"Redundant Design" of PLC Control System

The "redundant design" of the PLC control system is mainly used in two aspects: one is the "redundant design" of the control circuit, such as the emergency disconnection circuit, etc.; the other is the "redundant design" of the PLC itself.

The so-called "redundant design" of the control circuit is to ensure the safety and reliability of the control system and prevent safety and reliability accidents caused by the failure of a certain component. By artificially adding "redundant" control devices that are not needed under normal circumstances, reusing contacts and other measures, the circuit reliability is improved.

For example, for contactors used for emergency disconnection, several contactor contacts must work simultaneously to achieve "redundancy" and ensure that the safety circuit can still remain effective when one contactor fails.

The purpose of PLC "redundant design" is to further improve the system's operating reliability and avoid downtime and safety accidents caused by PLC failures.

The "redundant" system is also called a "hot backup" system. It is mainly used in situations where safety and reliability requirements are very high, such as large production lines, chemical equipment, etc., where major safety and quality accidents may be caused by PLC shutdown.

PLC "redundancy" requires the use of a CPU system with "redundancy" functions, such as SIEMENS's S7-400H. In order to achieve PLC "redundancy", two sets of identical power supply, communication, CPU and other modules need to be configured in the system. The two systems work at the same time, one (the main system) is used for normal control; the other (the backup system) runs the same control program, but its output is prohibited. When the main system fails, the backup system immediately takes over the system control and becomes the main system to ensure the normal operation of the equipment; at the same time, maintenance personnel can repair the failed system and install it into the system as a backup system after the repair is completed. Such continuous alternation ensures the continuous operation of the system without stopping.