Standard PLC refers to Programmable Logic Controllers that are widely used in industrial automation, rather than a specific brand. However, leading PLC manufacturers include Siemens (Germany), Allen-Bradley/Rockwell Automation (USA), Mitsubishi Electric (Japan), and Omron (Japan). These companies provide PLCs for industries such as manufacturing, energy, and automotive. PLCs are modular devices that control machinery and processes, featuring input/output modules, processors, and communication interfaces. Major PLC series include Siemens SIMATIC, Allen-Bradley ControlLogix, and Mitsubishi MELSEC.