Editing Programmable logic controller (section)

===Redundancy===
Some special processes need to work permanently with minimum unwanted downtime. Therefore, it is necessary to design a system that is [[fault tolerant]]. In such cases, to increase the system availability in the event of hardware component failure, [[Redundancy (engineering)|redundant]] CPU or I/O modules with the same functionality can be added to a hardware configuration to prevent a total or partial [[Plant process and emergency shutdown systems|process shutdown]] due to hardware failure.  Other redundancy scenarios could be related to safety-critical processes, for example, large hydraulic presses could require that two PLCs turn on output before the press can come down in case one PLC does not behave properly.