3:49 AM

Examples of embedded systems

Posted by Ravi

Embedded systems span all aspects of modern life and there are many examples of their use.

Telecommunications systems employ numerous embedded systems from telephone switches for the network to mobile phones at the end-user. Computer networking uses dedicated routers and network bridges to route data.

Consumer electronics include personal digital assistants (PDAs), mp3 players, mobile phones, videogame consoles, digital cameras, DVD players, GPS receivers, and printers. Many household appliances, such as microwave ovens, washing machines and dishwashers, are including embedded systems to provide flexibility, efficiency and features. Advanced HVAC systems use networked thermostats to more accurately and efficiently control temperature that can change by time of day and season. Home automation uses wired- and wireless-networking that can be used to control lights, climate, security, audio/visual, surveillance, etc., all of which use embedded devices for sensing and controlling.

Transportation systems from flight to automobiles increasingly use embedded systems. New airplanes contain advanced avionics such as inertial guidance systems and GPS receivers that also have considerable safety requirements. Various electric motors — brushless DC motors, induction motors and DC motors — are using electric/electronic motor controllers. Automobiles, electric vehicles, and hybrid vehicles are increasingly using embedded systems to maximize efficiency and reduce pollution. Other automotive safety systems such as anti-lock braking system (ABS), Electronic Stability Control (ESC/ESP), traction control (TCS) and automatic four-wheel drive.

Medical equipment is continuing to advance with more embedded systems for vital signs monitoring, electronic stethoscopes for amplifying sounds, and various medical imaging (PET, SPECT, CT, MRI) for non-invasive internal inspections.

In addition to commonly described embedded systems based on small computers, a new class of miniature wireless devices called motes are quickly gaining popularity as the field of wireless sensor networking rises. Wireless sensor networking, WSN, makes use of miniaturization made possible by advanced IC design to couple full wireless subsystems to sophisticated sensor, enabling people and companies to measure a myriad of things in the physical world and act on this information through IT monitoring and control systems. These motes are completely self contained, and will typically run off a battery source for many years before the batteries need to be changed or charged.

3:48 AM

Basic of Embedded system

Posted by Ravi

An embedded system is a computer system designed to perform one or a few dedicated functions,[1] often with real-time computing constraints. It is embedded as part of a complete device often including hardware and mechanical parts. In contrast, a general-purpose computer, such as a personal computer, is designed to be flexible and to meet a wide range of an end-user's needs. Embedded systems control many of the common devices in use today.

Since the embedded system is dedicated to specific tasks, design engineers can optimize it, reducing the size and cost of the product, or increasing the reliability and performance. Some embedded systems are mass-produced, benefiting from economies of scale.

Physically, embedded systems range from portable devices such as digital watches and MP3 players, to large stationary installations like traffic lights, factory controllers, or the systems controlling nuclear power plants. Complexity varies from low, with a single microcontroller chip, to very high with multiple units, peripherals and networks mounted inside a large chassis or enclosure.

In general, "embedded system" is not an exactly defined term, as many systems have some element of programmability. For example, Handheld computers share some elements with embedded systems — such as the operating systems and microprocessors which power them — but are not truly embedded systems, because they allow different applications to be loaded and peripherals to be connected.

3:47 AM

User interfaces of HMI

Posted by Ravi

In computer science and human-computer interaction, the user interface (of a computer program) refers to the graphical, textual and auditory information the program presents to the user, and the control sequences (such as keystrokes with the computer keyboard, movements of the computer mouse, and selections with the touchscreen) the user employs to control the program.

Types

Currently (as of 2009[update]) the following types of user interface are the most common:

* Graphical user interfaces (GUI) accept input via devices such as computer keyboard and mouse and provide articulated graphical output on the computer monitor. There are at least two different principles widely used in GUI design: Object-oriented user interfaces (OOUIs) and application oriented interfaces[verification needed].
* Web-based user interfaces or web user interfaces (WUI) accept input and provide output by generating web pages which are transmitted via the Internet and viewed by the user using a web browser program. Newer implementations utilize Java, AJAX, Adobe Flex, Microsoft .NET, or similar technologies to provide real-time control in a separate program, eliminating the need to refresh a traditional HTML based web browser. Administrative web interfaces for web-servers, servers and networked computers are often called Control panels.

