using COM1 to measure two MFC devices

[springby]

Hello,

My lab just bought two MFC(Mass Flowrate Controller)'s from Alicat Scientific, and they provided us with their own software which we'll have to pay after one month, and a Labview code which can be used to control the devices. We have two MFC's connected to one port, i.e. COM1.

When I connect just one device, then the program works fine and I can control the flow pretty well. When I connect two and try to give each Unit(A, B) a different value, however, the program seems to have some conflicts and the front panel doesn't show the values of the MFCs. But, the flowrate of the real device actually changes to the set value. (sometimes yes, sometimes no.. but pretty unstable i would say)

 I attached the example file the company provided for us. Can anyone help me figuring out how i can control the two devices w/o conflicts??? thank you!!

[Wayne.C]

springby,

Do your MFC's have rs232 or rs485 communications?

[springby]

it's rs232.

[Wayne.C]

Each MFC will require its own RS-232 COM port. 

[springby]

but we're using a device called "RS-232 Multi-Drop Model: BB9" which has only ONE COM PORT that connects the all the outputs of the devices.

is there no way to control one COM PORT but two different UNITS?

so far, by changing the Unit ID from A to B, I can control the flowrate, it's just that I don't see the rsults through front panel for some reasons

[Wayne.C]

It should work using the multi-drop device.  You should have mentioned this additional device in your original post.  It sounds like you have not given each MFC its own unique UnitID.

Still unclear as to what you have tried so far.  Do things work properly with the factory supplied program?  ( NOT the LV stuff )

[springby]

i DID give the UnitID, one as A and the other as B.

Like I said, I am somehow able to change the flowrate of the mfc as the way I want it to be.

The only problem is, on the front panel of the labview, all the values (pressure, temp, flowrate) that are supposed to show the values on the mfc, read nothing!! it just simply shows NaN...and this happens only when I connect two devices(units) to one COM. 

the software from the alicat works fine, it's just that after the trial days, i have to pay for it to continue using it.

[Wayne.C]

If the vendor software works, then it sounds like you have sucessfully given each MFC an unique UnitID and that all your cabling is correct.

Are you running one of the example vi's from Alicat or have you written your own? 

[springby]

I'm using example vi's from Alicat.

that's why i don't understand why the values don't show up on the front panel while i can control the values.

Message Edited by springby on 09-29-2009 04:00 PM

[Wayne.C]

Exactly which example are you using?  Exactly how are you using it?  These examples can only talk to one MFC at a time.  It that what you are doing?  Running the vi once for device 'A' and then running again for device 'B'.   Or have you put two instances of the example in your own vi?