Calibrating the HUD with less than 100% O2

[nickb]

When I was in Bikini recently, the O2 we used was generated onboard resulting in around 92-93%.

The Shearwater controller can handle this just fine but it didn't occur to me until it was too late that the HUD has no way of knowing that the calibration gas is not pure oxygen. This resulted in the HUD generally showing a PO2 0.1 greater than the controller.

Not much of an issue but worth bearing in mind when travelling to parts of the world where 100% is not readily available.

[zellnera]

It also do not know the atmospheric pressure. So if you 1000m high you will also get a 0.1 higher reading.

The only way I know to solve that is the following method
1) Calibrate SW computer
2) close mouthpiece
3) add o2 until you have a ~1.0 reading on the SW computer
4) calibrate HUD

[nickb]

Quote: (Originally Posted by zellnera)

It also do not know the atmospheric pressure. So if you 1000m high you will also get a 0.1 higher reading.

The only way I know to solve that is the following method
1) Calibrate SW computer
2) close mouthpiece
3) add o2 until you have a ~1.0 reading on the SW computer
4) calibrate HUD

Nice

[ccrdave]

Also in generated o2 (was it membrane separation?) isnt the remaining gas argon?

might be mistaken but I am sure I read that somewhere

[nickb]

Quote: (Originally Posted by ccrdave)

Also in generated o2 (was it membrane separation?) isnt the remaining gas argon?

might be mistaken but I am sure I read that somewhere

That's what we were discussing on the boat.

I'm sure it is argon and figured that's what made the loop seem a lot more narcotic than I normally experience with 16/50 dil. We did some fag-packet calculations but I'll have to try and repeat them. It makes quite a marked difference though.

[Peter L]

Quote: (Originally Posted by nickb)

That's what we were discussing on the boat.

I'm sure it is argon and figured that's what made the loop seem a lot more narcotic than I normally experience with 16/50 dil. We did some fag-packet calculations but I'll have to try and repeat them. It makes quite a marked difference though.

OOOOOhh........................................... .
Do tell more about this!!!

Ox gen's are cheap and they use a molecular mass separator aka heavier than N2 is retained the rest is discarded. No way to date would I have willingly gone diving on Arg-ox because in a loop if you think about it, if that 7% is Argon and your adding 1L of gas but removing the O2 that 7% residual is going to be creeping up to be a significant part of your inert gas loading by the end of a dive if not flushing the loop....

How'd it feel to be a guinea pig, milder than acid, more like mescalin, dope or other?

[nickb]

Quote: (Originally Posted by Peter L)

OOOOOhh........................................... .
Do tell more about this!!!

Ox gen's are cheap and they use a molecular mass separator aka heavier than N2 is retained the rest is discarded. No way to date would I have willingly gone diving on Arg-ox because in a loop if you think about it, if that 7% is Argon and your adding 1L of gas but removing the O2 that 7% residual is going to be creeping up to be a significant part of your inert gas loading by the end of a dive if not flushing the loop....

How'd it feel to be a guinea pig, milder than acid, more like mescalin, dope or other?

Well, the loop didn't contain 7% Ar, at least to start with. By my reckoning, the dil would have contained less than 1%, so let's be generous and say maybe 2% of the loop was argon on the bottom.

Granted, the argon would have concentrated over time - assuming 0.7l/min O2 consumption that would added .06l of argon to the loop per minute. So, after around 16 minutes on the bottom, 1 litre of Argon would have been added to the loop. I don't know what the loop volume of the JJ is so can't really take this much further.

The narcosis (and work of breathing) was noticeably more than I'm used to with that diluent at those depths.

Nobody seemed to be complaining though. There was one very mild skin rash part way through the week that was resolved by surface O2 and 24 hours out of the water but we'll never know why that happened.

[Peter L]

Quote: (Originally Posted by nickb)

Well, the loop didn't contain 7% Ar, at least to start with. By my reckoning, the dil would have contained less than 1%, so let's be generous and say maybe 2% of the loop was argon on the bottom.

Granted, the argon would have concentrated over time - assuming 0.7l/min O2 consumption that would added .06l of argon to the loop per minute. So, after around 16 minutes on the bottom, 1 litre of Argon would have been added to the loop. I don't know what the loop volume of the JJ is so can't really take this much further.

The narcosis (and work of breathing) was noticeably more than I'm used to with that diluent at those depths.

The loop is circa 3-5L depending on unit and your right it would be only after a long run time that it builds up, flushing the loop would have helped but it's of interest because a few places I have been to only have this type of O2 and I have always stayed away from it.

[nickb]

Quote: (Originally Posted by Peter L)

The loop is circa 3-5L depending on unit and your right it would be only after a long run time that it builds up, flushing the loop would have helped but it's of interest because a few places I have been to only have this type of O2 and I have always stayed away from it.

The loop has to be a lot more than 3-5 litres. Don't forget it includes one's lung volume too.

I'm sure ccrdave will be along in a minute with a ballpark figure, but I'd start north of 15l

[ccrdave]

Pretty good guess i reckon about 18l including diver

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