Programmable logic controller

PLCPLCsprogrammable logic controllersprogrammable controllersprogrammable logic controlProgrammable controllerprogrammable logic controller (PLC)central process controller (PLC)CNCcontrol computer
A programmable logic controller (PLC) or programmable controller is an industrial digital computer which has been ruggedized and adapted for the control of manufacturing processes, such as assembly lines, or robotic devices, or any activity that requires high reliability control and ease of programming and process fault diagnosis.wikipedia
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Computer

computerscomputer systemdigital computer
A programmable logic controller (PLC) or programmable controller is an industrial digital computer which has been ruggedized and adapted for the control of manufacturing processes, such as assembly lines, or robotic devices, or any activity that requires high reliability control and ease of programming and process fault diagnosis.
Computers are used as control systems for a wide variety of industrial and consumer devices.

SCADA

supervisory control and data acquisitionSupervisory Control and Data Acquisition (SCADA)Supervisory control (SCADA)
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 a count of thousands of I/O, and which are often networked to other PLC and SCADA systems.
Supervisory Control and Data Acquisition (SCADA) is a control system architecture that uses computers networked data communications and graphical user interfaces(GUI) for high-level process supervisory management, but uses other peripheral devices such as programmable logic controller (PLC) and discrete Proportional Integral Differentiator (PID) controllers to interface with the process plant or machinery.

Dick Morley

Richard E. Morley
One of the people who worked on that project was Dick Morley, who is considered to be the "father" of the PLC.
Richard E. "Dick" Morley (December 1, 1932 – October 17, 2017) was an American mechanical engineer who was considered one of the "fathers" of the programmable logic controller (PLC) since he was involved with the production of the first PLC for General Motors, the Modicon, at Bedford and Associates in 1968.

Ladder logic

Ladder diagramRelay Ladder LogicLadder programming language
It was for this reason PLCs were programmed in "ladder logic", which strongly resembles a schematic diagram of relay logic. IEC 61131-3 currently defines five programming languages for programmable control systems: function block diagram (FBD), ladder diagram (LD), structured text (ST; similar to the Pascal programming language), instruction list (IL; similar to assembly language), and sequential function chart (SFC).
Ladder logic is used to develop software for programmable logic controllers (PLCs) used in industrial control applications.

Relay

relayslatching relayelectric relay
Before the PLC, control, sequencing, and safety interlock logic for manufacturing automobiles was mainly composed of relays, cam timers, drum sequencers, and dedicated closed-loop controllers.
Although such relays once were the backbone of automation in such industries as automobile assembly, the programmable logic controller (PLC) mostly displaced the machine tool relay from sequential control applications.

Instruction list

Statement Liststatement lists
Other early PLCs used a form of instruction list programming, based on a stack-based logic solver. IEC 61131-3 currently defines five programming languages for programmable control systems: function block diagram (FBD), ladder diagram (LD), structured text (ST; similar to the Pascal programming language), instruction list (IL; similar to assembly language), and sequential function chart (SFC).
It is designed for programmable logic controllers (PLCs).

Cam timer

drum sequencersequencerDrum sequencer (controller)
Before the PLC, control, sequencing, and safety interlock logic for manufacturing automobiles was mainly composed of relays, cam timers, drum sequencers, and dedicated closed-loop controllers.
Cam timers in industry were superseded with the introduction of programmable logic controllers (PLCs), which offer improved flexibility and more complicated control logic functions.

Sequential function chart

Discrete process controlSFC
The majority of PLC systems today adhere to the IEC 61131/3 control systems programming standard that defines 5 languages: Ladder Diagram (LD), Structured Text (ST), Function Block Diagram (FBD), Instruction List (IL) and sequential function chart (SFC). IEC 61131-3 currently defines five programming languages for programmable control systems: function block diagram (FBD), ladder diagram (LD), structured text (ST; similar to the Pascal programming language), instruction list (IL; similar to assembly language), and sequential function chart (SFC).
Sequential function chart (SFC) is a graphical programming language used for programmable logic controllers (PLCs).

Allen-Bradley

Allen BradleyAllen-Bradley CompanyA-B
He was involved in the invention of the Allen-Bradley programmable logic controller (PLC) during 1958 to 1960.
The company, with revenues of approximately US $6.4 billion in 2013, manufactures programmable logic controllers (PLC), human-machine interfaces, sensors, safety components and systems, software, drives and drive systems, contactors, motor control centers, and systems of such products.

State logic

Another method is state logic, a very high-level programming language designed to program PLCs based on state transition diagrams.
A state logic control system is a programming method created for PLCs.

