SCADA System Layers
Field instruments, PLCs, communication networks, and the HMI each play a distinct role.
Field instruments (sensors and actuators) generate the raw data and physically execute control actions like opening a valve or starting a pump.
Programmable Logic Controllers (PLCs) execute local control logic close to the equipment, continuing to operate correctly even if communication to the central system is temporarily lost.
A communication network (fiber, radio, or cellular) carries data between distributed PLCs and the central SCADA server, with reliability requirements that scale with the criticality of what's being monitored.
The Human-Machine Interface (HMI) presents data to operators and allows manual control input, and is typically what people picture when they think of 'SCADA' despite being just the visible top layer of the system.
The industry's most useful newsletter, straight from the plant floor.
One email. No fluff. New lessons, equipment breakdowns, and process control notes, delivered when there's something worth reading.