On 7 Nov 2014, at 10:36, Robert Helling <[email protected]> wrote:
> Now, in the CCR case, things are a bit more complicated as there is not _the_
> current cylinder, there are two, diluent and oxygen. For the purpose of deco
> calculation (and anything that is related to what gas is the diver currently
> breathing), I would still argue that the “current” cylinder should be the
> diluent as we have to know the diluent for fill_pressures to determine the
> breathing gas.
I would say that the notion of the “Current Cylinder” being the diluent works
well. It’s the only gas that might ever change during a CCR dive. That is, you
may change diluent, but you’ll never change from O2 to something else.
Also if you look at the three types of SCUBA equipment that exist from a
philosophical point of view:
OC Equipment allows you to take a gas, breath it once, and vent it.
SCR Equipment allows you to take a gas, breath it ’n’ times, and vent it.
CCR Equipment allows you to take a gas, breath it a infinite number of times,
with no venting (in theory)
It’s fairly obvious (to me) that the common element is the breathing gas /
drive gas / diluent gas, but for some reason we call it different things. The
difference on SCR / CCR is the mechanisms employed to extend that gas. It just
so happens that a CCR has an O2 supply to make it work, almost the same way
that it could have a battery.* It’s a resource you track, and make sure it
doesn’t run out, but apart from that it’s of little interest. (I’d actually be
tempted not to have it as part of the normal gas list for this reason. Instead
have it in it’s own special area.)
I think you’ll find more commonality in the code for different dives types if
you go this way.
Paul
* Of course, what makes CCR more complex is that we take advantage of the O2
supply to mix an ideal inspired gas, so that’s no longer constant. If it wasn’t
for that, gas consumption rate would be the only difference between the 3.
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