MV reading check

[lermontov]

Ive made up a spreadsheet for checking MV readings - its a ss I found in another thread and added to it somewhat - if anyone is willing to check to see if there any issues or way to improve id appreciate feedback

On another note when doing the calibration we check MV at 21% then again at 1.0 but if the controller fo2 is set to 98% and we only reach .98 at calibration shouldnt that be the multiplier calculation not 1.0?

eg .21 mv = 11 so 1.0 = 52.4 * .98= 51.3

 

[rjack321]

Ive made up a spreadsheet for checking MV readings - its a ss I found in another thread and added to it somewhat - if anyone is willing to check to see if there any issues or way to improve id appreciate feedback

On another note when doing the calibration we check MV at 21% then again at 1.0 but if the controller fo2 is set to 98% and we only reach .98 at calibration shouldnt that be the multiplier calculation not 1.0?

eg .21 mv = 11 so 1.0 = 52.4 * .98= 51.3

You are adding errors here and you need to be doing better flushes for calibration if you thing there's 2% N2 left in your loop. Or better yet use a separate calibration attachment so you aren't relying on the loop flushes at all. Although seeing as how you have 5 cells I am guessing this is a revo and there is no other way to calibrate.

I divide mV in air by 0.209. Your way is "hiding" 2% drift right off the bat.

 

[lermontov]

You are adding errors here and you need to be doing better flushes for calibration if you thing there's 2% N2 left in your loop. Or better yet use a separate calibration attachment so you aren't relying on the loop flushes at all. Although seeing as how you have 5 cells I am guessing this is a revo and there is no other way to calibrate.

I divide mV in air by 0.209. Your way is "hiding" 2% drift right off the bat.

correct its a revo -

dont you mean .002% ?

 

[wedivebc]

correct its a revo -

dont you mean .002% ?

no 2% = .02

 

[lermontov]

no 2% = .02

oh ok thought he was referring to the difference from .209 and .21 (which is .001 anyway) but yes using a po2 of .98 is losing 2% straight away hence multiplying the MV reading by .98 to correct it -isnt the goal to get a mv reading against an as high a po2 as possible- your plotting a point on a graph.

so what is the relationship between the f02 setting on the controller and your po2 reading at calibration ? if the controller f02 is set to .98

 

[rsingler]

So, as a guy still 8 days away from starting MOD 1 (if 'Rona doesn't close Key Largo), help me understand what's being discussed here.

Yeah, I've built a spreadsheet too, and I understand tracking my mV over time. I understand calibration theoretically, but am really skeptical (with zero RB experience) that you can displace all the air in a calibration cycle that doesn't use up a whole 3L cylinder, with all the eddies, nooks and crannies in the loop.

So calibrating your controller to what maybe does amount to 98% actual oxygen rather than 100% (and I'll bet there is some difference among designs) makes sense.

But why does the controller set point matter?

So if you can't really get your unit to 100% in a cal cycle, it makes sense to call 98% what it is, rather than 100%. But if a cal cycle can't be adjusted to what the sensors are really seeing instead of 100%, I don't know what to do.

On the other hand, if you really do get the gas at the sensors up to 100%, then I'd compare the mV with what I calculated for 100%. And having the controller at 98%? Well, I don't know what that means. I'm going to start my dive set at 0.6-0.7 and fly on the bottom at 1.2-1.3. So 0.98 isn't really relevant, unless that's a Revo calibration setting.

Can y'all educate me?

 

[lermontov]

So, as a guy still 8 days away from starting MOD 1 (if 'Rona doesn't close Key Largo), help me understand what's being discussed here.

Yeah, I've built a spreadsheet too, and I understand tracking my mV over time. I understand calibration theoretically, but am really skeptical (with zero RB experience) that you can displace all the air in a calibration cycle that doesn't use up a whole 3L cylinder, with all the eddies, nooks and crannies in the loop.

So calibrating your controller to what maybe does amount to 98% actual oxygen rather than 100% (and I'll bet there is some difference among designs) makes sense.

But why does the controller set point matter?

So if you can't really get your unit to 100% in a cal cycle, it makes sense to call 98% what it is, rather than 100%. But if a cal cycle can't be adjusted to what the sensors are really seeing instead of 100%, I don't know what to do.

On the other hand, if you really do get the gas at the sensors up to 100%, then I'd compare the mV with what I calculated for 100%. And having the controller at 98%? Well, I don't know what that means. I'm going to start my dive set at 0.6-0.7 and fly on the bottom at 1.2-1.3. So 0.98 isn't really relevant, unless that's a Revo calibration setting.

Can y'all educate me?

The default Fo2 setting on the controller is .98 for pure oxygen but assumes 2% water vapour due to divers breathing on the loop during flushing so i guess its possible to actually reach 1.0 .
One would assume that you are trying to calibrate what your cells read against what you know your calibration gas is.

My question is if your computer fo2 is set at 98% shouldn't you be also reading the mv readings as they should be at .98 because when you push calibrate the screen shows Cal.@FO2=.98. if you extrapolate the readings base on .21 or .209 aren't your mv reading high? ( ie based on 1.0 not .98)

in a extreme example to magnify the question- what if your supply gas was only 80% pure wouldnt you have to adjust the mv readings to allow for that otherwise wouldn't your cells mv readings be shown to be too far out

maybe someone can clarify

 

[rsingler]

I'm working solely from theory and zero experience, but that seems to make sense.
Fully saturated water vapor at 1 atm is 47mm/760mm, or 6.2%. So a 2% corr'n for water vapor must have another factor.
If you calibrate the Revo while breathing on the loop, then that might be an empirical value including a bit of water vapor on the intake side, diluted by a lot of injected O2. My JJ is supposedly calibrated to 100٪ O2, but my cal is done passively with an open DSV, and the solenoid injecting away.

Need some experienced folks to chime in here. But it seems if Revo has determined that loop O2 only reaches 98% during a cal, then you should put the 98% value in your spreadsheet for the multiplier, not 100%.

 

[lermontov]

I thought all controllers could set the fo2

 

[broncobowsher]

...

in a extreme example to magnify the question- what if your supply gas was only 80% pure wouldnt you have to adjust the mv readings to allow for that otherwise wouldn't your cells mv readings be shown to be too far out

maybe someone can clarify

I don't know about others, but the Shearwater on the rEvo you put in 80% O2 if that is what you have. I've never tried calibrating on O2 that screwed up, but 90% works.

Typically less than 100% O2 is from a concentrator. You get a lot of Argon. Need to do flushes to keep a known DIL in the loop and dump the Argon creep that is coming from the O2