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A programmable logic controller (PLC), or programmable controller is a digital computer used for automation of industrial processes, such as control of machinery on factory assembly lines. Unlike general-purpose computers, the PLC is designed for multiple inputs and output arrangements, extended temperature ranges, immunity to electrical noise, and resistance to vibration and impact. Programs to control machine operation are typically stored in battery-backed or non-volatile memory. A PLC is an example of a real time system since output results must be produced in response to input conditions within a bounded time, otherwise unintended operation will result. ImageMetadata File history File links Download high resolution version (1600x1200, 239 KB) deux automates siemens reliés via MPI avec ses modules entrées-sorties(TOR, ana, rapide) & de communication déportés via profibus codeur analyseur de trame boitier de simulation des entrées-sorties TOR & analogiques File links...
ImageMetadata File history File links Download high resolution version (1600x1200, 239 KB) deux automates siemens reliés via MPI avec ses modules entrées-sorties(TOR, ana, rapide) & de communication déportés via profibus codeur analyseur de trame boitier de simulation des entrées-sorties TOR & analogiques File links...
Energy Input: The energy placed into a reaction. ...
This article does not cite any references or sources. ...
Non-volatile storage is a category of computer storage. ...
It has been suggested that Real-time computing be merged into this article or section. ...
Features The main difference from other computers is that PLC are armored for severe condition (dust, moisture, heat, cold, etc) and have the facility for extensive input/output (I/O) arrangements. These connect the PLC to sensors and actuators. PLCs read limit switches, analog process variables (such as temperature and pressure), and the positions of complex positioning systems. Some even use machine vision. On the actuator side, PLCs operate electric motors, pneumatic or hydraulic cylinders, magnetic relays or solenoids, or analog outputs. The input/output arrangements may be built into a simple PLC, or the PLC may have external I/O modules attached to a computer network that plugs into the PLC. Image File history File links Size of this preview: 383 × 600 pixelsFull resolution (428 × 670 pixel, file size: 495 KB, MIME type: image/png) Made by me of a constructed panel with my digital camera I, the creator of this work, hereby release it into the public domain. ...
Image File history File links Size of this preview: 383 × 600 pixelsFull resolution (428 × 670 pixel, file size: 495 KB, MIME type: image/png) Made by me of a constructed panel with my digital camera I, the creator of this work, hereby release it into the public domain. ...
Energy Input: The energy placed into a reaction. ...
Not to be confused with censure, censer, or censor. ...
An actuator is a mechanical device for moving or controlling a mechanism or system. ...
Electrical switches. ...
Machine vision (MV) is the application of computer vision to industry and manufacturing. ...
For other kinds of motors, see motor. ...
Pneumatics, from the Greek πνευματικός (pneumatikos, coming from the wind) is the use of pressurized air in science and technology. ...
Hydraulics is a branch of science and engineering concerned with the use of liquids to perform mechanical tasks. ...
Automotive style miniature relay A relay is an electrical switch that opens and closes under the control of another electrical circuit. ...
Various solenoid actuators from Trombetta Motion Technologies A solenoid is a loop of wire, often wrapped around a metallic core, which produces a magnetic field when an electrical current is passed through it. ...
PLCs were invented as replacements for automated systems that would use hundreds or thousands of relays, cam timers, and drum sequencers. Often, a single PLC can be programmed to replace thousands of relays. Programmable controllers were initially adopted by the automotive manufacturing industry, where software revision replaced the re-wiring of hard-wired control panels when production models changed. Automotive style miniature relay A relay is an electrical switch that opens and closes under the control of another electrical circuit. ...
A cam timer is an electromechanical system for controlling a sequence of events automatically. ...
Relay as used in cars A relay is an electromechanical switch that uses an electromagnet to open or close one or many sets of contacts. ...
Many of the earliest PLCs expressed all decision making logic in simple ladder logic which appeared similar to electrical schematic diagrams. The electricians were quite able to trace out circuit problems with schematic diagrams using ladder logic. This program notation was chosen to reduce training demands for the existing technicians. Other early PLCs used a form of instruction list programming, based on a stack-based logic solver. Ladder logic is a method of drawing electrical logic schematics. ...
Instruction List is one of the 5 languages supported by the IEC 61131-3 standard. ...
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 data handling, storage, processing power and communication capabilities of some modern PLCs are approximately equivalent to desktop computers. PLC-like programming combined with remote I/O hardware, allow a general-purpose desktop computer to overlap some PLCs in certain applications. Process control is an engineering discipline that deals with architectures, mechanisms, and algorithms for controlling the output of a specific process. ...
