UNIVERSITI TEKNIKAL MALAYSIA MELAKA

Design and Modeling of Multiple Tank Control for Fluid

Circulation System Using Fuzzy Controller

Thesis submitted in accordance with the partial requirement of the

Universiti Teknikal Malaysia Melaka for the

Bachelor of Manufacturing Engineering (Robotic & Automation) with Honours

By

GWEE CHIOU CHIN

Faculty of Manufacturing Engineering

April 2008

v

ABSTRACT

A tank level control is one of the important systems which are used widely in

industry. This control system keeps developing from time to time to replace the

ordinary system which applies mechanical functions in its control in order to

improve the system reliability. There are many applications in industries that are

utilizing this system such as water dam, water treatment system, industry tank

control and also boiler. In order to develop a successful tank fluid level control

system, full understanding on the function and principle of the system is required. In

this project, Matlab Simulink will be used as a main platform in developing the

simulation of the exact control system for the Lamella Filtration system. The system

that been study in this project is the Lamella Filtration system of Bukit Sebukor

Water Treatment Plant. This study is to upgrade the mechanical water level control

system of the Lamella Filtration system to an automatic system. The automation of

the system can reduce the burden of the technicians on shift and prevent human error

on manual operation. The system will be tested to gain the desired control function.

The end result of this project will be a smooth and low error water level control

system for the Lamella Filtration system.

vi

ABSTRAK

Pengawalan paras tangki merupakan salah satu sistem penting yang luas digunakan

dalam industri pada masa kini. Sistem ini terus membangun untuk menggantikan

sistem biasa yang mengaplikasikan fungsi mekanik dalam pengawalan untuk

memperbaiki kebolehpercayaan sistem. Terdapat banyak aplikasi dalam industri

yang menggunakan sistem ini seperti empangan air, sistem rawatan air, kawalan

tangki industri dan juga pemanas air. Untuk membangun suatu sistem kawalan paras

air yang berjaya, pemahaman yang menyeluruh terhadap fungsi dan prinsip sistem

tersebut diperlukan. Dalam projek ini, Matlab Simulink akan digunakan sebagai alat

uatama dalam menghasilkan simulasi sistem kawalan yang tepat and betul untuk

Sistem Penapisan Lamella. Sistem yang dikaji dalam projeck ini adalah Sistem

Penapisan Lamella Loji Air Bukit Sebukor Melaka. Kajian ini adalah bertujuan

untuk menaik tarafkan sistem mekanikal kawalan air yang ada pada Sistem

Penapisan Lamella yang sedia ada kepada sistem automasi. Pengautomasian sistem

tersebut dapat mengurangkan beban teknisian yang bertugas dan mengurangkan

kesilapan manusia dalam operasi manual..Sistem tersebut akan diuji untuk mendapat

fungsi kawalan yang diingini. Hasil daripada projek ini merupakan satu sistem

kawalan paras air untuk Sistem Penapisan Lamella yang lancar dan rendah

kesalahan.

1

CHAPTER 1

INTRODUCTION

1.1 Project Introduction

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

circulation system for variety of purpose. It can be used to control either fluid or

even air for pneumatic or hydraulic system. There are few types of process that use

the level and flow control system, such as water treatment centre, water dam, tank

level control, and liquid flow control and circulation system.

In this project, the Lamella Filtration system of Bukit Sebukor Water Treatment

Plant is studied. The objective of this project was to upgrade the mechanical water

level control system of the Lamella Filtration system to an automatic system. The

automation of the Lamella Filtration system can help reducing the burden of the

technicians on shift and prevent human error on manual operation.

Previous study on fluid level control using SIMULINK was carried out by previous

student. [15] In his study, the design and modeling tank control for fluid circulation

system using SIMULINK had been designed. Unfortunately, the system is not

suitable to be applied at the current Lamella Filtration system.

