Mv output on new Bud R22 Cells?

Mark Chase

Hi all.

Mt HH failed calibration on two brand new cells and i am wondering where I stand on this.

I have three C6 cells three weeks old, and after soaking them overnight in a bag of 02 and doing a bag flushed test I am getting 45mv on two cells and 39mv on the third. Also a cell new in September is giving me 35Mv. The 35 and 39mv cells are not good enough to pass calibration on the Hammerhead.
In air I am getting 9, 10 and 12 Mv on the new cells 9mv obviously being on the cell offering 39mv in ambient pure o2.

So are these failed cells? They cirtainly wont work below 40mv on the HH so why are they OK on the YBOD? Is 45Mv acceptable or are they failed as well?

My old cells are 13months+ old and output 50mv in pure 02 ambient.

ATB



Mark Chase

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Mdemon

When you calibrate them on the Inspo, what figures appear before the calibration is complete? Usual range? Might be the cells are OK and the HH is duff...

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It's as easy as abc;

a) "Carry adequate bailout"

b) "If in doubt, bail out"

c) "Always know your PO2"

If you find that hard, stick to crochet.

"Once the agenda-monkeys and perfect-worlders have moved on, perhaps we can do some diving?"

nigelh

I don't like the idea of leaving them in O2 for hours as that just runs them down but I don't like any of those numbers.

9mV in air should be 43mV in O2

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nigelh

SimonK

Assuming that you tested all seven cells in exactly the same way then the new ones all appear to be duff - wierd?

If air is 20.9% and you are getting 98% in the bag then the mV reading in the bag should be approx 4.7 x what you get in air. That is 42, 47 and 56 mV.

Might be worth sticking them in the classic head a seeing what it does.

Simon

jradomski

Mark,

If they are reading 9,10, and 12 and the cells are still linear, you might not be flushing as well as you think..

1) make sure the adv has a flow stop on it and shut when flushing..

2) make sure you insure gas passes through the enite loop.. dont forget the exhale part of the DSV hose to exhale lung..

It does take a bit of practice to get it correct..

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

Mark Chase

If the HH is duff, its duff in an unusual way. If the swap the cells it will swap the Mv readings to the new cell position. No matter which cell I check the MV readings are constant for that cell be that 50mv for the year old cell or 35mv for the cell new in september?

I could check them in the YBOD but you know what a PITA that is to set up.

I checked with AP and they said they sell cells that give 8mv to 14mv in air as an oporational range. 8-9mv fails on a HH as its shows below 40mv in 02 at ambient.

After a bit of initial "sorry we cant help" when i mentioned the HH they ended up going through it quite well and suuring me 8mv was fine. They also said I could order cells with a min 10mv output so they would work in the HH.

It does beg the question as to why the HH considers these cells duff?

I have orderd a repalcement cell with not less than 10mv in air.

ATB


Mark Chase

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Mark Chase

Yeah but dosent it round up from 8.5mv?

ATB

Mark Chase

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Mark Chase

I am doing this in a plastic bag and getting exactly the same readings as I was getting on the unit. This makes me think I am doing it OK on the unit.

ATB

Mark Chase

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jradomski

If your getting it in a baggies it sounds as if you really have bad cells. for dsiplay purposes 8.5mv - 9.4mv will display as 9..

In 100% a cell that is linear will be accepted as it would be 40mv for an 8.5mv cell (at 98% oxygen it wouln't be).. If you arent using 100% oxygen you should build tha cal kit like I use, so that you can properly cal it when not using 100%

yes moving them around the readings should follow.. The mv reading will always give you the true reading.. the po2 readings will be disabled for cells that failed and wrong for others..

it also sounds to check things out I wuld make up a simple harness and do the oxygen in a baggie while a cell is connected to a volt meter..

the appproximate reading should be reading in air * 4.72 * oxygen percentage

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CCR Trimix Instructor Trainer
ANDI Instructor Trainer Director #10

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

heyydude

Mark,

Here's why the HH rejects cells that are LESS than 40 mV when you go to Calibrate them:

Since 1995 or so, we've only used ACTUAL cells in a Pressure Pot for testing and calibration. The reason for that had a lot to do with the experience I've gained through using lots of different cells from lots of different manufacturers - some of whom are no longer around.

I wanted to test whatever system we were building against real Sensors. This way, we could eliminate any noise or other fluctuations from an "artificial" source (I once spent an entire day trying to figure out what was wrong with a set of electronics, only to find a variable potentiometer in our mV generator took a dump). We have both mV generators here, as well as pressure pots aplenty, but we use the pressure pots more.

--> Point 1: I once found a set of cells - brand new - that were current limited to what would have been the equivalent of 1.1 ppO2. Had I gone diving with those cells, they would have killed me.

