process control concept

8/6/2019 Process Control Concept

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Process Control Concept


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Process Control Hierarchy

PROCESS

Basic Regulatory Control(Feedback)

Advance Regulatory Control

(Ratio, Cascade, Feedforward, Override, Decoupling)

Optimation

(Advance Process Control)

Corporate Level Controls

(ERP)


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PROCESS

CONTROLLER

Process ControlManual With Off line Computer Assistance

OPERATINGINSTRUCTION

LOG

DELAYOFF LINE

ANNUNCIATOR

RECORDERS


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PROCESS

CONTROLLER

Process ControlManual With On line Computer Assistance

LOG

RECORDERS

ON LINE


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PROCESS

CONTROLLER

Process ControlAutomatic with Feedback

LOG

RECORDERS

ON LINE


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TWO BASIC LOOPING IN SYSTEM MEASUREMENT

OPEN LOOP INDICATING, RECORDING ,ALARM ANNUCIATING ONLY

CLOSE LOOP CONTROL TO FINAL ELEMENTPLUS CAPABILITY ON

INDICATING, RECORDING, AND ALARMANNUNCIATOR

BASIC CONTROL LOOP


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PROCESS

DATA

LOGGER

RECORDING

ALARM

OPEN LOOP

INDICATING

OPERATOR WILL ACTUATE

THE VALVE BASE ON DEMAND

SHOWN BY PANEL DISPLAY


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PROCESS

CONTROLLER

SET

POINT

CLOSE LOOP

DATA LOGGER

FINAL

ELEMENT

PRIMARY

ELEMENT

FIELD

ELEMENT

CONTROLELEMENT


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Control System

ON-OFF Control SystemExample : Motor Control, ESD Valve, Interlock System

Variable (Regulatory) Control System

Feedback Control Loop, Cascade Control, Ratio Control


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Automatic Control

FIELD ELEMENT: Orifice, RTD, T/C, etc

PRIMARY ELEMENT: Transmitter

CONTROLLER: Manipulated device

CONTROL SIGNAL: 3-15psig, 4-20 mA, HART/ Fieldbus

CONTROL MODE: Proportional, Integral and Derivative

SET POINT: value to be given to any controller

FINAL ELEMENT: Control valves, switches etc.


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Types of Automatic Control Loop

OPEN LOOP is used to indicate or record a process fluid

without any control output CLOSED LOOP or Feedback Control uses the output ofcontroller to manipulate the final control element (e.g.control valves)

SPLIT RANGE CONTROL is used to split two outlet flowwithin a range of controller output

RATIO CONTROL: is used to ensure two or more flow(mixed flow) are kept at the same ratio even if the floware changing

CASCADE CONTROL: uses the output of primarycontroller to manipulate the set point of the secondary

controller as if it were the final control element OVERRIDE CONTROL :is used to take control of an

output from one loop to allow a more important loop tomanipulated the output


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Control Diagram of a Typical Control Loop

F1

T1

T

F2

T2

T CC o n t r o l l e r

A c t u a t o r

S y s t e m

T T

S e n s o r

S y s t e m


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Components and Signals of a Typical Control Loop

T

F2

T2

T h e r m o c o u p l e

m i l l i v o l t s i g n a l

T r a n s m i t t e r4 - 2 0 m aD C S

C o n t r o l

C o m p u t e r

A / D

3 - 1 5 p s i g

D / A4 - 2 0 m a

O p e r a t o r

C o n s o l e

T s p

I / PA i r

F1

T1

T h e r m o w e l l


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Feedback

A feedback control configuration measures the error after the processas correction factor to be transmitted to controller in order to give

signal input to final control element

Feedback

ControllerProcess

Manipulated

Input

Process

Output


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Cascade Control Loop

R S P

T T

F C

G a s

F T

T C T s p

P r o c e s s

S t r e a m


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Feedforward

A feedforward control configuration measures the disturbance directlyand takes control action to eliminate its impact on the process output.

Feedforward

Controller

Disturbance

Manipulated

Input

Process

Output

Process


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Ratio Control Loop

CONTROLLERFIELD

A

PID

MLD-SW

MLD-SW

FIELD

B

OUT1

OUT2

OUT

SPLIT

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PV

MV

0

50

100

MV

PV

10050

0

50

100


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Pneumatic Controller

Introduced in the 1920s

Installed in the field next to the valve

Use bellows, baffles, and nozzles with an air supply to implement PID

action.

Provided automatic control and replaced manual control for many

loops Transmitter type pneumatic controllers began to replace field mounted

controllers in the late 1930s.

Controller located in control room with pneumatic transmission from

sensors to control room and back to the valve.

Allowed operators to address a number of controllers from a

centralized control room.


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Pneumatic Controller

T

F2

T2



T r a n s m i t t e rP n e u m a t i c

C o n t r o l l e r

3 - 1 5 p s i g

Ts p

A i r

F1

T1

T h e r m o w e l l

3 - 1 5 p s i g A i r


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Electronic Analog Controller

Became available in the late 1950s.

