Setting up Mass Flow Controller

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John Myers
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Re: Setting up Mass Flow Controller

Post by John Myers » Mon Jun 12, 2017 5:31 pm

I would leave the unused pins floating till you know if their active high or low signals.
Grounding the EXT ZERO may be forcing it to continuously try and zero out the flow reading.

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Richard Hull
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Re: Setting up Mass Flow Controller

Post by Richard Hull » Mon Jun 12, 2017 7:23 pm

If I were testing an MFC I would leave the inlet open to air and hook the outlet to a vacuum chamber with a good gauge on it and go with a control signal from a simple 5 volt wipered potentiometer and watch the vacuum gauge as I adjust the pot. The Arduino, at this point, is a needless appendage and can be dealt with later provided the MFC works simply in a crude manner just described. Use the least complex and simplest scenario in tests. Once you have a proven device, you can add all sorts of fancy complications and then debug those with confidence.

I work with Arduinos a lot and love them, but I only apply them when I have a working device that needs control or feedback in a complex or rapid response, (sub-millisecond), time frame. I tend to design them into nuclear instrumentation or when I design multi-level control situations. There are a ton of Arduino like controllers out there, but few are as in-expensive to use and implement. Tiny PICs can be used when an Arduino is over kill and a propellar where you want to control large power plants and need the COGs. However, at $3.95 to a rip off price of $5.00 each, the Arduino pro-mini can wipe out the PIC at price and leave room for the "feature creature" to crawl into your design in future with unused ports and capabilities that you have left dormant.

I bought a MEGA 2650 for $24.00. I now consider this an insane moment in my life. I have yet to stress a pro mini to it's limits. The tons of ports and A to D on the mega just have not found a need in my world yet. The mega resides in my folly bin.

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
Retired now...Doing only what I want and not what I should...every day is a saturday.

Jerry Biehler
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Re: Setting up Mass Flow Controller

Post by Jerry Biehler » Mon Jun 12, 2017 9:18 pm

Yup, ditch the arduino and use a pot set up as a voltage divider. And do NOT just start randomly shorting pins. This is how you kill stuff. Leave everything but power and control in floating.

Tom McCarthy
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Re: Setting up Mass Flow Controller

Post by Tom McCarthy » Wed Jun 14, 2017 1:20 pm

Thanks John, Jerry, Richard.

Lesson learned not to short pins without due consideration.

Set up as per Richard's instructions. Used a 10K pot and a variable 12v 2.5A supply for the voltage input. Set the supply at 5v across the pot. Watched output from MFC with a multimeter, a constant -160mV, with slight fluctuation. From the Pirani gauge on the chamber, pressure was 30 mbar ~ 20 microns.

With 5V input to the MFC, there was no current draw. As mentioned, output signal was a constant -160mV. Notice the negative output, should be in the range +0-5 V. ±15V was going in, and the PWR GROUND and SIGNAL GROUND pins were grounded to the commons of the 12V supply and ±15V supply.

The EXT ZERO, POS SHUT OFF (HI), POS SHUT OFF (LO), and DC VALVE RTN. (UV), CASE GROUND and duplicate PWR GROUND and SIGNAL GROUND pins were left floating.

Some calculations on detecting if the MFC is open with the vacuum gauge:
Chamber volume is 14 litres = 14000 cm3, 14000 SCCM at STP. At given pressure (30 mbar) 14 litres of air is equivalent to 0.00003 * 14000 SCCM ... About 0.5 SCCM. So, if I have the MFC fully open, giving a flow of 10 SCCM, I'd expect the pressure to rise about 20 times in the space of a minute to 600 mbar. However there is no such large rise, and instead a very slow leak, of 10 microns/minute.

How to proceed from here? MFC seems to be absolutely closed to any flow and the -160mV output is odd. Perhaps it requires another pin to be grounded/powered to open up. I'd rather not kill the thing, though it may already be gone. Can open it up for a look to see if any components are obviously crapped out.

I've also contacted Brooks Instruments, who provide support for legacy products from Tylan General, Unit, Millipore etc. In 2009 Brooks acquired Celerity which included Millipore spin off Mykrolis which in turn included Tylan General and so Vacuum General. Guy who deals with the old stuff is in office next week, may be able to help with information.

Tom

Jerry Biehler
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Re: Setting up Mass Flow Controller

Post by Jerry Biehler » Thu Jun 15, 2017 4:08 am

Ground pins must be grounded.

Tom McCarthy
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Re: Setting up Mass Flow Controller

Post by Tom McCarthy » Thu Jun 15, 2017 11:35 am

Grounded all the ground pins, same result, had no effect as far as I can tell.

I think it might be best to cut my losses, both time and money, and get a variable leak valve, use the laser orifice I've already got and I can even measure flowrate with the flowmeter previously described. Brooks might get back to me with a manual to confirm pinout, but the likelihood of that seems low.

Tom

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