Level and control system for Lamella Filtration system will be discussed in this

report. By conducting a case study that implement this system, problem that been

faced by the system were carefully taken into consideration. New proposed system

will be develop and evaluate to find the best solution for the problem faced.

2

1.2 Problem Statement

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

control to control the circulation system. [15] Floating limit switch, diaphragm valve

and solenoid which connected by simple wiring are the examples of main control

device that normally used in mechanical control.

The current Lamella Filtration system of Bukit Sebukor Water Treatment Plant uses

a mechanical control system. Technicians are required on shift to monitor the control

system twenty four hours a day.

The main criterion that needs to be controlled in level and flow of a fluid circulation

is the rate of the main supply and the distribution system. Complete system with

suitable control need to be considered to achieve this.

The mechanical control system’s device is subjected to tear and wear itself. For the

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.

Over flow is another problem that regularly been faced by this system, which caused

by insufficient control of the inlet. The reason for system overflow can be failure of

the device to calculate the level of the main tank before signaling the inlet device.

Other problems such as supply drainage cause by the device failure, which in return

can affect the production process.

Although a tank control for fluid circulation system using SIMULINK has been

developed before, but it is not practical enough to be use in the industrial sector

because the limitation of single tank design. Beside that, the previous system is not

suitable to be applying in this study’s system.

3

1.3 Objective

The main objective of this project is to control and model multiple tank fluid level

control system using Fuzzy Controller. In order to achieve the main objective,

following are some additional objectives to be completed:

a) To evaluate the current fluid level control.

b) To design and propose an automatic fluid level control system that can

replace the current mechanical system.

c) To control and simulate the designed Lamella Filtration tank fluid control

system.

1.4 Scopes

The scopes of this project are:

a) Data Collection

A case study will be conducted to collect data about the current Lamella

Filtration system at Bukit Sebukor Water Treatment Plant Malacca. In

this case study, a few visits will be pay to the Bukit Sebukor Water

Treatment Plant, and the technician on duty will be interview for the data

collection purpose. After that limitation of the current system will be

identify and carefully taken into consideration for the further

improvement. Besides that, data for literature review will be collect from

internet, books, and previous student’s research.

4

b) Design and Simulation

New automation control system will be designed to improve the current

system. The new control system will be design by using Fuzzy Logic

Toolbox in Matlab. The designed system will then be simulated.

5

CHAPTER 2

LITERATURE REVIEW

2.1 Introduction

The literature review that have been done to gain more information on the project

that been carried out is describes in this chapter. Firstly, the basic explanation on the

control system is discussed. After that, it is followed by the discussion of the lamella

filtration tank fluid level control and the devices that needed in controlling this

system. Finally is the control application using the Fuzzy Logic Toolbox with the aid

of Matlab is discussed.

Mechanical controls are used to control the simple level and flow system, for the

examples: limit switches, mechanical valve, and electro-pneumatic valve. However,

mechanical system could not give an accurate and precise output in controlling.

Further more, the mechanical control performance are affected by the tear and wear

process. Automation control by the application of control system can be used to

achieve a better performance.

6

2.2 Control System

According to Wikipedia [1], a control system is a device or set of devices to manage,

command, direct or regulate the behavior of other devices or systems.

Control systems are an integral part of modem society. Nowadays, there are many

applications using control system. Lots of example can be found in daily life, such as

washing machine, air-conditioner, and microwave.

There are also control systems that exits in the naturally. For the example, pancreas

which regulates human blood sugar level and photosynthesis by plants.

A control system consists of subsystem and processes assembled for the purpose of

controlling the outputs of the processes [2]. The air-conditioner that produces more

cool air as the result of the room temperature increase is an example. Air conditioner

use thermostat to measure the temperature of the room. Thermostat is as a subsystem

that will be the input for the system. The control system will provide an appropriate

output or response for the given input or stimulus. Figure 2.1 [2] shows the process.

