CCR Gas use tutorial

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dalenvigil
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CCR Gas use tutorial

Post by dalenvigil »

Is it possible to get a tutorial on the wiki page regarding how to use the gas management tab for a CCR dive?

Right now I've got Air Dil, O2, and a Bailout tank in the available gases (I've made them myself, size, volume, pressure, etc. all entered manually). I've added them to a dive, but while the profile has gas switches to bailout, the gas display under the profile just shows air diluent for the whole dive. In the tab it shows the air diluent tank showing the duration of the entire dive.

Secondly, I have a different dive that has multiple bailouts (training dive), except it has a new tank for each bailout (in fact, 11 of them), and considers the switch back to the loop as a new tank, then new diluent tank, and it does this back and forth throughout the dive.

Dive 1
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Dive 2
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nick
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Re: CCR Gas use tutorial

Post by nick »

Wow those screenshots are ridiculously huge.

The bar under the main graph shows only air I assume because your Air starts at 00:00 and runs the length of the dive. The tanks are displayed according to how long they are breathed. If you want others to show, you need to give them a duration so it knows how long to display them for. You can see it failing to draw the others correctly because of this - note the weird text at the start, an EAN32 at the end. That's where those particular tanks/mixes start/end.

Look at your other mixes and I expect you'll see "Start Time: 00:00", "Duration: 00:00" for the first. "Start Time: 58:40", "Duration: 00:00" for the last. Either the duration is wrong because it has not been added, or, it wasn't breathed so it shouldn't exist here.

There's already a Managing Tanks/Gases page in the wiki, perhaps you could let us know what is not adequate on that page. We are currently rewriting the user guide and can make some specific improvements to it. Although, generally speaking a CCR computer would have this information added automatically so that you don't actually have to manually enter these things. Is there a reason you're doing so? Do you just want to log it differently or something?

Also keep in mind, for both of these points, this is not showing what gases you took with you on the dive. It is showing what you were breathing at any particular time. This is used to calculate the SAC, etc, although this is likely of less importance with CCR. So switching back and forth is fine, that's the intention. It's switching to what you were breathing.

For example if you took a bailout tank with you and never breathed from it, then it should not appear in that tab - it wasn't breathed. Does that make sense?

If you want to just record the fact you took some tank with you, then this is not really the place to do it.

The terminology is perhaps off. It's not a "tank" so much as "a tank / mix combination at this point of the dive"

At any rate, if you have any specific questions or suggestions please email us so we can address this in the user guide. I hope that the information above helps in some way, but please let us know if you have any further questions.

Thanks
dalenvigil
Posts: 10
Joined: Thu Feb 19, 2015 9:15 am
Dive Computer: Shearwater

Re: CCR Gas use tutorial

Post by dalenvigil »

Alright, so I let this sit for a bit to see if I could figure out the best way of explaining what my desire is regarding CCR tank management. I realized I might be making some assumptions, but this is how I would envision gas would work.

Since the computer logs the information, it should be simple to extrapolate some things.

Diluent and oxygen usage. The duration should be the start and end of the dive (roughly, prebreathe won't use much) and you would input start and end pressures and it would extrapolate the divers metabolic rate throughout the dive. Unfortunately it won't allow you to put the same duration for 2 tanks, so you can't actually figure that out since it assumes only one tank, even when "Supply Type -> Closed Circuit" is selected. As far as informational purposes that's fine, but I think it could be smarter than that. Realistically you're only concerned with O2, but it would be nice to know all the data.

Second, bailout. You are correct, the computer does log gas switches, in and out from CCR to OC and back again. The computer also has all of the requisite gas data for each switch tagged in the raw data pane as "gas_switch." Based on the depth and PO2 the gas contents it should be easy to extrapolate which gas, even if the specific data does not have a tag with the mix (if gas PO2 is .42 and your depth is 10m it's obvious that the bailout gas is air, etc.). However, it appears that the software creates a new tank for each bailout scenario, even if it's the same tank, and it also makes no automatic duration calculation, despite the gas switches being in the raw data. It knows it switches to bailout, why is that duration not apparent when it is switched back to the loop? And again, the computer logs the switch to OC, and the PO2 based on the gas it knows you're breathing, so it should be able to extrapolate the mix, and whether you're OC or CC. You might have to edit the helium content for trimix after the fact, but it seems like the rest should be easily identifiable by the software, and the proper data input. It should be obvious that if there's a gas switch, the duration for what you're switching FROM should end and start for the duration you're switching TO. For a single tank the setup works fine as usual, for the CCR stuff it should just accumulate time spent on loop.

I'm thinking that maybe the Predator does not log all of the information I think it logs and that may be causing an issue. It logs CC->OC as a gas switch, not as CC->OC. Could that be a possible reason for the multitude of tanks? It sees each gas switch as a new tank regardless of whether or not it's an actual tank or the loop? It's also entirely possible that I screwed up all the data that actually came off the computer while futzing around with it.

Basically the gas management is super awesome for OC diving. For CCR I think a couple tweaks could better represent a CCR dive when one comes off the loop. In an ideal world you would input dil and O2 and it would calculate your usage of both across the course of a dive and that's all it would need to do. But sometimes we come off the loop, sometimes we're bailing out and changing bailout mixes during the ascent. I think the software already has the capability to do the majority of the work, just in CCR mode it needs to be a little bit smarter about the way CCR divers dive. Or I need to be a little bit smarter. If that's the case by all means let me know that I'm the one screwing it up.

Now this also could be me just misunderstanding the way it works. I'm not seeing the gas management FAQ anymore so I can't tell you if I just grossly misunderstood how to do it. And please feel free to push this to the back burner while you put out iOS fires for a while, it's not essential, however a CCR specific set of instructions on the FAQ would be great.
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nick
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Re: CCR Gas use tutorial

Post by nick »

Wow, hey thanks for the super-detailed info!

I didn't quite finish rewriting the gas usage help, it's still available in the old format if you need the link, but I'm hoping to get to it shortly, revamped and tidier.

There's a lot to take in here. I'm currently pretty slammed, so give me a bit to settle down and I'll come back to this.

-nick
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