Redundant Modbus Communication
We have multiple unit PLCs which are connected with ABB 800xA over redundant Modbus RS485 links thru redundant MOXA terminal server. We are using Kep server for ethernet encapsulation of Modbus data coming from PLCs. This data is then available as OPC service for our redundant aspect/connectivity servers. Kep server is running on both ABB servers. When Kep server OPC service is enabled on any one of the ABB server every thing works fine (one master, multiple slaves) but when service is enabled on both ABB servers to make it redundant on ABB server level then we have two masters polling for data and eventually PLCs stop providing data and all communication fails. Is there any way to make OPC service on secondary server as standby so that it only start polling data after primary server fails.
Is the MOXA device the Master on the RS485 line.From your description, what I understand is that Kepserver is talking to Moxa device and collecting polled data obtained from the slaves.This data is in turn made available to OPC clients such as 800xa by the kep server. Am i correct?.If not, kindly explain briefly.
Also, there may be a possibility that the Moxa device allows connection only to a single OPC server. For example, AC500 PLCs can connect to a maximum of three OPC servers simultaneously.In this case, the solution by Mr.Wees will help.