What they don't teach you in Nitrox class...

[Warren_L]

Does your sensor ever read above 100%. Maybe it's grossly off and when you measure mostly pure O2, it's just pegging the meter. I agree with the other guys that 3% between ambient and tank is HUGE. I could believe .3% as in 20.9% versus 20.6%

I've heard that every once in a while, you get a DOA sensor..

That's an interesting thought, I never thought to try that. I use an Analox II analyser. I may just run it off my O2 deco bottle when I get home just to see what it reads.

 

[lamont]

I analyze mixes between 21% and around 36% at sea level. Calibrating to ambient and then using a very slow rate flow restrictor always gets me to a few decimal points of whatever I got at the shop using a different O2 sensor calibrated to constant flow out of a bottle of 21%.

 

[do it easy]

Soggy, the sensor is from Analytical Industries. It's a PSR-11-39-JD

http://www.aii1.com/diveoxygensensors1.html

This is from the footnote:

2. At constant temperature and pressure. Caution: To avoid erroneous readings: 1) calibrate at operating pressure of sample, and, 2) calibrate with 100% oxygen for use at elevated oxygen levels above 30%.

So yes, it is about the flow rate, but I couldn't sleep at night if my sensor read 17% in ambient and 21% off of an air tank...

 

[Jason B]

Any one using the R17D sensor from oxycheq.
I may order one up to try and alleviate this problem.

 

[cmalinowski]

Air flow across the sensor will affect the reading. I use the sensor like the el cheapo with the blue "T" for air flow. I calibrate to ambient by swinging it around for a while. Then when I put it on the tank and take a reading, I figure that was good. Then, in my DIRf class the instructor came up while I was taking my tank reading and put his thumb over the air outlet for the sensor and the reading changed by about 1.5% or so. Try it sometime...

I now, for the time being, have an air tank that I will calibrate with much like was said before (ambient calibrate, air tank calibrate, reading on EAN tank, re-calibrate on air tank).