Programmable logic controller
digital computer used for automation of electromechanical processes
A programmable logic controller (PLC) or programmable controller is an industrial computer that has been ruggedized and adapted for the control of manufacturing processes, such as assembly lines, machines, robotic devices, or any activity that requires high reliability, ease of programming, and process fault diagnosis.
PLCs can range from small modular devices with tens of inputs and outputs (I/O), in a housing integral with the processor, to large rack-mounted modular devices with thousands of I/O, and which are often networked to other PLC and SCADA systems. They can be designed for many arrangements of digital and analog I/O, extended temperature ranges, immunity to electrical noise, and resistance to vibration and impact.
PLCs were first developed in the automobile manufacturing industry to provide flexible, rugged and easily programmable controllers which could replace hard-wired relay logic systems. Dick Morley is credited with having invented the first PLC, the Modicon 084, for General Motors in 1968.
A PLC is an example of a hard real-time system: output results must be produced in response to input conditions within a limited time, so that unintended operations do not result. Programs to control machine operation are typically stored in battery-backed-up or non-volatile memory.
Invention and early development
The PLC originated in the late 1960s in the automotive industry in the US and was designed to replace relay logic systems. Before, control logic for manufacturing was mainly composed of relays, cam timers, drum sequencers, and dedicated closed-loop controllers.
The hard-wired nature of these components made it difficult for design engineers to alter the automation process.
“Programmable logic controller” enters the record as digital computer used for automation of electromechanical processes. Crown Archives preserves that source wording while asking what Programmable, logic and controller can confirm, complicate or overturn.
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