Programmable logic controller: Difference between revisions

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Programmable logic controllers are intended to be used by engineers without a programming background. For this reason, a graphical programming language called [[ladder logic]] was first developed. It resembles the schematic diagram of a system built with electromechanical relays and was adopted by many manufacturers and later standardized in the [[IEC 61131-3]] control systems programming standard. {{As of|2015|post=,}} it is still widely used, thanks to its simplicity.<ref name=":6">{{Harvnb|Bolton|2015|pp=16–18}}</ref>

{{As of|2015|post=,}} the majority of PLC systems adhere to the [[IEC 61131-3]] standard that defines 2 textual programming languages: [[Structured Texttext]] (similar to [[Pascal (programming language)|Pascal]]) and [[Instruction Listlist]]; as well as 3 graphical languages: [[ladder logic]], [[function block diagram]] and [[sequential function chart]].<ref name=":6" /><ref>Keller, William L Jr. ''Grafcet, A Functional Chart for Sequential Processes'', 14th Annual International Programmable Controllers Conference Proceedings, 1984, p. 71-96.</ref> Instruction Listlist was deprecated in the third edition of the standard.<ref>{{Cite web|url=https://plcopen.org/status-iec-61131-3-standard |title=Status IEC 61131-3 Standard |date=2018-07-19 |website=PLCopen |access-date=2020-04-01 }}</ref>

Modern PLCs can be programmed in a variety of ways, from the relay-derived ladder logic to programming languages such as specially adapted dialects of [[BASIC]] and [[C (programming language)|C]].<ref>{{Cite web |title=Programmable logic controller for automation systems |url=https://www.isisvarese.edu.it/wp-content/uploads/2016/03/CLIL-5B-MEC-PLC.pdf |access-date=April 8, 2024 |website=www.isisvarese.edu.it}}</ref>