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Earlier today I spoke to one of the tech guys at Mine Safety Appliances Company, makers of the Miniox O2 analyzer. Among other things, I asked about storing sensors in inert gas such as Helium or Argon. He recommends storing sensors in a cold, low O2 environment, but not a Zero O2 environment. He told me that he has done tests where he stored sensors in low or zero O2 and found that in 5% O2 or less, lead plates out on on the gold electrode inside the sensor, then the zero point of the sensor drifts. Normally the Miniox sensor has a zero level of 0.1-0.25 mv which is how they get by without having a zero adjustment on the display. After long improper storage, the zero can drift a couple of millivolts. In the tests I was told about it took about 5 weeks for the damage to accumulate. If you have a 1-2mv error in your zero and calibrate to air at 20.8%, you are looking at 1-2mv error at 40%, and 4-8mv error at 100%. Using the calibration factor of 10mv/20%O2 that the tech quoted, that means an error of 2-4% at 40% and 8-16% at 100%. Read David Drake's posting "More (long)than you ever wanted to know, was O2 Sensor" from January 25 for an explanation of the calibration error. So put your sensors in a baggy or in tupperware and refrigerate them. Maybe gas them, but don't try too hard to completely purge the air from the bag. Sounds like you want to periodically let them breathe if you plan to store them for a long time like over the winter. If you have the option, get a sensor with a Zero adjustment as well as a Span adjustment. That way, when the sensor drifts, you can zero it back in. Tim Taylor taylor@ru*.ne* Great Lakes Shipwreck Festival 2/24/96. http://www.rust.net/~taylor
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