Programmable logic controller: Difference between revisions

Revision as of 19:47, 8 November 2024

Revision as of 22:16, 10 November 2024

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=== Communication ===

PLCs use built-in ports, such as [[USB]], [[Ethernet]], [[RS-232]], [[RS-485]], or [[RS-422]] to communicate with external devices (sensors, actuators) and systems ([[programming software]], [[SCADA]], [[Useruser interface|HMI]]). Communication is carried over various industrial network protocols, like [[Modbus]], or [[EtherNet/IP]]. Many of these protocols are vendor specific.

PLCs used in larger I/O systems may have [[peer-to-peer]] (P2P) communication between processors. This allows separate parts of a complex process to have individual control while allowing the subsystems to co-ordinate over the communication link. These communication links are also often used for [[Useruser interface|HMI]] devices such as keypads or [[Personal computer|PC]]-type workstations.

Formerly, some manufacturers offered dedicated communication modules as an add-on function where the processor had no network connection built-in.

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[[File:Control-panel-plc.jpg|thumb|upright|Control panel with a PLC user interface for [[Thermal oxidiser|thermal oxidizer]] regulation]]

PLCs may need to interact with people for the purpose of configuration, alarm reporting, or everyday control. A [[SCADA#Human-machine interface|human-machine interface]]{{Broken anchor|date=2024-11-08|bot=User:Cewbot/log/20201008/configuration|target_link=SCADA#Human-machine interface|reason=Anchor "SCADA#Human-machine interface" links to a specific web page: "Human Machine Interface". The anchor (Human-machine interface) [[Special:Diff/1194043441|has been deleted]].}} (HMI) is employed for this purpose. HMIs are also referred to as man-machine interfaces (MMIs) and graphical user interfaces (GUIs). A simple system may use buttons and lights to interact with the user. Text displays are available as well as graphical touch screens. More complex systems use programming and monitoring software installed on a computer, with the PLC connected via a communication interface.

==Process of a scan cycle==