Programmable logic controllers or industrial controllers
April 14th, 2012 | No Comments
THIS ARTICLE provides you an interesting knowledge about an industrial control. I have searched its history and is giving you a little idea about this industrial control. In this era everything is computerized almost every industrial equipment is software based. Software consists of huge and more complex programming for a common man. To overcome the complexity technology gave us PLC (programable logic control). What is PLC?
Every aspect of industry – from power generation to automobile painting to food packaging-uses programmable controllers to expand and enhance production. Its a history of their evolution. Programmable logic controllers, also called programmable controllers or PLCs, are solid-state members of the computer family, using integrated circuits instead of electromechanical devices to implement control functions. They are capable of storing instructions, such as sequencing, timing, counting, arithmetic, data manipulation, and communication, to control industrial machines and processes.
PLCs can be thought of in simple terms as industrial computers with specially designed architecture in both their central units (the PLC itself) and their interfacing circuitry to field devices. Programmable logic controllers are mature industrial controllers with their design roots based on the principles of simplicity and practical application.
Now let me discuss its background with my readers. The Hydramatic Division of the General Motors Corporation specified the design criteria for the first programmable controller in 1968. Their primary goal was to eliminate the high costs associated with inflexible, relay controlled systems. The specifications required a solid-state system with computer flexibility able to (1) survive in an industrial environment, (2) be easily programmed and maintained by plant engineers and technicians, and (3) be reusable. Such a control system would reduce machine downtime and provide expandability for the future.
The product implementation to satisfy Hydramatics specifications was underway in 1968; and by 1969, the programmable controller had its first product offspring. These early controllers met the original specifications and opened the door to the development of a new control technology. The first PLCs offered relay functionality, thus replacing the original hardwired relay logic, which used electrically operated devices to mechanically switch electrical circuits. They met the requirements of modularity, expandability, programmability, and ease of use in an industrial environment. These controllers were easily installed, used less space, and were reusable. The controller programming, although a little tedious, had a recognizable plant standard: The ladder diagram format. In a short period, programmable controller use started spreading to other industries. By 1971, PLCs were being used to provide relay replacement as the first steps towards control automation in other industries, such as food and beverage, metals, manufacturing, and pulp and paper.
Now I want to give you its design idea what was considered. The first programmable controllers were more or less just relay replacers. Their primary function was to perform the sequential operations that were previously implemented with relays. These operations included ON/OFF control of machines and processes that required repetitive operations, such as transfer lines and grinding and boring machines. However, these programmable controllers were a vast improvement over relays. They were easily installed, used considerably less space and energy, had diagnostic indicators that aided troubleshooting, and unlike relays, were reusable if a project was scrapped.
As the necessity is the mother of invention, one can never ignore its advancement and more technological form. Many technological advances in the programmable controller industry continue today. These advances not only affect the programmable controller design, but also the philosophical approach to control system architecture. Changes include both hardware (physical components) and software (control program) upgrades.
After advancement an engineer always starts thinking about the future. The future of programmable controllers relies not only on the continuation of new product developments, but also on the integration of PLCs with other control and factory management equipment. PLCs are being incorporated, through networks, into computer-integrated manufacturing (CIM) systems, combining their power and resources with numerical controls, robots, CAD/ CAM systems, personal computers, management information systems, and hierarchical computer-based systems. There is no doubt that programmable controllers will play a substantial role in the factory of the future. New advances in PLC technology include features such as better operator interfaces, graphics user interfaces (GUIs), and more human-oriented man/machine interfaces (such as voice modules). They also include the development of interfaces that allow communication with equipment, hardware, and software that supports artificial intelligence, such as fuzzy logic I/O systems. Software advances provide better connections between different types of equipment, using communication standards through widely used networks. New PLC instructions are developed out of the need to add intelligence to a controller. Knowledge based and process learning-type instructions may be introduced to enhance the capabilities of a system.
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