SCADA Systems and Concepts

SCADA means Supervisory Control and Data Acquisition, and mainly pertains to the management system of the industry. It is a computer system that manages and monitors a certain process, which can be industrial, infrastructure or facility based. The process can be described as industrial, which covers fabrication, refining, production, manufacturing and power generation. The process can be operated in batches, discrete, repetitive or constant modes. Being infrastructure means that the process can be public or private, covering areas like electrical power transmission and distribution, water treatment, water distribution, communication systems and civil defense systems. Being facility-based means that the process covers airports, space stations, ships, HVAC and consumption.

About the Subsystems

The SCADA system also includes several subsystems. Included is the apparatus that shows the human operator all the processed information. Through the human operator, the system can manage and operate the different process, also known as HMI or human-machine interface. A subsystem also includes a supervisory system that gets all the needed information regarding the process, thereby sending all the commands to the process.

There are RTUs or remote terminal units that link to the process sensors, thereby supporting the conversion of sensor signals to the digital data. The digital data will then be sent to the supervisory stream. There are also PLCs or programmable logic controllers that function like field devices. These are described as configurable, economical, versatile and flexible. The subsystem may also be a communication infrastructure that links the RTUs to the supervisory system.

Some Concepts

SCADA also pertains to the central systems that manage and observe the full sites. These can be system complexes that are distributed over huge areas. Almost all the commands or control actions are immediately done by the RTUs or the PLCs. There are restrictions to the host management actions such as basic overriding. Information gathering will begin at the RTU or PLC level, including the equipment status reports and meter measurements that are passed on as needed by the SCADA system. The information will be sorted out via the HMI. SCADA systems also execute the tag database or the distributed database that has the points or tags.


The human machine interface or HMI will show the processed information to the human operator. The information given by the HMI to the person is usually graphical or in mimic diagrams. The HMI software can present flow rates or the mimic diagrams will present digital photos, schematic symbols, animated symbols or line graphics to show the different elements of the process. Alarms are among the most vital executions of SCADA systems. The alarm can present either normal or alarm. A good example is when a vehicle’s fuel tank is running empty. The alarm will be activated and alert the driver by turning the alarm light on.

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