Design and Implementation of Seismic Sensor (2)

7/28/2019 Design and Implementation of Seismic Sensor (2)

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ABSTRACT

Seismic sensor is nothing but a sensor which detects the seismicwaves occurred due to vibrations. As, now a days seismic waves cause disastrousearth quakes. There is a pressing need to arrange a circuit which is capable ofdetecting vibrations occurred. Generally these seismic waves are recorded onRichter scale.

Here in this arrangement of detecting vibrations, we use piezoelement, which is used to detect vibrations, in simple words it is used to sense thevibrations as sensors.

The lead zirconate crystals present in the piezo element canreadily store current and can release the current when orientations of crystals aredisturbed through mechanical vibrations, IC1 LM741 amplifies signals from piezoelement and high output from IC1 switches on T1. When T1 conducts, trigger pin2of monostable(IC2) NE555 will grounded to give 3 minutes high output.

The high output is used to sound alarm and to light led.

KEYWORDS: - LM741, NE555, PIEZO ELEMENT.

1 |D e s i g n & I m p l e m e n t a t i o n O f S e i s m i c S e n s o r


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CHAPTER ONE

INTRODUCTION

1.1 Overview

There are two basic types of seismic sensors: inertial seismometers which measure

ground motion relative to an inertial reference (a suspended mass), and

strainmeters or extensometers which measure the motion of one point of the

ground relative to another. Since the motion of the ground relative to an inertial

reference is in most cases much larger than the differential motion within a vault

of reasonable dimensions, inertial seismometers are generally more sensitive to

earthquake signals. However, at very low frequencies it becomes increasingly

difficult to maintain an inertial reference, and for the observation of low-order free

oscillations of the Earth, tidal motions, and quasi-static deformations, strainmeters

may outperform inertial seismometers. Strainmeters are conceptually simpler than

inertial seismometers although their technical realization and installation may be

more difficult.

An inertial seismometer converts ground motion into an electric signal but its

properties cannot be described by a single scale factor, such as output volts per

millimeter of ground motion. The response of a seismometer to ground motion

depends not only on the amplitude of the ground motion (how large it is) but also



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on its time scale (how sudden it is). This is because the seismic mass has to be

kept in place by a mechanical or electromagnetic restoring force. When the ground

motion is slow, the mass will move with the rest of the instrument, and the outputsignal for a given ground motion will therefore be smaller. The system is thus a

high-pass filter for the ground displacement. This must be taken into account when

the ground motion is reconstructed from the recorded signal, and is the reason why

we have to go to some length in discussing the dynamic transfer properties of

seismometers.

The dynamic behavior of a seismograph system within its linear range can, like

that of any linear time-invariant (LTI) system, be described with the same degree

of completeness in four different ways: by a linear differential equation, the

Laplace transfer function, the complex frequency response, or the impulse

response of the system. The first two are usually obtained by a mathematical

analysis of the physical system (the hardware). The latter two are directly related

to certain calibration procedures and can therefore be determined from calibration

experiments where the system is considered as a black box (this is sometimes

called an identification procedure). However, since all four are mathematically

equivalent, we can derive each of them either from knowledge of the physical

components of the system or from a calibration experiment. The mutual relations



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between the time-domain and frequency-domain. Practically, the

mathematical description of a seismometer is limited to a certain bandwidth of

frequencies that should at least include the bandwidth of seismic signals. Withinthis limit then any of the four representations describe the system's response to

arbitrary input signals completely and unambiguously. The viewpoint from which

they differ is how efficiently and accurately they can be implemented in different

signal-processing procedures.

In digital signal processing, seismic sensors are often represented with other

methods that are efficient and accurate but not mathematically exact, such as

recursive (IIR) filters. Digital signal processing is however beyond the scope of

this section. A wealth of textbooks is available both on analog and digital signal

processing, for example Oppenheim and Willsky (1983) for analog processing,

Oppenheim and Schafer (1975) for digital processing, and Scherbaum (1996) for

seismological applications.



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1.2 Literature Review

As indicated earlier on, the most commonly used description of a seismograph

response in the classical observatory practice has been the magnification curve,i.e. the frequency-dependent magnification of the ground motion. Mathematically

this is the modulus (absolute value) of the complex frequency response, usually

called the amplitude response. It specifies the steady-state harmonic responsivity

(amplification, magnification, conversion factor) of the seismograph as a function

of frequency. However, for the correct interpretation of seismograms, also the

phase response of the recording system must be known. It can in principle be

calculated from the amplitude response, but is normally specified separately, or

derived together with the amplitude response from the mathematically more

elegant description of the system by its complex transfer function or its complex

frequency response.

