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.

Many 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, Plant SCADA 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), Plant SCADA will switch to the standby data path with minimal or no interruption to the system.

• Plant SCADA 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

Multiple Device Redundancy (Standby Data Paths)