ATMOS ai Temperature Reading

[lucidblue]

Used my ATMOS ai for the first time yesterday. After I downloaded my dives I realized that the temperature reading was pretty off at different depths. How long does it take the computer to register changes in temperature?

[ScubaToys Larry]

It takes about 3-5 mintues, depending on the temp to chill or warm the entire unit to get the new reading. I always use the - "If it's cold - come up" technique, no matter what the temp reads!

[Zenagirl]

Yeah, I don't pay much attention to the temperature readings either...for me it's more of a curiosity as to how warm the water was. Did I mention I only dive warm??

[lucidblue]

Yeah, I wasn't looking at the temp in the dive details for anything other than curiosity. It just know it was dramatically wrong.

I prefer warm water diving too, but I have to vacation for that. Cold water is a pain with thick wetsuits, hoods, etc., but it's better than not diving.

[cummings66]

I've noticed there are some computers that register the temperatures faster than others. My Oceanic is faster than a buddies Beuchat computer for example. I'm not sure who makes his though. In general it takes a few minutes at least at depth, heres what you do. Go down, look at temp, when it quits dropping and stays that way for 5 minutes you're done. Now come up.

[bullshark]

yeah I like Larry's methid its pretty reliable

[tc_rain]

Just a quick thought, is the temp tied in with the sampling rate?

[ScubaToys Larry]

No... temp does not affect the algorithm at all. Some computers used to set up that if the temp was cold, they would make the algorithm more conservative - but in all honesty.. that's kinda stupid. You could do a 40 degree dive in a toasty dry suit and be warmer than someone doing a 75 degree dive in a bathing suit... so what was the point?!

[bperrybap]

Originally Posted by ScubaToys Larry

No... temp does not affect the algorithm at all.

While it isn't used in any of the the algorithms,
a temperature change of the air inside the tank will affect
your air time remaining as the computer is "tricked" by
the pressure changes do to the change in air temperature.

If the tank is cooling it thinks you are breathing faster
than you really are, and if the tank is warming, it thinks
you are breathing slower than you really are.

The amount of pressure change is dependent on the
pressure in the tank not its volume.
If you do the do the math, the change is
about 5.5 degrees F at 3000 PSI and around 1 degree F
at 500 PSI.

Air time remaining results get interesting in
conditions like I dove out at CSSP last weekend
where the surface temperature was around 90 F and
below 40 feet was was down in 50s.

If you take a tank with 3000 PSI at 90 degrees F and
then cool it down to 70 degrees F. The pressure will
drop to around 2890 or a loss of 110 PSI.

The computer has no knowledge of the temperature of
the air in the tank and has to assume you breathed
that 110 PSI. This will make your air time remaining
temporarily look shorter than it should be.

BTW, I did notice on my Aeris AI,
(from looking at my temperature graphs from my CSSP
dives) that the temperature didn't move more than 1
degree per minute up or down. It was a very consistent
1 degree F per minute adjusting. After 20 minutes
it dropped down from 90 to 70.
It has always kind of bothered my how slow it it is at
sensing the temperature.
For example, I have a $5 digital meat thermometer
that can sense temperature in about 5 seconds.

I still like the computer though.

--- bill