While for a purely electrical filter it is usually clear what the amplitude response is

- a dimensionless factor by which the amplitude of a sinusoidal input signal must

be multiplied to obtain the associated output signal - the situation is not always as

clear for seismometers because different authors may prefer to measure the input

signal (the ground motion) in different ways: as a displacement, a velocity, or an

acceleration. Both the physical dimension and the mathematical form of the



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transfer function depend on the definition of the input signal, and one must

sometimes guess from the physical dimension to what sort of input signal it

applies. The output signal, traditionally a needle deflection, is now normally avoltage, a current, or a number of counts.

Calibrating a seismograph means measuring (and sometimes adjusting) its transfer

properties and expressing them as a complex frequency response or one of its

mathematical equivalents. For most applications the result must be available as

parameters of a mathematical formula, not as raw data; so determining parameters

by fitting a theoretical curve of known shape to the data is usually part of the

procedure. Practically, seismometers are calibrated in two steps.

The first step is an electrical calibration in which the seismic mass is excited with

an electromagnetic force. Most seismometers have a built-in calibration coil that

can be connected to an external signal generator for this purpose. Usually the

response of the system to different sinusoidal signals at frequencies across the

system's passband, to impulses, or to arbitrary broadband signals is observed while

the absolute magnification or gain remains unknown. For the exact calibration of

sensors with a large dynamic range such as those employed in modern

seismograph systems, the latter method is most appropriate.



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1.3 Project Organization

This project work presented the design and implementation of seismic sensors for

industrial and domestic purpose using the piezo element and a piezo buzzer withits underlining principle of piezoelectricity. The circuit uses readily available

components and the design is straight forward. A standard piezo sensor is used to

detect vibrations/sounds due to pressure changes. The piezo element acts as a

small capacitor having a capacitance of a few nanofarads. Like a capacitor, it can

store charge when a potential is applied to its terminals. It discharges through

VR1, when it is disturbed.

The project work is organized as follows: chapter two will concentrate on the

hardware description which is most importantly the TL071 JFET op-amp and the

NE555 timer ICs while chapter three looks at piezoelectricity in details. Chapter

four focuses on the design and implementation of the seismic sensor for both

industrial and domestic application with piezoelectricity with detailed explanation

of the project topic in general as chapter five concludes the project work.



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1.4 Circuit Diagram:



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1.5 Components Used:


No.

Name Of Component Specification Quantity

Cost

Gh

1 Resistors R1R2R3R4R5

R6R7R8R9

R10VR1

100k10k

100k330k

1k

470k1M1k

470k10k1M

11111

111111

2 Capacitors C1C2C3C4C5

C6

10F,25V0.1F

100F,25V0.01F

100F,25V10F,25V

111111

3 Transistor T1T2

npn BC548npn BC548

11

4 Light Emitting Diode LED1LED2

GreenRed

11

5 IC1 TL071 low noiseJFET op-amp

1

6 IC2 NE555 Timer 1

7 PZ1 Piezo Buzzer 18 PIEZO ELEMENT 19 SWITCH ON/OFF 1


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CHAPTER TWO

HARDWARE DESCRIPTION

2.1 Introduction

This chapter will focus on the features of the TL071 Low noise JFET single

operational amplifier such as its description, electrical characteristics and its

operations, and further look also at the NE555 Timer IC such as its overview, pin

outs, pin descriptions, operating overview, electrical/environmental characteristics

and monostable and astable operations.

2.2 TL071Low Noise JFET Single Operational Amplifier

2.2.1Description

The TL071 is a high-speed JFET input single operational amplifier. This JFET

input operational amplifier incorporates well matched, high-voltage JFET and

bipolar transistors in a monolithic integrated circuit. The device features high slew

rates, low input bias and offset currents, and low offset voltage temperature

coefficient. The diagrams below show the pin out configuration and can package

of the IC



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(a) (b)

Fig 2.1 (a) can package of TL071 IC, (b) pin connection of Tl071 IC

The following are the description of the individual pin connections of the above IC

as shown in figure 2.1.

1 - Offset null 1

2 - Inverting input

3 - Non-inverting input

4 - VCC-

5 - Offset null 2

6 - Output



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7 - VCC+

8 - N.C.

2.2.2Features of TL071 IC

Tl071 IC is a slightly for powerful JFET single input operational amplifier which

has the following features;

Wide common-mode (up to VCC+) and differential voltage range

Low input bias and offset current

Low noise en = 15nV/ Hz

Output short-circuit protection

High input impedance JFET input stage

Low harmonic distortion: 0.01%

Internal frequency compensation

Latch-up free operation

High slew rate: 16V /s



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All voltage values, except differential voltage, are with respect to the zero

reference level (ground) of the supply voltages where the zero reference level is

the midpoint between VCC+ and VCC. The magnitude of the input voltage mustnever exceed the magnitude of the supply voltage or 15 volts, whichever is less.

