Current State Of Rebreather Electronics
- Thread starter AdamSa
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Well, you dive a rEvo, so you must trust them a little bit...
Otherwise, you could be diving a full manual unit - maybe even modify the rEvo to work like @silent running described. A needle valve and high output sensors that will drive a PO2 display without needing a battery? And Constant PO2 tables to calculate your deco?
silent running
Contributor
Well, you dive a rEvo, so you must trust them a little bit...
Remember, I was suggesting that the high output sensors also send signal to a NERD, so you would have the most simple, non powered secondary AND a fully modern deco computer and HUD, best of both worlds and redundancy..
Remember, I was suggesting that the high output sensors also send signal to a NERD, so you would have the most simple, non powered secondary AND a fully modern deco computer and HUD, best of both worlds and redundancy..
Yep. I got that. But, you don't have redundancy for deco computers. Why not regular sensors and 2 deco computers? If you REALLY want redundancy, 6 sensors and 2 computers. 2 completely separate systems for keeping track of what you're breathing and your deco requirements.
With the system you described, you would do what to accommodate a computer failure? Carry Constant PO2 tables and use your PO2 display and ... a bottom timer(? which is really just another computer) to work out your deco requirements?
silent running
Contributor
I was speaking strictly of redundancy in terms of PO2 monitoring, and particularly, redundancy which is accomplished without any battery current at all. Which means no additional cable glands or 1ATA compartments to flood. That kind of redundancy.
In terms of deco computer redundancy I would bring a standalone computer of the same make set to a lower PO2 than my target PO2 on the MCCR.
Your PO2 display is going to have a cable with a gland, right? And your NERD is also going to have a cable with a gland, right? So, 2 cables and 2 glands. If you replace the PO2 display with something like a Petrel with Fischer cable, you've got the same number of glands and cables, right? If you're going to carry a 2nd computer for redundancy, why not let it read the O2 sensors? Have 2 total displays, instead of 3? No more or less batteries to manage, in either scenario.
My rEvo came to me setup in a similar way to what you're describing. 1 computer as the controller, a HUD that was not a computer, and then another computer to backup the controller. 3 "displays" to pay attention to. I ditched the HUD and the backup computer and replaced the 2 things with 1 NERD. Now I only have 2 displays to give any attention to. I think that is a simpler, better solution compared to the concept of a computer, a PO2 display, and a 2nd, separate computer.
Anyway, I know it's all just idle conversation....
Personally, I'm not a fan of giving a computer incorrect info, so I would not run a standalone set to a lower PO2. It might make my deco more conservative, but it makes my O2 exposure tracking less conservative at the same time.
silent running
Contributor
You’re forgetting the analog secondary is powered by the sensors and not by a high current battery. Millivolts work in the 100% humidity of a loop, 9+ volts do not like humidity of any kind. No battery = no 1ATA compartment to leak, no battery capacity dump in cold water, no battery terminals to corrode, no high current electronics to short or fail under hundreds of pounds of water pressure per square inch. With that analog secondary there are at least much fewer possible problems with low current signal and electronic architecture designed to work at ambient pressure. Another integrated computer is another cable gland connection carrying battery voltage and another liability.
I won’t get into the weeds describing the cable differences between Fischer vs Lumberg vs Bendix for underwater use. Suffice to say that some are more fit for the task than others. Whichever cable manufacturer/application, cable glands and whether they carry high or low current through them = lesser or greater failure points to one degree or another.
If a particular design or method can provide reliable, useable deco info from a stand-alone computer to get me out of the water in an emergency, with total isolation from a failure of the unit electronics from a flood, short, software glitch or battery dump, that’s a very good thing. I use a standalone computer with my Prism, it holds SP very tightly. One need only periodically check TTS between an integrated deco computer and a standalone with a sensible offset, to know how good your MCCR dive habits and gear are at maintaining target SP.
Giving a deco computer incorrect info? Why do you assume that all the MV readings given to your SP controller/deco computer are going to translate into the completely “correct” reading? Never mind the various glitches in components which can occur between reading millivolts and converting them into digital data inside a CCR. Do you analyze your O2 every day, even when you are diving with the same operation multiple days and you watch the person fill the tank each day? Are you using their O2 analyzer? How old is the cell in it? Are you or someone else calibrating it everyday? Add to that the fact that deco calculations are still just an educated guess, given the scant data available for constant PO2 diving. O2 exposure is even less well understood and tested. Even when you are confident about most variables, your displayed PO2 is still an educated guess because the computer only “knows” so many variables. The computer has no knowledge of whether your CCR was handled roughly by the boat crew the day before, or left on the boat deck in the hot sun for hours earlier that day. But if your sensors suddenly start behaving unpredictably, you might think of these things and wonder about the readings you’re getting. You might remember the sensor wiring harness looked a little frayed last time you prepped, even though you thought you put a new one in last trip. But did you?
When the chips are down, the only computer that matters is the one between your ears. And given the variables in CCR diving (equipment, consumables, physiological and environmental conditions, deco theory) I’d rather be more involved in the decision making process than less. I find comfort in knowing my life is more in my hands than my gear. The price of freedom is eternal vigilance..!
silent running
Contributor
Meant to respond to this, yes, digital electronics are more reliable in most respects than their analog predecessors. Analog electronics are not updatable, but they do not require much if any code and therefore are less vulnerable to coding mistakes, which can sometimes take a long time to manifest. My P1 ECCR is an SP only type with mostly analog electronics, which are permanently potted. I see no reason why something so simple would ever need an update and there is very little that can go wrong with something which is completely potted. In this respect, a mostly analog SP only ECCR could be said to be more reliable than an ECCR which has multiple sub systems of sensors and a digital controller which may need updates to fix or improve its various functions.
Is a simple piece of life support a better, safer one than one which is more complex and has more potential failure points? What about the difference in mindset of the operator of the two units? What role does mindset play in the safe operation of a CCR? Which design approach fosters more awareness and skill?
I think we should always think twice, hopefully more than that, about whatever device/technology we might stake our life on...
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