And remember, in a Voting Logic system, any TWO cells that agree can also kill you.

---> Point 2: That is why one of the first things you see on the HH is the "FO2" command - the unit does a simple math function to tell you what your ppO2 should be at whatever particular depth you are at, based upon your selected Gas Mix. This serves as a "mental-health-check" for those stressful times when you're trying to figure something out very quickly.

When we started to develop the HH, one thing became clear from talking to Inspiration divers - they all had "issues" with the cells. Whether or not this was perception or reality is still a mystery to me, since we've had very GOOD luck with Teledyne products across their range. However, we HAVE found current-limited R-22's - enough, combined with my previous experience with cells to make us take a couple of steps to try to ensure you don't get hurt.

---> Point 3: ANY R-22 that outputs LESS than 40 mV in 100% Oxygen is, in our opinion, suspect. REMEMBER THIS. If you are using ANY kind of CCR and your mV in 100% is 35 mV or less, using an R-22 of any vintage - regardless of it's "in air" mV reading - you are taking a risk diving that set at anything above .75.


So what we did in the HH was install a bit of code that says - "if a cell = <40 mV during Cal, REJECT that cell. The older HH's (Pre Primary 7.06 and Secondary 5.05) used to insert a null value "0.00" in place of any Rejected Cell. That, however, led to lots of guys thinking that the HH was "broken" because no matter what cell they plugged in, it still read "0.00". We changed that to read "FAIL" now, so there is no question.

---> Point 4: In our shop, we use ACTUAL R-22 cells in our Test Pots. We leave these in 100% Oxygen FULL TIME. These cells last about a year, no matter how hard we treat them. As part of our REGULAR QC on each HH, we pressurize them to 3.00 ppO2 to verify linearity of the HH system - any deviation, and we check the mV output of the cell first. R-22's are VERY capable of Linearity to 3.00 and demonstrate so all the time in our shop.

Other CCR electronics allow divers to calibrate at LESS than 100% - Trying to be Polite, and with All Due Respect, WE DO NOT agree with this philosophy. In our Humble Opinion, there are TOO MANY ways a diver can wind up dead using that scenario, and we are not willing to allow our set to do that. Why would anyone trust a $50 "El Cheapo" O2 analyzer (no offence to my great friend, Pat Duffy), which is calibrated in AIR vs, a multi-thousand dollar piece of CCR electronics is beyond me.

And before anyone jumps down my throat about this - remember, the USN, RN and RAN all use Medical or Aviator Grade O2, and flow 4 lpm around their R-10D's for FOUR MINUTES before calibrating. I don't know any civilian that does that - but more of you should. It is a good policy. Gas is CHEAP compared to LIFE.

Joe Radomski and I have had this discussion/argument more times than I can count, but I still come back to the same thing - if you want to actually dive something less than 100% O2, you can always compensate via your Set-Point control and your Conservatism - giving you the actual mV output of each cell should be sufficient to help you calculate using a very precise instrument (the HH) what actual FO2 your O2 bottle has in it.

And, most importantly, 3 years of experience has borne out that the 40 mV limit WORKS.

---> Point 5: Calibrate your sensors back home on some verified 100% - keep track of the mV output of EACH cell. When you are in "Elbonia", or some other place where they can only give you 90%, then re-check your mV and do the math to make sure they are in line with what they should be. IF NOT, DON'T DIVE. Verify your readings with other analyzers and re-test. If ever in doubt - DIVE AT LOWER ppO2's or dive OPEN CIRCUIT.

Listen To Me: You should be doing this with ANY Rebreather you are diving - if for no other reason than to cross-check your Sensors and Analyzer. Since nearly all of us carry our PC's (or Mac's for the Enlightened among us), make up an Excel Spreadsheet to do the math for you, and to log your cells at the same time. Treat this information as if your life depended on it, because it DOES.

Nothing down there is worth dying for, no matter how much damn money you paid to go on that trip.


If there is enough of an upswell of desire, we can build copies of our O2 Sensor Pressure Pots. We've made them from time to time for friends and even one customer (who doesn't use it - not naming Names, but it's spelled "B-A-Z-Z-A" ). I'll send a picture of one to Joe so he can upload it to the site (I still don't know how to do that).


--> Last Point: eCCR's are NOT TOASTERS - these things are Life Support Devices, which means that you need to take them more seriously than you would your iPod. You don't need to know how the iPod plays your favorite tunes - but you DO need to know how your O2 Sensors work, and how your Electronics uses that information to keep you alive. If your iPod shits the bed, you just get mad at Steve Jobs and demand a new one. If your eCCR does the same, your widow gets to cash your policy, and your kids have an excuse to use in the future as to why they're such F**ked up adults...

Enough said...

Safe diving to everyone.

Kevin Juergensen
Juergensen Marine.