With the "Software Redundancy" software package, fault-tolerant control systems can be assembled at low cost with standard hardware components of the S7-300 and S7-400.

Software redundancy can be used for applications which do not make high demands for changeover speed, such as:

• Control of waterworks or water treatment plants
• Control of cooling circuits
• Monitoring and control of traffic flows
• Monitoring/control of temperature or levels

Depending on the application, the entire process or only parts of it can be redundantly designed.

The following failures are controlled:

• The failure of redundant components (PROFIBUS DP master interface, power supply) in a central controller
• The failure of a CPU on account of hardware faults or software errors
• Interruption of the redundancy link between both central controllers
• Interruption of one of the redundant PROFIBUS DP links to distributed I/O