What is SCADA- By: Musarrat Sheikh

Description : SCADA is an acronym that stands for Supervisory. Control and Data Acquisition. It refers to a system that collects data from various sensors at a factory, plant or in other remote locations and then sends this data to a central computer which then manages and controls the data. SCADA it a term that is used broadly to portray control and management solution in a wide range of industries. Some of the industries where SCADA is used are Water Management Systems, Electric Power, Traffic Signals, Mass Transit Systems, Environmental Control Systems and Manufacturing Systems.
There are many parts of a working SCADA system. And they include signal hardware, controllers, networks, user interface (HMI), communications equipment and software. The term SCADA refers to the entire central system that monitors data from various sensors that are either in close proximity or off site and may be many miles away. The systems are performed by the Remote Terminal Units or RTU. Which consists of a programmable logic converter that is usually set to specific requirements that allows human intervention, for instance, in a factory setting, the RTU might control the setting of a conveyer belt, and the speed can be changed or overridden at any time by human intervention. Any changes or errors are usually automatically displayed. A SCADA system will monitor and make slight changes to function optimally and is considered a closed loop systems that run with relatively little human intervention.
A SCADA system includes a user interface, usually called Human Machine Interface (HMI). This is where data is processed and presented to be viewed and monitored by a human operator. HMI's are an easy way to standardize the facilitation of monitoring multiple RTU's or PLC's (programmable logic controllers). They will run a pre programmed process, but monitoring each of them individually can be difficult, usually because they are spread out over the system. Because historically they had no standardized method to display or present data to an operator, the SCADA system communicates with PLC's throughout the system network and processes information that is easily disseminated by the HMI.
HMI's can also be linked to a database, which can use data gathered from PLC's or RTU's to provide graphs on trends, logistic info, schematics for a specific sensor or machine or even make troubleshooting guides accessible. In the last decade, practically all SCADA systems include an integrated HMI and PLC device making it extremely easy to run and monitor a SCADA system.
SCADA systems are an extremely advantageous way to run and monitor processes. They are great for small applications such as climate control or can be effectively used in large applications such as monitoring and controlling a nuclear power plant or mass transit system. SCADA can come in open and non proprietary protocols. Smaller systems are extremely affordable and can either be purchased as a complete system or can be mixed and matched with specific components. Large systems can also be created with off the shelf components. SCADA system software can also be easily configured for almost any application, removing the need for custom made or intensive software development.

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Author Resource : This article touched the basics of the topic. I have 2 more resources related to the above. They are scada and scada. They are worth a read.