Geezer gas.

[Finless]

Christmas is coming, so am I (to the point that is) and I am doing Trimix after Christmas.

I am hoping Santa will bring me an O2 analyser - should I be greedy and ask for an O2/He analyser?

Is it necessary to analyse He?

Fast replies would be much appreciated as I am waiting to throw my letter to Santa up the chimney.

[Ben Harris]

<font color='#8D38C9'>i know a couple of people who have he analysers, there expensive but good. Always worth analysing everything. Diveshops make mistakes. I dont own one but wouldnt get a mix off a shop who doesnt have one.

[Rob Evans]

He analysers are really bloody expensive &amp; I have to say I don't feel it's necessary to blow all that dosh.
As long you put a known quantity of all the relevant gases in an empty bottle- if the O2 analysis measures up to your calculations, the He will be correct also. &nbsp;It gets a bit trickier if you're doing subsequent tops but tables do exist to let you calculate what the projected He component will be after, say, an air,O2 and He top.
The thing with He is a few percent either way is not necessarily as much of a problem as it would be with O2 - you'll be slightly more or less narked depending on the error, but I wouldn't let an error of up to 5% make any difference to my deco obligations for example.
A fresh Heliar/Trimix fill can be calculated to within 1 percent even using a whip if you've got a decent enough guage on it.

I suppose if you thought your LDS was pulling a fast one with your fills it might be handy ..

[Rupert Bear]

I personally wouldn't remix a trimix fill more than once or possibly twice if I was fairly sure what it was. The errors are cumulative.
I use heliair rather than trimix for this reason as you can top off ad infinitum with nothing more than an O2 analyser.

[Rob Evans]

You're right, I should have mentioned that. Maximum 2 tops on a trimix fill. &nbsp;What % &nbsp;Heliar do you make your first mix though?

[Rupert Bear]

It doesn't matter. you can analyse any helium/air mix and do anything you want afterwards to it and still get an accurate mix with an O2 analyser. It is a fixed relationship rather than trimix where you are introducing a third variable.

[Finless]

Originally Posted by [b

Quote[/b] (Rob Evans @ Nov. 12 2003,14:03)]You're right, I should have mentioned that. Maximum 2 tops on a trimix fill.  What %  Heliar do you make your first mix though?

I don't - I haven't done the course yet!! &nbsp;

'choo doin scannin the forum - &nbsp;shouldn you be workin!!! &nbsp;

I think, on that basis, I will make do with the O2 anlyser.

Rgds
Bryan

[Rob Evans]

Originally Posted by [b

Quote[/b] ]It doesn't matter. you can analyse any helium/air mix and do anything you want afterwards to it and still get an accurate mix with an O2 analyser. It is a fixed relationship rather than trimix where you are introducing a third variable.

That much is obvious - just wondering what your typical startoff heliar mix is.  I'm thinking it'd have to be a pretty strong (&amp; hypoxic) mix to make it worth doing an air top the second time round and still get the benefit of a bit of He. Presumably for two deeper dives in a row you'd do a fresh mix for each one? Or put a squirt of He in the depleted original heliar &amp; top with air?

[Fiona]

Originally Posted by [b

Quote[/b] (Ben @ Nov. 12 2003,13:22)]I dont own one but wouldnt get a mix off a shop who doesnt have one.

<font color='#0000FF'>Any shop which sells you a nitrox mix should have an analyser for you to use to check the mix was as requested. &nbsp;If they haven't got one they shouldn't be selling it.

FB

[Ben Harris]

<font color='#8D38C9'>talking more about trimix, I know quite a few big shops that sell it without an analyzer. They just get you to sign something saying you buy without analisying. Helium analysers are fairly new arent they?