User interfaces that are common in various fields outside desktop computing:

* Command line interfaces, where the user provides the input by typing a command string with the computer keyboard and the system provides output by printing text on the computer monitor. Used by programmers and system administrators, in engineering and scientific environments, and by technically advanced personal computer users.
* Tactile interfaces supplement or replace other forms of output with haptic feedback methods. Used in computerized simulators etc.
* Touch user interface are graphical user interfaces using a touchscreen display as a combined input and output device. Used in many types of point of sale, industrial processes and machines, self-service machines etc.

Other types of user interfaces:

* Attentive user interfaces manage the user attention deciding when to interrupt the user, the kind of warnings, and the level of detail of the messages presented to the user.
* Batch interfaces are non-interactive user interfaces, where the user specifies all the details of the batch job in advance to batch processing, and receives the output when all the processing is done. The computer does not prompt for further input after the processing has started.
* Conversational Interface Agents attempt to personify the computer interface in the form of an animated person, robot, or other character (such as Microsoft's Clippy the paperclip), and present interactions in a conversational form.
* Crossing-based interfaces are graphical user interfaces in which the primary task consists in crossing boundaries instead of pointing.
* Gesture interface are graphical user interfaces which accept input in a form of hand gestures, or mouse gestures sketched with a computer mouse or a stylus.
* Intelligent user interfaces are human-machine interfaces that aim to improve the efficiency, effectiveness, and naturalness of human-machine interaction by representing, reasoning, and acting on models of the user, domain, task, discourse, and media (e.g., graphics, natural language, gesture).
* Motion tracking interfaces monitor the user's body motions and translate them into commands, currently being developed by Apple[1]
* Multi-screen interfaces, employ multiple displays to provide a more flexible interaction. This is often employed in computer game interaction in both the commercial arcades and more recently the handheld markets.
* Noncommand user interfaces, which observe the user to infer his / her needs and intentions, without requiring that he / she formulate explicit commands.
* Object-oriented user interface (OOUI)
* Reflexive user interfaces where the users control and redefine the entire system via the user interface alone, for instance to change its command verbs. Typically this is only possible with very rich graphic user interfaces.
* Tangible user interfaces, which place a greater emphasis on touch and physical environment or its element.
* Text user interfaces are user interfaces which output text, but accept other form of input in addition to or in place of typed command strings.
* Voice user interfaces, which accept input and provide output by generating voice prompts. The user input is made by pressing keys or buttons, or responding verbally to the interface.
* Natural-Language interfaces - Used for search engines and on webpages. User types in a question and waits for a response.
* Zero-Input interfaces get inputs from a set of sensors instead of querying the user with input dialogs.
* Zooming user interfaces are graphical user interfaces in which information objects are represented at different levels of scale and detail, and where the user can change the scale of the viewed area in order to show more detail.

3:45 AM

Introduction of HMI

Posted by Ravi

To work with a system, users have to be able to control the system and assess the state of the system. For example, when driving an automobile, the driver uses the steering wheel to control the direction of the vehicle, and the accelerator pedal, brake pedal and gearstick to control the speed of the vehicle. The driver perceives the position of the vehicle by looking through the windscreen and exact speed of the vehicle by reading the speedometer. The user interface of the automobile is on the whole composed of the instruments the driver can use to accomplish the tasks of driving and maintaining the automobile.

The term user interface is often used in the context of computer systems and electronic devices. The user interface of a mechanical system, a vehicle or an industrial installation is sometimes referred to as the human-machine interface (HMI). HMI is a modification of the original term MMI (man-machine interface). In practice, the abbreviation MMI is still frequently used although some may claim that MMI stands for something different now. Another abbreviation is HCI, but is more commonly used for human-computer interaction than human-computer interface. Other terms used are operator interface console (OIC) and operator interface terminal (OIT).

However it is abbreviated, the terms refer to the 'layer' that separates a human that is operating a machine from the machine itself.

