Current State Of Rebreather Electronics

[silent running]

For the initial CCR training - where the diver is limited to recreational depths (or less) and no deco, I don't see the problem with training that teaches the very simple rule: If there is any problem, switch to BO and end the dive. In this case, the over reliance you are talking about seems to only have the downside that the diver might have some dives cut short or missed altogether.

In my opinion, safe CCR diving starts with having a full understanding of what is happening inside the unit and inside your body. I do not want to be infantilized buy a piece of gear which can malfunction and lacks the ability to problem solve like a fully informed CCR diver can.

 

[tbone1004]

@silent running are we really going to use obsolete rebreathers to talk about modern CCR design? I agree in keeping signal and power lines separate as is common in all normal electronic applications, but I don't think using ancient CCR tech to justify opposition to some current designs is the right answer

 

[Peter Slater]

@silent running uhh what? The analog secondary is not powered by the sensors, to your point, they don't deliver nearly enough current to do much of anything. The monitors are all drive by a real battery.

The 9v battery is to drive the solenoid because lower voltage solenoids that can run with something like an 18650 are usually physically larger due to higher amp draw. The 9v can be used with stepdown converters to run a board, but the only time any real voltage draw is being used is when the solenoid fires. That voltage does not have to go between the handset and the head.
So in a DiveCAN setup, you have a 9v that is driving the canbus board *VERY low draw*, and the solenoid *intermittent fairly low draw*. The analog mv connection is then isolated and very short which minimizes chance of electrical interference *a problem if you have analog wires in the same cable as the solenoid power cable, a la Predator controller, Hammerheads, etc, where that impulse can cause a jump in the mV reading*, and with the short distance effectively removes any risk of voltage drop due to the cable length. Shouldn't be anything relevant, but it is there.
The cables going out are now spitting out digital signals that can report when there is an error in the signal.

Is it more complicated? Obviously, with very simple systems like this digital is always going to be more complicated than analog, but it's also more reliable and contrary to your point, minimizes the risk of a faulty reading because the the cells can plug directly into the board that is processing their signals. They don't have to plug into a cable, that then plugs into a computer, than then analyzes the signal.
The computers are already converting the analog mV value to a digital signal, processing it, and sending it out, but with the canbus systems, you are just allowing it to be more reliable. Two-way communication does have to happen, but it's all digital with no power transmission which is fine.

On your analyzer comment, are you calibrating with air? If so, does your analyzer factor in barometric pressure, temp, and humidity? Even if it does, you are relying on a purely linear output from the sensor at 5x the calibration value which is exceptionally rare. Having good O2 to calibrate to at ppO2=1.0 gives you infinitely more repeatable analysis and any change in the calibration is likely your sensors themselves shifting. Over-calibrating is not a good thing.... Most dive shops will calibrate at air, usually not adjust for temp/pressure/humidity, and when you go to analyze O2, even a few percent in linear deviation will make a surprisingly large difference in the gas analysis.

Things like the Poseidon were designed to be idiot-proof, and have a lot of things build into them to make them idiot-proof, to varying degrees of success. I don't think that's the answer. I think the DiveCAN concept of going to digital communication is vastly superior to analog communication, I run my Meg at 0.6 on the solenoid and manually run it at 1.0-1.1. I much prefer that to the concept of CMF rebreathers *which I also own* for a myriad of reasons, but at the same time, I'm a cave diver, and running off of a solenoid in most of the caves in Florida is horrifically inefficient because of the ups and downs. In training I had to maintain flat ppO2's as an emphasis on control and attention to the unit, but in reality my ppO2 in certain passages will bounce between 0.7 and 1.2 especially if I'm on a scooter. If I wasn't running it manually, the solenoid would be freaking out and my buoyancy would go to hell in a handbasket every time I was ascending.
I don't want my unit to lock me out, ever, and they don't.
One thing I do like with the Liberty is that you can choose to vote out a sensor yourself. I think this is a MASSIVE safety improvement over the standard voting logic process.

I think silent running is referring to the prism topaz rebreather. It had cells that were powerful enough to directly drive an analog needle display without a power source. I don't know where to source those cells still but I do think that it is an interesting backup technology.

 

[silent running]

@silent running are we really going to use obsolete rebreathers to talk about modern CCR design? I agree in keeping signal and power lines separate as is common in all normal electronic applications, but I don't think using ancient CCR tech to justify opposition to some current designs is the right answer

There is nothing obsolete about simplicity.

First of all, everyone knows that until there is a new development in oxygen sensor technology there will be no major advancements in CCR design. And even if Poseidon brings their SSS to market, it will need a lot of power, and I for one do not want to be even more dependent on batteries underwater than we are now.

