Design and Modeling of Tank Control for Fluid Circulation System Using Simulink - TJ220.N68 2007 - Noorul Mannan Shaik Alawdeen

8/10/2019 Design and Modeling of Tank Control for Fluid Circulation System Using Simulink - TJ220.N68 2007 - Noorul Mannan Shaik Alawdeen

http://slidepdf.com/reader/full/design-and-modeling-of-tank-control-for-fluid-circulation-system-using-simulink 1/26

UNIVERSITI TEKNIK L M L YSI MEL K

Design and Modeling of Tank Control for FluidCirculation ystem Using SIMULINK

Thesis submitted in accordance wit the partial nquhments of theUniversiti Teknikal Malaysia Melaka for the

Bachelor of M a n u f e g Engineering Robotic and Automation)

NOORUL M NN N BIN SH IK L WDEEN

Faculty of Manufacturing EngineeringMay 2007



BSTR CT

Tank level control is one of the important system which been used widely in industrynowadays. This control system keeps developing to replace the ordinary system which

applies mechanical functions in controlling in order to improve the system reliability.

There re many applications in industries that using this system such s water dam

water treatment system industrialtank control and also boiler. In order to develop a

successful tank fluid level control system ll understanding on the functions and

principles of the system is required. In this project MatLab Simulink willbe used s a

main platform in developing the simulation of the exact control system for an industrial

fluid circulation system. The system willbe tested to gain the most su itable and desired

control function. The end result of this project willbe a smooth and low error rate

control system for controlling the tank fluid level of the circulation system.



CHAPTER

INTRODUCTION

1 1 ntroduction

Level and flow control system is a technique used to control the level and flow of

circulation system for variety of purposes. Itc n e used to control either fluid or even

air for pneumatic or hydraulic system. Few types of processes that use the level and flow

control systemre

such as; water treatment centre water dam tank level control liquidflow control and circulation system.

In this project level and control system for a fluid circulation system wille discussed.

Starting by conducting ac se study that implement this system problem that been faced

by the system were studied. Then few proposed system will be developed and e

evaluate to find the best solution for the problem faced.



1 2 Problem Statement

n level and flow of a fluid circulation system the main criterion that needs to be

controlled is the rate of the main supply and the distribution system. To achieve this

complete system with suitable control need to be considered.

Nowadays most of the fluid level and flow systems are still applying the mechanical

control to control the circulation system. Main control device that normally used in

mechanical control is floating limit switch diaphragm valve and solenoid which

connected by simple wiring.

The problem with the mechanical control system is the device is subjected to tear and

wear itself. For example floating limit switch has a cycle rate which will turn to be

malfunction after the cycle rate. At the same time it is also subjected to tear and wear

caused by the movement of the switch.

Another problem that regularly been fixed by this system is overflow which caused by

insufficient control of the inlet. Reason for system overflow can be either device failure

to control or failure to calculate the level of the main tank before signaling the inlet

device.

Other than this problem there are also other problems such a s supply drainage cause by

the device failure which in return can affect the production process.



1 3 Objectives

The main objective of this project is design and modeling a fluid level and flow control

system by the aid o f simulation software. On top of that are some additional objectives

s follows:

To conductrese rch on th opic th t related to thissystem

b. To conductc se

studies that using this system.c. To implement the knowledge gained fiom the research studiesto improve the current

system h m he conductedcase study).d To propos a syst m th t can repl ce the cunwt system

e. To design a labm nu l for MatLabuser based on thisproject

1 4 Scopes

In order to design successfbl system, scopes are required to assist and guide the

development of the project. The scope shouldbe identified and planned to achieve the

objective of the projectsuccessfblly on the time.

