Question on NDL vs Graph

[DVD77]

Greetings!

I did my first 2 dives on a new Perdix AI. However, I was confused over what appeared to me to be conflicting info.

Both dives were shallow, ~50 ft, first on 35% Nitrox, the second on 32% Nitrox. Both gasses were programmed and selected. Only one enabled at a time.

I was surprised to see the Nitrogen loading graph nearly pegged, while the NDL time was still showing about 80 minutes. When there is conflicting info like that, which do I believe? I tend to think the NDL time was correct in this case, but it bothers my to have the conflict.

Any suggestions? Perhaps I'm missing something? I've scoured the manuals both before and after the dives.

Thanks in advance.

 

[tbone1004]

were you ascending when the loading graph was nearly pegged? was it all lines or only the first one or two?

 

[Shearwater]

And Greetings to you.

It's very hard to answer a question like this without analysis of the specific dive and tissue loading.

We have some videos on YouTube that might help explain how to interpret the tissue graph. The videos are at Shearwater Research Inc. There is one on the tissue graph here:

 

[DVD77]

were you ascending when the loading graph was nearly pegged? was it all lines or only the first one or two?

Hi tbone1004-

I was still at depth. Pretty even dive profile.

The graph I was referring to is the bar graph, middle right side. The green and orange was filled and it was edging into the red.

 

[DVD77]

And Greetings to you.

It's very hard to answer a question like this without analysis of the specific dive and tissue loading.

We have some videos on YouTube that might help explain how to interpret the tissue graph. The videos are at Shearwater Research Inc. There is one on the tissue graph here:

Thanks for the reply!

The tissues graph showed all was well; the graph I am referring to is the one on the far right of the main screen (OC Rec mode) as shown below:

 

[DVD77]

And Greetings to you.

It's very hard to answer a question like this without analysis of the specific dive and tissue loading.

Grr, the screen shot I posted didn't make it. Suffice to say it's the graph shown on the cover of "PerdixAI_Operating_Instructions_RevA.pdf".

 

[tursiops]

How long were your dives?

 

[DVD77]

How long were your dives?

58 minutes, max depth 49 ft, ave depth 40 ft
43 minute surface interval
54 minutes, max depth 55 ft, ave depth 47.7 ft

 

[razor635]

If you were diving Nitrox on a profile that shallow with the gradient factors set to medium then it is working fine. With the NDL timer at 80 min I would guess you were diving EAN32. I dove a similar profile last weekend and the timer didn't leave 99 on EAN36. My third dive that day the timer was at 60 min at the tail end of the dive. You really notice the NDL timer on deeper dives, especially the repetitive ones or while diving air.

Keep in mind the NDL time changes with depth in real time. The bar graph represents total tissue loading and changes as you on or off gas. So you can still get an increase in NDL time while the loading graph goes up as you go shallower, because on gassing is slower.

 

[DVD77]

If you were diving Nitrox on a profile that shallow with the gradient factors set to medium then it is working fine. With the NDL timer at 80 min I would guess you were diving EAN32. I dove a similar profile last weekend and the timer didn't leave 99 on EAN36. My third dive that day the timer was at 60 min at the tail end of the dive. You really notice the NDL timer on deeper dives, especially the repetitive ones or while diving air.

Keep in mind the NDL time changes with depth in real time. The bar graph represents total tissue loading and changes as you on or off gas. So you can still get an increase in NDL time while the loading graph goes up as you go shallower, because on gassing is slower.

Well said, Razor635! My confusion resulted from the N2 loading graph edging up to red, even though diving Nitrox at shallow depths and the NDL time was still exceedingly high. Wish I had a camera to take a picture of it.

I'll have to dive it again and watch it closely; hopefully it was a fluke.