Figure 2.1: Simplified Description of a Control System

Input; stimulus

Desired response

Output; response

Actual response

Control System

7

Control system where built for four primary reasons:

a) Power amplification.

A control system can produce the needed power amplification, or

power gain. For example, a radar 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 needed

can be produce by amplifying the power needed.

b) Remote control.

Robot design by control system principles can compensate for human

disabilities. Control systems are also useful for remote at dangerous

location. For example, a remote controlled robot arm can be used to

pick up material in a radioactive environment.

c) Convenience of input form.

Control system can be used to provide convenience by changing the

form of the input. A temperature control system as an example. The

position on the thermostat is the input, while the output is the heat.

Thus, a convenient position input yields a desired thermal output.

d) Compensation for disturbance.

The ability to compensate for disturbance is typically to control such

variable as temperature in thermal system, position and velocity in

mechanical system, and voltage, current, or frequently in electrical

systems. The system must be able to yield the correct output even

with disturbance. For example, an antenna system that point in

commanded direction. If wind forces the antenna from its commanded

8

position, or if noises enter internally, the system must be able to detect

the disturbance and correct the antenna’s position. The system’s input

is obviously will not change to make correction. 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.

A control system provides n 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 button of a speed and floor-leveling accuracy

designed for passenger comforts is shown in Figure 2.2 [2].

Figure 2.2: Elevator Response

The input is the push of the forth-floor button and it’s represented by a step

command. The input represents the desire output after the elevator stop; the elevator

itself follow the displacement describes by the curve marked elevator response.

9

There are two factors make the output different from the input. First is when

comparing the instantaneous change of the input against the gradual change of the

output in Figure 2.2. Physical entities such as position or velocity cannot change their

state instantaneously. The state is change through a path that is related to the physical

device and the way it acquires or dissipates energy. As the result, the elevator

undergoes a gradual change when it rise from the first floor to the forth floor. The

path of the response is transient response.

A physical system approaches its steady-state response after the transient response,

which is approximation to the command or desired response. In this elevator example,

the response occurs when the elevator reaches the fourth floor. The second factor that

could make the output different from the input is the accuracy of the elevator’s

leveling with the floor. As shown in Figure 2.2, the steady-state error is the

difference. Steady-state error need not exits only in defective control system. Steady-

state error is always inherent in the designed system. Control engineer will determine

whether the error leads to significant degradation of system function or not.

2.2.1 Open Loop and Closed Loop System

A direct output system which did not compensate to the disturbance applied to the

system is an open-loop system. It starts with a subsystem called an input transducer,

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

provides an output which called controlled variable. Open loop system has limitation

that it cannot make appropriate decision if disturbance were added to the controller’s

driving signal. Figure 2.3 [2] show the diagram of open-loop system.

Figure 2.3: Open Loop System

10

Open loop systems do not correct the disturbance and simply command by the input.

Toasters are example for open-loop system. The output or the controlled variable of

the toaster is the color of the toast. The device is designed with the assumption that

the longer it is subjected to heat, the darker the toast. The color of the toast does not

measure. The toaster does not correct for the fact that the toast is rye, white, or

sourdough. It also does not correct for the different thickness of toast.

Disadvantage of open-loop system, which is sensitivity to disturbance and inability

to correct to correct disturbances, may be overcome by closed-loop system. Figure

2.4 [2] shows the generic architecture of a closed-loop system.

Figure 2.4: Closed Loop System

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

Output transducer or sensor measures the output response and convert 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 can be converting

to a voltage by a potentiometer, a variable resistor, and the output temperature can be

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

with temperature.

11

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. As shown in Figure 2.4, the output signal is substrate from

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

system where both the input and output transducer have unity gain, 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 disturbance 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

correction. If there is no difference, the system does not drive the plant, since the

plant’s response is already the desired response.

