paulraymaekers
Active Member
yes, I'll give that presentation at A.I.R Bali
paul
paul
Do you check your cells at 6m?
- Thread starter Matt Reed
- Start date
I see no reason to not check your cells at 6 meters at the beginning of a dive in addition to later in the dive. If they fail at the beginning, the dive needs to be aborted regardless of any cell reaction later during the dive. In other words, if they fail at any point during the dive, it's time to abort the dive and replace the cells. I understand Paul's reasoning in wanting to check the cells at later points throughout the dive, but feel that it is also important to verify functionality at the beginning as well.
Jeppe
When In Doubt - Bail Out!
On every dive, when passing 6m. Automated by the breather, injecting oxygen on the cell surface. Hyperoxic Linearity check. Confirmed by unit when switching to high SP. I do not, however check my Petrel more than at the surface that it can read 1.0. It is my redundancy and yes, one could argue about why I am not checking that.
But then again, I think we can agree with the fact that we say one thing on a forum because it is the right way, and then when we go diving we do it differently :sarcy:
But then again, I think we can agree with the fact that we say one thing on a forum because it is the right way, and then when we go diving we do it differently :sarcy:
paulraymaekers
Active Member
hi Randy, I agree that checking sensors at any time is a good idea.
I only mentioned that there is a misconception that you can check your sensors for current limiting by flushing them with O2 at 6m at the start of the dive
kwinter
PITA
I think the bigger problem that Josh may have been getting at is that adding O2 just to spike cells without knowing the exact gas in the loop doesn't really tell you much about cell health other than they might be able to reach 1.6. But maybe they are reading 1.6 when the actual loop is actually at a very dangerous 3.0. Pumping in O2 just to get a high cell reading isn't smart. Cells are batteries and can act funny. Current limiting doesn't necessarily mean it is impossible to get a 1.6 reading; only that it won't get that reading at 1.6. And even if your cell turns out to be so limited that it won't reach 1.6, how do you know you haven't increased your pO2 to a dangerous level trying to spike it?
iPhone. iTypo. iApologize.
paulraymaekers
Active Member
Ken,
the simple solution to avoid this problem is to apply correct sensor rotation: current limited sensors will show up during the dive, but never all sensors at the same time
Captain Starfish
New Member
But there you're assuming that, by cycling cells, they won't fail simultaneously. Which is fine for normal deterioration but, if an event of some kind (heat, drowning, prolonged exposure to pure O2 etc) affects all cells to the point where two or more fail simultaneously? The whole "Rotate cells and you'll be fine" approach has lulled you into an assumption that everything's fine because the cells all read the same.
Most of the time, a good approach. But not necessarily the best of "habits" to get into, perhaps.
Most of the time, a good approach. But not necessarily the best of "habits" to get into, perhaps.
paulraymaekers
Active Member
our experience is that sensors with different dive history, age, heat exposure, pressure cycling etc, react in a different way to sudden 'events.
an event that is so dramatic that it will change the behaviour of 4 / 5 sensors that have all different history, in exactly the same way... is unlikely not to be noticed before that dive, during the predive / prejump check
If you run a setpoint of say 1.2, or 1.3, and spike it up to 1.4 or 1.6 then you know they will read higher than what you're currently demanding of them. If this is not sufficient the only way to confirm it is to either do a flush with pure O2 at depth or a gas with a higher PPO2 than 1.2/1.3. And that gas will not be your dil unless you are running a very hot diluent.
How likely is it really that 3 cells that passed calibration suddenly, or during the dive, will go that crazy above the 1.0 calibration? I understand it if the cells are not reacting above a certain value, but if they are responding to oxygen injection, how likely is it that you run a setpoint of 1.2 or 1.3, spike it to 1.4 or 1.6 with the cells reacting to your O2 addition, that the actual PPO2 will be somewhere in the range 2.0 to 3.0 or higher for that matter??
I do calibration as normal, and spike it a few times during the dive to check that it reads above my current setpoint or the value I'm flying manually at. I also do a pure O2 flush at the end of the dive every now and then at 15m (49-50ft) and verify they will read 2.4-2.5. At this point the cells are good and moist, all warmed up and if they read correctly I am quite happy with their performance using this information together with the normal calibration. While doing the O2 flush at depth I am obviously off the loop, on OC until I have done a dil-flush and the PPO2 is back to a safe value in the loop again.
I too find doing pure O2 flushes at the start of the dive does give me problems with high PPO2 during decent, even with a quite lean O2 dil unless I do a complete dil-flush before descending. I do however only add O2 in the shallows and never use the ADV <6m, but not flushing the loop with O2.
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Captain Starfish
New Member
Doesn't have to be four out of five, for most of us it only has to be two sensor. And most of us aren't watching the ppo2 continuously during a dive, we check it on regular occasions. So there's a good chance that, if something goes wrong, all we'll see is two of three cells agreeing - not the different paths they took to get there. I get where you're coming from but I think simply relying on a change interval to the exclusion of everything else is asking for trouble.
paulraymaekers
Active Member
I don't think anybody mentioned this. The misconception I wrote about is related to current limiting. Other types of failures of sensors are different of course.
