O2 sensor failures

doug allen

I searched...(not extensively mind ya'll)...this site about this subject and nothing came up immediately....but I do have a question about O2 sensor life.

Anyway....I've had to replace 4 O2 sensors in my rebreather since July 07....seems everytime I fire this sucker up on dive day I get a "Fail" error on one of the three sensors on the Hammerhead.....3 of them have been replaced under warranty...the other one was a spare that I got with the unit....

Has anyone else experienced early failure of O2 sensors this frequently?

ScubaDadMiami

Sensors tend to be similar if they came from the same batch. If you bought all four around the same time, and if they are all from the same batch, the odds increase that more of them will fail if the first fails.

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Howard Packer
IANTD CCR Instructor
Miami Beach, Florida
CCRDiveTraining.com

jradomski

Doug,
If you are using the HH, and using AI cells I suggest you choose the MHD version not the MD version as the MHD has a higher guaranteed output.. I find that with the AI cells if they last more than a few weeks they will last for a signifcant time (very little decay), otehrwise they fail quite quickly - many times reading 0mv..

If using Teledyne cells you want cells that are starting off around 9mv since they tend to decay over their life...

I also find that people that have problems with calibration repeatedly in many cases are not doing adequate o2 flushes.. You can try and calibrate with the cells in a baggie and flowing oxygen at a constant low rate..

If you are calibrating at any altitude make sure you select altitude calibration (new handsets only)

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Joe Radomski
CCR Trimix Instructor Trainer
ANDI Instructor Trainer Director #10

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

diverreb

Any chance you may have an issue with the wiring harness? Have you tried swapping it out? Early on I had a cell reading failure. Turned out to be a bad connection in the harness......Maybe your having an intermittent issue there. Just a thought.

Richie

Mark Chase

When I baught cells for the HH I had to specifie thay had a minimum 9mv output in air. AP had the test output on the bags and seemed happy to do this for me.

I would soak the cells for 24hours in pure 02 to wake them up, then air them for a while before initial calibration.

Thats about the best you can do. If that doesent work its dodgy cells or a loom problem.

Remember to use Biox or Pure Gold on the cell plug conectors when swapping cells.

ATB

Mark



ATB

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sfldiver

A few months ago, while taking my initial Optima CCR Certification Class, I had all three sensors fail the night before a dive with my instructor. The next mornint before the dive, I met the instructor at the shop and he attempted again flush with O2 and calibrate, but no luck, "Calibaration Failed" on all three sensor readouts. That morning, we had to replace all three sensors with new ones, apparently it was the result of a bad batch of cells. Since then, I have already replaced one of them again and about to replace another one, because they are not consistently holding the calibration.

That experience sure made it easy to decide whether to fork out the money for the forth cell on my VR3 - My experience has shown those cells to be so unreliable that I wish I had five cells on my unit.

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AD_ward9

I have seen bad batches from both the main suppliers, which can easily account for your problem, but wonder if it is due to shock.

O2 sensors are very fragile. Drop a sensor onto a block of wood from 5ft ten times and it most will not work afterwards. They loose electrolyte, which makes them drift high as well as low. If you see a sensor with a high output, yet the load resistor inside is still intact, then shock is the cause of the failure.

Try pack your Rebreather on its front, not its back. The front has the CLs to protect the electronics and sensors from shock. The shock on RIBs and boats can be very high: look how how RIBs are so good at destroying general SCUBA kit.

Cheers

Alex
'

bajaecotours

What exactly is the failure: bad reading, leaking membrane or other? I ask because there seem to be many types failures. I know if using teledyne, they had problems with their sensors and replaced all of mine due to the fact that they were leaking therefore giving off poor readings. They then changed their entire system of manufacture from cast molded bodies to machined bodies. Has been a HUGE problem for me in that I've replaced 9 sensors in a year. The new ones seem to be ok at the moment.

I'll post on this more when I find the Teledyne failure report so everyone can be clear on what exactly had happened and what to look for. I have a copy of the report some place and I'll dig it up and post.