Tittu reserach paper

IMPROVING THE ACCURACY OF VELOCITY WAVEFORM USING

TRANSFER FUNCTION OBTAINED BY GEOPHONE AND

ACCELEROMETER

TITTU BABU

Curtin University, Western Australian School of Mines

(WASM), Kalgoorlie WA, Australia

1. ABSTRACT: In order to break rocks at mines blasting operations are done. Along with rock

breakage blasting also produces unwanted by products such as air blast, seismic waves, noise and

fly rocks. Seismic waves result in ground vibrations .Noise and ground vibrations have a wider

impact on the environment and the people .When the vibration occurs each ground particle

possess a velocity and the maximum velocity is termed as Peak Particle Velocity (PPV).The

intensity of vibration is measured by PPV. If the ground vibration exceeds the PPV limit potential

damage will occur to the structure.So it is necessary to measure the ground vibrations precisely

inorder to avoid any kind of damages. In order to measure ground vibrations , measuring

instruments called Blast Seismographs ( geophone or accelerometer ) are used.Usually at mines,

blast vibrations are measured by geophones .But the measurement by a geophone is not precise as

that of an accelerometer and the usage of accelerometers at mines for vibration measurement is

limited due to its cost. The project objective is to improve the accuracy of velocity waveform

using transfer function obtained by geophone and accelerometer. For carrying out this research

project the blast vibrations produced by KCGM (Kalgoorlie Consolidated Gold Mine) will be

measured at WASM laboratory. Accelerometer selected for this research project is TEAC 708LF

and geophone selected for this project is PC-801 LPC.In order to acquire the same vibration both

geophone and accelerometer are attached together. Almost twenty six blast vibration readings are

taken. Only data with same units can be compared. So the acceleration data is integrated to

convert it into velocity data. Comparison of data in time domain has no meaning, so it is to be

converted to frequency domain. Then these values in time domain is converted to frequency

domain using FFT in OriginPro7J software. Then transfer function is obtained by dividing the

integrated acceleration data with geophone data. Finally in order to improve the accuracy of

velocity waveform, it is multiplied with the geophone data. Then this newly obtained waveform is

compared with the corresponding accelerometer and geophone data to obtain the desired result.

Finally suitable conclusions in support of the result are derived and it shows the degree of

accuracy of the final result.

Improving the accuracy of velocity waveform using transfer function obtained by geophone and accelerometer

Tittu Bbau 16320587 Curtin University, Western Australian School of Mines (WASM), Kalgoorlie WA, Australia 2

2. INTRODUCTION: Blasting operations are done in mines for rock breakage. Along with rock breakage

blasting also produces unwanted by products such as air blast, seismic waves, noise and fly rocks.

Seismic waves result in ground vibrations. Ground vibrations can produce a huge impact on the

environment by creating discomfort to the people and potential damage to the nearby structures. The

factor responsible for damages induced by ground vibration is its Peak Particle Velocity (PPV).Each

structure has a particular level of peak particle velocity(PPV).If the ground vibration exceeds the PPV

limit, potential damages will occur to the structure.So it is necessary to measure the ground vibrations

precisely inorder to avoid any kind of damages. In order to measure ground vibrations, measuring

instruments called Blast Seismographs are used.

Geophone and accelerometer are the commonly used blast seismographs.The out put of a geophone is

velocity waveform and that of an accelerometer is acceleration waveform. A geophone is a kind of motion

transducer with moving coil and a magnet and it is highly sensitive in nature. It converts the movement or

displacement produced in the ground into voltage and that voltage may be recorded at a recording station.

Accelerometer works on the principle of simple harmonic motion of a damped mass.

Usually in mines geophones are used for vibration measurement.It is due to the fact that geophones are

cheap compared to accelerometers.Eventhough geophones are cheap, vibration measured by geophones

are not precise when compared to an accelerometer. There lies the relevance of this research project.As

already stated that the blast vibration measurements should be precisely done inorder to avoid damages

associated with it.In order to carryout precise vibration measurement with a geophone , its accuracy is to

be improved.The aim of this research project is how to improve the accuracy of velocity waveform of a

geophone so that so that blast vibrations can be accurately measured.



