Type and source of interference in PLC operation and its anti-jamming design - Database & Sql Blog Articles

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Programmable Logic Controllers (PLCs) are widely used in industrial automation systems, often installed both in centralized control rooms and on-site near production equipment. These systems frequently operate in harsh electromagnetic environments created by strong electrical circuits and devices. To enhance the reliability of PLC-based control systems, it's essential for manufacturers to improve the anti-interference capabilities of their equipment, while application departments must focus on proper engineering design, installation, and maintenance. Collaboration between all parties is key to effectively addressing electromagnetic interference (EMI) and ensuring system stability.

Electromagnetic interference can originate from various sources, including sudden changes in current or voltage, and these disturbances often affect the performance of PLCs. Interference types are typically classified based on their cause, noise mode, and waveform characteristics. Common categories include discharge noise, surge noise, high-frequency oscillation noise, continuous noise, sporadic noise, common-mode interference, and differential-mode interference.

Common-mode interference occurs when there is a potential difference between the signal and ground, often caused by electromagnetic radiation or differences in ground potential. This type of interference can be significant, especially when using power supplies with poor isolation, leading to voltages as high as 130V. Such voltages can convert into differential-mode interference through asymmetric circuits, affecting signal integrity and potentially damaging components. Differential-mode interference, on the other hand, occurs between the two poles of a signal, often due to coupling from nearby electromagnetic fields. It directly impacts measurement accuracy and control operations.

The main sources of EMI in PLC systems include radiated interference from space, conducted interference via power and signal lines, and internal interference from the system itself. Radiated interference comes from power grids, electrical transients, lightning, radio, TV, radar, and high-frequency heating equipment. Conducted interference, which is more prevalent in China’s industrial settings, enters through power and signal lines. Poor grounding can also introduce serious issues, such as ground loops that disrupt signal integrity and cause malfunctions.

To mitigate these challenges, comprehensive anti-interference design is crucial. This includes selecting high-quality equipment with strong electromagnetic compatibility, using shielded cables, implementing proper grounding techniques, and incorporating software-based filtering and error-checking mechanisms. Power supplies with good isolation and UPS systems can further enhance system resilience. Proper cable layout, avoiding mixing power and signal lines, and using dedicated grounding points are also vital steps in reducing EMI effects.

In conclusion, managing electromagnetic interference in PLC systems requires a multi-faceted approach. From hardware selection to software design, every aspect must be carefully considered. By understanding the nature of interference and applying appropriate mitigation strategies, engineers can ensure reliable and efficient operation of industrial automation systems.