The Chairman
Chairman of the Board
Indeed. It's a false economy too. People do it to 'expedite' the process. Why? I always have plenty of time to check my tanks. I doubt I spend more than a minute a tank.
O2 Analyzer without decimal
- Thread starter Tedestam
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The Chairman
Chairman of the Board
OK, I have two DMs asking why. I'll answer that here. I had just bought two HP120 tanks and this was their first ever fill. I went to use his analyzer and it had crapped out. He could not fill NitrOx there, so he had picked them up from a shop that did. He claimed to have checked it then. I really wanted to dive the next day, so I believed him. When I hooked up my regs, the pressure was way, way low. I think it was 800psi in each tank. But big tanks, right? It's my belief that the guy had put the O2 in, but forgot to add the air. It's also my belief that the guy at the first shop told my guy that he had checked them too.
Dive only tanks you have analyzed. Let them adjust to ambient temps before you do. I don't have to deal with altitude changes here in Florida, but I believe John when he says it makes a difference. It's my opinion that you should own your own analyzer too. They're fairly cheap now. Don't rely on equipment that's been handled by a bazillion people. I don't mind lending mine out, but I often avoid lines when I'm on vacation. I remember one guy in Bonaire asking how I had gotten the analyzer before he did, and I told him I owned this one.
There must have been 40 people in there. He was an SBer, so he got to use it and so did his wife.On the dive boats I go on in Mexico nobody, nobody analyzes except me. Often at the dock I'm analyzing and don't know what tanks will be for my wife, friend and me so just do them all. I've had other divers get upset because I messed with their tanks. Not mad, just really snide about it. So I don't do that anymore. I try to get our tanks separated out first. Sometimes kind of hard if part of the tanks are stacked in the back. I guess I should just analyze before the 2nd tank goes on, but the DM's often do the changes even though I'd rather do my own.
The Chairman
Chairman of the Board
My analyzer allows me to measure straight from the tank or from a 2nd stage mouthpiece. It's in a waterproof box and will accompany me on the boat if needed. I own three, but only travel with one. I always change the battery before I go. One of them needs a new sensor, which is why I have multiple.
Yes, mine will measure straight from the tank, but I find I get better accuracy, or at lease repeatability through a flow control actually hooked up to the tank. I carry a spare analyzer and a spare sensor. And wear suspenders with a belt.
The Chairman
Chairman of the Board
That was from my first trip to Bonaire in 03. Most of my trips are with SBers. Surprise, a lot of them have imitated me on this and bring their own analyzer too. On our last trip, almost every couple seemed to have one. I gots lots of backups now!Yes, mine will measure straight from the tank, but I find I get better accuracy, or at lease repeatability through a flow control actually hooked up to the tank. I carry a spare analyzer and a spare sensor. And wear suspenders with a belt.
Just looked up the MaxO2+ which states it has an accuracy of +/-3% and the Palm which has an accuracy of <+/-2%. Am I misunderstanding what this means, because if these very popular O2 readers have an accuracy of +/- 2-3%, then a discussion of rounding decimal values is a moot point.
I suspect that's +/- 3% of the pO2 absolute, not percent of O2 in the gas you're measuring. E.g. air has about 21% O2, which is 0.21 atm pO2. +/-3% of 0.21 atm means a possible range of 0.204 - 0.216. Or at 1 atm total pressure, a range of 20.4 - 21.6%.
Also, 21% +/- 3% (18% - 24%) would be unacceptable in my former labs that used O2 analyzers (and we used the same teledyne sensors found in my personal analyzer.) I didn't look up the reported accuracy of the teledyne sensors; maybe it's better than in the MaxO2+?
I take that to mean that when you measure air with the Palm O2, you can expect a displayed reading between 20.5% and 21.3%. Measure 100% and you can expect a reading between 98% and 102%.
I have an AII Trimix 4001 analyzer. It claims an accuracy of +/- 1%. One of the Quality Control Checks before shipment is that it must be within .5% of the calibrated ambient air value (that would be .1% for 20.9%) If I were to assume an accuracy of 1% in the manner you describe, it means that a reading of 19.9% to 21.9% would be passing...and that is definitely not the case.
2-3% of 0.21 or whatever the mix is, makes more sense. That would put a mix of 36% O2 in a range of approximately 37.08% - 34.9%. Still means the MOD (using 1.4 ATA) would range from 99' to 92'. Not a small range, but reaching 1.4 ATA does not result in instant oxtox. Still, it's good to be reminded that limits in MOD and NDL are not to be trifled with by recreational Nx divers such as myself.
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