Oxygen sensor failure

[rmssetc]

You know, I just became aware of another failure scenario which could be rather unpleasant to a simple rec OC diver: the cell is current limited below 0.21, but the multiplier circuit can bring the voltage up to showing 0.21. But then the output would be flat from below 0.21 and beyond my max fO2, and my tank of properly mixed EAN36 would be identified as a tank of air. Could be nasty if I'm planning to go to 40m...

Fortunately, most of the unpleasant failure modes usually will be detected by using two different analyzers. And if they don't agree within the expected variance of ~1 percentage point, don't breathe the tank until it's been analyzed with a third unit which agrees with one of the others.

While accurate, that's a pretty amusing suggestion, considering that the original thread (Nitrox analyzer: to take or not to take?) had a lot of responses about the local analyzer being unavailable (missing, busted, busy). If you don't trust one analyzer, what are the odds of 3 being available? Maybe the question should be "Nitrox analyzers: to take three or not?"

 

[northernone]

While accurate, that's a pretty amusing suggestion, considering that the original thread (Nitrox analyzer: to take or not to take?) had a lot of responses about the local analyzer being unavailable (missing, busted, busy). If you don't trust one analyzer, what are the odds of 3 being available? Maybe the question should be "Nitrox analyzers: to take three or not?"

While I think that's an excellent point...

I do vote with my dollars, if a shop is selling a breathing gas without any way of reassuring me of the contents that is a trust me dive I won't be taking.

I'm fine with a straight air shop which sells air fills. But if there's partial pressure blending going on I want to know someone checked what's in the tanks they are sending out. It's my life if they top off with o2 instead of air.

 

[rmssetc]

While I think that's an excellent point...

I do vote with my dollars, if a shop is selling a breathing gas without any way of reassuring me of the contents that is a trust me dive I won't be taking.

I'm fine with a straight air shop which sells air fills. But if there's partial pressure blending going on I want to know someone checked what's in the tanks they are sending out. It's my life if they top off with o2 instead of air.

Right, but there's the problem. The shop could be using an analyzer with the kind of cell failure that you personally described:

I have one currently on my workbench that reads 16% to 25% accurately and afterwards drifts off to a current limiting maximum of 30%. Been that way a month now.​

If they calibrated against air, the tank they thought was 30% could really be 100%, right?

Yes, they are checking the tank. In their attempt to reassure you of the contents, they even hand you their analyzer so you can confirm that you get the same 30% reading as what's written on the scrap of tape.

 

[Johnoly]

..., they even hand you their analyzer.....

I think that's why so many of us are saying it's best to own and use your own analyzer. The main reason for me is I don't know the history behind "their" analyzer. But I do know the history behind "My" analyzer. And that's a huge difference when doing dives like us that are pushing the limits and beyond of our equipment and there is not much forgiveness room. When I posted the video in the above thread, I was seriously PISSED when the readings dropped out for no reason. I knew the history of it and how little things like temperature (FLA), blasting air, and how I should barely 'twiggle' the calibration knob each time.

Any thing that's even slightly unusual should set off alarm bells and call for a full stop. Here's a piece of equipment that I OWN and trust my life to, so it's only my fault if I continue to use it. I view every other analyzer in the world as a backup verification to mine because I know my history...not theirs. This will make almost no sense to you and others until you see it happen on a tank and it scares the heck out of you as a near miss. Just like that last car that almost hit you if you hadn't slammed on the brakes to a full stop.

 

[Storker]

While accurate, that's a pretty amusing suggestion, considering that the original thread (Nitrox analyzer: to take or not to take?) had a lot of responses about the local analyzer being unavailable (missing, busted, busy). If you don't trust one analyzer, what are the odds of 3 being available? Maybe the question should be "Nitrox analyzers: to take three or not?"

Don't be silly. I said analyze twice: with the filling station's analyzer after filling, then at the site with another instrument. If the on-site analysis doesn't match the marking on the tank, the prudent thing would be not to breathe the tank until you know which of the analyzers is off.