ISC posts test data

J. V.

Hi Paul,
How is the snow in Savoie?

__________________
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Jacques
NPSFQQA-EDS IT # 007
(remué non agité)

AD_ward9

3.15 J/L is just within EN14143, but it is still pretty high. I assume it is diver prone orientation, so vertical would be a bit higher still.

If you want a private suggestion or two, email me the calibration orifice Lissajou, your mouthpiece on its own Lissajou with mushrooms fitted, CLs on their own Lissajou, and a diagram showing the minimal hose size between each major part of the breathing loop. I can get the rest of the details from a photo of the rEvo to scale. I will put the details into the rebreather model we publish, and give you the predicted WOB for when the CLs are above the lung centroid. If you advise how much the CL centroid moves, it can even produce the Lissajou for you with the "elastance" shown! For diver orientations where the CL centroid is below the lung centroid, hydrostatic measurements are needed.

Formal models are by far the fastest way to debug what is wrong with a Rebreather, or compare different approaches. It matches practical results very closely on every test we do.

The offer is open because we are keen to see more science in Rebreather designs: specify it, verify the theory using a formal model, build it, measure it against the theory. Right now there is too much of build it, sell it, test it, puzzle over the results. The rEvo would make a nice simple example of how formal models can contribute. As you know, we have all the test facilities in house, but if you get into changing things based on test results instead of theory, you end up with a bodge on top of bodge.

Alex

jradomski

yes that was oxycheq's slogan for a long time...

here is a link using the internet arcive from feb 2003 showing oxycheq's main page.. I didn;t look hard enough to find when he started using it..

OxyCheq ... oxygen analyzers and oxygen sensors

__________________
Joe Radomski
CCR Trimix Instructor Trainer
ANDI Instructor Trainer Director #10

All posts are personal opinions and DO NOT reflect any affiliated agency unless specifically stated.

mempilot

The slogan police are on the prowel.

__________________
Eric Stadtmueller, otherwise known as, MEM "Da Pilot"

AD_ward9

This is probably a good a thread as any to pick, to illustrate some of the errors in making measurements, making standards, and making claims.

I will post on here the mouthpiece WOB and resistance Lissajous for the ISC Meg, Inspo, Dolphin and DL mouthpieces. Just the mouthpiece. I note ISC claim a 0.25J/L WOB figure. This is a lot less than we get for the same item.

Well, there is WOB and WOB.

First of all, what is the waveform? EN14143 states clearly that the flow should be a sine wave, and gives a calibration orifice that produces the 3.3J/L figure at 6 bar absolute. True sine wave pressure through the same orifice produces 3.98 J/L under the same conditions. A triangular wave piston movement has the same ratio of under measurement because there is a bigger area under 180 degrees of a sine wave than there is under 180 degrees of a triangular wave of the same height. Some people have spotted that, so do some sort of scaling: they take the sine figure and then scale it down, i.e. force the figures to agree, where in fact, it is a bit of inconsistency in the standard. In other cases, they use a breathing machine which produces a triangular waveform instead of doing what the standard says and use a sine wave. This is why I always want to see the calibration orifice figure before listening to anyone's WOB claims, and I want to check the machine does have true sinusoidal flow. A related issue, where EN14143 specifies the flow orifice conditions it states clearly it is 6 bar absolute (so 5 bar relative to surface), and then requires the WOB of the equipment be measured at 5 bar (so 4 bar relative to surface, assuming it is absolute figures still, i.e. 40msw).

Of course, if someone wants to measure at 40msw, and at the depth where they just hit the 3.3J/L figure, all well and good but both figures should be published.

Second, what is WOB? Is it actual WOB, or is it the additive WOB caused by the equipment? In EN14143 it is the actual, every where else it is the additive. There can be a big difference in these numbers.

So, let us clear the air by publishing figures, for the calibration orifice, for the ISC Meg mouthpiece, for the original Inspo mouthpiece, a Draeger Dolphin and for a respectable modern mouthpiece (one of the DL mouthpieces, I will pick one with the same general geometry as the Ouroboros, with very soft silicone mushrooms). I will try and get the Lissajous on this thread tomorrow: I have to extract them from other documents.

If anyone has any other little bits that get contentious and they think I should post figures on, let me know. Comparing mouthpieces is simple and seems a good place to start.

Alex

diverreb

I have a question... I am not an engineer nor so I have any sort of technical knowledge of testing procedures and claims arising from such procedures. So this is coming at you from the point of view of what is probably a typical consumer/user of rebreathers who is not familiar with all the measuring units and flow rates being discussed.

Ok.. Unit A has a WOB that is rated at 50% above unit B.

I'll use something I am familiar with.... Computers.

Years ago, if a computer was introduced with a faster processor, graphics card, faster architecture and bigger hard drive, there was a compelling argument to purchase the unit. A complex photoshop file or simple video render would go from taking 10 minutes to 5 minutes. Then the next generation would take it from 5 minutes to 2.5 minutes. The next upgrade would take it from 2.5 minutes to 1 minute... and so on. Until today, where the same process takes about 5 seconds on an 8 core dual processor.

