SCADA lets one control room watch pipelines, plants and railways across huge distances
A water utility may have pumps scattered over hundreds of square kilometres, some in places with no mains power at all. SCADA, short for supervisory control and data acquisition, ties them together so an operator at a screen can see every tank level and valve, get alarms, and step in when something drifts.
SCADA is a layered architecture rather than a single machine. At the bottom sit field devices: flow and temperature sensors, and actuators such as control valves. Above them, programmable logic controllers and remote terminal units run the moment-to-moment control logic. Supervisory computers gather their readings and present them to operators, and higher layers track production targets and scheduling. The design grew out of a need for one universal way to reach control modules from many different makers.
Remote terminal units are built for rough places. They often run on small solar panels, talk over radio, mobile or satellite links, and are hardened to work from minus 20 to plus 70 degrees Celsius, some even wider, without heating or cooling. Both they and logic controllers keep executing the last command they received, so a broken network link does not necessarily halt the plant. Critical systems may run two data highways along separate cable routes.
Operators see the plant through a human-machine interface, typically mimic diagrams that sketch pipes, tanks and machines with live values overlaid, plus trend graphs and alarm pages. Alarm handling is central: the system checks whether readings stray beyond set limits, then sounds sirens, flashes screens or sends texts, and certain alerts persist until the underlying fault is fixed, even after acknowledgement. Every instrument appears in a tag database, and a historian logs data for later analysis.
Field controllers are usually programmed in the IEC 61131-3 languages, such as ladder logic, which mimic old relay panels and need far less training than conventional code. Since about 1998 nearly all major controller makers have sold integrated SCADA packages, often on open protocols. Large networks such as railways and power stations frequently use SONET or SDH fibre links.
Source: SCADA
