A Comprehensive Review of PLC Automation for Industrial Process Control and Monitoring System

Abstract

Programmable Logic Controllers (PLCs) are key to modern industrial automation, offering reliable and flexible control for complex processes. This review outlines PLC architecture, operation, and their role in real-time monitoring, fault detection, and integration with sensors, actuators, and human–machine interfaces. Recent advances—faster processors, modular design, and open communication protocols—enhance scalability and interoperability. Emerging trends such as Industrial Internet of Things (IIoT) connectivity, cloud supervision, and AI-driven predictive maintenance are also discussed. The paper highlights how PLC automation improves safety, energy efficiency, and overall productivity in industrial process control and monitoring.

Introduction

???? Industrial Automation & PLCs – Summary

Industrial automation refers to the use of control systems—like computers, PLCs, and advanced technologies—to manage industrial equipment and processes with minimal human input. It enhances productivity, product quality, safety, and cost-efficiency in manufacturing and process industries.

?? Evolution and Modern Automation

• Evolved from mechanical relay logic to digital control systems.

• Introduction of Programmable Logic Controllers (PLCs) in the 1960s revolutionized automation by replacing hard-wired circuits with software-controlled systems.

• Modern automation integrates sensors, actuators, and distributed networks supported by protocols like Modbus, Profibus, and Ethernet/IP.

???? Industry 4.0 and IIoT

• The rise of Industry 4.0 and the Industrial Internet of Things (IIoT) has transformed automation:

  • Cloud computing, edge devices, AI, and predictive analytics now enable real-time monitoring and adaptive control.

  • Despite new technologies, PLCs remain central to industrial automation for their reliability and real-time performance.

???? PLCs: Architecture and Programming

• A PLC is a ruggedized digital computer designed for real-time industrial control.

• Core components:

  • Central Unit: CPU, memory, power supply

  • Programming Unit: Software interface (PC or console)

  • I/O Modules: Interface with sensors/actuators

  • Base Unit: Mounting and integration platform

• Programming Languages (IEC 61131-3 standard):

  • Ladder Diagram (LD)

  • Function Block Diagram (FBD)

  • Structured Text (ST)

  • Instruction List (IL - deprecated)

  • Sequential Function Chart (SFC)

???? Literature Review & Role in Industry

• PLCs acquire sensor data, execute control logic, and actuate outputs (motors, valves, etc.).

• Used in discrete, continuous, and batch processes across industries such as:

  • Manufacturing

  • Chemical/Petrochemical

  • Pharmaceutical

  • Utilities (water, power)

  • Infrastructure (building automation)

• Integrated with SCADA/DCS systems for high-level control and monitoring.

???? Communication and Networking

• Communication is key for integrating PLCs with field and enterprise systems.

• Uses industrial protocols: Modbus, Profibus, DeviceNet, Ethernet/IP, OPC UA.

• Network topologies include hierarchical, ring, and mesh structures with fault tolerance and cybersecurity features.

• IIoT integration allows remote monitoring, cloud data access, and predictive maintenance.

???? Modern Trends & Future Outlook

• Integration with AI/ML for adaptive control and process optimization.

• Advanced cybersecurity built into PLCs to protect against network threats.

• Emergence of soft PLCs (software-based on general-purpose hardware) for cost-effective, scalable solutions.

• Modular and compact hardware supports energy-efficient, space-saving deployment.

• Ongoing focus on real-time analytics, cloud connectivity, and edge computing.

????? Applications of PLCs

PLCs are used extensively in:

• Discrete Manufacturing: Robotic cells, assembly lines, packaging

• Process Industries: Control of temperature, flow, pressure, dosing, and mixing

• Utilities & Infrastructure: Power plants, water treatment, smart buildings

• Support predictive maintenance, remote diagnostics, and data-driven decision-making

• Seamlessly interface with SCADA, DCS, and enterprise systems

? Key Advantages of PLCs

• Rugged, reliable, and built for harsh environments

• Deterministic, real-time control

• Modular, scalable, and easy to maintain

• High compatibility with modern automation technologies

Conclusion

Programmable Logic Controllers (PLCs) continue to serve as the foundational element of industrial automation, offering deterministic, real-time control across discrete, continuous, and batch processes. Their adaptability, modular architecture, and robust design make them highly effective for integration with modern supervisory systems, communication networks, and Industry 4.0 frameworks, including IIoT, cloud-based analytics, and predictive maintenance. While Distributed Control Systems (DCS) and Programmable Automation Controllers (PACs) provide complementary solutions for large-scale or hybrid processes, PLCs remain indispensable due to their versatility, ease of programming, and reliability under harsh industrial conditions. Future developments in AI-driven control, edge computing, enhanced cybersecurity, and advanced data analytics are poised to further extend PLC capabilities, enabling more intelligent, resilient, and optimized industrial operations.

References

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Copyright

Copyright © 2025 Dr. D. A. Shahakar, Sai R Bhoyar, Priti V. Wath, Samir Deshmukh, Pratik Tayde, Sudhanshu Pusadkar, Hemant Tawale. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.