Reading MV output from cells

***schford*** · 19th April 2006, 10:09

Back to this old cheastnut......

The thread on calibration really got me thinking about this....

I was taught to and always dbl check my mili volt readings when I dive - that way you learn the 'personality' of your cells and roughly what readings they should have at your usual set points.

Now the usual argument against is whats the point - no different to being calibrated etc etc

But what about in this scenario - where I was rushing the calibration for some reason forgot to disconnect my external o2 sensor and got it wrong which resulted in the PPo2 display being considerably lower than the actuall PPo2

As I always check my raw Mv and I know (roughly) what to expect - I would see way way higher readings than normal and could bail before (hopefully) taking a hit...

decoweenie · 19th April 2006, 10:29

Stuart,

Please correct me if I am wrong since I only had 1 controller with the mV feature, but it only lasted 6 dives before going "kaput". So I didn't get to play with it at all.

If your sensor is showing 10mV on air on surface, then should the loop PO2 be at 1.05 when you see 10mV at 40m (5ATA) ?

***Beanie*** · 19th April 2006, 10:32

Quote: (Originally Posted by decoweenie)

Stuart,

Please correct me if I am wrong since I only had 1 controller with the mV feature, but it only lasted 6 dives before going "kaput". So I didn't get to play with it at all.

If your sensor is showing 10mV on air on surface, then should the loop PO2 be at 1.05 when you see 10mV at 40m (5ATA) ?

er shouldn't it be .21?

mV are directly related to PPO2 are they not?

Gibbon · 19th April 2006, 10:35

Quote: (Originally Posted by decoweenie)

Stuart,

Please correct me if I am wrong since I only had 1 controller with the mV feature, but it only lasted 6 dives before going "kaput". So I didn't get to play with it at all.

If your sensor is showing 10mV on air on surface, then should the loop PO2 be at 1.05 when you see 10mV at 40m (5ATA) ?

Maybe you could explain the rest of the theory behind this modus operandi for cells... I am with Stuart and Beanie on this one.

decoweenie · 19th April 2006, 10:43

Quote: (Originally Posted by Beanie)

er shouldn't it be .21?

mV are directly related to PPO2 are they not?

If you measure your R22D on air, shouldn't it read ~10mV output ?

And I am guessing that the mV output shown on the Meg display is the same sensor voltage output.

AFAIK, that the reason there is a need for calibration to correlate the sensor output in mV to PO2 (i.e. 10 mV = 0.21 PO2) for display purpose. Otherwise, the display just show the direct reading from the sensor.

Am I off ?

***Beanie*** · 19th April 2006, 10:48

Quote: (Originally Posted by decoweenie)

If you measure your R22D on air, shouldn't it read ~10mV output ?

And I am guessing that the mV output shown on the Meg display is the same sensor voltage output.

yes well ish mine are 8.5-9 ish
but really what its measuring isn't air its the content of O2 in the air

Quote: (Originally Posted by decoweenie)

AFAIK, that the reason there is a need for calibration to correlate the sensor output in mV to PO2 (i.e. 10 mV = 0.21 PO2) for display purpose. Otherwise, the display just show the direct reading from the sensor.

Am I off ?

no its does but .21 PPO2 is 10mv whether at 0m of 200m

I would expect air to read as 50mv at 40m assuming linear cells operation

decoweenie · 19th April 2006, 10:59

Quote: (Originally Posted by Beanie)

but really what its measuring isn't air its the content of O2 in the air

Really ?

Quote:

I would expect air to read as 50mv at 40m assuming linear cells operation

That's what I was asking, got it now. Had a brain fart. Thanks!

Muzz · 19th April 2006, 11:38

Quote: (Originally Posted by Beanie)

yes well ish mine are 8.5-9 ish

I was taught to rplace the sensor once it hits 9mv. Too conservative?

***Beanie*** · 19th April 2006, 11:39

Quote: (Originally Posted by Muzz)

I was taught to rplace the sensor once it hits 9mv. Too conservative?