The scopes for this project are such as below.

a. Collect Data

Collect necessary data on the current fluid level and flow control system by conducting a

case studies. From the case studies, current problem and limitation of the system are

identified.



b Develop Simulation

Simulation for the system that been proposed were developed by the aid o MatLab

Simulink

c Create User Manual

Create a experimental documentation and user manual for MatLab Simulink software

related to fluid level and flow control system



CH PTER

LITER TURE REVIEW

2 1 ntroduction

This chapter describes the literature review doneto gain more informationon the project that

been carried on. On the early of this chapter basic explanationo th control syst m is

discussed. Then followed with th discussion of the tank fluid level control and the devices

that needed in controlling this system Finally control application usingth Fuzzy Logic withthe aid ofMatLab w s discussed.

Basically for th simple leveland flow system mechanical controls re used to control the

system Mechanical control th t usually been used in controllingsyst m are such as limit

switches mechanical valve and electro-pneumatic valves.

But to control a larger system by the use of the mechanical controlare a bit difficult

because th mechanical system could not give an accurateand precise output in controlling.

Besides mechanical control performancesare also affected dueto tear and wearprocess.

To overcome this problem automation control bythe application of controlsyst m can be used

to achieve a better performance. By applying this automation applied controlsystem also

productioncan be inclleased dueto no d i e c e ccur fromthe level and flow system.



2.2 Control System

According to Wikipedia online dictionary [I] control system is a device or set of devicesto manage command direct or regulate the behavior of other devices or systems.

Control systems are an integral part of modem society. There re a lot of the applications

that using the control syst m nowadays. From as simple application such s air-conditioner

washing machine and microwave to complicated application such s robotdevelopment self-guided vehicle and guided missile launcher were using the control

system. There are a lot of examples which using control system in human daily life.

Control system also exists naturally in the world. An example of natural control system is

pancreas in human body which regulates the human blood sugar level. Another

example of the natural control system are photosynthesis process done by trees and

plants.

A control system consists of subsystem and proc ses assembled for the purpose of

controlling the outputs of the processes [2]. For example an air conditioner produces

more cool air s a result of room temperature increase. To determine the m m emperatwe

the air conditioner use thermost t to measure the level of the tern . The thermostat is

called the subsystem in this process. The subsystem will be the input to system and thecontrol system will provide an appropriate output or response for the given input or

stimulus. This process is shown in Figure 2.1 [2].

Figure 2.1 Simplified description of a control system



By the use of control system, a huge loadcan be replaced or m oved precisely using small

inputs and multiplier or gain. Control system also been applied in elevator. Because of

the control system, itc n c ny human or load to desired level or destination quickly, and

at the same time precisely.

Control systems were built for four primary reasons:

a. Power amplification.

b. Remote control.

c. Convenience of input form.

d. Compensation for disturbance.

Power amplification; a control systemc n produce the needed power amplification, o r

power gain. For example, ar d r antenna, positioned by the low-power rotation knob at

the input, requires a large amount of power for its output rotation. By using the

control system,the power that neededc n e produce by arnplitjing the power needed.

Robot designed by control system principlesc n compensate for human disabilities.

Control syst ms also us l in mnot or d ngerous location For example, a m o t e -

controlled robot m can be used to pick up material in a radioactive environment.

Control systemscan also e used to provide convenience by changing the form of the

input. For example, in a temperature control system, the input is a position on the

thermostat. The output is heat. Thus, a convenient position input yields a desired thermal

output.

The ability to compensate for disturbance; typically, to control such variable as

temperature in thermal system s, position and velocity in mechanical systems, and voltage,

current, orfrequently in electrical systems.The system must e able to yield the correct output

even with the disturbance. For example, consider n antenna system that point in



commanded direction. If wind forces the antenna from its commanded position, or if noise

enters internally, the syst m must be able to deted the disturbance and c o r n he antenna s

position Obviously, the system s input will not change to make cormtion Consequently, the

system itself must measure the amount that the disturbance has repositioned the antenna

and then return the antenna to the position commanded by the input.