3. METHODOLOGY: This research project aims at

improving the accuracy of velocity waveform of

geophone using transfer function obtained by

geophone and accelerometer. For carrying out

this research project the blast vibrations

produced by KCGM will be measured at WASM

laboratory. The KCGM Super pit is one of the

largest open pit gold mines in Australia. It is

located in the south east edge of Kalgoorlie,

Western Australia.

The main instruments used in this project are

accelerometer, geophone, amplifier, data logger

and a computer system. When the geophone is

subjected to blast vibrations an output voltage is

produced which is directly proportional to the

velocity of blast vibration. Similarly when the

accelerometer is subjected to blast vibrations the

output voltage produced is directly proportional

to the acceleration of blast vibration. After

measurement of blast vibrations the output

obtained from geophone is velocity waveform

and the output obtained from an accelerometer is

acceleration waveform. The output obtained

from a geophone is not precise when compared it

with an accelerometer. In order to compare the

output of geophone and accelerometer, both of

them will be attached together and will be

subjected to the same vibration.

The type of accelerometer used in this research

project is Touch 708LF.Geophone used in this

research project is PC-801 LPC, manufactured

by Oyo Corporation and it has a natural

frequency of 4.5Hz.The analog signal from the

geophone and accelerometer is collected by data

logger or data recorder. It acts an interface

between a personal computer and the vibration

measuring instrument. They have the ability to

collect data on a 24 hour basis. In the data logger

the analog to digital signal conversion takes

place.

Once the blasting took place corresponding

vibration is produced .Then these vibrational

waveforms are detected using a geophone and

accelerometer .Finally they are recorded using

the OPS software .The measured vibrational

waveforms are stored as CSV files in the

computer. The stored CSV files are then

subjected to various calculations in order to get

the desired result. In this chapter all the steps

related to research method and experimental

design are explained in detail under various sub

titles.

3.1 INSTRUMENTS USED

3.1.1 GEOPHONE

A geophone is a kind of motion transducer

which is highly sensitive in nature. It consists of

case (or housing), coil, magnet, a leaf spring and

a cylinder. The main part of a geophone is its

housing. The coil and the magnet assembly are

enclosed in the housing. The leaf spring supports

the coil mass and it helps in the axial movement

of the coil relative to the magnet. As a result of

ground vibrations the displacement produced in

the ground will be transmitted to the casing in



which the magnet is mounted .The magnet

moves while the coil remains stationary. Thus

the magnetic flux linked with the coil changes

.The relative motion between the coil and

magnet causes a voltage to be generated across

the coil windings. Thus the geophone operates

according to the Faradays law of electromagnetic

induction. Vα∂x

∂t .The output voltage produced is

directly proportional to the velocity .When the

frequency of a recorded waveform is higher than

the natural frequency of a geophone, the proof

mass displacement will be directly proportional

to the ground displacement .At higher

frequencies the output voltage produced by a

geophone is directly proportional to the ground

velocity. The geophone used in this research

project is PC-801 LPC. It is manufactured by

Oyo Corporation .Its natural frequency is 4.5 Hz.

The sensitivity of this geophone is 1 mV/m/s.

