What is SCADA?
SCADA stands for supervisory control and data acquisition. It is the software and hardware that collects data from PLCs, RTUs and sensors across a plant, pipeline or utility, shows it to operators on screens, stores its history, raises alarms, and lets operators send commands back to the equipment.
The two halves of the name describe the job. Data acquisition is gathering readings (levels, pressures, flows, run states) from equipment that may sit in one building or be spread across hundreds of miles. Supervisory control is the operator's side: starting a pump, changing a setpoint, acknowledging an alarm.
The word "supervisory" matters. The fast, moment-to-moment control is done by the PLCs and RTUs in the field. SCADA sits above them: it watches everything at once, tells people what is happening, and passes their decisions down. If the SCADA server goes away, the PLCs keep running the process.
A SCADA system has a few core parts: field devices and sensors; PLCs and RTUs that read them; a communication network using protocols such as Modbus, DNP3 and OPC; servers that poll the field and keep the history; and HMI screens where operators see it all and act.
You find SCADA wherever a process is large or spread out: power and energy, water and wastewater, oil and gas, manufacturing and transportation. A distributed control system (DCS) does a similar job inside a single continuous-process plant, with control and display tied more tightly together.