Most PLC, and PAC controllers exhibit a high degree of reliability but, certain critical industrial automation applications simply cannot tolerate downtime. The preferred solution in these cases is redundancy, as this greatly increases availability.
Traditionally, redundant automation systems have been very expensive and complex, particularly as compared to standard automation systems. Upfront hardware costs have been very high and implementation has been difficult, requiring extensive software development effort. An example is the triple modular redundant (TMR) system, often employed in critical process and other automation applications.
But now, redundant PAC automation systems are available that greatly reduce both cost and complexity. These solutions simply require the purchase of a CPU and implementation just requires an extra configuration step to select the redundant option.
Most PAC redundant automation systems provide redundancy at the power supply and CPU levels, the two most critical areas. Redundancy at the I/O, communications and cable levels can also be provided depending on the needs of the application.