As stated earlier, a control system provides an output or response for a given input or

stimulus. The input represents a desired response, and the output is the actual response.For example, when the fourth-floor button of an elevator is pushed on the ground floor,

the elevator rises to the fourth-floor with a speed and floor-leveling accuracy designed for

passenger comfort as shown in Figure 2.2 [2] The push of the fourth-floor button is the

input and is represented by a step command. Note that in the interest of passenger

comfort, not to mention the limited power available, we would not want the elevator

to mimic the suddenness of the input. The input represents what we would like the

output to be fter th elevator has stopped th elevator itself follows th displacement describes

by the curve marked elevator response.

Figure 2 2: Elevator response

Two factors make the output different fiom the input. First, compare the instantaneous

change of the input against the gradual change of the output in Figure 2.2. Physical entities

cannot change their st te (such as position or velocity) instantaneously. The st te changes



through a path that is related to the physical device and the way it acquires or dissipates

energy Thus, the elevator undergoesa gradual change as it rises h m he irst floor to the f o

floor. This p rt ofthe mqwnse s called reqxme

After the transient response, a physical system approaches its steady-state response, which

is its approximation to the commanded or desired response. For the elevator example, this

r spons occurs when lhe elevator rtx hes th fanth floor. The accuracy of the elevator s

leveling with the floor is a second factor that could make the output different from the

input. We call this difference, as shown in Figure 2.2 steady-state error. Steady-state error

need not exist only in defective control systems. Often steadystate error is inherent in the

designed system, and the control systems engineer determines whether or not that the error

leads to significant degradation of system functions.

2 2 1 Open Loop nd losed Loop System

An open-loop system is a direct output system, which did not compensate to the

disturbance applied to the system. It starts with a subsystem called an input transducer,

which converts the form of the input to that used by the controller. The controller will

provides an output which also called the controlled variable. The limitation of the open-

loop system is that it could not make appropriate decision if disturbance wereadded to the controller s driving signal. Diagram of open-loop system is s own in Figure 2.3

Figure 2.3: Open Loop system



Open-loop systems then do not correct for disturbances and are simply commanded by

the input. For example toasters are open-loop systems as anyone with burnt toast can

test The c~nmlled ariable output) of a toaster is the color of the toast The device is

designed with the assumption that the to st will be darker the longer it is subjected to heat.

The toaster does not measure the color of the toast it does not correct for the fact th t

the toast is rye white r sourdough nor does it coned for the t ct hat to st comes n different

thicknesses.

The disadvantages of open-loop systems namely sensitivity to disturbance and inability

to correct for these disturbances may be overcome in closed-loop systems. The generic

mhik me of a closed-loop system is shown n Figure 2.4 [2]

Figure 2.4: Closed Loop System

The input transducer converts the form of the input to the form used by the controller.

An output transducer or sensor measures the output response and converts it into the

form used by the controller. For example if the controller uses electrical signals to

operate the valves of a temperature control system the input position and the output

temperature are converted to electrical signals. The input position c n be converted to a

voltage y a potentiometer a variable resistor and the output temperature c n be

converted to a voltage by a thermistor a device whose electrical resistance changes with

temperature.



The first summing junction algebraically adds the signal from the input to the signal

from the output, which arrives via the feedback path, the return path from the output to

the summing junction. in Figure 2.4, the output signal is subtracted from the input

signal. The result is generally called the actuating signal. However, in systems where

both the input and output transducers have unity gain (that is, the transducer amplifies its

input by l , the actuating signal s value is equal to the actual difference between the

input and the output. Under this condition, the actuating signal is called the error.

The closed-loop system compensates for the disturbances by measuring the output

response, feeding that measurement back through a feedback path, and comparing that

response to the input at the summing junction. If there is any difference between the two

responses, the system drives the plant, via the actuating signal, to make a correction. If

there is no difference, the system does not drive the plant, since the plant s response is

already the desired response.