Obviously, closed-loop system has the advantage of grater accuracy compare to

open-loop system. Transient response and steady-state error can be controlled more

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

adjustment of gain in the loop and sometimes by redesigning the controller. Redesign

means compensating the system and to the result hardware as a compensator.

However, closed-loop systems are more complex and expensive than open-loop

system. A standard open-loop toaster is simple and inexpensive. However, a close-

loop toaster oven is much more complex and more expensive since it has to measure

both color and humidity in side the toaster oven.

12

2.2.2 Fuzzy Logic

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

continuously-varying system [1]. Basically, a measurement in a fuzzy logic system

can be partly true. Says that yes is 1 and no is 0, fuzzy measurement can be between

0 and 1.

The rules of the system are 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.

Measurement from the real world such as temperature of a furnace, 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 values which translate to “1”.

Fuzzy logic modifies Boolean logic to be arithmetical. Usually the “not” operation is

“output = 1 – input”, the “and” operation is “output = input.1 multiplied by input.2”,

and “or” is “output = 1-((1-input.1) multiplied by (1-input.2)).”

“Defuzzify” an output is the last step. The fuzzy calculations basically make a value

between zero and one. That number is used to select a value on a line whose slope

and height converts the fuzzy value to a real-world output number. The number then

controls real machinery.

If the triangles are defined correctly and rules are right the result can be good 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, the fuzzy logic paradigm

may provide scalability for large control systems where conventional methods

become unwieldy or costly to derive. Fuzzy electronics is an electronic technology

13

that uses fuzzy logic instead of the two value logic more commonly used in digital

electronics.

As the conclusion, systems that perform the previously described measurement and

correction are called close-loop, or feedback control system. Systems that do not

have this property of measurement and correction are called open-loop systems.

2.3 Level Controllers

Level controllers monitor, regulate, and control liquid or solid levels in a process [3].

There are three basic types of control functions that level controllers can use. Limit

control works by interrupting power through a load circuit when the level exceeds or

falls below the limit set point. A limit controller can protect equipment and people

when it is correctly installed with its own power supply, power lines, switch and

sensor. Advanced or non-linear control includes dead-time compensation, lead/lag,

adaptive gain, neural networks, and fuzzy logic. Level controllers can be used for

either liquid or powder or other dry material applications.

Linear level controllers can take many different styles. Feed forward control offers

direct control or compensation from the reference signal. It may be open loop or in

conjunction with PID control. Proportional, integral, and derivative (PID) control is

an intelligent I/O module or program instruction, which provides automatic closed-

loop operation of process control loops. Proportional plus integral (PI) control has

the error signal integrated and is used for eliminating steady state or offset errors. It

may also be called automatic reset/bias/offset control. Proportional plus derivative

(PD) control has the error signal differentiated to get the rate of change. This type of

control is used to increase controller speed of response, but can be noisy and make

the system less stable. In proportional (P) control, the control signal is proportional to

the error between the reference and feedback signals.

14

Level controllers differ in terms of specifications, user interface, and features.

Specifications include the number of inputs, control outputs and control feedback

loops. Control loops may be linked to improve control performance and/or stability.

The control output is usually analog current, voltage or a switched output. These

controllers can have discrete or TTL I/O as well and can handle high power

switching needs. The user interface for level controllers may be analog, digital or

computer controlled. Displays for level controllers can be analog meters, digital

numerical readouts, or video display terminals. Another possible type of display is a

strip chart or circle chart. When connecting to a computer host, level controllers can

use the standard serial, parallel or SCSI interfaces or can be networkable via Ethernet,

CANBus or a number of other network protocols. Features that are sometimes

optional for level controllers include sensor excitation current or voltage, built-in

alarms or indicators and wash down or waterproof ratings. Other features can include

programmable set points, auto tune or self-tuning functions and signal computation

functions or filters.

2.4 Flow Controllers

Flow controllers monitor and maintain proper humidity levels in environmental test

applications, or in other areas such as food storage or electronic room regulation [4].

