SAC decreasing with depth

[Foxfish]

I have the air-integrated verision. You are right, it does not transfer pressures. That's why it asks that question. The only way how to get pressure data in DM is that "simulation". I tried to re-calculate a profile from D9 and it didn't ask producing a nice realistic SAC profile with clearly non-linear pressure drop over time. Manual for D9 claims it transfers "real time tank pressure consumption (with optional wireless transmitter in use)".
I don't understand why they decided to implement this "simulation" feature since it has nothing to do with reality... Just misleading lies... The only realistic thing is the average SAC rate.

Don't know much about the air integrated systems. I've got a Suunto D4. In the DM software it always uses linearized pressures based on start and end pressures. Haven't worked out the reason for the "simulation" button so this thread is interesting. With the D4 nothing seems to change after pressing the button.

Does your computer give SAC while diving? If so, I would have thought the actual recorded tank pressures would be available somewhere in the DM.

 

[petmal]

But you can't obtain that information from a Vytec DS, or my Cobra.

I actually also have some Cobra (it may not be the very first version) profiles and they seem to include real pressure readings (producing believeable SAC profiles without "simulation") until 2009 when it stops. Manual says that "cylinder pressure at the beginning and at the end of the dive (i.e. pressure
drop ΔP during dive)" gets transferred. I have no idea what happened, it is probably yet another invention...

 

[petmal]

This is what it does with Cobra profiles. I take a dive from 2006. Nobody has ever messed with that dive. It shows only the pressure (blue) graph. Graph is obviously nonlinear. Profile shows pressure data. I hit "re-calculate" and it asks whether I want to "simulate" or not. I hit "No". It displays a realistically looking SAC profile. I hit "re-calculate" again answering "Yes" this time. It "linearizes" the pressure profile showing a screwed SAC plot (SAC decreasing with depth). I hit "re-calculate" again with the fond hope of recovering the original pressures and nothing happens, the original values are "gone with the wind"... You can probably fully believe Suunto DM only when it does not even ask about that "simulation", otherwise you have to be very careful.

 

[Foxfish]

That's okay. Happy to help and thanks for the chat! LOL

 

[diver_doug]

Hello.

What I found is that my SAC consistently decreases with increasing depth.

This is a common problem well-known in the Dive-Medicine industry as "Testinitrosis". The airway's in your testicles shrink with the increasing pressure experienced due to increasing depth, which results in a decreased SAC and, ultimately, complete "SAC collapse" if too great a depth is reached. This is where the term DCS or "Damn, Collapsed my Sac" comes from.

 

[Foxfish]

Always wondered why my voice sounded funny when I talk under water.