Quote: (Originally Posted by
MatV)
At first glance you don't notice what it is. Just the familiar mCCR with double cells, and the double handy Oxyscan/booster assembly. Even a close look the braided (rather wound) cable protection does not reveal the jewel of engineering hiding between the scrubber and a bottle. A tiny black Delrin cylinder, much smaller than a Barry Miller torch, holds the secret, a lithium-polysomething powered solenoid with its logic.
Actually not much of logic, and that for good. Setpoint is not _set_ like you program the unit to do something, it only, by design, injects oxygen coming from a 2l/min constant mass flow orifice, when the ppO2 falls below 1.0 bar, and stops if it exceeds 1.2 bar. Parallel to the solenoid ( talk about perfection..) there is the familiar KISS-Flow through the tunable needlevalve.
There is no logic giving a false sense of security. Both cells, and the controller, are totally isolated from each other in terms of pressure, and power. The cells are next to immune to moisture, and placed so that their reading is an immediate one, coupled directly to the inhale hose.
You calibrate the sensors to air, as calibrating to oxygen could be dangerous in places where the percentage of oxygen is, ah..... arbitrarily. (With my experience from these sensors I can say they perform quite linearly)
One touch at the wet sensors, and the procedure starts with some numbers, then a cell millivolts reading, calibrate, do what you have to do, go diving.
No menues, no worry.
"Setpoint" stability was excellent. Diving was usual. Easy.
Much easier and more reassuring than a diving the YBOD or the italian clutterbox.
My only wish was to have slightly increased loop volume, as I tend to breath slow and a bit deeper.
Matthias
Nice thing to limit the flow to the controller to 2 l/min and have a KISS flow in parallell. Probably works really nice and prevents a runaway solenoid getting to wild.
Is there also some form of gas accumulator linked to this flow restriction upstream of the solenoid, like in other more or less similar solenoid designs.
But...calibration at po2 ~0.21 used for measurment/control ~po2 1-1.2 bar. That cannot be anything but questionable practise from a classic engineering perspective for this kind of thing. Given its generally bad to extrapolate the cal further than necessary.
How do you notice if a cell is current limited around the "setpoint" upon air-calibration.
But sure I guess the error would _usually_ go slightly in the "right" conservative direction, underestimating the po2 a little (hoping its stays at a little).
How about the sensors. Are they to be completely removed from the Rebreather for calibration? If someone would happen to do the "air" cal with the cells in the Rebreather with some extra O2 inside things could get very funky.
I did not understand how the dual sensors trigger extra O2 injection? Do they trigger it indipendently or do they still have to agree in some way?
How about the unusual case of more than 2l/min O2 consumption? Yes, very unlikely. Especially without the user noticing the odd conditions...