History of PLC and SCADA

Published: 02nd June 2009
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PLC stands for programmable logic controllers that are designed to serve for an adequate and relevant substitution for large control panels that are relay based. The reason for the replacement or the substitution owes primarily due to the change demanded by the control sequence wit respect to any sort of functional disorder. With the onset of progress at the front of processing speed of processors that began way back from the period of mid 1970's the functional aspects of programmable logic controllers has assumed a much more enhanced area of responsibility in all the ways.

Further to this aspect the future advancements in 1980's that led to the introduction of the Personal Computer permitted the development of a computer based interface to the operator and this was accomplished through the effective channel and suitably designed route of simple Supervisory Control and Data Acquisition (SCADA) systems.

SCADA is the acronym that stands for Supervisory Control and Data Acquisition. It normally connotes an industrial control system comprising of a computer system monitoring and controlling a process. The process can be analyzed from three distinct perspectives which are

1 Industrial

2 Infrastructure

3 Facility based

When trying to understand SCADA from the perspective of the Industrial processes incorporates multidimensional genres that are associated with the areas of production, manufacturing, power generation, refining and production. Therefore in this aspect they may run either in continuous format or adopt a mode which may be in batch or repetition or may follow a discreet mode.

Secondly if we try to comprehend the aspect of the Infrastructure processes then the image connotation may either be public or private due to which it incorporates distribution and water treatment, oil and gas pipelines, electrical power transmission and distribution, wastewater collection and treatment and large communication systems.

The third aspect of the Facility processes envisages its appearance and occurrence in both the fields of public facilities and private one and therefore this aspect comprises of space stations, buildings, ships and airports.

They supervise and monitor the command of HVAC, access, and energy consumption.

The term SCADA generally connotes to centralized systems which helps to monitor and manage complete functioning of sites or the intricate network of systems stretch out over huge areas.

In most of the cases multiple control actions are performed in an automated fashion with the help of remote terminals units (RTU's) or through the properly routed application of programmable logic controllers (PLC's).

In terms of Host control functions these in the normal cases are most of the times confined to basic administrative or superseding level intervention.

Hence in the simplistic terms it can be said that in terms of the feedback control loop the RTU or PLC are simply passing points of the overall monitoring function whereas the SCADA system is completely responsible for monitoring the complete routine and the overall performance of the loop.

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