Plc or programmable controller

Allen-Bradley[edit]
In a parallel development Odo Josef Struger is sometimes known as the "father of the programmable logic controller" as well.^[11] He was involved in the invention of the Allen‑Bradley programmable logic controller^[14][15][16] and is credited with inventing the PLC initialism.^[11][14] Allen-Bradley (now a brand owned by Rockwell Automation) became a major PLC manufacturer in the United States during his tenure.^[17] Struger played a leadership role in developing IEC 61131-3 PLC programming language standards.^[11]
Early methods of programming[edit]
Many early PLCs were not capable of graphical representation of the logic, and so it was instead represented as a series of logic expressions in some kind of Boolean format, similar to Boolean algebra. As programming terminals evolved, it became more common for ladder logic to be used, because it was a familiar format used for electro-mechanical control panels. Newer formats, such as state logic and Function Block (which is similar to the way logic is depicted when using digital integrated logic circuits) exist, but they are still^[when?] not as popular as ladder logic. A primary reason for this is that PLCs solve the logic in a predictable and repeating sequence, and ladder logic allows the person writing the logic to see any issues with the timing of the logic sequence more easily than would be possible in other formats.^[18]
Up to the mid-1990s, PLCs were programmed using proprietary programming panels or special-purpose programming terminals, which often had dedicated function keys representing the various logical elements of PLC programs.^[9] Some proprietary programming terminals displayed the elements of PLC programs as graphic symbols, but plain ASCII character representations of contacts, coils, and wires were common. Programs were stored on cassette tape cartridges. Facilities for printing and documentation were minimal due to a lack of memory capacity. The oldest PLCs used non-volatile magnetic core memory.
Architecture[edit]
A PLC is an industrial microprocessor-based controller with programmable memory used to store program instructions and various functions.^[19] It consists of:

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  a processor unit (CPU) which interprets inputs, executes the control program stored in memory and sends output signals,
  
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  a power supply unit which converts AC voltage to DC,
  
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  a memory unit storing data from inputs and program to be executed by the processor,
  
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  an input and output interface, where the controller receives and sends data from/to external devices,
  
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  a communications interface to receive and transmit data on communication networks from/to remote PLCs.^[20]
  

PLCs require programming device which is used to develop and later download the created program into the memory of the controller.^[20]
Modern PLCs generally contain a real-time operating system, such as OS-9 or VxWorks.^[21]