Editing SCADA (section)

== PLC/RTU programming ==

"Smart" RTUs, or standard PLCs, are capable of autonomously executing simple logic processes without involving the supervisory computer. They employ standardized control programming languages (such as those under [[IEC 61131-3]], a suite of five programming languages including function block, ladder, structured text, sequence function charts and instruction list), that are frequently used to create programs which run on these RTUs and PLCs.  Unlike a procedural language like [[C (programming language)|C]] or [[FORTRAN]], IEC 61131-3 has minimal training requirements by virtue of resembling historic physical control arrays. This allows SCADA system engineers to perform both the design and implementation of a program to be executed on an RTU or PLC.

A [[programmable automation controller]] (PAC) is a compact controller that combines the features and capabilities of a PC-based control system with that of a typical PLC. PACs are deployed in SCADA systems to provide RTU and PLC functions. In many [[electrical substation]] SCADA applications, "distributed RTUs" use information processors or station computers to communicate with [[digital protective relay]]s, PACs, and other devices for I/O, and communicate with the SCADA master in lieu of a traditional RTU.