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SCADA acronym (supervisory control and data acquisition) generally refers to industrial control systems (ICS), that is computer systems that monitor and control industrial, infrastructure, or facility-based processes, as described below:
  • Industrial processes include manufacturing, production, power generation, fabrication and refining, and may run in continuous, batch, repetitive, or discrete modes.
  • Infrastructure processes may be public or private, and include water treatment and distribution, wastewater collection and treatment, oil and gas pipelines, electrical power transmission and distribution, wind farms, civil defense siren systems and large communication systems.
  • Facility processes occur both in public facilities and private ones, including buildings, airports, ships and space stations. They monitor and control HVAC, access and energy consumption.
SCADA usually pertains to centralized systems which monitor and control entire sites, or complexes of systems scattered on large areas (anything from an industrial plant to a nation). The majority of control actions are performed automatically by RTUs or by PLCs. Host control functions are usually restricted to basic overriding or supervisory level intervention.

Data acquisition begins at the RTU or PLC level and includes meter readings and equipment status reports that are communicated to SCADA as required. Data may also be fed to a Historian, often built on a commodity Database Management System, to allow trending and other analytical auditing..

SCADA systems typically implement a distributed database, commonly referred to as a tag database, which contains data elements called tags or points. A point represents a single input or output value monitored or controlled by the system. Points can be either “hard” or “soft”. A hard point represents an actual input or output within the system, while a soft point results from logic and math operations applied to other points. Points are normally stored as value-timestamp pairs: the value and the timestamp when it was recorded or calculated.