A distributed control system (DCS) refers to a control system usually of a manufacturing system, process or any kind of dynamic system, in which the controller elements are not central in location (like the brain) but are distributed throughout the system with each component sub-system controlled by one or...
Computer networks may be classified according to the network layer at which they operate according to some basic reference models that are considered to be standards in the industry such as the seven layer OSI reference model and the four layer Internet Protocol Suite model. ...
Desktop computer with several common peripherals (Monitor, keyboard, mouse, speakers, microphone and a printer) A desktop computer is a computer made for use on a desk in an office or home and is distinguished from portable computers such as laptops or PDAs. ...
Under the IEC 61131-3 standard, PLCs can be programmed using standards-based programming languages. A graphical programming notation called Sequential Function Charts is available on certain programmable controllers. IEC 61131-3 is a standard published in December 1993 by the IEC. It defines five PLC programming language standards: Ladder logic Sequential function chart Function block diagram Structured text Instruction list It is the third publication in the series IEC 61131. ...
Sequential function chart (SFC) is a graphical programming language used for PLCs. ...
PLC compared with other control systems PLCs are well-adapted to a range of automation tasks. These are typically industrial processes in manufacturing where the cost of developing and maintaining the automation system is high relative to the total cost of the automation, and where changes to the system would be expected during its operational life. PLCs contain input and output devices compatible with industrial pilot devices and controls; little electrical design is required, and the design problem centers on expressing the desired sequence of operations in ladder logic (or function chart) notation. PLC applications are typically highly customized systems so the cost of a packaged PLC is low compared to the cost of a specific custom-built controller design. On the other hand, in the case of mass-produced goods, customized control systems are economic due to the lower cost of the components, which can be optimally chosen instead of a "generic" solution, and where the non-recurring engineering charges are spread over thousands of sales.
For high volume or very simple fixed automation tasks, different techniques are used. For example, a consumer dishwasher would be controlled by an electromechanical cam timer costing only a few dollars in production quantities. A Dishwasher A two drawer DishDrawer dishwasher. ...
A cam timer is an electromechanical system for controlling a sequence of events automatically. ...
A microcontroller-based design would be appropriate where hundreds or thousands of units will be produced and so the development cost (design of power supplies and input/output hardware) can be spread over many sales, and where the end-user would not need to alter the control. Automotive applications are an example; millions of units are built each year, and very few end-users alter the programming of these controllers. However, some specialty vehicles such as transit busses economically use PLCs instead of custom-designed controls, because the volumes are low and the development cost would be uneconomic. It has been suggested that this article or section be merged with embedded microprocessor. ...
Very complex process control, such as used in the chemical industry, may require algorithms and performance beyond the capability of even high-performance PLCs. Very high-speed or precision controls may also require customized solutions; for example, aircraft flight controls.
PLCs may include logic for single-variable feedback analog control loop, a "proportional, integral, derivative" or "PID controller." A PID loop could be used to control the temperature of a manufacturing process, for example. Historically PLCs were usually configured with only a few analog control loops; where processes required hundreds or thousands of loops, a distributed control system (DCS) would instead be used. However, as PLCs have become more powerful, the boundary between DCS and PLC applications has become less clear-cut. This article or section is in need of attention from an expert on the subject. ...
A distributed control system (DCS) refers to a control system usually of a manufacturing system, process or any kind of dynamic system, in which the controller elements are not central in location (like the brain) but are distributed throughout the system with each component sub-system controlled by one or...
Digital and analog signals Digital or discrete signals behave as binary switches, yielding simply an On or Off signal (1 or 0, True or False, respectively). Pushbuttons, limit switches, and photoelectric sensors are examples of devices providing a discrete signal. Discrete signals are sent using either voltage or current, where a specific range is designated as On and another as Off. For example, a PLC might use 24 V DC I/O, with values above 22 V DC representing On, values below 2VDC representing Off, and intermediate values undefined. Initially, PLCs had only discrete I/O. A photoelectric sensor, or photoeye, is a device used to detect the presence of an object by using a light transmitter, often infrared, and a photoelectric receiver. ...
International safety symbol Caution, risk of electric shock (ISO 3864), colloquially known as high voltage symbol. ...
In electricity, current refers to electric current, which is the flow of electric charge. ...
