Customers sometimes wonder how to approach building a redundant or Hot-Backup configuration for their runtime server and PLCs. In our Sample Applications Download area, we have an application that demonstrates these principles. This week, we'll look at how this application works, and what you'll need in order to use the design properties in your own project.
Hot-Backup configurations help protect plant and production processes and keep them online by providing a constantly running HMI in the event that a runtime machine goes down or the communications or network fails. Sometimes, customers requiring such a configuration also maintain a backup or redundant PLC, each using independent connectivity to the processes and sensors, and each performing independent real-time operations. The Hot PLC does all the actual automation and the Backup PLC mimics it. Sometimes this configuration is also used to test for system anomalies, such as what might occur with a man-in the middle security breach, and trigger an alarm when the processing comparison falls outside of normalized parameters.
The programming for these devices incorporates a handshaking scheme and "heartbeat" monitors so that each PLC knows the health and status of the other. The InduSoft Web Studio HMI Hot-Backup configuration operates exactly the same way utilizing handshaking and a heartbeat monitor of the hot machine by the backup machine using a predetermined time period of no heartbeat in order to hand off process focus to the backup machine.
To get the "System Redundancy" app, simply click here: http://www.indusoft.com/Products-Downloads/Sample-Applications?EntryId=87&Command=Core_Download and it will download to your machine.
There also is a companion webinar that goes into some detail about how the application works: http://www.indusoft.com/Marketing/Article/ArtMID/684/ArticleID/230/System-Redundancy-