RFC: PSCR dive plots: Part 2.

[Anton Lundin]

On 13 March, 2018 - Willem Ferguson wrote:

> On 13/03/2018 12:28, Robert Helling wrote:
> >On 12. Mar 2018, at 15:58, Willem Ferguson
> ><willemferguson at zoology.up.ac.za
> ><mailto:willemferguson at zoology.up.ac.za>> wrote:
> >>
> >>b) Adapting the gas partial pressure graphs to reflect what the
> >>diver breathes during bailout. When rendering the dive by
> >>creating a plot_info structure for each sample, the easiest
> >>mechanism of incorporating bailout would be to use the
> >>Shearwater approach: have a byte indicating Loop or Bailout and
> >>perform the appropriate calculation for gas partial pressures.
> >>Alternatively, it may be possible to reference the linked list
> >>of existing events, find the next bailout event and plot the pO2
> >>depending on the type of bailout event (i.e. Bailout or
> >>OC->Loop). But this would incur significantly more computational
> >>overhead since this lookup will be needed for each plot_info on
> >>the dive profile.
> >
> >how is a bailout different than a gas change event (except
> >semantics of “emergency”). Why don’t you insert a gaschange to OC
> >(i.e. with set point 0)?
> >
> >Best
> >Robert
> >
> A bailout can be an event where one changes from the loop to open
> circuit, but using the same cylinder.
> 
> For instance a CCR diver can use the bailout valve to switch from
> recycling gas to using the same diluent cylinder but using it in an
> OC way.
> 
> For PSCR, a diver can do the last part of the dive using EAN50, but
> recycling the EAN50. However, the last 10-15 m is usually done on OC
> (no emergency implied, just because the pO2 drop across the injector
> valve becomes very large at shallow depths). So, this PSCR diver
> switched to OC without switching cylinders.

Eh. There's no drop across a injector. The drop in po2 is due to the
diver metabolising the o2, and a fraction is evicted and replaced.

> So, in the case of rebreathers, bailout does not automatically mean
> a change of gas or cylinders.
> 
> Hopes this makes sense?

>From subsurface point of view, it really doesn't matter if we represent
a bailout as a gasswitch event or not. The problem with the gasswitch
and setpoint change, is that it doesn't work for dives with po2 sensors
or the SCR steady state approximation.


A setpoint change to 0 is sort of a clever hack which just works for
planed/setpoint-only CCR dives, and not for CCR dives with po2-sensors,
or SCR dives.


I'd suggest we clean that up into some bailout sematics which works for
both SCR and CCR code, with or without o2 sensors.


If we implement that as a divemode switching event, a gaschange event
with some special flags, i don't really have a opinion until i see a
real suggestion. Nothing says we can't have a gaschange event which
switches to the same gas as we're currently using...


//Anton


-- 
Anton Lundin	+46702-161604