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Divejunkie · 25th March 2008, 18:29

Can someone help me with this please.

When I switched the meg handsets on after a week off, in air they were both reading 0.18%.

Even though I went outside to ventilate the head they remained at 0.18%. I continued with the calibration in oxygen. When I removed the O2 supply and the head ventilated, the handsets were reading 0.21

My question is to do with how the sensors are calibrated-

I understand the electronics use a two point calibration system i.e. it needs to start the calibration in air (21%) and finish at the max o2 you have set the handset (99%). But what if the cells wont reach .21?

Is the calibration of the 3 O2 cells similar to an O2E11 analyser in that they need to know that they are in 'air' at 20.9 to start with before they can give an accurate O2%?

or- does it not matter what the initial O2 reading is because you flush with a known 100% (albeit the unit is set at 98%) O2 supply and the electronics basically assign 100% as the maximum and works backwards?

I'm concerned that if the cells start at 0.18 (3% down) p02 then the calibration will be incorrect and will result in a potential decompression probelm.

Does this make sense?

25th March 2008, 18:29	#1 (permalink)
Divejunkie New Member Current Rebreather/s: Megalodon Other Rebreather/s: Inspiration Classic Join Date: Nov 2005 Location: Cumbria Posts: 29	Initial reading before calibration Can someone help me with this please. When I switched the meg handsets on after a week off, in air they were both reading 0.18%. Even though I went outside to ventilate the head they remained at 0.18%. I continued with the calibration in oxygen. When I removed the O2 supply and the head ventilated, the handsets were reading 0.21 My question is to do with how the sensors are calibrated- I understand the electronics use a two point calibration system i.e. it needs to start the calibration in air (21%) and finish at the max o2 you have set the handset (99%). But what if the cells wont reach .21? Is the calibration of the 3 O2 cells similar to an O2E11 analyser in that they need to know that they are in 'air' at 20.9 to start with before they can give an accurate O2%? or- does it not matter what the initial O2 reading is because you flush with a known 100% (albeit the unit is set at 98%) O2 supply and the electronics basically assign 100% as the maximum and works backwards? I'm concerned that if the cells start at 0.18 (3% down) p02 then the calibration will be incorrect and will result in a potential decompression probelm. Does this make sense?
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