## PLC - Areas of application

Every machine or system has a controller. Dependent on the technology type used, controllers can be separated into hydraulic, pneumatic, electronic and electrical controllers. Often, a mixture of different technologies is applied. Moreover, differentiation is created between hard-wired programmable (e.g. wiring of electro-mechanical or electronic components) and PLCs. The initial is utilized principally in cases, where any reprogramming by the user is out of the query and the task size guarantees the development of a special controller.

Characteristic applications for such controllers can be found in cars, video cameras, and automatic washing machines. Nevertheless, if the task size does not guarantee the development of a special controller or if the user is to include the facility of setting timers and counters, or of making easy or independent program changes, then a universal controller use, where the program is written to a memory of electronic, is the ideal option? The PLCstands for such a universal controller. It can be applied for different applications and, through the program installed in its memory, offers the user with an easy means of changing, expanding and optimizing control processes.

The creative task of a PLC engaged the input signals interconnection along with a specified program and, if "true", to switch the corresponding output. Boolean algebra forms the basis of mathematical for this operation, which recognizes accurately two defined statuses of one variable: "0" and "1". Consequently, an output can only think these two statuses. For example, a linked motor could thus be either switched on or off, i.e. controlled.

This function has coined the name PLC: Programmable logic controller, i.e. the behavior ofinput/output is related to that of a pneumatic switching valve or electromagnetic relay controller; the program is saved in a memory of electronic. However, the PLC tasks have quickly multiplied: the functions of timer and counter, setting and resetting of memory, mathematical computing operations all stand for functions, which can be implemented by practically any of PLCs nowadays.

The requirement to be met by PLC‘s continued to grow up in line with their speedily spreading usage and the automation technology development. Visualization is the representation statuses of machine for instance the control program being executed, through display or monitor. Also controlling, i.e. the facility to intervene in control processes or, alternatively, to make such intervention by unauthorized persons impossible. It also became required to interconnect and harmonize individual systems controlled via PLC by means of automation technology. Therefore a master computer makes easy the means to issue higherlevel commands for program processing to some PLC systems.

The networking of some PLCs as well as that of a master computer and PLC is affected through special communication interfaces. To this effect, a lot of the more current PLCs are well-matched with open, standardized bus systems, for instance Profibus to EN 50170.

End of the seventies, binary inputs and outputs were finally extended with the analogue inputs and outputs addition, since many of today‘s technical applications need analogue processing such as speed setting, force measurement, servo-pneumatic positioning systems. At the same time, the analogue signals acquisition or output allows an actual/set point value comparison and as a result the automatic control engineering realization functions, a task, which broadly exceeds the scope suggested by the name as programmable logic controller.

The PLCs presently on offer in the market place have been modified to customer demands to such an extent that it has become possible to buy a highly suitable PLC for virtually any application. As such, miniatures PLCs are currently available with a minimum number of inputs/outputs beginning from just a few hundred Pounds. Also available are larger PLC swith 28 or 256 inputs/outputs. A lot of PLCs can be extended by means of additional input/output, positioning, communication and analogue modules. Special PLCs are available for shipping or mining, safety technology tasks. Yet further PLCs are capable to process numerous programs concurrently or multitasking. Lastly, PLCs are coupled with other automation components, accordingly creating significantly wider areas of application.

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