Cis Lunar Mk 6

Nad

It isn't my statement, it is the usual way made by agencies, but if you think that you guys up there could do something better, great.

This is anyway a RAID problem and I never ever take them in consideration.

Nad

__________________
The Impossible is often the Untried

Nad

Oh wow, do you mean that one of the two stoled design to the other ???

Micropore or prepacked or whatever else, is also used by other CCR so isn't a big deal. BOV mouthpiece, oh this is a great invention, thanks Sentinel and Mk6 to invent it...

Ok for no manual O2 ad, still not a big deal really.
The user can't change the setpoint on the Sentinel? Oh sorry I didn't noticed it...

Ok I'm too tired to keep going on...

Nad

__________________
The Impossible is often the Untried

henckell

That was an interesting interpretation!

That's what it says in the Sentinel document:

"Oxygen setpoint control is also dynamic. The set can be put in 'auto-setpoint' mode (only levels 2 & 3 are selectable, level 1 is auto only). Level 1’s maximum PO2 is set to 1.2 other levels are selectable upto 2 bar PO2."

Actually, the HUD patterns are also different, and in the level 1 unit it more or less only tells the user to continue diving or bail out. Very much the same thinking as in the Disco...

Maybe it's because they both will be part of the new RAID training system?

__________________
http://www.rekodeko.se

najones

I've been lurking here since DEMA and thought it's about time I introduced myself. I'm Nigel Jones and my claim to fame (notoriety?) is that I've been responsible for the electronics on the Cis-Lunar MKII, MKIII, MKIV, MKV and now the MKVI rebreathers. I've never bothered to post in the past because too many of the participants on the then BBS and now Internet forums were more interested in confrontation rather than intelligent discourse. Thankfully this seems to have changed.

Anyway, the purpose of this introduction is to let the forum readers know that with Rich Pyle wrapped up in fish nerd stuff, I'll be happy to try and answer questions you have about the MKVI. First, some caveats:

1. I am not an employee of Poseidon. Any opinions expressed here are mine and do not necessarily represent the opinions of Poseidon.
2. I'm an electronics / firmware weenie. You can ask me questions about non electronics / firmware issues. However intelligent and / or correct answers are not guaranteed.
3. There is a tremendous amount of proprietary knowledge built in to the MKVI. Please be understanding if I decline to answer some questions.
4. At least one statement I make on this forum (including this one) will be wrong.
5. As you may imagine, I have a lot on my plate. Rapid answers are not guaranteed.

Although I am British, I live on the east coast of the USA (GMT - 5). I'll generally try and log on to the forum sometime in the 6-9pm period.

dave t

Excellent stuff Nigel good to see you here, any chance you can answer the above please

thanks

Dave

silent running

Hello Nigel, welcome to Rebreather World, nice to see you on here adding more to the braintrust.

I had asked before about the deco function of the computer. Even though it is meant for recreational use, does the computer have normal air diluent deco function and what algorhythm is used? Does the unit penalize the diver in any special way for going into deco?

And as orders are being taken, I assume some testing of the unit has been done. What sort of testing has been done up to this point? -Andy

najones

For what it's worth, I was the initial proponent of the single PO2 sensor architecture and as such have given a tremendous amount of time to thinking through its ramifications. As a result, I was really struck by Rich Pyle's post in response to a question from dave_t about the reliability of the ambient pressure sensor. I thought I'd offer up a slightly different perspective that you may find interesting.

First, a short anecdote. Recently I was at Poseidon and we were taking the electronics for a chamber dive in O/C mode. I'd asked the chamber operator to take the rig down to 20m. He was astonished when I told him that we weren't at the correct depth and he asked how I knew this since he knew I couldn't see the depth reading. The answer was simple, I could see the PO2 reading and it wasn't at 0.63 Bar. His comment was perfect "You could use this thing (the PO2 sensor) as a depth sensor".

In a nutshell, that's what the single sensor system is all about. In fact, if PO2 sensors were as reliable as depth sensors, and depth sensors were as (un)reliable as PO2 sensors, then we wouldn't be talking about a system for automatic PO2 calibration and validation. Instead we would be talking about a system for automatic depth calibration and validation.

To put it another way, the system ensures that the PO2, FO2 and depth are consistent. If they aren't, then something is seriously wrong and it's time to bail. Which of the three is wrong is almost irrelevant.


I hope this helps shed some light.

silent running

This is very interesting Nigel, but I'm a bit confused about what the reference is at any given point during the dive. If it's true that sensors can and do need frequent calibraion, somtimes even during the dive, how then can the PO2 be trusted for depth sensor cal/reference? Thanks, -Andy

najones

1. The rig has to know the FO2 in the diluent. The FO2 in the diluent may be (must be) configured by the diver. This is done using a a configuration program that runs on phones / PDAs / laptops which talks to the rig via an IrDA link. Of course most dives will be using air, and so no change will normally be necessary.
2. The Oxygen is assumed to be pure. This isn't a particularly onerous assumption. The teledyne sensors are linear to +/-1% (PO2 0.0 ... 1.0) and +/2% (PO2 1.0 ... 2.0). If you throw in the errors introduced by the manual calibration on other rigs, I think you'll find the difference between 99% oxygen and 100% oxygen is irrelevant.
3. The electronics work. The wet switch pads on the DEMA rigs were a bit small and so it was hard to activate the electronics with wet fingers. This probably resulted in less people being exposed to the electronics than would otherwise have been the case.
4. I'd rather not answer your question about the HUD as there are some IP issues involved.
5. By the sensors, I assume you mean the PO2 sensors. The rig has support for both the Molex and Phone jack style sensors. All contact points are gold plated. The system makes it very easy to change the sensors (kudos to Bill, Rich & Jorgen).
6. Scrubber questions are above my pay grade.

najones

First PO2 sensors do not need frequent calibration per se. What they do need is frequent checking as their failure modes can be insidious and catastrophic.

To answer your Question:

PO2 = FO2 * absolute_pressure

absolute_pressure ~= (1 + depth/10) with depth in meters

Thus:
FO2 = PO2 * (1 + depth/10)

If any two of these three variables are known, then the third may be validated. Thus in the normal case, FO2 is known and depth is assumed to be accurate, thus PO2 can be computed and compared to what the PO2 sensors are reading.

Conversely, if the PO2 sensors were known to be extremely reliable (which may be the case one day when there is a breakthrough in PO2 sensor technology), then we may rearrange the equation to give us:
(1 + depth/10) = FO2/PO2
(10 + depth) = 10 * FO2 / PO2

depth = (10 * FO2 / PO2) - 10;

In which case, we could use this equation to validate the depth sensor.

I hope this helps.