Differential voltages are the non-inverting input terminal with respect to the

inverting input terminal. Short-circuits can cause excessive heating. Destructive

dissipation can result from simultaneous short-circuits on all amplifiers. Rth are

typical values. The output may be shorted to ground or to either supply.

Temperature and/or supply voltages must be limited to ensure that the dissipation

rating is not exceeded. Human body model: 100pF discharged through a 1.5k

resistor between two pins of the device, done for all couples of pin combinations

with other pins floating. Machine model: a 200pF cap is charged to the specified

voltage, then discharged directly between two pins of the device with no external

series resistor (internal resistor < 5 ), done for all couples of pin combinations

with other pins floating. Charged device model: all pins plus package are charged

together to the specified voltage and then discharged directly to the ground. The

input bias currents are junction leakage currents which approximately double for

every 10C increase in the junction temperature.

2.3 NE555 Timer IC



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2.3.1Overview

The 555 Timer IC is an integrated circuit (chip) implementing a variety

oftimerand multivibratorapplications. The IC was designed by Hans R.

Camenzind in1970 and brought to market in 1971 by Signetics (later acquired

by Philips). The original name was the SE555 (metal can)/NE555 (plastic DIP)

and the part was described as "The IC Time Machine". It has been claimed that the

555 gets its name from the three 5 k resistors used in typical early

implementations,[2] but Hans Camenzind has stated that the number was

arbitrary. The part is still in wide use, thanks to its ease of use, low price and good

stability. As of 2003, it is estimated that 1 billion units are manufactured every

year.

Depending on the manufacturer, the standard 555 package includes over20 transistors, 2 diodes and 15 resistors on a silicon chip installed in an 8-pin mini

dual-in-line package (DIP-8). Variants available include the 556 (a 14-pin DIP

combining two 555s on one chip), and the 558 (a 16-pin DIP combining four

slightly modified 555s with DIS & THR connected internally, and TR falling edge

sensitive instead of level sensitive).

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Ultra-low power versions of the 555 are also available, such as the 7555 and

TLC555. The 7555 requires slightly different wiring using fewer external

components and less power.

The 555 has three operating modes:

Monostable mode: in this mode, the 555 functions as a "one-shot".

Applications include timers, missing pulse detection, bounce free switches,

touch switches, frequency divider, capacitance measurement, pulse-width

modulation (PWM) etc

Astable - free running mode: the 555 can operate as an oscillator. Uses

include LED and lamp flashers, pulse generation, logic clocks, tone generation,

security alarms,pulse position modulation, etc.

Bistable mode orSchmitt trigger: the 555 can operate as a flip-flop, if the

DIS pin is not connected and no capacitor is used. Uses include bounce free

latched switches, etc.

2.3.2 Pin Outs & Descriptions

The 555 integrated circuit is a highly accurate timing circuit that is capable of

producing either time delays or oscillation.

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Fig 2.2 Pin out diagram of NE555 Timer IC

V+ is the supply voltage. GND is also Ground (0V) connection for supply

voltage. Threshold is an active high input pin that is used to monitor the charging

of the timing capacitor. Control Voltage is used to adjust the threshold voltage if

required. This should be left disconnected if the function is not required. A

0.01uF capacitor to Gnd can be used in electrically noisy circuits. The Trigger is

also an active low trigger input that starts the timer. Discharge is the output pin

that is used to discharge the timing capacitor. Out is known as the Timer output

pin. Reset is also an active low reset pin. Normally connected to V+ if the reset

function is not required.



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Fig 2.3 NE555 Timer IC block diagram

2.3.3 Monostable Operation

The circuit diagram illustrates the monostable configuration of the NE555 Timer

IC.



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Fig 2.4 Monostable configuration of Timer IC NE555

In monostable mode the device produces a 'one shot' pulsed output. The pulse is

started by a taking the trigger input from a high (V+) to a low voltage. Once

triggered the circuit remains in this state even if triggered again during the pulse

interval.

The pulse high time is given by: t = 1.1 x R1 x C1

The high to low voltage transition on the trigger input causes the Flip-Flop to

become set. This releases the short circuit (created by holding of the discharge pin

low) across capacitor C1. At this point the output goes high. Capacitor C1 then

begins to charge and the voltage across it begins to increase. When it reaches 2/3

V+ the Flip-Flop is reset. This causes capacitor C1 to discharge very quickly and

the output goes low.



