using ni 9401 with visa, rs232 connection

[yp21]

Hello all, 

I am using an ni 9401 Digital I/O module with an ni cDAQ-9178 Chassis. I would like to connect two mass flow controllers made by alicat to the 9401 module, and read and write to said controllers. The controllers use a serial rs232 connection, and I had vis built with the assistance of another community member that allowed me to communicate with them. I have made an adapter that connects the 2 9 pin cables to the 25 pin port on the 9401 module. I also know which specific pins are used for input and output to each controller. What would I need to do to control my controllers in this manner?

Any help is greatly appreciated

Thank you,

yp21

[GerdW]

Hi yp,

if you insist on using the 9401 module to communicate to your MFCs you need to make your own routines to replicate the RS232 protocol. And you need some electronics between your 9401 and your MFCs to convert the different voltage levels on both ends of your RS232 cable: 9401 uses TTL, MFC expects ±12V…

[Dennis_Knutson]

Pretty expensive way for serial communication when a couple of $10 USB-RS232 adapters could be used with your VISA driver and you would not need to spend weeks trying to create the protocol. Why?

[yp21]

I plan on adding more instrumentation to my experiment, and having a chassis with interchangeable modules allows an easy ability to do so. In regards to the voltage difference, is that for the rs232 input and output connections? 

[GerdW]

Hi yp,

just read the Wikipedia entry on RS232. It also explains the voltage levels an RS232 input expects. Then compare those information with the specification of your 9401 module…

It's all basic information easily found on the internet!

[Dennis_Knutson]

Your justification for serial communication and the 9401 does not make any sense to me but if you have the months to spend on recreating the wheel, go ahead.