The design of a metal detector by the induction balance system in
Metal detector design through the system constant induction
James 2 1 Agaja Azihar Conelius
State Department of Electrical and Electronic Engineering Federal Polytechnic, Auchi, Edo Nigeria
Phone: +2348053312732, email@example.com
Abstract: A system logic integrated approach has been used for metal detection. The controller is simulated to achieve it. Three technologies have been used very low frequency (VLF) Pulse Induction (PI) beat frequency oscillation (BFO), the issue of security and safety were also highlighted.
Keywords: microwave, low frequency, detector, security, oscillators, sensors
Towards the end of the 19th century, many scientists and engineers have used their increased knowledge of electrical theory in an attempt to design a machine that detects metal. The use of this device to find ore rocks that would give a huge advantage for any child who used it. The German physicist Heinrich Wilhelm Dove invented the induction balance system, which has been incorporated into metal detectors a hundred years later. Early machines were crude, widely used battery power, and worked in a very limited extent. Alexander Graham Bell used a device to try to find a bullet in the chest U.S. President James Garfield in 1881, the attempt failed because the metal bed Garfield was to confuse the detector .
Many manufacturers of these new devices brought their own ideas on the market. Whites Electronics of Oregon has begun in the 50s by building a machine called Oremaster Geiger counter. Another leader in detector technology was Charles Garrett, who developed the BFO (beat frequency oscillator) of the machine. With the invention and development of the transistor in 50s and 60s, manufacturers of metal sensors and light designers in small motorcycles with the circuit of improvement, running on low battery packs. The U.S. companies increased and Britain to meet the growing demand .
Portable metal detectors are used by larger archaeologists and treasure hunters to find metal objects such as jewelry, coins, bullets and other objects buried in the ground various surface .
Metal detectors use one of three technologies:
- VLF (VLF)
- induction pulse (IP)
- Beat-frequency oscillation (BFO)
1.4 VLF technology
Very low frequency (VLF), also known as induction balance, detector is probably the most popular technology in use today. In a VLF metal detector, there are two different coils:
- question Coil – This is the external coil loop. It is within a coil of wire. Electricity is sent along this thread, first one side then the other, thousands of times every second. The number of times the current direction changes every second establishes the frequency of the device.
- Reel – This loop interior contains another coil of wire coil. This wire acts as an antenna to pick up and amplify frequencies coming from target objects in the soil. 
The current move by the transmitter coil creates an electromagnetic field, which is like what happens in an electric motor. The polarity of the magnetic field is perpendicular to the coil of wire. Every time the tide is turning, the polarity of the magnetic field changes on the ground. This means that if the coil of wire is parallel to the ground, the magnetic field is constantly pushing down on the floor, then folding it over.
1.5 IP Technology
A less common form of metal detector is based on pulse induction (PI). Unlike VLF intellectual property systems can use a single coil as transmitter and receiver, or may have two or even three coils working together. This technology sends powerful, short bursts (pulses) of current through a coil of wire. Each pulse generates a brief magnetic field. When the pulse ends, the magnetic field reverses polarity and collapses suddenly, resulting in a strong increase in power. This council has a few microseconds (millionths of a second) and causes another current flowing through the coil. This current is called the reflected pulse and is extremely short, lasting only about 30 microseconds. Another dozen pulses per second over a thousand. Pulse induction detectors are widely used in industry construction; White PI-150 is an industrial machine that can detect large objects to 10 meters with a roll of 12 or 15 inches.
2.0 Analysis MODULE
- Dc power
This unit provides the voltages required for circuit operation DC
- reference oscillator coil
This oscillator provides the reference coil as the inductive element and set the frequency with which the search coil oscillator inductive element. The inductance of the coil to check for changes when a metal is located, which in turn changes the frequency of the oscillator. This frequency was compared with that of an oscillator to produce a beat note.
The pulses from each oscillator are mixed in the pipes and the sum filters into the ground.
