Why are my Vytec and Cobra so different?

[Ari]

As much as I am enjoying this discussion (and I really am), I do not think that either name calling or insults are really contributing.

Plaese try to tone down the personal notes.

Ari

 

[Genesis]

if you'd like.

I'll be happy to do a 107' "sit at depth" dive just for your edification if you are willing to pay for the fuel for my boat that I need to burn in order to do this.

To the extent that I can plan for such a dive in the future, I will. I pointed out that this weekend I may be able to simulate one with an OW dive that I will be doing if my g/f does her certification dives, but it won't be at 107' - it will be between a 1.4 and 1.5 PO2 that I will have to set on the computer (57' is according to the computer a 1.4 PO2 on 50/50), provided I can actually get to 57 - its not easy to do on that site, but it is possible. As a "tag along" on her cert dive I may or may not be able to accomplish this, depending on exactly where the instructor places here to do the skills.

Again, the point is that IF you have set a PO2 exposure of 1.5 or 1.6, OR if you run into the rounding error with a 1.4 PO2 setpoint, the Vyper and Cobra inappropriately accelerate the CNS loading.

THAT has been the point all along, I've proven it, you refuse to accept the proof, and you further have tried to redirect the issue even when shown that the Vytec does not have the same problem.

Ari, the personal attacks and name-calling by Jamie on both this and the previous thread (he has removed several of them there, however) are and should be addressed. It is not, however, in any way inappropriate for me point out that he has in fact intentionally misrepresented the behavior of the COBRA - he has.

 

[jamiei]

Glad to see you are enjoying yourself Ari. Sadly, I can't shy away from a good discussion/argument... especially when its with our friend Karl. I really just have developed a dislike for him and all his negativity towards those people and company's that do so much for our sport.

Karl, if you'll email me a big picture of you I'll leave you alone and let you convince all those that don't know any better that the vyper and cobra are death trap works of the devil. Deal? I won't even make you see my dive info after my "research" dive which I will still do. I think I may even try to borrow my lds' vytec for the dive and attach it to the cobra so the depths will be identical or at least as close as possible. I'm sure you would do the same if it were possible. Congratulations on your excellent arguments. You certainly have proven a lot to me good friend. I really hope you can rid yourself of the vyper and cobra and get another couple vytecs. Have you ever thought about publishing your own dive tables Karl? I'm sure they would be a big hit.

 

[jamiei]

LOL... funny guy you are.

I don't mind doing the dive at all, to 107' as you actually did indicate as the problem with the vyper... you later got off topic with the 1.5 po2 when you couldn't prove that. I've seen proof of neither. Thats what I want.

Save your fuel my friend. I never asked for a dime from you to do the dive myself and since I have a calm lake to do it in, we wont be bothered with those pesky surges contaminating the evidence. Feel free to do the dive if you would like, but I seriously doubt you ever will nor will you ever built the pot you claimed you would to do the dive in. You won't provide proof, but its ok... I will for you. would anyone care for me to dig up the quote about the original topic straight from Karl's mouth?

I think Ari already did address me Karl... I bet you want him to ban me because I cause I show you for what you are, right?

Karl, will you be diving 50/50? And will you conveniently go over the 57'... I bet so

Does a po2 of 1.5 or 1.6 not warrant an accelerated OLF calculation? I think so... your point being???

I've not misrepresented anything... the pics are on my site and will stay there... the link will remain below. I said the cobra would not "tox out" at 15 minutes and it never did. Thats a FACT.

I will attempt to make arrangements to complete this dive this upcoming week. I will make all dive info available for this and any other dives made that same day. The sample rate will be set at 10 sec.

There's no evidence of a problem with the po2 calcs above 1.4. You provide it and we will all have it. I'll also do such a dive and provide actual dive information. For this dive, however, I will not violate the mod of the po2 that I set. I will not dive the mix (dives over 1.4 are a major safety concern), but will set the mix in the cobra.

 

[jamiei]

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




FOLLOWED BY A SIMPLE EXPLANATION BY CHARLIE99 THAT KARL COULD NOT ACCEPT:

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'.

One adjustment is for round off..
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.

You didnt catch that did you Karl? The use a 60 min halftime instead of a 90 minute halftime... so you really aren't comparing apples to apples at all. Heck Charlie99's two posts blows your whole issue out of the water.

Your own post proved you wrong. My pictures prove it. The OLF alarm would never go off while its in the green. It is in the green in the pictures and you can see that a 32% nitrox setting was used. 107' at 15 minutes and its still in the green, no alarm. When I do the dive to 107', at 15 minutes there won't be an alarm either. The downloaded and exported dive profile will absolutely prove this. Do the dive to 106 and you're cool. There's probably no way you can do a 15 min dive and stay precisely at 107' without going over or under it. A foot isn't that big of a deal is it Karl? I'll try my best, but the dive will prove two things... You can't stay precisely at 107' so you should never plan a 15 min or greater dive at that depth because you will not maintain it and you will go over the 1.4 po2 setting and just as suunto says... you will experience a faster OLF increase rate... There's nothing new and nothing flawed... thats just how it is. The fact that even while the only reason for the dive is stay right at 107', it most likely can't be done without violating the MOD or ascending to 106' for at least part of the dive which will change the OLF rate. is reason enough to say that its rediculous to say there's a dangerous error with the computer. It's conservative... pure and simple. I'll get back in touch with the dive info and we'll dispell this batch of myths

 

[jamiei]

