Hi All,

Is there anybody have experience linking four sets of the above VSD thru Modbus?

We encounter some problem when sending a modbus command to a one of the drive in the loop. it suspose one of the drive is powered and running the pump, when another VSD has just power up and we try to send the initial command to the VSD, this command causing the active VSD to stop. We have confirm the Modbus address and command are correct. Now we are in the stage of testing, we need your valuable feedback.

Thank you.

E. Chun

 

What type of master are you using and what is the inital command? Is the initial command sent to the control word?

 

E. Chun,

We have linked two of the drives via MODBUS with a flowmeter and pressure transmitter on the same multi-drop line. WE have not had any issues with the drive shutting off. We have had problems with the communications link when a drive is powered off and not seen by the master node.

One thing you need to know about sending commands to the drives. If you try to send a Function Code 03 or 16 for a list of registers in a Group, you will receive error codes and mo data if there are addresses that are not used in the Group. Example: If you wanted to read the contiguous registers in Group 01 0117-0121, You will receive an error message because 0120 is missing. We had to modify or master program to group the contiguous registers together and read them as subsets within in the Group.

You may have this issue or an addressing issue on the line. Once we worked out this little issue, I think it stemmed from the Master hardware we were, we have not had any other problems. In fact I am in the process of setting up four drives at the wastewater plant to work on the same network.

If you need more info, feel free to contact me directly via email.

Bob Dusza

Robert J. Dusza, Jr.
Project & Technical Support Manager
(V) 1-860-647-3219
(F) 1-860-647-3150
E-mail - [email protected]
Manchester Water & Sewer Dept.
125 Spring St. P.O. Box 191
Manchester, CT 06045-0191