Need help communicating with an OMEGA FMA6500 MFC using rs485

[KCC66]

I am trying to control an OMEGA FMA6500 mass flow controller via RS485.  I am using an NI USB-RS485/4 converter.  I have the port configured as follows;

Baud Rate - 9600

Data Bits - 8

Parity - None

Stop Bits - 1

Flow Control - None

Transceiver Control - 2 wire auto

When I send a simple command such as !0B,M,D\0D (to switch the mfc to digital mode) I get no response.

The mfc is wired for two wire plus ground.  The ground is connected to pin 1 on the converter.  I have the positive lead connected to pins 4 and 8 on the converter and the negative lead connected to pins 5 and 9 on the converter.  I also tried using only pins 4 and 8 with no success.

Any ideas?

[Sarah_R]

KCC66,

Thank you for contacting National Instruments.

Open Measurement & Automation (MAX) and right click on the COM port you are using and choose Open VISA Test Panel. You then can do a loop back test to check what is being sent. The following KnowledgeBase: Pinout For Serial Ports, goes through each of the pins of the connector and how to setup the loop back.

Please test out this suggestion and check the pin connection you currently have.

[KCC66]

Thanks Sarah.  I ran the loopback test successfully.  This told me the port was not the problem so I started looking onto the commands being sent.  I now have the instrument communicating.  It turns out the command structure shown in OMEGA's manual is incorrect.

Thank you for the help.

[osh]

I am facing the same problem. Can you tell me please what is the right command structure for the OMEGA Flow controller.

Thanks.

[LaurenLL]

Osh,

You should still try the loopback test to verify that the port is communicating properly.  From there, you may need to contact the device manufacturer in order to determine what the correct command structure is.

Good luck getting everything working.

Regards,

Lauren L.