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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.
Part 3 of IEC 61131 deals with basic software architecture and programming languages of the control program within PLC. It defines three graphical and two textual programming language standards: Ladder diagram (LD), graphical; Function block diagram (FBD), graphical; Structured text (ST), textual
Function Block Diagram is one of five languages for logic or control configuration [2] supported by standard IEC 61131-3 for a control system such as a programmable logic controller (PLC) or a Distributed Control System (DCS). The other supported languages are ladder logic, sequential function chart, structured text, and instruction list.
Block diagram of a basic computer with uniprocessor CPU. Black lines indicate control flow, whereas red lines indicate data flow. Arrows indicate the direction of flow. In computer science and computer engineering, computer architecture is a description of the structure of a computer system made from component parts. [1]
A von Neumann architecture scheme. The von Neumann architecture—also known as the von Neumann model or Princeton architecture—is a computer architecture based on the First Draft of a Report on the EDVAC, [1] written by John von Neumann in 1945, describing designs discussed with John Mauchly and J. Presper Eckert at the University of Pennsylvania's Moore School of Electrical Engineering.
It is also possible to insert LD (Ladder Diagram) actions inside an SFC program (and this is the standard way, for instance, to work on integer variables). SFC is an inherently parallel programming language in that multiple control flows — Program Organization Units (POUs) in the standard's parlance — can be active at once.
The accompanying diagram is a general hierarchical model which shows functional manufacturing levels using computerised control of an industrial control system. Referring to the diagram; Level 0 contains the field devices such as flow and temperature sensors, and final control elements, such as control valves
Siemens SIMATIC S7-300 PLC CPU with three I/O modules attached. As with other programmable logic controllers, SIMATIC devices are intended to separate the control of a machine from the machine's direct operation, in a more lightweight and versatile manner than controls hard-wired for a specific machine. Early SIMATIC devices were transistor ...