Cobra vs Vyper: Air Integration or Not

[reefduffer]

The Cobra does record your usage during the dive the problem is that SDM software does not show you that info. It only gives you starting pressure and ending pressure and an a linear graph between the 2 points. If you use a different software to extract the info from the computer you will see actual air usage during the dive. ...

Hmmm ... I don't actually know that's wrong, but it's quite a surprise to this Cobra user. I base my understanding on the following:

1) The Cobra user's manual Specification page (page 65) describes the Logbook/Profile memory as "records the maximum depth of each [sampling] interval". No mention of tank pressure.

2) The description of the PC interface (section 4.1.3, pages 45-46) lists the data transferred. This includes "depth profile of the dive" and "cylinder pressure at the beginning and at the end of the dive (i.e., pressure drop deltaP during dive)" among other data, but nothing about any other pressure profile data.

3) The on-screen access to the log available through the Cobra buttons and screen (no PC needed) includes delta-P, and then in screen 4, a continuous scrolling of the profile intervals. During this profile scrolling, only depth is displayed; tank pressure is not. This is based on the manual page 44, and also I just took out my Cobra and looked at my most recent dive. Only depth, no pressure or temperature. If it was in the history, there's certainly room on the screen to display it. Just sayin' ...

4) At papers:suunto_vyper [Markus Fritze (MMM)] the author (Pascal Pellmont if I've got that right) has posted his reverse-engineering of the protocol. The description makes clear that the profile records only depth, in one byte per sample. There are some special codes injected in the profile to record "events" like alarms of several kinds, but no tank pressure info appears except for start/end of dive.

5) DiveLog the s/w I use, only gives me start and end pressures. I expect Mark wouldn't hide pressure profile data if it was available.

All that said, Suunto doesn't publish the protocol. Maybe the author of Macdive has figured out some secret access method nobody else has. But I'm skeptical. Are you sure you're not talking about a Cobra II or some other model? Can the author of Macdive comment?

 

[ClayJar]

Interesting. So, would MacDive be showing "false data" (not fabricated data, but unsupported extrapolation)? Might it be calculating the SAC from the starting pressure, ending pressure, and average depth and then applying that SAC across the profile to show what your PSI-per-minute air consumption rate would be if you maintained a uniform SAC (RMV, whatever!) through the entire dive? (I can't tell without more information... or at least the rest of the window.)

 

[TSandM]

Just wanted to post and apologize for the misinformation I put in above -- I was mixed up about my Suunto models.

 

[fyrsout]

I just went with the Viper II and love it. By the way, as I understand from my research, the Viper is pretty much the non-air integrated counter part (with a few exceptions) to the Cobra. The big difference between the Viper and Viper II (with a few exceptions) is the electronic compass. I wasn't quite ready to trust my air guage entirely to a computer just yet. Plus I had a problem once fitting my first stage to the air tank at a resort and it was nice to be able to pop my computer out of the console and wrist mount it. By the way, the best advice on this whole thread is from ClayJar about air consumption / monitoring. Don't get all caught up in the technology and the hype. It's not rocket science. Just jump in the water, follow a few simple rules, and have fun...

 

[t0w]

Can the author of Macdive comment?

I can. It's not a cobra, if that's the data from it. The cobra records start and end pressure, nothing in between. Suunto Dive Manager just draws a line between the two points. With MacDive, I don't bother - there is no data there, a straight line is meaningless.

I would assume it's probably a Cobra2, which does record pressure per sample.

 

[Beatlejuice]

Boy, did I open a can of worms, or should I say snakes?! (Get it?...Cobras, Vypers ...ok, sorry. )

Clayjar, thanks for the lesson! Your last paragraph about using "air consumption point out things in my diving that could use some attention" is what I had in mind. In the end though, I think I have to agree with Fyrsout, "Don't get all caught up in the technology and the hype. It's not rocket science. Just jump in the water, follow a few simple rules, and have fun..."! I'm going to go with my gut and go with the Vyper and a mechanical SPG. Thanks everyone for your input!

Now, should we discuss the advantages/disadvantages of the Vyper and the Vyper 2 or save that for another thread?

 

[LowVizWiz]

I can. It's not a cobra, if that's the data from it. The cobra records start and end pressure, nothing in between. Suunto Dive Manager just draws a line between the two points. With MacDive, I don't bother - there is no data there, a straight line is meaningless.

I would assume it's probably a Cobra2, which does record pressure per sample.

t0w, I can assure you that the info comes from a Cobra and NOT a Cobra2. As a matter of fact every dive I have put into MacDive where there's pressure info available it shows the same type of graph. I only own a Vyper and a Cobra.

I'll even email you the exported dive logs from MacDive to you check them out if you'd like.

Check these:

 

[t0w]

t0w, I can assure you that the info comes from a Cobra and NOT a Cobra2. As a matter of fact every dive I have put into MacDive where there's pressure info available it shows the same type of graph. I only own a Vyper and a Cobra.

Did you import them from the dive computer itself, or from another format (suunto SDE, UDCF etc) ?

 

[LowVizWiz]

They came from the dive computer into MacDive

 

[LowVizWiz]

I would obviously defer to t0w after all he programed MacDive, it's just an oddity. I was only speaking from my personal experience and came to what I thought was a reasonable conclusion after observing the data from the 2 different programs.
One has it, the other one does not. Not only that but it seems consistent with the consumption numbers that both programs are giving me.

Where would the program get the info if it's not there to begin with?

Now it does seem odd that SDM would not show this info if it's there, but Sunnto has disabled features in computers just to change the price point at which they sell. For example the Gekko vs. Vyper. This is all speculation in my part I know... very odd!