ABB PLC573-ETH N/W drop

We have a client site where in 8 no's PLC-573 Eth PLCs are networked over Modbus TCP/IP. In recent past 1st PLC started loosing Ethernet link everyday at specific time and recovering in a may be 500-800 ms. This PLC network is interfaced to plant network too. With the help of plant IT team we tried to find for ghost IPs but found none.

If any of you got into similar issues and came out of it or have an idea on how to resolve may please advice us and we thank them all in advance.

The ABB PLC's have a timeout for the Modbus/TCP connections. If it sees no activity for a set amount of time, then it closes the connection. Your master will then have to open the connection again. ABB calls that OMB Time in the Modbus TCP/IP settings. You might have to increase that value.