programmable logic controller

programmable logic controller
Name	Programmable logic controller
Invented	1960s
Inventors	Bedford engineers at General Motors Corporation and later firms such as Modicon, Allen-Bradley
Developer	Modicon, Rockwell Automation, Siemens AG, Schneider Electric, Mitsubishi Electric
Application	Industrial automation, process control, discrete manufacturing

programmable logic controller

A programmable logic controller (PLC) is a ruggedized industrial digital computer used for automation of electromechanical processes in factories, plants, and infrastructure. PLCs originated in the late 1960s to replace relay logic in manufacturing lines and evolved through contributions by companies such as General Electric Company, Modicon, and Siemens AG into modular, networked controllers central to modern automation. Major vendors including Rockwell Automation, Schneider Electric, Mitsubishi Electric, ABB, and Omron Corporation advanced hardware, software, and networking to meet requirements from industries served by International Electrotechnical Commission and Institute of Electrical and Electronics Engineers standards.

History

Early PLC concepts grew from military and aerospace programmable devices developed by firms like Honeywell International and laboratories at MIT. The first commercial PLC was introduced by Modicon to serve General Motors Corporation assembly lines, replacing complex panels of relays used in automotive plants in Detroit. Subsequent development involved companies such as Allen-Bradley and Siemens AG, with each contributing to standardization efforts by organizations like IEC and IEEE. The 1970s and 1980s saw transition from proprietary ladder logic to vendor-supported development environments influenced by computing advances at firms such as Intel Corporation and Microsoft Corporation. The 1990s and 2000s introduced Ethernet-based communication influenced by Cisco Systems networking, and the 2010s emphasized convergence with Rockwell Automation and Schneider Electric solutions integrating safety and cybersecurity guidelines from NIST and ISO.

Architecture and Components

A typical PLC chassis contains a central processing unit produced by firms like Siemens AG or Mitsubishi Electric, input/output modules from suppliers such as Schneider Electric or ABB, and power supplies offered by vendors like Phoenix Contact. The CPU hosts a real-time operating system influenced by embedded designs from Wind River Systems and includes memory modules, clock circuits, and firmware often developed in collaboration with companies such as Texas Instruments. I/O modules provide digital and analog interfaces compatible with field devices from Emerson Electric and Endress+Hauser. Specialty modules include motion control by Yaskawa Electric and safety-rated modules conforming to ISO and IEC functional safety frameworks advocated by Safety Instrumented Systems committees. Enclosures and physical mounting adhere to standards promulgated by National Electrical Manufacturers Association.

Programming and Languages

PLC programming historically used ladder diagram influenced by relay logic and popularized by vendors like Allen-Bradley; other languages include function block diagram and structured text specified in IEC 61131-3, a standard developed with input from Siemens AG and Schneider Electric. Development environments from Rockwell Automation, Siemens AG (STEP 7), and Mitsubishi Electric provide editors, compilers, and simulation tools; integration with version control systems from Atlassian or GitLab aids lifecycle management. High-level integration with systems from Siemens AG and ABB uses OPC UA promoted by OPC Foundation and supports model-based engineering influenced by research at Fraunhofer Society.

Applications and Industries

PLCs are deployed across sectors served by major industrial firms: automotive lines of Toyota Motor Corporation and Volkswagen Group, process plants of Royal Dutch Shell and BP plc, and utilities managed by companies such as Siemens AG and General Electric Company. They control packaging machinery used by Procter & Gamble and Nestlé S.A., building automation in projects by Johnson Controls International, and conveyor systems in logistics operations by Amazon.com, Inc. and DHL. Specialized applications include water treatment overseen by municipal authorities influenced by World Health Organization guidelines, oil and gas facilities operated by ExxonMobil, and renewable energy sites by Vestas Wind Systems.

Communication and Networking

Modern PLCs integrate industrial protocols promoted by organizations such as ODVA and FieldComm Group, including EtherNet/IP supported by Rockwell Automation, PROFINET championed by Siemens AG, and Modbus maintained by Schneider Electric affiliates. Gateways and switches from Cisco Systems and Hirschmann Automation and Control enable segmented networks complying with IEC 62443 cybersecurity guidelines influenced by NIST. Integration with supervisory systems from Wonderware and historians by OSIsoft (now part of AVEVA) uses OPC UA endorsed by the OPC Foundation for cross-vendor interoperability.

Safety, Reliability, and Standards

Safety standards such as IEC 61508 and ISO 13849 guide design of safety PLCs used by manufacturers including Pilz and Schneider Electric. Reliability practices draw on quality frameworks from ISO and lifecycle processes advocated by ISA (International Society of Automation). Certification bodies like Underwriters Laboratories and TÜV SÜD test safety functions, while cybersecurity standards from NIST and IEC 62443 shape secure deployment in critical infrastructure managed by entities like National Grid plc.

Maintenance and Troubleshooting

Maintenance procedures follow asset management practices from ISO 55000 and predictive maintenance techniques promoted by General Electric Company's industrial analytics units. Troubleshooting uses vendor tools from Siemens AG, Rockwell Automation, and Schneider Electric for online diagnostics, firmware updates, and ladder logic simulation; field technicians often train with institutions such as Technical and Further Education colleges or corporate programs at ABB and Siemens AG. Spare parts and lifecycle support rely on vendor networks including Rockwell Automation and regional distributors certified by Underwriters Laboratories.

Category:Industrial automation