In science fiction, HMI is sometimes used to refer to what is better described as direct neural interface. However, this latter usage is seeing increasing application in the real-life use of (medical) prostheses—the artificial extension that replaces a missing body part (e.g., cochlear implants).

The system may expose several user interfaces to serve different kinds of users. For example, a computerized library database might provide two user interfaces, one for library patrons (limited set of functions, optimized for ease of use) and the other for library personnel (wide set of functions, optimized for efficiency).

In some circumstance computers might observe the user, and react according to their actions without specific commands. A means of tracking parts of the body is required, and sensors noting the position of the head, direction of gaze and so on have been used experimentally. This is particularly relevant to immersive interfaces.

3:41 AM

Wireless SCADA System

Posted by Ravi

Wireless media can also be a communication medium for the master unit and the remote unit. Systems using this type of media are termed "wireless SCADA systems." A few examples of wireless media are explained below.

  • Spread Spectrum Radio - The frequency band for this is 900 MHz to 5.8GHz and is free for general pubic use. Spread spectrum radio modems are used to ensure efficient network communication.
  • Microwave Radio - In this case signals are transmitted at high frequencies using parabolic dishes installed on towers or on the tops of buildings. However, one disadvantage of this communication is that transmission may get interrupted due to misalignment and/or atmospheric conditions.
  • VHF/UHF Radio - This is an electromagnetic transmission with frequencies of 175MHz-450MGz-900MHz. Special antennas are required to receive these signals.

Benefits of a Wireless SCADA system

A perfectly designed wireless SCADA system offers the following benefits:

  • Monitors in real time
  • Minimizes the operational costs
  • Provides direct information of system performance
  • Improves system efficiency and performance
  • Increases equipment life
  • Reduces labor costs required for troubleshooting or servicing the equipment
  • Automated report generation reduces errors in calculations and interpretations
  • Uses advanced technologies

3:40 AM

SCADA Systems

Posted by Ravi

SCADA comes under the branch of Instrumentation Engineering. The term SCADA stands for Supervisory Control And Data Acquisition. Scada systems are used for controlling and monitoring chemical or transport processes and can be used in a factory environment such as electic power generation, water supply systems, gas and oil pipelines or any other distributed processes.

A typical SCADA system comprises of i/o signal hardware, controllers, software,networks and communication. SCADA system is normally used to monitor and control a remote site or a distribution that is spread out for a long distance. An RTU (Remote Terminal Unit) or a PLC (Programmable Logic Controller) is usually used to control a site automatically. The SCADA system also provides a host control functions for the supervisor to control and define settings.

For example, in a SCADA system a PLC can be used to control the flow of cooling water as part of an industrial process. At the same time the supervisor can use the Host control function to set the temperature for the flow of water. It can also have alarms and can record the flow of water temperature and report back to the SCADA system.

The RTUs and PLCs are responsible for data collection such as meter readings, equipment status etc and communicate back to the SCADA system. This data can be stored in a database for later analysis or monitored by a supervisor to take appropriate actions if required.

SCADA systems typically implement a distributed database, commonly referred to as a tag database, which contains data elements called tags or points. A point represents a single input or output value monitored or controlled by the system. Points can be either "hard" or "soft". A hard point is representative of an actual input or output connected to the system, while a soft point represents the result of logic and math operations applied to other hard and soft points. Most implementations conceptually remove this distinction by making every property a "soft" point (expression) that can equal a single "hard" point in the simplest case. Point values are normally stored as value-timestamp combinations; the value and the timestamp when the value was recorded or calculated. A series of value-timestamp combinations is the history of that point. It's also common to store additional metadata with tags such as: path to field device and PLC register, design time comments, and even alarming information.

3:26 AM

What is SCADA?

Posted by Ravi

SCADA is an acronym that stands for Supervisory Control and Data Acquisition. SCADA refers to a system that collects data from various sensors at a factory, plant or in other remote locations and then sends this data to a central computer which then manages and controls the data

SCADA systems are used not only in industrial processes: e.g. steel making, power generation (conventional and nuclear) and distribution, chemistry, but also in some experimental facilities such as nuclear fusion. The size of such plants range from a few 1000 to several 10 thousands input/output (I/O) channels. However, SCADA systems evolve rapidly and are now penetrating the market of plants with a number of I/O channels of several 100 K: we know of two cases of near to 1 M I/O channels currently under development.