Analog signals are like volume controls, with a range of values between zero and full-scale. These are typically interpreted as integer values (counts) by the PLC, with various ranges of accuracy depending on the device and the number of bits available to store the data. As PLCs typically use 16-bit signed binary processors, the integer values are limited between -32,768 and +32,767. Pressure, temperature, flow, and weight are often represented by analog signals. Analog signals can use voltage or current with a magnitude proportional to the value of the process signal. For example, an analog 4-20 mA or 0 - 10 V input would be converted into an integer value of 0 - 32767. International safety symbol Caution, risk of electric shock (ISO 3864), colloquially known as high voltage symbol. ...
In electricity, current refers to electric current, which is the flow of electric charge. ...
4-20 ma is an analog electrical transmission standard for industrial instrumentation. ...
An analog-to-digital converter (abbreviated ADC, A/D, or A to D) is a device that converts continuous signals to discrete digital numbers. ...
Current inputs are less sensitive to electrical noise (i.e. from welders or electric motor starts) than voltage inputs. A current loop describes two different electrical signalling schemes. ...
Example As an example, say the facility needs to store water in a tank. The water is drawn from the tank by another system, as needed, and our example system must manage the water level in the tank.
Using only digital signals, the PLC has two digital inputs from float switches (tank empty and tank full). The PLC uses a digital output to open and close the inlet valve into the tank.
If both float switches are off (down) or only the 'tank empty' switch is on, the PLC will open the valve to let more water in. Once the 'tank full' switch is on, the PLC will automatically shut the inlet to stop the water from overflowing. If only the 'tank full' switch is on, something is wrong because once the water reaches a float switch, the switch will stay on because it is floating, thus, when both float switches are on, the tank is full (see also truth table). Two parallel float switches (a logical OR) are used to prevent a 'flutter' (a ripple or a wave) condition where any water usage opens the valve or activates the pump for a very short time and then deactivates for a short time, and so on, causing the system to wear out faster. Truth tables are a type of mathematical table used in logic to determine whether an expression is true or whether an argument is valid. ...
Series (left) and parallel (right) circuits with two resistors and measurements of voltage and current. ...
Logical disjunction (usual symbol or) is a logical operator that results in true if either of the operands is true. ...
An analog system might use a water pressure sensor or a load cell, and an adjustable (throttling) valve. The PLC could use a PID feedback loop to control the valve opening. The load cell is connected to an analog input and the valve is connected to an analog output. This system fills the tank faster when there is less water in the tank. If the water level drops rapidly, the valve can be opened wide. If water is only dripping out of the tank, the valve adjusts to slowly drip water back into the tank.thank Digital air pressure sensor A pressure sensor measures the pressure, typically of gases or fluids. ...
A single-point load cell A load cell is typically an electronic device (transducer) that is used to convert a force into an electrical signal. ...
In this system, to avoid 'flutter' adjustments that can wear out the valve, many PLCs incorporate "hysteresis" which essentially creates a "deadband" of activity. A technician adjusts this deadband so the valve moves only for a significant change in rate. This will in turn minimize the motion of the valve, and reduce its wear. A system with hysteresis exhibits path-dependence, or rate-independent memory. Consider a deterministic system with no hysteresis and no dynamics. ...
attention Deadband is an area of a signal range or band where no action occurs (the system is dead). ...
A real system might combine both approaches, using float switches and simple valves to prevent spills, and a rate sensor and rate valve to optimize refill rates and prevent water hammer. Backup and maintenance methods can make a real system very complicated. Water hammer (or, more generally, fluid hammer) is a pressure surge or wave caused by the kinetic energy of a fluid in motion when it is forced to stop or change direction suddenly. ...
System scale A small PLC will have a fixed number of connections built in for inputs and outputs. Typically, expansions are available if the base model does not have enough I/O.
Modular PLCs have a chassis (also called a rack) into which is placed modules with different functions. The processor and selection of I/O modules is customised for the particular application. Several racks can be administered by a single processor, and may have thousands of inputs and outputs. A special high speed serial I/O link is used so that racks can be distributed away from the processor, reducing the wiring costs for large plants.
PLCs used in larger I/O systems may have peer-to-peer (P2P) communication between processors. This allows separate parts of a complex process to have individual control while allowing the subsystems to co-ordinate over the communication link. These communication links are also often used for HMI (Human-Machine Interface) devices such as keypads or PC-type workstations. Some of today's PLCs can communicate over a wide range of media including RS-485, Coaxial, and even Ethernet for I/O control at network speeds up to 100 Mbit/s. The user interface is the part of a system exposed to users. ...
