ABSTRACT
The project concerns the design and construction of a metal detector with siren alarm. A metal detector is a device which responds to metal that may not be readily apparent. The simplest form of a metal detector consists of an oscillator producing an alternating current that passes through a coil producing an alternating magnetic field. If a piece of electrically conductive metal is close to the coil, eddy currents will be induced in the metal and this produces an alternating magnetic field of its own. If another coil is used to measure the magnetic field, the change in the magnetic field due to the metallic object will be detected. The system will be use in banks, institutions, homes and airports purposes to restrict unauthorized personnel from gaining access to sensitive business and personal information in our society.
TABLE OF CONTENTS
Title Page i
Declaration ii
Certification iii
Dedication iv
Acknowledgements v
Table of Contents vi
List of Tables x
List of Figures xi
List of Plates xii
Abstract xiii
CHAPTER 1: INTRODUCTION 1
1 .1 Background of the Study 1
1 .2 Problem Statement 2
1 .3 Aims and Objectives of the Study 3
CHAPTER 2: LITERATURE REVIEW 4
2.1 Historical Background 4
2.2 Discriminators 5
2.3 New Coil Design in Metal Detectors 6
2.4 Pulse Induction in Metal Detection 7
2.5 Industrial Metal Detectors 8
2.5.1 Metal detector security screening 8
2.6 Models of Metal Detectors 9
2.6.1 Model T-2000 metal detector 9
2.6.2 Model 5500 metal detector 9
2.6.3 Model 8600 metal detector 10
2.6.4 Model 9300 metal detector 10
2.6.5 Model 600 metal detector 10
2.6.6 Model 8050 metal detector 11
2.6.7 Model 9100 metal detector 11
2.7 Features and Benefits of Some Metal Detectors 11
2.7.1 Model 9300 metal detector 11
2.7.2 Model 600 metal detector 12
2.7.3 Model 9100 metal detector 12
2.7.4 Model 8050 metal detector 12
2.8 Metal Detection Principle of Operation 13
2.8.1 Electromagnetic induction 13
2.8.2 Eddy current 14
2.9 Application of Metal Detector 15
2.9.1 Consumer-oriented metal detector 15
2.9.2 Industrial metal detector 17
2.10 Description of Some Component Used in Designing this Project 18
2.10.1 Power supply 18
2.10.2 Capacitor 18
2.10.3 Transistor 19
2.10.3.1 Transistor symbols 20
2.10.3.2 Transistor types 21
2.10.3.3 Bipolar junction transistor (BJT) 21
2.10.3.4 Field effect transistor (FFT) 22
2.10.4 Diodes 23
2.10.5 Inductor 26
2.10.6 Factors affecting inductance 26
2.10.6.1 Numbers of wire wraps “turns” in the coil 26
2.10.6.2 Coil area 27
2.10.6.3 Core material 27
2.10.6.4 Coil length 28
2.10.7 Low-pass filter 30
2.10.7.1 Low-pass RC filter 30
2.10.7.2 Low-pass RL filter 31
2.11 Colpitt Oscillator 32
2.12 Advantage of Colpitts Oscillator 34
2.13 555 Timer IC 35
2.14 Some Important Features of 555 Timer IC 36
2.14.1 555 timer working 37
2.14.2 Astable 37
2.14.3 Mono-stable mode 39
2.14.4 Bi-stale mode (or schmtt trigger) 39
CHAPTER 3: MATERIALS AND METHODS 40
3.1 Materials 40
3.2 Block Diagram of a Metal Detector 41
3.2.1 Explanation of the block diagram 41
3.3 Circuit Diagram of a Metal Detector 42
3.4 Principle of Operation of a Metal Detector 43
3.5 555 Timer Calculation 43
3.6 Audio Frequency Amplifier 45
3.7 Beat Frequency Oscillator (BFO) 45
3.8 Search Coil 46
3.9 Principle of Operation of Search Coil 46
3.10 Police Siren Alarm Circuit Diagram 47
3.11 Principle of Operation of Police Siren Alarm 48
CHAPTER 4: RESULT AND DISCUSSION 49
4.1 Results 49
4.2 Discussion 51
4.3 Testing of Model 51
CHAPTER 5: CONCLUSION AND RECOMMENDATIONS 53
5.1 Conclusion 53
5.2 Recommendations 53
References 55
LIST OF TABLES
4.1 Result obtained with the detector in its functional and none functional state. 49
LIST OF FIGURES
2.1: Archway detector 16
2.2: Hand held metal detector 16
2.3: Ground search metal detector 17
2.4: Types of capacitors 19
2.5: Transistors symbols 20
2.6: Bi-polar junction transistor 21
2.7: Diagram of FET 23
2.8: Graphic diagram of diode 24
2.9: Forward and reverse bias of a diode 25
2.10: Symbol of a diode 25
2.11: Number of turns wrap 27
2.12: Coil area inductance 27
2.13: Core material 28
2.14: Coil length (more length, less inductance) 28
2.15 Schematic circuit symbol of inductance 29
2.16: Low-pass filter 30
2.17: Low-pass RC filter 30
2.18: Low-pass RL filter 31
2.19: Colpitt oscillator 33
2.20: Tank circuit in a colpitt oscillator 34
2.21: 555 timer IC pin diagram 35
2.22: 555 timer circuitry block diagram 36
2.23: Standard 555 astable diagram 38
2.24: Astable output graph 38
3.1: Block diagram of a metal detector with siren alarm 41
3.2: Circuit diagram of a metal detector with siren alarm 42
3.3: 555 timer calculation 44
3.4: Search coil 46
3.5: Police siren alarm system circuit diagram 47
