What is Distributed control system | Process Automation

A distributed control system (DCS) is a computerised control system for a process or plant usually with a large number of control loops, in which autonomous controllers are distributed throughout the system, but there is central operator supervisory control. This is in contrast to systems that use centralized controllers; either discrete controllers located at a central control room or within a central computer. The DCS concept increases reliability and reduces installation costs by localising control functions near the process plant, with remote monitoring and supervision.

Distributed control systems first emerged in large, high value, safety critical process industries, and were attractive because the DCS manufacturer would supply both the local control level and central supervisory equipment as an integrated package, thus reducing design integration risk. Today the functionality of SCADA and DCS systems are very similar, but DCS tends to be used on large continuous process plants where high reliability and security is important, and the control room is not geographically remote.

dcs architecture
dcs architecture

What is the difference between PLC and DCS?

  1. PLC stands for Programmable Logic Controller which can handle the binary input and output of the logic statement which are stored in its memory.its a digitally operating system which are logic stored in its memory by programming system.

See also: 

  • Programmable Logic Controllers, are frequently used to synchronize the flow of inputs from sensors (Physical) and events with the flow of outputs to actuators and events. This leads to precisely controlled actions that permit a tight control of almost any industrial process.
  • This is actually a control device that consists of a programmable microprocessor, and is programmed using a specialized computer language.
  • Before, a programmable logic controller would have been programmed in ladder logic, which is similar to a schematic of relay logic.
  • A modern programmable logic controller is usually programmed in any one of several languages, ranging from ladder logic to Basic or C.
  • Typically, the program is written in a development environment on a personal computer (PC), and then is downloaded onto the programmable logic controller directly through a cable connection.
  • The program is stored in the programmable logic controller in non-volatile memory.Programmable logic controllers contain a variable number of Input/Output (I/O) ports, and are typically Reduced Instruction Set Computer (RISC) based.
  • They are designed for real-time use, and often must withstand harsh environments on the shop floor. 

    2. DCS stands for Distributed Control systems 

  • Distributed control system it controls all types of process variable at a time through this we can control the whole plant,we can see the status of plant,and handling unit.
  • It is a system of dividing plant or process control into several areas of responsibility, each managed by its own controller, with the whole system connected to form a single entity, usually by means of communication buses.
  • (DCS) refers to a control system usually of a manufacturing system, process or any kind of dynamic system, in which the controller elements are not central in location (like the brain) but are distributed throughout the system with each component sub-system controlled by one or more controllers. The entire system of controllers is connected by networks for communication and monitoring.
  • A DCS typically uses custom designed processors as controllers and uses both proprietary interconnections and Communications protocol for communication.
  • Input & output modules form component parts of the DCS. The processor receives information from input modules and sends information to output modules.
  • The input modules receive information from input instruments in the process (a.k.a. field) and transmit instructions to the output instruments in the field.
  • Computer buses or electrical buses connect the processor and modules through multiplexer or de-multiplexers.
  • Buses also connect the distributed controllers with the central controller and finally to the Human-Machine Interface (HMI) or control consoles.

Application of Distributed Control System :

Distributed control systems (DCS) are dedicated systems used in manufacturing processes that are continuous or batch-oriented.

Processes where a DCS might be used include:

  • Chemical plants
  • Petrochemical (oil) and refineries
  • Pulp and Paper Mills 
  • Boiler controls and power plant systems
  • Nuclear power plants
  • Environmental control systems
  • Water management systems
  • Water treatment plants
  • Sewage treatment plants
  • Food and food processing
  • Agro chemical and fertilizer
  • Metal and mines
  • Automobile manufacturing
  • Metallurgical process plants
  • Pharmaceutical manufacturing
  • Sugar refining plants
  • Agriculture Applications
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