathe through the hose like you would while diving, watch the bulb and be enlightened.

 

[fnog]

It's actually very simple: you need a little electric motor with a little fan and a flashlight bulb with a socket. (Do lego kits come with those? -- I know when I was a kid I had those in my toy box.) Connect motor to the bulb, put fan on the motor, stick the motor+fan assembly in a vaccum cleaner hose, breathe through the hose like you would while diving, watch the bulb and be enlightened.

Uh. Simple. I love simple...and lawyers. and politicians.

Take a compressor that is set to fill your tank at exactly the same speed as you would breathe it at 60fsw. Take the compressor engine away. Put the engine in a portable electric alternator. Plug the alternator onto a three pieces of 1kilowatt LED flood lights. Take a cool beverage, sit down, throw the switch. Wait two second for good measure. Go to the bathroom and grab a tube of hydrocortisone. Be *so* enlightened that you are yourself glowing.

You motivated me to look it up: the theoretical energy storage capacity of air is about 100 kJ/m3
(For those who find useful measurement units too alien : we have got 3 to 4 cubic meters in our tanks).

The storage in a 18650 Lithium ion battery is about 4 ampere*hour and they give about 3.7 Volts. With power 3.7*4 ~= 15W , discharged in one hour, you get 60*60 second of 15W, that is 54 kJ.

So the energy wasted by not reusing the decompressed gas from your tank is about the equivalent of a canister of 8 batteries. Discharge a canister like that in just one hour dive and you can light up a bit of wreck. Someone can plug in the amount of lumens here because I am done with numbers for today. In any case we are not talking about blowing candles with lego fans here.