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

2/51 Process Control Introduction, Course Organisation

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


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


Benefits of Process Control

I Safety

I Performance: maximising profits, etc.

I Being good to environment


Example Processes


Fluid heater

Heats the process stream with the help of aheating medium


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


Mixing Process

x, w

ValveControl

Pure Ax2 = 1w2 =?

MixtureA, B

x1, w1

Mix two streams to get a desiredconcentration


Flow System

Qi(t)

Q(t) = x(t)h(t)

h(t)

Maintain height by adjusting valve


Plant in the Single Board Heater System

Heater

Plant

Fan

Maintain temperature by heating/cooling


System

We will use the words process and systeminterchangeably


Variables from Control Perspective

SystemControlled

Disturbance

Manipulated


How the variables are used

I Manipulated variables are adjusted

I to remove the effect of disturbancevariables

I on the controlled variables


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


Examples


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



Temperature of the process stream at theinlet is a




Answer: Disturbance variable



The flow rate of the heating medium used is a




Answer: Manipulated variable


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


Schematic of Distillation Column

hB

LT

LT

AT

PT

Feed

Coolant Exit

Reflux, R

Bottoms: B, xB

Distillate: D, xD

Heat

hD

AT


Recall our variables

I Manipulated variables are adjusted

I to remove the effect of disturbancevariables

I on the controlled variables


Distillation Column: A Control Strategy

?

LT

PT

Feed

Coolant Exit

Reflux, R

Bottoms: B, xB

Distillate: D, xD

Heat

hD

hB

AT

AT

LT


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


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


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!


Course Organisation


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


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


Scilab

I A good open source alternative to Matlab


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


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


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


Lab


Picture of the single board heater system


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


What does SBHS have?

I Plant

I Micro controller

I Sensor - temperature

I Actuator - current


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


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


Virtual Experimentation

I 40 units are available

I Accessible through Internet

I 40 students can work simultaneously

I Each can try out their algorithm


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!


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


Slot booking rules

I Will be explained later


Part of Virtual Lab

I Potential users can try remotely

I If convinced of its use, can acquiresufficient numbers for hands on training


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


Thanks


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

To return, click here


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



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!



Thanks

I [email protected]


Documents

Process Control lecture - 1