Figure 1-Geophone PC-801 LPC

3.1.2 ACCELEROMETER

Accelerometers are sensors that can detect

acceleration. It works on the principle of simple

harmonic motion. The vibration measurement by

an accelerometer is more precise than that of a

geophone. Accelerometers are of different types

such as capacitive, piezoelectric, piezoresistive,

strain gauge based, servo accelerometers etc. In

this project only piezoelectric accelerometer is

used. The main components of a piezoelectric

accelerometer are accelerometer base, center

post, seismic mass and piezoelectric element. A

piezoelectric accelerometer consists of base,

seismic mass, center post and piezoelectric

element. Out of this, the basic element is its

seismic mass and its active element is

piezoelectric material. One side of the

piezoelectric material is attached to the center

post at accelerometer base and the other side to

the seismic mass. The seismic mass is mounted

to the case of the accelerometer. When the body

of the accelerometer is subjected to vibration, the

seismic mass attached to the piezoelectric

crystals moves. But it actually wants to stay in

its original place due to inertia force. So the

compression and stretching of the piezoelectric

material will takes place .When a piezoelectric

material is subjected to a compression or shear

force correspondingly an output charge

proportional to the applied force will be

produced. Thus the force which causes the

movement of the seismic mass or piezoelectric

material is the product of acceleration and



seismic mass (As per Newton’s second law of

motion F = ma).Since the seismic mass is

constant the output produced will be

proportional to the acceleration of the mass. The

accelerometer used in this research project is

TEAC 708 LF manufactured by Teach

Instruments Corporation Japan. It has range of ±

150 G. Sensitivity of this accelerometer is 9.97

mV/G and the frequency response varies from

0.2 to 22000Hz.

Figure 2-Accelerometer TEAC 708 LF

3.1.3 AMPLIFIER

The output voltage produced by an

accelerometer is not quite good enough for

measurement .So it has to be amplified or

boosted up to the required level. So an amplifier

is used to perform this job. The amplifier used in

this research project is TEAC SA- 611 Charge

Amplifier. SA- 611 is mainly used for

piezoelectric accelerometers (for both charge and

pre-amplifier type of accelerometers).Its

sensitivity can be set by a three digit digital

switches and it is easy to set up for different

accelerometer sensors. This amplifier is compact

and light weight .It can be operated with three

types of power supplies such as built in batteries

(4 AA batteries), external dc and ac adaptor. It

has two types of inputs .The first one is

‘CHARGE’ for charge type sensors and second

is ‘FET’ for IEPE type sensors.

Figure 3- TEAC SA- 611 Charge Amplifier

SA-611 main specifications

Input Switched Charge Type or

IEPE Type

Sensitivity Setting Three Digits Digital Switch

Input Ranges 1, 10, 100

Output Filter Low Pass Filter(LPF) : 1kHz,

10kHz

High Pass Filter(HPF) :5Hz

Calibration Voltage

(CAL)

Rectangular Wave

200Hz±20Hz,

Current Sources 0.5mA, 4mA,24V DC



3.1.4 DATA LOGGER AND COMPUTER

Geophone and accelerometer transmit

continuous analog signal A computer cannot

detect analog signal, so a data logger is used to

convert the anlog signal to digital signal. It is

impossible and inefficient to record every bit of

transmitted data. So the data collection

instrument (data logger or data recorder) is to be

manipulated in order to get the readings at

specific intervals. Three important parameters

are to be controlled in data logger in order to

obtain accurate measurement. They are sampling

frequency, sampling time and number of samples.

A data logger is an instrument which can record

the measured data over time .they can be used in

interface with a personal computer. Thus it can

act as a local interface device with a computer.

Data loggers are generally used for wide range

of applications. The main components of a data

logger are input channel, analog to digital

convertor, microprocessor, memory, power

supply, data output port, weatherproof enclosure

and software. The output from the geophone and

accelerometer are connected to the input channel

of data logger. The channel composed of

circuitry design which is specially designed to

guide a sensor signal (output voltage of

geophone and accelerometer) to data logger

processor .Usually a data logger has four to eight

channels. The next main component is analog to

digital convertor. It converts the analog signal

obtained from the sensors (geophone and

accelerometer) to digital signal. Microprocessor

is a basically a logical circuit which has the

ability to process the necessary basic instructions

to run a computer or a data logger. Then the

measured data are recorded in the memory of

data logger. Data logger uses two types of

memory such as RAM (Random access Memory)

and EEPROM (Electronically Erasable and

Programmable Read Only Memory).Another

unique feature of a data logger is its low power

requirement. Most data logger requires a 12 V dc

power. But the one used in this research project

utilizes ac power for its working. A data logger

communicates with a computer through a serial

port. It allows the data to get transfer in a series

to the computer. Some kinds of data loggers are

embedded with special software in order to get

synchronized with the computer. Finally using

the OPS software the measured data are recorded

and stored in the computer as CSV files.

