PLC (programmable logic controller)

PLC (programmable logic controller)
Name	PLC (programmable logic controller)
Caption	Industrial programmable logic controller rack and modules
Invented	1968
Inventor	Bedford Associates
Country	United States
Used for	Industrial automation and control

PLC (programmable logic controller) is an industrial digital computer used for automation of electromechanical processes. It originated in the late 1960s for automotive manufacturing lines and has since been adopted across General Motors, Ford Motor Company, Toyota Motor Corporation, Siemens, and Schneider Electric. PLCs interface with sensors and actuators to execute control algorithms in manufacturing plants, power plants, and transport systems, and are central to digital transformation initiatives led by organizations such as ABB and Rockwell Automation.

History

The concept emerged after a 1968 request from General Motors to replace hard-wired relay controls during automobile production, leading to work by Bedford Associates and early products from companies like Modicon and GE. Early adoption was driven by the needs of Ford Motor Company, Daimler-Benz, and Nissan Motor Co., Ltd. as assembly lines expanded. The 1970s and 1980s saw standards and market consolidation influenced by Siemens, Schneider Electric, Rockwell Automation, Mitsubishi Electric, and Yokogawa Electric Corporation. Globalization and initiatives such as International Electrotechnical Commission committees and Institute of Electrical and Electronics Engineers working groups shaped interoperability and the growth of PLCs into sectors overseen by entities including ExxonMobil, Shell plc, and Siemens Gamesa Renewable Energy.

Design and Components

A PLC's hardware architecture typically includes a central processing unit influenced by microprocessor developments at Intel, Motorola, and ARM Holdings; modular input/output modules patterned after designs by Honeywell International; power supplies comparable to those used by ABB; and communication ports supporting protocols championed by OSI model proponents and vendors such as Cisco Systems and Siemens AG. Fieldbuses and industrial Ethernet options implement standards from PROFIBUS, PROFINET, Modbus, EtherNet/IP, and DeviceNet. Enclosures and ruggedization draw on military and aerospace practices from Lockheed Martin and Boeing, while human–machine interface design parallels work by General Electric and Schneider Electric.

Programming and Languages

PLC programming evolved from relay-logic replacements to formal languages standardized by International Organization for Standardization in IEC 61131-3, influenced by contributors including Siemens, Rockwell Automation, and Mitsubishi Electric. Common languages include Ladder Logic (rooted in relay schematics used by General Electric), Function Block Diagram (used by ABB and Schneider Electric), Structured Text (influenced by programming languages in Microsoft and Borland ecosystems), Instruction List, and Sequential Function Chart (adopted by Siemens for complex sequences). Development environments are provided by vendors such as Rockwell Automation's Studio 5000, Siemens's TIA Portal, and Schneider Electric's EcoStruxure Control Expert.

Operation and Control Functions

PLCs perform cyclic scanning, deterministic real-time scheduling, interrupt handling, and watchdog supervision comparable to real-time systems from Wind River Systems and QNX Software Systems. Control strategies include PID loops implemented per algorithms popularized by Siemens and Emerson Electric, motion control integrated with drives from Yaskawa Electric Corporation and Fanuc, and safety functions aligned with standards from International Electrotechnical Commission and Occupational Safety and Health Administration. Communications for supervisory control and data acquisition tie PLCs to systems by Schneider Electric and Siemens and to historians such as OSIsoft's PI System.

Applications and Industry Use

PLCs are ubiquitous across sectors: automotive assembly at Toyota Motor Corporation and Volkswagen Group, process control at BASF and Dow Chemical Company, energy management in Siemens Gamesa Renewable Energy wind farms, water treatment operations overseen by Veolia, and building automation projects by Johnson Controls. Transportation applications include railway signaling by Alstom and Siemens Mobility and airport baggage systems by ThyssenKrupp. PLCs also integrate into smart grid pilots led by General Electric and Eaton Corporation, and into pharmaceutical manufacturing regulated by agencies like U.S. Food and Drug Administration.

Safety, Reliability, and Standards

Safety-rated PLCs comply with standards such as IEC 61508 and ISO 13849, with supplier certification practices influenced by Underwriters Laboratories and TÜV Rheinland. Cybersecurity frameworks from National Institute of Standards and Technology and incident response coordination through organizations like Industrial Control Systems Cyber Emergency Response Team guide secure deployment. Redundancy schemes mirror high-availability patterns used by AT&T and Deutsche Telekom, while functional safety implementations reflect practices from Emerson Electric and Honeywell International.

Future Trends and Integration

Trends include edge computing architectures promoted by Microsoft Azure and Amazon Web Services IoT services, Industry 4.0 initiatives driven by Siemens and Bosch, and convergence with 5G wireless deployments advocated by Ericsson and Nokia. Machine learning integration references research from Google DeepMind and IBM Research for predictive maintenance, while open automation movements echo efforts from OPC Foundation and the Linux Foundation's industrial projects. Adoption in renewable energy and autonomous systems will involve partnerships among Siemens Gamesa Renewable Energy, Tesla, Inc., and General Electric.

Category:Industrial control systems