OMS Oxygen analizer ????

[nyresq]

I have a small (6 ft) bottle I use for drysuit inflation thats filled with air... cause argon is an urban ledgend... ooo fan the fire... but when I need to check a mix I hook the meter up to the little bottle to calibrate it. all of my regular tanks are filled with some type of mix so I just keep the pony filled with air. unless your at extream altitudes when you get a tank filled with air, it will have 20.7-20.9% O2 in it. like the man said "air is air... dude".
As for using pure O2... when filling prescription medical O2 (yes O2 is considered a prescription drug when used for medicinal purposes) the empty tanks have to be pumped out to draw a vacuum before being filled with O2 drawn from a liquid O2 reservoir. Your local gas supply is not going to do that for someone besides a medical facility, where they test O2 batches from time to time with gas analyzer alot more expensive then we are using.
And your scuba shop isn't buying their O2 from a medical supply... unless they have a doctor willing to write a presription for them.

The prescription thing is no BS.. the medical director for my fire company has to write us a yearly script for O2 so we can get our tanks filled. And the medical O2 costs about 3x as much as the same K cyl we get filled for the cutting and welding torches we use... from the same supplier.. but without the suck job...

So the "pure O2" in that tank could be anywhere from 97% to 99.9% and that range is large enough to kill you if you miss an MOD by 3%.

 

[NAM001]

I am scheduled for the Nitrox class this January.

The OMS is a x-mas present from my wife that I..ehhh... opened a little early, shhhhhh.

I was thinking to calibrate it, it had to be under pressure to be calibrated. Waving it works, duh. Thanks.

Now for the 100%. I'm sure I could figure out some way to get that locally for calibration purposes but what about on a dive boat?

I'm pretty sure they will not let me tap into there oxygen safety kit to calibrate my tester. Can it be calibrated prior to leaving on a trip? Or possibly setting to the standard 20.9% by waving then read the nitrox?

Thanks Mech and Capt. It's starting become clear now.

Scott

edited for typo

scott,

perhaps there are a number of issues that affect the o2 tester, not to mention the battery. as the battery degrades the reading's will reflect a greater error. as the sensor degrades it generates signals that are now in error. that is why you calibrate it each tiome you use it. that way you correct for the sum of all errors in the unit.

now lets use a hypothetical tester that has a 10% error from calibration point. so that if you cal it at 21% and you sniff 71% o2 air then the difference is 50% +/- 5% (5% is 10% of the deviation from cal point). in this case your 71% gas would read as 66-76%. this is unexceptable. for this situation you would snif a known source of say 60% and calabrate to that then when you read the 71% gas its error would only be 1% instead of 5%. got it??? making sence?? good. now lets look at the real world for a minute. the errors are not 10 percent. probably closer to 1% of the deviation. second you are going to use nitrox of probably 32%-36% so long as you can calibrate using a gas that is close to what you are going to use the resultant error is kept to a minimum. there for insuring calibration accuracy at 90% o2 is useless if you are going to be measuring 30% gasses. given the asumptions of 1% error . you cal to atmosphere which is 20.9% you measure 32% gas the differential is 11% the error is 1% of that so the 32% gas will read 31.9-32.1%. following me so far. lastly the dive tables you use are in 1 or 2 percent increments if you can find them. being .1% off is of no concequence to your dive planning. you will probably be given a 21 32 36 % dive table to work with. if you get a weird mix of say 27% then you will be taught methods of how to deal with it in the course. lastly you will probably use a dive computer to keep up with the calculation of the gasses you are loading up with when not in a training role. the computer takes the reading you measured as an input from a menu in 1% increments. in short air is a sutable gas to calibrate with for the less than 40% nitrox users. the errors are non esistant for your purpose once you cal to atmosphere at 20.9.

my recomendation is to keep this issue in mind alond with all the feedback you have received from my self and others and see how the nitrox course treats it. i think you will find that you concern with the accuracy is solidly valid but the drgree of error is not an issue in the scope of the training or the environment you are being trained for. when you later, move up to advanced nitrox and beyond then you will be in a different environment and accuracy will become more critical.

enjoy your course and dont stop asking questions. after all you are paying to have you questions resolved.

regards