Figure 4-TEAC Data logger

3.2 EXPERIMENTAL SET UP

As already stated that in order to obtain the

project objective transfer function is required. So

the transfer function between a geophone and

accelerometer is to be obtained. Thus for the

sake of this purpose both the instruments are

attached together so that they can acquire the

same blast vibration. The site selected to carry

out this research project was a small area located

close to the geology building



Figure 5-geophone and accelerometer attached together

After attaching the geophone and accelerometer

together, output of the accelerometer is

connected to the amplifier .From the amplifier

connection goes to the data logger. On the mean

while the output of the geophone is connected

directly to the data logger. Finally the output of

the data logger is connected to the computer.

Amplifier is very essential to boost the output

signal of an accelerometer. Figure 6 shows the

schematic diagram of experimental set up

Figure 6-Experimental set up

3.4 OBTAINING THE AMPLIFICATION FACTOR

The next step, after the experimental set up, is

obtaining the amplification factor. The type of

amplifier used in this research project is TEAC

SA-611 charge amplifier. An amplifier is used to

increase or amplify the power of a signal. It

performs this job by acquiring energy from the

power supply and it controls the output to match

with the shape of the input signal but with

greater amplitude. An accelerometer output is

not quite strong enough to detect and measure

.So it has to be amplified up to a certain level to

make it easy to detect and measure. In order to

obtain the amplification factor some connection

rearrangements are done in the experimental set

up. It is shown clearly in figure 7.

Figure 7-Experimental set up to obtain amplification

factor

Figure 7 shows the experimental set up to obtain

the amplification factor. In order to obtain this

some rearrangements are done in the previous

experimental set up connections. Accelerometer

is detached from the geophone. Geophone output

has two connection leads. One connection wire

goes directly to the data logger and the other

connection wire is connected to the data logger

via an amplifier. Then the geophone is subjected

to vibrational input and corresponding output is

obtained and recorded. Thus two output

waveforms are obtained. The first one is the

native one and the second one is the magnified

or amplified one. The amplification factor is

obtained by dividing the amplified output

waveform with the normal output waveform. So



after careful calculations and considerations the

amplification factor is obtained as 10.Thus it can

be concluded that the accelerometer data

(acceleration waveform) is amplified ten times

by the amplifier.

3.5 MEASURING THE BLAST VIBRATIONS

The blast vibrations from KCGM are recorded

using the OPS software. It is one of the best

professional and functional blast wave recording

software. Before taking measurements all the

necessary settings in the software should be

done. The first step is to set up the range. It is

essential to define the range of blast waves. At

first the range was set as 500 mV for the first

channel and 200 mv for the second channel

.Later on it was identified as 500 mV was too

large for the blast vibration waves which would

make the recorded wavelet too much steady .So

it would be too difficult to analyse. Finally the

range for the first and second channel was set as

200 mv and 100 mV respectively. This newly

selected range was absolutely perfect to offer the

exact wavelet for the analysis. The trigger level

was set as 1% (1 % of 200 mV = 2 mV).The

filter type selected was low pass filter. Then the

filter frequency was set up. It is the filter

frequency which decides up to what range of

frequency an instrument can detect and record.

Filter frequency was set as 500 Hz, so that blast

vibrations with frequency above 500 Hz will not

be recorded. Next step was to determine the

sampling frequency. Sampling frequency is

defined as the number of samples per unit time

(in seconds) taken from a continuous analog

signal in order to make it discrete.

In this research project the sampling frequency

was set as 10000 Hz. Finally the memory was set

as 100µs/10 KHz and the block size was

32KW*32.So all the above said settings were

done and proceeded to the experiment. Before

recording the blast vibrations, all the electrical

connections were rechecked in order to avoid

any kind of loose contacts. Then the OPS

software was selected in the simulation mode.

