Megalodon Calibration Procedures

Drmike · 6th April 2006, 09:01

Is there anything about the way a Meg is calibrated that would explain certain possible problems through poorly done calibration?

This is not meant to start a flame war or speculation - just an honest search for information.

Regards
Mike

JonnyB · 6th April 2006, 10:55

Quote: (Originally Posted by Drmike)

Is there anything about the way a Meg is calibrated that would explain certain possible problems through poorly done calibration?

This is not meant to start a flame war or speculation - just an honest search for information.

Regards
Mike

Hi Mike, i can see a problem with the calibration of the Meg, but then you as a diver need to either screw up or you dont really know your original gas.
If you have the APECS 2 electronics you can choose the purity of the O2 and if you set it to lets say 96% and you have 99% at depth that will give you wrong calibration... If i am not wrong that will contain higher pO2 that the display will show...

/Jonny

Drmike · 6th April 2006, 11:05

Quote: (Originally Posted by JonnyB)

Hi Mike, i can see a problem with the calibration of the Meg, but then you as a diver need to either screw up or you dont really know your original gas.
If you have the APECS 2 electronics you can choose the purity of the O2 and if you set it to lets say 96% and you have 99% at depth that will give you wrong calibration... If i am not wrong that will contain higher pO2 that the display will show...

/Jonny

Sure, same as the inspiration.

Is the Meg dual point calibration?

Could this be leading to error if there is residual O2 in the loop when the air cal is done?

Or could it be just too hard to get true 100% in the loop?

I read several posts where people are having problems calibrating correctly
http://www.rebreatherworld.com/megal...t=expected+po2

rogeringebo · 6th April 2006, 11:22

You measure against air (at ambient preasure)and if you have the cal-kit you dont involve the hoses(loop)at all.....just blow O2 throught the very head of the machine...let it blow trough till you get stable readings (for me about 4 minutes) and then hit cal..

Drmike · 6th April 2006, 11:25

Quote: (Originally Posted by rogeringebo)

You measure against air (at ambient preasure)and if you have the cal-kit you dont involve the hoses(loop)at all.....just blow O2 throught the very head of the machine

Is the measurement against air done with the lid off?
Could the use of a cal kit on an older Meg result in over pressure (above atmospheric) O2 when calibrating against 100%?

rogeringebo · 6th April 2006, 11:30

Hi Mike
Yes,this you do before mounting the head in the cannister...first check air(while holding the head in your hands without hoses or anything) then connect cal-kit and start varifying O2 reading.....the mv reading will go up to 40-50mv andv stay there....when stable for while you hit cal...

rogeringebo · 6th April 2006, 11:31

There should be a tread and photos on the Meg-forum on how to use the cal-kit

***jradomski*** · 6th April 2006, 11:34

Quote: (Originally Posted by rogeringebo)

You measure against air (at ambient preasure)and if you have the cal-kit you dont involve the hoses(loop)at all.....just blow O2 throught the very head of the machine...let it blow trough till you get stable readings (for me about 4 minutes) and then hit cal..

I see several potential problems with calibrating the meg.. I verified several of these while I was at the factory..

If the "air" present in the head is greater than normal it screws up calibration..

The official meg cal kit also can cause a po2 reading lower tha true, it can easily screwit up by several percent..

The way its taught has some flaws.. when I was at the factory, everyone was told to flow oxygen using this cal kit and it calibrate when the oxygen alalyzer read what the gas was analyzed at..

This is a BIG potential for error (but not in all cases).. HOW big the error is depends on the meter (how restricted the outlet and hose is) and how much flow is actually being passed through the head.. The higher the flow the higher the back pressure..

I purposedly tried as many screw ups as I could think of, some produced miniscule errors, some produced large errors.

Look at my article on "accurate po2 calibration", This is the crux of the problem..

I agree with the concept, but before calibrating IT is absolutely necessary to disconnect the analyzer and let gas flow freely..

How bad or good the cal is can be verified pretty easily.. Do the cal as was recommended.. you should see something like a .98/.99 now disconnect the meter, the PO2 WILL drop if there is any back pressure... if it was calibrated correctly it wouldn't

This means there is back pressure and the chamber is NOT at ambient pressure.. At altitude this will get worse..

Drmike · 6th April 2006, 11:43

As you rightly state If there is any amount of back pressure when you calibrate you will calibrate high.

Does the Meg also assume a reduced ppo2 in the loop at calibration like some units? (Some units do/used to assume say 98% when you hit cal as they assume a non complete flush)

If this is the case the two combied could have quite an effect I should imagine

DonalWalsh · 6th April 2006, 11:45

Thanks Joe thats very informative especially for the less technical among us.

If I understand you correctly we'd be best connecting the cal kit (for the o2 part of calibration) as usual but leaving thethe analyser end free, flowing o2 throught the head for a few minutes until the cells stablise and THEN connect the analyser ?

