SCADA- It means Supervisory Control And Data Acquisition and refers to centralized systems which monitor and control sites spread over large areas (may be miles or kilometers).It mainly consists of three components, RTU(Remote Terminal Unit), Master Station and Human Machine Interface (HMI) and the third one is communication Infrastructure. Individual sites are run independently through RTU. These RTUs collect and send the status data to the Master Unit. The operator at the Master Station, with the help of MHI (computer),can change the set points or give commands to these sites.
DCS- It means Distributed Control System which is a term used in variety of industries to monitor or control distributed equipment. Input and Output modules form component parts of DCS. These modules receive and give signal to input and output instruments respectively. Elements of a distributed control system may directly connect to physical equipment such as switches, pumps and valves.DCS are dedicated systems used in industries such as oil refining, petrochemicals, central station power generation, pharmaceuticals, food & beverage manufacturing, cement production, steelmaking, and papermaking.