Subsurface UI for CCR dives

[Paul Sargent]

Hi Willem,

On 14 Oct 2014, at 08:35, Willem Ferguson <willemferguson at zoology.up.ac.za> wrote:

> Oxygen analysis:
> I propose that we add another button to the profile tool bar, perhaps something like the attached icon "o2icon.jpg", indicating "Oxygen Analysis”.

Would there be any scope to make the button visible only when a CCR dive is being viewed? That way it’s not around to confuse / annoy anyone who doesn’t need it. I don’t know if that’s practical / desired, but I think we should be sure that CCR features don’t get in the way of OC divers.

> When this button is activated, the normal gas partial pressures are replaced with graphs for the setpoint as well as for the po2 as measured by each of the sensors.

In time, and log data dependant, it would be nice to be able to view sensor millivolt readings in the same way. I think that tends to be a better way to see the age of a cell compared to the others.

> Cylinder gas pressures:
> The Poseidon is possibly the only CCR system with gas integration on both cylinders but the demand for gas integration is growing (e.g. for the Shearwater Nerd which is basically a modified Petrel).

I think you’re right that the Poseidons are the only units logging cylinder pressures, but I don’t think that means others are going to. The NERD certainly doesn’t <http://www.shearwaterresearch.com/nerd-faq/#faq9>

> With CCR dives, cylinder 0 is assumed to be the oxygen cylinder and cylinder 1 is assumed to hold the diluent gas. If baleout takes place, it would be to cylinder 2.

I’d be careful about assumptions like that, especially if it has any knock on effect to other parts of the program (e.g. the planner). Multiple diluents are possible, and some people dive that way (High helium trimix diluent for depth, and then having a low or no helium diluent to help decompression). It seems to be falling out of fashion, but some do it. Both the Shearwater and OSTC I use support 5 CC gases and also 5 OC gasses, and you can switch diluents during a dive.

I not saying you need to cope with that sort of thing now, or even ever, but being a bit flexible over which cylinder is which may prove useful in the future.

> Two lines, indicating the pressures in the two cylinders need to be draw, as opposed to the single line that has been the case to date.

I’m not a Poseidon user, so I’m more interested in the case where no pressure data is logged, but start and end pressures are entered by the diver after the fact. In this case it probably not necessary to draw them at all, but if they are drawn then both need to be drawn together and the consumption rate shouldn’t be depth dependent (as it is on an OC dive). It’s probably too difficult to work out the rates of gas use of each throughout the dive (diluent most on decent, O2 most on ascent), so I’’d just use a linear rate of use.

Now I’m thinking about it, hand entered gases are probably a good example where Gas 0 = O2 / Gas 1 = Dil could break down.

I wrote some notes on a ticket about gas consumption on CCR dives several months ago (before I knew the Poseidon logged cylinder pressure). Maybe those are useful. <http://trac.subsurface-divelog.org/ticket/80>. Unfortunately the attachments I added seem to have been lost.

Paul