They can have three main ways of controlling low: limit control, linear control and

advanced or nonlinear control. Limit control interrupts power through the load circuit

when flow exceeds or falls below the limit set point. A limit controller can protect

equipment and people when it is correctly installed with its own power supply,

power lines, switch and sensor. Advanced or nonlinear control uses process control

strategies beyond PID loop control, such as dead-time compensation, lead/lag,

adaptive gain, neural networks, and fuzzy logic. Common functionalities for flow

controllers are rate indication and control as well as batch or totalize indication and

control.

15

Flow controllers with linear control use a classical type of control and can

incorporate linear regulation, proportional, integral and derivative (PID), and feed

forward methods. Proportional, Integral, and derivative control use an intelligent I/O

module or program instruction, which provides automatic closed-loop operation of

process control, loops. With Proportional plus integral control the error signal is

integrated and is for eliminating steady state or offset errors. This may also be called

automatic reset/bias/offset control. Proportional plus derivative control has the error

signal differentiated to get the rate of change. This type pf control is used to increase

the controller’s speed of response, but can be noisy and make the system less stable.

Proportional control by itself has a control signal that is proportional to the error

between the reference and feedback signals. Feed forward control is a direct control

or compensation from the reference signal. It may be open loop or in conjunction

with PID control.

To choose a flow controller, one important piece of information is the number of

inputs and control outputs and control or feedback loops desired. These controllers

can have multiple controls modes or functions, which may or may not use different

inputs and outputs. Also, multiple control loops may be linked to improve control

performance and/or stability. Typical control signals for flow controllers are analog

voltage or current or else a switch turning on or off. Update rate is also an important

specification. This is the frequency with which devices take readings and adjust their

output. Flow controllers can have PLC and discrete control and can be compatible

with TTL type I/O. Some controllers are able to handle high power switching such as

relays and opt isolators.

Displays for flow controllers can be simple analog indicators, numeric or

alphanumeric digital readouts, or video terminal displays. User interfaces are similar.

Analog interfaces can have switches, dials and potentiometers. Digital user controls

are typically keypads, menus and other digital interfaces. A remote computer can

also program these controllers. Common computer interfaces are serial and parallel,

but other options such as SCSI or network connections may be specified.

16

2.5 Water Level and Flow Control Devices

2.5.1 Level Sensor

Level sensors are used to detect liquid or powder levels, or interfaces between liquids

[5]. These level measurements can be either continuous or point values represented

with various output options. Continuous level sensors are devices that measure level

within a specified range and give output of a continuous reading of level. Point level

sensors devices mark a specific level, generally used as high alarm or switch.

Multiple point sensors can be integrated together to give a stepped version of

continuous level. These level sensors can be either plain sensor with some sort of

electrical output or else can be more sophisticated instruments that have displays and

sometimes computer output options. The measuring range is probably the most

important specification to examine when choosing a level sensor. Field adjustability

is a nice feature to have for tuning the instrument after installation.

Depending on the needs of the application, level sensing devices can be mounted a

few different ways. These sensors can be mounted on the top, bottom or side of the

container holding the substance to be measured. Among the technologies for

measuring level are air bubbler technologies, capacitive or RF admittance,

differential pressure, electrical conductivity or receptivity, mechanical or magnetic

floats, optical units, pressure membrane, radar or microwave, radio frequency,

rotation paddle, ultrasonic or sonic and vibration or tuning fork technology. Analog

outputs level sensors can be current or voltage signals. Also possible is a pulse or

frequency. Another option is to have an alarm output or a change in state of switches.

Computer signal outputs that are possible are usually serial or parallel. Level sensors

can have displays that are analog, digital or video displays. Control for the devices

can be analog with switches, dials and potentiometers; digital with menus, keypads

and buttons; or controlled by a computer.