I do believe however that changing sensors at different intervals is a far better practice than changing all at the same time.
matt
Well-Known Member
I don't check mine at the start of a dive, I'm busy doing other stuff. Same on the dive - busy enjoying myself. Only check if there is an error/issue/wobble.
After any break from diving I go to a pond and check them at the end of the dive, 8m, 1.6+. I've found that cells under 18 months from manufacture that show 0.21 with the lid off, have the same end-cal-value (Inspo) as previous and can reach 1.6+ at the end of the dive do not give trouble. Any variation is to be watched during the dive.
That's what I do, but there are many alternatives. I have and have played with a cell-checker - it's perhaps the most non-useful piece of kit I have - I've tried known knackered cells that pass a "quick test" and I've tested cells that work fine that show non-linearity (due to the completely inadequate pressure gauge on the one I have). Folks swear by them, I'd rather check my cells in a pond.
Matt.
After any break from diving I go to a pond and check them at the end of the dive, 8m, 1.6+. I've found that cells under 18 months from manufacture that show 0.21 with the lid off, have the same end-cal-value (Inspo) as previous and can reach 1.6+ at the end of the dive do not give trouble. Any variation is to be watched during the dive.
That's what I do, but there are many alternatives. I have and have played with a cell-checker - it's perhaps the most non-useful piece of kit I have - I've tried known knackered cells that pass a "quick test" and I've tested cells that work fine that show non-linearity (due to the completely inadequate pressure gauge on the one I have). Folks swear by them, I'd rather check my cells in a pond.
Matt.
paulraymaekers
Active Member
+1
I think the problem with cell checkers is dual:
on one side they give the user false confidence that sensors are ok if you can spike them to > 1.6
on the other side users will reject good sensors when they find non-linearity of a few % when they extrapolate readings from 0.21 to 2.0 bar
Your lucky a mate of mine is yet to get out the pond with 3 cells still working, they were brand new when he got in ! Guess who's
I have one & I use it occasionally but by no means swear by it, it is a small tool in a big locker. I have 8 cells in total to worry about so am not going to throw any away needlessly !
matt
Well-Known Member
I have 4 from N@90. Rotating them in every 3-4 months, rotating and routine preparation works for me - no missed dives in 12 years.
Matt.
Mark Chase
ATB=AlwaysTalkingBollocks
Before the dive all i know about my cells is they can read 1.0.
Not a lot of help seeing as i want to run 1.3
It takes maybe 5 seconds to do this test and is best done during the bubble check but at 8m as IMHO you want to be spiking 1.7 1.8 to make sure the cells can read well over anything you may want to dive on.
Paul goes on to sugest that cells reading 2.0 went on to fail 30mins later? For me 30mins is probably two thirds of the way through my bottom time on a deep dive and ill have checked the cells can go above 1.3 long before then with little spikes mid dive.
There simply is no excuse for not doing this test.
You jump in and have your ECCR injecting 02 desperatly trying to get to 1.3 on current limited cells and you could be diving 2bar+ without knowing and working hard to get down the shot.
Look at the fatality stats and look at the divers who convulsed. How do you think that hepened?
Being on pure 02 on the surface is common sense and using that pure 02 to spike the cells and check for curent limiting before you go deep is both simple and unobtrusive to the dive
So why not do it?
Further checks mid dive are equaly important especialy on long duration dives.
ATB
Mark
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Matt Reed
New Member
Randy can you confirm or deny if this is supposed to be part of Hammerhead user training?
Thanks.
Yes, cell verification is part of the HammerHead CCR training as well as the TDI training protocols.
lizardland
Active Member
I've always dived on a fairly low SP in comparison to most. 1.0 normally and when my Mk15 was stock the original pod runs 0.8-.0.9 without fooling it during calibration.
I do an air and full oxygen flush at the surface. On the descent I check it will read past at 6m, I expect 1.55'ish and found AII cells pretty reliable in hitting it.
I like my cell checker. Possibly because it didnt cost me much to make, I think we tend to rate the benefit we get in comparison to how much the piece of kit cost. I find it useful and run the cells through it before every trip. I've always been wary of doing a quick check with it, I tend to let them sit in the pot for 30min while I do other stuff (usually more like an hour) and I vary the pressure during the soak as well. Dont know if the last bit makes any difference but it feels more like what a real cell is going to see in use.
It is such a cheap and easy tool to make I am surprised more people dont have one.
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I do an air and full oxygen flush at the surface. On the descent I check it will read past at 6m, I expect 1.55'ish and found AII cells pretty reliable in hitting it.
I like my cell checker. Possibly because it didnt cost me much to make, I think we tend to rate the benefit we get in comparison to how much the piece of kit cost. I find it useful and run the cells through it before every trip. I've always been wary of doing a quick check with it, I tend to let them sit in the pot for 30min while I do other stuff (usually more like an hour) and I vary the pressure during the soak as well. Dont know if the last bit makes any difference but it feels more like what a real cell is going to see in use.
It is such a cheap and easy tool to make I am surprised more people dont have one.
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