Pass mine where around 9 new

So long as they read over 1.6 bar, whihc mine do

dave t · 19th April 2006, 11:58

the point is the millivolt reading and the po2 display are the same thing the computer converts the milivolt reading to a po2 through the A to D converter. whatever the cell milivolt output is the po2 reading will be a direct equivelent, right or wrong.
What I mean is you cannot look at your po2 and then see a different milivolt output, they will be the same just displayed differently by the computer

teleydyne cells come out the factory with a milivolt range (in air) of 8 -11.5mv
usually you cannot tell when a cell is dying by measuring its milivolt output, it can maintain a healthy output but still be current limited to below your choosen setpoint

The cells in my vision are at 8.6 millivolts and have been that way since new, they are about 12 months old and two of them are current limited to 1.65bar

Dave

19th April 2006, 10:09	#1 (permalink)
*schford* RBW Founder Current Rebreather/s: Megalodon Sport Kiss Other Rebreather/s: Join Date: Jan 2005 Location: UK Posts: 3,564	Reading MV output from cells Back to this old cheastnut...... The thread on calibration really got me thinking about this.... I was taught to and always dbl check my mili volt readings when I dive - that way you learn the 'personality' of your cells and roughly what readings they should have at your usual set points. Now the usual argument against is whats the point - no different to being calibrated etc etc But what about in this scenario - where I was rushing the calibration for some reason forgot to disconnect my external o2 sensor and got it wrong which resulted in the PPo2 display being considerably lower than the actuall PPo2 As I always check my raw Mv and I know (roughly) what to expect - I would see way way higher readings than normal and could bail before (hopefully) taking a hit... __________________ Bailout and Kit Management account for Murphy's Law The only bad question is one you did not ask and later wish you had. Use of RBW is subject to the Rebreather World Terms & Conditions of Use
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19th April 2006, 10:29	#2 (permalink)
decoweenie Crash Test Dummy Current Rebreather/s: Other CCR Other Rebreather/s: Other CCR Join Date: Feb 2005 Location: Cairo Posts: 5,487	Re: Reading MV output from cells Stuart, Please correct me if I am wrong since I only had 1 controller with the mV feature, but it only lasted 6 dives before going "kaput". So I didn't get to play with it at all. If your sensor is showing 10mV on air on surface, then should the loop PO2 be at 1.05 when you see 10mV at 40m (5ATA) ?
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19th April 2006, 10:32	#3 (permalink)
*Beanie* Gallery Administrator Current Rebreather/s: Inspiration Classic Other Rebreather/s: Inspiration Vision Join Date: Jan 2005 Location: In da house! yeah baby! Posts: 3,311	Re: Reading MV output from cells Quote: (Originally Posted by decoweenie) Stuart, Please correct me if I am wrong since I only had 1 controller with the mV feature, but it only lasted 6 dives before going "kaput". So I didn't get to play with it at all. If your sensor is showing 10mV on air on surface, then should the loop PO2 be at 1.05 when you see 10mV at 40m (5ATA) ? er shouldn't it be .21? mV are directly related to PPO2 are they not? __________________ Beanie Gallery Admin & Library Assistant. www.outlawdivers.org.uk www.beandiving.co.uk www.beanengineering.co.uk
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19th April 2006, 10:35	#4 (permalink)
Gibbon Southern Monkey Current Rebreather/s: Megalodon Other Rebreather/s: Join Date: Aug 2005 Location: East Devon Posts: 224	Re: Reading MV output from cells Quote: (Originally Posted by decoweenie) Stuart, Please correct me if I am wrong since I only had 1 controller with the mV feature, but it only lasted 6 dives before going "kaput". So I didn't get to play with it at all. If your sensor is showing 10mV on air on surface, then should the loop PO2 be at 1.05 when you see 10mV at 40m (5ATA) ? Maybe you could explain the rest of the theory behind this modus operandi for cells... I am with Stuart and Beanie on this one.
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19th April 2006, 10:43	#5 (permalink)
