Data Path Redundancy

Data path redundancy is another form of redundancy involving defining data paths between the I/O Server and the connected I/O Devices. By providing a second (parallel) data path, you improve the chances that if one data path to the I/O Device is disconnected, the other can be used.

Most brands of PLCs have the facility to allow you to install a parallel data path from the I/O Server to the I/O Device.

The diagram above shows that an additional data path (running in parallel) has been defined. The redundancy is provided as follows:

• When you start your runtime system, CitectSCADA connects to the I/O Device using the primary data path.
• If communications with the I/O Device is lost at any time (for example if the communications cable is disconnected), CitectSCADA will switch to the standby data path with minimal or no interruption to the system.
• CitectSCADA reconnects through the primary data path when it is returned in to service.

On a larger system (such as one running on a network), you can also use data path redundancy to maintain device communications with multiple I/O Server redundancy, as shown in the following diagram.

The redundancy is provided as follows:

• By using a redundant data path from the I/O Device (one path to each I/O Server), you can maintain I/O Device communication.
• If communications with either the primary I/O Server or standby I/O Server be disconnected, the I/O Device is still accessible.

See Also