Suunto Vyper CNS tracking.

[Kim]

Because of some information that was raised in another thread I have just been Googling information about this topic. To my surprise I have found out that there may be a flaw in the Vypers CNS tracking causing it to give a warning far too early. Does anyone have any information about this?

 

[Charlie99]

IIRC, there's an old thread on SB about Vypers and/or Cobras spinning up the CNS clock super fast just a tad bit too early. It looked to me like it was going to 10x speed at 1.4bar rather than 1.4atm, so you had to be within a foot or two of the 1.4ata MOD to be in the strange condition where you didn't have a high ppO2 alarm, but the CNS clock was screaming along at warp speed. The manual said something about being accelerated above 1.4ata, but the original poster was shocked that Suunto chose to allow only 1/10 the NOAA allowed time between 1.4 and 1.6ata ppO2.

People also get confused a bit by the Suunto practice of the diver truncating the measured %O2 before entering it,then the computer using the next % higher for MOD/CNS calcs. Example: For any O2 analyzer reading from 32.0 to 32.9% you enter 32. Computer uses 33 for O2 calculations, 32 for N2 calculations. Makes good sense to me.

 

[Kim]

Thanks Charlie. I saw that old thread but as it involved a former member who's posts are no longer there it was a bit difficult to follow. Recently I did a lot of Nitrox dives close to MOD and I noticed that the CNS warning did kick in VERY early. I couldn't understand why as the OTU was still minimal. It's a little strange as there don't seem to be any warning indicators on the graphs from the profiles although the first bar on the meter was blinking.

 

[Charlie99]

Recently I did a lot of Nitrox dives close to MOD and I noticed that the CNS warning did kick in VERY early. I couldn't understand why as the OTU was still minimal.

OTU or whole body toxicity calculations are quite different than CNS calculations. If you are close to MOD it's normal to hit the CNS limits while staying far away from the UPTD/OTU/whole body/pulmonary limits.

Suunto doesn't give any info on their OTU calculations, but if they use 300 as their repetitive dive limit, then above ppO2 of 1.0bar CNS will dominate; OTU's will dominate below 1.0bar ppO2, especially with multiple dive and multi-day exposure.

One strange thing about Suunto O2 calculations is that they use a 75 minute decay on the CNS dose, rather than the more normal, and more conservative, 90 minute decay. I didn't see anything on the OTU decay time that Suunto uses, but the whole pulmonary issue is a much, much slower sort of thing with time constants associated with the rate the body can heal lung irritation/damage.