Distributed Control System with PLC VS DCS

 Overview :- 

Automation is one of the rising field and it has become the backbone of the process and Manufacturing Industries. 

Industrial Automation has a Control of all Industries machines and Industrial Process by replacing human Operator.

In Current Scanario two Automation Component are using.

1. Programmable Logical Controller (PLC)

2. Distributed Control System (DCS)

Tool of Automation

Microcontroller

Microcontroller is a best tool for Application.

Vending machine and Home Appliances is a Good Example of Microcontroller

Common MCUS Include the Intel MCS-51, often Referred to as an 8051 microcontroller, which was 

first developed 1985. The AVR  Microcontroller developed by  ATMEL in 1996.

Microcontroller preferred, when application is low Cost and Small Size.

Programmable Logic Controller 

Programmable Logic Controller is a digital electronic device that uses a Programmable memory 

to store instructions and to implement specific function such a logic, sequencing, timing, counting, 

and arithmetic to control machines and process.

PLC were develop to replace relay based control.

it is used for automation of small plants.

It is used for application containing digital I/O and Limited analog.

Distributed Control System

Distributed Control System refer to a Control system Usually of Manufacturing system,

Process in which the control element not Centralized but are distributed throughout the system with each component sub -system controlled by one or more controller.

Mostly Used in Process Plant, Chemical Plant , Power Plant , water management system, automobile Industries etc.

unlimited I/O.

History of DCS

DCS was Introduced in 1975 by Honeywell-TDS2000, Yokogawa - Centum

DCS Concept

It distributes information and control functions that previously required central computer.

A DCS typically uses computer (usually custom designed processor) as a controller and proprietary interconnection and protocol for communication.

DCS Architecture

DCS Element

Data Acquisition Unit: Digital (discrete) and analog I/O can be handle.

Batch Sequencing Unit: This unit controls a timing counters, arbitrary function generators, and internal logic.

Local Display: This device provides analog display stations, and video display for readout. 

Bulk Memory Unit: This unit is used to store and recall Process Data .

General Purpose Computer : This unit is programmed by a customer or third party to perform optimization, advance control, expert system, etc 

Central Operator Display: This unit typically contain several consoles for operator communication with the system, and multiple video color graphics display units 

Data Highway : A serial digital data transmission link connecting all other components in the system. It allow for redundant data highway to reduce the risk of data loss.

 Advantage of DCS

1. Handle complex Structure :-  DCS has an Inbuilt Distributed controller for each different control operation, and even when we want to expand I/O, Its Very easy to Configure or Modify the Controller in DCS. 

2. System Redundancy :-  DCS Facilitates system redundancy at entry- Level. Redundancy rise system reliability by maintain system operation endlessly during the Time of some abnormalities even when the system is in Operation Mode means system switch the another controller.

3.Scalable Platform :-  The Structure of DCS can be easily scalable just by adding some control units or process unit. I/Os Can be easily expanded by just adding some I/O Modules to the controller.

4. System Security :- Distributed Control System Design offers a perfect secured system to handle system function for better Plant Automation Control. Security is also  provided at different levels such as Admin Level, Operator Level, Supervisor Level.

Compression Between PLC and DCS

Sr.No.	Function	PLC	DCS
1	Redundancy	No. Redundancy	Controller Redundancy is available
2	Control Algorithms	Engineered	Built in Configurable Complex Algorithms
3	PID Function Blocks	Limited Loops with limited functionality	Multiple loops with enhanced functionality
4	Networking	Engineered Networking as per requirement	Normally all Components tightly Integrated on the network
5	I/O variety	Large Collection of I/O	Limited Variety
6	Third party Connectivity	Yes	Limited

Available DCS in the Market

• Yokogawa-Centum CS3000 

• Emerson-Delta V

 • Siemens • Bailey

 • Foxboro

 • Fisher-Rosemount 

• Honeywell-EPKS