There are many parts of a working SCADA system. A SCADA system usually includes signal hardware (input and output), controllers, networks, user interface (HMI), communications equipment and software. All together, the term SCADA refers to the entire central system. The central system usually monitors data from various sensors that are either in close proximity or off site (sometimes miles away).

An industrial measurement and control system consisting of a central host or master (usually called a master station, master terminal unit or MTU); one or more field data gathering and control units or remotes (usually called remote stations, remote terminal units, or RTU's); and a collection of standard and/or custom software used to monitor and control remotely located field data elements. Contemporary SCADA systems exhibit predominantly open-loop control characteristics and utilise predominantly long distance communications, although some elements of closed-loop control and/or short distance communications may also be present.

Systems similar to SCADA systems are routinely seen in factories, treatment plants etc. These are often referred to as Distributed Control Systems (DCS). They have similar functions to SCADA systems, but the field data gathering or control units are usually located within a more confined area. Communications may be via a local area network (LAN), and will normally be reliable and high speed. A DCS system usually employs significant amounts of closed loop control.

SCADA systems on the other hand generally cover larger geographic areas, and rely on a variety of communications systems that are normally less reliable than a LAN. Closed loop control in this situation is less desirable.

3:24 AM

MicroLogix 1200 Controllers

Posted by Ravi


System Overview

The MicroLogix 1200/1762 system provides functionality between the MicroLogix 1000/1761 and MicroLogix 1500/1764 systems, using the proven MicroLogix and SLC family architecture. The 6K-word memory provides for a maximum program of 4K words and maximum data of 2K words with 100% data retention. An optional memory module provides program and data backup with program upload and download capability. The optional real-time clock enables time scheduling of control activities. The flash upgradeable operating system lets you upgrade system software without replacing hardware.

Benefits

  • Small Footprint—The MicroLogix 1200 controller is designed to optimize panel space. Integrated packages just 90mm (3.54 in) high (110mm high including mounting tabs) and 110 or 160mm (4.33 or 6.30 in) wide include processor, embedded inputs and outputs, and power supply. Expansion I/O modules add only 40mm (1.57 in) each in width.
  • Flexibility—A range of I/O and communication options let you configure a MicroLogix 1200 controller for a variety of applications:
    • 24 or 40 built-in I/O. The inputs are either 24V DC (sink or source) or 120V AC. Outputs are relay contact or FET.
    • Add up to 96 I/O in up to 6 digital and/or analog I/O modules (within the limits of power supply capacity, for a total of 136 I/O maximum).
  • Wide range of communication options:
    • DF1 full- or half-duplex, DF1 Radio Modem, Modbus RTU slave and RTU master. Communication interface modules support DH-485, DeviceNet, and EtherNet/IP.
    • MicroLogix 1200R controllers also provide a Programming / HMI port with fixed communication parameters to provide an additional means to communicate to the controller.
  • High Functionality—The MicroLogix 1200 / 1762 system provides powerful features that let you tackle tough applications:
    • 20k-Hz high-speed counter.
    • 20k-Hz PTO (Pulse Train Output) or PWM (Pulse Width Modulation).
    • 6K-word non-volatile memory (4K-word maximum program, 2K-word maximum data).
    • 4 interrupt inputs.
    • 4 latching inputs.
    • 2 built-in trim potentiometers.
    • optional memory, real-time clock, or memory/real-time clock module.
    • powerful instruction set with support for PID and ASCII.
    • uses RSLogix 500 programming software.
    • field-upgradeable flash operating system.
  • Low Price—This compact but powerful control solution will fit well within your budget.

3:23 AM

MicroLogix 1100 Controllers

Posted by Ravi


With online editing and a built-in 10/100 Mbps EtherNet/IP port for peer-to-peer messaging, the MicroLogix 1100 controller adds greater connectivity and application coverage to the MicroLogix family of Allen-Bradley controllers. This next generation controller's built-in LCD screen displays controller status, I/O status, and simple operator messages; enables bit and integer manipulation; offers digital trim pot functionality, and a means to make operating mode changes (Prog / Remote / Run).

