Dive Computer Error

[supergaijin]

I don't think it is accurate to call decompression models a "best guess". The models we used are all corelated with data taken from real human trials, and they are based on substantial investigation into decompression theory. While none are perfect, they are far from a "best guess".

I understand what you're saying. I was referring to things like this:

Richard Pyle Scuba & Rebreather Diving Physics and Fizzyology
If you ask a random, non-diving person on the street to explain what's really going on inside a diver's body that leads to decompression sickness, the answer is likely to be "I don't know".

..............

If, however, you seek out the world's most learned scholars on the subject of decompression and decompression sickness, the top 5 or 6 most knowledgeable and experienced individuals on the subject, the ones who really know what they are talking about; the answer to the question of what causes decompression sickness will invariably be: "I don't know".

2012 July « Doppler's Tech Diving Blog
According to the divers I know and respect, decompression theory is more fiction than fact, less science than art.

There was a poster here who quipped "Never assume an unexploded goat is evidence of a good decompression profile".

 

[ajduplessis]

I don't think it is accurate to call decompression models a "best guess". The models we used are all corelated with data taken from real human trials, and they are based on substantial investigation into decompression theory. While none are perfect, they are far from a "best guess".

Theory is best guess btw. The word "speculative" is used widely to define the term theory. Is it a good guess? Yes, but still a guess.

If this was not the case please explain why divers well within NDL and in good health still take hits? Divers have different physical compositions and this make-up changes on a daily basis. The data collected and tests conducted to develop these algorithms are best guesses as there as so many know and unknown factors that influence these models. To apply all these considerations in a model for the general diving community is guess work.

There is no black and white! Accept, understand and plan for the potential risk. That is diving.

 

[PfcAJ]

And yet I know more than a few instructors who have had chamber rides even after diving within the 'artificially conservative' limits imposed by Suunto's RGBM algorithm. It is strange to call one model "artificial"; they all are artificial- just someone's best guess as to what is likely to happen.

I would be interested in that allow longer dive times than any modern computer- care to name one?

RGBM can be considered 'better' for most recreational divers who tend to do multiple dives following a reef slowly upwards from a max depth of around 25m.

If it's longer time at depth- eg. deep wrecks that are your main reason for diving, then go Buhlmann but this model isn't called 'Bend and Mend' for nothing.

I'm sure that I could come up with examples of people getting bent using any algorithm... That's not a good argument. Getting bent in rec diving has such a low rate of occurrence anyways, its almost hard to test.

I've had to call dives short because of overly conservative algorithms. But if that's your thing, then go for it.

 

[vladimir]

What is a far more likely failure mode is that the pressure transducer will stop functioning correctly.

The one failure I have had was, indeed, in the pressure transducer.

If that happens, and it is your only depth gauge, you can compare to the tables all you want. Since you are using the same incorrect depth that your computer is using, you will come up with the same incorrect result. I think, rather than comparing the computer results to the tables, it is important to compare the computer functions to other sources, like a second depth gauge, dive watch, or your buddy's computer.

Sometimes a common-sense reality check is all that is necessary. In my case, the fact that the computer read 4-feet deep on the surface was a clue.

If your computer malfunctions, there's only one (approved/trained) recourse - immediately ascend and end your dive. You don't need gauge redundancy for that.

Even in my easy tropical recreational diving I can think of dives where surfacing immediately, while possible, was not the safest course of action. Dives that were planned to end in the lee of an island, for example, rather than in a fast current. I'm sure you agree that a direct ascent to the surface is not always necessary.

If you're in to sitting on the boat while other people are diving, than buy a computer that's extremely conservative, sure. Go nuts.

If you're like me and you want to actually go diving and not be limited by a goofy algorithm that doesn't represent reality, then you need to look elsewhere.

My Suunto has allowed me to do ~30 dives in 8 days in Cocos, for example, where maximum depths on the first two dives of the day were usually ~100' to ~120'.

 

[DiveNav]

...... How does the SB braintrust feel about an SPG/depth gauge/timer and one computer in agreement? Still thumb the dive?

Can you really read those tiny numbers on the tables while diving?
I wish I had your eyes

Alberto (aka eDiver)

 

[drbill]

Having had a computer fail on a long deco dive, I believe in redundancy and always wear two computers. If I notice any significant discrepancy in their depth readings, I'd use extra caution. So far that has not happened. However, the temperature sensor on one has been wildly inaccurate telling me I've been diving in waters with temperatures of 80-82 F at depth! When I download my other computer, I gert a reality check of perhaps 68-72 F.

 

[DiveNav]

.... However, the temperature sensor on one has been wildly inaccurate telling me I've been diving in waters with temperatures of 80-82 F at depth! When I download my other computer, I gert a reality check of perhaps 68-72 F.

Hi Dr. Bill,
I suggest you get the computer showing wild temperatures inspected / fixed.

In most dive computers, the depth pressure is ALSO the temperature pressure ... AND the temperature reading is actually "used" by the compensation algorithm to calculate the pressure reading.

Alberto (aka eDiver)

 

[vladimir]

Hi Dr. Bill,
I suggest you get the computer showing wild temperatures inspected / fixed.

In most dive computers, the depth pressure is ALSO the temperature pressure ... AND the temperature reading is actually "used" by the compensation algorithm to calculate the pressure reading.

Alberto (aka eDiver)

Interesting, Alberto. Can you explain this more fully? I assumed the computer used temperature to adjust the depth calculation based on a direct measurement of the pressure.

What about a typical water column that starts at, say, 28° at the surface and cools to 20° at depth? Does it use ambient temperature or does it integrate the values from each depth to arrive at a water density?

 

[GrumpyOldGuy]

Hi Dr. Bill,
I suggest you get the computer showing wild temperatures inspected / fixed.

In most dive computers, the depth pressure is ALSO the temperature pressure ... AND the temperature reading is actually "used" by the compensation algorithm to calculate the pressure reading.

Alberto (aka eDiver)

Are you saying its actually the same transducer or rather that the sensor package contains 2 transducer circuits (pressure and temp) that might interact with each other in a failure mode?

 

[tursiops]

That would be the point behind the test. If you ask, they will probably show you the test results.

I'm pretty sure the 200 ft test has nothing to do with calibrating your depth gauge and everything to do with making sure there is no leak from opening the unit to change the battery,

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