Re: 1 vs 3 - a story from the techncial diving world ....
This is a great point for debate .... well ... not 1 vs 3 ... that is a no brainer ...
But 2 Vs 3.
its been going on for 20yrs in the rebreather diving community.
We have galvanic O2 cells in our closed cuircut rebreathing loop. They regulate the partical pressure of O2 in the loop. Too little, we die ... nicely. Too much, we die ... horribly. So it does focus the mind.
Problem with O2 cells is they are desiged for surface pressure, medical equipment. Not 5-10atm being halled around a boat in the north sea full of salt water. So they fail, regularly.
So, early manufacturers started putted 3 cells in (at great expense) and used simple voting logic to decide what our O2 reading were. Trouble is ... cells could and would fail at the same time due to being in same batch and subject to same conditions ... therefore you get 2 duff votes, but as they agree, you still die. DOH!
Poseidon have come up with a new solution .... and only uses 2 cells. Not for voting, but for redundancy. In their design they validate both cells against konwn conditions thoughout the dive (every 3mins) by blowing pure O2 over them an watching the electrical responses. If readings are good, you continue your dive, if either cell misbehaves, it is ignored and the good cell is used to keep you alive while you start your dive abort process. (If both fail, its kicks you off the breathing loop to a completely redundant Open Cuircuit backup ... a 2nd plane if you will!)
Sorry for going on ... but I do like Poseidons approach and its the unit I dive. It would be interesting to work out a way if Piezo tubes could somehow be re-designed to allow realtime validation against a known state mid flight? (James Bonds Q style gagdet comes out of plane and covers the tube completely and uses compressed air at set pressue to mimic a given air speed) .... as you can tell, I more at easy under water than above it ;-)
Good debate thou!
Cheers!
Biting the hand that feeds IT