LIST OF PLATES
4.1: Photography of the designed metal detector with siren alarm 50
CHAPTER 1
INTRODUCTION
1.1 BACKGROUND OF THE STUDY
A metal detector device composed of an oscillating circuit whose resonant frequency is altered by the presence of metal. The proximity of the metallic mass changes the value of the inductance of the coil that is part of an oscillator and is converted into an acoustic signal transmitter through a speaker or earphones, (Ajuzie, 2003).
A metal detector reveals the presence of metallic material/object by measuring the change in the inductance of coil near a metallic mass. Any metal that conducts electricity can be detected by a metal detector because of the change in the inductance of a coil place near a metallic mass, (Nnaekezie and Anokwu,1998).
The operation principle of a metal detector is based on the principle of ELECTROMAGNETIC INDUCTION, metal detector contain one or more inductor coils that used to interact with metallic elements on the ground. Because of magnetic property and electrical conductivity of metals, metals can be detected by metal detectors; therefore metal detectors are based on measuring electrical conductivity and magnetic permeability of metals. This means that even poor metals with permeability are not easily detected. So any material that has a conductivity surface will be detected because a sign is heard since an electromagnetic field is generated, flows out into space away from the search coil. As the lines of the electromagnetic field penetrates the surface of the materials tiny circulating currents called eddy current are caused to flow in the surface of the metal, (Chirlian,1987).
The eddy current that generates its own electromagnetic fields radiates in all direction in space. Today, modern detectors do practically everything; they detect the metal, pinpoint its size and shape, and measure its depth. In early years, the metal detector was used mostly for prospecting precious metals. It was not until well after World War II that metal detectors began to be used to a great extends for hunting. Other kinds of treasure, and as the year passed, metal detectors usage has greatly expanded into many fields which include the searching of coins, relics, treasures, gold and others, (Horowitz and Hill, 1997).
The traditional metal detector has moved from certain applications such as pip findings or probing to more detailed operation such as detection of ferrous and non ferrous metals application of metal detectors to law enforcement and security situation has been recorded in which metal detection equipment was used for law enforcement and investigative tool, (Philips, 1980).
1.2 PROBLEM STATEMENT
One major problem in our country is security; with all the dangers that the world experiences today, it is important for everyone to be cautious. This is why establishments and building arm their guard with “metal detectors’’
Metal detectors detect metal objects such as guns, knives, buried metal pipelines. In the past, metal detectors detect only small pieces of metals but cannot detect heavy metals. What allowed detectors to disseminate metal was the fact that every metal has a different phase response when exposed to alternating current. Scientist had long known of this fact, so by the time detectors were developed that could selectively detect desirable metal while ignoring undesirable ones.
This problem can be solved by creating a scan circuit with a reference from the data already gotten in order to differentiate a parameter of harmful and un-harmful metals.
This project is focused on the design and construction of a metal detector with siren alarm in order to minimize security risk in industries, homes, banks and commercial purposes.
1.3 AIMS AND OBJECTIVES OF THE STUDY
The main aim of this project is to design and construct a metal detector with siren alarm. The objectives are:
(i) To design and construct a metal detector with siren alarm which is capable of detecting and identifying metallic items.
(ii) To achieve a reliable and efficient electronic devices that can detect concealed metal objects such as guns, knives, bunch of key or buried metal pipelines.
(iii) To design and construct a system that can analyze the responses of the detector with respect to the different metallic materials with regards to the ranges of detection.
(iv) To design and construct an electronic system that could be identified as a security device that can be used in banks, industries, homes or for commercial applications.
(v) To design and construct a device that could be used to detect the presence of metals in some raw materials and products.
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