Improving immunization of programmable logic controllers using weighted median filters.

Area of Science:

• Electrical Engineering
• Control Systems Engineering
• Signal Processing

Background:

• Programmable Logic Controllers (PLCs) are susceptible to electromagnetic interference (EMI).
• Impulsive EMI can disrupt PLC functionality, leading to operational failures.
• Existing solutions may require additional hardware or are incompatible with legacy systems.

Purpose of the Study:

• To propose a novel filtering structure for enhancing PLC immunity to impulsive EMI.
• To develop a filter that can be implemented in legacy PLCs without additional hardware.
• To improve the robustness and reliability of PLCs in noisy environments.

Main Methods:

• A filtering structure based on weighted median filters is proposed.
• The filter operates in the binary domain, processing discrete input signals.
• Two filter variants are developed by modifying the sampling clock structure, exploiting the PLC's cyclic nature.
• An N-sample observation window is utilized to determine status changes, considering multiple samples.

Main Results:

• The proposed filter effectively removes impulsive noise from discrete PLC inputs.
• The filter enhances PLC robustness against EMI without requiring extra hardware.
• Statistical analysis demonstrates the comparative performance of the two filter variants.
• The N-sample window approach prevents single impulses from affecting PLC functionality.

Conclusions:

• The developed weighted median filter offers an effective, hardware-free solution for improving PLC immunity to impulsive EMI.
• The filter is suitable for implementation in legacy PLCs, offering a cost-effective upgrade.
• The proposed method significantly enhances PLC reliability in electromagnetically challenging environments.