Editing Control system (section)

==Logic control==
Logic control systems for industrial and commercial machinery were historically implemented by interconnected electrical [[relay]]s and [[cam timer]]s using [[ladder logic]]. Today, most such systems are constructed with [[microcontroller]]s or more specialized [[programmable logic controller]]s (PLCs). The notation of ladder logic is still in use as a programming method for PLCs.<ref name="Kuphaldt LADDER LOGIC">{{cite web|last=Kuphaldt|first=Tony R.|title=Chapter 6 LADDER LOGIC|url=http://www.ibiblio.org/kuphaldt/electricCircuits/Digital/DIGI_6.html|work=Lessons In Electric Circuits -- Volume IV|access-date=22 September 2010|url-status=live|archive-url=https://web.archive.org/web/20100912090415/http://www.ibiblio.org/kuphaldt/electricCircuits/Digital/DIGI_6.html|archive-date=12 September 2010}}</ref>

Logic controllers may respond to switches and sensors and can cause the machinery to start and stop various operations through the use of [[actuator]]s.  Logic controllers are used to sequence mechanical operations in many applications. Examples include elevators, washing machines and other systems with interrelated operations. An automatic sequential control system may trigger a series of mechanical actuators in the correct sequence to perform a task. For example, various electric and pneumatic transducers may fold and glue a cardboard box, fill it with the product and then seal it in an automatic packaging machine.

PLC software can be written in many different ways – ladder diagrams, SFC ([[sequential function chart]]s) or [[Instruction list|statement lists]].<ref name="Ian Brady PLCs">{{cite web|last=Brady|first=Ian|title=Programmable logic controllers - benefits and applications|url=http://www.optimacs.com/wp-content/uploads/2012/03/PLC-report.pdf|work=PLCs|access-date=5 December 2011|url-status=live|archive-url=https://web.archive.org/web/20140202000040/http://www.optimacs.com/wp-content/uploads/2012/03/PLC-report.pdf|archive-date=2 February 2014}}</ref>