Rebreather Question

[tbone1004]

@wedivebc Have you thought about doing the O2 flush on your way from your 30ft to your 20ft stop? Basically guarantees that you'll see a 1.6 or slightly over for at least a second or two and then will stabilize at 1.4-1.6 on the 20ft stop?
Have heard this from several people that validate on the end of their dive since the cells are warm/wet and will save the frustration/o2 of trying to flush the loop several times to get that 1.6?

 

[northernone]

These questions are just fun easy questions for rebreather divers. I know these answers. I took the Tec 40 ccr course.

Am I understanding correctly you created a thread asking for answers to questions you already know the answers to? I'd be interested towards which purpose.

 

[Sidediver77]

Am I understanding correctly you created a thread asking for answers to questions you already know the answers to? I'd be interested towards which purpose.

I wanted to see what people had to say when I wrote these questions. Sometimes I second guess myself when I read something out of my materials and then I feel like I have to say something. I wanted to make sure that I wasn’t wrong. I want to thank everyone who replied back to my questions.

 

[1c3d1v3r]

If you calibrate the cell with air or O2 it is already a 2-point calibration. The other point is assumed 0mV at 0%.
If a computer/controller supports two calibration gases at the same time then it is a 3-point calibration.
0mV for 0% and two other gases like air and 100% O2. If they are not linear then you have to match a curve through all three points.
Are there any models with 3-point calibration support?
IMHO the third point should be used for linearity check only. A cell with non-linear curved response is bad.

 

[OceanEyes]

Am I understanding correctly you created a thread asking for answers to questions you already know the answers to? I'd be interested towards which purpose.

Like you @nothernone, I was a bit perplexed to read @Jordan D’s statement regarding already knowing the answers to his initial questions. The immediate reaction of my evil-half was to feel a bit put off as I’d bothered to reply with a brief but pertinent posting, as if I’d wasted a few minutes of my life.

Upon revisiting the thread this morning though, I noted that it has been viewed nearly 1,300 times, and there have been several clearly worded posts regarding cell calibration, behavior, and linearity, all vital concepts that are not always understood by many CCR divers, especially newer ones like the OP.

As an instructor, I presume that you are aware of the benefits of repetition, reinforcement, clarification, and practice in developing skills and building informed, capable divers. I’ve thus been soothed by the better angels of my often erratic nature, and am glad to have made my contribution as I presume that someone in addition to the OP will put it to good use.

 

[tbone1004]

@1c3d1v3r the Liberty is probably going to come out with 3-point support. It is the only unit out there that has a setting from the factory where you can actually pressurize the head, and get values up to 1.7 I believe. The linearity accuracy for me is less of a concern than the current limiting so while my Meg does 2-point calibration, since I don't use the unit much below 1.0, the accuracy down there doesn't really matter to me. Would much rather have two point at 1.0 and 1.6, or single point at 1.0

 

[joshk]

below 1.0, the accuracy down there doesn't really matter to me

You don't care about the accuracy for 45% of the workable range? What do you think happens during a diluent flush?

 

[tbone1004]

You don't care about the accuracy for 45% of the workable range? What do you think happens during a diluent flush?

I'm not saying that, but if I have to choose a 2-point calibration range and that range is .21 to 1.0, or 1.0 to 1.6, I'll choose the 1.0 to 1.6 every time. If I can get 3 point then even better.
Which example do you deem more risky? A displayed 1.6 being a 1.8 if you have a cell that is starting to get limited and has a shallower slope than below 1.0, or the unit reading accurately between 1.0 and 1.6 because that's where it was calibrated and a really low dil flush saying .4 when it should say .3?
I dive standard gases, so my dil will typically have a ppO2 of at least .6. I want it as accurate as possible obviously, but if I have to choose a range of accuracy, it's going to be my target ppO2's over my dil flush ppO2's every time.

 

[joshk]

I'm not saying that

But you literally did say that.

 

[joshk]

if I have to choose a range of accuracy, it's going to be my target ppO2's over my dil flush ppO2's every time.