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Sure. > Do people have any preferences on Oxygen analyzers? > > Comments would be appreciated on the vandergraph, Teledyne and the Mini-ox. They are all bad for use as dive meters. I recently obtained the specs for the electrochemical sensors that they use, and they are not linear throughout their range. They are only correct within about 4% of their calibration point. If you calibrate at 21% (air) you will be off (reading a low O2 value) at 32-36%. If you calibrate at 100% (pure o2) you will be off by as much as 10% at 32-36%. If you use 2 points, and move the curve about until it crosses at 21% and 100%, then you will be off by about 4%. The ONLY way to use those meters properly is to use a calibration gas, say a known 34% mixture. Then the sensor will be nearly linear from 32%-36%. This assumes, of course, that you are trying to calibrate for NOAAI or II. If you are trying to calibrate for another mix, you must use a known calibration gas within 4% of the value you are trying to reach or your results will be off. Also, these sensors have BAD hysterisis (sp?) meaning the values are not the same going up as coming down, instead of drawing the same line, it draws a crescent moon type shape. The effects of this are reduced with proper calibration procedures too. The only meter that I've seen that works are the paramagnetic type. They measure the O2 via its magnetic properties. Yes, Oxygen has magnetic properties, as it is a metal. Which I guess I could have deduced, but didn't. Anyway, paramagnetic sensors cost about $1500 just for the sensor, at wholesale (OEM) prices. Complete instruments cost about 4k. But they are linear over the range 0-100% O2, there is no hysterisis, and very good repeatability. -- /***************************************************************************/ /* 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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