What is a SCADA? 
The term SCADA usually refers to centralized systems which monitor and control entire sites, or complexes of systems spread out over large areas (anything from an industrial plant to a nation). Most control actions are performed automatically by RTUs or by PLCs. Host control functions are usually restricted to basic overriding or supervisory level intervention. For example, a PLC may control the flow of cooling water through part of an industrial process, but the SCADA system may allow operators to change the set points for the flow, and enable alarm conditions, such as loss of flow and high temperature, to be displayed and recorded. The feedback control loop passes through the RTU or PLC, while the SCADA system monitors the overall performance of the loop. continue..

SCADA (supervisory control and data acquisition) has been around as long as there have been control systems. The first ‘SCADA’ systems utilized data acquisition by means of panels of meters, lights and strip chart recorders. The operator manually operating various control knobs exercised supervisory control. These devices were and still are used to do supervisory control and data acquisition on plants, factories and power generating facilities continue..

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.  continue..

The simplest possible SCADA system would be a single circuit that notifies you of one event. Imagine a fabrication machine that produces widgets. Every time the machine finishes a widget, it activates a switch. The switch turns on a light on a panel, which tells a human operator that a widget has been completed. Obviously, a real SCADA system does more than this simple model. But the principle is the same. A full-scale SCADA system just monitors more stuff over greater distances. Let’s look at what is added to our simple model to create a fullscale SCADA system: continue..

Supervisory Control and Data Acquisition (SCADA) Systems are frequently used in Water and Waste Water Systems to monitor and control tank levels, remote well pumps, lift station pumps, high service pumps, valves, and chemical pumps. SCADA Systems monitor a variety of plant data including flows, motor current, temperatures, water levels, voltages, and pressure. Alarms at central or remote sites triggered by any abnormal conditions are propagated to the HMI computer for operator's attention. In addition to alarms, important plant information such as, levels, flows, pressure will be logged in the HMI computer database for reports and trends. continue..

In power system, SCADA system is most widely used, the most mature technology development. Energy management system as (EMS System) subsystem of one of the most important, with complete information, improve efficiency, to accurately grasp the state of the system, speed up decision-making, can help quickly diagnose system failures and other advantages of the state, has become a power dispatch is not indispensable tool. Improve the operation of its power grid reliability, safety and economic efficiency, to reduce the burden on dispatchers to achieve automation and modernization of power dispatching and improve the efficiency and the level of activation in the area plays an irreplaceable role.continue..

The advantages of the PLC / DCS SCADA system are:
• The computer can record and store a very large amount of data
• The data can be displayed in any way the user requires
• Thousands of sensors over a wide area can be connected to the system
• The operator can incorporate real data simulations into the system
• Many types of data can be collected from the RTUs
• The data can be viewed from anywhere, not just on site
The disadvantages are:
• The system is more complicated than the sensor to panel type
• Different operating skills are required, such as system analysts and programmer
• With thousands of sensors there is still a lot of wire to deal with
• The operator can see only as far as the PLC continue..

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