Incident with high PO2. Help, please :)

[SergiE]

Incident with rEvo.

I went diving with my rEvo (I bought it new two months ago). I set up the machine following the check list as usual. I calibrated both the Shearwater and the rEvodream sensors correctly.

I started the dive and do a 6.5 - 7m sensor check until the 4 sensors I have on the unit reach 1.55. I return to a suitable PO2 of 0.7 by adding diluent. At 12 metres I switch to the high SetPoint of 1.2, which I have pre-set. I slowly descend to 16m, but still add a little diluent because the PO2 is rising above 1.2 and I want to master the machine, the PO2 is dropping correctly. I get slowly to 21m and the PO2 is now at 1.3, so I add diluent to bring it down to 1.2 again. The sensors read a little less than 1.2 after the addition of diluent, but gradually it goes back up again, 1.22, 1.24, 1.26, 1.30, 1.33.... of course I keep breathing normally to mix the circuit well. It stays more or less stable at 1.35, so I add diluent again to bring it back down to 1.2, and the same thing happens again.

Finally I stop at 25m and continue doing the same thing with the diluent, I notice that sensor number 1 always lags a bit behind, it takes longer for the PO2 to rise compared to the other sensors. Once again I add diluent, this time with a little more momentum, the readings go down and I stay very attentive watching how the readings go up, sensor 1 is at 1.10, sensor 2, is already at 1.30, and sensor 3, is at 1.45 and going up, the HUD is green/red (sensor 4)... then I keep breathing to mix the circuit well but the readings are too high and they don't stop at all, so I decide to switch to OC and continue the dive in OC.

Also, I hear the Solenoid injecting O2 even with sensors 2, 3 and 4 reading over 1.30... but the pre-set SetPoint is 1.2...

What do you think is going on in my machine? I think I have sensor 1 very slow, and sensor 2 too but not so slow, and that makes the machine keep injecting when it is not necessary anymore. Any other idea? am I doing something wrong?

Thank you very much for your help.

 

[broncobowsher]

So many questions, so many assumptions...

You say you got it 2 months ago. How much experience do you have with it? Is this the first dive with it? If you have done with it before, how did it act then?
Is this a first rEvo? Are you taking classes? have you had classes on the rEvo? Have you talked with your instructor about this?
Where were the cells sourced from? Brand, age, etc. What is the mV reading of each?
Looks like you were doing a 25m dive? What were you using for DIL?
You say you calibrated them correctly, I have done calibrations before where one cell was a hair off what the others were. Just needed a recal to get everything back in sync.
This is where I would rotate cells and see if it follows the cell, or the connector, or the holder position, or...

 

[SergiE]

Hi broncobowsher, thanks for the help. I didn't put some of the details you ask for because some seemed obvious to me. But there are others that are not so obvious to those reading my thread for the first time, so I'll go with it:
The last 27 dives went well, always seeing cel #1 a bit slow compared to the rest. Cells were new, out of the plastic bag on 3/12/2022. Brand bvba. The mV reading of each (home calibration test):
Cell #1: 54 mV (0.98PO2).
Cell #2: 54 mV (0.98PO2)
Cell #3: 53 mV (0.98PO2)
I calibrated correctly, yes. I calibrate every day I dive, and always the same result for a month now.
Yes I was doing a 25m dive. My diluent was air.
My idea was to rotate the cells as well and see what happens to determine if it's a cell thing, connector thing, etc.
I will report back once I have done the tests.
Thanks again for your help and time.
Best regards,
S

 

[nickb]

...I calibrate every day I dive...

Is anybody else doing this?

I calibrate new cells and then that's it until I either change them or rotate them if I suspect a problem. I expect to see 0.21 across the board when I take the head off and I keep an eye on the mV when at low and high setpoints.

Blindly calibrating every day just masks any issues that may be happening.

I dive a JJ, YMMV

 

[sprockjohnson]

Is anybody else doing this?

I calibrate new cells and then that's it until I either change them or rotate them if I suspect a problem. I expect to see 0.21 across the board when I take the head off and I keep an eye on the mV when at low and high setpoints.

Blindly calibrating every day just masks any issues that may be happening.

I dive a JJ, YMMV

I re-calibrate if it has been over a month since I last dived with the unit or if I have replaced any of the cells. I also agree that calibrating every day isn't ideal as it doesn't let you see mV trends between the cells which might allow you to notice if one is significantly lower than the others or acting erratically as in the case of corrosion.

 

[broncobowsher]

Rotate the cells, maybe you just got a laggy one. Just because it is new doesn't mean it is perfect. And they are starting to reach a year old as well. I am a fan of the change one cell at a time so none are the same age/batch. Cell #1 might be time to start that.

I also go with the others, no daily cal. Daily check, yes. But not calibration. Only do that when a cell is replaced or moved to a different location. You get a better idea of a cell drift that way. It may have made figuring out what is happening now easier to figure out.

 

[SergiE]

Hi to everyone! Thanks for your comments. I rotate the cell, and it seems that was the problem. I got a laggy one, quiet new but laggy.
About calibrating... my instructor says the following: If you dive everyday, calibrate every 2 o 3 days. Then because this thread, I ask to a another instructor and friend and he told me: If I dive every day I just calibrate the first day, and then I check every day the readings makes sense .21 when is on the air and .50 when the low SP. If I don't dive for a week or more, then I calibrate again. He says once per year o once every few months (when changing sensors for example) it's not enough. I am not an expert as you know, so I add this information from experienced instructors, but sure one can have a different opinion.
Thanks a lot again, so good to have people answering questions in this forum. I appreciate it.
Best!