Node-RED Lost Connection to PLC

General
1

Hello,

I'm looking for some help troubleshooting a PLC connection issue.

I'm using the node-red-contrib-cip-st-ethernet-ip nodes to communicate with an Allen-Bradley ControlLogix L83 PLC. The connection has been working reliably for about a month, but today the PLC connection node suddenly started showing Offline.

Here are a few things I've checked:

  • I can successfully ping the PLC's IP address from the PC running Node-RED.

  • No configuration changes have been made on the PLC.

  • The PLC is still running normally and controlling the process.

  • The only issue is that Node-RED can no longer establish a connection to it.

I'm trying to figure out what could cause this behavior and where I should start troubleshooting. Has anyone experienced something similar or have suggestions on what to check next?

Any advice would be greatly appreciated. Thanks!

2

What do you see in the node red log?

Have you tried restarting node red and the plc?

3

This is the message I see in the Node-RED debug pane:

"Error communicating with the PLC: Error: TIMEOUT occurred while attempting to establish TCP connection with Controller."

Yes, I have already restarted Node-RED and power-cycled the PLC

4

Do all the tags you are reading exist in the PLC?