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Michael, > I Adjust my Minox to 20.9% to 21.0% O2 using air as a reference. I have then > checked pure O2 and gotten values between 99.6 and 100.2 % which I consider to > be o.k. accuracy. Then I have checked the sensor on a nitrogen tank and have > gotten values under 00.3% which is also o.k. I can only assume that the minox > sensor is accurate to 0.4% of full scale if calibrated between 20.9 and 21.0% > using air as a calibration gas. No - this assumes linearity. In actuality, you have a non-linear response which crosses the calibration line in 2 spots, at 21% and 100%. > Sorry but I don`t see a calibration or accuracy problem. Do you? Yes, in several respects. First, you didn't indicate, but if you calibrate with non-compressed air, then your measurement will be off if you're measureing compressed air, even if you try to control the flow. Secondly, the curve is designed to cross at about 21% and 100%, because its designed to be used on low pressure low flow home units, and people at home calibrate on air to test for 100% O2. In the middle of the range is where the curve is the furthest from the linear response. The correct test, it to take compressed air and run it across the sensor at say 2lpm. Then take 100% O2 and run it across the sensor at the same flowrate, and you'll be within 1%. Now, take a 34% calibration gas, and you'll read about 3% off. At 60% you'll be almost 6% off. We measure around 32-50% for most nitrox applications, in the range where the O2 sensor will read low. Now, for trimix, this is worse, because you calibrate on air, the curve goes above the line there, so the O2 will be higher than indicated. The sensor is accurate to 1% full scale, when calibrated properly, which is within 4% of the desired final mix. -- /***************************************************************************/ /* William E. Sadler | email: sadler_b@bs*.bs*.bl*.co* */ /* | batchmo@cr*.co* */ /* Divers Down! [\] | CI$: 71005,1241 */ /* | POTS: (404) 332-2314 */ /***************************************************************************/ /* Keep your Honor, be Bold, and remember: */ /* The only things in the middle of the road are yellow stripes and */ /* squished possums. */ /***************************************************************************/
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