One cell slow to wake up. Your thoughts?

[kensuf]

Throw the cell out.

 

[taimen]

See that's the real concern I have here. Is there something with the calibration procedure itself? People have said "PO2 is PO2", but the point is that we are all relying on whatever procedure we use to put 100% O2 on the cell face. If that isn't happening with reproducible precision, then everything downstream is off as well.

Well the calibration procedure on my unit is very reproducible done even once. But I have noticed that I get 1-2 mV higher readings with a second run. Again very consistently.
It may be due to oxygen diluting with air or a cell response time issue, but it is consistent. Some divers have noticed the same with newer batches of JJ-CCR cells and think it is due to slower response time of their new cells.

 

[rddvet]

Seems like you already know what to do. Throw it in the cell checker just for your own knowledge/learning, then throw it in the trash

 

[rjack321]

Well the calibration procedure on my unit is very reproducible done even once. But I have noticed that I get 1-2 mV higher readings with a second run. Again very consistently.
It may be due to oxygen diluting with air or a cell response time issue, but it is consistent. Some divers have noticed the same with newer batches of JJ-CCR cells and think it is due to slower response time of their new cells.

Not getting the same results with 2 calibrations in a row means the calibration sequence or instructions are wrong. 2 calibrations 10mins apart? You need to be getting exactly the same answer. My guess is there is not enough flushing to ensure a 100% o2 content in the loop.

 

[Wookie]

That rebreather is just waiting to kill you.

 

[doctormike]

Not getting the same results with 2 calibrations in a row means the calibration sequence or instructions are wrong. 2 calibrations 10mins apart? You need to be getting exactly the same answer. My guess is there is not enough flushing to ensure a 100% o2 content in the loop.

So that's a criticism of the Shearwater control process, right? I guess they make some choice balancing accuracy and O2 usage...

 

[taimen]

Not getting the same results with 2 calibrations in a row means the calibration sequence or instructions are wrong. 2 calibrations 10mins apart? You need to be getting exactly the same answer. My guess is there is not enough flushing to ensure a 100% o2 content in the loop.

Instructions are clear. That is how the unit works. My cells and calibration process have been very stable for 12 months now (new cells just arrived and I will change them all at once, another can of worms).
Calibrations 10 minutes apart, with loop full of oxygen tend to give the slightly higher value. Starting with air filled loop, it seems to have a tad too short flush.

 

[Norrm]

I saw the thread title and thought it was about BRAIN cells and a typical Monday morning rant.

 

[sunnyboy]

the unit is very clean and this has been from the beginning, but that’s a good point. Will try the cell checker (although I have the mini checker which uses the rebreather head)

Actually, that may be irrelevant. My unit always looks super clean, but I still have to clean the gold contacts or I get odd cell results. With gold contacts, 'dirty' contacts can look identical to clean contacts. You only know they were dirty after the fact (i.e. after cleaning the odd behaviour goes away).

The procedure for my unit is: if any cell acts up, clean the contacts before doing any other diagnostic procedure. In my case, 90+% of the time that fixes the issue.

Calibrations should be repeatable, as stated by many in this thread. Even a bad calibration process should not see only one cell drifting during the dive. If the calibration wasn't effective, then all 3 cells should show the same 'odd' behaviour during the dive. The fact that only cell 3 does this strongly suggests cell 3 is bad.

Any cell that 'drifts' during a dive is either EOL or faulty and need to be replaced.

All, of cousre, IMO.

 

[Valyngar]

Now just think the probleb, that is you life or aborted dive worth saving 50€/$, when you have already 9000$ machine. Cos of time and gas to divesite is probably already over that. If you already think there might be problem, just fix it and don't wait it happen.