PLC Characteristics, Structure, and Control System Architecture: 2026 Update
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PLC Characteristics, Structure, and Control System Architecture: 2026 Update
A programmable logic controller (PLC) is still the workhorse of factory automation in 2026. The architecture has not changed in spirit since the Modicon 084, but IEC 61131-3, OPC UA, and IIoT have reshaped how we program, secure, and integrate the control system. This Engineering Note revisits the characteristics, internal structure, and control-system topology that every maintenance engineer, sys
Detail
PLC characteristics in 2026: deterministic scan, modular I/O, IP-based networking, and built-in cybersecurity.
Core structure: CPU + memory, input module, output module, power supply, and communication interface.
IEC 61131-3 v4 (2026 FDIS) keeps the five languages and adds object-oriented extensions.
Modern control systems are hybrid: PLC + SCADA + edge gateway + cloud IIoT, not PLC alone.
EOL is the dominant procurement reality: source both new and refurbished, with cross-reference data.
A PLC remains the deterministic heart of any modern control system. In 2026 its value comes from openness (OPC UA over TSN, IEC 61131-3 v4), cybersecurity (IEC 62443-4-2), and smoothly coexistence with edge and cloud, not from raw I/O count.
Three core blocks: input module, CPU + memory, output module, plus power and communication.
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