- Filter Gain
The gain filter processes and amplifies the difference pulses common mixer drives a piezo buzzer it.
- transducer output (load)
The transducer converts the electrical output signal into audible sound to give an audible indication of the presence of a metal.
The project aims to alleviate the pain of trying to locate a metal useful in a particular environment or specific. As the penalty to stretch the eye is considerably reduced when the metal detector used in the workshop where you can easily move small metal. Stations always searching for people and their luggage.
P = IV = I2R = V2 / R
The three equations are equivalent. The first is derived from Joule's law, and two derived from Ohm's law.
The amount total thermal energy released is the integral of power over time:
W =? V (t) i (t) dt.
If the average power dissipation is greater than the power of resistance, the resistance may deviate from its nominal resistance, and may be damaged by overheating. Excessive power dissipation may raise temperature resistance to a point at which it burns, which could cause a fire in the adjacent parts and materials.
2.2 Series same potential difference (voltage). To find the equivalent total resistance (REQ):
1/Req = 1/R1 +1 / R2 … .. + .. 1 / Rn
R1R2 / (R1 + R2)
- series circuit
The current in the resistors in series stays the same, but the voltage in each resistor can be different. The sum of potential differences (voltage) is equal to the total voltage. To find the total resistance:
Req = R1 + R2 + … .. R2 +
Parallel and serial network
A network of resistance that is a combination Serial and parallel can sometimes be divided into smaller pieces that are one or the other. For example,
Req = (R1 / R2) + R3 = (R1R2) / (R1 + R2) + R3
However, many resistor networks can be divided in this direction. Consider a cube Each plate has been replaced by a resistor. For example, the determination of the resistance between two opposite vertices requires matrix methods for the general case. However, a capacitor is connected to a power source, the load is transferred between the plates at a rate i (t) = dq (t) / dt. As the tension between the plates is proportional to the load, it follows that
V (t) = 1/cq (t) = 1 / c? I (?) D?
By contrast, if a capacitor is connected to a voltage source, resulting in the displacement of course is given by
I (t) APV (t) / dt
For example, if you connect a 1000 mF capacitor to a voltage source, then increase the voltage source at speeds 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, a switch and a constant (DC) voltage source VSRC (t) = V0 in series is known as a load circuit. From the Kirchhoff voltage law follows that
Vo = Vr (t) + Vc (t) = i (t) RI / c? i (?) d?
where r (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 fall corresponding voltage across the capacitor is
v (t) = Vo [1-exp (-t/RC)]
Therefore, with increasing charge on the plates of the capacitor, the voltage across the capacitor increases until it reaches a stable value for the state V0, and the current drops to zero. Both the current and the difference between the source and the capacitor voltage decay exponentially with time. The time constant of decay is given by? = RC.
2.4 Arrangements Series or parallel
- parallel circuits
The 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 is to increase the total charge stored. In other words, more capacity also increases the amount of energy they can store. Expression is the following:
= ½ CV2 Estore
- series circuit
The current in the series capacitor remains the same, but the voltage across each capacitor can be different. The sum of potential differences (voltage) is equal to the total voltage. Its total capacity is equal to:
1 / Ceq = 1 / C1 + 1 / C2 + … … .. + 1 / Cn
At the same time, the effective area of the combined capacity has increased This increases the total capacity. However, in series, the distance between the plates was actually increasing, the total capacity reduction.
Ø RFI filters, starters motor and dampers
When an inductive circuit is opened, the current through the inductance collapses quickly, creating a major strain on the switch open circuit or relay. If the inductor is large enough, energy will create a spark, causing the points of contact to oxidize, deteriorate, or sometimes welding, or destroying a solid-state detector. A buffer capacitor through the newly opened circuit creates a path for this impulse to pass ignore contact points in order to preserve their lives, they are often found in systems of automatic ignition, for example. Similarly, in scale circuits small, the spark may not be sufficient to damage the switch, but still transmit unwanted interference radio frequency (RFI), which absorbs a capacitor filter. snubber capacitors are typically used with a low resistance value in series, to dissipate energy and minimize RFI. This combination of capacitors resistance are available in one package.
