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dave t · 23rd January 2008, 11:36

[quote=Gilles;164283]At calibration time, this is where you may be in error. The purpose of calibration is to make settings so that mV are correctly translated to PO2.>>>>

sorry dont understand that, as I said before the controller interprets the MV output as a po2, all you do in calibration is to correct the reading to a known factor (stored?) dont you? but you cant change the MV output so if the cell puts out say 10MV in air and air is assumed to be 0.21 thats the reading you will see??

<<<<In practise, if you calibrate your PO2=1 point at the correct mV reading, and then you in water test to 1.6 @6m with oxygen, you have certainty in both your calibration, and in cell health.>>>>>

only as long as you are accurate with cal gas and depth measurement!

<<<<If your on the bench calibrating, you have no indication of cells going off unless you're checking the mV response. I have cells that started off good, and then started not reaching their theoretical mV's @PO2 = 1.0. This helps me to prevent gearing up, jumping in the water only to find out I've got a dying cell.>>>>>

agreed but whats the difference in watching a po2 decay or a MV decay?

<<<Contrary to your opinion on the matter, you can catch a faulty cell at least some of the time. This is quite easy with handset mV readings.>>>

if you have a test chamber, yes but still the po2 readout or MV readout from a raw data will decay the same

<<<A 2 point scheme mitigates a current limited cell response. Note current limited = non-linear.>>>>

dont agree, with a 2 point cal you are correcting the error at two points (maybe) introducing an error that wasnt there due to inacurate cal gas/depth sensor/ atmos pressure. There are some that say calibrating in air is better than calibrating in (O2 or both) due to the fact that an air sample is more consistantly reliable than an o2 sample (at least in our operational field) and most cells stay linear beyween 0.21 and 1.00bar anyway. A current limited cell will still calibrate within its range but unless you can calibrate higher than your setpoint how do you know where the current limit is if its outside your one or two cal points?

<<<<Attached is an essay on the topic I uploaded a long time ago. The impact of 1 and 2 point calibration is therein illustrated.>>>>

thanks interesting stuff

best

Dave

23rd January 2008, 11:36	#19 (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=Gilles;164283]At calibration time, this is where you may be in error. The purpose of calibration is to make settings so that mV are correctly translated to PO2.>>>> sorry dont understand that, as I said before the controller interprets the MV output as a po2, all you do in calibration is to correct the reading to a known factor (stored?) dont you? but you cant change the MV output so if the cell puts out say 10MV in air and air is assumed to be 0.21 thats the reading you will see?? <<<<In practise, if you calibrate your PO2=1 point at the correct mV reading, and then you in water test to 1.6 @6m with oxygen, you have certainty in both your calibration, and in cell health.>>>>> only as long as you are accurate with cal gas and depth measurement! <<<<If your on the bench calibrating, you have no indication of cells going off unless you're checking the mV response. I have cells that started off good, and then started not reaching their theoretical mV's @PO2 = 1.0. This helps me to prevent gearing up, jumping in the water only to find out I've got a dying cell.>>>>> agreed but whats the difference in watching a po2 decay or a MV decay? <<<Contrary to your opinion on the matter, you can catch a faulty cell at least some of the time. This is quite easy with handset mV readings.>>> if you have a test chamber, yes but still the po2 readout or MV readout from a raw data will decay the same <<<A 2 point scheme mitigates a current limited cell response. Note current limited = non-linear.>>>> dont agree, with a 2 point cal you are correcting the error at two points (maybe) introducing an error that wasnt there due to inacurate cal gas/depth sensor/ atmos pressure. There are some that say calibrating in air is better than calibrating in (O2 or both) due to the fact that an air sample is more consistantly reliable than an o2 sample (at least in our operational field) and most cells stay linear beyween 0.21 and 1.00bar anyway. A current limited cell will still calibrate within its range but unless you can calibrate higher than your setpoint how do you know where the current limit is if its outside your one or two cal points? <<<<Attached is an essay on the topic I uploaded a long time ago. The impact of 1 and 2 point calibration is therein illustrated.>>>> thanks interesting stuff best Dave
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