After obtaining a steady waveform from

geophone and accelerometer, the record button

in OPS software was clicked. Then waited for

the blasting from KCGM. Once the blasting had

occurred corresponding waveforms were

recorded using the OPS software and they were

stored as CSV files in the computer. Almost 26

different blast vibration data were collected and

measured.

Figure 8-recorded blast vibration waveform

Figure 8 shows an example of recorded blast

vibration waveform. The waveform is in time

domain. The waveform shown in red colour is



the accelerometer data and the waveform shown

in blue colour is the geophone data. Here the X

axis is time in µs and Y axis is voltage in mV.

From this two waveforms it can observe that the

output waveforms of both the instruments are in

the same trend. There is some difference is in

amplitude due to the difference in sensitivity of

both the instruments.

3.6 SUMMARY OF RESEARCH METHOD &

EXPERIMENTAL

The method and procedure of carrying out this

research project is clearly summarised in this

chapter. This chapter is mainly categorised under

five titles including the introduction. The main

titles are instruments used, experimental set up,

obtaining amplification factor and measuring

blast vibrations. The title, instruments used is

again categorised into geophone, accelerometer,

amplifier, data logger and computer. All the

essential features and requirements of these

instruments are described in detail under each

title (geophone, accelerometer, amplifier, data

logger and computer).It also includes the

specifications of each instrument. Under the title

experimental set up the method of conducting

the research project is explained. It also reveals

the strategy adopted to obtain the desired result.

This section incorporates the entire vital

schematic diagram necessary for the better

understanding of the research project from a

wider perspective. It shows the connection

between various instruments used for the

research project. It is then followed by the title

obtaining the amplification factor. This section

explains how to obtain the amplification factor.

Accelerometer output waveform is not strong

enough for recording and measurement. So it has

to be boosted up .Amplification factor is

obtained by doing some rearrangements in the

connections made for experimental set up.

Finally the amplification factor is obtained as

10.Therefore it can be concluded that output

waveform of an accelerometer is amplified by

ten times. After that the obtained blast vibrations

from KCGM are recorded. They are measured

and recorded using the OPS software. It is one

most functional and professional blast wave

recording software. Before taking measurements

all the necessary settings in the software should

be done. First among this was setting up of the

range. So the range for the first and second

channel was set as 200 mv and 100 mV

respectively. Then the filter frequency was as

500 Hz. It is the filter frequency which decides

up to what range of frequency an instrument can

detect and record. Next the sampling frequency

was set as 10000 Hz. The trigger level was set as

1%. At the end memory and block size was set

as 100µs/10 KHz and 32KW*32 respectively.

The vibrational waveforms detected and

recorded by the OPS software are stored in

computer as CSV files. Almost 26 different blast

vibration data were collected and measured.



4. RESULT AND ANALYSIS

4.1 BLAST VIBRATIONAL WAVEFORM

Almost twenty six blast vibration data were

obtained .Among them the best twenty data are

collected and compared. Using OPS software the

velocity waveform and acceleration waveform

for the corresponding blast vibrations are

recorded. A sample of the recorded blasting

wavelet is shown in figure 9.

Figure 9- recorded blasting wavelet

Figure 9 shows an example of recorded blasting

wavelet. Here the wave form is in the time

domain. The blue waveform indicates the

geophone data and the red waveform indicates

the accelerometer data. Both the output

waveform will be in mV and the time interval is

0.0001 s. Both the velocity and acceleration

waveform shows the same trend and there are

some differences in amplitude for both these

waveforms due to the difference in sensitivity of

geophone and accelerometer.

