Measuring O2 in enriched air

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...provided the flow rate is low enough that you don't get an increased pressure at the sensor.

An O2 sensor is an electrochemical cell. Its voltage output is proportional to the PO2 close to it, not the FO2. So if the flow is so high that the cell experiences a pressure significantly above ambient, it will give a too high reading.


As well as very likely damaging the cell/cell membrane...

W...
 
its better to calibrate in air AND with 100 % o2..........just don't think having 2 units means 1 is right
 
its better to calibrate in air AND with 100 % o2..........just don't think having 2 units means 1 is right
Yes. Some good analyzers, like Divesoft, allow 2 or 3 point calibration.
 
its better to calibrate in air AND with 100 % o2..........just don't think having 2 units means 1 is right
Do you have an analyzer that can be calibrated with O2 and air at the same time? Which one?
 
Do you have an analyzer that can be calibrated with O2 and air at the same time? Which one?
Useful for OC deco gas, that's about it
 
It is also a good way to know if a cell has died. If all you ever do is measure 21 and 32 it is not quite so obvious.
 
Do you have an analyzer that can be calibrated with O2 and air at the same time? Which one?
Most "recreational" analyzers have only single-point calibration. Which probably is a good thing, since if you have two-point calibration you need two calibration knobs which makes it very easy to dial the analyzer way off.

It is also a good way to know if a cell has died. If all you ever do is measure 21 and 32 it is not quite so obvious.
No matter whether you¹ have single-point or two-point calibration it's good practice to check one point below your expected measurement value and one point above it. That's the only way to ensure that your measurement is decent. If you calibrate with air, there's a risk that your cell is current limited somewhere between 21% and the mix you're trying to fill. Which means that you could easily get a too rich mix.

If you only have single-point calibration, you ought to at least check that the calibrated instrument shows the correct value at a concentration above the one you're planning to measure. And no, I don't do that very often either. But since I fill inline, I always check if the mixer and my handheld agree on what the mix is. If they do, I'm most probably good.


¹ General "you"
 
The rate of air flow should not, and does not have any effect on the readings. What has an effect, is the temperature. You open the valve, the pressurized gas quickly expands and cools down.
wrong
 
https://www.shearwater.com/products/peregrine/

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