Predictably non-linear cell

Janos

An interesting one for you:

Running a KISS with Shearwater, I calibrate when the head is dry before the start of the dive. Normally this means that the cells read a little low at the end of the dive when the head is wet.

However, one cell (Cell 2) now reads high at the end of the dive. It tracks the other two cells perfectly at the start, but by the end it reads 0.2 high. This is routine and predictable, and if I calibrate at the end of the dive, then it reads low at the start of the dive, but comes back into line by the end.

I'm going to swap it out. But I was just wondering if anyone had heard of anything like this.

Janos

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Hanssing

Well, I have one cell reading +0.07 or two cells reading low depending on how you see it. They all read fine at start of dive, but after app. 45mins the difference occurs. The difference is present througout the rest of the dive.

O2-flush seem to indicate that the two cells are reading low, but I think due too BMCL being hard to flush completely.

Being new to Rebreather's I've just ordered a spare cell, and will dive with 4 cells for a while since the rEvo allows this in standard setup. I dont like cells showing more than a few % apart... But Paul Raymakers (rEvo-daddy) thinks cells are ok until they show 0.1 apart. I'll scrap the cell(s) that does not perform linear.

Also I think I read something about cells could act as a battry, and get tired after functioning fine at high PPO. Then after a resting period in air, they'll work fine again in high PPO for a while. Just can't remember who wrote it?

So are you sure your cell is reading high?

Nicolai

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lizardland

Yep, I posted a thread about the same thing last year on an un-mod'd KISS. Cal in air and it would read 1.1 in O2, cal in O2 and it would read low on air. I wasn't convinced it was a cell problem so rewired the display and replaced the molex and it worked fine.

I take it you've tried swapping the cell positions around to see if the same thing happens when it's on another plug?

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Janos

Sorry. Non-linear is perhaps the wrong term to use. It's a noticeable (ppO2 of 0.25) difference between the start of the dive (dry) and end of the dive (wet).

It's definitely reading high, (and not the other two low) as it was reading 1.7 at 6m on Friday.

Cell 2 is the one that's reading high. My next dive is on Friday, and I'm going to swap Cell 1 (which I know is working) into Cell 2's position, and swap the spare in to Cell 1.

Janos

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