Thursday, September 30, 2010

SCADA Server Virtual PLC





Virtual PLC are an extension to the SCADA Server Host unique to control Microsystems. The virtual PLCs allow the SCADA Server Host to act as slave device on Modbus networks. This can be used to implement report by exception operation.

The SCADA Server Host can be configured to provide one or more virtual PLCs on each communication network. Multiple virtual PLCs can simplify the programming in report by exception systems. The program in each field controller can use the same Modbus register in virtual PLC. Only the station number to which it reports has to change.

Each virtual PLC appears to Modbus devices on the network as a normal Modbus slave device. Each virtual PLC has the following registers. Memory for the registers is allocated when the virtual PLC is first created and may be optionally saved on shutdown and restored on subsequent startups.
Modbus devices
Virtual PLCs are unique to the serial port or server connection for which they are created. A virtual PLC can not be shared by more than one connection. Multiple devices may communicate with a single virtual PLC on the connection.

Each virtual PLC has a station address, which is set using the server user interface. The user must ensure that the station numbers of the virtual PLCs are unique for the network to which they are connected.

The virtual PLC appears to the SCADA Server Host as a controller. OOPC clients access the virtual PLCs in the same manner as all other controllers. The access path for the OPC item determines connection’s virtual PLC is being addressed.


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