With 10 digital inputs, 2 analog inputs and 6 digital outputs, the MicroLogix 1100 can handle a wide variety of tasks. The MicroLogix 1100 controllers also support expansion I/O. Up to four 1762 I/O modules (also used on the MicroLogix 1200 and 1400) may be added to the embedded I/O, providing application flexibility and support of up to 80 digital I/O.

Features

  • Built-in 10/100 Mbps EtherNet/IP port for peer-to-peer messaging — offers users high speed connectivity between controllers, with the ability to access, monitor and program from anywhere an Ethernet connection is available
  • Online editing functionality — modifications can be made to a program while it is running, making fine tuning of an operating control system possible, including PID loops. Not only does this reduce development time, but it aids in troubleshooting
  • Embedded Web server — allows a user to custom configure data from the controller to be displayed as a web page
  • Isolated RS-232/RS-485 combo port — provides a host of different point-to-point and network protocols
  • Embedded LCD screen — allows user to monitor data within the controller, optionally modify that data, and interact with the control program. Displays status of embedded digital I/O and controller functions, and acts as a pair of digital trim pots to allow a user to tweak and tune a program

3:17 AM

MicroLogix 1000 System

Posted by Ravi

Communication Choices

Ethernet Connectivity for MicroLogix 1000 Controllers

The 1761-NET-ENI provides Ethernet connectivity for all SLC, MicroLogix, and CompactLogix controllers and other DF1 full-duplex devices. The ENI helps you easily connect these controllers onto new or existing Ethernet networks and upload/download programs, communicate between controllers, and generate email messages via SMTP (simple mail transport protocol).

As with other MicroLogix communication devices, the ENI can be powered via the RS-232 communications cable when attached to a MicroLogix controller, or externally with 24V dc when connected to other DF1 full duplex devices. It can be DIN-rail mounted, or panel mounted to meet your installation requirements.

NEW Series D Enhancements

The series D has been updated with a new Ethernet communications processor and several ease-of-use features. In addition to the features of previous versions, Series D provides:

  • Added the capability for configuration via Ethernet, with a Configuration Security Mask provision.
  • Ability to force Ethernet to 10 Mbps or 100 Mbps and half-duplex or full-duplex. (default is still Auto Negotiate).
  • Added an optional Username and Password fields for Email authentication.
  • Added a new Diagnostics web page that displays a list of current Ethernet connections.
  • Updated the ENIW web pages to more closely conform to the style used on other RA web-enabled products (more like 1756-EWEB module pages).

Series B Enhancements

The 1761-NET-ENI, series B:

  • Lets any device that can initiate a CIP data table read or write on an EtherNet/IP link through a 1761-NET-ENI/B (e.g., PanelView, ControlLogix, RSLinx) access a Logix processor data table. This eliminates the requirement of mapping PLC/SLC file numbers to Logix tag names.
  • Provides more functional integration with CompactLogix processors by eliminating the need for an additional ENI in CompactLogix systems to communicate with RSLogix 5000 (1761-NET-ENI/A requires an additional ENI at the PC running the programming package for communication with RSLogix 5000).
  • Incorporates several data handling improvements, such as additional buffering and increased message queues and provides more robust communications at increased throughput rates. In general, ENI series B users should expect upload/download times to be about 33% longer than transferring the same file over DF1.

ENI and ENIW series B and series C firmware can be upgraded in the field by downloading the Upgrade Utility.

The ENI series A firmware cannot be upgraded in the field. For information on upgrading your ENI series A unit to series B, please contact Rockwell Automation technical support.

Series C Enhancements

The 1761-NET-ENI, series C:

  • Provides 10/100 Mbps EtherNet/IP capability, which results in significant upload/download performance improvements. Performance tests indicate that with a 100 Mbps EtherNet/IP connection and a 38.4 Kbaud serial connection, upload/download times are typically half as long as with Series B units.
  • Due to RSLinx EtherNet /IP driver efficiency, Series C upload/download times are typically 15-30 percent faster than a direct 38.4 Kbaud serial connection.
  • Provides improved performance access for Allen-Bradley SLC 500, MicroLogix, and CompactLogix controller platforms.
  • Is included as an upgrade option in the Step Forward Program. This offer presents users of Series A or B units with a credit incentive when upgrading to a Series C product.