A personal computer (PC) is a computer whose price, size, and capabilities make it useful for individuals. ...
Programming Early PLCs, up to the mid-1980s, 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. Programs were stored on cassette tape cartridges. Facilities for printing and documentation were very minimal due to lack of memory capacity. More recently, PLC programs are typically written in a special application on a personal computer, then downloaded by a direct-connection cable or over a network to the PLC. The very oldest PLCs used non-volatile magnetic core memory but now the program is stored in the PLC either in battery-backed-up RAM or some other non-volatile flash memory. A computer terminal is an electronic or electromechanical hardware device that is used for entering data into, and displaying data from, a computer or a computing system. ...
A 16×16 cm area core memory plane of 128×128 bits, i. ...
Look up RAM, Ram, ram in Wiktionary, the free dictionary. ...
A USB flash drive. ...
Early PLCs were designed to be used by electricians who would learn PLC programming on the job. These PLCs were programmed in "ladder logic", which strongly resembles a schematic diagram of relay logic. Modern PLCs can be programmed in a variety of ways, from ladder logic to more traditional programming languages such as BASIC and C. Another method is State Logic, a Very High Level Programming Language designed to program PLCs based on State Transition Diagrams. Ladder logic is a method of drawing electrical logic schematics. ...
A State logic control system is a programming method created for PLCs. ...
A Very high-level programming language (VHLPL) is a programming language with a very high level of abstraction, used primarily as a professional programmer productivity tool. ...
State diagrams are used to graphically represent finite state machines. ...
Recently, the International standard IEC 61131-3 has become popular. IEC 61131-3 currently defines five programming languages for programmable control systems: FBD (Function block diagram), LD (Ladder diagram), ST (Structured text, similar to the Pascal programming language), IL (Instruction list, similar to assembly language) and SFC (Sequential function chart). These techniques emphasize logical organization of operations. IEC 61131-3 is a standard published in December 1993 by the IEC. It defines five PLC programming language standards: Ladder logic Sequential function chart Function block diagram Structured text Instruction list It is the third publication in the series IEC 61131. ...
This article needs to be cleaned up to conform to a higher standard of quality. ...
Ladder logic is a method of drawing electrical logic schematics. ...
Description Structured Text is one of the 5 languages supported by IEC 61131-3 standard. ...
Pascal is an imperative computer programming language, developed in 1970 by Niklaus Wirth as a language particularly suitable for structured programming. ...
Instruction List is one of the 5 languages supported by the IEC 61131-3 standard. ...
See the terminology section, below, regarding inconsistent use of the terms assembly and assembler. ...
Sequential function chart (SFC) is a graphical programming language used for PLCs. ...
While the fundamental concepts of PLC programming are common to all manufacturers, differences in I/O addressing, memory organization and instruction sets mean that PLC programs are never perfectly interchangeable between different makers. Even within the same product line of a single manufacturer, different models may not be directly compatible. bye for ever
User interface PLCs may need to interact with people for the purpose of configuration, alarm reporting or everyday control. A Human-Machine Interface (HMI) is employed for this purpose. The user interface is the part of a system exposed to users. ...
A simple system may use buttons and lights to interact with the user. Text displays are available as well as graphical touch screens. Most modern PLCs can communicate over a network to some other system, such as a computer running a SCADA (Supervisory Control And Data Acquisition) system or web browser. SCADA is the acronym for Supervisory Control And Data Acquisition. ...
Communications PLCs usually have built in communications ports usually 9-Pin RS232, and optionally for RS485 and Ethernet. Modbus or DF1 is usually included as one of the communications protocols. Others' options include various fieldbuses such as DeviceNet or Profibus. Other communications protocols that may be used are listed in the List of automation protocols. RS-232 (also referred to as EIA RS-232C or V.24) is a standard for serial binary data interchange between a DTE (Data terminal equipment) and a DCE (Data communication equipment). ...
EIA-485 (formerly RS-485 or RS485) is an OSI Model physical layer electrical specification of a two-wire, half-duplex, multipoint serial connection. ...
Ethernet is a large, diverse family of frame-based computer networking technologies that operate at many speeds for local area networks (LANs). ...
Modbus is a serial communications protocol published by Modicon in 1979 for use with its programmable logic controllers (PLCs). ...
In the field of telecommunications, a communications protocol is the set of standard rules for data representation, signalling, authentication, and error detection required to send information over a communications channel. ...
