Suunto Vyper **SERIOUS BUG** in CNS O2 computation

[Genesis]

Take your Vyper, plug in a 32% mix, 1.4 PO2, then go into SIMDIVE and dive to 107' (the MOD) and SIT.

In 15 minutes or so the CNS alarm will go off.

That's wrong and effectively makes the CNS exposure tracking capability of the computer useless. The single exposure limit for 1.4 is 150 minutes according to the NOAA tables.

I have sent in an inquiry to Suunto on this, and will post their reply here.

Unless there is a fix for this, be aware of this (severe) limitation in the Vyper when used as a Nitrox computer.

BTW, the Vytec does NOT have the same problem; it computes CNS loading correctly.

 

[Ari]

But in any case, please keep us posted if and when you get the reply from Suunto.

A bug in a diving computer's algorithem is an important issue.

Ari

 

[Genesis]

Actually Rich over at SDN was whining about it, and I said that I KNEW the Vytec didn't have the problem, verified it, then grabbed my Vyper and reproduced it (thinking perhaps he had an older one or had made some mistake in how he set up his "test".)

Oops - it definitely IS real and definitely IS a problem in the Vyper - but not the Vytec.

I dove the Vyper for about 4 months before switching to the Vytec with AI, but still have the Vyper.

Further simulation shows what's going on. Suunto adds the "error margin" to their PO2 computations - thus resulting in a "safe" PO2 of 107' for 32%, .vs. the "real" 111' (the error margin for O2 measurement is 1%)

They are ALSO adding that 1% margin to their CNS clock computation, additively. Thus, the real MOD for "not exceeding 1.4" is actually right around 105', not 107! (Look at the SSI/NOAA/anyone else's tables and back off one box from 107; you find that 105 is the "setpoint" for the next lower O2 percentage.)

At 105', the tox graph does not limit out in 15 minutes; at 43 minutes exposure I have only three bars on the graph. This looks to be "on target" for the 150 minute single-exposure limit for a 1.4 PO2 according to NOAA.

 

[Charlie99]

Genesis once bubbled...
I now need to make a quite-dilligent investigation of EXACTLY what is going on with the CNS O2 clock in that unit before going any further with that course of action.

Suunto says that they use NOAA up to 1.4, but a highly accelerated clock above 1.4ppO2. Maybe they added in a bit of fudge factor for depth or mix measurement errors, in addition to calculating MOD for the next even integer up (that's why MOD=107' for 32.x%).

What happens if you back off just a couple of feet to 105 or 106'.

 

[Genesis]

they're adding the error margin for measurement TWICE (they've already added it in when they did the MOD computation; doing it again is a bug.)

Its not terribly likely to hose you, but it is nonetheless a programming error. The 1% margin of safety is reasonable (considering that this is the often-accepted tolerance for O2 percentage measurement) but to add it TWICE, with the second one only in the tox computation, is an error.

The bad news is that the PO2 alarm for the 1.4 setpoint DOES NOT GO OFF until you decend below 107', which means you could easily rack up their "accelerated clock" time without any way to know that it has happened.

This is still serious, in that as little as a couple of minutes of time below that depth, which can happen without any warning from the computer, can lead to grossly-erroneous CNS computations from that point forward for the dive series - making the CNS warnings useless.

 

[Charlie99]

If you have a mix of 32.x%, whether its 32.1% or 32.9%, Sunnto says to enter 32%. They then round up to 33% for O2 calculations, down to 32% for N2 calculations. This is NOT an error nor is it a fudge factor. It is just their way of handling the rounding off of EAN% to integer numbers.

Cranking the CNS clock up to warp speed at 105' rather than 107' isn't all that unreasonable and I doubt that in real life you would ever notice it. It just adds a bit of conservatism. What you have brought to light is that when Suunto says they have more conservative limits above 1.4ppO2, that they mean 1/10 of NOAA. Extremely conservative.


OTOH, if you want to run yet another experiment, try running a whole series of 1.38ppO2 dives with 30 to 60 minute SIs. You will see that Suunto will let you violate the 24hr NOAA limits, since they use a 60 minute halftime surface decay of CNS%. All other computers I've looked at use a more conservative decay halftime of 90 mintues. So in this area, very much out of character with the rest of Suunto algorithms, they are LESS conservative than most.

 

[Genesis]

Cranking the CNS clock up to warp speed at 105' rather than 107' isn't all that unreasonable and I doubt that in real life you would ever notice it. It just adds a bit of conservatism. What you have brought to light is that when Suunto says they have more conservative limits above 1.4ppO2, that they mean 1/10 of NOAA. Extremely conservative.

Yes it is all that unreasonable.

Cranking it up to warp speed is unreasonable when you violate 1.4, since there is a published value for 1.5 and 1.6!

Doing so if you violate 1.6 is not unreasonable, but doing so when you violate 1.3, when you set 1.4, IS both unreasonable and seriously flawed.

The point is not that they crank up the clock, its that they do so without warning. If you violate the 1.4 PPO2 the computer gripes at you. Cranking up the timer would be defensible in that circumstance (still wrong, since there is a published number for 1.5 and 1.6) but at least defensible.

Cranking it up when you've received no warning that it is about to happen, or is happening, is unreasonable - and broken.

 

[yogi]

Genesis is never wrong

At least he will never admit it

your friend

Yogi

 

[Genesis]

with a two-line response.

Why not address the issue?

A flaw that causes a computer to, without warning, tox you out when there is really nothing wrong with your dive profile, thereby making the O2 computation that it does worthless from that point forward is potentially dangerous.

Its dangerous because you will stop using that computation since its obviously wrong, which could conceivably lead to you taking a REAL tox hit.

 

[jamiei]

.