The design of a metal detector to balance the intake system
Design using a metal detector system implementation of the induction balance
Santiago January 2 Azihar Agaj Conelius
Department of Electrical and Electronic Engineering, Polytechnic Federal, State Auchi, Edo Nigeria
Phone: +2348053312732, agajojul@yahoo.com
SUMMARY: A logical integrated approach was used for metal detection. The controller is simulated to achieve. Three technologies have been used very low frequency (VLF) Pulse Induction (PI) beat frequency oscillation (BFO), the security and safety were also highlighted.
Keyword: microcontroller, detector low frequency, safety, oscillators, sensors
1.0 INTRODUCTION
Towards the end of the 19th century, many Scientists and engineers used their growing knowledge of electrical theory in an attempt to design a machine that identifies metal. The use of a device to find mineral bearing rocks would give a great advantage for all children who used it. German physicist Heinrich Wilhelm Dove invented the induction balance, who joined a metal detector hundred years later. Early machines were crude, used a lot of battery power, and worked in a very limited. Alexander Graham Bell used as a device to try to find a bullet in the chest by U.S. President James Garfield in 1881, tried not to because the bed Metal Garfield was lying on confused the detector [1].
1.2 Trends
Many manufacturers of these new devices brought their own ideas to market. Whites Electronics of Oregon began in the 50's by building a machine called Geiger Oremaster. Another leader in detector technology was Charles Garrett, who started the BFO (Beat Frequency Oscillator) machine. With the invention and development of the transistor in the 50's and 60 manufacturers metal detectors and designers in small lighter machines with improved circuitry, operates on low battery packs. Companies increased in France and Britain to meet the growing demand [2].
Great portable metal detectors are used by archaeologists and treasure hunters to find metal objects such as jewelry, coins, bullets and other various objects buried below ground surface [3].
1.3 Methodology
Metal detectors use a three technologies:
- Very low frequency (VLF)
- Pulse Induction (PI)
- Beat-frequency oscillation (BFO)
- [4]
1.4 VLF Technology
Very low frequency (VLF), also known as the balance of induction is probably the most popular detector technology in use today. In a VLF metal detector, there are two different coils:
- coil Issuer – This is the outer loop of the coil. Within it is a coil of wire. The electricity is sent along in this thread, first one way then the thousands, of times every second. The number of times the current direction changes every second establishes frequency of the unit.
- reel – This inner coil loop contains another coil of wire. This wire acts as an antenna to capture and amplify frequencies coming from target objects on earth. [5]
The current through the transmitting coil creates a magnetic field that is like what happens in an electric motor. The polarity of the magnetic field is perpendicular to the coil of wire. Each When the tide is turning, the polarity of the magnetic field changes on the ground. This means that if the coil is parallel to the ground wire, the magnetic field is constantly pushing down on the floor, then pulling it back.
1.5 feet of Technology
A less common form of metal detector is based on pulse induction (PI). Unlike VLF, IP systems can use a single coil as both transmitter and receiver, or may have two or even three coils working together. This technology sends bursts powerful, short (pulse) current through a coil of wire. Each pulse generates a brief magnetic field. When the pulse ends, the magnetic field reverses polarity and suddenly collapses, resulting in a sharp increase in electric. The tip lasts a few microseconds (millionths of a second) and causes another current to running through the coil. This current is called the reflected pulse and is extremely short, lasting only about 30 microseconds. Another pulse is sent and the process repeated. A typical metal detector sends about 100 pulses per second IP, but the number can vary widely by manufacturer and model ranging from a few pulses per second over a dozen thousand. Pulse induction detectors are widely used in the construction industry; White PI-150 is a machine manpower that can detect large objects 10 feet, using a roll of 12 or 15 inches.
2.0 Analysis Module
- DC Food
This unit provides the voltages required to operate the DC circuit
- oscillator Reference coil
This oscillator provides the reference coil as the inductive element and set the oscillator frequency that the two concerns.
- search coil oscillator
This is the second oscillator which contains the inductive element detector. The inductance of the coil changes in research when it is located a metal, which in turn changes the frequency of the oscillator. This frequency is compared with that of an oscillator to produce a hit.
- Mixer
Pulses generated by each oscillator are mixed in the mixing unit and filter through to ground.
- Filter Gain
The process of increasing the filters and amplifies the difference between the contradictory impulses of mixing units and a buzzer piezoelectric with it.
- transducer output (load)
The transducer converts the electrical signal output in a sound signal to give an audible signal the presence of a metal.
2.1 OBJECTIVE
The project's objective is to facilitate the job of trying to locate a metal useful in a particular or specific. As the soft penalty eyes is greatly reduced when the metal detector used in the workshop where metal parts can be moved easily. Stations also search for people and their luggage.