General Features

  • Program upload/download - Upload or download user programs over Ethernet using the ENI. The only requirement is that you use RSLinx version 2.20 SP2 or newer.
  • Peer-to-Peer communication - The ENI allows the attached controller to initiate or receive messages with other controllers. The controllers can be connected directly to Ethernet like the SLC 5/05, Ethernet PLC-5, or ControlLogix processors, or with other ENIs (MicroLogix, SLC 5/03, CompactLogix, etc.).
  • Email communication - The ENI enables a controller to send an ASCII string to an Email address. Send production data, alarms, or other status information to any computer, cell phone, or pager capable of receiving an Email message. This feature requires a valid SMTP Email server (Simple Mail Transport Protocol). SMTP servers are readily available via Internet Service Providers (ISPs).
  • EtherNet/IP compatibility - The ENI uses the open EtherNet/IP protocol. This industry standard open protocol provides inter device compatibility. The ENI can exchange information with other A-B Ethernet controllers (SLC, PLC, CompactLogix, FlexLogix and ControlLogix) in a peer-to-peer relationship, so you don't need any master type device.
  • Easy to configure - The ENI can be configured via messages from the attached controller, or via the ENI utility, a free Windows-based configuration package.
  • 10 base-T port with embedded LEDs - Use any standard RJ Ethernet cable to connect to your network. This minimizes connection problems and improves startup. Embedded LEDs provide easy to see link and transmit/receive status.
  • Isolated mini-DIN RS-232 port - The RS-232 port provides isolation and will auto baud on power up to detect the communications port setting of the attached controller. Supported baud rates include 2400, 4800, 9600, 19.2k and 38.4k. This autobaud feature can also be disabled if desired.
  • Small and compact - The ENI uses the same packaging as the AIC+ and DNI communication interfaces. This packaging is rugged and can be either panel or DIN rail mounted.

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 or millions of units.

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 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.

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.

Programmable controllers are widely used in motion control, positioning control and torque control. Some manufacturers produce motion control units to be integrated with PLC so that G-code (involving a CNC machine) can be used to instruct machine movements.[citation needed]

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. As PLCs have become more powerful, the boundary between DCS and PLC applications has become less distinct.

PLCs have similar functionality as Remote Terminal Units. An RTU, however, usually does not support control algorithms or control loops. As hardware rapidly becomes more powerful and cheaper, RTUs, PLCs and DCSs are increasingly beginning to overlap in responsibilities, and many vendors sell RTUs with PLC-like features and vice versa. The industry has standardized on the IEC 61131-3 functional block language for creating programs to run on RTUs and PLCs, although nearly all vendors also offer proprietary alternatives and associated development environments.

3:04 AM

Features of PLC

Posted by Ravi

The main difference from other computers is that PLCs are armored for severe conditions (such as dust, moisture, heat, cold) 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 use machine vision. On the actuator side, PLCs operate electric motors, pneumatic or hydraulic cylinders, magnetic relays, 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.

3:02 AM

Origin of PLC

Posted by Ravi

The PLC was invented in response to the needs of the American automotive manufacturing industry. Programmable controllers were initially adopted by the automotive industry where software revision replaced the re-wiring of hard-wired control panels when production models changed.

Before the PLC, control, sequencing, and safety interlock logic for manufacturing automobiles was accomplished using hundreds or thousands of relays, cam timers, and drum sequencers 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.

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. Modicon used the 84 moniker at the end of its product range until the 984 made its appearance.

The automotive industry is still one of the largest users of PLCs.

3:00 AM

Basic of PLC

Posted by Ravi

A programmable logic controller (PLC) or programmable controller is a digital computer used for automation of electromechanical processes, such as control of machinery on factory assembly lines, amusement rides, or lighting fixtures. PLCs are used in many industries and machines, such as packaging and semiconductor machines. 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.