Aqualung dive computer and Nitrox diving

[Itay]

Hi,
I am a new user of the Aqualung I550 and despite reading the entire product manual there is something that is not fully clear to me - what is the best way to use this computer for nitrox?
I am reading that you can set upto 3 different gases where one of them will always be air. Say Gas 1 is air and then you set gas 2 to 32% O2 - according to the manual 10 minutes after I choose Gas 2 - if I don't start my dive it will automatically revert back to Gas1... so this to me sounds like a serious source of problems..
Should one set Gas1 to Nitrox and so that it will always be set to that mixture?
My second question - after a nitrox dive - will the computer maintain this mixture for the next dives (within 24 hrs)? I assume it should as this is how it will calculate the parameters for the next dive - unfortunately I did not find any info on this matter.
Thanks!
Itay

 

[jaseUK666]

You should set gas 1 to your backgas and use gases 2 and 3 for deco/travel gas. If you're only using one has, just use gas 1

 

[Marie13]

I know the AL computers are very similar to the Oceanics. On my Geo 2.0 (now a backup), it would NOT hold the Nitrox setting for 24 hours. I believe I may have had to even reset it back to Nitrox between dives, but my memory could very well be incorrect.

 

[Itay]

Thanks for the reply Jase!
Let me just make sure I understand correctly - if I now go out for a 5 days safari in which I will be using nitrox, I should set Gas 1 to the desired mixture (I guess Gas 2 will be converted to air), and then the computer will always use Gas 1 (unless I intentionally change it) and during the entire trip the computer will remain on the mixture I set for Gas 1 - even if I do 3 dives on day 1 and then I start day 2 and more than 10 hrs passed?
Itay

 

[Itay]

I know the AL computers are very similar to the Oceanics. On my Geo 2.0 (now a backup), it would NOT hold the Nitrox setting for 24 hours. I believe I may have had to even reset it back to Nitrox between dives, but my memory could very well be incorrect.

According to the I550 manual - it is written that if you set a specific mixture it will be reset if 10 hrs passed without diving. If that is the case - it is quite bad - I would expect that the computer will maintain its gas setting until your body is all cleared from nitrogen.

 

[Bob DBF]

The 10 minute limit on settings before the dive would concern me more than the 10 hours after the dive. It's easy to get hung up on starting the dive and have the computer reset, and if one didn't catch it there would be problems. After the dive, the computer only has to continue tracking your decompression on air, and assumes you will dive the same mixes if you get into the water, and after ten hours figures you won't dive or may have different mixes. Tracking decompression only needs your mixes when you are using them in the water, it assumes you are breathing air on the surface.

Although I use an AL computer now, Oceanic before, if I was doing tech dives with mixed gasses, I'd probably go with a tech computer that was designed as such, it might have more latitude in how it can be used.


Bob

 

[Itay]

Bob - the 10 minutes thing is referred to when you set a dive to use Gas 2 or 3 - it will revert back to Gas 1 if you have not started the dive within 10 minutes. If you set Gas 1 as your nitrox mixture then you have 10 hours without diving before it will be reset back to air...

 

[JackD342]

According to the I550 manual - it is written that if you set a specific mixture it will be reset if 10 hrs passed without diving. If that is the case - it is quite bad - I would expect that the computer will maintain its gas setting until your body is all cleared from nitrogen.

Where did you read that 10 hour reset? I do not find it in either i550 or i550c manual. I think it is at 24 hours after your last dive, when it will revert from EAN to Air.

 

[Itay]

My bad... it is indeed 24 hrs... I guess I mixed it with the 10 minutes switch to Gas 1... sorry...

 

[johndiver999]

I know the AL computers are very similar to the Oceanics. On my Geo 2.0 (now a backup), it would NOT hold the Nitrox setting for 24 hours. I believe I may have had to even reset it back to Nitrox between dives, but my memory could very well be incorrect.

I think it is like this for the Oceanic: There are two settings you can toggle between.

One setting automatically re-sets the gas mix to 50% on the second dive (for Oxygen exposure setting) and assumes you are on air for the deco calculation. My understanding is that this is an attempt to "be safe" to account for people who change gases between dives and forget to adjust the computer. The computer goes wacko at depth, in this case normally if you are below 70 feet.

The other setting is to have the computer NOT change the mix between repetitive dives. So if you punch in 32 % for the first dive then the computer assumes you will use 32% for the remainder of dives that day. I always try to set for this second option, because I typically use the same mix on repetitive dives.

I think if you don't mess with the F O2 at all for the first dive, it defaults to air and will remain there (assuming air) for all subsequent dives.

Maybe I got that right?