4.2 TIME DOMAIN SPECTRA

The recorded blasting wavelets are stored as

CSV files. Then all the manipulations are done

in these files. Suitable time interval of 0.0001

second is provided. For each recorded blasting

wavelet there are 32000 data. So the time

interval is defined up to 32000 data. The next

step is to divide the accelerometer data by 10. It

is because the amplification factor has to be

taken to consideration. In this case the

amplification factor is 10.It is obtained by

dividing the amplified geophone data with the

original geophone data subjected to same input

vibration. The output of geophone and

accelerometer is in mV. But for this research

project the data from the geophone is to be

obtained in m/s and the data from the

accelerometer is to be obtained in m/s2. The

sensitivity of geophone is 1 mV/m/s. and that of

accelerometer is 9.97mv/G or 9.97mV/9.98m/s2

which is equivalent to 1 mV/m/s2 .From this it

can concluded that for an output of 1 mv from

the geophone the corresponding velocity will be

1 m/s. Similarly for an output of 1 mV from the

accelerometer the corresponding acceleration

will be 1 m/s2.In order to obtain the transfer

function, both the geophone data and

accelerometer data has to be compared. But only

data with same units can be compared. Here

geophone and accelerometer detect the same

wave but the output will be in different unit, one

is m/s and the other in m/s2.So the obtained

acceleration data is integrated to convert it into

velocity data.



-0.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5

-10

-5

0

5

10

15

Volta

ge (m

V)

Time (s)

Figure 10-velocity waveform from geophone (case 1)

-0.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5

-25

-20

-15

-10

-5

0

5

10

15

20

Vol

tage

(mV

)

Time (s)

Figure 11- velocity waveform from geophone (case 2)

Case 1 and case 2 shown in figure 10 and 11 are

two examples of velocity waveform obtained

from geophone during the experiment (blast

vibration measurement). The graphs show the

variation of voltage with time (with a time

interval of 0.0001s).As it is mentioned before

that 1 mV is equal to 1 m/s .So the above shown

graphs can be considered as velocity waveforms.

-0.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5

-0.10

-0.05

0.00

0.05

0.10

0.15

Acc

eler

atio

n (m

/s2 )

Time (s)

Figure 12-acceleration waveform from accelerometer

(case 1)

-0.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5

-0.2

-0.1

0.0

0.1

0.2

0.3

Acc

eler

atio

n (m

/s2 )

Time (s)

Figure 13- acceleration waveform from accelerometer

(case 2)

Case 1 and case 2 shown in figure 12 and 13 are

two examples of acceleration waveform obtained

from an accelerometer during the experiment

(blast vibration measurement).The graphs show

the variation of acceleration with time in seconds

(time interval is 0.0001s).As already stated that

the output data of both accelerometer and

geophone must be compared to get the transfer

function. But in order to compare, both the data

should be in the same unit. So the acceleration

data is integrated to obtain the velocity data.

Thus it can be easily compared with geophone

data. Integration of acceleration data shown in

figure 12 (case 1) and figure 13 (case 2) gives



the velocity data shown in figure 14(case 1) and

figure 15 (case 2).

-0.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5

0.000

0.005

0.010

0.015

0.020

0.025

0.030

Velo

city

(m/s)

Time (s)

Figure 14-Integrated accelerometer data (case 1)

-0.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5

0.00

0.01

0.02

0.03

0.04

0.05

0.06

0.07

Velo

city (

m/s)

Time (s)

Figure 15- Integrated accelerometer data (case 2)

4.3 FILTERING OFF LOW FREQUENCY SIGNALS

The values obtained after the integration of

accelerometer data has some drift components

.These drift components are unnecessary low

frequency signals. It is shown in red coloured

lines in figure 14 and 15. So it has to be

eliminated before doing all the calculations. It is

done in OriginPro 7J software. Thus the low

frequency signals are removed from the

integrated accelerometer data. The required

filtered data from figure 14(case 1) and figure 15

(case 2) is shown below in figure 16 (case 1) and

17 (case 2).

