SCADA - Supervisory Control and Data Acquisition
The big difference between a Supervised PLC system and a SCADA system is that the SCADA system doesn’t have a microprocessor local to the I/O.
A SCADA I/O unit is called a Remote Terminal Unit (RTU).
A basic SCADA system has RTU’s located at different locations in a facility/plant. The outputs of each RTU is connected to a central communication device called a Master Terminal Unit (MTU).
The MTU is connected to a computer (usually a server) and the data is delivered to a HMI using a database just like the PLC HMI.
Because the RTU’s have no local processor, the RTU’s cannot provide any control automation. All device viewing and operation is done by an operator using the HMI
RTU’s and MTU’s can also be at distant locations and require some type of long distance communication