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Minimum output pulse = 5 S

Maximum output pulse = 5 minutes

R1 minimum resistance = 1K ohm

R1 maximum resistance = 1Mohm

2.3.4 Astable Operation

The circuit diagram illustrates the astable configuration of the NE555 Timer IC.

Fig 2.5 Astable configuration of Timer IC NE555

In astable mode the timer continually triggers itself and runs as a multi vibrator.

This results in a continually repeating signal being generated on the output pin.

The external capacitor C1 charges through both R1 and R2 but discharges only



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through R2. Therefore the duty cycle is determined by the ratio of this resistor. If

the value of the two resistors is the same the duty cycle will be 50% and a square

wave will be output.

The 'High' output time is given by: t1 = 0.693 (R1 + R2) x C1

The 'Low' output time is given by: t2 = 0.693 (R2) x C1

Therefore the total period is given by: T = t1 + t2 = 0.693 (R1 + R2) x C1

The frequency of oscillation is given by: f = 1 / T = 1.44 / ((R1 + R2) x C1)

2.3.5 Example Applications

Joystick interface circuit using quad timer 558

The original IBM personal computer used a quad timer 558 in monostable (or

"one-shot") mode to interface up to two joysticks to the host computer. In the

joystick interface circuit of the IBM PC, the capacitor(C) of the RC network (see

Monostable Mode above) was generally a 10nF capacitor. The resistor(R) of the

RC network consisted of thepotentiometerinside the joystick along with an

external resistor of 2.2 kilo ohms. The joystick potentiometer acted as a variable

resistor. By moving the joystick, the resistance of the joystick increased from a

small value up to about 100 kilo ohms. The joystick operated at 5 V.

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Software running in the host computer started the process of determining the

joystick position by writing to a special address (ISA bus I/O address 201h). This

would result in a trigger signal to the quad timer, which would cause the capacitor(C) of the RC network to begin charging and cause the quad timer to output a

pulse. The width of the pulse was determined by how long it took the C to charge

up to 2/3 of 5 V (or about 3.33 V), which was in turn determined by the joystick

position.

Software running in the host computer measured the pulse width to determine the

joystick position. A wide pulse represented the full-right joystick position, for

example, while a narrow pulse represented the full-left joystick position.

Atari Punk Console

One ofForrest M. Mims III's many books was dedicated to the 555 timer. In it, hefirst published the "Stepped Tone Generator" circuit which has been adopted as a

popular circuit, known as the Atari Punk Console, by circuit benders for its

distinctive low-fi sound similar to classic Atari games. The 555 can be used to

generate a variable PWM signal using a few external components. The chip alone

can drive small external loads or an amplifying transistor for larger loads.

CHAPTER THREE

PIEZOELECTRICITY

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3.1 Introduction

In this chapter is a focus on piezoelectricity as the backbone behind the operation

of this proposed circuit. We are going to look at the history of piezoelectricity,

features of piezo element, buzzer, the proposed circuit diagram and some

applications of the piezoelectricity.

3.2 History of Piezoelectricity

3.2.1definition of Piezoelectricity

Piezoelectricity is a form of electricity created when certain crystals are bent or

otherwise deformed. These same crystals can also be made to bend slightly when a

small current is run through them, encouraging their use in instruments for which

great degrees of mechanical control are necessary. This is called converse

piezoelectricity. For example, scanning tunneling microscopes (STMs) use

piezoelectric crystals to scan the surface of a material and create images of great

detail. Piezoelectricity is related topyroelectricity, in which a current is created by

heating or cooling the crystal. The property of piezoelectricity is dictated by both

the atoms in the crystal and the particular way in which that crystal was formed.

Some of the first substances that were used to demonstrate piezoelectricity

are topaz, quartz, tourmaline, and cane sugar. Today, we know of many crystals

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which are piezoelectric, some of which can even be found in human bone. Certain

ceramics andpolymers have exhibited the effect as well.

A piezoelectric crystal consists of multiple interlocking domains which have

positive and negative charges. These domains are symmetrical within the crystal,

causing the crystal as a whole to be electrically neutral. When stress is put on the

crystal, the symmetry is slightly broken, generating voltage. Even a tiny bit of

piezoelectric crystal can generate voltages in the thousands.

