Caution to everyone using hoseless computers!

[Charlie99]

Charlie99,
Are you refering to the new Smart computers or the older ones? Couldn't find my SP book to check myself.

This "workload adaptation" was implemented in the mid '90s and predates the Smart computers.
http://www.uwatec.com/english/homebot.htm

 

[jviehe]

In my opinion there should be some type of annual inspection where the unit is calibrated and verified accurate.

Doesnt the manual say to have an annual inspection by sending to uwatec? I was looking at an Aeris Elite, and it does say to get annual inspections. In fact, it says any time you notice anything odd, take it in.

 

[Jai Bar]

Uh, yeah - I have a big problem believing this. Air consumption has nothing to do with nitrogen loading or off-gassing... so no computer is going to let you say longer just because you're not using as much air.

Well, as Charlie99 wrote, there is a grain of truth in the original message. Uwatec make *shorter* NDL times if there is a high air consumption or if cold since cold and effort are regarded as DCS risk factors. Whether it is "smart" to do this or not- I am not so sure.

Anyway, *there* is something to do between air consumption (or better say, "breathing") and nitrogen loading and off-gassing.. The air you breathe during your dive contains all the Nitrogen that you are going to absorb, isn't it? Then, while ascending, your breathing is the main mechanism to get rid of the excess of nitrogen from your lungs to the sea And by all means, you can affect nitrogen off-gassing with inappropiate lung ventilation (along with CO2 accumulation and other problems ).

 

[Rick Murchison]

Well, as Charlie99 wrote, there is a grain of truth in the original message. Uwatec make *shorter* NDL times if there is a high air consumption or if cold since cold and effort are regarded as DCS risk factors. Whether it is "smart" to do this or not- I am not so sure.

Well, now, that would make one wonder how this marvel of modern electronics handles, oh, a regular set of LP 104's, doesn't it?
Seems a bit less than rocket science to marry a computer to an AL 80 and have it give out bogus information whenever used on a larger (or smaller) tank. But then maybe it "knows" what it's attached to?
Hmmmm....
Rick

 

[jviehe]

Well, now, that would make one wonder how this marvel of modern electronics handles, oh, a regular set of LP 104's, doesn't it?
Seems a bit less than rocket science to marry a computer to an AL 80 and have it give out bogus information whenever used on a larger (or smaller) tank. But then maybe it "knows" what it's attached to?
Hmmmm....
Rick

No, it calculates your SAC on the fly. It has nothing to do with the amount of air in the tank, but how often you are breathing.

 

[Teufel-Hundin]

Computers calculate the ammount of breathing you are doing by the change in pressure in your tank. This is why it does not matter what tank you have attatched.Most only use this as a means of converting units from PSI to minutes allowing for estimated air time remaining. But if the computer were to change its algorithm based on your air consumption you could go into DCS. The reason being that if it used time as well as gas usage and you breathed in twice as many breaths thats twice as much nitrogen.If the computer was off it would have your saturation levels off badly.That is why computers use a base algorithm and do not stray to the lenient side but rather to the conservative side.Meaning more percieved gas usage=less no-deco time but less still=base algorithm for "normal" saturation at that depth/temp.A perfect example of more nitrogen= less no-deco time is the difference between Air and Nitrox.In summation if she got Bent it was from something other than a faulty HP guage, that is why the computer will work without one.
I hope this helps.

People sleep peaceable in their beds at night because rough men stand ready to do violence on their behalf. God Bless and Protect our Warriors.
--Orwell--

 

[5615mike]

..................I love the hose-less computer systems but I wonder if an old style pressure gage would be a better idea.

Which is exactly why anyone using an AI hose less computer should ALWAYS have an SPG as a backup. IMO, if you do this then one defeats the reason most, not all but most of the reason that people want to go this route. It gets rid of a hose. But does not if you do it correctly.

Don't want to flame you here suckair but why in the world would you trust that electronic piece of equipment with your life? They are all subject to error and you must treat them that way. Take this to an extreme. This is exactly why most technical divers don't even use computers. They use tables on the fly. If they use a computer they always double-check them against tables. Now, if your going to do that, then why even use it.....at least in computer mode, not in gauge mode.

Just my .02 worth

 

[Teufel-Hundin]

Simple rule "Normal Diving" have a backup. "Technical Diving" backup the backup. The more critical the information is needed the more margin for error and failure I build in.Redundancy was drilled into us early on in training.

 

[Charlie99]

But if the computer were to change its algorithm based on your air consumption you could go into DCS. The reason being that if it used time as well as gas usage and you breathed in twice as many breaths thats twice as much nitrogen.If the computer was off it would have your saturation levels off badly.

Twice as many breaths is does NOT mean twice as much nitrogen absorbed into your tissues.

There have been previous threads about whether an air hog is more at risk for DCS than a low air consumption diver on the same dive profile. The answer is that N2 loading is NOT directly related to air consumption.

There is a small, indirect effect. Higher workload / activity level increases blood flow. This increased blood flow reduces the halftime of some tissues, thereby increasing N2 loading. The faster breathing / increased air consumption is a possible indicator of a higher workload / activity level / blood circulation. The faster breathing is not the cause of increased N2 absorption.

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Rick Murchison:

While I don't know the details of the Uwatec adaptive algorithm, it is clear that one could sense high workload by the breathing RATE (i.e. breaths per minute) and therefore whether the tank is an single AL80 or a LP104 doubles isn't important. In the link above, Uwatec mentions breathing pattern as what they use to adjust the deco model.

Charlie Allen

 

[Teufel-Hundin]

People do not usually just start hyperventilating for fun. I was going under the assumption that the rapid breathing or above normal air usage was due to an outside factor.Like ......Higher workload / activity level increases blood flow. This increased blood flow reduces the halftime of some tissues, thereby increasing N2 loading. The faster breathing / increased air consumption is a possible indicator of a higher workload / activity level / blood circulation. And stress and release of adrenaline can add to this as well. These computers that use your air consumption rate as part of their algorithm go under the belief that more breathing=more work or load.
If you had a computer that would become more lenient with your tables for less air "usage" and it was not reading properly..AND...you were breathing heavily NOT just to test the ability of your reg to deliver more air for no reason for extended periods of time. You could go into DCS...THIS is why I said that they use a base algorithm and then only modify to the conservative side during periods of greater air consumption.