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DISTRIBUTED CONTROLSYSTEMSubmitted by:

Roll no :35 to 59

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WHAT IS DISTRIBUTED CONTROLSYSTEMS?A distributed control system (DCS) refers to a controlsystem usually of a manufacturing system, process or any kind

of dynamic system.

In which the controller elements are not central in location (likethe 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.

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GENERATIONS OF DCS

First Generation: The Early

DCS The introduction of microprocessor-based control occurred shortlybefore 1980 with simple single-loop controllers. This technologyquickly evolved into a DCS with control processor redundancy,high-density input/output (I/O) systems, and a human machineinterface (HMI).

Perhaps the most significant feature of the early DCS was theability to geographically distribute control system processors andI/O components

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cond Generation: The Open System DCS

The open system DCS provided standard

communication interfaces for connecting the variousautomation subsystems.

Enterprise management solutions, also enabled bythe open system, provided new opportunities for fleetmanagement centers to improve operations byremotely monitoring processes, analyzing unitefficiencies, and supporting coordination betweenoperating units.

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Third Generation: The ExtendedAutomation DCSThe current business goals focus on increasing operational efficiency

and overall equipment effectiveness (OEE).

The third-generation DCS employ powerful object-oriented designtechnology to enable efficiency improvements within daily operationsand maintenance (O&M) activities.

Asset optimization is available to improve production reliabilitythrough improved process stability as well as through asset monitoringfor predictive maintenance.

Control system technology also now integrates several field busprotocols, thus enabling more flexibility in designs as well as improved

data for maintenance.

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Distributed Control SystemArchitecture

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Architecture

Engineering Workstation (EWS)

for project development, includingconfiguration of graphics, logic,alarms, security, etc.

Operator Workstation (OWS)provides the operator interface,including color graphics, faceplates,

alarms, logging, trends, diagnostics,etc.

Process Historical Archiver (PHA)

stores and retrieves historical data

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Field Control Unit (FCU)executes sequential and regulatorylogic and directly scans I/O.

I/O Subsystem supportsI/O from allthe standard industry suppliers

SCADA Data Server (SDS)interfaces UCOS to PLCs, Field bustechnologies, RTUs, PLC I/O, andother devices.

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microFCU small PLC that executessequential and regulatory logic anddirectly scans onboard I/O.

Networking and Communicationssupports redundant and non-redundant fiber optic and Ethernetlocal networks

The LAN/WAN can be extended toother sites inside or outside the plantusing such remote

communications

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DCS Elements

Local Control Unit

Data Acquisition Unit

Batch Sequencing Unit Local Display

Bulk Memory Unit

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CONTROLLERS IN DCS

Basic Controller (CB)

Extended Controller (EC)

Multifunction Controller (MC)

Advanced Multifunction Controller(AMC)

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How DCS control is better

Back up scheme-A back up computer

-Analog Controller

-Manual loading stations

-Various combinations of above

Reduction of wiring cost

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SCADA V/S DCS

1. DCS is process oriented, while SCADA is dataacquisition oriented.

2. DCS is process state driven, while SCADA is eventdriven.

3. DCS is commonly used to handle operations on asingle locale, while SCADA is preferred forapplications that are spread over a widegeographic location.

4. DCS operator stations are always connected to itsI/O, while SCADA is expected to operate despitefailure of field communications.

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Computer Control Networks

Operator

Control

Panel

Main

Control

Computer

Operator

Control

Panel

Archival

Data

Storage

Supervisory (host)Computer

PROCESS

Local

Computer

Local

Computer

Local

Computer

Local Display Local Display

Data highwayTo other Processes To other Processes

Local data acquisition and

control computers

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DCS Elements-1

Local Control Unit: This unit can handle 8 to 16individual PID loops.

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

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

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

Bulk Memory Unit: This unit is used to store andrecall process data.

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DCS Elements-2

General Purpose Computer: This unit isprogrammed by a customer or third party toperform optimization, advance control, expert

system, etc Central Operator Display: This unit typicallycontain several consoles for operatorcommunication with the system, and multiplevideo color graphics display units

Data Highway: A serial digital datatransmission link connecting all othercomponents in the system. It allow forredundant data highway to reduce the risk ofdata loss

Local area Network(LAN)

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Modes of Computer control

FC

signals from digital

computer

Local PIDcontroller

Supervisory Control mode

Direct digital Control mode

valve setting

from computer

Flow measurement

to computer

1.Supervisory Control

Mode2.Direct Digital

Control Mode

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Interface between digital computerand analog instruments

(A/D) Transducers convert analogsignals to digital signals. (Sensor

Computer)

(D/A) Transducers convert digital

signals to analog signals.(Computer Valve)

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Data resolution due todigitization

Accuracy depends on resolution.

Resolution depends on number ofbits:

Resolution = signal range 1/(2m -1)

m = number of bits used by thedigitizer (A/D) to represent the

analog data

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Data Resolution Signal = 0 - 1 Volt, 3 bit digitizer:

Binaryrepresentation

DigitalEquivalent

Analogequivalent

Analog rangecovered

0 0 00 0 10 1 0

0 1 11 0 01 0 11 1 01 1 1

012

34567

01/72/7

3/74/75/76/71

0to 1/141/14to 3/143/14to 5/14

5/14to 7/14 7/14to 9/149/14to 11/1411/14to 13/1413/14to 14/14

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Utilization of DCS

DCS vendor job:

installation

Control Engineer Job: Configuration

Built-in PID control:

How to Tune the PID control?

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Advanced control topology

DCS

Workstation

Pr

ocess

Two-ways

Data Bus

Online: Real-time data

PI interface

PI interface: C++ or Fortran

PI

system

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DCS Vendors

Honeywell

Fisher-Rosemont

Baily Foxboro

Yokogawa

Siemens

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Advantages of DCS

Access a large amount of current information fromthe data highway.

Monitoring trends of past process conditions.

Readily install new on-line measurements togetherwith local computers.

Alternate quickly among standard control strategiesand readjust controller parameters in software.

A sight full engineer can use the flexibility of theframework to implement his latest controller designideas on the host computer.

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Additional Advantage

Digital DCS systems are moreflexible. Control algorithms can bechanged and control configurationcan be modified without having

rewiring the system.

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Distributed Control System

Example Of ThermalPower Plant

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Objective

Safe operation of plant

Lowest cost of generation

Longest equipment life Minimum environmental effect

Maximum efficiency

Energy conservation

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Benefits of DCS

High reliability

Improved response time

Improve operator interface to plant Improve accessibility of plant data to

engineering & management

personals Historical storage and retrievalsystem

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DCS hardware

Controller card

- Input cards(4-20 mA,thermocouple,RTD,Digital)

.-Outputs cards(4-20mA,digital)

-Power supply module.

-Commnucation card-Cables

Controller withinput/output card

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DCS architecture

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Operator work station

Alarm monitoring graphic displayTrend display

operator guidance display System & diagnostic display Control Bar chart Sequence display Fault analysis display

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Logs/Reports

Event activated logs- alarmlog,trip analysis,start up log

Time activated logs-shift log,dailylog

Operator demand logs-summarylog,performancelog,maintenance log

Sequence of events log

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Boiler control system

Burner management system

Secondary air damper control

Aux pressure desuper heatingsystem

Soot blower control

Hp by pass

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Turbine control system

Turbine governing system

Turbine protection

Automatic turbine run up systemTurbine stress controller

Lp by pass

Sequence controls for turbine driver Generator aux monitoring

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THANK YOU