Piezoelectricity is used in sensors, actuators, motors, clocks, lighters,

and transducers. A quartz clockuses piezoelectricity, as does any cigarette lighter

without a flint. Medical ultrasound devices create high-frequency acoustic

vibrations using piezoelectric crystals. Piezoelectricity is used in some engines to

create the spark which ignites the gas. Loudspeakers use piezoelectricity to

convert incoming electricity to sound. Piezoelectric crystals are used in many

high-performance devices to apply tiny mechanical displacements on the scale of

nanometers. Even though a piezoelectric crystal never deforms by more than a few

nanometers when a current is run through it, the force behind this deformation is

extremely high, on the order of mega newtons. This deformational power is used

in mechanics experiments and for aligning optical elements many times heavierthan the piezoelectric crystal itself.

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3.2.2 History

The first experimental demonstration of a connection between macroscopic

piezoelectric phenomena and crystallographic structure was published in 1880 by

Pierre and Jacques Curie. Their experiment consisted of a conclusive measurement

of surface charges appearing on specially prepared crystals (tourmaline, quartz,

topaz, cane sugar and Rochelle salt among them) which were subjected to

mechanical stress. These results were a credit to the Curies' imagination and

perseverance, considering that they were obtained with nothing more than the foil,

glue, wire, magnets, and a jewelers saw. In the scientific circles of the day, this

effect was considered quite a "discovery," and was quickly dubbed as

"piezoelectricity" in order to distinguish it from other areas of scientific

phenomenological experience such as "contact electricity" (friction generated

static electricity) and "pyroelectricity" (electricity generated from crystals by

heating).

The Curie brothers asserted, however, that there was a one-to-one correspondence

between the electrical effects of temperature change and mechanical stress in a

given crystal, and that they had used this correspondence not only to pick the

crystals for the experiment, but also to determine the cuts of those crystals. To

them, their demonstration was a confirmation of predictions which followed



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naturally from their understanding of the microscopic crystallographic origins of

pyroelectricity.

The Curie brothers did not, however, predict that crystals exhibiting the direct

piezoelectric effect (electricity from applied stress) would also exhibit the

converse piezoelectric effect (stress in response to applied electric field). This

property was mathematically deduced from fundamental thermodynamic

principles by Lippmann in 1881. The Curies immediately confirmed the existence

of the "converse effect," and continued on to obtain quantitative proof of the

complete reversibility of electro-elasto-mechanical deformations in piezoelectric

crystals.

1882 1917 At this point in time, after only two years of interactive work within

the European scientific community, the core of piezoelectric applications science

was established: the identification of piezoelectric crystals on the basis of

asymmetric crystal structure, the reversible exchange of electrical and mechanical

energy, and the usefulness of thermodynamics in quantifying complex

relationships among mechanical, thermal and electrical variables.

In the following 25 years (leading up to 1910), much more work was done to

make this core grow into a versatile and complete framework which defined

completely the 20 natural crystal classes in which piezoelectric effects occur, and



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defined all 18 possible macroscopic piezoelectric coefficients accompanying a

rigorous thermodynamic treatment of crystal solids using appropriate tensorial

analysis. In 1910 Voigt's "Lerbuch der Kristallphysik" was published, and itbecame the standard reference work embodying the understanding which had been

reached.

During the 25 years that it took to reach Voigt's benchmark, however, the world

was not holding its breath for piezoelectricity. A science of such subtlety as to

require tensorial analysis just to define relevant measurable quantities paled by

comparison to electro-magnetism, which at the time was maturing from a science

to a technology, producing highly visible and amazing machines. Piezoelectricity

was obscure even among crystallographers; the mathematics required to

understand it was complicated; and no publicly visible applications had been

found for any of the piezoelectric crystals. The first serious applications work on

piezoelectric devices took place during World War I. In 1917, P. Langevin and

French co-workers began to perfect an ultrasonic submarine detector. Their

transducer was a mosaic of thin quartz crystals glued between two steel plates (the

composite having a resonant frequency of about 50 KHz), mounted in a housing

suitable for submersion. Working on past the end of the war, they did achieve their

goal of emitting a high frequency "chirp" underwater and measuring depth by



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timing the return echo. The strategic importance of their achievement was not

overlooked by any industrial nation, however, and since that time the development

of sonar transducers, circuits, systems, and materials has never ceased.

3.3 Applications

Piezoelectric sensors have proven to be versatile tools for the measurement of

various processes. They are used forquality assurance,process control and for

research and development in many different industries. Although the piezoelectriceffect was discovered by Curie in 1880, it was only in the 1950s that the

piezoelectric effect started to be used for industrial sensing applications. Since

then, this measuring principle has been increasingly used and can be regarded as a

mature technology with an outstanding inherent reliability. It has been

successfully used in various applications, such as in medical, aerospace,

nuclearinstrumentation, and as a pressure sensor in the touch pads of mobile

phones. In the automotive industry, piezoelectric elements are used to monitor

combustion when developing internal combustion engines. The sensors are either

directly mounted into additional holes into the cylinder head or the spark/glow

plug is equipped with a built in miniature piezoelectric sensor.