For the most part the real meaningful improvements have been done already. When working commercially you can see where time savings would have justified a new computer somewhere along the scale.

Today we have a very hard time selling a new machine based on 50% or even a 100% improvement in speed, because in actual real time it's meaningless.

This brings me to the Rebreather WOB tests... When I first was deciding which Breather to buy the different lung positions seemed to be a huge factor in the WOB claims from different manufacturers.

Turns out that after diving with guys with all kinds of Breathers, if you dive the units properly, with Minimum Loop Volume, there doesn't seem to be much practical difference in WOB. Not saying that in some positions it's easier to breath one over another, but I don't know of anyone who's put their recently purchased unit up for sale because it didn't breathe well.

Same can be said for the Golem BOV. Are there exceptions that I don't know about... maybe. But there sure aren't many used Golem BOV's for sale on the board.

So the question is, what do these numbers actually mean in terms of real usage?

Are they just being used as a marketing tool, or are they truly meaningful to someone using the product?

Are they meaningful only at extreme depths?

After seeing how tests and results have been interpreted and used by marketing companies & departments of most industries worldwide, I have a deep distrust of what those numbers actually mean.

Being honest, after reading this thread, I have no idea, practically speaking if they make any difference at all.

Help me out here.

Richie

diverklondike

Alex,

Do you have a list of key tests that a Rebreather should be put through in your mind that should be performed on a given model of CCR that would be significant to the average user? While I am sure that an exhaustive one could be created, I am wondering what the key ones would be. The key ones that initally come to mind for me are:

1) WOB
2) Scubber Duration
3) Ability for the electronics to hold a given set point in a given controled enviroment. - Accent etc...
4) PP02 differential between electronics reading and PP02 at mouthpiece in given controled enviroment.

(I am sure that I am missing things but it's a start)

While I am sure that we could come up with an exhaustive list, I am interested in what a core set would be. This would be in an effort to then get the various MFGs to provide this type of information. As an inital start we could at least start some matrix of what information is known in each of these areas.

The above plus a list of percieved design flaws would give a consumer a good point of reference and comparision. (Hats off to Mark Chase on already starting the design flaw part.) While at BTS this weekend, I had several people mention the value of something like this. Potentially the initeation of this information being collected in a public forum would drive the various MFG's to level the playing field when it comes to testing information. Obviously the "design flaw" part will be very subjective but so be it... At least it's a starting point.

Mark

paulraymaekers

hello Alex, the test was done in vertical position, so in horisontal it will be a bit better

I'll think about your offer

paul

ps jacques: the snow is fresh!!!!!!! :-)

__________________
www.rEvo-rebreathers.com

.... the earth is flat, Elvis is alive, and radial scrubbers give longer dwell time than axials...

AD_ward9

Each of the standards do cover the relevant and important points: EN14143, NORSOK U101, the US Naval 1994 Procurement spec etc.

The main item missing is the EN61508 compliance.

Returning to the breathing parameters, the devil is in the small print: ensuring test conditions are the same so comparisons can be made. EN14143 does a reasonable job, and companies like CCR Ltd have stuck to it well. The problem with the ISC numbers is that neither the HSE nor ISC read the spec carefully enough, so did the tests at the wrong depth. With major errors like that, one suspects others, such as ensuring the breathing machine is set to the correct waveform and is in calibration. I am very keen for companies to publish data, it is a big step forward in safety. What I would like to try and achieve here is simply create awareness of what to look out for when doing tests, so the test results are valid and not disputed.

On Diverreb's question: it is not like computer X is 50% faster than computer Y. It is computer X is unsafe and will kill you under specific circumstances, whereas computer Y will not. WOB, scrubber endurance etc, are very basic safety measurements. All equipment should comply with minimum standards: EN14143 is a minimum safety standard, not a guarantee. The first stage in getting compliance is for companies to test what they are selling (or better still, test what they are designing). ISC made a good step forward, as has Paul with the rEvo. It is a complex area, so sharing information on how to do this properly and what errors to look out for should make it easier for companies to go down this route.

On Paul's post below. Good. So 3.15J/L is a pass point from the WOB issue.

Alex

silent running

Hello Richie, under normal, favorable dive conditions most of the units for sale these days have acceptable WOB. When I say favorable I mean no hard work and the unit is trimed out to it's optimal orientation. By way of example, when I spoke to one of the Navy guys at the NEDU about the MK16 they had on display, he reminded me that the unit breathes great in an upright position, which is the position one needs to be in for diffusing mines. He then went on to say that it breathed poorly in a horizontal position.

And given that CO2 hits always start with our bodies retaining CO2 and how hard it is to get rid of the CO2 once we begin retaining it, WOB becomes critical when we are working hard and expecially at depth. And differences in WOB that may seem small in favorable conditions will be amplified in bad conditions, like the ones I sometimes find myself doing exploratory dives in places like Indonesia. And as I said recently, I needed all the help I could get trying to fight my way up after getting blown down to 75M in a 3 knot down diving at Banta Island in Komodo... _Andy