Two more rebreather patches

[Rodrigo Severo]

On Mon, Oct 27, 2014 at 1:43 PM, Paul Sargent <paul.lionseye at icloud.com> wrote:
>
>
> On Oct 27, 2014, at 03:42 PM, Rodrigo Severo <rodrigo at fabricadeideias.com>
> wrote:
>
> Bill,
>
> I agree: 1/2 foot is noise, 10 m is significant.
>
> What value do you think we should use as limit? I just proposed 1 m on
> my previous email to Robert but I'm not sure if this value is big
> enough.
>
> What do you think?
>
>
> It'd be interesting to put some code together, run it on real dive data and
> see how the predicted number compared with the measured one. Until you do I
> think it'd be difficult to know where the noise filter level needs to be
> set.
>
>> Would tracking only the size of the counter lungs be sufficient?
>
> I don't think any of this is necessary, neither counter lungs volume
> nor loop volume as I mentioned on my previous email.
>
>
> Without knowing has much gas is in the loop (note: not counter lung size,
> which is part of the maximum loop volume) you can't know how much diluent to
> add to maintain it*.
>
> Example: 5l of gas in the loop. Decend from surface to 10m (2bar). I need to
> double the mass of gas in the loop to maintain volume, hence I need to add
> 5l (surface equivalent mass**).
>
> Counter lung (maximum) volume is irrelevent, because divers try not to run
> maximum volume. In fact they try to run minimum volume (i.e. 1 human lung
> full) because doing so uses less gas and is easier to control (buoyancy).
> You probably need to work out an average of what this diver tends to do
> (like SAC) and use that in predictions.
>
> Paul
>
> * Similarly, You can't know how much O2 to add to raise the ppO2 by some
> amount without knowing how much gas is in the loop. Hence ascents are tricky
> too

I believe this kind of thing could be usefull for dive planning if we
decide to took the complex approach. But I'm afraid it could get
REALLY complex with not much added benefit.

As I mentioned before, for SAC calculation after the dive, the
simplier method I proposed seems to me easier and precise enough.

And if you have your diluent and oxygen SAC salculated using the
simplier methods I proposed, you could use these same figures for dive
planning. In this cenario, gas consumption on dive plans should be
calculated using the same simplier methods.


Rodrigo