The rise of piezoelectric technology is directly related to a set of inherent

advantages. The high modulus of elasticity of many piezoelectric materials is

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comparable to that of many metals and goes up to 105 N/m. Even though

piezoelectric sensors are electromechanical systems that react to compression, the

sensing elements show almost zero deflection. This is the reason why piezoelectricsensors are so rugged, have an extremely high natural frequency and an excellent

linearity over a wide amplitude range. Additionally, piezoelectric technology is

insensitive to electromagnetic fields and radiation, enabling measurements under

harsh conditions. Some materials used (especially gallium

phosphate ortourmaline) have an extreme stability even at high temperature,

enabling sensors to have a working range of up to 1000C. Tourmaline

showspyroelectricity in addition to the piezoelectric effect; this is the ability to

generate an electrical signal when the temperature of the crystal changes. This

effect is also common topiezoceramic materials.

One disadvantage of piezoelectric sensors is that they cannot be used for truly

static measurements. A static force will result in a fixed amount of charges on the

piezoelectric material. While working with conventional readout electronics,

imperfect insulating materials, and reduction in internal sensorresistance will

result in a constant loss ofelectrons, and yield a decreasing signal. Elevated

temperatures cause an additional drop in internal resistance and sensitivity. The

main effect on the piezoelectric effect is that with increasing pressure loads and

temperature, the sensitivity is reduced due to twin-formation. While quartz sensors

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need to be cooled during measurements at temperatures above 300C, special

types of crystals like GaPO4 gallium phosphate do not show any twin formation

up to the melting point of the material itself.

However, it is not true that piezoelectric sensors can only be used for very fast

processes or at ambient conditions. In fact, there are numerous applications that

show quasi-static measurements, while there are other applications with

temperatures higher than 500C.

Piezoelectric sensors are also seen in nature. Drybone is piezoelectric, and is

thought by some to act as a biological force sensor.

3.4 Principle of Operation

Depending on how a piezoelectric material is cut, three main modes of operation

can be distinguished: transverse, longitudinal, and shear.

Transverse effect

A force is applied along a neutral axis (y) and the charges are generated along the

(x) direction, perpendicular to the line of force. The amount of charge depends on

the geometrical dimensions of the respective piezoelectric element. When

dimensions a,b,c apply,

Cx = dxyFyb / a, (eqn. 3.1)

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Where a is the dimension in line with the neutral axis, b is in line with the charge

generating axis and dis the corresponding piezoelectric coefficient.

Longitudinal effect

The amount of charge produced is strictly proportional to the applied force and is

independent of size and shape of the piezoelectric element. Using several elements

that are mechanically in series and electrically inparallel is the only way to

increase the charge output. The resulting charge is

Cx = dxxFxn, (eqn. 3.2)

Where dxx is the piezoelectric coefficient for a charge in x-direction released by

forces applied along x-direction (inpC/N).Fx is the applied Force in x-direction

[N] and n corresponds to the number of stacked elements.

Shear effect

Again, the charges produced are strictly proportional to the applied forces and are

independent of the elements size and shape. Forn elements mechanically in series

and electrically in parallel the charge is

Cx = 2dxxFxn. (eqn. 3.3)

In contrast to the longitudinal and shear effects, the transverse effect opens the

possibility to fine-tune sensitivity on the force applied and the element dimension.

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3.5 Electrical Properties

A piezoelectric transducer has very high DC output impedance and can be

modeled as a proportional voltage source and filter network. The voltage Vat the

source is directly proportional to the applied force, pressure, or strain. The output

signal is then related to this mechanical force as if it had passed through the

equivalent circuit.

Fig 3.1 Frequency response of a piezoelectric sensor; output voltage vs

applied force

A detailed model includes the effects of the sensor's mechanical construction and

other non-idealities.[3] The inductanceLm is due to the seismic mass and inertia of

the sensor itself. Ce is inversely proportional to the mechanical elasticity of the

sensor. C0 represents the static capacitance of the transducer, resulting from an

inertial mass of infinite size. Ri is the insulation leakage resistance of the

transducer element. If the sensor is connected to a load resistance, this also acts in

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parallel with the insulation resistance, both increasing the high-pass cutoff

frequency.

Fig 3.2 Equivalent circuit of sensor

For use as a sensor, the flat region of the frequency response plot is typically used,

between the high-pass cutoff and the resonant peak. The load and leakage

resistance need to be large enough that low frequencies of interest are not lost.

