Indicated air pressure on AI computer

[reo]

Not knowing which gauges are which in this case makes this all speculation, but here goes: the AI computers that I am familiar with do not "ramp off" to zero, they ramp off to somewhere between 300 and 500 PSI, that is to say their "air time remaining" is really "air time remaining till X psi." It maybe that they will, in fact, read zero when you still have a few hundred PSI in the tank. If I were you I'd experiment, I'd breathe a tank down till the AI computer says zero and then I'd mechanically gauge it.

I love a good diving science experiment! I have a Hog pressure gauge and a Uemis transmitter on my reg set. I'll compare readings between the two during my dive tonight and report back. I'm not going to breathe my tank down to zero, but down to a few hundred PSI.

Ron

 

[Thalassamania]

Please, after you get to the surface, run it down to 100 PSI and check it every 100 along the way. This will be interesting.

 

[Jax]

Cannot speak of any but my Uwatec Aladin SmartTEC, but the AI pressure is routinely 50-60psi under my mechanical SPG, from 3000 on down to about 200. I believe that is simply adjustment error.

 

[Altamira]

I talked to an Aeris rep and he said that the computer shows the pressure that is in the tank, and there is no built in buffer to the pressure reading. Of course, I can set in an end dive time pressure which is subtracted from the dive time remaining computation, but the pressure I see on the computer screen is the actual pressure in the tank. On some occasions, I felt the pressure difference might be justified by virtue of the tank being recently filled, but I did not know how much pressure drop to expect after an hour, a couple of hours, or overnight after the tank was filled. After that discussion and reading your posts, I think my intial assumption of what I see on the gauge is what I have in the tank and dive appropriately should help keep me out of trouble. It also reinforces my inclination to rely on logic, my gut feelings, and avoid assumptions that one computer product works the same as another brand's product to avoid putting myself in a possible compromised position. Thanks again for all of the inputs.

 

[Saudi-Diver]

Hi just read the manual for the Aladin Air Z dive computer and in the trouble shooting guide it says " It compensates for temperature and the pressure reading is only valid at 20 C" http://www.simplyscuba.com/pdf/ScubaManuals/DiveComputers/Aladin%20Air%20Z%20Manual.pdf its on page 76. I wander if the OP AI computer has the same temperature compensation. looks like there is an algorithm between the readout and the sensor unlike in a analogue pressure gauge

 

[Altamira]

I would be very interested to hear the results of the "science experiment". As they say "knowledge is power", and I can use all the knowledge I can get.

 

[Jax]

Cannot speak of any but my Uwatec Aladin SmartTEC, but the AI pressure is routinely 50-60psi under my mechanical SPG, from 3000 on down to about 200. I believe that is simply adjustment error.

Or maybe not!

 

[Crush]

Does any one know if AI dive computers calculate tank pressure at a standard temperature. That would cause a big difference between an Analogue gauge and a AI read out in a hot environment?

The computer can sense the temperature of the water, but not the tank temperature. The tank and the water might be at different temperatures. The computer can't compensate for SP since it doesn't know T.

 

[Crush]

Or maybe not!

Unless I am missing something, Jax, that is the stupidest conversion I have ever read about!!! The computer will be converting from water temperature and adjusting to 20C, irrespective of what the tank air temperature is?! WHY??? Neither reflects the true temperature of the air when it hits your lungs...

 

[Jax]

Mmm, that's called "normalized" in the vernacular . . .