PID controle mixing? Or better yet FUZZY logic? You do it cheap and I'll buy one. No scratch that. I'll take two. One for in the shop and one for on the road. You got my interest!
WARNING - LDS rant enclosed
- Thread starter Genesis
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Did you explain the situation? They might be willing to just keep a couple of bottles on hand for you during the season. That would allow them to do it when and how they wanted and give you the gas you want when you need it. Just a suggestion.
Simple is just an O2 sensor, calibrated against a reference (air), with a feedback control system via a steppered needle valve to inject the O2. Simple and it will work, but the output of the first 30 seconds or so after the compressor is started will have to be dumped since the O2 output will have to be slowly ramped otherwise you risk sending a "slug" of O2 into the compressor and blowing it up.
More sophisticated would include a mass airflow sensor so that the system knows how much gas has passed through the intake of the compressor, and thus can more quickly and precisely react to changes and avoid "hunting" for the mixture you set. That will be a LOT more stable, but is both more complicated and expensive, not to mention having a more complex calibration procedure.
Fuzzy logic is not necessary for something like this. This is a deterministic, closed system - a dirt trivial closed-circuit feedback design. The only reason to use a microprocessor is ease of monitoring and setup, along with the ease of handling out-of-bounds conditions (e.g. too high FO2 - you must shut down or the compressor may blow up); without the safety requirements you could build something like this with an analog output control, power transistors and op-amps!
If I decide to build one, the second would be a lot cheaper (since the prototyping effort would be most of the "cost"
)
Mike - yes, I did. They are aware of where I intend to dive and why I needed the cut mix. "Keeping a couple of bottles around" means me buying a couple of bottles and leaving them there - that's starting to get expensive. They have a significant rental tank farm including Nitrox tanks, but they won't custom fill anything in it (for obvious reasons - if someone grabs the wrong tank by accident......)
I suspect there's a solution here, and it may involve only going in there for fills when a guy who I know will do this without trouble is working. That's unfortunate and may have a bad effect on my willingness to go out of my way to use these folks though - there is a closer shop to me, but I've tried to patronize these guys since I like them in general.
I won't give up diving on my schedule and where I want to dive though because of this kind of problem though - it will get solved, one way or another.
More sophisticated would include a mass airflow sensor so that the system knows how much gas has passed through the intake of the compressor, and thus can more quickly and precisely react to changes and avoid "hunting" for the mixture you set. That will be a LOT more stable, but is both more complicated and expensive, not to mention having a more complex calibration procedure.
Fuzzy logic is not necessary for something like this. This is a deterministic, closed system - a dirt trivial closed-circuit feedback design. The only reason to use a microprocessor is ease of monitoring and setup, along with the ease of handling out-of-bounds conditions (e.g. too high FO2 - you must shut down or the compressor may blow up); without the safety requirements you could build something like this with an analog output control, power transistors and op-amps!
If I decide to build one, the second would be a lot cheaper (since the prototyping effort would be most of the "cost"
)Mike - yes, I did. They are aware of where I intend to dive and why I needed the cut mix. "Keeping a couple of bottles around" means me buying a couple of bottles and leaving them there - that's starting to get expensive. They have a significant rental tank farm including Nitrox tanks, but they won't custom fill anything in it (for obvious reasons - if someone grabs the wrong tank by accident......)
I suspect there's a solution here, and it may involve only going in there for fills when a guy who I know will do this without trouble is working. That's unfortunate and may have a bad effect on my willingness to go out of my way to use these folks though - there is a closer shop to me, but I've tried to patronize these guys since I like them in general.
I won't give up diving on my schedule and where I want to dive though because of this kind of problem though - it will get solved, one way or another.
Sounds like you are pretty smart on this kinda stuff...
Well then... you sure don't need any advice or help from me...
Or Omar...
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