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Ken Sallot wrote:
>Go and buy a Mini-Ox sensor (or any other sensor you like that will 
>work with a miniox). Should cost you about $75-$85.
>
>Go to Radio Shack. Buy a couple of stereophone miniture plugs. The 
>type that will fit into the O2 sensor bottom.
>
>Hook the sensor up to a voltmeter. Set the meter to DC, Millivolts. 
>You may need to do some soldering to connect wires to the stereo plug.
>
>Take out a calculator. Use a solar powered one to save batteries (and 
>money).
>
>Meter air. You should get a number like "11.7mv". negative or 
>positive doesn't matter.
>
>Take the O2 content of air (20.9) and divide it by 11.7. For those of 
>you who are truly technical types take out the calculator, type 
>"20.9" then the divide button then the mv on the sensor reading.
>
>Now throw the sensor onto a tank of mix. You'll probably want some 
>sort of flow regulator (you'll need one with a miniox anyway). Alex 
>Varouxis makes this great little flow regulator that fits on top of a 
>sensor and plugs into a power inflator hose, I think he sells them 
>for $15. Of course you could buy the dive rite flow meter for $49 
>which doesn't do half as much.
>
>Let the sensor sit on the flow for a minute or so. Meter the sensor 
>with the sensor still in the flow. Take the previous number (remember 
>20.9/11.7) and multiply it by whatever the readout on your meter is 
>now. That's your O2 content.
>
>A few words of warning. Chemical sensors (such as Miniox sensors) are 
>not 100% accurate. They're considered valid within 1-2%, so it may 
>say "32%" when really it's 34% or 30%. This would be the case if you 
>use a miniox as well. Also, these sensors will change calibration 
>over time, and different temperatures as well, so you're an idiot if 
>you don't calibrate your sensor before analyzing any tanks. The 
>primary reason to analyze your tanks is for that "sanity check" to 
>make sure you're within the ballpark. Obviously if you're expecting 
>EAN 34% and your analysis says 50% you screwed up somewhere.
>

If you want to check the linearity, you can also measure the content of 100%
oxygen in addition to air. The air measurement will give you %O2 per
millivolt multiplier. Invert this number to get millivolts / %O2 and
multiply it by 100%. You should get a millivolt reading close to this (+/- 1
to 2% full scale static error band) when you measure the O2 tank (providing
the O2 tank is 100%). If it is way off, you have a problem, or did it
incorrectly. 

Great post Ken, good information.

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