PLC Scan Cycle & Execution: A 2026 Engineer's Experimental Design Guide
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PLC Scan Cycle & Execution: A 2026 Engineer's Experimental Design Guide
The scan cycle has not changed in principle since 2024, input, program, output, but 2026 controllers add deterministic event tasks and OPC UA Pub/Sub side-channels.
Detail
IEC 61131-3:2025 tightens the definition of "task" and clarifies how multi-tasking affects the cycle budget.
Experimental design in 2026 is less about one-variable-at-a-time and more about Design of Experiments (DoE) profiling of cycle jitter.
Modern debuggers (Studio 5000 v36, TIA Portal V19, GX Works3 1.100) now expose per-rung timing, making variable sweeps far easier than in 2024.
A 2026 refresh of the 2024 scan-cycle guide, what changed, how to run a defensible experimental design, and how to debug deterministic latency on nine major PLC brands.
still holds up, input scan, program scan, output scan, but the controllers sitting on the bench in 2026 have moved on. This Engineering Notes refreshes the original article for the IEC 61131-3:2025 era, ties scan-cycle intuition to a modern experimental-design workflow, and links to the latest KOEED cross-references for the nine brands we ship daily.
The three-stage scan is still the model; everything else (event tasks, jitter budgets, OPC UA Pub/Sub) layers on top.
Run a 2-level fractional-factorial DoE on rung count, MSG frequency, and task priority before declaring a scan budget "good enough".
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