6th April 2006, 09:01	#1 (permalink)
Drmike RBW Member Current Rebreather/s: MK 15.X Ouroboros Other CCR Home Build Other Rebreather/s: Inspiration Classic Other CCR Home Build Join Date: Feb 2005 Posts: 3,378	Megalodon Calibration Procedures Is there anything about the way a Meg is calibrated that would explain certain possible problems through poorly done calibration? This is not meant to start a flame war or speculation - just an honest search for information. Regards Mike __________________ Cave diving is a sport Wreck diving is a sport Diving in general is a sport 'Rebreather diving' is not a sport its the delusional obsession with a highly dangerous and often inappropriate piece of equipment Last edited by ROB DAVIE : 7th April 2006 at 03:01.
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6th April 2006, 10:55	#2 (permalink)
JonnyB Johnny The Hatch Current Rebreather/s: MK 15.X Titan Other CCR Other SCR Home Build Other Rebreather/s: Not Bought Yet Inspiration Classic Megalodon Sport Kiss Classic Kiss Other CCR Other SCR Home Build Join Date: Jan 2005 Location: Sweden (Stockholm)/Cyprus(Ayia Napa) Posts: 991	Megalodon Calibration Procedures Quote: (Originally Posted by Drmike) Is there anything about the way a Meg is calibrated that would explain certain possible problems through poorly done calibration? This is not meant to start a flame war or speculation - just an honest search for information. Regards Mike Hi Mike, i can see a problem with the calibration of the Meg, but then you as a diver need to either screw up or you dont really know your original gas. If you have the APECS 2 electronics you can choose the purity of the O2 and if you set it to lets say 96% and you have 99% at depth that will give you wrong calibration... If i am not wrong that will contain higher pO2 that the display will show... /Jonny __________________ A quote from Crazyduck - In remembering our own Rob Davies. "Outbound flight 777 heavy you are cleared for flight Due west into that warm red Texas sunset You have angels on your wings and divers memories on your six." Rest In Peace http://www.divetekcyprus.com http://www.diveccr.com Last edited by ROB DAVIE : 7th April 2006 at 03:35.
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6th April 2006, 11:05	#3 (permalink)
Drmike RBW Member Current Rebreather/s: MK 15.X Ouroboros Other CCR Home Build Other Rebreather/s: Inspiration Classic Other CCR Home Build Join Date: Feb 2005 Posts: 3,378	Megalodon Calibration Procedures Quote: (Originally Posted by JonnyB) Hi Mike, i can see a problem with the calibration of the Meg, but then you as a diver need to either screw up or you dont really know your original gas. If you have the APECS 2 electronics you can choose the purity of the O2 and if you set it to lets say 96% and you have 99% at depth that will give you wrong calibration... If i am not wrong that will contain higher pO2 that the display will show... /Jonny Sure, same as the inspiration. Is the Meg dual point calibration? Could this be leading to error if there is residual O2 in the loop when the air cal is done? Or could it be just too hard to get true 100% in the loop? I read several posts where people are having problems calibrating correctly http://www.rebreatherworld.com/megal...t=expected+po2 __________________ Cave diving is a sport Wreck diving is a sport Diving in general is a sport 'Rebreather diving' is not a sport its the delusional obsession with a highly dangerous and often inappropriate piece of equipment Last edited by ROB DAVIE : 7th April 2006 at 03:35.
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6th April 2006, 11:22	#4 (permalink)
rogeringebo Life starts at 100 Current Rebreather/s: Pelagian Other Rebreather/s: Megalodon Classic Kiss Pelagian Join Date: Sep 2005 Location: Stockholm Sweden Posts: 739	Megalodon Calibration Procedures You measure against air (at ambient preasure)and if you have the cal-kit you dont involve the hoses(loop)at all.....just blow O2 throught the very head of the machine...let it blow trough till you get stable readings (for me about 4 minutes) and then hit cal.. __________________ Life starts at 100 Last edited by ROB DAVIE : 7th April 2006 at 03:36.
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6th April 2006, 11:25	#5 (permalink)
Drmike RBW Member Current Rebreather/s: MK 15.X Ouroboros Other CCR Home Build Other Rebreather/s: Inspiration Classic Other CCR Home Build Join Date: Feb 2005 Posts: 3,378	Megalodon Calibration Procedures Quote: (Originally Posted by rogeringebo) You measure against air (at ambient preasure)and if you have the cal-kit you dont involve the hoses(loop)at all.....just blow O2 throught the very head of the machine Is the measurement against air done with the lid off? Could the use of a cal kit on an older Meg result in over pressure (above atmospheric) O2 when calibrating against 100%? __________________ Cave diving is a sport Wreck diving is a sport Diving in general is a sport 'Rebreather diving' is not a sport its the delusional obsession with a highly dangerous and often inappropriate piece of equipment Last edited by ROB DAVIE : 7th April 2006 at 03:36.
