Mass flow controller with Labview

[Blokk]

"Everybody knows how to do it with money. It is a challenge."

So is this a kind of project about how to build cheap system from salvaged old hardware? I see, interesting... 🙂 It is cool, but the time what you waste for the hardware/software building is lost for the valuable part: research.

"I have to assemble the equipment from nuts and bolts in order to understand how it works and repair it easily after that."

If you open a book or check on wikipedia you can understand how a mass flow controller works (PID, etc...). What you do is great for example for educational purpose to teach control basics to students, but I do not see what is the benefit in this when we talk about research...?

Anyway, back to the topic, just a guess, but I think you have problems with the wiring...Try to check it again, and compare it to the manual...

[altenbach]

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@Blokk wrote:

As much as I see these devices are not controllable via serial (RS232 or RS485), so it does not have a built-in PID controller. If this is true, it is bad news, since it will require much more suffering during the development, specially if you are beginner in LabVIEW...

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They are mass flow controllers, so they have PID built in. Nothing is needed except a 0-5V setpoint voltage and +-15V to power it all. The datasheet defines a settling time, which cannot be defined if the PID is external. 

I have a few mass flow controllers and mine allow several ways to control them (0..5V, RS232, 5-20ma). The absence of RS232 does not imply that they are not smart. The 0-5 V output is just as an indicator to show the actual flow and is only interesting if the input pressure is too low to achieve the desired flow rate or if there is another problem.

Look at page 2-2 of your quoted manual:

"The control valve adjusts gas flow through the MFC based on the flow sensor reading and the set point to ensure a stable gas flow ..."

 

[Blokk]

Thanks altenbach, now it is clear to me 🙂

So this is good, no need for PID control from LV 🙂

But what about the wiring? The OP should try to control the MFC then with a constant voltage changed manually just to see how the MFC operates...

[Bozhidar4o]

So if "they have PID built in" I have to use only the voltage (0 - 5) as set point and just to compare visually with the MFC output.
I tried 3-4V to the setpoint (A) but there was no flow (2bar applied).

[Blokk]

What you show here:

http://forums.ni.com/ni/attachments/ni/170/937661/1/wiring%20MFC%201.jpg

It is not totally what they describe in the manual at page 40. It says, "pin2 and pinB must be connected"...? Also, I would use the differential analog input on the USB-6009 just in case (to connect pin 3/pin C to AI0/AI4) to read out the actual flow rate.

But I am not really an electrical engineer, so lets wait for someone who is more experienced (specially after I made a fool of myself here regarding to MFCs, after a short googling I see now it is still a very widely used industrial standard to use analogue drives for MFCs... :D).

So good luck!

[altenbach]

Can your power supply provide 3-4W? (~200mA on the -15V)

Are all the polarities correct?

Are all connections right (make sure you don't do a 180deg on the connector, but I assume it is keyed in some way)

Are there huge floating voltages?

Is the valve inserted in the correct flow direction?

Did the valve work correctly in the original setup?

[Bozhidar4o]

Can your power supply provide 3-4W? (~200mA on the -15V)

1.7A attached

Are all the polarities correct?

Checked several times

Are there huge floating voltages?

The output MFC shows 0.18-0.2V but the valve is closed

Is the valve inserted in the correct flow direction?

Yes

Did the valve work correctly in the original setup?

I bought 4MFC from ebay as used but in "good condition".

[altenbach]

That's a +15V. Where does the -15V come from? You need both -15V and +15V.

It could be that the solenoid is stuck. Does it make a noise or get warm?

[Bozhidar4o]

Please clarify. So it is only +15V. Attched the wiring.
It wasn't warm because I tested for not more than 20 sec.

[altenbach]

Yes, you need a power supply that provides +15V AND -15V.

(i.e. three wires: ground, -15V, +15V)