Since its birth in the late 1960s, PLC (Programmable Logic Controller) has undergone significant technological evolution and application expansion, and has become a core device in industrial automation. The following are the key stages and trends of its development:

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### I. Development History
1. Origin (1960s-1970s
– ** Background ** : The demand was proposed by General Motors (GM) in 1968 to replace the complex relay control system in the automotive manufacturing industry.
– ** First-generation PLC** : In 1969, Modicon (now part of Schneider) launched the 084 model, which adopted ladder diagram programming and had basic logic control functions.
– ** Features ** : Large in size, simple in function, and only supports switch control.

2. Technological Upgrading (1980s
– ** Microprocessor Applications ** : Faster cpus are adopted to enhance processing capabilities.
– ** Function Expansion ** : Supports analog control, PID regulation, and data storage.
– ** Communication capability ** : The RS-232/485 interface is introduced to achieve communication between PLCS.

3. Standardization and Openness (1990s
– **IEC 61131-3 standard ** : Unified five programming languages (ladder diagram LD, Structured text ST, etc.).
– ** Network Integration ** : Supports fieldbuses (such as Profibus, CAN) to achieve device-level networking.
– ** Software Ecosystem ** : Graphical programming software (such as Siemens Step7) to enhance development efficiency.

4. High Performance and Integration (post-2000s
– ** Processing capacity ** : Multi-core CPU, large-capacity memory, supporting complex algorithms (such as motion control).
– **IT/OT Convergence ** : Integrate Ethernet, Web services, and OPC UA protocol, and seamlessly connect with MES/ERP systems.
– ** Modular design ** : Supports hot plugging and distributed I/O (such as Profinet, EtherCAT).

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### II. Trends in Technological Evolution
“Hardware Innovation
– ** Parallel miniaturization and high performance ** : Micro PLCS (such as the Siemens LOGO!) Used for simple tasks; Large PLCS support multi-axis motion control (such as Rockwell ControlLogix).
– ** Security Integration ** : Built-in security functions (Security I/O, Security PLC), in compliance with ISO 13849 standard.

2. “Software and Ecosystem
– ** Open Platform ** : Supports high-level languages such as C/C++, Python (such as B&R Automation Studio).
– ** Cloud connection ** : Connect to the cloud (such as Siemens MindSphere) via MQTT/HTTP protocols.
– ** Simulation and Digital Twin ** : Virtual debugging technology reduces development risks.

3. ** Communication Protocol Evolution **
– ** Industrial EtherNet dominates ** : Profinet and EtherNet/IP account for over 70% of the global market (HMS 2023 Report).
– ** Time-Sensitive Networking (TSN) ** : Achieves deterministic real-time communication and supports the coexistence of multiple protocols.

4. “Edge Computing Convergence
The PLC integrates edge gateway functionality to process data locally (such as Schneider EcoStruxure), reducing the load on the cloud.

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### III. Future Direction
“AI Integration
Embed machine learning algorithms to achieve predictive maintenance (such as the collaboration between Rockwell and NVIDIA).
2. ** Network Security Enhancement **
Hardware-level encryption and zero-trust architecture address OT security threats.
3. Popularization of Soft PLC
Pc-based software controllers (such as CODESYS) reduce costs and enhance flexibility.
4. “Sustainability
Low power consumption design, supporting green manufacturing (energy management function).

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### IV. Market Impact
– ** Application Field Expansion ** : Extended from traditional manufacturing to new energy (photovoltaic, energy storage), logistics, and smart buildings.
– ** Market Size ** : The global PLC market exceeded 13 billion US dollars in 2023 and is expected to reach 18 billion by 2027 (MarketsandMarkets data).
– ** Chinese Role ** : The rise of domestic brands (Xinjie, Inovance), with a market share of over 40% in the mid-to-low-end market.

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“Summary
PLC has evolved from a simple substitute for relays to a core node of Industry 4.0. In the future, it will continue to drive the automation revolution through openness, intelligence and security. Its deep integration with IT technologies (such as AI and cloud computing) will reshape the boundaries of industrial control systems.