process control lecture - 1
DESCRIPTION
Process Control lectureTRANSCRIPT
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Lecture 1Introduction
Course Organisation
Process ControlProf. Kannan M. Moudgalyakannan at iitb dot ac dot in
IIT BombayMonday, 23 July 2013
Slides used in the course CL-417 in Autumn 20131/51 Process Control Introduction, Course Organisation
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Outline
I What is process control?I Examples
I Fluid heaterI Distillation columnI Mixing systemI Flow systemI Single Board Heater System (SBHS)
I Types of variables from control point ofview
I Applied to the above examples
I Course organisation
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Bird’s Eye View of Plant Operation
Plant level: what to make, how much to makeGoal: Overall profitability
Possible tool: Linear Programming
Unit level: Fixing the levels of different variablesFlow rate of coolant, reflux ratio, etc.Possible tool: Model predictive control
Variable level: Achieving intended levelsHow to get a specified flow rate, etc.
Possible tool: PID control
Will study mainly the last part in this course
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What is Process Control?
I It is an area that deals with control ofprocesses
I Objective: maintaining variables atdesired values
I If deviation, manipulate some otherquantities
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Benefits of Process Control
I Safety
I Performance: maximising profits, etc.
I Being good to environment
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Example Processes
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Fluid heater
Heats the process stream with the help of aheating medium
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Distillation Column
hB
LT
LT
AT
PT
Feed
Coolant Exit
Reflux, R
Bottoms: B, xB
Distillate: D, xD
Heat
hD
AT
Maintain compositions at desired values
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Mixing Process
x, w
ValveControl
Pure Ax2 = 1w2 =?
MixtureA, B
x1, w1
Mix two streams to get a desiredconcentration
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Flow System
Qi(t)
Q(t) = x(t)h(t)
h(t)
Maintain height by adjusting valve
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Plant in the Single Board Heater System
Heater
Plant
Fan
Maintain temperature by heating/cooling
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System
We will use the words process and systeminterchangeably
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Variables from Control Perspective
SystemControlled
Disturbance
Manipulated
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How the variables are used
I Manipulated variables are adjusted
I to remove the effect of disturbancevariables
I on the controlled variables
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Controlled, Disturbance, ManipulatedVariables
Controlled variable (CV): Variable to becontrolled.
I We wish to maintain this at aparticular value.
Disturbance variable (DV): Variables that causechanges in CV.
I We have no handle on these.Manipulated variable (MV): Variables that can
offset DV.I Also known as control effort.
MV are not free - have to pay.15/51 Process Control Introduction, Course Organisation
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Variables from input-output point of view
Input
Controlled
Disturbance
Manipulated
System
Output
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Examples
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Fluid heater: heats a process stream
Temperature of the process stream at the exitis a
1. Controlled variable
2. Manipulated variable
3. Disturbance variable
Answer: Controlled variable
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Fluid heater: heats a process stream
Temperature of the process stream at theinlet is a
1. Controlled variable
2. Manipulated variable
3. Disturbance variable
Answer: Disturbance variable
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Fluid heater: heats a process stream
The flow rate of the heating medium used is a
1. Controlled variable
2. Manipulated variable
3. Disturbance variable
Answer: Manipulated variable
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Fluid heater: A Summary
Heats the process stream with a heatingmedium
I Controlled variable (CV): Temperature ofthe exit stream on process side - set point
I Disturbance variable (DV): Inletconditions on process fluid
I Manipulated variable (MV): Temperatureor flow rate of the heating medium
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Schematic of Distillation Column
hB
LT
LT
AT
PT
Feed
Coolant Exit
Reflux, R
Bottoms: B, xB
Distillate: D, xD
Heat
hD
AT
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Recall our variables
I Manipulated variables are adjusted
I to remove the effect of disturbancevariables
I on the controlled variables
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Distillation Column: A Control Strategy
?
LT
PT
Feed
Coolant Exit
Reflux, R
Bottoms: B, xB
Distillate: D, xD
Heat
hD
hB
AT
AT
LT
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Distillation Column: A Control Strategy
I Bottoms withdrawal rate controlsbottoms level
I Distillate rate controls top drum level
I Reflux rate controls top composition
I Example of a multivariable system
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Mixing Process
x, w
ValveControl
Pure Ax2 = 1w2 =?
MixtureA, B
x1, w1
I Mixing of twostreams
I Variablestream hascomposition(x1) varying
I Want outputcompositionconstant
I Controlstream’s flowcan bechanged
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Feed concentration
I Feed concentration is, in general, a1. Manipulated variable2. Disturbance variable3. Controlled variable
I Answer: Disturbance variable
I Feed temperature is similar
I Feed flow rate is decided by otherconsiderations, however!
