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Distributed Control System  (DCS)

A Distributed Control System is an automated control system that monitors and provides instructions to different parts of a machine, plant or process. Commonly used in manufacturing environments, a DCS utilizes input and output protocols to control distributed equipment. DCS systems are commonly used in process industries controlling breweries, refineries, chemical plants, paper mills etc.  The elements of a DCS may connect directly to physical equipment, such as controllers, historians and to Human Machine Interface (HMI) via SCADA. The key advantage of DCSs is that they divide up the control tasks among multiple distributed systems; if any single part of the system should fail, the plant could keep operating. DCS systems also introduced the concept of data networking, thereby allowing hard wiring of each control point, adding flexibility and reducing the cost of making changes in the production process. The different types of DCS include: Conventional DCS: a pure “process-only” control system. Typically purchased from one vendor and arranged into categories PLC-based DCS: a network of PLCs used to perform the task of conventional DCS and programmable functionality when required. Hybrid DCS: Performs both process and sequential control. Open DCS System: A Field-Bus control. Advantages include: low wiring costs, less failure, lower expansion costs and multi-vendor interoperability. DCS and PLCs can be more interconnected. Differences Between DCS and SCADA In the past, SCADA and DCS were separate entities, however with the advancement in technology, they sometimes appear to be similar. The solutions, process orientation and connectivity are what make these systems contrasting entities. A DCS is usually more process-oriented in contrast to SCADA, which focuses on gathering data. DCS scans and concentrates on the controlled process and presents the information to the operators. SCADA, on the other hand, concentrates mainly on the control center as well as the operators. The remote equipment is mainly used to collect data even though it can be used to carry out other multifaceted process controls. In a DCS system, the operator has a closed-loop control at the PCS/RTU levels. However, closed-loop control is unavailable in a SCADA system. In its place, you can access the control via the HMI, using human as supervisory control. In this regard, most DCS systems today have integrated HMI and supervisory facilities, DB connectivity as well as all basic facilities that come with SCADA system.
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