Hi Brock, Don't feel so bad about TDI. I teach full cave and trimix for TDI myself. There are a number of good TDI instructors. Remember, depend primarily on the instructor, and secondarily on the agency. Take care and dive safe, Scott In a message dated 8/20/00 12:22:01 PM, Bfrede1615@em*.ms*.co* writes: << 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 >> > -- > Send mail for the `techdiver' mailing list to `techdiver@aquanaut.com'. > Send subscribe/unsubscribe requests to `techdiver-request@aquanaut.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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