PLC Scan Cycle Timing Analyzer (Python Script)
The PLC Scan Cycle Timing Analyzer is a Python-based diagnostic tool that measures, logs, and visualizes the duration and variability of individual PLC scan cycles—comprising input scanning, program execution, and output updating—in real time or from captured log data. It enables engineers to identify timing anomalies, bottlenecks, and jitter that may compromise deterministic control performance. The tool supports both simulated PLC environments (e.g., via OPC UA or Modbus TCP) and post-processed timestamped scan logs.
📖 Overview
📑 Key Components
🎯 Applications
- ✓ Diagnosing intermittent control instability in high-speed packaging lines
- ✓ Validating scan time compliance for safety-critical motion control systems
- ✓ Benchmarking ladder logic optimization impact before and after refactoring
📐 Key Formulas
Cycle Time
CT_i = t_{start,i+1} - t_{start,i}
Computes the duration of the i-th PLC scan cycle using timestamps of consecutive scan start events
Jitter (Cycle Time Variation)
J_i = |CT_i - \mu_{CT}|
Absolute deviation of the i-th cycle time from the mean cycle time, used to quantify timing instability
Determinism Index
DI = 1 - \frac{\sigma_{CT}}{\mu_{CT}}
Dimensionless metric quantifying timing predictability; higher values (closer to 1) indicate greater determinism
🔗 Related Concepts
📚 References
📐 Prerequisites
Understand these before this topic
🔗 Engineering Applications
See how this applies across industries