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Kepware Knowledge Base: Solution

How Can I Configure KEPServerEX to Connect to an S7-400H PLC with Redundant CPUs?

Last Update: 11/12/2018

A non-redundant connection to a redundant S7-400H PLC (such as the 414-4H, 416H, or 417-4H) is the same as a connection to a non-redundant S7-400 PLC; however, communications will be lost when the redundant controller fails to the secondary CPU. When utilizing the secondary redundant CPU, users can do the following:

  • Programmatically change the rack number of the device created in KEPServerEX from the client application
  • Utilize KEPServerEX's Media Level Redundancy Plug-In
  • Utilize OPC server-level redundancy

Programmatically Changing the Rack Number from the Client Application
System Tags were added in KEPServerEX version 4.300.188.0 for the Controller Rack and Slot Number. Because the S7-400H changes the Rack Number and IP Address when failing over to the redundant CPU, users should monitor device communications. When they fail, users can write the new Rack Number and IP Address to the _Rack and _DeviceID System Tags and start communicating with the other CPU.

Note: This method does not have automatic failover, and will not return to the Primary CPU.

Utilizing Media Level Redundancy
Support for Media Level Redundancy was added in KEPServerEX version to most drivers. For a redundant Ethernet connection to the two CPUs and their CP443 Ethernet modules, users can utilize Kepware's Siemens TCP/IP Ethernet Driver to configure two channels with one device per channel. The two devices should have different IP Addresses and Rack Numbers. For more information, refer to the instructions below.

  1. To start, open the device's Device Properties and select the S7 Comm. Parameters tab.
  2. Beneath CPU Settings, specify the Rack and CPU Slot. Then, click Apply.
  3. For the Primary CPU, open the Redundancy tab.
  4. Then, locate and select the Secondary Device. Once finished, click Apply.
  5. Click OK.

Note: All client applications will connect to the Primary CPU connection. The server will manage failover to the Secondary CPU upon communications failure. For more information, refer to Media Level Redundancy Plug-In Help.

Utilizing OPC Server Redundancy
Switchover can be accomplished automatically with RedundancyMaster and two copies of the server. One server should have the primary device; the other server should have the secondary device. The names of the channel, device, and tags should match in both, and the servers must run on two different PCs or virtual machines. With RedundancyMaster, multiple OPC client applications on the same PC can switchover at the same time (without switchover logic in the clients themselves). For more information, refer to the RedundancyMaster Help File.