Analyzing multiple nitrox tanks

[Storker]

My analox has the little dome with a barb for testing, if I pop that off the cell is open to the atmosphere so no gas retention. I calibrate carefully with ambient air, correcting for temp and humidity as per the little table that came with it then I don't fiddle with it until the next day I'm analysing.

My Analox' calibration dial is so easily nudged that I don't even trust that the analyser is correctly calibrated between tanks. Especially if I'm being handed the analyser from my son after he has analyzed his tank. So given that, plus my - IMNSHO fairly decent - experience with analysis equipment in general, I always take my time and make sure that the analyser returns to 20.9% (or whatever the value adjusted for temp and humidity is) between tanks. If it doesn't, I pop the dome off the sensor and wave the analyser around in the air to be sure all residual gas is flushed, adjust the calibration and re-analyze the tank. Bonus points if the reading on the site is within a few tenths of a percentage point from the number already on the tank.

I'm pretty certain that some people would see this as somewhat excessive.

 

[Patoux01]

So, eliminate the errors you can.

Bah. How far off are you gonna end up anyway? 2% ? Doesn't sound that scary to me

 

[tursiops]

Bah. How far off are you gonna end up anyway? 2% ? Doesn't sound that scary to me

Why don't you just guess the percentage? It'd be a lot faster and easier.

 

[tursiops]

I always take my time and make sure that the analyser returns to 20.9% (or whatever the value adjusted for temp and humidity is) between tanks.

What purpose does this serve?

 

[Patoux01]

As a matter of fact I did that for a year... 2 dives a week, still here to tell the story . Occasionally I'd verify the guess. IMO analyzing serves mainly to catch a ****-up, eg it's been pumped on pure O2, or only air when you needed nitrox. Those mistakes will be > 10% off.

Anything that comes within a few % of my expectation is fine with me.

 

[tbone1004]

My Analox' calibration dial is so easily nudged that I don't even trust that the analyser is correctly calibrated between tanks. Especially if I'm being handed the analyser from my son after he has analyzed his tank. So given that, plus my - IMNSHO fairly decent - experience with analysis equipment in general, I always take my time and make sure that the analyser returns to 20.9% (or whatever the value adjusted for temp and humidity is) between tanks. If it doesn't, I pop the dome off the sensor and wave the analyser around in the air to be sure all residual gas is flushed, adjust the calibration and re-analyze the tank. Bonus points if the reading on the site is within a few tenths of a percentage point from the number already on the tank.

I'm pretty certain that some people would see this as somewhat excessive.

over calibration can be about as bad as under calibration. There is no need to recalibrate multiple times per day so long as the knob isn't bumped. Unfortunately that sounds like a poor design choice for that analyzer

regarding the waiting until it returns to 20.9, that's a waste of time, just hook up the next tank and wait for it to stabilize

 

[Storker]

What purpose does this serve?

My Analox' calibration dial is so easily nudged

 

[IBjones]

We got an analyzer at the shop like that. The number ranges all over back and forth between 20 and 21% without even touching the button. No matter how long you let the air flow over it, it never stops bouncing around from number to number, So a "calibration" with that one is basically a "within two percent guess".

 

[Storker]

We got an analyzer at the shop like that. The number ranges all over back and forth between 20 and 21% without even touching the button. No matter how long you let the air flow over it, it never stops bouncing around from number to number, So a "calibration" with that one is basically a "within two percent guess".

That's a totally different issue. If my analyzer was jumping like that, I'd never trust the values it gave me. An easily nudged calibration dial is not the same thing.

 

[tbone1004]

We got an analyzer at the shop like that. The number ranges all over back and forth between 20 and 21% without even touching the button. No matter how long you let the air flow over it, it never stops bouncing around from number to number, So a "calibration" with that one is basically a "within two percent guess".

your shop needs a new sensor. no way it should bounce around that much