Ari, since you're watching this thread... do you feel that I misrepresented how my cobra reacts based on the pictures you see on my website? Sorry to further involve you Ari, but honestly, do you see any OLF alarms? Isn't the OLF bar graph in the green at 15 minutes as I said? Where are my lies? By the way, on the first series of pictures, the descent rate is as fast as the cobra will allow which seems to be well over 75ft/min. Apples to apples would use 50 feet/min

I'll be glad to personally verify the simulations with anyone in the atlanta area if it will make a difference. I have no reason to lie at all. In fact, by weeks end if at all possible, I will provide a video of the actual simulation from setup to surface. I'll buy a larger memory stick for my video camera today and gather the info. We all want the truth, right? The sim dive to 107 for 15 minutes, a dive to 106' up to the NDL. I'll even do Karl's sim for the 107 for 15 minutes using the rocket descent he used for his evidence. All descents will be timed to provide an accurate descent rate. Given his own data using the v planner software, we will shoot for a rate of 50 feet/min so the descent time should be just over 2 minutes. If time provides, I'll also do a sim dive of the 50/50 to 57' that Karl mentioned and provide it.

 

[Genesis]

There's no evidence of a problem with the po2 calcs above 1.4. You provide it and we will all have it. I'll also do such a dive and provide actual dive information. For this dive, however, I will not violate the mod of the po2 that I set. I will not dive the mix (dives over 1.4 are a major safety concern), but will set the mix in the cobra.

Yes, there is.

At least on the Vyper and Cobra. There is not, however, on the Vytec.

Set a PO2 limit of 1.6. Note that you get no alarm, but you DO get the gross acceleration of the CNS clock - the same issue that this entire thing is about. This only happens on the Cobra and Vyper; it does NOT on the Vytec.

The 107' thing is an artifact of a round-off error. That much is obvious from the behavior of the computer.

It does not, however, change the basic issue, which is that the computer grossly accelerates CNS exposures if you exceed a 1.4 PO2 (in its view, with the rounding error), it does so at a rate that results in roughly 10x the claimed exposure that NOAA and other accepted sources state, and it does so even if you specify that you want to dive a 1.5 or 1.6 PO2, ignoring your decision, as a diver, to dive at a higher PO2.

Again, that is and has been the point through this entire discussion, and all of the rest is nothing more than you attempting to obfuscate the matter with half-truths or worse - including your removal of the evidence of your misstatements in the previous thread.

 

[Ari]

I do not consider your statements as missrepresentations.

Do you think that we can all agree on a test procedure, which will satisfy the debate? I am sure we can figure something out.

Ari

 

[Genesis]

Set the Vyper or Cobra to a PO2 of 1.6, and set a Vytec to the same exposure.

Pick a mix (set it richer than the one you intend to dive if you're queasy about exceeding 1.4, and use a second computer for actual dive timing), and set both Cobra/Vyper and Vytec for that.

Do the dive for at least 22 minutes at a PO2 of between 1.4 and up to but not exceeding 1.6.

Note the OLF graph on the Cobra/Vyper is full-on in the red, and the alarm is continually sounding, even though you have not exceeded the MOD. Note that the OLF display on the Vytec is showing an appropriate amount of CNS clock consumed.

Now look at any other source for the CNS loading of the dive you just performed on the mix you set, and note that the actual CNS clock exposure is somewhere between 10-15%, and is very close (if not spot-on) to the OLF loading showing on the Vytec.

If you wish to validate the PRECISE 107' issue on 32% and a 1.4 PO2, then you need to be able to hold an EXACT 107' profile for 18-20 minutes. Not impossible if you can find a hard bottom somewhere, but more than a bit of a PITA (moving your arm, or having the computer on a console could invalidate the test by inadvertantly breaching the MOD.) Thus, if you really want to run THAT test, the best way is a pressure pot where you can "dive" the computer with absolute control of ambient pressure (and thus depth.)

However, the precise 107' issue is a symptom, not the actual issue. The issue is that the Vyper and Cobra perform the acceleration without warning if you set an exposure limit of over 1.4, and in fact, diving a 1.5 PO2 exposure on those computers is quite reasonable if you are compensating for Suuntio's conservatism (it almost exactly cancels out the 1% O2 "addition" they do in their software.)

 

[Charlie99]

jamiei once bubbled...
Heck Charlie99's two posts blows your whole issue out of the water.

Not at all. I merely clarified for Karl how Suunto rounds UP to the next integer value for O2% and that is why on a Suunto the EAN32 MOD is 107', not 111'. The 60 minutes halftime decay is just a tidbit of info that has nothing to do with what Karl claims. I mentioned it because it is an area where Suunto seems to be more liberal that other computers.

Karl claims that Suunto Vyper and Cobra have a couple of "quirks" in how they track O2 CNS loading. I think he has described them clearly, and while I don't know enough about the computers to be absolutely sure, it appears that he has shown good evidence that they perform as he describes.

Where Karl and I differ is in our opinions on how significant of an impact these "quirks" would have on a diver, and whether these "quirks" should be considered bugs. [old programmer's joke: the difference between a bug and feature is that one of them is documented].

Jamiei, I didn't really see any direct answers to my 2 questions. Perhaps a more precise question would help:
If you set the Cobra to EAN32, and set the ppO2 alarm to 1.6 (which should be 127' after rounding up to 33%), how long can you spend at 110' before the O2 clock hits 100%?

The answer doesn't have to be super-precise. I just want to know if it is something like 120 minutes or more like 20 minutes.