First O2 Sensor failure

[tomsch]

So basically I just wanted to share my experience and some graphs of my first O2 Sensor failure.
I did a fresh water dive yesterday, water temp 4C, max depth 30m, dive time around 1h with no-deco, and when diving back to the entry at 10m of depth I had one of the three O2 sensors showed way different values then the other 2 sensors did, with values ranging from 1.5 to 0 ppO2 at a SP of 1.2. I flushed and after watching the values I bailed out and ascended without problems and without panicking, still in the beginning of my ccr journey but especially because of practicing switching to bailout during the same dive I had a quick reaction time, which wouldn't have been necessary but a failing sensor was a big surprise for me so I still bailed out. Analysing the data after the dive it showed that the mV readings of this O2 Sensor where around 5 mV off for the entire dive till it failed. The reason for this failure probably the electrolyte in the sensor(potassium hydroxide) leaking out of the cell chamber which was noticeable after 6 hours by the sensor partially filling up with a rusty looking fluid, the electrolyte. This was on a sensor produced and built into the device in 9/2022.

 

[davehicks]

What brand sensor and ccr was involved?

I've never had one leak in over 1,000 CCR dives, but had plenty fail or fade out early in their cycle. Never had to scrub a dive for a sensor issue though.

 

[tomsch]

What brand sensor and ccr was involved?

I've never had one leak in over 1,000 CCR dives, but had plenty fail or fade out early in their cycle. Never had to scrub a

What brand sensor and ccr was involved?

I've never had one leak in over 1,000 CCR dives, but had plenty fail or fade out early in their cycle. Never had to scrub a dive for a sensor issue though

JJ-CCR with the official sensors

 

[rsingler]

Sounds like you diagnosed it well after the fact.
I'm not picking on you, but how did the voltage on air or 100% O2 during calibration compare with your last dive?
In other words, do you track cell voltage over its lifetime? I wonder if that would have alerted you to an impending issue, or whether this failure occurred unexpectedly right during the dive window.
I keep a log of air, 100% (and spike voltages from my last 20 ft stop) to crosscheck my JJ during the next build, cal and dive.

 

[tomsch]

Sounds like you diagnosed it well after the fact.
I'm not picking on you, but how did the voltage on air or 100% O2 during calibration compare with your last dive?
In other words, do you track cell voltage over its lifetime? I wonder if that would have alerted you to an impending issue, or whether this failure occurred unexpectedly right during the dive window.
I keep a log of air, 100% (and spike voltages from my last 20 ft stop) to crosscheck my JJ during the next build, cal and dive.

It would have probably warned me from an failure because at my last dive the voltage values were fine and for this dives they were off since calibration.

 

[jale]

Hi
You did the good thing but personally, I would not have BO.
Yes I know I am going to get for that but it was a good opportunity to do a dil flush and check the cells.
Why do we always rely on this voting logic ?
I started diving RB with a two cell monitor.
Now I have three but it doesn't disturb me to dive with only two sensors.
Shouldn't we do a regular flush to check if the sensors are fine?
I am not trying to troll but frankly, with the rEvo with 5 cells, the Liberty with 4 (I think), the options of adding a fourth sensor here and there and so on, shouldn't we back to the basic and incorporate regular dil checks during the dive?
A real question.

 

[tomsch]

Hi
You did the good thing but personally, I would not have BO.

I mean bailing out is never wrong, but if it wouldn't be at the end of the dive I probably would have gone back into cc.

Yes I know I am going to get for that but it was a good opportunity to do a dil flush and check the cells.

It was a good learning experience watching the sensor die in the end and monitoring it and if I would have been calmer, I didn't panic but I wasn't relaxed either it would have been good if I stayed a little bit longer at 6m and just watched the values change.

Why do we always rely on this voting logic?

Idk, I wouldn't rely on it but you can safely dive with 2 sensors as long as you can validate that only one sensor is dead.

I started diving RB with a two cell monitor.
Now I have three but it doesn't disturb me to dive with only two sensors.
Shouldn't we do a regular flush to check if the sensors are fine?
I am not trying to troll but frankly, with the rEvo with 5 cells, the Liberty with 4 (I think), the options of adding a fourth sensor here and there and so on, shouldn't we back to the basic and incorporate regular dil checks during the dive?

Imo everything over three sensors is overkill because if we say chance of a sensor failing in a dive is 1%, with two sensors it's only 0.01 percent that both fail and with a third sensor for validation of the other two sensors that's enough redundancy. Because all three sensors failing without at least one of them having a complete failure could be put into the category of stuff Facebook groups make up.

 

[rddvet]

Hi
You did the good thing but personally, I would not have BO.
Yes I know I am going to get for that but it was a good opportunity to do a dil flush and check the cells.
Why do we always rely on this voting logic ?
I started diving RB with a two cell monitor.
Now I have three but it doesn't disturb me to dive with only two sensors.
Shouldn't we do a regular flush to check if the sensors are fine?
I am not trying to troll but frankly, with the rEvo with 5 cells, the Liberty with 4 (I think), the options of adding a fourth sensor here and there and so on, shouldn't we back to the basic and incorporate regular dil checks during the dive?
A real question.

I wouldn't have either, but I have some hours under my belt. As a newer ccr diver I probably would have bailed out or bailed out and figured it out then gone back on the loop if appropriate.

 

[tomsch]

I wouldn't have either, but I have some hours under my belt. As a newer ccr diver I probably would have bailed out or bailed out and figured it out then gone back on the loop if appropriate.

Also it's what I think is the best option you have, and imo it's the right thing to teach the procedure of Diluent flush, if high/low po2 do the drill, if that doesn't change anything, bailout, think, fix the problem, and then go back. Because then you are safe to any further problems which may occur. It's especially valuable if you are new because it takes most of the stress out of problem solving.

 

[broncobowsher]

To have it belly up and read zero is a good failure, you know it is not working. My first failure I would get high readings. That one was a lot harder to figure out what was going on. It would read in range, and I could cal it. But it was a little drifty. Moved that cell to the NERD and it was happy(ish). Went for a dive and it started reading really high. Got home, it was fine in air and would cal at 100%. While fussing with it I noticed the readings would change if I touched the harness. Started wiggling more and if I put any load on the connection on the pins going into the cell the voltages would go up. I never cracked that cell open but suspect a cold solder on the board in the cell. I suspect that from how it behaved under stress and how I have had other boards in other electronics over the years that didn't like stresses applied.

I didn't bail. Still had 4 cells I trusted. The 5th is the one I suspected anyway. Did learn something about Shearwater programming. With 2 cells reading widely apart, it will calculate deco on the low cell and CNS on the high cell. The NDL was a match for the Petrel (with the 3 good cells) but the CNS was through the roof.