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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.
--
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