Closed-loop systems, then, have the obvious advantage of greater accuracy than open

loop systems. They are less sensitive to noise, disturbances, and changes in the

environment. Transient response and steady-state error can be controlled more

conveniently and with greater flexibility in closed-loop systems, often by a simple

adjustment of gain (amplification) in the loop and sometimes by redesigning the

controller. Redesign means compensating the system and to the resulting hardware as acompensator. On the other hand, closed-loop systems are more complex and expensive

than open-loop systems. standard, open-loop toaster serves s an example: it is simple

and inexpensive. closed-loop toaster oven is more complex and more expensive since

it has to measure both color (through light reflectivity) and humidity inside the toaster

oven.



2.2.2. Fuzzy ogic

Fuzzy logic is an attempt to get the easy design of logic controllers and yet control

continuously-varying systems [3] Basically, a measurement in a hzzy logic system c n

be partly true, that is if yes is 1 and no is 0, a fuzzy measurement can be between 0 and

1.

The rules of the system re written in natural language and translated into fuzzy logic.

For example, the design for a furnace would start with: If the temperature is too high,

reduce the fuel to the furnace. If the temperature is too low, increase the fuel to the

furnace of

Meamements iwn he world such as the temperatme of a fhme) are converted to

values between 0 and 1 by seeing where they fall on a triangle. Usually the tip of the

triangle is the maximum possible value which translates to i.

Fuzzy logic them modifies Boolean logic to be arih ical . Usually the not w o n s

output 1- input, the andn operation is output = input.1 multiplied by input.2, and

or1' is output I- ] input. 1) multiplied by 1 input.2)).11

The last step is to defimify an output. Basically, the fuzzy calculations make a

value between z m nd one. That number is used to select a value on a line whose slope

and height converts the fi my value to a real-world output number. The number then controls

real machinery.

if the triangles re defined correctly and rules re right the result can be a goo control

system.

When a robust fuzzy design is reduced into a single, quick calculation, it begins to

resemble a conventional feedback loop solution. For this reason, many control engineers think



one should not bother with it. However thef zzy logic paradigm may provide scalability

for large control systems where conventional methods become unwieldy or costly to

derive. Fuzzy electronics is an electronic technology that uses fuzzy logic instead of

the two value logic more commonly usedin digital electronics.

So simply we can say that systems that perf the previously d e s c r i i measurement and

correction are called closed-loop or feedback control systems. Systems that do not have this

p.operty of measurement and mmxtion are called open-loop systems

2 3 evel and low ontrol System

The liquid level control system is a pressure responsive element comprises a valve

including a pair of spaced moveable diaphragm members[4]-of a kind non-permeable to

fluids-associated for coordinated movement and a valve body cooperating with

respective ones of said associated diaphragm members to define first and second pressure

sensing cavities and cooperating with both of said diaphragm members to define a third

valve cavity and in which said first and second pressure sensing cavitiesare coupled to

respectively a reference pressuresource and said fluid amplifier means for displacing said

associated diaphragm members between said spaced positions in accordance with the

relative signal pressures introduced into said first and second pressure sensing cavities andhrther in which said pressure responsive element includesan inlet communicating with

said third valve cavity when said associated diaphragmmembers ~ in either of saidsp ced

positions and an outlet coupled to said third valve cavity and having a valve seat portion

spaced from said associated diaphragm memberswhen said members r n said fkd position

to pennit flow between said inletand outlet o f said third va lve cavity and in which one o f

said associated diaphragm members engages said valve seat portion of said third cavity

upon movement of said associated diaphragm members to said second position to close

said outlet of said third valvecavity said inlet and out of said thii valve c vity being

mupled in s ri s with t least one of said inlet and outlet of said reservoir means for



regulating flow through said one of said inlet and outlet of said reservoir meansto

maintain the liquid within said reservoir means t a desired level.

