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Parallel network topology (using PRP)

Each CI52x module and PLCs as single ended devices are connected by PRP switches to both networks. Here the failure of the switch which connects the primary CPU will also lead to a switchover.

Fig. 335: Parallel-redundant network, PRP switches to connect each device, CPU and communication inter- face modules
PRP_switches

Redundancy switchover timing should match the settings in the program and communication interface modules for time-out and freeze periods. The networks for larger systems are often seen as a separate entity and done by a separate company. Make sure to have the redundancy status information of the network at least in SCADA, to repair in time. If the I/O field network responsibility is with the automation/ PLC part, the redundancy status should be also monitored by the PLC. A warning to initiate repair may be created from the managed switches in the I/O field network.

Examples

  • Alarm output(s) wired (e.g. to a CI52x input and related settings of the switch(es)).

  • Settings of the switch(es) to send (e.g. SNMP traps, which can be received in PLC (AC500 SNMP library)).

  • Use of “automation switches” which can also communicate their status directly via Modbus.

It is also possible to connect switches in ring combination with CI modules connected to them in daisy chain. User needs to do the relevant setting based on type of switch and protocol (Ex: MRP, RSTP).

If RSTP ring configuration is used in the system, ring reconfiguration time is slower than other ring protocols. During this reconfiguration, connection to the CI modules will be lost.