I am currently working on a project in which the PCS consists of various Quantum PLC's, each of which are on a subnet that also contains various ethernet devices (VFD's, MPR's, various switches, etc.). These PLCs then communicate on a primary network via TCPIP NOE 771-11 modules. Every week or so, we will lose communication from one of these PLCs back to SCADA, and the only way we have found to reestablish communication is by simply cycling power to the primary PLC (all PCS PLCs are in a Hot Standby configuration).
When the PLC is in this "down" state, I am able to ping the IP address assigned to the NOE module from the primary network. However, I am unable to connect to the PLC remotely in Unity XL, and all communications to this PLC appear to be down from our SCADA system. I believe this is an overloading issue of the NOE module. I have ran a quite a few Wireshark traces at the network switch that this NOE module is connected to, and I do see many TCP errors. However, after attempts to cut back on the sheer volume of traffic on this module by disabling communications from the PLC in question to Ethernet devices it is polling, among other things, the issue persists. What are the most effective ways to address this potential overload of our NOE 771-11 module?