Quote: (Originally Posted by
spunkmire)
I start calibration with the loop squeezed down slightly, mouthpiece closed (until it gets to 50-60%) as this gets the ppO2 up much quicker on bag flushing. Opening the mouthpiece at 50-60% to let the gas out!
Two cells get to 96-98%, with some effort, one cell gets to 94-95% but it looks like the readings are still climbing up (the number flicker like they are on the cusp of changing) when the heads decides "calibrating".
Unit dives well, but when back in the base and the head dry, the cells comminly read 17-19% in air - somehow I am making the unit under-read the cells?
Hi,am not sure why you want to get a much quicker flushing? I do one every day prior to diving. I think a nice long flush is better as this optimises the amount of o2 across the face of the cells. I do the usual tests eg pos and neg etc. Then I just follow the handset instructions - easiest way then you don't make a mistake.
My understanding of the calibration is that you want to have pure O2 across the face of the cells at atmospheric pressure (1000mb is fine - if you have say a VR3 you can put the actual reading). If you are keeping the mouthpiece closed and then opening you are not doing a cal at atmospheric pressure. This could be why your getting a slight low reading in air. All a callibration does is that a cell does not know what partial pressure of o2 is across it - all it does is produce an electric charge (ie voltage) in response to the oxygen across it. By callibrating it you are telling the handsets at what voltage the cell is reading 100% (I use 98% on the menu) oxygen. From this the handset can then work-out the partial pressure from the voltage that is given off.
The readings during calibration are voltages not partial pressure. It is only once the unit has done its double bleep that you get a partial pressure.
So in summary - I just follow the instructions that the handset says everytime I switch the unit on - that way you don't make a mistake. Once the cal is over I do a pre-breathe check (often like to lower the pO2 to get an alarm) before the solenoid clicks in and raises the pO2 and then a continue to breathe ensure all 3 readings are stable around the 0.7 mark.
Hope this helps.