SCADA stands for “Supervisory Control and Data Acquisition.” These are used for monitoring and controlling large areas, typically a full site or plant.
SCADA systems are a combination of many systems including sensors, RTUs or Remote Terminal Units, and PLCs.
Data from all of these systems is then sent to the central SCADA unit. That SCADA unit has its own HMI. This is why a lot of people get confused and think SCADA and HMI are one and the same.
That HMI or “Human Machine Interface” unit on the SCADA can monitor and control anything that is connected to it. In conclusion, HMI can be part of SCADA but SCADA cannot be part of an HMI. It’s that simple.