industrial//industrial automation//SCADA

SCADA, or Supervisory Control And Data Acquisition, is a class of industrial software system that supervises processes and acquires their data across a plant or a distributed network. It receives information from PLCs, RTUs and other equipment and lets people see states, show alarms, keep histories, send setpoints, plot trends and operate processes remotely.

SCADA, or Supervisory Control And Data Acquisition, is a class of industrial software system that supervises processes and acquires their data across a plant or a distributed network. It receives information from PLCs, RTUs and other equipment and lets people see states, show alarms, keep histories, send setpoints, plot trends and operate processes remotely.

It is the supervision layer of the plant's stack of loops, where a person watches and decides: below it the PLCs close loops in milliseconds, above it production management plans in hours (automation pyramid). The operator is part of a slow outer loop, reading trends and alarms over seconds to minutes and changing setpoints that the fast loops then hold.

Its native question is the present state of the plant: motor on or off, level 73 %, alarm active, valve open. That present-tense focus is also its limit: SCADA data are not automatically contextualized for finance, logistics, maintenance, analytics or benchmarking, which is how a plant ends up with data silos (data contextualization).

It serves both factories and geographically distributed infrastructure: electricity, water, gas and oil pipelines. In the distributed case the field side is an RTU and the center is a master station, joined by radio, cellular, fiber or satellite.

A SCADA should not execute the fast, critical control. That stays in the PLC or DCS; SCADA supervises. The difference with a DCS is architectural: SCADA supervises controllers that stay autonomous, so losing it leaves the PLCs running, while a DCS designs control and supervision as one system and its operator station is part of the control system itself. The operator's screen is the HMI, which can be part of a SCADA or a local panel on a machine.

Historically each PLC vendor exposed data its own way, so a SCADA would have needed a driver per protocol. The OPC layer was created to give it one interface instead (OPC).