Gould Electronics

GouldGould-National BatteriesGould NavCom Systems
The Modicon brand was sold in 1977 to Gould Electronics, later acquired by German Company AEG, and then by French Schneider Electric, the current owner.
From 1977 to the mid-1980s the company owned the Modicon brand of programmable logic controller that is now owned by Schneider Electric.

Odo Josef Struger

In a parallel development Odo Josef Struger is sometimes known as the "father of the programmable logic controller" as well.
Struger was involved in the invention of the Allen-Bradley programmable logic controller (PLC) during 1958 to 1960.

Function block diagram

IEC 61131-3 currently defines five programming languages for programmable control systems: function block diagram (FBD), ladder diagram (LD), structured text (ST; similar to the Pascal programming language), instruction list (IL; similar to assembly language), and sequential function chart (SFC).
The Function Block Diagram (FBD) is a graphical language for programmable logic controller design, that can describe the function between input variables and output variables.

IEC 61131-3

IEC61131 Common ElementsIEC 1131-3Part 3
Under the IEC 61131-3 standard, PLCs can be programmed using standards-based programming languages.
IEC 61131-3 is the third part (of 10) of the open international standard IEC 61131 for programmable logic controllers, and was first published in December 1993 by the IEC.

RS-232

RS232RS-232Cserial
The computer is connected to the PLC through USB, Ethernet, RS-232, RS-485, or RS-422 cabling.
RS-232 is still used to connect older designs of peripherals, industrial equipment (such as PLCs), console ports, and special purpose equipment.

Process control

controlindustrial process controlProcess Controls
The functionality of the PLC has evolved over the years to include sequential relay control, motion control, process control, distributed control systems, and networking.
Commonly used controllers are programmable logic controller (PLC), Distributed Control System (DCS) or SCADA.

Structured text

Structured Control Language
IEC 61131-3 currently defines five programming languages for programmable control systems: function block diagram (FBD), ladder diagram (LD), structured text (ST; similar to the Pascal programming language), instruction list (IL; similar to assembly language), and sequential function chart (SFC). In some software packages, it is also possible to view and edit the program in function block diagrams, sequence flow charts and structured text.
Structured text, abbreviated as ST or STX, is one of the five languages supported by the IEC 61131-3 standard, designed for programmable logic controllers (PLCs).

Stuxnet

cyberattacksIran in 2010Staxnut
Prior to the discovery of the Stuxnet computer worm in June 2010, security of PLCs received little attention.
Stuxnet specifically targets programmable logic controllers (PLCs), which allow the automation of electromechanical processes such as those used to control machinery and industrial processes including centrifuges for separating nuclear material.

RS-485

RS485EIA-485Serial
The computer is connected to the PLC through USB, Ethernet, RS-232, RS-485, or RS-422 cabling.
These are used in programmable logic controllers and on factory floors.

Rockwell Automation

RockwellRockwell Automation Inc.Reliance Electric
Allen-Bradley (now a brand owned by Rockwell Automation), the manufacturer of the controller, became a major programmable logic controller device manufacturer in the United States during the tenure of Struger.

Automation

automatedindustrial automationautomatic control
PLCs are well adapted to a range of automation tasks.
Special computers called programmable logic controllers were later designed to replace these collections of hardware with a single, more easily re-programmed unit.

Magnetic-core memory

core memorymagnetic core memoryferrite core memory
The oldest PLCs used non-volatile magnetic core memory.
These were important advantages for some applications like first-generation industrial programmable controllers, military installations and vehicles like fighter aircraft, as well as spacecraft, and led to core being used for a number of years after availability of semiconductor MOS memory (see also MOSFET).

Distributed control system

DCSdistributed controldistributed control system (DCS)
The functionality of the PLC has evolved over the years to include sequential relay control, motion control, process control, distributed control systems, and networking.
The 1980s also witnessed the first PLCs integrated into the DCS infrastructure.

PLC technician

PLC technicians design, program, repair and maintain programmable logic controller (PLC) systems used within manufacturing and service industries ranging from industrial packaging to commercial car washes and traffic lights.

Limit switch

electromechanical limit switcheswire arm
PLC input can include simple digital elements such as limit switches, analog variables from process sensors (such as temperature and pressure), and more complex data such as that from positioning or machine vision systems.
Rarely, a final operating device such as a lamp or solenoid valve will be directly controlled by the contacts of an industrial limit switch, but more typically the limit switch will be wired through a control relay, a motor contactor control circuit, or as an input to a programmable logic controller.