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Course Organisation
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Textbooks and References
I Process Dynamics and ControlSeborg, Edgar & MellichampWiley (2006)
I Digital ControlKannan M. MoudgalyaJohn Wiley & Sons (2007)
I Last few year’s video course and slides
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Distribution of Marks
Assignment 10Discussion (classroom and Forum) 10Scilab programming 10Labs 10First quiz (1 hour) 5Second quiz (1 hour) 10Midsem exam (2 hour) 20Endsem exam (2 hour) 25Total 100
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Scilab
I A good open source alternative to Matlab
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What is Scilab?
I Advanced computational environmentI Uses state of the art numerical
computational engines, such as, linpack,eispack, lapack, odepack and dassl
I Has a large number of built-in functions(c/fortran)
I eigenvalue, eigenvector computations,decompositions (svd), inverses
I numerical solution of differential equationsI etc.
I Has a built-in high level language:scilab:c = c:assembly
I Has several functions built using the highlevel language
I FreeI Check out www.scilab.org or
www.scilab.in
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CNES Talk
I Scilab is used extensively in CNES
I CNES launches Ariane rockets
I Ariane has placed several of our satellitesin orbit
I See the talk:Use of Scilab for Space Mission Analysisand Flight Dynamics Activities
I by Thierry Martin
I Senior Manager, CNES
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Scilab
I Story of cost of Matlab to SMEs
I People with Scilab knowledge are in shortsupply
I May be useful to get jobs
I Useful to entrepreneurs also
I Visit http://scilab.in - run by us
I Close to 200 textbook companions
I Can also execute them on the GARUDAcloud
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Lab
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Picture of the single board heater system
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What does this system do?
Controlling the temperature of a plant
I by heating with current
I by cooling with a fan
More details here
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What does SBHS have?
I Plant
I Micro controller
I Sensor - temperature
I Actuator - current
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Sample Control Experiments
I Step and ramp response identification
I Frequency testing, leading to Bode plots
I P, PI, PID tuning
I 2-DOF pole placement controller
I Internal model controller
I Self tuning and simple adaptive controller
I Auto tune testing
I Minimum and generalised minimumvariance controller
I PRBS and closed loop identification
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Pricing
I Available for Rs. 3,000
I Design is available as open source withbill of materials
I Can be built for less than Rs. 2,000
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Virtual Experimentation
I 40 units are available
I Accessible through Internet
I 40 students can work simultaneously
I Each can try out their algorithm
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Time Slots
I Time constant = 30 seconds
I Possible to do one experiment within 7-8minutes
I One hour is enough for experimentation
I 24 one hour slots in a day
I For 40 SBHS, there are 960 slots in a day!
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Slot Booking System
I A student books a slot through MoodleI Chooses a SBHS (amongst 40) alsoI Tries to access this SBHS at the
appointed timeI Python server validates
I eligibility to access that SBHSI calculates the balance time available
I If validated, informs the balance timeavailable
I Connection is establishedI Up to 40 people can access the machines
in this way
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Slot booking rules
I Will be explained later
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Part of Virtual Lab
I Potential users can try remotely
I If convinced of its use, can acquiresufficient numbers for hands on training
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What is learnt today
I Introduction to Process ControlI Variables
I Set pointI Controlled (= output) variableI Manipulated (= control effort, input) variableI Disturbance variable (= input)
I Process ExamplesI Heat exchangerI Distillation columnI Mixing
I Course organisation
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Thanks
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Details of single board heater systemI Designed and developed at IIT BombayI Consists of a heater assembly, fan,
temperature sensor, microcontroller(ATmega16) and associated circuitry
I Heater assemblyI Consists of an iron plate placed at a distance
of about 3.5 mm from the nichrome coilI Gets heated on passage of current
I Computer fanI Positioned below the plateI Meant for cooling the assembly
I The temperature is sensed by thetemperature sensor, AD590
I Reading in Kelvin scale
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ATmega16
I Is a 8-bit Microcontroller with advancedRISC Architecture
I Provides Up to 16MIPS throughput at16MHZ
I Has 16K bytes (8K X 16) of In-systemprogrammable Flash, 512 bytes ofEEPROM and 1K byte of internal SRAM
I Two 8-bit Timer/Counter and one 16-bitTimer/Counter
I Four PWM channelsI 8-channel, 10-bit ADCI Programmable serial USARTI Operating voltage: 4.5-5.5VI Speed: 0-16 MHz
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What is special about this system?
I The time constant is less than 1 minuteI Can see meaningful (and noisy)
measurements with naked eyeI Can do a realistic experiment in 10
minutesI Suitable for carrying out ALL experiments
of a few control coursesI Only need 220V power supply and a PCI Easy to carryI Costs only Rs. 3,000I Design is open source!
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