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Fig 3.3 Schematic symbol and electronic model of a piezoelectric sensor

A simplified equivalent circuit model can be used in this region, in

which Cs represents the capacitance of the sensor surface itself, determined by the

standard formula for capacitance of parallel plates. It can also be modeled as a

charge source in parallel with the source capacitance, with the charge directly

proportional to the applied force, as above.

3.6 Proposed Circuit Diagram

The circuit diagram below illustrates or shows the proposed circuit diagram for

implementation of the seismic sensor project.

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Fig 3.4 Proposed project circuit diagram

CHAPTER FOUR

DESIGN & IMPLEMENTATION OF SEISMIC SENSOR

4.1 Introduction

This chapter will concentrate on the general architecture and design, circuit

description and operation, come design calculations, the operational flow chart

and the data sheet for the design and implementation of the seismic sensor.

4.2 General Architecture of the Seismic Sensor

The diagram below shows the general architecture of the proposed circuit for the

project.

Fig 4.1 General architecture of seismic sensor using a piezo element


XLV1

Input

PIEZO

BUZZER/SPEAKER

AMPLIFIER

CIRCUIT/UNITPIEZO

ELEMEN

T

TIMER

CIRCUIT/UNIT

PIEZO

ELEMEN

T

AMPLIFIER

CIRCUIT/UNIT


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4.3 Circuit Diagram & Description

The below diagram shows the circuitry for the seismic sensor with its description

below.

Fig 4.2 Circuit diagram for the seismic sensor

The circuit uses readily available components and the design is straight-forward.

A standard piezo sensor is used to detect vibrations/sounds due to pressure



36/41

changes. The piezo element acts as a small capacitor having a capacitance of a few

nanofarads. Like a capacitor, it can store charge when a potential is applied to its

terminals. It discharges through VR1, when it is disturbed. In the circuit, ICTLO71 (IC1) is wired as a differential amplifier with both its inverting and non-

inverting inputs tied to the negative rail through a resistive network comprising

R1, R2 and R3. Under idle conditions (as adjusted by VR1), both the inputs

receive almost equal voltages, which keeps the output low.

TLO71 is a low-noise JFET input op-amp with low input bias and offset current.

The BIFET technology provides fast slew rates. Capacitor C1 is provided in the

circuit to keep the differential input of IC1 for better performance.

4.4 Circuit Operation

When the piezo element is disturbed (by even a slight movement), it discharges

the stored charge. This alters the voltage level at the inputs of IC1 and the output

momentarily swings high as indicated by green LED1. This high output is used to

trigger switching transistor T1, which triggers monostable IC2. The timing period

of IC2 is determined by R7 and C5. With the shown values, it will be around two

minutes. The high output from IC2 activates T2 and the buzzer starts beeping

along with red light indication from LED2.



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4.4.1 Design Calculation

The below calculation is the basic design calculations for the transistors T1 and T2

as well as the timing period for the circuit to produce its beeping sound along with

the red LED.

Biasing Voltage = 1.7v (Theoretical Value)

Vcc = VBE + IRRL

T1; IB = 1.7/R4

= 1.7/330

= 0.0052 A,

T2; IB = 1.7/R8

= 1.7/1 *103

= 0.0017 A,

The timing period of IC2 is determined by R7 and C5.

T = 1.11 *R5 * C7

= 1.11 * 1 x 106 * 100 x10-6



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= 111 seconds.

4.5 Flow Chart

The chart below shows the flow control or processes of operation of the seismic

sensor.


DISTURBANC

E OF PIEZO

ELEMENT

IC1

VOLTAGE

LEVEL IS

ALTERED

SWITCHING

TRANSISTORT2 IS

TRIGGERED

MONOSTABLE

TO IC2 trigger

HIGH OUTPUT

OF IC2

ACTIVATES T2

BUZZER

STARTS TO

BEEP


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Fig 4.3 Flow chart for seismic sensor using piezo element

CHAPTER FIVE

CONCLUSSION & FUTURE WORKS

In conclusion, the disturbance made by any moving object using the piezo element

seismic sensor implemented. The disturbance discharges the stored charge. This

caused the IC1to produce a high output. This high output is used to trigger

switching transistor IC2 and the vibration or sound or movement made is caused

the buzzer to beep.

The sound and vibration caused movements can also be detected by new and

growing technology.



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REFERENCES

[1] van Roon, "pg. 1"

[2] Scherz, Paul (2000) "Practical Electronics for Inventors," p. 589. McGraw-Hill/TAB Electronics. ISBN: 978-0070580787. Retrieved 2010-04-05.

