Redundant Control Systems: Siemens S7 400H Series PLC and WinCC

There are certain control systems, such as in nuclear power plants and airplanes, that cannot be disabled or shut down, even momentarily, because of the threat to people’s lives. In these applications, a redundant control system must be in place to take over instantaneously if the primary system fails.

I recently deployed one such redundant control system for train tunnel ventilation at a major international airport. The system's main objective is to control, reduce, and help extinguish a fire if it occurs in the train tunnel.

One off-the-shelf solution to implement redundant control systems is using Siemens products: WinCC is a redundant SCADA system and the S7-400 H series PLC are redundant PLC's.

The airport project was implemented using these products. The system is configured using a master and a backup component. If the master WinCC server fails or loses power, the backup WinCC server takes control immediately. The same scenario occurs for the S7-400 H PLC.

The advantage of both WinCC and the S7-400 H PLC is that there is no additional programming needed to enable redundancy. The hardware and software handles the switchover to the backup component if the master component fails.

Programming a WinCC system is done using SIMATIC WinCC. A redundant WinCC system is developed the same way as a non-redundant one, except for some minor settings.

Programming the S7-400 H PLC is no different than programming a non-redundant system; SIMATIC Step 7 is used.

The Siemens redundant products are very reliable and robust. I would definitely recommend using them for a redundant application.

Learn more about DMC's Siemens S7 PLC programming services.