1-introduction To Process Control (1).ppt 1xv5z
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Chemical Process Control
What if….
….you drive your car with your eyes shut?
IMPORTANCE
OF PROCESS CONTROL
SAFETY PRODUCT QUALITY PRODUCTION RATES REDUCE ENERGY
Why
we need to control a process?
◦ Because processes are dynamic – changes always occurred What
does a control system do?
◦ Maintain certain variables within some limit e.g temperature in a room
*dynamic time-dependent behavior of a process.
There
are many applications where part or all of a process has to be controlled. e.g. temperature pressure flow level composition others
Automatic
Control
◦ Maintaining the process variables (temperature, pressures, flows, compositions) at some desired operating value. ◦ Systems that control the variables without requiring intervention from the operator.
System
input SYSTEM
output
VARIABLES
Controlled variables – the variable that must be maintained at the desired value (set point)
Manipulated variables – the variable that need to be regulated in order to maintain the controlled variable at the set point
Disturbances – variables that tend to drive the controlled variable away from the set point
c. Uncontrolled variables. Variables in the process that are not controlled.
An Everyday Example of Process Control Control Objective (Setpoint): Maintain the temperature in the room (27oC) Controlled variable: Temperature in the room Manipulated variable: Speed of the fan Disturbance: Weather
An Everyday Example of Process Control Driving a Car Control Objective (Setpoint): Maintain car in proper lane. Controlled variable-
Location of car on the road Manipulated variableOrientation of the front wheels DisturbanceCurve in road
Exercise Select one control objective from a simple process and determine the controlled variable, manipulated variable and disturbances of the process.
HEAT EXCHANGER Steam in
Fluid in
Fluid out Heat Exchanger
Ti
T desired Steam out
HEAT EXCHANGER Steam in (Manipulated variables) (Controlled variables) Fluid out
Fluid in Heat Exchanger Ti (Load disturbances )
T desired Steam out (Uncontrolled variables)
THREE BASIC COMPONENT OF CONTROL SYSTEM Measurement (M) ◦ measure the variable to be controlled. sensor-transmitter combination Decision (D) ◦ Controller decides what to do to maintain the variables at its desired value controller Action (A) ◦ System must take an action based on controller’s decision control valve (final control element)
Another
important term
◦ Set point (SP)-desired value of the control variable. ◦ Open loop system - The behavior with no controllers in the system ◦ Closed loop system– the controller is connected to the process, comparing the set point to the controlled variable and determining and taking corrective action
Action Steam in
SP
Decide
TC TT
Fluid in
Fluid out Heat Exchanger
Ti
T desired Steam out
Measured = T desired (sensor transmitter) Control = Steam in Action = valve (final control element)
Measure
Steam in (Manipulated variables)
TC TT
Fluid in
Fluid out Heat Exchanger
Ti (Load disturbances )
T desired (Controlled variables)
Steam out (Uncontrolled variables)
Question
- How to ensure that T remains at or near the set point? w ,T 1
1
Q
M
w, T
Unit 1: Process & Instrumentation Diagram Process & Instrumentation Diagram (P&ID) Purpose 1. To indicate the instruments or control devices attached to the process. 2. To indicate the control system architecture associated with the process.
How it is done? Standard symbols and notations representing instruments or control devices are placed to the pipings and vessels.Standard symbols and notations are available from ISA-5.1(1984) standard.
Methodology? Process piping and sub-piping
A thick straight line represent main process piping A thin straight line represent process sub-piping either to instruments or by- process line.
© Abdul Aziz Ishak, Universiti Teknologi MARA Malaysia (2009)
PG
Unit 1: Process & Instrumentation Diagram Symbols Instruments / control devices:
A circle representing locally mounted instrument
A circle with horizontal line A circle with horizontal line representing control room inside a square representin mounted instrument. its function in DCS.
© Abdul Aziz Ishak, Universiti Teknologi MARA Malaysia (2009)
Unit 1: Process & Instrumentation Diagram Final control elements
Control valves
=
Manual valve
=
O R
Manual
=
O R
valve
Solenoid valve
Not darkened Always open
Darkened Always closed
=
© Abdul Aziz Ishak, Universiti Teknologi MARA Malaysia (2009)
Unit 1: Process & Instrumentation Diagram Naming rule
P T L F A
1
2
3
4
Measurement
Device
Device / Condition
Condition
Controller Transmitter Recorder Indicator Alarm Switch / Safety Gauge
C T R H L V
Pressure Temperature Level Flow Analysis
C T R I A S G
Controller Transmitter Recorder High Low Valve
H L
High Low
Complete guide on P&ID symbols & notations are available from ISA 5.1 (R1984) Examples PC PIC LG FR TAL TALL TAHL
Pressure Controller Pressure Indicating Controller Level Gauge Flow Recorder Temperature Alarm Low Temperature Alarm Low Low Temperature Alarm High Low
PCC PTC PTR PIR TRR TRA TAV
No such devices yet.
