Wet sensors

MikeH

A few days ago, I had an interesting thing happen during a dive. It was one of my training dives, so, of course, there were lots of skills involved. On one of the dives, we were at approximately 100' when I was called upon to do a full flood recovery drill. I had been doing some head down just prior to that as well, trying to get counterlungs adjusted just right.

When I began the drill, I had a 1.1 setpoint, but manually maintaining a 1.2(and all three sensors read between 1.2 and 1.24). Of course, when I started pumping in diluent(air) to clear the counterlung, that dropped, and the solenoid started firing. My HUD then started a strange sequence that I had not yet seen(5 red, 1 red, 6 red). I checked my primary, and showed approximately .55, .92, and .40. Of course, the first and last weren't even possible since I had 1.2 prior to the diluent add, and added diluent with a PO2 of approximately .85 at that depth.

I assumed the sensors were just wet from the head down attitude, so I stayed upright and went semi-closed for a few minutes. The sensors finally stabilized showing about .80, .30, and .82. Sensors 1 and 3 checked with the diluent, but sensor 2 did not....the opposite of what happened just after the drill. We continued, I maintained MLV, and I just used sensors 1 and 3(2 was voted out anyways, of course) expecting #2 to dry out and start working fine in a few minutes. After a couple minutes, and moving up to about 70', I did another full flush...and this time, sensors 1 checked with the diluent, but 2 and 3 were way out(.65, .20, .25). The good one was voted out, and the solonoid began to fire(setpoint was at .4 at this time). I set it to manual, and called the dive. During the ascent to 20', which took about 4 minutes, all 3 sensors gave extremely odd readings, bouncing between .18 and 1.1. When we got to 20', I did an O2 flush and showed 1.4, .4, and .45.

After the dive, we pulled the sensor carriage out and, as expected, all three sensors were wet...but there was no standing water in the canister, the absorbent wasn't wet, and the exhalation counterlung had a couple tablespoons of my industrial strength mask defog ... The next 2 days of diving was uneventful, with none of the sensors being more than .05 apart from each other.

Has anybody else seen this happen, or was it just a fluke? All the experienced Meg divers I talked to said they had not seen something nearly that bad with all the sensors...and nobody seemed concerned. I'm not worried about it happening again, because I know I can just go semi-closed and call the dive if all three are unreliable....just curious if this is something that happens now and then.

Mike

schford

The only thing I can think of and it happened to me once is that you are a big Co2 producer and end up with water in your inhale counter lung then you don't clear said lung for several dives.

Then when you roll around it can get into the head. I killed a cell that way!

Stuart

babar

I don't get it. How would that cause those kind of sensor readings?

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MikeH

I drain/disinfect/dry the counterlungs at the end of each day. This was the second dive, and about 45 minutes into it(previous dive was about 65 minutes). I'll keep that in mind, though.

Mike

Joseph Grech

I have had similar odd readings which at the time I tought that they were caused by the cells being wet. Alas when I checked again it all resulted to bad contact between the cells ( R22 ) and the molex connector. Problem was solved by soldering the wires directly to the pins. Now I know this might look as an overkill but I assure you that these cell errors are really freightening at depth.

Joseph

RichClark

This may not be the best resolution, there's another thread on here somewhere suggesting that the wires should be crimped rather than soldered. Soldering adds a stress point which could cause the connect to become brittle and snap.

The posts are here and here

Cheers

Rich

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schford

A shed load of water cascading on your cells is detrimental to their health

Drmike

I used to get similar problems all the time. I solved it by selling my Rebreather and buying one that doesnt have sensors in a position where they are prone to getting wet from condensation sorry I cant be of any help, but its worth looking at the connectors as pointed out

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schford

The time i destroyed it - it was not condensation on the cells but condensation in the inhale counter lung getting past water trap and back onto the cells.

although I have noticed with long run times in warm water I do get condensation - something I had not noticed in cold UK water!