liquid level sensing system comprising a reservoir means having an inlet and an outlet

and adapted for receiving a quantity of liquid therein flow control means including a

pressure responsive element for regulating flow at least one of said inlet and outlet of

said reservoir means accordingto a sensed pl ssur condition; nd fluid amplifier means having

serially aligned inlet interaction and outlet zones comprisingan inlet flow channel

positioned above the desired liquid sensing level in said reservoir with the terminus of said

flow channel approximately contiguous said sensing leveland oriented for directing a liquid

flow transversely to the surface of the liquid in said reservoir meansnd htth r comprising

outlet means sep r ted h m aid inlet flow channel bythe free space o f said interaction

region and coupled to said flow control means the liquid from said inlet flow

channel im pinging on said outlet me ans with a first predetermined pressure when

the level in said reservoir is below said sensing level and second substantially lesser valuewhen the liquid in said reservoir moves above said sensing level for actuating said flow

control means.

Level control system comprising; reservoir means having an inlet and outlet andadapted

for receiving a quantity of liquid therein fluid amplifier means comprising an inlet for

developing a fluid power stream and an outlet spaced from said inlet said amplifier

means being constructed and arranged for developing at said outlet a fluid pressure

signal of a first predetermined magnitude when the liquid level in said reservoir is

displaced from a desired level and of a second substantially different

magnitude when said liquid is t said desired level and a valve means comprising a pair

of spaced diaphragm members of a kind non-permeable to fluidsassociated for

coordinated movement between a pair of spaced positions resilient means for normally

biasing one of said diaphragm members toward one of said spaced positions and a valvebody cooperatingwit ve ones of said diaphragm r n e m to define h t nd se ond

closed signal pressure sensing cavities and cooperating withboth of said diaphragm



members to define a third valve cavity and in which saidfirst and second pressure sensing

cav ities are coupled respectively to a reference pressure source and the outlet of

said fluid amplifierme ns ibr displacing said associateddi phr gm members etween said

sp ced positions in accordance with the relative signal pressures introduced into said first

and second pressure sensing cavities and M h e r comprising an inlet communicating with

said third valve cavity when said associated diaphragm membersre in either of said

spaced positions and an outlet coupledto said third valve cavity having valvese t

pottion sp ced f b m said associateddiaphragm memberswh n said members re in said fast

position to permit flow between said inlet and outlet of saidthii valve c vity and in whichone of saidassociated diaphragm mem ers eng ges said valve seat portion of said outlet of

said third cavity upon movement of said associated diaphragm members to said second

position to close said outlet of said third valvecavity s id inletand outlet of said third v lve

c vity eing coupled in series with t least one of said inlet and outlet of said reservoir

means to maintain the liquid within said reservoir means at a desired level.



2 4 Tank Level ontrol

Water flows into the first tank through pump at the rate offJ, which obviously affects

the height of the water in tank t denoted by h, . Water flows out of tank into tank 2 at

a rate ofJ2 affecting both hl and h2 Water then flows out of tank 2 at a rate off,

controlled by pump 2. The illustration of this system is shown in Figure 2 5 [ 5 ]

Figure 2 5: Controller for pairs of tanks

To control the heights of the tanks, sensors were used in order to gain input. However, a

problem arose when the sensor for the height of tank failed. According to Graham, he

suggested that it would be possible to build a virtual sensor or observer/soft

sensor) to estimate the height of tank I based on measurements of the height of tank 2

and the flowsfi andfi

Before continue with the observer design, model of the system need to be made. The

height of tank can be described by the equation



Similarly, r is given by

The flow between the two tanks c n be approximated by the fr fall velocity for the

difference in height between the two tanks,

Now, if the heights of the tanks measured in (where 0 is empty and 100 is full),

flow rates of the system can be converted into equivalent values in per second (where

fi is the equivalent flow into tank and is the equivalent flow out of tank 2 . The

model for the system is

Where

Then, it can be defined to linearise this model for a nominal ste dy state height difference