© Abdul Aziz Ishak, Universiti Teknologi MARA Malaysia (2009)
Transmission signal 3
principle type of signals in in in process industries Signal
Range
Pneumatic
3 – 15 psig
Electrical
4 – 20 mA 1 to 5 V
Digital/discrete
Usually
signal is in percent
Example
0-100% = 3-15 psig
Symbol
Signal
are used by devices – transmitters, controllers, final control element to communicate.
Change
type of signal using transducer / converter
Example of transducer Current to pneumatic (I/P) Digital-to-analog (D to A) Pneumatic to current (P/I)
Steam in (Manipulated variables)
TC TT
Fluid in
Fluid out Heat Exchanger
Ti (Load disturbances )
T desired (Controlled variables)
Steam out (Uncontrolled variables)
Unit 1: Process Control Loop Process control loop
Process
Sensor
Transmitter
Controller
Transducer
Control valve
Pressure Flow Level Temperature pH dP cell Capacitance Radar, Sonic Magnetic Resistance IR/Laser 4-20 mA 1-5 Vdc
PID Fuzzy logic
4-20 mA 3-15 psig
Linear Equal percentage
© Abdul Aziz Ishak, Universiti Teknologi MARA Malaysia (2009)
I/P
Unit 1: Tutorial 1
02:01
Can you read the following P&ID. Main process line Process instrument piping Temperature transmitter Temperature controller
product Feed
Flow controller
TT
Current to pnuematic transducer Control valve
Fuel
Electrical signal
Pneumatic signal Temperature controller DCS function
I/P
12
11 Automatic shut down PLC unit 12 Solenoid valve
© Abdul Aziz Ishak, Universiti Teknologi MARA Malaysia (2009)
FC
TC SP
FT ASD
11
TC
Regulatory and servo control For
process that the controlled variable deviates from set point because of disturbance – regulatory control
For
process that the most important disturbance is the set point itself – servo control
What if….
….you drive your car with your eyes shut?
IMPORTANCE
OF PROCESS CONTROL
SAFETY PRODUCT QUALITY PRODUCTION RATES REDUCE ENERGY
Why
we need to control a process?
◦ Because processes are dynamic – changes always occurred What
does a control system do?
◦ Maintain certain variables within some limit e.g temperature in a room
*dynamic time-dependent behavior of a process.
There
are many applications where part or all of a process has to be controlled. e.g. temperature pressure flow level composition others
Automatic
Control
◦ Maintaining the process variables (temperature, pressures, flows, compositions) at some desired operating value. ◦ Systems that control the variables without requiring intervention from the operator.
System
input SYSTEM
output
VARIABLES
Controlled variables – the variable that must be maintained at the desired value (set point)
Manipulated variables – the variable that need to be regulated in order to maintain the controlled variable at the set point
Disturbances – variables that tend to drive the controlled variable away from the set point
c. Uncontrolled variables. Variables in the process that are not controlled.
An Everyday Example of Process Control Control Objective (Setpoint): Maintain the temperature in the room (27oC) Controlled variable: Temperature in the room Manipulated variable: Speed of the fan Disturbance: Weather
An Everyday Example of Process Control Driving a Car Control Objective (Setpoint): Maintain car in proper lane. Controlled variable-
Location of car on the road Manipulated variableOrientation of the front wheels DisturbanceCurve in road
Exercise Select one control objective from a simple process and determine the controlled variable, manipulated variable and disturbances of the process.