Ø tuned circuits
At a tuned circuit like a radio receiver, the selected frequency is a function inductance (L) and capacitance (C) in series, and is given by:
. F = 1 / 2? SC
This is the frequency at which resonance occurs in a circuit LC.
An inductor is a passive electrical component with significant inductance. Inducers are executed by a spiral conductive winding which may surround a ferromagnetic core. Large inductors used at low frequencies may have thousands of laps around an iron core of very high frequencies right a piece of wire (ie, with towers and the core is reduced to zero) has significant inductance.
Inductance "ideal" has an inductance, not resistance or capacitance, and do not dissipate energy. A real inductor is equivalent to a combination of important ideal inductor, the resistance and capacitance, usually small. Resistance, a necessary property of a superconductor cable with the exception of temperatures, can contribute significantly to the impedance, and may dissipate significant power in some applications. In a certain frequency, usually much higher than the voltage, a real inductor behaves like a resonance circuit, and can cause spurious oscillations.
3.0 AGREEMENT inductor circuit
Parallel · Tour
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
The current in inductors in series is the same, but the voltage in each coil can be different. The sum of potential differences (voltage) is equal to the total voltage. To find the inductance total:
Leq = L1 + L2 + …. L + n
These simple relations valid when there is no mutual coupling between fields induce magnetic individual.
This chapter deals design methods and analysis used in the design of electronic metal detector. These tests are necessary to make the correct choice of values components for effective performance.
DESIGN 4.1 Specifications
Any two PP3 9V battery is ideal.
220uF 16V Electrolyte 2 OFF.
Discount of 5, 01 uF polyester.
5 out, 1 uF polyester.
All resistors 1 / 4 Watt 5%
6 OFF 10k
1K 1 OFF
1 OFF 2.2 million
2 OFF 39k
All 337B Columbia British. Almost all small-signal NPN with a gain of 250 + will do. There are hundreds to choose from.
A 2.5-inch speaker 8 ohms work, but the headset or handset ringer, it is recommended, the impedance is better.
4.2 Fuel System
The main power circuit is two 9V batteries in series to produce 18V regulated and maintained at 12 V using a voltage regulator 7812.
The input of the 7812 is calculated as
Batteries connected in series is given by pt = p1 + P2 + P3 + …
Therefore, the power controller is P = P1 + P2
pt = 9 +9 = 18 V
3.1.2 Oscillator Circuit
The circuit oscillator consists of two different oscillators, the local oscillator reference sensor I oscillator. Its frequency of oscillation was set at 124khz, as they are to function the same frequency. The two oscillator circuits are series LC circuit including a NPN transistor a. C. 337 for each oscillation effectively.
- The sensor oscillator
To calculate the inductance of the inductor of the resonant frequency formula is used
F = (2? (LC) 1 / 2) -1
Where F = frequency in Hertz, which is at 124khz
L = inductance of the coil
C = capacitance
L = 1 / (4? 2CF2)
L = 1 / (4 x (3142) 2-6 x0.1×10 x (124 x 103) 2)
L = 16.47μH
Then calculate the number of turns, coil formula Wheeler applies
The N2 = r2 / 9r + 10l
Where n = number of turns
r coil physical length (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 that
2.54 cm – 1 inch
0.57 / 2.54 = 0.23inches
L = 2.36 inches
L = N2 (9R + 10 l) / r2
= 16.47 (+ 9×0.23 10×2.36) / 0232
N2 = 89 laps
Applying the formula to calculate the frequency of resonance of the coil we have here:
L = 1 / (4? 2CF2)
When F = 124khz, C = 0.1μF
L = 1 / (4 x (3142) X0.1×10 2-6 x (124 x 103) 2)
L = 16.47μH
Then, using the formula to find the rpm Wheeler
The N2 = r2 / 9r + 10l
When r = C / 2? = 52 / 2?
