A Beginner’ Guide To Distributed Control Systems (DCS)

What is DCS?

DCS stands for Distributed Control Systems. DCS is a control system designed to function in a plant or in a process where the control systems lie distributed throughout the system. The controller hierarchy is connected via networks for monitoring and command.

dcs scada

 

Working of a DCS system

The most basic DCS systems consist of geographically distributed digital controllers. These are capable of executing regulatory control loops from 1 to 256 in one control box. The I/O is either integral or located on a remote field network.

Typically, the processors of a DCS are custom designed as controllers. They use both standard and proprietary communication protocols for to and fro connection. The component part of DCS comprise of the input and output modules. The input modules feed data into the processor, and the information is received at the output modules. The input modules use the input instruments which is transmitted in the form of instructions via the output modules.

The inputs and outputs are either analog or discrete signals. The processor and the modules are connected to the computer buses via multiplexer and demultiplexers. The buses also connect the distributed controllers with the central controller which ultimately connect to the HMI.

The Distributed control systems employ one or more workstations. These can be configured offline by a personal computer or at the workstation itself. The local communication is handled by controlled networks of fiber optic, coaxial or twisted-paired cables. To facilitate reporting, data collection and other computations, server or application processors may be included within the system.

How can DCS features be applied to the SCADA systems?

The DCS systems are primarily designed for process control. With DCS, adjustments to actuators and control valves can be made. These also contain HMI for managing trends, graphics and alarms for supervisory purposes in a SCADA system.

a. Architecture

Since the systems are distributed, the workflow is geared towards process control. The controllers are located fairly close to the instruments.

b. Time Horizon Feature

The DCS systems are execution systems. This means that they are concerned with managing the plant or process at any given moment in time.

The Applications of DCS

DCS systems are dedicated and are used for controlling manufacturing processes that are batch oriented or continuous. Significant examples of such processes include petrochemicals, fertilizers, oil refining, power generation plants, foods and beverage industries, steel and paper-making industries.

Over the years, Distributed Control Systems have found applications in multiple domains. Today’s systems come with the configuration software that are capable of enabling the end user for customizing the system without performing low-level programming. These systems also allow the user to focus on an application without having to go through a thorough training for acclimatizing with the DCS peripherals. But, a certain level of proficiency is required to work with the software. Considerable system knowledge, skill and deftness is required to handle the software deployment, hardware maintenance and applications. Most of the modern plants have dedicated personnel who focus on these tasks. A majority of the vendors provide dedicated support round the clock which may include customer support contracts and maintenance.

 

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