3 Cell Voting Logic on eCCRs?

[toby43]

ding ding, and I know quite a few instructors that incorporate something like TDI's Advanced Recreational Trimix into their courses for that reason

TDI Helitrox I believe

 

[toby43]

Interesting, but I guess I should have expected something like this from an agency that will give you a normoxic dil card and after a certain number of hours graduate to a hypoxic dil card without even seeing the instructor again. Seems rather idiotic to take a brand new CCR diver and having them doing deco when their mid-water shallow stop capability is never going to be strong. Blow a bag and hang I suppose

What complete idiotic crap

 

[fsardone]

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

That might be the case but I did Air Dil Deco and after a bit of experience Mixed gas. So there is no difference in price from doing so or doing helitrox and then mixed gas. I think.

Cheers

 

[Seya]

That might be the case but I did Air Dil Deco and after a bit of experience Mixed gas. So there is no difference in price from doing so or doing helitrox and then mixed gas. I think.

Cheers

Yes you are right. You can do your 30m no deco then your 60m. Or go 45m with deco to 60m

 

[manni-yunk]

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

I think you need to reread who this course is for......it clearly has 2 distinct groups of people that this course is for. Your interpretation tries to couple them together. The "prerequisites" are where it defines what you must do in order to qualify....not the "who this course is for" section....

 

[wedivebc]

Interesting, but I guess I should have expected something like this from an agency that will give you a normoxic dil card and after a certain number of hours graduate to a hypoxic dil card without even seeing the instructor again. Seems rather idiotic to take a brand new CCR diver and having them doing deco when their mid-water shallow stop capability is never going to be strong. Blow a bag and hang I suppose

Please show me where in TDI's standards that is permitted.
If you are going to disparage the agency at least get your facts straight.

 

[String]

A few comments here

From what I understand, voting logic finds the two cells that are most alike and then averages them, ignoring the cell that is must unlike the other two.

Correct BUT not the only thing. A lot units will also through a warning if any of the cells differ by a certain amount (0.2 bar for example) whether that one is used for voting logic or not so the very least you'll get is a warning which you can then address via a diagnostic diluent flush or similar to work out exactly what is or isnt working.

very likely to effect the other cells in the rebreather which are usually nearby, subjected to the same environment,

Yes and no. Lid design and layout can have a massive effect here and quite a lot of care is taken regarding moisture etc to not be able to soak the cells at once.

have similar ages,

If you're using a proper cell cycling method (4 months,6 months of whatever) then they should be different batches and different ages.
You wouldnt want 3 cells from the same batch in a unit for sure but when you cycle cells as above you wont get that.

You get some dampness in your loop that makes one cell report a tenth of an ATM lower, it is likely at least one other cell will also be effected.

See above. Physical design comes into play here to make sure thats unlikely. Also on lots of units there are methods you can employ to deal with cell moisture or blast it off.
If it gets to screwy in worst case again you'll likely see a cell warning as they are all out of range of each other.

In addition, voting logic always assumes that one cell is broken.

No it doesn't - see the above about cell warnings.

It doesn't assume that NO cells are broken. It doesn't assume that two are broken. It won't assume that all the cells are broken. It always assumes that exactly one cell is broken.

Not true. It firstly checks all cells are within specific range of each other BEFORE it makes any voting assumptions. And the user has methods of verifying the cells are reporting correctly by dilulent flushing etc anyway to verify.


It seems like every manufacturer's approach is to avoid engineering a solution to the problem and just cramming in more and more cells with more computers to do more voting logic and maybe a bunch of other cells that are separate from the voting logic so that the diver can see a whole assload of different PPO2 numbers during a dive and try to figure out which one is the most accurate one. I mean, I guess it is OK to assume that if you have a hundred cells in your rebreather, at least one of them is going to work, right? But how do you know which one is the working one when they all say different things? Should you even have to worry about that? How is this even remotely considered an efficient solution to the problem of cell accuracy?

Why not just use two cells and some clever routing of the gas additions to the loop and use them to check and calibrate each other?

One cell can provide readings to the diver and drive the main O2 addition solenoid, while the other can get validated periodically during the dive by the electronics by using two other solenoids to blow tiny gusts of O2 and known composition

You mean like Poseidon do? Its a method that work but isn't foolproof by any means

basically if the cells ever say two significantly different things, or the voltage linearity of the secondary cell is not confirmed,

No different to range checks in 3 cell logic or a manual diagnostic diluent flush.

then something is CLEARLY wrong and the user goes to open circuit. Why?

So, is there something I am missing? How did voting logic become so popular among eCCR users and manufacturers?

Because it works. It works for diving, it works for aviation,it works for industrial controllers. Its not a perfect method but with good physical design the method quite simply has proven itself safe and effective.
Its not perfect by any more but it works and has a large amount of usage data showing it works.

 

[fsardone]

Because it works. It works for diving, it works for aviation,it works for industrial controllers. Its not a perfect method but with good physical design the method quite simply has proven itself safe and effective.
Its not perfect by any more but it works and has a large amount of usage data showing it works.

Wholeheartly agree, with one addition: good procedures and sound training which leads to good emergency (or abnormal) management from the operator. The operator needs to understand how the system operates in normal and fault conditions in order to enact proper response.

Cheers