For all of you Homebrewers out there...

[Doppler]

omar once bubbled...
SNIPPED

You can get the typical oxy-hacker oxygen analyzer to provide an accuracy of better than +/- 1% by following standard gas analysis methods.

SNIPPED

I guess it's all in a word... I would not call an accuracy of plus or minus 1% "Scientific"... acceptable, yes. But not scientific. That margin of error allows for too much slop to ensure repeatable results as defined by any scientific methodology.

And using set procedures (including calibration and flow meter) I find my accuracy is probably within 0.3%+ - , but that's still not scientific.


Are you always so testy?

And to get back to the original question... Oh, think it's already answered.

Doppler

 

[deepstops]

Doppler once bubbled...
I use two digital gauges from Cole Parmer (el cheapo $114 job mentioned above) on the fill whip I take into the field. Frankly in several years of mixing with analog gauges, they are an improvement. The one thing that annoys me is the reading jumps around while filling at a constant flow... 1345 psi - 1356 psi - 1346 psi and so on. Both guages do it and more or less out of sync. It's pretty, but annoying.

As for general accuarcy, I think they're fine since the analysers we use to measure gas ratios give results that are somewhat dubious and far from scientific.

DD

This is the ONLY problem w/ the Econo gauge. 1% accuracy at 1500 psi is 15 psi. Anyone that thinks 1% error in the O2 psi reading needs to loose the pocket protector and go diving.... It would be difficult to get more gauge for your money.

 

[Scuba_Vixen]

When you look at advertised accuracy specs for various gages, it's important to compare apples to apples here. MOST specs list accuracy as a percentage of the Full Scale. This would mean for a PSI Tronics for example, with a FS of 10,000psi and .25% accuracy, the error, AT Any Reading, can be +/- 25psi. There are some gages, (Very Expensive) that specify accuracy as percentage of the Indication. A 10,00psi gage of this type would then be +/- 2.5psi at a 1000psi reading. It always pays to read the fine print. In the McMaster Carr catalog, you'll find both types, and one model with .025% FS accuracy, but they are in the $800+ price range. Seems that each increment in accuracy gets exponentially more expensive. I use the PG7 which is a 5000psi gage with 0.25% FS accuracy. That's 12.5psi at any reading, very acceptable for any DIY blending. When you're looking for gages, read carefully, do the math,and know what you're going to be blending before you decide on an el-cheapo.

Darlene

 

[Bullfrog]

Doppler once bubbled...

...
I would not call an accuracy of plus or minus 1% "Scientific"... acceptable, yes. But not scientific. That margin of error allows for too much slop to ensure repeatable results as defined by any scientific methodology.

Are you always so testy?
...

Doppler, I may be a newbie to SCUBA, but as he used the Method and gave a margin of error, he's allowed for reproduction of his work to test it's validity, and that's good enough for me. I'd like to know your techniques, as well. That way I can test both and see what I like. The more I read and hear, the more I can learn. I just learned a bit. Thanks Omar and Doppler.

 

[Genesis]

"scientific" if it includes the margin of error - irrespective of what it is.

The measurement may be unacceptable in its precision, but its still scientific.

 

[100days-a-year]

Confuscious say "Man who argue moot points and semantics often fool"Yes he's normally that cranky,also right too.Run some tables and see if 1% affects your safety margins appreciably,if it does you are most likely an accident waiting to happen."Results are more important than methods"

 

[Doppler]

Bullfrog once bubbled...


Doppler, I may be a newbie to SCUBA, but as he used the Method and gave a margin of error, he's allowed for reproduction of his work to test it's validity, and that's good enough for me. I'd like to know your techniques, as well. That way I can test both and see what I like. The more I read and hear, the more I can learn. I just learned a bit. Thanks Omar and Doppler.

Bullfrog... and others... I'm not at odds with Omar's methods for calibrating an O2 sensor... they're pretty much standard... just the assertion implied that 1/ oxygen analysers deliver scientific accuracy or are scientific 2/ ergo partial pressure gas mixing is scientific... All I said -- or at least meant, but it was obviously not clearly stated -- was that for mixing in the field, the cheaper digital gauges deliver an acceptable marking of accuracy in my opinion since there are so many other variables.

My use of the phrase it's more art and alchemy than science seems to have pissed some of you off... sorry but I just don't think that one can say that the normal practice for mixing gases for diving is scientific. I think is more art and alchemy... Hands up all those who use van de waals equation when doing their gas ratio calculations?! How many of us use a helium analyser?? (Well, I sometimes do but that's another story.)

OK I am not trying to pick a fight here, but telling me I there's something wrong with me because I think the "gold standard" for mixing gas in the world of scuba could use some tightening up, is stupid.

Someone said... and it's a pretty telling remark... that if a 1% deviation in your gas / deco planning affects your safety margins appreciably, then you're cutting things too close anyway. Truth is we plan for the inaccuracies and vagaries of the methods and instuments we use... we allow for margins of error... we plan with a wide margin of safety... This, I argue, is not science, it's art. I am a scientist -- well, I was trained as one -- and if you can present me with a neatly bundled piece of mathematics that defines all this stuff accurately, I will congratulate you and I will use the time-honored phrase that you: "Have turned art into science."

Have to go... need to start mixing gas to go diving.

Doppler