gas handling and Mass Flow Controllers

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r_c_edgar
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gas handling and Mass Flow Controllers

Post by r_c_edgar »

The simpler forms of a Deuterium handling system have been pretty well discussed here - needle valves and capillary leaks and associated equipment - but I haven't really seen any discussion of more advanced forms of gas handling systems. In particular, I am interested in how a system built around a Mass Flow Controller would be set up.

What would be the simplest and more complex ways to go? Merits of closed-loop vs. open-loop control, etc. It seems like going this route would definitely add to the repeatability and accuracy of experiments, but what kind of difficulties are there?

-Ryan Edgar
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Richard Hull
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Re: gas handling and Mass Flow Controllers

Post by Richard Hull »

The biggest difficulty met with using mass flow contollers is, of course, cost! Given that you might acquire a nice mass flow controller at a good surplus price or nearly free, we can still find problems. First, most such controllers are for the coatings or semiconductor industry and let through a lot of gas or have large flow rates which are beyond the fusor's operating level normally.

The solution, if you have your heart set on the real nice repeatability of the controller is to spritz, in micro controlled bursts, your gas into the system with a mass flow controller which is for low volume flow rates.

Most modern mass flow units use an analog 0-5 volt signal to adjust flow and this is normally close loop controlled off of a pressure gauge whose output is bridged or compared to a reference "pressure set" potentiometer.

The amateur could do it either way open or close loop. I prefer closed loop control. Needless to say, all could be computer controlled.

Most MFC's are cal'd for a specific flow rate of a gas like CO2 and a correction factor would be needed for Deuterium.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
r_c_edgar
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Re: gas handling and Mass Flow Controllers

Post by r_c_edgar »

I have a few Aera FC-980 mass flow controllers. They are calibrated for N2 and have a range of 10sccm. I picked up the lot for basically nothing from ebay because they were mislabelled as being 10scmm!

These should be useable, correct? I think that a 10sccm (max) flow rate should be low enough...

-Ryan Edgar
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Richard Hull
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Re: gas handling and Mass Flow Controllers

Post by Richard Hull »

That is a great buy you got there.

A 10sccm unit is just fine for a flow controller used as a leak. You might still have to throttle it by pulsing it at lower operating pressures.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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