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dave t · 21st January 2008, 15:12

Quote: (Originally Posted by Gilles)

Linear response means that for a given input, an output responds proportionally via a constant. This contant depends on the nominal voltage in air. For e.g., your nominal air mV(MVair) is 8.1

lets say your O2 purity is 96%, thus the mV reading of 96% O2 at 1 ATA is

0.96/0.209 x 8.1 = 37.2 mV.

If you had a cell checker and you used the same purity to 2 ATA then

2 x 0.96/0.209 x 8.1 = 74.4 mV

Cells are not perfectly linear however. Often they go above this theoretical value and so far I consider this a sign of a healthy cell. If the same starts to go below the theoretical value at 1 ATA, then I consider this a sign of wear and current limitation and I'll start scrutinizing it more in water.

You can do this without a mV display, but it is more hassle as you have to make contact across two small leads inside your head with a potentiometer.

I attach a mV table for your convenience.

Hope this helps.

H

Ok thanks for the explanation but all that does is show you are good at maths

A cells output is in milivolts, the computer or controller converts it to a po2 reading, so if you take a reading and youir maths dont add up how do you know where the error is? is it the A-D converter or is the o2 content not what you think it is!

sorry but in realtime I cant see any value in that, and anyway what we should be worrying about is current limiting, a much more hazardous situation in my humble opinion.

best

Dave

21st January 2008, 15:12	#14 (permalink)
dave t Custom Title Allowed! 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: 654	Re: MV reading on cell Quote: (Originally Posted by Gilles) Linear response means that for a given input, an output responds proportionally via a constant. This contant depends on the nominal voltage in air. For e.g., your nominal air mV(MVair) is 8.1 lets say your O2 purity is 96%, thus the mV reading of 96% O2 at 1 ATA is 0.96/0.209 x 8.1 = 37.2 mV. If you had a cell checker and you used the same purity to 2 ATA then 2 x 0.96/0.209 x 8.1 = 74.4 mV Cells are not perfectly linear however. Often they go above this theoretical value and so far I consider this a sign of a healthy cell. If the same starts to go below the theoretical value at 1 ATA, then I consider this a sign of wear and current limitation and I'll start scrutinizing it more in water. You can do this without a mV display, but it is more hassle as you have to make contact across two small leads inside your head with a potentiometer. I attach a mV table for your convenience. Hope this helps. H Ok thanks for the explanation but all that does is show you are good at maths A cells output is in milivolts, the computer or controller converts it to a po2 reading, so if you take a reading and youir maths dont add up how do you know where the error is? is it the A-D converter or is the o2 content not what you think it is! sorry but in realtime I cant see any value in that, and anyway what we should be worrying about is current limiting, a much more hazardous situation in my humble opinion. best Dave
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