Basics of Distributed Control Systems


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Distributed Control Systems

Generally, the concept of automatic control includes accomplishing two major operations; the transmission of signals (information flow) back and forth and the calculation of control actions (decision making). Carrying out these operations in real plant requires a set of hardware and instrumentation that serve as the platform for these tasks.

Distributed control systems (DCS) is the most modern control platform. It stands as the infrastructure not only for all advanced control strategies but also for the lowliest control system.

A Distributed Control Systems (DCS) is an automated control system that monitors and provides instructions to different parts of a machine. Distributed control 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.

A Distributed control systems is then a powerful tool for any large commercial plant. The engineer or operator can immediately utilize such a system to:

  • Access a large amount of current information from the data highway.
  • See trends of past process conditions by calling archival data storage.
  • Readily install new on-line measurements together with local computers for data acquisition and then use the new data immediately for controlling all loops of the process.
  • Alternate quickly among standard control strategies and readjust controller parameters in software.
  • A sight full engineer can use the flexibility of the framework to implement his latest controller design ideas on the host computer or on the main control computer

Advantages of Distribution control systems (DCS):

The key advantage of Distribution Control Systems (DCS) is that:-

  • Functional hardware distribution are flexibility in system design, ease of expansion, reliability, and ease of maintenance.
  • In distribution control system complete loss of the data highway will not cause complete loss of system capability. Often local units can continue operation with no significant loss of function over moderate or extended periods of time.
  • Divide up the control tasks among multiple distributed systems.
  • In distribution control systems (DCS) network allows different modes of control implementation such as manual, auto, supervisory, computer operation for each local control loop.

Types of Distribution control system:

The different types of DCS include:

  • Conventional DCS: a pure “process-only” control system. Typically purchased from one vendor and arranged into categories; small, medium and large.

  • 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.

Future of Distributed Control Systems:

Today’s industrial companies are looking for DCSs that provide a common approach across their systems to simplify design, implementation, and operation. To help process-driven businesses address these issues, automation systems have become increasingly capable of adapting to process changes quickly and easily.

The evolution of DCS technology has been driven by the increasing speed and complexity of business, and the need to respond to market changes in real-time. Modern control systems offer faster processors than previous generations of technology, enabling integration of workflow engines at the platform layer of the automation software architecture.

This allows engineering, operation, and maintenance procedures to be embedded into the system environment for on-demand access. The network infrastructure of the DCS and the network architecture for plant information are becoming increasingly intertwined. That means DCS systems are being affected by server visualization, smartphone and tablet mobile interfaces, and other general IT trends.