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Scott:
I agree with you on the need to take at least some basic Nitrox
course. With the slap-dash OW instruction nowadays, none of what I was
reading here made full sense until I took a class and relearned what I
vaguely picked up in AOW. After that my "DOH!" factor went down and my "ahh
gotchas" went up. My only regret was that it had to be a TDI ( I really
resent giving Gilliam my money) course, but Rick turned it into a 2 day
course to make sure we were getting things and threw in a couple of fills
for us to practice our analysis skills on.
I'm still sometimes fuzzy , but at least now I know what to ask
(sorta) ;-)
Dive safe
Brock
----- Original Message -----
From: <ScottBonis@ao*.co*>
To: <techdiver@aquanaut.com>
Sent: Saturday, August 19, 2000 10:09 PM
Subject: Oxygen measuring (was "OMS Like" DIN flow regulator)
> Hi Paul,
>
> You are correct in that if gas is flowing out to the ambient air, the
> pressure must be somewhat above ambient. The trick is to make it as
little
> above ambient as possible and yet still have gas flowing. Many divers
choose
> to use some form of flow meter or flow control device while a bunch of us
> older guys simply turn the tank valve gradually closed until we can just
> barely hear the gas flowing.
>
> Chris Elmore has mentioned that it is the partial pressure of oxygen that
the
> sensor is responding to. And we know from Dalton's law that the PP(O2) is
> equal to the fraction of oxygen in a gas multiplied by the total pressure
of
> the gas. So if the gas pressure at the sensor is above ambient and
ambient
> was the pressure at which the sensor was calibrated, the sensor will
measure
> a higher partial pressure of oxygen and will therefore display an
> artificially high fraction of oxygen for the gas under analysis.
>
> If these terms are not familiar to you or this explanation is difficult
for
> you to understand, then I recommend strongly that you take a course in
Nitrox
> diving. It really is the best way to start learning about the use of
gasses
> other than air for diving. You can get some good information from these
> lists, but occasionally you can get some bum dope also (of course never on
> "techdiver.")
>
> Take care and dive safe, Scott
>
>
> In a message dated 8/18/00 1:10:30 PM, Bakalite@ba*.co* writes:
> << I guess this doesn't make sense to me. If gas is flowing, how can
> the pressure be ambient? What is the error induced by having a
> higher PP due to a flow over the element versus a resing pressure.
> It seems to me that if the flow is off by 10% you'd get a 10% reading
> error, although in practice this doesn't seem to bear out. Sorry if
> these are stupid questions, but I'd rather ask some of those than tox
> on o2.
>
> Thanks.
>
> Chris Elmore wrote:
> ~
> >Paul,
> > For flow rate, get a needle valve from the brass fittings
> >section at Lowes and use a flow meter to calibrate it. Once it's
> >calibrated epoxy the adjustment shaft and you're set to go- total
> >cost: about $5. You can even oxygen clean it if that makes you
> >happy. Flow rate doesn't really matter as long as you have enough to
> >purge the lines and move the gas over the sensor but not enough to
> >produce back pressure. Sensors measure partial pressure so you have
> >to keep the pressure at ambient. If you can hear gas flowing that's
> >enough.
> >C.
> --
> Paul Braunbehrens mailto:Bakalite@ba*.co*
> http://www.daw-mac.com Mailing list for digital audio on the mac >>
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