An HMI is the machine-level interface an operator uses on the line, while SCADA supervises devices across an entire facility. As a plant-wide monitoring system, it adds centralized reporting, a data historian search tool and facility-wide alarm management. A SCADA system can integrate many HMIs beneath it.
Supervisory control extends beyond a single HMI:
- HMI scope covers one machine or a single line, giving the operator local visualization and control at the point of work.
- SCADA scope covers the whole facility, pulling data from many HMIs, PLCs and remote sites into one supervisory layer.
- Data historian, a time-stamped database tool inside SCADA, stores months of process data for trend analysis and compliance reporting.
- Alarm management at the SCADA top-down level aggregates faults across sites, so a control room sees live plant-wide events in an emergency.
If a line-level HMI goes offline, then SCADA still logs and alarms on the underlying PLC data it collects directly. An HMI controls one machine or line, while SCADA supervises many machines and lines across the plant. It also pulls data from the PLCs beneath. See the backbone that carries it on our Network Panels page.
