Programmable logic controller: Difference between revisions

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The hard-wired nature of these components made it difficult for design engineers to alter the automation process. Changes would require rewiring and careful updating of the documentation. Troubleshooting was a tedious process.<ref>{{Cite web |url=https://www.controlsystemsandautomation.com/learn/plc/plc-programming-basics-i/ |title=PLC Programming Basics Part I |date=2019-07-23 |website=Control Systems & Automation |access-date=2020-02-23 }}</ref> When general-purpose computers became available, they were soon applied to control logic in industrial processes. These early computers were unreliable<ref>{{Harvnb|Laughton|Warne|2002|p=16/3}}: "The first industrial computer application was probably a system installed in an oil refinery in Port Arthur USA in 1959. The reliability and mean time between failure of computers meant that little actual control was performed."</ref> and required specialist programmers and strict control of working conditions, such as temperature, cleanliness, and power quality.<ref>{{Harvnb|Parr|1998|p=437}}</ref>

The PLC provided several advantages over earlier automation systems. It toleratedwas designed to tolerate the industrial environment better than thesystems formerintended systemsfor office use, and was more reliable, compact, and required less maintenance than relay systems. It was easily extensible with additional I/O modules. While relay systems required complicated hardware changes in case of reconfiguration, a PLC can be reconfigured by loading new software. This allowed for easier iteration over manufacturing process design. With a simple programming language focused on logic and switching operations, it was more user-friendly than computers using [[general-purpose programming language]]s. Early PLCs were programmed in [[ladder logic]], which strongly resembled a schematic diagram of [[relay logic]]. It also permitted its operation to be monitored.<ref>{{Harvnb|Bolton|2015|p=6}}</ref><ref>{{Harvnb|Parr|1998|pp=438, 450–451}}</ref>

===Modicon===