Replaced the pneumatic tubing with wires.

Used resistors, capacitors, and transistors based amplifiers to

implement PID action.

Out sold pneumatic controllers by 1970.

Allowed for advanced PID control: ratio, feedforward, etc.


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Electronic Analog Controller

T

F2

T2



T r a n s m i t t e r4 - 2 0 m aE l e c t r o n i c

A n a l o g

C o n t r o l l e r

3 - 1 5 p s i g

4 - 2 0 m a

Ts p

I / PA i r

F1

T1

T h e r m o w e l l


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Computer Control System

Based upon a mainframe digital computer.

Offered the ability to use data storage and retrieval, alarm functions,

and process optimization.

First installed on a refinery in 1959.

Had reliability limitations.


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Computer Control System

P r i n t e rV i d e o D i s p l a y

U n i t

I n t e r f a c i n g

H a r d w a r e

A n a l o g

C o n t r o l

S u b s y t e m

A l a r m i n g

F u n c t i o n s

S u p e r v i s o r y C o n t r o l C o m p u t e r

D a t a S t o r a g e

A c q u i s i t i o n

S y s t e m

. . .


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Evolution - Microprocessor Base Controller

Field Instrument

Multi Loop Continuous

& Discrete Controller

Field Instrument

Multi Loop

Programmable Controller

PLCPC


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Evolution - Direct Digital Control (DDC)

PC

FIELD INDTRUMENTS

SEGREGATED

I/O RACK

CPU

RS 232

HARD WIRED


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PLC

A PLC (i.e. Programmable Logic Controller) is a device that was

invented to replace the necessary sequential relay circuits for machine

control

PLC for safety


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Evolution Programmable Controller (PLC)

PC

FIELD INDTRUMENTS

SEGREGATED

I/O RACK (See Detail)

HARD WIRED

BUS


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POWE

RSUPPLY

PLC System - Rack/Card Configuration

POWE

RSUPPLY

PROCESS

ORCARD

PROCESS

ORCARD

I/OCA

RD

I/OCA

RD

I/OCA

RD

I/OCA

RD

PROGR

AM

ABLECARD

PROGRAM

ABLECARD

I/OCA

RD

I/OCA

RD

I/OCA

RD

I/OCA

RD

COMM

UN

ICATION

COMM

UN

ICATION

1 2 3 164 5 6 7 8 9 10 11 12 13 14 15

Field InstrumentTo Others Rack, orOthers Devices

Note::

Normally a Rack can be filled in max. 16 Cards

This Rack has redundancy in power supply ,

Communication and CPU/ Processor


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DCS

Introduced in the late 1970s.

Based upon redundant microprocessors for performing control

functions for a part of the plant. SUPERIOR RELIABILITY

Less expensive per loop for large plants.

Less expensive to expand.

Facilitates the use of advanced control.


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DCS

P r o c e s s T r a n s m i t t e r s a n d A c t u a t o r s

D a t a H i g h w a y

( S h a r e d C o m m u n i c a t i o n F a c i l i t i e s )

L o c a l

C o n s o l e

L o c a l

C o n t r o l

U n i t

. . . . . . . . . . . . . .

D a t a

S t o r a g eU n i t

H o s tC o m p u t e rS y s t e mC o n s o l e s P L C

L o c a l

C o n t r o l

U n i t

L o c a l

C o n s o l e


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Evolution - Distributed Control System (DCS)

MMI

FIELD INDTRUMENTS

INPU/ OUTPUT

RACK

CONTROLLER

RACK

MMI

DATA BASE

RACK

DAT LOGGER

ETHERNET / BUS

PLC SYSTEMGATEAWAY

SYSTEM


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DCS

Small controlled area Distributed, no master

High capacity

Microprocessor - base

Continues & discrete

control Dynamic system

Medium speed, 100mSec

Bus, Ring and Star

topology Mostly configurable

Connectable to othersystem

Peer to peercommunication

SIL 2 (IEC 60518)

PLC

Small limited I/O

Originally Programmableonly

Low capacity


Batch and DiscreteControl

Dynamic System

High speed, less 10 mSec

Star Topology

Mostly programmable Connectable to othersystem


SIL 3 (IEC 60518)

AK5 & AK6 (TUV Class)

DCS VERSUS PLC SYSTEM


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SCADA

Basic concept: Definition, Automation or remote, SCADA

Architecture

Communication

Field Device

RTU

MTU Data communication


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SCADA

SCADA : A system for monitoring and controlling for geographically

dispersed process from a central location.

