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8/10/2019 Design and Modeling of Tank Control for Fluid Circulation System Using Simulink - TJ220.N68 2007 - Noorul Mannan Shaik Alawdeen
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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
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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.
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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.
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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.
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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.
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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
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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.
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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
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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
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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
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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
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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.
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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.
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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
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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
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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
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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.
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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
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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
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Then
ince
then
This yields the following linear model
Where
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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:
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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
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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).
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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.
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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
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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
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