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6th April 2006, 11:30	#6 (permalink)
rogeringebo Life starts at 100 Current Rebreather/s: Pelagian Other Rebreather/s: Megalodon Classic Kiss Pelagian Join Date: Sep 2005 Location: Stockholm Sweden Posts: 739	Megalodon Calibration Procedures Hi Mike Yes,this you do before mounting the head in the cannister...first check air(while holding the head in your hands without hoses or anything) then connect cal-kit and start varifying O2 reading.....the mv reading will go up to 40-50mv andv stay there....when stable for while you hit cal... __________________ Life starts at 100 Last edited by ROB DAVIE : 7th April 2006 at 03:36.
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6th April 2006, 11:31	#7 (permalink)
rogeringebo Life starts at 100 Current Rebreather/s: Pelagian Other Rebreather/s: Megalodon Classic Kiss Pelagian Join Date: Sep 2005 Location: Stockholm Sweden Posts: 739	Megalodon Calibration Procedures There should be a tread and photos on the Meg-forum on how to use the cal-kit __________________ Life starts at 100 Last edited by ROB DAVIE : 7th April 2006 at 03:37.
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6th April 2006, 11:34	#8 (permalink)
*jradomski* Moderator Current Rebreather/s: Inspiration Classic Sport Kiss Optima rEvo Other CCR Other Rebreather/s: Inspiration Vision Evolution Megalodon Classic Kiss rEvo Other CCR Join Date: Mar 2005 Location: "Da" Bronx Posts: 3,113	Megalodon Calibration Procedures Quote: (Originally Posted by rogeringebo) You measure against air (at ambient preasure)and if you have the cal-kit you dont involve the hoses(loop)at all.....just blow O2 throught the very head of the machine...let it blow trough till you get stable readings (for me about 4 minutes) and then hit cal.. I see several potential problems with calibrating the meg.. I verified several of these while I was at the factory.. If the "air" present in the head is greater than normal it screws up calibration.. The official meg cal kit also can cause a po2 reading lower tha true, it can easily screwit up by several percent.. The way its taught has some flaws.. when I was at the factory, everyone was told to flow oxygen using this cal kit and it calibrate when the oxygen alalyzer read what the gas was analyzed at.. This is a BIG potential for error (but not in all cases).. HOW big the error is depends on the meter (how restricted the outlet and hose is) and how much flow is actually being passed through the head.. The higher the flow the higher the back pressure.. I purposedly tried as many screw ups as I could think of, some produced miniscule errors, some produced large errors. Look at my article on "accurate po2 calibration", This is the crux of the problem.. I agree with the concept, but before calibrating IT is absolutely necessary to disconnect the analyzer and let gas flow freely.. How bad or good the cal is can be verified pretty easily.. Do the cal as was recommended.. you should see something like a .98/.99 now disconnect the meter, the PO2 WILL drop if there is any back pressure... if it was calibrated correctly it wouldn't This means there is back pressure and the chamber is NOT at ambient pressure.. At altitude this will get worse.. __________________ 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. Last edited by jradomski : 21st May 2006 at 15:31. Reason: spelling and grammar
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6th April 2006, 11:43	#9 (permalink)
Drmike RBW Member Current Rebreather/s: MK 15.X Ouroboros Other CCR Home Build Other Rebreather/s: Inspiration Classic Other CCR Home Build Join Date: Feb 2005 Posts: 3,378	Megalodon Calibration Procedures As you rightly state If there is any amount of back pressure when you calibrate you will calibrate high. Does the Meg also assume a reduced ppo2 in the loop at calibration like some units? (Some units do/used to assume say 98% when you hit cal as they assume a non complete flush) If this is the case the two combied could have quite an effect I should imagine __________________ Cave diving is a sport Wreck diving is a sport Diving in general is a sport 'Rebreather diving' is not a sport its the delusional obsession with a highly dangerous and often inappropriate piece of equipment Last edited by ROB DAVIE : 7th April 2006 at 03:38.
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6th April 2006, 11:45	#10 (permalink)
DonalWalsh Third Class Snorkeller Current Rebreather/s: Megalodon Other Rebreather/s: Evolution Join Date: Nov 2005 Location: Moving to London in Sept.....which way to the South Coast?? Posts: 133	Megalodon Calibration Procedures Thanks Joe thats very informative especially for the less technical among us. If I understand you correctly we'd be best connecting the cal kit (for the o2 part of calibration) as usual but leaving thethe analyser end free, flowing o2 throught the head for a few minutes until the cells stablise and THEN connect the analyser ? Last edited by ROB DAVIE : 7th April 2006 at 03:38.
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