17

2.5.2 Flow Meter

Flow meters are devices for measuring the flow rate or quantity of a moving liquid or

gas [6]. There are four basic categories of devices: differential pressure (DP),

positive displacement (PD), velocity, and true mass. Differential pressure flow

meters obtain the flow rate by measuring the pressure differential and extracting the

square root. Choices for DP meters include cone-type devices, elbow tap meters,

flow nozzles, laminar flow elements, orifice plates, Pitot tubes, Rota meters, target

meters, variable area flow meters, and Venturi tubes. Positive displacement flow

meters divide the media into specific increments which can be counted by

mechanical or electronic techniques. Examples of PD meters include nutating disc

devices, oval gear meters, and piston-based designs. Velocity flow meters operate

linearly with respect to the flow rate. Because there is no square-root relationship,

their range is greater than DP devices. Choices for velocity meters include

electromagnetic meters, paddlewheels, sonar-based devices, turbine meters,

ultrasonic meters and vortex or shedding meters. True mass flow meters are used to

directly measure the mass rate of flow. These flow meters include both thermal

meters and Coriolis meters.

Specifications for flow meters include pipe diameter, mounting style, end fittings,

electrical outputs, and interface options. There are three basic mounting styles: in-

line, insertion, and non-invasive. In-line flow meters are installed directly in the

process line. Insertion-type devices are inserted perpendicular to the flow path and

usually require a threaded hole in the process pipe. Non-invasive flow meters do not

require mounting directly in the process flow and can be used in closed piping

systems. Fittings can be flanged, threaded, or compression-style devices. Clamps,

plain ends, socket welds, tube ends, and hose nipples are also available. In terms of

electrical outputs, choices include: analog current, analog voltage, frequency, and

switch. Some flow meters provide signal outputs in serial, parallel, Ethernet, or other

digital formats. Others format output signals according to industrial field bus,

networking, or industrial automation protocols.

18

Flow meters differ in terms of features, applications, and operating performance. A

flow meter’s technology determines the type of media that it can measure. Media

temperature is largely dependent on construction and liner materials. Flow meters

that can measure temperature, density, or level are commonly available. They may

include audible or visual alarms, averaging and controller functions, programmability,

and recorder or totalize functions. In terms of operating performance, turndown ratio

is the effective dynamic or operating range of the flow meter. For example, a 500

SCCM flow rate device with a turndown ratio of 50:1 will operate effectively and

resolve flow down to 10 SCCM. If the same device has a turndown of 100:1, then it

will resolve effectively to 5 SCCM.

2.5.3 Water Valve

Water valves are designed to handle and control hot water, cold water, ground water,

potable water, salt water and/or wastewater [7]. They are made from metal or plastic.

Metal water valves are made of aluminum, brass, bronze, cast iron, ductile iron,

copper, steel, or stainless steel. Plastic water valves are made of acetal polymers,

polyvinyl chloride (PVC), chlorinated PVC (CPVC), polytetrafluoroethylene (PTFE),

polyethylene (PE), polypropylene (PP), and polyvinylidene fluoride (PVDF). Acetal

polymers offer excellent lubricity, fatigue resistance, and chemical resistance. PVC

provides good flexibility, smooth surfaces, and nontoxic qualities. CPVC is suitable

for high temperature applications and is used in hot water distribution. PTFE exhibits

a high degree of chemical resistance and a low coefficient of friction. PE is a soft,

flexible and tough plastic with outstanding electrical properties but poor temperature

resistance. It is prone to stress cracking and has poor resistance to ultraviolet (UV)

light. PP is similar to PVC, but can be used in exposed applications because of its

resistance to UV, weathering and ozone. PVDF has good wear resistance and

excellent chemical resistance, but does not perform well at elevated temperatures.

19

There are many types of water valves. Ball valves provide tight shut-offs, but are not

suitable for sanitary applications. Butterfly valves permit flow in only one direction.

