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> Okay, so if I have a sensor that might be going bad, I can hook it up to my > voltmeter and check what voltage its at. If I want to check the voltage on > a mix greater than air with strictly the voltmeter, is it a linear relation, > a curve, a guess or what? How do you figure out X volts at 21% = Y volts per > % O2 > 21 %. The relationship is close enough to linear that you'll get adequate calculations for safe mixtures, at least for mixtures most divers will be using and at 1 ATA Ambient pressure. On a brand new sensor, I get 0mV with 0% O2, 12.7mV at 21% O2, and about 54mV at 100% O2 (all at 1 ata ambient pessure). The problem is, you need to calibrate the sensor each time to make sure you've got the right offset. I don't think you can just draw a line through the origin from the reading at air and expect to get correct measurements for higher-O2 nitrox mixtures. Instead, you should establish a value for both air and 100% O2 each time, and then calculate the slope from that. > Is that different than the the MiniOX's algorithm? What is the > algorithm the MiniOX uses? I don't know how the MiniOX works because I own a Teledyne analyzer and teledyne sensors. > What is the threshold voltage where the sensor > is not considered reliable and therefor useless? I replace my sensors when they drop below about 8mV in air at 1ATA. > What is the little connector > that I'd get at Radio S. that will allow for easy checking? I don't know what George was refering to here: I suspect he meant the approrpiate electrodes for a DVM (digital volt meter) that can easily plug into whatever socket your particular O2 sensors are equiped with (mine have bare wire leads, so I just use normal DVM electrodes). > IOW, tell me all > about the sensor/calibration please. Pretty please with pretty fishes on top > please? I'm not sure what else I haven't covered...let me know if you have any more questions. > <start insert> > Yes, this works but you need to consider the accuracy of your volt meter. > Most inexpensive meters are are only rated to 3% or worse accuracy. > Richard Chapski > <end insert> > > Does anyone know how to easily and accurately check the accuracy? > I don't have a lab at home, but can get access to a "board room" and friends at > my plant if that is neccessary. The reading only needs to be accurate at the same scale that decompression algorithms and/or PO2 limits are accurate. In other words, it won't help you much to know the O2 percentage to within a hundredth of a percent, if the probability of DCI or O2 toxicity varies by several orders of magnitude more. > Where is the cheapest place to pick up sensors, in the US for each company? Try contacting Randy Bohrer at Underwater Applications Corp. I don't have his phone number but he has a compuserve address (I can dig it up for you if you want, but I'm sure others on the list know his conatct info). > Do you use the same sensor/miniox to check mixes less than 21% O2? Yup - I use the Teledyne Hope this has been useful.... Aloha, Rich Richard Pyle deepreef@bi*.bi*.ha*.or* ******************************************************************* "WHATEVER happens to you when you willingly go underwater is COMPLETELY and ENTIRELY your own responsibility! If you cannot accept this responsibility, stay out of the water!" *******************************************************************
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