Calibration question

[joshk]

To put it bluntly I wouldn't dive with electronics that lost calibration / memory. If my Shearwater did that I'd send it in.

Short of rejecting that circumstance as a possibility, what would I do if I lost electronics in a cave? SCR sounds like a good option. I could also consider doing a diluent flush add a bit of O2. Maintaining loop volume by replacing the O2 consumed gives you a reasonable PPO2 at constant depth, even if it's indirectly monitored. Deco calculations go all out the window though.

I don't consider a “lights out” electronics event a possibility because I dive with two systems that are separate and independent. Mine happen to be analog but two digital DiveCan systems are separate and independent as well.

 

[tbone1004]

@joshk unsure of any independent divecan systems. Liberty has a pair of computers in there, but unaware of any DiveCAN system that does

 

[joshk]

@joshk unsure of any independent divecan systems. Liberty has a pair of computers in there, but unaware of any DiveCAN system that does

DiveCan has two boards, SOLO (SOLenoid and Oxygen Electronics) and OBOE (Oxygen BOard Electronics). These function as two independent systems. Only one controls the solenoid though. What is DiveCAN® and why should I care? - Shearwater Research

The names are terrible but I didn't make them up.

 

[tbone1004]

@joshk that's different than the actual oxygen board though. One board feeds info to both the solo and oboe. Those buses are separate, but are still fed from one board. Can't have that independent unless like the Liberty you have two cells on each board. Unsure if some of the mfg's do that, but don't know of any. Revo and Dive Rite would be the only two that would potentially make sense since they have more than 3 cells. I.e. on the dive rite, 1/2 are on board 1, 3/4 are on board 2 and cell 3 is sent to both buses

 

[joshk]

@joshk that's different than the a2d oxygen board though. One board feeds info to both the solo and oboe. Those buses are separate, but are still fed from one board. Can't have that independent unless like the Liberty you have two cells on each board. Unsure if some of the mfg's do that, but don't believe so

The board doing cell monitoring isn't what you're calibrating. So “losing” calibration data in that sense is impossible as a single point of failure. You could lose cell monitoring entirely, and an analog backup is nice to have if you're concerned about that case.

 

[tbone1004]

The board doing cell monitoring isn't what you're calibrating. So “losing” calibration data in that sense is impossible as a single point of failure. You could lose cell monitoring entirely, and an analog backup is nice to have if you're concerned about that case.

part of the problem with analog backup though is what Larry brought up a few pages ago with interference between the two. Anytime that analog signal is split there is huge amounts of room for problems. ISC made the isolator boards to handle that. If I bought a digital rebreather and was concerned about it, I'd buy a Liberty and be done with it, but realistically it's not an issue and not something I'm worried about. If I were buying a new CCR, I'd want one with a NERD controller and I would likely not put a secondary monitor on it. If the cells sh!t the bed, then go to SCR or bailout, but I'd argue the digital bus systems are much more reliable than the analog ones

 

[joshk]

digital bus systems are much more reliable than the analog ones

Agreed. I'd rather have two DiveCan boards but alas, that's not what was equipped with my unit.

 

[kensuf]

Meg 2.7 primary handset
Rev C+ hammerhead (I think)
You can get 0.0 on ppO2 (on one or more cells) and still get a mV output on that cell plus the other.

If for instance you have:
1.19, 0.0 , and 0.0 on ppO2
and yet have
49, 52, and 51 mV on three cells

Are you going to bail, SCR, or feel fairly safe running manually that you are at roughly ppO2 1.2?

For me on an OW trimix dive I would bail and just go up. Its not worth mucking with on the bottom accumulating deco time.
For me on a 32% dil cave dive (i.e Ginnie or Jackson Blue) I would dil flush to confirm the cells are "alive" and responding, then stay on that loop and run it manually as I exited. Watching not just cell1 but that cells 2 and 3 were comparable too. While I could go SCR, that wouldn't really make me feel any safer, especially coming up shallower.

If the cell values were all crazy up and swinging all over the place I'd bail - since in my experience that indicates the cells are flooding. But a flat zero (ppO2 & mV) indicates a wiring issue, whereas a flat zero with a mV output still is a good hint of lost calibration, flash memory failure, or internal processor issue. But I am not especially skeptical that those 52 and 51 mV values are way off base. Plus I can double check that they are actually responding by doing the dil flush.

If I had 32% DIL in Ginnie or Jackson I wouldn't hesitate to use variable mode SCR and exit on SCR mode. You won't go through that much DIL. I regularly practice this to confirm and practice my counting abaility, my most recent one was in May and I was able to get out from the dome room in Little River on a total of 5 DIL refreshes.

 

[rjack321]

If I had 32% DIL in Ginnie or Jackson I wouldn't hesitate to use variable mode SCR and exit on SCR mode. You won't go through that much DIL. I regularly practice this to confirm and practice my counting abaility, my most recent one was in May and I was able to get out from the dome room in Little River on a total of 5 DIL refreshes.

I don't have any issues going SCR. At least at depth I can do 20 breaths. But I have only had 3 electrical failures (knock on wood). The first was a complete secondary board failure on my Meg on the surface (skipped that dive). The second was a single failed cell before I even got to the sign at Ginnie (exited on 2 cells). The third was a partial flood on my sidewinder which drove 2 of 3 cells crazy (stayed on the loop since I had no inhale gurgling and ran it off the 3rd cell).
The only time I see myself in SCR is if I somehow lose both displays, not saying that couldn't happen, just that I tend to have other issues that don't call for SCR to me.

Oh and I don't think calibrating more or less often is a critical matter. I do at the start of every trip, when replacing batteries or if the cells are no longer tracking each other very well (but still basically linear) due to high use a few days in a row.