Quote: (Originally Posted by
Gilles)
Close but not quite. Your conclusion is based on the following 2 premises;
1) The nominal air mV's have not changed during this time
2) You have been using the same O2 purity
Did you check both of these? Nominal mV changes happen and I don't understand the reason why, just that it does. If it happens to drop in a healthy cell, so will its corresponding O2 mV. This is why there needs to be periodic cell cal's.
Actually, you are likely to observe nominal mV drop (and a corresponding reduced PO2) after diving when your cells are still damp. The same occurs when flushed with O2. (see above attached essay). Hence there is a third premise;
3) Did all these measurements occur on dry, or damp cells, or some combination of both?
As long as the linear response is maintained (or better), the cell remains healthy.
1) The nominal air mV's have changed slightly. I have noticed that the mv readings will drop about 1-2 every month. Thus recalibration needs to be done every once in a while (checked every time though).
2) I am using the same O2 purity and analyzed to exactly 100.00% each time.
3) All readings were done with sensors and ambient temperatures the same. All sensors were dry (1 week since diving).
Like I said ".....as the amount of change from reading to reading that
may be an early indication of cell failure."
I was told that there is no guaranteed way to check cells each and every time by mere mv readings or calibrations.
IMHO The cells are the least reliable part of any Rebreather and the failure rate is alarming for anything that is life supporting. Makes me wonder why any of us trust them! OH YEAH - 3 cells.