Sunday, January 29, 2012

Introduction to Programmable Logic Controllers

A programmable controller or commonly called as programmable logic controller (PLC) is a digital computer utilized for electromechanical processes automation, for example machinery control on factory assembly lines, rides of amusement, or fixtures of light. PLCs are implemented in many machines and industries. Different with general purpose computers, the PLC is planned for arrangements of multiple inputs and output, enlarged the ranges of temperature, electrical noise immunity, and resistance to vibration and impact. The programs to operation of control machine are normally saved in backed up of battery or memory of non-volatile. A PLC is a model of a difficult actual time system as the results have to be created in reaction to input situations within a bounded time, otherwise unintentional operation will result.

The PLC functionality has developed over the years to incorporate sequential motion control, relay control, distributed control, process control networking and systems. The handling of data, storage of data, processing power and capabilities of communication for some modern PLCs are around the same to desktop computers. PLC is like programming joint with remote I/O hardware, enable a general purpose desktop computer to partly cover some PLCs in some applications. Concerning the practicality of these computer desktop based on logic controllers, it is vital to take down that they have not been usually established in heavy industry as the desktop computers work on less constant operating systems than accomplish PLCs, and due to the hardware of desktop computer is characteristically not designed to the same tolerance levels to vibration, humidity, temperature, and longevity same as the processors that used in PLCs. Additionally to the limitations of hardware desktop based logic, operating systems for example Windows do not loan to execution of deterministic logic, with the result that the logic might not always react to changes in input status or logic state with the great consistency in timing as is anticipated from PLCs.

In more current years, small products called as programmable logic relays (PLRs), and also by same names, have become more general and accepted. These are very much similar with PLCs, and are utilized in industrial light where only a several points of I/O are involved, and low cost is most wanted. These small devices are characteristically built in a common physical shape and size by some manufacturers, and branded by the manufacturers of bigger PLCs to fill in their low end range of product. The popular names of low end PLCs are include NANO PLC, PICO Controller, and other names involving very small controllers. The majority of these have between up to 2 analog inputs, 8 & 12 digital inputs, and 4 & 8 digital outputs. The size is generally around 4 inc wide, 3inc high, and 3inc deep. The majority such devices comprise a small postage stamp sized screen of LCD for showing simplified ladder logic and the status points of I/O, and normally these screens are convoyed by a 4 way rocker push button plus point four more divide push buttons, alike to the buttons of key on a remote control of VCR, and utilized to find the way and amend the logic. The majority have a small plug for linking through RS 485 or RS 232 to a PC so that programmers can utilize simple applications of Windows for programming instead of being pushed to utilize the small LCD and the set of push button for this purpose. Different with standard PLCs that are generally modular and significantly flexible, the PLRs are generally not expandable or modular, but their charge can be two magnitude orders less than a PLC and they still recommend forceful design and the logic deterministic execution.

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