CCR Liberty: Pre-dive procedures Part 3 - Calibration
- Thread starter lof
- Start date
diverklondike
Member
Cool!
The video is there and is playing back fine.
lof
Member
Or you can go to vimeo directly
https://vimeo.com/121637550
I created a channel there to keep them all together
https://vimeo.com/channels/886697
https://vimeo.com/121637550
I created a channel there to keep them all together
https://vimeo.com/channels/886697
erikradstrom
Deep Pursuit 001
I have been reading about this rebreather and found it interesting until now. This is a deal breaker for me.
To many parts and to complicated to calibrate. The risk of doing wrong or people skip calibration is big when you have to do like this.
Why don´t you calibrate by opening the solenoid like AP or JJ?
To many parts and to complicated to calibrate. The risk of doing wrong or people skip calibration is big when you have to do like this.
Why don´t you calibrate by opening the solenoid like AP or JJ?
That's complicated? Its 2.5 minutes and requires an isolator to keep the O2 flow on the sensors. Seems pretty simple to me.
My concern would be is it doing a two point air and O2 calibration? What if the gas in the head to start with is not air to start, e.g. some O2 got injected before calibration started.
Calibrating to "O2" which is as little as 20% oxygen doesn't make any sense to me. So I'm wondering if its actually a 1 point calibration.
lof
Member
Of course you can calibrate using the solenoid. The cal tool helps you save the O2, but it is not required. I do not see the cal procedure any more complicated than on any other unit.
Go to menu
Select calibration
Fill loop with oxygen or use Calibration kit
Wait for values to stabilize
Confirm calibration.
I have shown in video additional steps of being able to calibrate at different O2 concentrations.
That might have made it look more complex.
It is a 1 point calibration. Only you can choose the O2 concentration you calibrate at. Obviously the recommended O2 concentration for cal is 99.5%
You must purge entire system with known gas before starting the calibration (Cal kit helps with that), that is why the system does not initiate the calibration until the sensor mV readings have stabilized.
If you are going to do a 1 point calibration (which I think is fine), I don't think the unit should be allowing you to calibrate that 1 point to air. Being so far below the actual pp2 in use and without any control on the "tail" of the calibration curve that's pretty sketchy IMO. Off the top of my head 80% is the minimum calibration point you'd want.
lof
Member
The unit is not your "nanny"
, it will allow you to calibrate at any O2 concentration between 20% and 100%. It is up to you to determine what is appropriate for your mission. For example you might be at the 5th siphon and need to get new cells from your buddy with only air left. It might be better to be able to calibrate at all than use uncalibrated cells.Of course the recommended procedure is to calibrate as close to your operating PPO2 as possible, thus the default cal value is 99.5%
The unit is not your "nanny"
Sounds like something from Sanctum.
How is someone supposed to dive a CCR without some sort of hyperoxic mix around? If you don't have something greater than air you are just diving as an SCR anyway. Seems kind of silly to calibrate to air "cause you don't have any O2 around" then dive a CCR using something richer than air as an O2 source.
I don't know what cells you are using, but you should work up the error bars around a ppO2 of 1.2 when calibrating at a ppO2 of 0.209. Would need a variety of cells and ages, but it might not be as bad as I imagine.
diverklondike
Member
It's actually pretty simple from my point of view in the situation that Jakub described. If I have fixed resources including the amount of O2 that I have, it may be preferable to calibrate using air or some other known gas that I have a greater quantity of...
Sounds like something from Sanctum.
How is someone supposed to dive a CCR without some sort of hyperoxic mix around? If you don't have something greater than air you are just diving as an SCR anyway. Seems kind of silly to calibrate to air "cause you don't have any O2 around" then dive a CCR using something richer than air as an O2 source.
I don't know what cells you are using, but you should work up the error bars around a ppO2 of 1.2 when calibrating at a ppO2 of 0.209. Would need a variety of cells and ages, but it might not be as bad as I imagine.
