Heterogeneous PLC-Based Distributed Controller with Embedded Logic-Monitoring Blackbox for Real-Time Failover

This study presents a heterogeneous PLC-based distributed controller integrating an embedded logic-monitoring blackbox for real-time failover and fault detection in industrial control environments. Industrial automation and water treatment systems heavily rely on programmable logic controllers (PLCs) for process and equipment control. However, frequent failures, transient errors, and unknown malfunctions threaten system reliability and operational continuity. To address these issues, this study proposes a heterogeneous redundancy architecture consisting of a primary PLC and a standby distributed controller equipped with a logic-monitoring blackbox. The blackbox continuously monitors the I/O logic status of the primary PLC, records abnormal behaviors such as I/O faults, and enables the standby controller’s I/O to selectively execute failover operations. Unlike conventional homogeneous redundancy, which depends on identical hardware, the proposed approach adopts a Linux-based platform, offering advantages in flexibility, cost efficiency, and elimination of vendor lock-in. Furthermore, the standby controller integrates both a ladder editor and an HMI editor, allowing for direct on-site modification and editing of faulty I/O without external tools. Experimental validation was conducted using a laboratory testbed, while durability and electromagnetic compatibility (EMC) assessments were performed by an accredited institute to verify industrial applicability. Quantitatively, the mean time between failures (MTBF) increased by 17.2%, the average switchover latency was reduced to 41 ms, and the detection probability (g) reached 0.986 under multi-vendor configurations. All tests were performed under controlled industrial conditions using IEC 61508-compliant PLC testbeds. The results confirm that the proposed heterogeneous redundancy method significantly enhances fault detection capability, ensures rapid failover, and improves overall operational reliability in industrial automation systems.