== 8.27cm 3.26inches
== L = 0.6 cm 0.24inches
L = N2 (9R + 10 l) / R2
N2 = 16.47 (+ 9×3.26 10×0.24) / 3262
N = 7 Tours
4.3 Amplifier Circuit
A common emitter (CE) transistor amplifier has been used because of its features include:
- Its output resistance is large enough (50k or so)
- His current gain (?) Is high (50 – 300)
- It features high voltage gain of Agenda 1500 and beyond
- It produces very high power gain of about 10,000 times or 40dB.
BC337 Transistor NPN transistor is used.
In a good circuit design amplifier operates normally when
VCE = ½ VCC
Also a CE configuration
VCE = VCC – ICRL
hfe = IC / IB
When VCE = collector emitter voltage
Gain HFE = absolute minimum for the selected transistor is 100
IC = current collector
= Base current IB
So LR = (VCC – VCE) / IC
The voltage gain is given by
AV = ro / Re
When the output resistance ro = scene
Re = resistance of the emitter junction
25mV / IE.
4.4 Technology beat frequency oscillator
The circuit uses two radio frequency oscillators called research and oscillators reference and is granted on the same frequency. the oscillator output is fed into a blender, producing a signal that contains the sum and difference frequency components two input signals.
- The output of the mixer is inserted into a low pass (gain) when the harmonic filter is removed, leaving the difference component frequency to survive, albeit in 0Hz theory, following the departure will be no difference. However, when the metal is introduced in the vicinity of the coil search frequency oscillators of the research is slightly offset, so there is a difference frequency, which is in the audio frequency range, appears in 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 was conducted on follow-up projects to ensure the different phase state and the whole project:
Connections were checked with a multimeter set to continuity to ensure that there is a short circuit. The test was carried out and not short-circuit has been found.
Open circuit test
Different connections have been open-circuit tested and found several meters.
The value of the voltage and current value were measured at each stage and all were found in confirmation with the design specifications.
Test isolation was performed on all circuit units including units that require adequate insulation. For example, the coil used in oscillators.
Performance system and test results
The metal detector was used to test different sizes of metal at different distances of the search coil and obtained the following results.
(I) metal Lager, the height of the sound output by the speaker and the metal, the low output of the speakers – although this also depends on the size of the search coil.
(Ii) The minimum distance between the search for the head and metal, plus the sound output speaker and further, the lower the sound from the speaker, as his death at a certain critical distance the theory that the magnetic field due to search for the head is zero.
The time oscillator (BFO) is one of the principle of principles expressed simply building a reliable and efficient metal detector. Himself While some prices paid for these benefits to mind and understand that.
(I) low sensitivity
(Ii) short-range detection. Well that depends on the size of the search coil.
(Iii) not be able to discriminate between metals
Everything is anything, it is interesting to note that the design and construction of a metal detector is a success. Since the project during the test the desired effect. In particular, this research has made the principle of electromagnetic induction very clear to me and any literate person on average about me. In general, the invention of metal detectors, the effort involved in establishing the metal components in a workshop has been drastically reduced. So banks and the shame of the institution, on the other, their customers has been resolved that some metal detectors are mounted on the door to activate a alarm when the metal is detected in a person tries to enter.
1 Edeka, FP, "Hardware Electronic Design "Tour 2008
2 A textbook of electrical technology by BL and AK Theraja Theraja, S. Chard and Company, 2005.
3 Study of electronic components by Judge Smith (2nd edition), 1999
4 electronic circuit analysis and design by Donald A. Neumann, Mark Grawhill Book Company, USA 1996.
5 amps comparison and special functions, Texas Instruments, a data collection Volume B, Custom Printing Company, 1997.