Acquires Data

Supervisory Control


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MASTER

Station

Sub Master

Station #.1

Sub Master

Station #.2

REMOTE

Station #.2

Field Devices

REMOTE

Station #.1

REMOTE

Station #.3

Half-Duplex

Transmission Mode

Point to Multipoint

Topology

SCADA SYSTEM CONFIGURATION

SCADA SYSTEM COMPONENT


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Master

Station

Master

Station

DCE

DCE

DCE

C

Pipeline Remote

Shutdown Valve

VAX-BASE COMPUTER

MASTER STATION

Point-to Multipoint, Half

Duplex, PSTN, TCP/IP

Protocol, Telemetry

Network

ANALOG DIAL UP

MODEM

ANALOG DIAL UP

MODEM

SCADA SYSTEM COMPONENT

MASTER STATION P l C t


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MASTER STATION Personal Computer

DCE

DTE

DCE

DCE

DTE

DCE

Master

Station

RS 232 LINK

REMOTESTATION #.1

REMOTESTATION #. 2

MASTER STATION VAX UNIX Wi d B C t


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MASTER STATION VAX- or UNIX or Windows - Base Computer

ETHERNETNETWORK

DTE

DCE

DTE

DCE

RS 232 LINK

Work

Station

Work

Station

CONTROLLER ANDI/O MODULE

DCE

DTE

DCE

REMOTESTATION #. 1

REMOTESTATION #. 2

VAX OR UNIX-BASESERVER

SUB MASTER STATION PLC BASE


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SUB MASTER STATION PLC BASE

DCE

DCE

DTE

ETHERNET

REMOTESTATION #. 1

DCE

DTE

DCE

PROGRAMMABLECONTROLLER BASE

REMOTESTATION #. 2

DCE

COMMUNICATIONWITHMASTER STATION

REMOTE STATION PLC BASE


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REMOTE STATION PLC BASE

DCE

DCE

ETHERNET

PUMP STATION

DCE

DCE

MASTERSTATION

DCE

DCE

DCE

DCE

PUMP STATION

GAS METERINGSTATION

WASTE WATERTREATMENT PLANT

MMI


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DCS VERSUS SCADA SYSTEM


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DCS

Small controlled area Distributed, no master

High capacity


Continues & discrete

control Dynamic system

Medium speed, 100mSec

Bus, Ring and Star

topology Mostly configurable

Connectable to othersystem


SIL 2 (IEC 60518)

SCADA

Big & wide controlledarea

Centralized, master -slave

Low capacity


Remote, supervisorycontrol

Static, shutdownpurposes

High speed, less 10 mSec

Point to point/multipoint Mostly programmable

Limited capability


SIL 3 (IEC 60518)

DCS VERSUS SCADA SYSTEM


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FieldBus Technology

The open, nonproprietary all-digital, serial two-way, multi-drop

communication link among intelligent field devices and automation

systems.

Based upon smart valves, smart sensors and controllers installed in the

field.

Uses data highway to replace wires from sensor to DCS and to thecontrol valves.

Less expensive installations and better reliability.

Can mix different sources (vendors) of sensors, transmitters, and

control valves.

Now commercially available and should begin to replace DCSs.


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Field Bus Configuration

P l a n t - W i d e N e t w o r k

. . . . . . . . . . . . . . . . .

S m a r t

S e n s o r sS m a r t C o n t r o l

V a l v e s a n d

C o n t r o l l e r s

L o c a l

A r e a

N e t w o r k

S m a r t

S e n s o r sS m a r t C o n t r o l

V a l v e s a n d

C o n t r o l l e r s

L o c a l

A r e a

N e t w o r k

F i e l d b u s N e t w o r kF i e l d b u s N e t w o r k

a


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Fieldbus Vs Conventional

Field wiring Information flow Quantity ofinformation

Information type Controlfunctionality

Maintenancelocation

Maintenance type

Conventional 4 to20 mA

Point-to-point Unidirectional Single data value Measurementnumerical value

Centered on acontrol system

Mainly in the fieldCorrectivemaintenance

Fieldbus Multi-drop Bidirectional Multiple data

values

Various data types Optimally

allotted to controlsystem and/orfield devices

From a remote

location

Predictive

maintenance


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Fieldbus Control

Fieldbus Fieldbus

AI AO PIDAI

AO

PID

Integrated Fieldbus/Host Control Fieldbus Control on the Wire

Controllersand

FieldbusModules


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Foundation Fieldbus

Foundation H1

Foundation Ethernet


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Fondation H1

Intended primarily for process control, field-level interface and device

integration.

Running at 31.25 kbit/s,

The technology interconnects devices such as transmitters and

actuators on a field network.

Twisted pair instrument cabling with power and signal on the samewire. Fiber optic media is optional. It also supports Intrinsic Safety

(IS) applications.


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Foundation HSE

Ideally suited for use as a control backbone.

Running at 100 Mbit/s,

Designed for device, subsystem and enterprise integration.

Fieldbus capabilities: including standard function blocks and Device

Descriptions (DDs), Flexible Function Blocks (FFBs) for advanced

process and discrete/hybrid/batch applications Supports complex logic functions, such as those performed by

Programmable Logic Controllers (PLCs), or data-intensive process

devices, such as analyzers and gateways to other networks. HSE

enhances access to H1 fieldbus technology via linking devices, while

providing expanded capabilities for high-speed automation devicesand hybrid/batch applications


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Typical Fieldbus Network

process control concept

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