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GDPLEDGER, Does this mean we might as well not bother testing our mix before diving, seeing we could never be sure within at least 22% either way our readings are correct? I was under the impression that calibrating an O2 sensor before use to nitrox 21 (air) was key to having a good reading (give or take a few tenths with ambient temperature change). Are you saying this is all bollocks then? And if not, what are you saying here? Or is this another troll? rgrds --- Adri KC Haine darkangel@en*.co* " Doing deep dives on air is like having sex without a condom. The technology is there. It's stupid not to use it." Dick Rutkowski - Int'l Association of Nitrox Divers <GDPLEDGER@ao*.co*> wrote: There is a lot of good science being discussed on this list in this thread. Here at Oceanspec we have been conducting a government equipment survey and reliability test on several different types of equipment. I have already made the statement to this list that most O2 sensor equipment should not be trusted. Most notable the gas sensor and testing equipment available to the dive community from this country. I probably spoke to soon. I am sure I will be corrected by somebody but our count shows 22 brands of equipment available to test for O2 content of gas, all can be used in portable mode all are battery operated. The test gear that was evaluated was both new and used. The units were tested using Swan or IoneticBM test comparators calibrated with certified CRG or National Calibration gas in 10/85 21/70, 35/60 and 52/45 gas concentrations. Each test received control samples from ambient air. All were tested at 88 F,72F, 60 F ,40 F . All of the equipment was tested then sent off to be recalibrated (by manufacture recommendations), and then tested again. The average negative error (low reading) was 22% of total tested concentration. That would mean a 52% O2 concentration show 39% on the test gear. The average positive test reading was 29% above the cal gas values for that test. The most disturbing was several test that indicated. a 10/85 cal gas as being a 32% concentration. The total test package is not yet complete, so I will not talk about each machine. The errors that we see at the two lower ambient temperatures are so great that I do not see the utility of even trying to use the equipment. This problem gets much better if the portable test gear is kept at standard temp. Gas flow fluctuations against the test head was as big A problem as temp was. A cheap and safe way out of this problem is to carry a small bottle of cal gas, probable the 35/60 , give your trusty old "STROKE" machine A sniff and compare it's read to a known Percentage in the cal gas cylinder. Remember that not any cal gas will do must be O2 and An inert That should tell you if there is A problem. Somebody on this list just recently alluded to the fact that there is no He test gear that was cheap, try a Draeger tube and a balloon, that will run about $7.00 per test. Draeger claims an accuracy of + or -05% . That is better that the Abbot or RocheBM converted gear. __________________________________________________________________ Get your own free England E-mail address at http://www.england.com -- Send mail for the `techdiver' mailing list to `techdiver@aquanaut.com'. Send subscribe/unsubscribe requests to `techdiver-request@aquanaut.com'.
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