An overview of SCADA, DCS, and PLC

SCADA is a distributed control system architecture used to control geographically dispersed assets. Distribution systems such as electrical power grids, oil and natural gas pipelines, water distribution, railway transportation, and so on heavily rely on centralized data acquisition and control. A SCADA control center monitors alarms and processes data for field sites, usually over long-distance communications networks. This information from the remote stations is used to push automated or operator-driven supervisory commands to remote field devices (which will be discussed later in this section) to control local operations such as the opening/closing of valves, breakers, collecting sensor data, and so on (NIST-800-82r2).

A DCS is functionally similar to SCADA, though it is typically used for localized control in continuous manufacturing process use cases, for example, a fuel or steam flow in a power plant, petroleum in a refinery, and distillation in a chemical plant. As DCS localizes control functions near the process plant, it is a more cost-effective, secure, and reliable option for uses cases where the control room is not geographically remote.

PLCs are extensively used in most industrial processes. PLCs are solid-state closed-loop control system components that are used in SCADA and DCS to provide operational control of discrete processes such as automobile assembly lines.

Being localized within a factory or plant, DCS and PLC communications use reliable and high-speed local area network (LAN) technologies. On the contrary, SCADA systems cover larger geographical territories, and need to account for long-distance communication challenges, delays, and data loss in remote sensor networks.

An ICS is an overarching industrial technology that usually includes SCADA, DCS, and PLC functionalities.