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>Is there some chemical process that occurs in the sensor itself that >produces this voltage Yes, the sensor is a little fuel cell which produces electricity when exposed to O2. The gauge measures mV, not resistance. >Either way, it doesn't seem too terribly complicated - one can use plain >old compressed air from a tank as the "standard" to derive Volts/PO2 and >just do the simple math to determine the PO2 of the cylinder under test. > >And to compensate for soft batteries and/or wear and tear on the sensor >itself, one need only go through the plain jane air calibration prior to >checking any mix. Right? > Basically, right, though it's a good idea to also check calibration with few nitrox mixes, and cross check it with other gauges, before you start putting too much trust in it, at least until you get a feeling what kind of accuracy you are getting. Check the archives for this list. There's a lot of good stuff about sensors there. Also, there's a book, THE OXY HACKERS COMPANION which has some stuff about how to use a voltmeter to read a sensor, or make a dedicated Miniox style gauge for about $15 that reads directly in PO2, as well a lot of other info about 02 and homebrewing nitrox. Incidently, the problem with the automotive types, is apparently that they are designed to work with PO2's below 21% - since they made to measure combustion efficiency, and there's no predicting how well they'll do at nitrox PO2's. Plus they need to be hot - later ones have heater circuits built in, but that takes a heck of a lot more than a 9V to run - and they cost as much/more than a proper med O2 sensor. -- Send mail for the `techdiver' mailing list to `techdiver@aquanaut.com'. Send list subscription requests to `techdiver-request@aquanaut.com'.
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