A fieldbus or field bus is an industrial computer network for real-time distributed control. ...
This page may meet Wikipedias criteria for speedy deletion. ...
PROFIBUS (Process Field Bus) is the most popular type of fieldbus with worldwide more than 10 million nodes (2004) in use. ...
Communication network protocols used for Building, Industrial and machine automation applications. ...
History The PLC was invented in response to the needs of the American automotive industry. Before the PLC, control, sequencing, and safety interlock logic for manufacturing automobiles was accomplished using relays, timers and dedicated closed-loop controllers. The process for updating such facilities for the yearly model change-over was very time consuming and expensive, as the relay systems needed to be rewired by skilled electricians. In 1968 GM Hydramatic (the automatic transmission division of General Motors) issued a request for proposal for an electronic replacement for hard-wired relay systems.
The winning proposal came from Bedford Associates of Bedford, Massachusetts. The first PLC, designated the 084 because it was Bedford Associates eighty-fourth project, was the result. Bedford Associates started a new company dedicated to developing, manufacturing, selling, and servicing this new product: Modicon, which stood for MOdular DIgital CONtroller. One of the people who worked on that project was Dick Morley, who is considered to be the "father" of the PLC. The Modicon brand was sold in 1977 to Gould Electronics, and later acquired by German Company AEG and then by French Schneider Electric, the current owner. Location in Massachusetts Coordinates: , Country United States State Massachusetts County Middlesex County Settled 1640 Incorporated 1729 Government - Type Open town meeting - Town Administrator Richard Reed Area - Town 13. ...
Dick Morley is known as the father of the PLC since he was involved with the production of the first programmable logic controller (PLC) for GM, the Modicon, at Bedford and Associates in 1968. ...
Gould Electronics Inc. ...
AEG volt-meter designed by Peter Behrens AEG (Allgemeine Elektrizitäts-Gesellschaft, General Electricity Company) was a German producer of electronics and electrical equipment. ...
Kenny Acheson Schneider Electric is a French global company. ...
One of the very first 084 models built is now on display at Modicon's headquarters in North Andover, Massachusetts. It was presented to Modicon by GM, when the unit was retired after nearly twenty years of uninterrupted service. North Andover is a town in Essex County, Massachusetts, United States. ...
The automotive industry is still one of the largest users of PLCs, and Modicon still numbers some of its controller models such that they end with eighty-four. PLCs are used in many different industries and machines such as packaging and semiconductor machines. Well known PLC brands are Allen-Bradley, Mitsubishi Electric, ABB Ltd., Honeywell, Siemens, Modicon, Omron, General Electric, Square-D (Telemecanique) and Panasonic (a brand name of Matsushita). A Milwaukee-based company that specializes in industrial control and automation products. ...
Mitsubishi Electric Corporation ) (TYO: 6503 ) is a Japanese company based in the Tokyo Building in Tokyo, manufactures electric and architectural equipment, as well as a major worldwide producer of photovoltaic panels. ...
ABB, formerly Asea Brown Boveri, is a multinational corporation headquartered in Zürich, Switzerland, operating mainly in the power and automation technology areas. ...
Honeywell Heating Specialties Company Stock Certificate dated 1924 signed by Mark C. Honeywell - courtesy of Scripophily. ...
Siemens redirects here. ...
Modicon is: The name of an oral contraceptive formulation. ...
OMRON is a Japanese electronics company in Kyoto, Kyoto. ...
General Electric Fanuc, a joint partnership between FANUC LTD. of Japan and General Electric, is a business unit of General Electric Industrial Systems. ...
Panasonic is an international brand name for Japanese electric products manufacturer Matsushita Electric Industrial Co. ...
Logo for the Panasonic brand Matsushita Electric Industrial Co. ...
Less known PLCs that are programmable in BASIC are available from CUBLOC or Tri-PLC.
See also IEC 61131-3 is a standard published in December 1993 by the IEC. It defines five PLC programming language standards: Ladder logic Sequential function chart Function block diagram Structured text Instruction list It is the third publication in the series IEC 61131. ...
A fieldbus or field bus is an industrial computer network for real-time distributed control. ...
The Simatic S5 PLC is an automation system based on Programmable Logic Controllers. ...
SCADA is the acronym for Supervisory Control And Data Acquisition. ...
A programmable automation controller (PAC) is a compact controller that combines the features and capabilities of a PC-based control system with that of a typical programmable logic controller (PLC). ...
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