My opposition is to further complexity without any big benefit and the blurring of the lines between fault tolerance and idiot proof. We all know that idiots do not belong at 100 m breathing hypoxic mix.

I’m in favor of maximum diver awareness and involvement with the unit and the dive. I’m not in favor of any system which diminishes these capacities. I actually enjoy this type of maximum situational awareness, I find it relaxing and stimulating at the same time. I do not want to be lulled into a false state of comfort by bells and whistles and manufacturer hype while in the most human hostile environment on earth.

 

[silent running]

I think silent running is referring to the prism topaz rebreather. It had cells that were powerful enough to directly drive an analog needle display without a power source. I don't know where to source those cells still but I do think that it is an interesting backup technology.

I think AI sell them directly? I get mine from Steam Machines as they work with the supplier closely, so there is best QC...

 

[RainPilot]

And even if Poseidon brings their SSS to market, it will need a lot of power,

They are being used and sold for use in 3rd cell reader, takes power (very little) from the computer used to read it (digital so does require a small amount of power supply)

I have had a multitude of sensors going weird on me over the years, never had a charged computer die on me so I’ll take that trade off anytime.

I get that you’re a fan of mCCR, that’s fine. I am in a day job that had the same issues with automation initially but now it is the default. The fact is that the vast majority of aircraft fatalities are caused by human error not system failure, I would be surprised if CCR is any different.

I personally don’t get smarter the deeper I go, the computer doesn’t care about narcosis and task loading etc.

 

[stuartv]

@silent running are we really going to use obsolete rebreathers to talk about modern CCR design? I agree in keeping signal and power lines separate as is common in all normal electronic applications, but I don't think using ancient CCR tech to justify opposition to some current designs is the right answer

Yes. This. Thus what I said in the first place about tech developing from "I wouldn't trust that with my life" to "I don't even think about that."

Someday, I expect that CCR divers will talk about O2 sensors in a way that signifies that it is just accepted that they work and nobody ever even thinks anymore about all the things we need to be prepared for with regards to O2 sensors failing or reading incorrectly.

 

[silent running]

They are being used and sold for use in 3rd cell reader, takes power (very little) from the computer used to read it (digital so does require a small amount of power supply)

I have had a multitude of sensors going weird on me over the years, never had a charged computer die on me so I’ll take that trade off anytime.

I get that you’re a fan of mCCR, that’s fine. I am in a day job that had the same issues with automation initially but now it is the default. The fact is that the vast majority of aircraft fatalities are caused by human error not system failure, I would be surprised if CCR is any different.

I personally don’t get smarter the deeper I go, the computer doesn’t care about narcosis and task loading etc.

Yes, sorry I forgot they are in market now. But if there are no big drawbacks, why haven’t they designed a new CCR around them?

As I said a bunch above, I don’t like battery voltage underwater when it’s not absolutely necessary, but to each his own. Anything higher than MV and which needs 1ATA isolation is a liability in my opinion.

Glad you’ve never had a computer die or fail underwater. It wasn’t that long ago that computers flooded regularly, they certainly haven’t been trouble free in any event.

The airline industry is often cited in safety discussions about rebreathers. My problem with this is simple, The reason why avionics are so safe and automation so dependable in that industry is the enormous amount of money and time that went into developing those systems. The money, expertise and motivation were all present in abundance because of the millions of people who depend on air travel. It was an imperative from government, many businesses and probably the insurance industry. I doubt there are more than 10,000 active rebreather divers on the whole planet, and while I am impressed with much of the ingenuity and dedication some manufacturers have shown, there have also been some spectacularly bad designs and terrible mistakes made, and we know far less about hyperbaric medicine and deco theory than we do about air travel.

I will be glad if CCR electronics get to the failsafe level of avionics, but I don’t want to be a physical or financial lab animal in what is likely to be a lengthy process...

 

[RainPilot]

why haven’t they designed a new CCR around them?

The Poseidon Seven with SSS was at a dive show two months ago, there were some issues with building a setup that would take either galvanic or SSS. Any Poseidon bought now will get a free upgrade to SSS capable, and the units being built from the start of next year will be SSS and galvanic compatible.

The Dive By Wire system the Poseidons use also comes from aviation system architecture so in a sense the aviation industry RnD has helped with the evolution of their CCR.

 

[silent running]

The Poseidon Seven with SSS was at a dive show two months ago, there were some issues with building a setup that would take either galvanic or SSS. Any Poseidon bought now will get a free upgrade to SSS capable, and the units being built from the start of next year will be SSS and galvanic compatible.

The Dive By Wire system the Poseidons use also comes from aviation system architecture so in a sense the aviation industry RnD has helped with the evolution of their CCR.

Thanks again for the info, but I don’t understand, if the sss is such an improvement, why even bother with galvanic sensors at all? Why are they being so tentative with this new technology?