Comfort Zone - What range of Gas Analysis?

[Akimbo]

…When the sensor fails, the reading doesn't stabilize.

When the battery fails, there is a warning light to replace it - but the equipment doesn't act wonky…

Next time you are in the bell snapping the hot water into your suit just let it wash down the sensor. Works every time.

Seriously, for the most part instruments I have used are within a 1/2% the great majority of the time. I have always been able to track discrepencies down by checking calibration against a mid-range cal gas, which is air for Nitrox and maybe pure O2. Industrial through medical grade compressed Oxygen is produced through cryogenic separation so it is reliably pure far beyond what any hand-held sensor can measure. However, I have never had the occasion to check O2 above sea level or at very low humidity.

 

[Jax]

View attachment 202507

Pretty sure you already use this to begin your calibration... but just in case.

Add this chart to an altitude where the Shearwater reads the PPO2 to be .18, and you have quite the fun, here.

 

[The Chairman]

The chart is used if you're calibrating to ambient air. It's not neccesary if you are using comprewssed air or calibrating in a closed loop (where humidity will be more or less constant). Even then, for most of us, you're only looking at a half percent variance.

 

[geoff w]

Actually, my point is not the analysis, it is, "At what point do you question your analyzer?"

I bought a new oxygen analyzer last year, and the readings were always kind of squirrely. I asked about it here on ScubaBoard, used it some more on vacation, then talked to the manufacturer last year at DEMA. I sent it in and they said the O2 analyzer was bad and replaced it. These things are electrochemical magic devices, so you might want to compare it against another known good one, or have the manufacturer check it out before you drive yourself crazy

 

[Jax]

I bought a new oxygen analyzer last year, and the readings were always kind of squirrely. I asked about it here on ScubaBoard, used it some more on vacation, then talked to the manufacturer last year at DEMA. I sent it in and they said the O2 analyzer was bad and replaced it. These things are electrochemical magic devices, so you might want to compare it against another known good one, or have the manufacturer check it out before you drive yourself crazy

Exactly!

Something told you, this isn't right.

Unfortunately, it seems a lot of people believe whatever said computer / measure device says. I thought I would hear more people give a 'brain check'.

 

[Akimbo]

Jax

Do you feel like you have a satisfactory answer to your question? I have lost track a little myself.

Aside from the actual numbers on your instrument, how is the repeatability?

 

[Jax]

Jax

Do you feel like you have a satisfactory answer to your question? I have lost track a little myself.

Aside from the actual numbers on your instrument, how is the repeatability?

My device is very repeatable.

It seems like most people don't consider the "what if" the device was out of whack . . . guess it was the old guard engineers that beat it into me to have an expected range against which you test, so you know when something is wrong.

In the meantime, I will trust mine within +/- 1% . . . until I replace the sensor again.

 

[Akimbo]

My device is very repeatable.

<snip>

In the meantime, I will trust mine within +/- 1% . . . until I replace the sensor again.

How do you know the analyzer is off by as much as 1%? That seems high. Nearly all the sensors I have used are Teledyne branded or OEM&#8217;d if that could be a factor. Are you saying it is up to 1% off between a cal gas and the sample but repeatable? Or is it between the instrument and your calculated mix?

 

[Jax]

How do you know the analyzer is off by as much as 1%? That seems high. Nearly all the sensors I have used are Teledyne branded or OEM&#8217;d if that could be a factor. Are you saying it is up to 1% off between a cal gas and the sample but repeatable? Or is it between the instrument and your calculated mix?

No . . . I did say that wrong. If my analyzer comes within 1%, or a swing of +/- .5 % . . . of what I expect.

With the current sensor, which has an error of +/-1%, and the equipment error of +/-.5%, my analyzer routinely reports +/- .5% of the value I expect, and that swing is well within my comfort zone.

Because, of course, the physiology is so precise thereafter . . . [/facetious]

 

[The Chairman]

Unfortunately, it seems a lot of people believe whatever said computer / measure device says. I thought I would hear more people give a 'brain check'.

That was precisely my point: you needed to give a brain check.

How many accidents per year are caused by equipment failure?
How many accidents per year are caused by brain farts? The second is like the earth and the first is like the moon. It's there, but the real problem is the grey matter not following protocol.