P = IV = I2R = V2 / R
The three equations are equivalent. The first is derived from Joule's law, and the other two are derived from Ohm's law.
The total thermal energy released is the integral power over time:
W =? V (t) i (t) dt.
If the average power dissipated is greater than the power of resistance, resistance may deviate from its nominal resistance, and can be damaged by overheating. Excessive power dissipation may raise the temperature of the resistance to a point in which burning, which could cause a fire in the adjacent components and materials.
2.2 Series and parallel circuits
- parallel
Resistors in parallel co nfiguration everyone has the same potential difference (voltage). To find the total equivalent resistance (Req):
1/Req = 1/R1 + 1 / R2 … .. + .. 1 / Rn
The parallel property can be represented in the equations of two vertical lines "| |" (as in geometry) to simplify the equations. For two resistors,
Req = R1 / / R2 = R1R2 / (R1 + R2)
- series circuit
The current in the resistors in series stays the same, but the voltage across each resistor can be different. The sum of the potential differences (voltage) is equal to the total voltage. To find the total resistance:
Req = R1 + R2 + … .. + R2
Parallel and serial
A resistance network is a combination of parallel and series can sometimes be divided into smaller one or the other. For example,
Req = (R1 / / R2) + R3 = (R1R2) / (R1 + R2) + R3
However, many resistor networks can not be divided in this way. Consider a title = "Cube"> cube, each edge of which was replaced by a resistor. For example, the determination of the resistance between two opposite vertices requires methods matrix for the general case. However, if the twelve resistors are equal, from corner to corner resistance is 5? 6, one of them.
2.3 Electrical circuits
When a capacitor is connected to a power source, the charge is transferred between the plates at a rate of i (t) = dq (t) / dt. Since the voltage between the plates is proportional to the load, it follows that
V (t) = 1/cq (t) = 1 / c? I (?) D?
For Conversely, if a capacitor is connected to a source of stress, displacement resulting current is given by
I (t) CDV (t) / dt
For example, if you connect a capacitor of 1000 uF with a voltage source, then increase the power supply at a rate of 2.5 volts per second the current through the capacitor
I = Cdv / dt = (1000 x10-6F) (2.5 V / s) = 2.5 mA
Ø DC sources
A circuit containing only a resistor, capacitor switch, and a constant (DC) voltage source VSRC (t) = V0 in series is known as a circuit load. In the tension of the Kirchhoff law, it follows that
Vo = r (t) + Vc (t) = i (t) IR / C? I (?) D?
where vr (t) and vc (t) are the voltages on the resistor and capacitor, respectively. This reduces to a first order differential equation
Assuming that the capacitor is discharged in the first place, there is no internal electric field and the initial current is I0 = V0 / R This initial condition allows solution of the differential equation
. I = Vo / Rexp (-t/RC)
The corresponding voltage drop across the capacitor is
v (t) = Vo [1-exp (-t/RC)]
Therefore increases the load on the plates of the capacitor, the voltage across the capacitor increases until reaching a V0 steady state, and the current drops to zero. Both the current and the difference between the source and the capacitor voltage decay exponentially with time. The constant time decay is given by? = RC.
2.4 Series and parallel arrangements
- parallel circuits
Capacitors in a parallel configuration each have the same potential difference (voltage). Total capacity (CEQ) is given by:
C eq = C1 + C2 + … … .. + Cn
The reason for putting capacitors in parallel to increase the total charge stored. In other words, the increased capacity also increases the amount of energy they can store. Expression is:
Blinds = ½ CV2
- series circuit
Capacitor current in the series remains the same but the voltage across each capacitor can be different. The sum of the potential differences (Voltage) is equal to the total voltage. Its total capacity is equal to:
1 / C eq = 1 / C1 + 1 / C2 + … … .. + 1 / Cn
At the same time, cross section of the total capacity has increased, increasing total capacity. However, in series, the distance between the plates is increased, The total capacity reduction.
Ø Noise filters, motor starters, shock absorbers and
When an inductive circuit is opened, the current through inductance collapses quickly, creating considerable tension in the open circuit breaker or relay. If the inductance is large enough, the energy is to generate a spark, so the points of contact for rust, deterioration, or welding times or destroy a solid state switch. Capacitor switching on the circuit open new creates a path of this pulse to avoid the contact points, and preserving their lives, and these are often in contact systems switch, for example. Similarly, in smaller scale circuits, the spark may not be enough to damage the switch, but still emit any unwanted frequency radio (RFI), which removes a filter capacitor. snubber capacitors are used with a low value resistor in series to dissipate energy and reduce RFI to a minimum. These resistor-capacitor combinations are available in one package.