HEAT EXCHANGER Steam in
Fluid in
Fluid out Heat Exchanger
Ti
T desired Steam out
HEAT EXCHANGER Steam in (Manipulated variables) (Controlled variables) Fluid out
Fluid in Heat Exchanger Ti (Load disturbances )
T desired Steam out (Uncontrolled variables)
THREE BASIC COMPONENT OF CONTROL SYSTEM Measurement (M) ◦ measure the variable to be controlled. sensor-transmitter combination Decision (D) ◦ Controller decides what to do to maintain the variables at its desired value controller Action (A) ◦ System must take an action based on controller’s decision control valve (final control element)
Another
important term
◦ Set point (SP)-desired value of the control variable. ◦ Open loop system - The behavior with no controllers in the system ◦ Closed loop system– the controller is connected to the process, comparing the set point to the controlled variable and determining and taking corrective action
Action Steam in
SP
Decide
TC TT
Fluid in
Fluid out Heat Exchanger
Ti
T desired Steam out
Measured = T desired (sensor transmitter) Control = Steam in Action = valve (final control element)
Measure
Steam in (Manipulated variables)
TC TT
Fluid in
Fluid out Heat Exchanger
Ti (Load disturbances )
T desired (Controlled variables)
Steam out (Uncontrolled variables)
Question
- How to ensure that T remains at or near the set point? w ,T 1
1
Q
M
w, T
Unit 1: Process & Instrumentation Diagram Process & Instrumentation Diagram (P&ID) Purpose 1. To indicate the instruments or control devices attached to the process. 2. To indicate the control system architecture associated with the process.
How it is done? Standard symbols and notations representing instruments or control devices are placed to the pipings and vessels.Standard symbols and notations are available from ISA-5.1(1984) standard.
Methodology? Process piping and sub-piping
A thick straight line represent main process piping A thin straight line represent process sub-piping either to instruments or by- process line.
© Abdul Aziz Ishak, Universiti Teknologi MARA Malaysia (2009)
PG
Unit 1: Process & Instrumentation Diagram Symbols Instruments / control devices:
A circle representing locally mounted instrument
A circle with horizontal line A circle with horizontal line representing control room inside a square representin mounted instrument. its function in DCS.
© Abdul Aziz Ishak, Universiti Teknologi MARA Malaysia (2009)
Unit 1: Process & Instrumentation Diagram Final control elements
Control valves
=
Manual valve
=
O R
Manual
=
O R
valve
Solenoid valve
Not darkened Always open
Darkened Always closed
=
© Abdul Aziz Ishak, Universiti Teknologi MARA Malaysia (2009)
Unit 1: Process & Instrumentation Diagram Naming rule
P T L F A
1
2
3
4
Measurement
Device
Device / Condition
Condition
Controller Transmitter Recorder Indicator Alarm Switch / Safety Gauge
C T R H L V
Pressure Temperature Level Flow Analysis
C T R I A S G
Controller Transmitter Recorder High Low Valve
H L
High Low
Complete guide on P&ID symbols & notations are available from ISA 5.1 (R1984) Examples PC PIC LG FR TAL TALL TAHL
Pressure Controller Pressure Indicating Controller Level Gauge Flow Recorder Temperature Alarm Low Temperature Alarm Low Low Temperature Alarm High Low
PCC PTC PTR PIR TRR TRA TAV
No such devices yet.
© Abdul Aziz Ishak, Universiti Teknologi MARA Malaysia (2009)
Transmission signal 3
principle type of signals in in in process industries Signal
Range
Pneumatic
3 – 15 psig
Electrical
4 – 20 mA 1 to 5 V
Digital/discrete
Usually
signal is in percent
Example
0-100% = 3-15 psig
Symbol
Signal
are used by devices – transmitters, controllers, final control element to communicate.
Change
type of signal using transducer / converter
Example of transducer Current to pneumatic (I/P) Digital-to-analog (D to A) Pneumatic to current (P/I)
Steam in (Manipulated variables)
TC TT
Fluid in
Fluid out Heat Exchanger
Ti (Load disturbances )
T desired (Controlled variables)
Steam out (Uncontrolled variables)
Unit 1: Process Control Loop Process control loop
Process
Sensor
Transmitter
Controller
Transducer
Control valve
Pressure Flow Level Temperature pH dP cell Capacitance Radar, Sonic Magnetic Resistance IR/Laser 4-20 mA 1-5 Vdc
PID Fuzzy logic
4-20 mA 3-15 psig
Linear Equal percentage
© Abdul Aziz Ishak, Universiti Teknologi MARA Malaysia (2009)
I/P
Unit 1: Tutorial 1
02:01
Can you read the following P&ID. Main process line Process instrument piping Temperature transmitter Temperature controller
product Feed
Flow controller
TT
Current to pnuematic transducer Control valve
Fuel
Electrical signal
Pneumatic signal Temperature controller DCS function
I/P
12
11 Automatic shut down PLC unit 12 Solenoid valve
© Abdul Aziz Ishak, Universiti Teknologi MARA Malaysia (2009)
FC
TC SP
FT ASD
11
TC
Regulatory and servo control For
process that the controlled variable deviates from set point because of disturbance – regulatory control
For
process that the most important disturbance is the set point itself – servo control
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