(or operating point). Let



Then

ince

then

This yields the following linear model

Where



Since the h2 can be measured and h cannot, set C [ 0 I ] and D=[ 0 01. The resulting

system is both controllable and observable (which can easily be verified). Now to design

an observer

to estimate the value of h2. he mcteristic polynomi l of the observer is

s th o seruet pol s sele ted which gives the values for J and J2. If opefatifig pif i t is

assumed at OO , th n k 0.041 1 If tfi poles nee e is at s -0.9822 and s=0.053 1

then calculate that J I 0.3 and J2 0.9. If two poles needed at s=-2 then J I = 3.9178

and J2 =93.4 I

The equation for the observed system is then

Where hm2 s the measure value of ht. Here odeled as follows;

Where u represents measured noise,

Alternatively, non-linear model can also been used in the observer to attempt to get

better performance:



The purpose of this simulation is to investigate the difference between the linear

observer as shown in Figure-2.6[5] and non-linear observeras shown in Figure 2.7 [5].

The graph has a vertical scale of 25 per division nd a horizontal scale of 1 sec per

division. It shows the set-point (the orangetrace , the actual r (the blue trace , the

estimatedhi (the red trace) and the actual z (the green trace).

mWid 425 orrrrqlrtnra setpoinr

blue m l adsrP klhmzontplscrdcd1 a~ r u l b r r a e 6 t n m d h i

gmatracy adrmlhz

Figure 2.6: Tank level plotting with linear observer



Figure 2.7: ank level plotting with non-linear observer

From both figures, there is a difference which can be seen clearly that is, the non-linear

observer has no error in its output, nd whereas the linear observer does (the linear

observer uses a nominal height difference of lo , nd performs poorly when the system

is far rom this operating point).



2.5 Level and Flow Control Devices

2.5.1 Filling level con trol

As can seen in many of nowadays conventional system the mechanical input device that

been used can cause a lot of problem because of the wear that will occur. Example of the

mechanical input device is floating limit switch. ear is defined as the progressive loss

or removal of material from a surface [6] To avoid h m his kind of problem to occur

frequently the input device that more reliable can be replace such s ultrasonic sensor

Ultrasonic transmitter is on types of sensor which will give an input to the system.

Sensor is the first link between the typical automated system and the conventional

process [7].The transmitter emits an ultrasonic wave and determines the propagation

time of the signal reflected at a surface. On the basis of this time the device calculates

the distance between the lower edge of the sensor and the surface s illustrated in Figure2 8 [8] The influence of the sound velocity dependent on the surrounding atmosphere is

automatically compensated for by entering specific values and measurement of the

ambient temperature by the transmitter. If the distance between the lower edge of the

sensor and the bottom of a t nk is known the device is able to indicate the filling level

or if the tank geometry is known the volume still inside the tank can be indicated.

Various disturbance echo filters even enable use in containers with built-in fixtures

generating a disturbance echo.



Figure 2 8: Filling level control using ultrasonic sensor

2 5 2 ixing

Several fluids are to be mixed in predetermined ratio in a mixing tank Containers are

filled with the product after thorough mixing The system is shown in the Figure 2 9 [9]

The first component is added to the empty mixing t nk via a solenoid valve until the

required quantity is reached Figure 2 10 101 shows the solenoid valve that been used

The volume is determined by the level sensor on the basis of the filling height and tank



geometry. The controller closes the solenoid valve when the required quantity is reached

and opens the valve for the second component and so on.

Figure 2.9: Mixing process using solenoid valve

AAer adding the last component the components are thoroughly mixed by an agitator to

provide a homogenous product which is then filled into containers or further processed.

During the filling process the product is added to a container until a load cell determines

that the required filling quantity has been reached.

igure 2.10: Solenoid valve

Documents

Design and Modeling of Tank Control for Fluid Circulation System Using Simulink - TJ220.N68 2007 - Noorul Mannan Shaik Alawdeen