Based on the time in the video and the use of a standard looking 2l/min flow restrictor, calibration appears to take 3 or 4L of O2. Perhaps 5mins worth of bottom time.
I imagine the error bars on a 1 point air calibration start small get much bigger as the cell ages. I'm curious what they might be though.
I imagine the error bars on a 1 point air calibration start small get much bigger as the cell ages. I'm curious what they might be though.
lof
Member
The example I gave was an extreme one, where you are stuck in the cave with no resources, and you need to get out. The unit will not prevent you from doing that and will give you all possible resources to get out. ( one of them being able to dive it even when no handsets or HUDs are connected - it will default to last PPO2 setpoints)
The more important takeaway is that YOU are responsible for calibrating the unit in a way that is appropriate for your dive. Why should the not "unit be allowing you to calibrate that 1 point to air"? It is just a machine, "the final decision is up to you"
http://ccrliberty.com/technical/decision-is-up-to-you/
The more important takeaway is that YOU are responsible for calibrating the unit in a way that is appropriate for your dive. Why should the not "unit be allowing you to calibrate that 1 point to air"? It is just a machine, "the final decision is up to you"
http://ccrliberty.com/technical/decision-is-up-to-you/
1) Why does the unit need to be recalibrated in a cave in the first place? Does it not retain calibration data from day to day or is this a battery replacement situation?
2) Because in non-life support analytical instrument applications (like pH, dissolved oxygen, free chlorine, GC/MS and ICP/MS analysis etc) we don't calibrate that far away from the expected measurement point. In fact calibration is expected to bracket the expected concentrations and if it doesn't, the analyte of interest is diluted or pre-concentrated until its concentration is within the calibration range of the instrument. That's for non-life support chemistry, nevermind life support applications.
3) You haven't presented any actual data that supports your position that a used liberty cell, using a 1 point calibration of 0.209 (or possibly less if at altitude) is "good enough" in the 1 to 1.3 range (or any other plausible setpoint). That this is intended for emergencies is all well and good, but why not present the statistical error bars on the 1 point 0.209 calibration technique before leaving it up to a diver (under stress in your hypothetical cave) who is likely to not be an analytically qualified person to make a decision under the best of circumstances?
4) I'm willing to accept this as a valid emergency technique that's "good enough" but I need some actual data to support it. So far its just faith without evidence of efficacy.
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diverklondike
Member
To your questions.....
1) You did not fully read the posts... The reason for recal was that a cell needed to be replaced...
2) No one is forcing you to have to do this... The key is that it's designed purposefully to allow you to calibrate in air or anything between as an option..
3) I think your missing the point... This is about providing options....
4) I am not saying that this capability is a must have but.... The design preference is to allow you an option.. No more no less....
1) You did not fully read the posts... The reason for recal was that a cell needed to be replaced...
2) No one is forcing you to have to do this... The key is that it's designed purposefully to allow you to calibrate in air or anything between as an option..
3) I think your missing the point... This is about providing options....
4) I am not saying that this capability is a must have but.... The design preference is to allow you an option.. No more no less....
lof
Member
I work with lab instrumentation day in and day out so I understand your calibration concerns. As Mark listed above, you seem to be missing the point:
It is about the options. You do not need to carry a spare cell, you might borrow one from your buddy in the emergency. It is better to have some calibration, than none. That is the OPTION.
Nobody is advocating that you do that (but you can) . The unit defaults to 99.5% O2 and that is where you should calibrate. It will even sense atmospheric pressure so you do not need to make any adjustments for calibrations at higher elevations.
The unit works exactly as advertised.
It holds calibration just fine for days and weeks.
It is about the options. You do not need to carry a spare cell, you might borrow one from your buddy in the emergency. It is better to have some calibration, than none. That is the OPTION.
Nobody is advocating that you do that (but you can) . The unit defaults to 99.5% O2 and that is where you should calibrate. It will even sense atmospheric pressure so you do not need to make any adjustments for calibrations at higher elevations.
The unit works exactly as advertised.
It holds calibration just fine for days and weeks.