CCR Electronic Controls?

navycurtissc

Hello everyone,

Before I get into to this let me preface it by saying that my background is in mechanical and nuclear engineering.

I can't help but notice that just about every CCR out on the market utilizes the same basic mechanical design and that it is only a question of durability and construction materials. My question is regarding the electronics used to maintain the correct PO2 level in the breathing loop.

I have only noticed a couple systems out there (the new vision, the hammerhead, and sharewater). It seems to me (from the research that I have been able to do) that they simply sample via multiple O2 sensors, take a weighted average, and then admit the applicable amount of O2 when apropriate.

Is the major differences between the units in the type of decompression algorithms use?

After this consideration, is the discission based on the user interface and/or asthetic value?

Are any of these syetems interchangable between the mechanical portions of the Rebreather's on the market (could I take a vision control system and slap it on a MEG)?

I understand that the most restrictive part of this may be the cost in doing it, but it seems to me that the electronic control systems and mechanical portions of the Rebreather's are independant of each other.

Also, I have noticed that there are quite a large number of passive computers out there for Rebreather's (like the HS Explorer and the VR3).

Are these simply for back-up in order to be able to fly manually?

Do any of these "passive computers" offer control features via expansion software and/or hardware?

__________________
Sincerely,
navycurtissc

"If you are not part of the solution, you are the problem."

ROB DAVIE

Curtis,

Man, I must say that when you ask questions you really get into the heart of the matter!

More or less in order, the first thing to remember is that the basic Rebreather is really a simple system. You have a bag, or bags to breathe in and out of, a cannister of kitty litter, and some way to supply oxygen.

Once you get deeper than 20 fsw or so, you have to add a diluent supply. As far as it goes, that's it, until you start getting fancy.

Now you have a sensor system, usually three, and a logic circuit that polls the sensors, ignores the out of range signal (if any), and sends a signal to the solenoid valve to squirt some O2 into the system. It's kind of hard to drift away from that basic model. (I'll let the designers and engineers argue the merits of which logic model to use! )

Now, when you add a deco function to your computer, you get into arguments over which algorithm is "best" for doing the job.

Nevertheless, the APD Vision, the Shearwater, and the HammerHead are all excellent computers offering wide feature-sets, and great performance. Unfortunately, due to differing fittings, cannister sizes, and mounting points, they are not interchangeable.

The electronic control systems are semi-independant of the mechanical systems. If the solenoid fails, the needed gas can be added manually and still read on the displays.

The H-S Explorer, and the VR-3 are excellent deco computers in themselves and can operate in the stand-alone mode, but are best used with a link to an independant O2 sensor. You can, as you say, fly the unit manually on the one sensor and manual addition if the main system fails. They do not have any connection to the gas addition systems.

Hope that helps.

Cheers!

Rob

__________________
[SIZE=2]"CC Rebreathers will become a viable part of tech diving [U]WHEN PIGS FLY[/U]!!"--GI3[/SIZE]