3 Cell Voting Logic on eCCRs?

[fsardone]

Look into the TDI pre requisites for their:

TDI CCR HELITROX DECOMPRESSION PROCEDURES


Who this course is for:

• The certified TDI Air Diluent Diver (or equivalent) who is looking to extend their depth limitations, learn CCR decompression procedures, and reduce narcosis
• The open circuit TDI Advanced Nitrox and Decompression Procedures or Helitrox Diver looking to utilize CCR technology to extend their depth limits and bottom times

Course prerequisites:

• Minimum age 18
• Proof of 50 logged dives
• Minimum certification level of TDI Advanced Nitrox Diver, Deco Procedures Diver or Helitrox diver or equivalent from agencies recognized by TDI
• If the rebreather is a TDI approved sidemount rebreather, the student must hold the TDI Sidemount Diver Certification or equivalent and provide proof of 10 logged sidemount dives

If you look in 'who this course is for' it clearly states that you have to be a "TDI Air Diluent Diver" to do this. Then you have to meet the course pre requisites.
I was hipoxyc trimix in OC and I was made first air diluent deco diver, I was allowed into helitrox/mix d gas only after 35 hours of air dil.
So TDI does not allow nn rebreather divers to start with helium. At least according to what I read here and what my TDI instructor told me ....

Cheers

 

[EricTheDood]

How often does one experience some major discrepancy between any two cells?

If/when you do, is the standard procedure to trust the voting logic and continue the dive, or abort the dive and bail out to OC as soon as practically possible?

 

[fsardone]

I have been diving CCR only 2 years, I am in the second cell change cycle.
My rebreather gives a cell warning if a cell is off from the average of the other 2 by more than .2.
I never had a real cell warning, only a transient (cleared even before I could read it, found out in the download) due to a too rapid descent. One of the cells was slow, was the oldest one and was planned for replacement in a couple of weeks, the new one was alredy on its way to me.
A good primer on how to deal with cell warning and how to correctly do a dil flush for checking cells (it is for the reb I dive but easily applicable to any) is here:
Cell Warning Advice by Mike Fowler

Cheers

 

[Seya]

If you look in 'who this course is for' it clearly states that you have to be a "TDI Air Diluent Diver" to do this. Then you have to meet the course pre requisites.
I was hipoxyc trimix in OC and I was made first air diluent deco diver, I was allowed into helitrox/mix d gas only after 35 hours of air dil.
So TDI does not allow nn rebreather divers to start with helium. At least according to what I read here and what my TDI instructor told me ....

Cheers

You're wrong that can be your first CCR course. The prerequisites are the requirements before starting the course.

 

[fsardone]

Ok,
I might be wrong, but TDI has this graph here and no instructor I have got in touch with would allow me to go from hypoxic trimix OC straight into helitrox CCR without doing air dil CCR firts and get a bit of experience. I would say quite sensiby ....

Become a Certified Technical Diver | SDI | TDI | ERDI

 

[rjack321]

How often does one experience some major discrepancy between any two cells?

If/when you do, is the standard procedure to trust the voting logic and continue the dive, or abort the dive and bail out to OC as soon as practically possible?

Are you CCR certified?
You have 3 cells, and hypothetically speaking 2 are similar and 1 different is that what you mean?

 

[EricTheDood]

Are you CCR certified?
You have 3 cells, and hypothetically speaking 2 are similar and 1 different is that what you mean?

Not certified, but interested in getting into it.

Yes, I'm talking 2 similar, 1 different (substantially). Typical response is to dil flush while the computer uses voting logic.

Why isn't the typical response to bail out first and figure out the problem later, especially if you're in open water or shallow penetration with plenty of bailout gas?

 

[Seya]

Ok,
I might be wrong, but TDI has this graph here and no instructor I have got in touch with would allow me to go from hypoxic trimix OC straight into helitrox CCR without doing air dil CCR firts and get a bit of experience. I would say quite sensiby ....

Become a Certified Technical Diver | SDI | TDI | ERDI

They do that so you can give them more money. That's the only reason. Many instructors will train you to helitrox first.

 

[rjack321]

Typical response is to dil flush while the computer uses voting logic.

Only eCCRs have voting logic. hCCR would be it wouldn't get used much so I'll skip over that.

But no, flushing and leaving the setpoint "as is" (1.2 or 1.3) would not be the ideal response. You flush the loop and then drop the setpoint to something like 1.0 which is a typical dil ppO2 as well. This stops the solenoid from messing with your ppO2 as you test the loop. The important part is that you now have a breathable loop. And it will stay basically breathable for a few minutes. Because if you bailed the gas won't flow around the loop and the cells won't respond.

Now you recheck the cells. Do you have 1.0, 1.0, 1.0? Add o2 and watch how they respond. Chances are good that two cells will climb to 1.2 or 1.3 and one will lag behind. That is a single current limited cell and the most common issue. You could stay on the RB and run it manually with a low setpoint or even return to eCCR mode (not likely but you could). Your deco calcs will be based on the 2 valid cells.

If one cell rise to 1.3 and the others lag behind you either have 1 defective high reading cell or 2 current limited cells. You can still run the unit manually with a low eCCR setpoint based on the cell(s) you believe are valid. You probably have to adjust your deco.

You can always bailout and if you're shallow with lots of bailout you might as well. If you're really shallow on deco (<25ft) just run it as an O2 rebreather and ignore the cells. If you are a very long way from "home" (the surface) and have flushed and spiked your cells with O2 and decided you know what the problem is (a good argument for lots of helium) it might be better to stay on the loop.

 

[rjack321]

How often does one experience some major discrepancy between any two cells?

what's major? consistently more than 0.1 ppO2 would be not very often

one cell being slower to respond or off by 0.05 ppO2 is fairly common.