decoweenie Crash Test Dummy Current Rebreather/s: Other CCR Other Rebreather/s: Other CCR Join Date: Feb 2005 Location: Cairo Posts: 5,487	Re: Reading MV output from cells Quote: (Originally Posted by Beanie) er shouldn't it be .21? mV are directly related to PPO2 are they not? If you measure your R22D on air, shouldn't it read ~10mV output ? And I am guessing that the mV output shown on the Meg display is the same sensor voltage output. AFAIK, that the reason there is a need for calibration to correlate the sensor output in mV to PO2 (i.e. 10 mV = 0.21 PO2) for display purpose. Otherwise, the display just show the direct reading from the sensor. Am I off ?
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19th April 2006, 10:48	#6 (permalink)
*Beanie* Gallery Administrator Current Rebreather/s: Inspiration Classic Other Rebreather/s: Inspiration Vision Join Date: Jan 2005 Location: In da house! yeah baby! Posts: 3,311	Re: Reading MV output from cells Quote: (Originally Posted by decoweenie) If you measure your R22D on air, shouldn't it read ~10mV output ? And I am guessing that the mV output shown on the Meg display is the same sensor voltage output. yes well ish mine are 8.5-9 ish but really what its measuring isn't air its the content of O2 in the air Quote: (Originally Posted by decoweenie) AFAIK, that the reason there is a need for calibration to correlate the sensor output in mV to PO2 (i.e. 10 mV = 0.21 PO2) for display purpose. Otherwise, the display just show the direct reading from the sensor. Am I off ? no its does but .21 PPO2 is 10mv whether at 0m of 200m I would expect air to read as 50mv at 40m assuming linear cells operation __________________ Beanie Gallery Admin & Library Assistant. www.outlawdivers.org.uk www.beandiving.co.uk www.beanengineering.co.uk
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19th April 2006, 10:59	#7 (permalink)
decoweenie Crash Test Dummy Current Rebreather/s: Other CCR Other Rebreather/s: Other CCR Join Date: Feb 2005 Location: Cairo Posts: 5,487	Re: Reading MV output from cells Quote: (Originally Posted by Beanie) but really what its measuring isn't air its the content of O2 in the air Really ? Quote: I would expect air to read as 50mv at 40m assuming linear cells operation That's what I was asking, got it now. Had a brain fart. Thanks!
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19th April 2006, 11:38	#8 (permalink)
Muzz New Member Current Rebreather/s: Megalodon Optima Other Rebreather/s: Join Date: Mar 2005 Location: Pompano Beach FL Posts: 146	Re: Reading MV output from cells Quote: (Originally Posted by Beanie) yes well ish mine are 8.5-9 ish I was taught to rplace the sensor once it hits 9mv. Too conservative?
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19th April 2006, 11:39	#9 (permalink)
*Beanie* Gallery Administrator Current Rebreather/s: Inspiration Classic Other Rebreather/s: Inspiration Vision Join Date: Jan 2005 Location: In da house! yeah baby! Posts: 3,311	Re: Reading MV output from cells Quote: (Originally Posted by Muzz) I was taught to rplace the sensor once it hits 9mv. Too conservative? Pass mine where around 9 new So long as they read over 1.6 bar, whihc mine do __________________ Beanie Gallery Admin & Library Assistant. www.outlawdivers.org.uk www.beandiving.co.uk www.beanengineering.co.uk
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19th April 2006, 11:58	#10 (permalink)
dave t RBW Member Current Rebreather/s: Inspiration Classic Inspiration Vision Evolution Sport Kiss Classic Kiss Dolphin Ray Azimuth Home Build Other Rebreather/s: Dolphin Ray Azimuth Home Build Join Date: May 2005 Location: UK Posts: 662	Re: Reading MV output from cells the point is the millivolt reading and the po2 display are the same thing the computer converts the milivolt reading to a po2 through the A to D converter. whatever the cell milivolt output is the po2 reading will be a direct equivelent, right or wrong. What I mean is you cannot look at your po2 and then see a different milivolt output, they will be the same just displayed differently by the computer teleydyne cells come out the factory with a milivolt range (in air) of 8 -11.5mv usually you cannot tell when a cell is dying by measuring its milivolt output, it can maintain a healthy output but still be current limited to below your choosen setpoint The cells in my vision are at 8.6 millivolts and have been that way since new, they are about 12 months old and two of them are current limited to 1.65bar Dave
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