[3] Ward, Jack (2004). The 555 Timer IC - An Interview with HansCamenzind. The Semiconductor Museum. Retrieved 2010-04-05.

[4] van Roon, Fig 3 & related text.[5] Jung, Walter G. (1983) "IC Timer Cookbook, Second Edition," pp. 4041.

Sams Technical Publishing; 2nd ed. ISBN: 978-0672219320. Retrieved2010-04-05.

[6] van Roon, Chapter "Monostable Mode."

[7] van Roon Chapter: "Astable operation."

[8] Engdahl, pg 1.

[9] Engdahl, "Circuit diagram of PC joystick interface"

[10] Engdahl, "Joystick construction".

[11] Engdahl, "PC analogue joystick interface".

[12] Eggebrecht, p. 197.

[13] Eggebrecht, pp. 197-9

[14] Piezocryst website. Retrieved 2006-06-02.

[15] "Interfacing Piezo Film to Electronics" (PDF).Measurement Specialties.March 2006. Retrieved 2007-12-02.

http://www.sentex.ca/~mec1995/gadgets/555/555.htmlhttp://en.wikipedia.org/wiki/McGraw-Hillhttp://en.wikipedia.org/wiki/McGraw-Hillhttp://en.wikipedia.org/w/index.php?title=TAB_Electronics&action=edit&redlink=1http://www.semiconductormuseum.com/Transistors/LectureHall/Camenzind/Camenzind_Page2.htmhttp://www.semiconductormuseum.com/Transistors/LectureHall/Camenzind/Camenzind_Page2.htmhttp://www.semiconductormuseum.com/http://www.epanorama.net/documents/joystick/pc_joystick.html#introductionhttp://www.epanorama.net/documents/joystick/pc_joystick.html#pc_interfacehttp://www.meas-spec.com/myMeas/download/pdf/english/piezo/Interfacing%20to%20Electronics.pdfhttp://www.sentex.ca/~mec1995/gadgets/555/555.htmlhttp://en.wikipedia.org/wiki/McGraw-Hillhttp://en.wikipedia.org/wiki/McGraw-Hillhttp://en.wikipedia.org/w/index.php?title=TAB_Electronics&action=edit&redlink=1http://www.semiconductormuseum.com/Transistors/LectureHall/Camenzind/Camenzind_Page2.htmhttp://www.semiconductormuseum.com/Transistors/LectureHall/Camenzind/Camenzind_Page2.htmhttp://www.semiconductormuseum.com/http://www.epanorama.net/documents/joystick/pc_joystick.html#introductionhttp://www.epanorama.net/documents/joystick/pc_joystick.html#pc_interfacehttp://www.meas-spec.com/myMeas/download/pdf/english/piezo/Interfacing%20to%20Electronics.pdf


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[16] Alfredo Vzquez Carazo (January 2000).Novel Piezoelectric Transducersfor High Voltage Measurements. Universitat Politcnica de Catalunya. pp.242.

[17] Karki, James (September 2000). "Signal Conditioning PiezoelectricSensors" (PDF). Texas Instruments. Retrieved 2007-12-02.

[18] Ludlow, Chris (May 2008). "Energy Harvesting with PiezoelectricSensors" (PDF). Mide Technology. Retrieved 2008-05-21.

[19] B. L kakrati and A. K fsator, PLC, 24th Edition, Scand and Company,

New Delhi, 2000.

[20] J. B Gupta, Electrical Technology, 12th Edition, S. K Kataria and Sons,

Delhi, 2003.

[21] D. G. Fink and H. W. Beaty, Standard Handbook for Electrical Engineers,13thEdition, McGraw Hill, Singapore, 1993.

[22] J. O. Bird and P. J Chivers, Engineering and Physical Science PocketBook, Newnew 1995.

[23] H. Uppal , Electrical Power System, 3rd Edition, New Delhi, India, 1995.
http://focus.ti.com/lit/an/sloa033a/sloa033a.pdfhttp://focus.ti.com/lit/an/sloa033a/sloa033a.pdfhttp://www.mide.com/pdfs/vibration_harvesting_conference_2008.pdfhttp://www.mide.com/pdfs/vibration_harvesting_conference_2008.pdfhttp://focus.ti.com/lit/an/sloa033a/sloa033a.pdfhttp://focus.ti.com/lit/an/sloa033a/sloa033a.pdfhttp://www.mide.com/pdfs/vibration_harvesting_conference_2008.pdfhttp://www.mide.com/pdfs/vibration_harvesting_conference_2008.pdf

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Design and Implementation of Seismic Sensor (2)