Utility of bag mounted O2 sensor?

4ster

This is a question about the effectiveness of an O2 sensor in combination with a VR3 or HS Explorer.

I am thinking about purchasing one of these to use with my Drager.

Review/assumtions: Both the VR3 and the Explorer can be set up with an O2 sensor that mounts in a P-port on the inspiration bag. The advantage being that actual, inspired O2 is measured and used in decompression calculations. So far, so good.

I am currently using an Oxygauge to monitor pO2. I *think* I am seeing a decrease in sensitivity of the O2 cell as the dive progresses due to condensation in the loop. At the end of my dives my VO2 (metabolized O2)drops to zero, which obviously ain't happinin since I am still here.

I've checked calibration, and the gauge reads as expected at the begining with the supply gas and at the end of the dive after it is pulled from the bag and tested in air. I am in a steady state in the water while taking the reading, not ascending or decending. The longer the dive the closer my VO2 gets to zero. I am diving in water temperatures in the 48-50 degree F range at the moment.

I see no point in having a computer calculate O2 exposure and deco from faulty data. You can't dry a cell with a loop flush on a Drager like I gather you can on at least some CCRs.

So is it my o2 cell or me that is all wet? What are your experiences using a VR3 or Explorer to measure inspired O2?

Gregv

I haven't noticed any deterioration in function of my O2 cell in the inhale bag in 12 months (Teledyne R-22 connected to a VR3). The readings always match up well with the two other sensors in the system for dives of up to two hours in temperate waters (14-20 degrees).

I did have a similar problem before I switched to the VR3. My oxygauge was reading progressively lower during dives a few years back. Never got to zero though. The cell failed calibration a short time later and had to be replaced. Slightly before the oxygauge itself flooded. If you're intending on using the oxygauge for any length of time, check the o-ring seal where the cable enters the housing. I know of four different oxygauge units that have flooded via that o-ring.

Greg

mortenkjerulff

Hi.

I have never had any problems with condensation either. I am using a VR3, and my longest dives are about 2 hours in cold waters.

The only two people with oxygauges I know of, have both had problems with flooding, and one of them have had strange pp=2 readings along a dive too.

Morten

zèècalcoene

Hello All,

Me 2 never had readout problems with VR3 fitted oxygen sensor in inhale bag
(with original Delta P P-Port sensor holder !)
However, what has been worrying me the last 2 years is accurate calibration
of the 2 or 3 sensors fitted in a Dolphin.
By properly flushing the breathing loop with pure oxygen for several times, we can never be sure that the loop is COMPLETELY filled with the same oxygen content in oxygen cilinder !
Other (E)CCR's do can since the position of the sensors is very close to where O2 is put into the system.
Therefor I fitted a 3 sensor T-Piece made by Tecme (thanks again Martin) which is fitted between inhale bag and inhale breathing hose..
One sensor is for VR3 and 2 others to rEvodream display and HUD (Works excellent Paul !) Check out some pictures here :
http://www.rebreatherworld.com/photo...8/limit/recent
Still I am not sure that I can properly calibrate but my procedure has changed.... after reading Jradomski's article "accurate PO2 calibration" (thank u Joe !)

When I want to calibrate my 3 sensors, I unscrew the T-piece from breathing loop and use Joe's calibration method.. Takes about 5-7 minutes..
On a liveaboard in choppy sea a very handy method.. I can do the cal 'inside'..

Just wanted to share my experience
safe diving

Ivan

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mCCR Dolphin Diver