NITROX computer questions

[GrumpyOldGuy]

If you are going to trust your life with any dive computer, you need to read the manual!

All dive computers have some quirks and what you don't know can hurt you.

I personally like the oceanic / pelagic computers but they have a few quirks.

1) The default to 50% rule needs to be turned off.

2) If you turn on the computer, set the mix the night before the dive and let it shut down a few hours later (without diving), it will reset the mix percent. Check the mix before you dive! (Learned this the hard way)

3) The altitude sensor drives the Fresh Water / Salt Water logic, so diving fresh water at or near sea level is calculated as SW (minor), but at 2000ft+ is calculated as FW and the altitude adjustments are made automatically. IT DOES NOT INDICATE THIS ON THE SCREEN.

4) The batter meter says full for 40 dives or so, until nearly expended. Once it drops below full, you probably have less than 1/4 of a full charge, 10-12 dives or so till drained. Change it before the next dive day.

 

[theduckguru]

As Marek noted, you don't get "a very long NDL." You get an air NDL, and are 'held' to the depth which corresponds to whatever the max PO2 you set assuming EAN50, and you rack up CNS (and OTU if your computer counts that).

As to where they get it (i.e. 50%, as opposed to 40% or 80% or 100%), I have no idea. It's arbitrary. They probably took the richest "basic nitrox" blend and added 10% more.

I agree with you. The computer is going to keep you <60 ft using the MOD for 50% O2and you are not going to have a longer NDL based on the 79% for nitrogen vs a lower nitrogen fraction.

 

[Marek K]

As to where they get it (i.e. 50%, as opposed to 40% or 80% or 100%), I have no idea. It's arbitrary. They probably took the richest "basic nitrox" blend and added 10% more.

50% happens to be the highest FO2 value you can set on these Pelagic hockey pucks.

 

[charlesml3]

The newer Oceanic computers still have this stupid option but the default values is now "Off." You should turn it off and leave it off.

Analyze your tanks, know what's in them and set your computer accordingly. You want ACCURATE information from your computer so provide it accurate data. Like one of the DM's on the T&C Aggressor said "Be good to your computer and it'll be good to you."

On a liveaboard or somewhere like Cocoview or Bonaire where 32% is the norm I just set my computer to 32% and leave it all week. As far as I'm concerned, anything between 31 and 33 is 32.... I really don't want my computer trying to 2nd guess me and shooting the value to 50 after each dive. That's just one more thing I have to remember to change.

-Charles

 

[Pinto]

Wisdom 2

 

[Pinto]

What's worse is I didn't know it had defaulted to 50% during SIT, jumped in and on my way to 100' it alarmed PO2 and went into guage mode.

 

[Pinto]

Agreed. For 24hrs the DC went into guage mode thinking I was diving 50% O2. I had to revert to the back to tables to contine my dives.

 

[Pinto]

Thanks. It is a Wisdom 2. I figured it might be a safety precaution to make sure you reset to your new tank mixture.

 

[Pinto]

I have shut it off but was still curious. Mine is a Wisdom 2 but my buddy just bought a new Oceanic and asked me the same question. I read his manual hoping Oceanic had a better explaination then Sherwood did.....not. Scuba board replies much more comprehensive then the manuals. Thanks

 

[HJeffreyM]

Just wanted to point out that although most computers must stay in nitrox mode for at least 24 hours after the first nitrox dive, you can still dive air on a subsequent dive by setting the P02 to 21.

This happened to me recently after doing a late afternoon shallow (<60fsw) nitrox dive and then doing a >100fsw dive on air the next morning.

I have an Aeris Elite T3 and have the automatic "you're screwed if you don't reset the PO2 after each dive function" turned off!