Check valves are self-actuating and prevent the reversal of process flow. Diaphragm

valves separate the flow of water from the closure element. Directional valves steer

flow through selected passages. Diverter valves redirect process flow. Drain valves

reduce surplus media. Float valves open or close automatically as the level of a fluid

changes. Foot valves are check valves with a built-in strainer. Gate or knife valves

are linear motion valves in which a closure element slides into the flow to shut off

the stream. Globe and pinch valves are other types of linear motion devices. Needle

valves have a slender, tapered point at the end of a valve stem. Poppet valves open

and close ports with a sealing device and spring. Plug or stop-cock valves are

designed for both on/off and throttling functions. Other types of water valves include

sanitary or hygienic valves, sampling or dispensing valves, shut off valves, solenoid

valves, and toggle valves.

Selecting water valves requires an analysis of performance specifications, actuation

methods, and connection types. Performance specifications include valve size,

pressure rating, number of ports or ways, media temperature, and valve flow

coefficient. Suppliers specify valves according to metric or English (imperial)

measurements. Some water valves are actuated manually, by a hand wheel or crank,

or with mechanical devices such floats and cams. Others are actuated by electric,

pneumatic, electro-hydraulic, or electro-hydraulic methods. There are many

connection types for water valves. Examples include compression fittings, bolt

flanges, clamp flanges, union connections, tube fittings, butt welds, and socket welds.

Water valves with internal or external threads for inlet or outlet connections are also

available. AWWA certified valves meet the requirements of the American Water

Works Association (AWWA).

20

2.5.4 DC Powered Pumps

DC powered pumps use direct current from motor or solar power to move fluid in a

variety of ways [8]. Motorized pumps operate on 6, 12, 24, or 32 volts of DC power

and use hand-operated, electric, pneumatic, or hydraulic motors. Solar-powered DC

pumps use photovoltaic (PV) panels with solar cells that produce direct current when

exposed to sunlight. Many DC powered pumps use centrifugal force or positive

displacement to move fluids. Centrifugal pumps apply centrifugal force to generate

velocity, use rotating impellers to increase velocity, and push fluids through an outlet

valve. Positive displacement pumps use rollers, gears, or impellers to move fluid into

a fixed cavity so that when liquid exists, the vacuum that is created draws in more

fluid. Diaphragm pumps are the most commonly used positive displacement pumps.

They include a single diaphragm and chamber, as well as suction and discharge

check valves to prevent backflow.

A variety of special DC powered pumps are available. Drum pumps are designed to

transport or dispense the contents of drums, pails, or tanks. Macerator pumps empty

holding tanks for sewage and typically include a bronze cutter to grind waste down

to a small particle size. Sump pumps fit in compartments and remove unwanted

water build-up that threatens to encroach on living or equipment space. Bilge or

ballast pumps are used onboard boats and ships to remove water from the bilge or to

lower or remove water for ballast. Micro pumps use a flexible structure to help move

fluids in miniaturized systems and circulation pumps keep media circulating through

distribution or process systems. Sampling pumps remove small amounts of media for

analysis. Magnetic drive pumps use a magnetic or electromagnetic drive and are

suited for laboratory, production line, chemical processing, general transfer utility,

and original equipment manufacturer applications.

DC powered pumps are available with a variety of specifications and features.

Devices vary in terms of maximum discharge flow, minimum discharge pressure,

inlet size, and discharge size. Adjustable speed pumps can operate at speeds selected

by an operator while continuous duty pumps maintain performance specifications at

21

100% duty cycle. Run dry pumps can operate without pumped fluid or external

lubrication for an extended period of time. Some DC powered pumps are corrosion-

resistant, explosion-proof, or meet strict guidelines established for sanitary process

applications. Others are configured to pump sticky or stringy materials, include an

integral grinding mechanism, or have centerline suction or discharge. DC powered

pumps can move media either vertically or horizontally, depending on the direction

of the pump stator / rotar assembly. Level control devices turn pumps on and off

automatically, depending on the level of the media.

