O2 Analyzer without decimal

[broncobowsher]

Calibrated in air, put it on a bottle of 100% and it returned 99.2%. I got what I was expecting. Were you expecting a different result?

https://youtu.be/kVr4Aj6oapk

I would say you are good. But those expecting accurate reading to the 1/10th percent would be off by 8/10ths. I'm good with it, would even re-cal at the 100% level and verify with air. I bet there are bigger errors if the sample size goes up.

 

[tursiops]

Much easier to just use the lower O2% and then not go deeper than the MOD of the higher O2%.

Exactly. I usually keep my computer on 31...so long as the analyzer is a number greater than that, and my MOD as 100 ft. I'm good for all mixes 31-34%.

 

[EmotionalSupportTrevally]

I was diving nitrox in a mine recently, and they calibrated the sensor to atmosphere [underground] and called it 21%. It's a mostly academic point, but I wouldn't be surprised if the mine air dropped to 20% O2 in the winter (1% CO2, with a ~1.1:1 O2 reduction per CO2 produced.). I've measured as low as 15% O2 in a cave, and would assume mines have similar potential. But that's extreme, and you start to feel anything above about 1-2% CO2.

 

[BoltSnap]

So if I measure 31.8% and enter 31% into my Suunto as the manual states, the NDL calculations are made at 30%?

That's what I remember from my D9 but now you are putting doubt in my mind. I'll have to search my old computer's HD to find the manual and check.

 

[crofrog]

I would say you are good. But those expecting accurate reading to the 1/10th percent would be off by 8/10ths. I'm good with it, would even re-cal at the 100% level and verify with air. I bet there are bigger errors if the sample size goes up.

O2 sensors often display some degree of non-linearity, though.

The Palm O2 Sensor manual specifically calls out:

And the Divesoft O2/He analyzers call out a 1,2 or 3 point calibration, of either room air, room air + pure O2, or room air + pure O2 + O2 free gas (argon/He)

 

[tursiops]

Of course, put in the actual figure into your PDC, but 32% gives you a 20% increase in time.

I assume you mean you get a 20% NDL benefit on 32% versus using air? How do you figure that?
For air the PADI RDP Rule of 110 applies, for 32% 125 applies.
For Navy/NOAA tables air is a Rule of 118, 32% is 128.

 

[The Chairman]

How do you figure that?

For planning only. It's way close enough for planning. Most divers never plan because peeps have made it way too difficult. This gives you nothing but a beginning point for your dive to start. It's a sanity check and nothing more.

 

[Dan G]

Yes. But please use it for planning only. I used to dive with that as my only guide, even to guessing my depth based on a red ribbon tied to my harness. Then it got complicated albeit safer with tables and a real depth gauge. The advent of the PDC makes it easy, but the rule of 120 is still a quick shortcut for planning. You don't need to blindly follow that PDC, if your using the rule of 120 as a sanity check.

It's 120- max planned depth=NDL. As mentioned, it's just for rough planning.

I totally get it and never considered using this for anything other than a rough idea of what my BT might be.

 

[BRT]

To the OP and the original post, find a different analyzer to comply with the PADI rules.
To the rest of the world, you are not going to get a basic Nitrox analyzer to calibrate down to a tenth of a percent. Most of the basic Nitrox analyzers you can slightly tweak the flow rate and how tight you press the ball against the tank and move the reading a full percent point.

As for the rounding up/down, depends on what you are trying to do. MOD, round up. Deco, round down.
Now factor in the science isn't a knife edge, but a blurry transition. In the real world there really isn't anything gained with that extra decimal point.

Calibrating a Nitrox analyzer in air? Ever try that then put it on a bottle of 100% and see what you actually get back?

Yes I have tried that. But the mixes I breath are a lot closer to air than to 100%

 

[Gone for diving]

In this whole mess does anybody check their air and adjust the DC according?
Oh wait, that's the calibration point.

I am quite sure in cities o2 in the air could be lower....