What programming standard governs PLCs?

The programming standard that governs Programmable Logic Controllers (PLCs) is IEC 61131-3. This standard is specifically tailored for industrial automation and provides a framework for PLC programming languages, including ladder diagram, structured text, function block diagram, instruction list, and sequential function chart. Each of these languages allows for various paradigms of programming, catering to different application needs and ensuring consistency in how PLCs are programmed and understood across different systems.

IEC 61131-3 defines not only the programming languages but also the overall structure for documenting and implementing programs, thus providing a unified approach for manufacturers and engineers. This ensures interoperability and comprehensibility of PLC software across various hardware and environments, which is essential for the seamless integration of automation systems.

The other standards mentioned, like ISO 9001, focus on quality management systems; ANSI C is a general-purpose programming language standard; and IEEE 802.3 pertains to Ethernet networking standards, none of which specifically address the programming and operation of PLCs. Each of these has a different scope and application area that does not align with the requirements and methodologies involved in PLC programming.