DC powered pumps are used in a variety of general industrial and commercial

applications, as well as in the aerospace, automotive, food service, and medical

industries. DC powered pumps are used to move liquids such as acids, chemicals,

lubricants and oil, as well as water, wastewater, and potable water. Some devices

move combustible or corrosive fluids, while others transport non-liquid gas or air

media.

2.6 Fuzzy Logic Controller

Fuzzy logic controller is an automatic controller in which the relation between the

state variables of the process under control and the action variables, whose values are

computed from observations of the state variables, is given as a set of fuzzy

implications or as a fuzzy relation [9].

Fuzzy controllers are used to control consumer products, such as washing machines,

video cameras, and rice cookers, as well as industrial processes, such as cement kilns,

underground trains, and robots. Fuzzy control is a control method based on fuzzy

logic [10]. Just as fuzzy logic can be described simply as ’’computing with words

rather than numbers’’; fuzzy control can be described simply as ’’control with

sentences rather than equations’’. A fuzzy controller can include empirical rules, and

that is especially useful in operator controlled plants.

22

Fuzzy controllers are being used in various control schemes (IEC, 1996). The most

obvious one is direct control where the fuzzy controller is in the forward path in a

feedback control system (Figure 2.5) [10]. The process output is compared with a

reference, and if there is a deviation, the controller takes action according to the

control strategy. In the figure, the arrows may be understood as hyper-arrows

containing several signals at a time for multiloop control. The sub-components in the

figure will be explained shortly. The controller is here a fuzzy controller, and it

replaces a conventional controller, say, a PID,' (proportional integral- derivative)

controller.

Figure 2.5: Direct Control

In feed forward control (Figure 2.6) [10] a measurable disturbance is being

compensated. It requires a good model, but if a mathematical model is difficult or

expensive to obtain, a fuzzy model may be useful. Figure 2.6 shows a controller and

the fuzzy compensator, the process and the feedback loop are omitted for clarity. The

scheme, disregarding the disturbance input, can be viewed as a collaboration of

linear and nonlinear control actions; the controller C may be a linear PID controller,

while the fuzzy controller F is a supplementary nonlinear controller.

23

Figure 2.6: Feed Forward Control

Fuzzy rules are also used to correct tuning parameters in parameter adaptive control

schemes (Figure 2.7) [10]. If a nonlinear plant changes operating point, it may be

possible to change the parameters of the controller according to each operating point.

This is called gain scheduling since it was originally used to change process gains. A

gain scheduling controller contains a linear controller whose parameters are changed

as a function of the operating point in a preprogrammed way. It requires thorough

knowledge of the plant, but it is often a good way to compensate for nonlinearities

and parameter variations. Sensor measurements are used as scheduling variable that

govern the change of the controller parameters, often by means of a table look-up.

Figure 2.7: Fuzzy parameter adaptive control.

24

2.6.1 Structure of a Fuzzy Controller

There are specific components characteristic of a fuzzy controller to support a design

procedure. In the block diagram in Figure 2.8 [10], the controller is between a

preprocessing block and a post-processing block. The following explains the diagram

block by block.

Figure 2.8: Blocks of a Fuzzy Controller

2.6.2 Fuzzy Logic Toolbox

The Fuzzy Logic Toolbox extends the MATLAB technical computing environment

with tools for designing systems based on fuzzy logic [11]. Graphical user interfaces

(GUIs) guide users through the steps of fuzzy inference system design. Functions are

provided for many common fuzzy logic methods, including fuzzy clustering and

adaptive neurofuzzy learning.

The toolbox lets user’s model complex system behaviors using simple logic rules and

then implements these rules in a fuzzy inference system. Users can use the toolbox as

a stand-alone fuzzy inference engine. Alternatively, users can use fuzzy inference

blocks in SIMULINK and simulate the fuzzy systems within a comprehensive model

of the entire dynamic system.