Programmable logic controller: Difference between revisions

Revision as of 21:20, 14 June 2025

Revision as of 21:23, 14 June 2025

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[[File:PLC Control Panel.png|thumb|upright|Control panel with PLC (gray elements in the center). The unit consists of separate elements, from left to right: power supply, controller, relay units for input and output.]]

The main difference compared to most other computing devices is that PLCs are intended for and therefore tolerant of more severe environmental conditions (such as dust, moisture, heat, cold), while offering extensive [[input/output]] (I/O) to connect the PLC to [[sensor]]s and [[actuator]]s. PLC input can include simple digital elements such as [[limit switch]]es, analog variables from process sensors (such as temperature and pressure), and more complex data such as that from positioning or [[machine vision]] systems.<ref>Harms, Toni M. & Kinner, Russell H. P.E., ''Enhancing PLC Performance with Vision Systems''. 18th Annual ESD/HMI International Programmable Controllers Conference Proceedings, 1989, p. 387-399.</ref> PLC output can include elements such as indicator lamps, sirens, [[electric motor]]s, [[pneumatic]] or [[hydraulic]] cylinders, magnetic [[relay]]s, [[solenoid]]s, or analog outputs. The input/output arrangements may be built into a simple PLC, or the PLC may have external I/O modules attached to a fieldbus or computer network that plugs into the PLC.<!--[[User:Kvng/RTH]]-->

The functionality of the PLC has evolved over the years to include sequential relay control, motion control, [[process control]], [[distributed control system]]s, and [[computer network|networking]]. The data handling, storage, processing power, and communication capabilities of some modern PLCs are approximately equivalent to [[desktop computer]]s. PLC-like programming combined with remote I/O hardware, allows a general-purpose desktop computer to overlapserve someas PLCsa PLC in certain applications.{{citation needed|date=November 2014}} Desktop computer controllers have not been generally accepted in heavy industry because desktop computers run on less stable operating systems than PLCs, and because the desktop computer hardware is typically not designed to the same levels of tolerance to temperature, humidity, vibration, and longevity as the processors used in PLCs. Operating systems such as Windows do not lend themselves to deterministic logic execution, with the result that the controller may not always respond to changes of input status with the consistency in timing expected from PLCs. Desktop logic applications find use in less critical situations, such as laboratory automation and use in small facilities where the application is less demanding and critical.{{citation needed|date=November 2014}}<!--[[User:Kvng/RTH]]-->

===Basic functions===