Struggling with setting up a RS-485 connection from a mass flow controller to NI cDAQ

[Mango17]

I am an absolute beginner starting from the ground up trying to connect the RS-485 port from a Sierra Instruments mass flow controller (MFC) to the NI cDAQ.

The intended pathway that someone before me laid out for the connection is:

1) Cable from MFC COM1 to the 4-Port Ethernet Interface for RS485/RS422 (DB-9 to DB-9)

2) Ethernet cable from 4-Port Ethernet Interface for RS485/RS422 to NI cDAQ

I am struggling to understand exactly how the pins should be lined up for the 1st part of the interface. The pinout for MFC COM1 is given below:

The pinout for DB-9 male shown in NI's Serial Quick Reference Guide is shown below:

I am not sure which pins at the MFC side should connect to which pins at the ENET-to-485 side. The obvious one is ground-to-ground (Pin 7 to Pin 1). Beyond that I'm stumped. Trying to read up references online has just served to confuse me even more at this point...

Any help would be much appreciated!

[Dennis_Knutson]

It looks like the vendor stuffed a lot of signals into a couple of DB9 connectors besides the RS485 signals. Do you have the manual that you can attach?

[Mango17]

I think I figured out the pin connections I need to make from one end to the other if I choose to go this 9-pin to 9-pin route. It appears the MFCs are 2-wire RS-485 while the receiving end (NI terminal) is setup for 4-wire RS-485. So I will need to wire the TxD+ & RxD+ at the NI terminal to RS-485-A pin of MFC COM1, and wire the TxD- & RxD- at the NI terminal to RS-485-B pin of MFC COM1. The other signals (ID-0, etc.) are optional for the MFC & the power will be supplied to the MFCs through a separate connection. So that takes care of all the necessary connections.

I've also identified another pathway into the computer using an USB to RS-485  converter. I think at the end of the day this will be an easier setup to follow. Thanks for the reply & I will see where this takes me.

[Mango17 · Accepted solution]

To follow-up: I purchased a B&B Electronics ULinx USB to 9-pin RS-485 converter as well as a cable from Sierra Instruments. I was able to confirm communication between the cDAQ and the MFC using Sierra's own HMI provided as well as through NI-MAX.