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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
10050
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 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 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 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 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
Microprocessor - base
Batch and DiscreteControl
Dynamic System
High speed, less 10 mSec
Star Topology
Mostly programmable Connectable to othersystem
Peer to peercommunication
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
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)
SCADA
Big & wide controlledarea
Centralized, master -slave
Low capacity
Microprocessor - base
Remote, supervisorycontrol
Static, shutdownpurposes
High speed, less 10 mSec
Point to point/multipoint Mostly programmable
Limited capability
Peer to peercommunication
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
Recommended