Ø tuned circuits
In a tuned circuit as the receiver selected radio frequency is a function of the inductance (L) and capacitance (C) in series, and is given by:
. F = 1 / 2? SC
The frequency that resonance occurs in an LC circuit.
INDUCTOR 2.5
An inductor is a passive component with major electrical inductance. Inductors are implemented by a spiral conductive winding which may surround a ferromagnetic core. Large inductors used at low frequencies may have thousands of turns around an iron core at very high frequencies over a piece of the right (ie, with towers and the core is reduced to zero) has inductance significant.
An "ideal bottlenecks" has inductance, but not the strength or capacity, and do not dissipate energy. A real inductor is equivalent a combination ideal inductance significant resistance, and capacity, usually small. Resistance, a property necessary except a superconducting cable temperatures, can contribute significantly to the impedance, and can dissipate a major power in some applications. In a certain frequency, usually much more higher than the operating voltage, a real inductor behaves as a resonant circuit, and can cause parasitic oscillations.
3.0 inductor circuit
• The parallel circuit
Inductors in a parallel configuration each have the same potential difference (voltage). To find their total equivalent inductance (L eq)
= 1/L1 + 1/L2 + … 1/Leq … + 1/LN
series circuit
The inductor current through the series remains the same but the voltage in each coil can be different. The sum of the potential differences (voltage) is equal the total voltage. To find their total inductance:
Leq = L1 + L2 + … N + L.
These relationships simple truth when there is no mutual coupling between individual magnetic fields induce.
4.0 Introduction
This chapter deals with the design and analysis methods used in the design of electronic metal detector. These tests are necessary to make the correct choice of component values to be effective.
4.1 Design specification
Power Source:
9V PP3 battery is ideal both.
Capacitors:
220UF 16V electrolytic 2.
5 at 0.01 uF polyester.
5 0.1 uF polyester exterior.
Resistances:
All the 1.4-watt resistors 5%
6 in the 10k
1 on 1 K
1 in 2.2 million
2 in the 39k
Transistors:
All British Columbia 337B. Almost all small-signal NPN with a gain of 250 will do. There are hundreds of use.
Audio Output
A 2.5-inch speaker 8 ohms work, but the headphones, alarm or headset is best, the higher the impedance the better.
4.2 Power Circuit
The main power circuit is two 9V batteries in series to produce 18V regulated and then carried through a voltage regulator 12v 7812.
circuit power
The entrance to the controller 7812 is calculated as
Log batteries in series is given by PT = P1 + P2 + P3 + …
Therefore, the power drawn by the regulator is pt = p1 + p2
pt = 9 +9 = 18v
3.1.2 Oscillator Circuit
The oscillator circuit consists of two different oscillators are in the sensor oscillator and local oscillator or reference. Its frequency of oscillation was set at 124khz, as are to operate in the same frequency. The two oscillator circuits are series LC circuit comprising an NPN transistor BC 337 for each oscillation effectively.
- The sensor oscillator
To calculate the value of the inductance of the resonant frequency formula is used
F = (2? (LC) 1 / 2) -1
When F = frequency in Hertz, which is set at 124khz
L = inductance value
C = capacity of condenser
L = 1 / (4? 2CF2)
L = 1 / (4 x (3142) 2 x0.1×10-6 x (124 x 103) 2)
L = 16.47μH
Then, to calculate the number towers, Wheeler's formula is applied to the coils
N2 = r2 / 9r + 10l
Where N = number of turns
r = outer spool Radio (Inches)
l = physical length of the coil (inches)
L = radius of the coil 16.47outer (inches)
l = physical length Coil (inches)
L = 16.47μH
r = C / 2? where C = circumference of the coil former
r = 3.6 cm / 2? = 0.57cm
The conversion of inches
1 inch – 2.54 cm
0.57cm -?
0.57 / 2.54 = 0.23inches
L = 2.36 inches
N2 = L (9r + 10l) / r2
= 16.47 (+ 9×0.23 10×2.36) / 0232
N2 = 89 laps
Applying formula to calculate the resonant frequency of the coil we have here:
L = 1 / (4? 2CF2)
When F = 124khz, C = 0.1μF
L = 1 / (4 x (3142) 2 x0.1×10-6 x (124 x 103) 2)
L = 16.47μH
Then, using the formula to find the rpm Wheeler
N2 = r2 / 9r + 10l
When r = C / 2? = 52 / 2?
