Question O2 sensor calibration

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This document has been debated on this forum before.

However all cells are non-linear at some level ... Take all the cockamaimy schemes discussed on this post and run them on this set of cells and tell me how your stategy goes.

View attachment 907795

source: Understanding Oxygen Cells

I agree with you. For me, they need to be linear in the range I will be using them which is 0.5-1.6. I am happy to dive with sensors that flatten out past 2.0 like sensor 1 in your chart but would replace sensors 2 and 3.
 
Mods, please move this to Basic Scuba.


To check cell performance at any time, use your computer to select available gas that will produce PPO2 close to or equal to the target PPO2. Note the expected PPO2 and flush the loop. If you hit the expected target, your cells are linear up to that PPO2.

If cells read lower than expected, select the next leaner mix and try again. Determine the PPO2 that cells can read while staying linear and use that PPO2 to finish the dive on the loop, if you want to. Exercise common sense, if your cells are linear only to 0.5, staying on the loop is probably not the best idea.

If cells read higher than expected, there is something off. Select the best emergency procedure for the conditions and turn the dive.

This is the best procedure to figure out what is wrong once you see something is off (see the anecdote from a few weeks ago in a previous post). However I don’t do this as a routine to preserve dilout gas (a proper full flush at significant depth burns not a huge but a noticeable amount of gas) and because it takes a minute to do (again eating into short TTS in serious dives).
 
@LFMarm, first of all, I am sorry. Somehow my unedited phrase referring to "basic scuba" got into the final draft of the message. It was uncalled for, even in my sarcastic mood.

Secondly, there is a lot to unpack here based on some of your recent replies.

Whether you check / calibrate daily depends on your personal preference. Many divers calibrate only once per trip. Some manufactures suggest a list of events that should lead to calibration, e.g., sensor replacement, new scrubber pour, change in altitude, change in reference gas. Exercise your best judgement.

Reference gas switches and dill flushes should not take much time or effort. If takes more than 30 seconds to select the best gas to check cell linearity and loop flush, you need to practice more. Your gasses (and your team gasses) should be in your computers. Tanks must have easily visible to you MOD stickers. All mechanical and computer work must be second nature. Gas supplies should always be adequate and on a conservative side, e.g., NSS CDS recommends 1.5x of estimated bailout needs.

If your computers or cells exhibit weird behavior on descend, troubleshoot to your best ability and then turn in the dive. It is unlikely that things will fix themselves or get better at depth. Do not set your controller to 1.5 set point, change cables, etc. There are many other procedures that can get you back safely.
 
No hard feelings — sensor calibration is definitely one of the basics for closed circuit.

I do all as you say — all hoses are marked with MOD and doing a flush is probably less then 1 minute. However that may be +10 mins of TTS if done at the bottom. This is why I will start doing the quicker tests by manually adding a little of O2 unless I detect a problem in which case I would definitely test with a dil flush and probably also start ascending.
 

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