With the use of PLC redundancy, the reliability of the control system can be significantly enhanced. This redundant design ensures that in the event of a primary PLC failure, the standby PLC can seamlessly take over the execution of the application, avoiding production interruptions and system crashes. Redundant PLC not only provides safety for the control system, but also effectively prevents system failures and ensures the continuity and stability of the production process. Therefore, the use of PLC redundancy in critical control systems is an efficient strategy to improve system reliability and ensure production safety.
Overview of PLC redundancy
In a redundant control system, the application runs on two PLCs at the same time: the master PLC is active (1) and the slave PLC is in standby mode (2). The PLC in standby mode reads the input via a redundant link (3) and synchronizes with the active PLC. In this way, the standby PLC can be started immediately in the event of a failure of the main PLC and take over control of the fieldbus (4) without interruption.
In addition, visual redundancy can be used in redundancy control systems when the visualization function is run in the browser as CODESYS WebVisu. During the master-slave PLC switchover, the visualization client will continue to run seamlessly.
Configure the CODESYS redundancy system
First, right-click on the Application to add redundancy configuration, and click Add in the Add Redundancy Configuration pop-up window
In the redundancy configuration, the IP addresses of the two PLCs (used for mutual communication and connection) are set separately, and then the points are written. The write here is to write the parameters to the configuration file, so the control needs to be restarted.
After restarting, log in directly and see that the two controllers are already in the master-slave state. The two PLCs can be switched by the conversion button.
In the logs, you can see the redundant system boots:
Of course, dual-link redundancy, as well as EtherCAT, Profibus bus redundancy, etc., can also be configured in the redundancy configuration, and the principle is the same.
Redundant system architectures from other vendors
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