Quote: (Originally Posted by
dave t)
So if you cal in o2, flush it back with air and get 0.21 whats the point of doing a 2 point cal (and its potential for more error)? and if you dont get 0.21 it could be the o2 cal that is off not the cell being non-linear.
No point of 2 point cal in this case. We should be checking and knowing our O2 purity before using it
Quote:
And anyway how much non-linear do we actually care about!!!
I take your point about maybe a bit of non linear at the cal point MAY show an impending current limit and it is my belief that all rebreathrs should be able to calibrate at or above your chosen setpoint. Thats what they do on the Divex stealth!
If/when you're extrapolating from PO2=1 (like almost everyone does), I utilize a 2 mV under-reach/ED cut-off.
In water PO2 cal? That's an idea but would require pretty good skill.
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Actually I agree with almost everything you say but I still dont understand why you cant do all of that with a po2 reading as opposed to a MV reading ? especially as you agree the are the same output!
Actually you can do all with PO2 only, using 1 point cal and checking your air reading after cal. Now that we have had this conversation, I now see that it is only those of us having to do 2 point cals, that need the mV readings. The 2 point allows air to O2 calibration at a product different than the above-mentioned 4.8x, and we need to check this. In your case, the same check is done when you let the cell relax in air. If/when it falls back to .21, then Bob's your uncle.
Thanks for the insightful discussion.