== 8.27cm 3.26inches
== L = 0.6 cm 0.24inches
N2 = L (9r + 10l) / r2
N2 = 16.47 (+ 9×3.26 10×0.24) / 3262
N = 7 laps
4.3 Amplifier circuit
A common-emitter (CE) transistor amplifier is used because of its features include:
- Its output resistance is large enough (50k or more)
- (?) The current gain is high (50 – 300)
- It features high voltage gain of Agenda 1500 and above
- There is an increase of very high energy times about 40db or 10,000.
The transistor is used BC337 NPN transistor.
In a good design amplifier circuit is operating normally when
VCE = ½ VCC
Also for the CE configuration
VCE = Vcc – ICRL
hfe = ic / IB
When VCE = collector emitter voltage
HFE = absolute minimum gain for the transistor is selected 100
IC = collector current
= Base current IB
So RL = (VCC – VCE) / IC
The voltage gain is given by
AV = r / re
When the output resistance ro = scene
Emitter resistance Re =
25mV / IE.
4.4 Oscillator Technology The beat frequency
The circuit uses two radio frequency oscillators oscillators called research and reference given to the same frequency. oscillator output is fed into a blender, producing a signal containing components quantity and frequency difference of two input signals.
- The mixer output is fed into a low pass (gain) in the harmonic filter is removed, leaving the frequency component of the survival difference, although in theory from 0 Hz, following the departure will be no difference. However, when the metal is introduced in the vicinity of the search coil, the frequency of oscillators research moves slightly, then there is a difference frequency, which is in the range audio frequency, appears at the output of the filter. This output is amplified by an audio amplifier and fed to a speaker that produces audio output that indicates the presence of metals
5.0 TESTING AND ANALYSIS
The next test took place in the circuit of a project ensure the rule of different phase and the whole project:
Short-circuit proof
Connections were checked with a multimeter adjusted for continuity to ensure that there is a short circuit. The test was carried out and no short circuit was found.
Open circuit test
We reviewed the different connections to open and has not been found several meters.
Test run
The value voltage and current value were measured at each stage and all were found in the confirmation of design specifications.
Insulation Test
Insulation test was performed on all the circuit units including units that require adequate insulation. For example, the coil used in oscillators.
SYSTEM IMPLEMENTATION AND TEST RESULTS
The metal detector is used to test different sizes of metal at different distances of the search coil and after the results were obtained.
(I) of gold metal, the strongest out of the speakers and the smaller metal, reducing sound output by the speaker – but this also depends on the size of the search coil.
(Ii) The distance between the head research and more output metal speakers and the distance to the lower production of sound from the speaker, as his death at a critical distance determined theoretically the magnetic field due to the sensing head is zero.
6.0 CONCLUSION
The oscillator time (OFB) is a principle of simple and reliable fusion of the principles of effective construction of a metal detector. While some prices paid for these benefits and understand apparently.
(I) the low sensitivity
(Ii) short detection. Although it depends on the size of the search coil.
(Iii) not be able to discriminate between metals
All these are nothing, it is interesting that the design and construction of the detector is a success. This because the project during a test produces the desired effect. In particular, this research has made the principle of electromagnetic induction is very clear to me, so like any average literate person around me. In general, the invention of metal detectors, the stress involved in locating components in a metal workshop has been drastically reduced. So the banks and the shame of another institution because of their customers was resolved a few metal detector mounted on the entrance doors to trigger an alarm in place when the metal is detected in a person attempting to enter.
REFERENCES
1 Edeka, FP, "Material design of electronic circuits" 2008
2 A textbook of electrical technology by BL and AK Theraja Theraja, S. Beet and Society, 2005.
3 Study of electronic components J. Smith (second edition), 1999
4 electronic circuits analysis and design of Donald A. Neumann, Mc Book Company Grawhill, USA 1996.
5 amplifiers comparators and special functions, Texas Instruments, Product data volume B, Printing Company, 1997.
About the Author
James Agajo is into a P.H.D programme in digital signal processing related area, he has a Master Degree in Electronics and telecommunication Engineering and also possesses a Bachelor degree in Electronics and Computer Engineering from the Federal University of Technology Minna Nigeria. To he’s record he has carried out researches in various areas as it concern telecommunication with particular emphasis on wirless communication network. His interest is in intelligent system development with a high flare for Engineering and Scientific research.He has Designed and implemented the most resent computer controlled robotic arm with a working grip mechanism 2006 which was aired on a national television , he has carried out work on using blue tooth technology to communicate with microcontroller. Has also worked on thumb print technology to develop high tech security systems with many more He is presently on secondment with UNESCO TVE as a supervisor and a resource person. James is presently registered with the Nigeria Society of Engineers.
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