Capt Jim Wyatt
Hanging at the 10 Foot Stop
Staff member
ScubaBoard Business Sponsor
ScubaBoard Sponsor
ScubaBoard Supporter
Scuba Instructor
Divemaster
Answer the poll please.
Were you taught this math in your entry level CCR class?
- Thread starter Capt Jim Wyatt
- Start date
Please register or login
Welcome to ScubaBoard, the world's largest scuba diving community. Registration is not required to read the forums, but we encourage you to join. Joining has its benefits and enables you to participate in the discussions.
Benefits of registering include
- Ability to post and comment on topics and discussions.
- A Free photo gallery to share your dive photos with the world.
- You can make this box go away
That was foundational. I almost voted yes but didn't understand it because I've been realizing it's value more and more.
I know it's not taught in some classes because I ask every rebreather diver I talk about it to gain better understanding and application. Some have no memory of this whatsoever...
I know it's not taught in some classes because I ask every rebreather diver I talk about it to gain better understanding and application. Some have no memory of this whatsoever...
I disagree with the mv range in pure O2.
If the range on 8-13mv is used the range of mv in O2 should be 38 - 62mv (38.02 to 61.88 for you pedantic types)
Not the actual voltage just the fact that no matter what the air value is the O2 value will be 4.76 X that value.
8 X 4.76 is 38.02 not 43 as shown on Jim's wetnotes.
Being a math nerd, I had noticed that as well. I just figured I didn't know enough about the subject.
It seems like doing these calculations for you would be a feature someone would add to a CCR dive computer.
I mean, if you calibrate at 0.21 ATA, then check it with 1.0, the computer could have an alternate screen to go to to show you calculated versus metered mV values and also show linear deviation. Ditto for checking at 1.6 ATA.
Or something like that. Bottom line: It's a straightforward process and simple arithmetic (or so it seems), so why not have your computer do it for you?
Last edited:
Due to the potential for a diver to fail at getting a good O2 flush before calibration I have my students calculate the expected mv in O2 based on the air mv reading. That way they have a sanity check before pushing the button to commit to the calibration.
I was taught this in my basic MOD 1, but Jim's arithmetic error in his post is exactly why I don't teach it for underwater use to a new CCR diver. It's too easy to make a math mistake, and look for some value that ends up being erroneous.
With modern CCR electronics, there is absolutely no reason to do this underwater, as with a few button pushes, you can get your FO2 for your given depth and easily validate your cells off this value and a dil flush.
Dave, to expand upon your methods, and avoid the poor O2 flushes - I teach to do the o2 flush, calibrate, and then either flush with your dil, or expose to ambient air. If the cells don't show .21 afterwards, then you didn't get a good flush.
With modern CCR electronics, there is absolutely no reason to do this underwater, as with a few button pushes, you can get your FO2 for your given depth and easily validate your cells off this value and a dil flush.
Dave, to expand upon your methods, and avoid the poor O2 flushes - I teach to do the o2 flush, calibrate, and then either flush with your dil, or expose to ambient air. If the cells don't show .21 afterwards, then you didn't get a good flush.
OP
Capt Jim Wyatt
Hanging at the 10 Foot Stop
Staff member
ScubaBoard Business Sponsor
ScubaBoard Sponsor
ScubaBoard Supporter
Scuba Instructor
Divemaster
The numbers 8-13 / 43-62 are numbers I memorized many years ago, and I do not recall doing the proofs as I should have. Thus the egg.
I now use R-22 cells and the output in air is 7-13.
In any event this is the way to proof and predict cell output mV in cells, but do the math correctly.
Similar threads
