Process Control lecture - 1

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

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

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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Thanks

I kannan@iitb.ac.in

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