Supervisory Control and Data Acquisition Systems (SCADA) present a means of networking industrial infrastructure monitoring and control systems.
From a central reading location a SCADA system can track a number of remote sites equipped with Remote Terminal Units (RTUs) or Programmable Logic Controllers (PLCs). The RTUs can measure an array of conditions and a wider variety of parameters, including temperature, current, voltage flow, and tank levels. Real-time measurements are obtained from the RTU’s via the different sensors they have inside. The data acquired is then sent back via the communication link. Some of the larger systems can monitor 10-20,000 remote sites, with each site handling as many as 2000 input/output (I/O) points. These units in turn report back to the Central Processing Unit (CPU) that carries out the control functions and needed analysis.
Here’s a document from the National Communications System explaining SCADA and its role in emergency preparedness and national security. The tables on pages 43 to 45 look interesting.