Sensors: which gas shall I have in the loop when not in use?

[broncobowsher]

@tbone1004 I read on you other posts that you tend to run a lower set point @ 1.2 on your CCR. Are you proposing for a 30 m dive to run a rich dil higher than your high setpoint and breathe it down? I was taught to target a dil mix with 1.1 PpO2 at max depth, when I asked why not 1.0 or 1.2 I never really got an answer? Feel free to move to new post if not relevant to O2 cell longevity strategies of the OP.

I would suggest starting a new thread inquiring about setpoints and why you would run what you run, with a side of DIL mix choices. That question is rather far from sensor storage and anyone searching for information later won't find it.

 

[Heat Miser]

Here we see why testing up to 3.5 bar makes much more sense then 1.0 bar only. Between 0 and 1 bar the green cell seems to be worst of them, lower voltage. But from 1 to 3.5 bar the green cell works perfectly linear. The yellow cell seems to be perfect when testing from 0 to 1 bar but becomes weak at 1.5 bar.

Testing up to 1 bar only: perhaps you kick out the green cell, definitely not the yello one.
Testing up to 3.5 bar: you keep the green one, you kick out the yellow one.

By the way testing was not perfectly made, in the beginning (first measuring point) there was not air in there but some nitrox, therefor wrong reading at 0.21 bar. My fault.

Why can't you read this as get rid of both the green and the yellow cell? Is it the absolute change in Mv or the percentage change that is important?

EDIT sorry I know absolute Mv changes are the important thing, but if the slopes are different for different cells, doesn't that mean some cells are slower to respond then others and that you would eventually throw out the cells that were slow. although not necessarily limited. in your rotation, barring another choice?

 

[Agro]

Why can't you read this as get rid of both the green and the yellow cell? Is it the absolute change in Mv or the percentage change that is important?

EDIT sorry I know absolute Mv changes are the important thing, but if the slopes are different for different cells, doesn't that mean some cells are slower to respond then others and that you would eventually throw out the cells that were slow although not necessarily limited in you rotation, barring another choice.

No, the percentage change is important. As long as a cell is linear it may have lower or higher voltage than the other cells.

Green cell is absolutely perfect, linear from zero to 3.5. Lower voltage, yes, but linear.

Yellow cell must be kicked out, not linear. On a test zero to 1 bar or even zero to 1.6 bar you can not detect this faulty green cell. I do like this test option Divesoft is offering, zero to 3.5 bar.

 

[tbone1004]

Why can't you read this as get rid of both the green and the yellow cell? Is it the absolute change in Mv or the percentage change that is important?

EDIT sorry I know absolute Mv changes are the important thing, but if the slopes are different for different cells, doesn't that mean some cells are slower to respond then others and that you would eventually throw out the cells that were slow. although not necessarily limited. in your rotation, barring another choice?

There are three variables that really matter for a cell.

Slope=linearity which is different from the absolute change in mV from the cell. From an engineering standpoint mV is very important vs Mv for reference. This determines how accurate the readings will be across some range and is the reason that we calibrate the cells in oxygen instead of calibrating in air. The closer you are to the calibration gas the more accurate the cell will be. You really don't care what the cell does in air since you should never have a ppO2 of 0.21, but you do need to know how linear the cell will behave if you are going to run a setpoint over the calibration value.
Current limiting is the cells ability to respond at some maximum value and that can only be evaluated under pressure. Liberty is the only unit that has a pressure kit to test the head outside of the water. You can use cell checkers if you remove the cells from the heads, but the Liberty head checker is much better.
Speed of response is the least discussed of the three and is more of a subjective test *though the manufacturer does have response time called out in their certificates of analysis*.

what is important to note is that these are completely independent variables. You can have a slow cell that leads perfectly, a current limited cell that is fast and perfectly linear, etc etc. One of the three going out typically leads to one of the others going shortly thereafter but not necessarily.