On 27.10.2014, at 12:10, Rodrigo Severo <[email protected]> wrote:
Rodrigo,
> AFAICT the consensus about diluent consumption is that it should be
> calculated as if spend only during descends.
>
> In other words, use the same method to calculate for OC, but consider
> that during ascends and when maintaining depth the consumption is
> zero. Distribute all consumption on descends taking in consideration
> depths.
what I meant was: I did not yet have time to code it. You are more than welcome
to send a patch. Let me mention a few thoughts:
Not diving rebreathers myself, I can only guess how that would be computed. I
would think that when descending from depth d1 to d2 with associated ambient
pressures depth_tp_mbar(d1) and depth_to_mbar(d2) and the total loop volume
(the actual rebreather loop plus your lung volume) is V than we need a total
volume of
(depth_to_mbar(d2) / depth_to_mbar(d1) - 1) * V
of dillutant. This means that at least V is another parameter from the
preferences (actually per dive) that the user needs to supply. If we track O2
consumption as well, we need the metabolism rate for that as well (but we have
that for PSCR anyway). This needs UI and we should be a bit careful not having
too many options/parameters.
What I am more worried about is that “dillutant is consumed on descent” only
considers significant descents. So we should not just compare the current depth
with that of the previous sample as otherwise we would pick up all the noise
from the depth sensor. Just as an example: The depth resolution of my Vytec is
one foot (or 30cm). This means that even when I think I am at constant depth
the reading in the samples tends to oscillate by that amount due to sensor
noise. That mean that on average on every other sample (i.e. every 20s) I am
descending by 30cm. Over a one hour dive this sums up 54m of completely bogus
descent (which if taken into account would completely ruin any dillutant
consumption calculation as this is likely the order of magnitude of the total
descent. To avoid this amplification of noise we have to take into account only
“real” descends that are big enough in magnitude to make the CCR actually add
dillutant which it does not when you hover around one depth and only oscillate
slightly.
What do you think?
Best
Robert
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Robert C. Helling Elite Master Course Theoretical and Mathematical Physics
Scientific Coordinator
Ludwig Maximilians Universitaet Muenchen, Dept. Physik
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