-0.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5

-0.0006

-0.0004

-0.0002

0.0000

0.0002

0.0004

Vel

ocity

(m

/s)

Time (s)

Figure 16-Low frequency filtered data (case 1)

-0.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5

-0.0008

-0.0006

-0.0004

-0.0002

0.0000

0.0002

0.0004

0.0006

0.0008

0.0010

Vel

ocity

(m

/s)

Time (s)

Figure 17- Low frequency filtered data (case 2)



4.4 FREQUENCY DOMAIN SPECTRA

Comparison of data in time domain has no

meaning, it has no real life applications .It is not

a better method to describe the relationship

between geophone and accelerometer in time

domain. So the measured velocity data from the

geophone and integrated accelerometer data has

to be converted from time domain to frequency

domain. This is done through the Fourier

Transform. Using FFT function (Fast Fourier

Transform) in OriginPro7J software

accelerometer data and geophone data from time

domain is converted to frequency domain. It is

shown in figures below

Figure 18 –Acceleration waveform after FFT (case 1)

Figure 19- Acceleration waveform after FFT (case 2)

Figure 18 and 19 shows the acceleration

waveform after Fast Fourier Transformation for

both case 1 and case 2.

Figure 20-Velocity waveform after FFT (case 1)

Figure 21- Velocity waveform after FFT (case 2)

Similarly FFT is done for geophone data in the

OriginPro7J software and is shown in above

figures. Figure 20 and 21 shows the velocity

waveform after Fast Fourier Transformation for

both case 1 and case 2.

4.5 OBTAIN TRANSFER FUNCTION

Next step was to obtain the transfer function

between the geophone and accelerometer .Thus

in order to obtain the transfer function almost

twenty vibration measurements are collected for

both geophone and accelerometer. The transfer

function is obtained by dividing the integrated

accelerometer data in frequency domain with the

geophone data in frequency domain.

Let G (ω) is the velocity waveform obtained by

geophone after Fourier transformation. V(ω) is

the velocity waveform obtained by



accelerometer after integration. Therefore

transfer function will be

T (ω) = V(ω)

G(ω)

-6000 -4000 -2000 0 2000 4000 6000

0.0000

0.0002

0.0004

0.0006

0.0008

0.0010

0.0012

0.0014

0.0016

0.0018

0.0020

Four

ier

Am

plitud

e

Frequency (Hz)

Figure 22-Graphical representation of transfer

function

The transfer function obtained in this research

project is graphically represented in figure 43

with transfer function in the Y axis and

frequency in the X axis .It is obtained from

OriginPro 7J software. There are 32770 different

frequency points. The frequency ranges from -

5000 Hz to 5000 Hz .from the graph it is clear

that the maximum Fourier amplitude is 0.00021

and the average Fourier amplitude is

0.0001.Using this transfer function the accuracy

of velocity waveform of a geophone can be

improved.

4.6 IMPROVING THE ACCURACY OF VELOCITY WAVEFORM

The project objective is improving the accuracy

of velocity waveform using transfer function

obtained by geophone and accelerometer. So the

next step is to utilize this transfer function to

improve the accuracy of velocity waveform.

Besides twenty vibration measurements three

additional readings are taken. Then these three

readings were subjected to Fourier

transformation using fft function in OriginPro7J

software .After that the transfer function is

multiplied with the three geophone data ( case 1,

2 and 3).Then newly obtained improved velocity

waveform is compared with the corresponding

geophone and accelerometer data.

Case 1

0 50 100 150 200

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

Four

ier

Am

plitu

de

Frequency Hz

Figure 23-Velocity waveform obtained by multiplying

transfer function with geophone data

0 50 100 150 200

0.0

0.1

0.2

0.3

0.4

Four

ier A

mpl

itude

Frequency Hz

Figure 24-Integrtaed Acceleration waveform (

acceleration data)



0 20 40 60 80 100 120 140 160 180 200

0

2000

4000

6000

8000

Fou

rier

Am

plitud

e

Frequency Hz

Figure 25-Velocity waveform (geophone data)

Case 2

0 50 100 150 200

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

Four

ier

Am

plitu

de

Frequency (Hz)

Figure 26- Velocity waveform obtained by multiplying


0 50 100 150 200

0.0

0.1

0.2

0.3

0.4

0.5

0.6

Four

ier

Am

plitu

de

Frequency (Hz)

Figure 27-Integrated Acceleration waveform

(acceleration data)

0 50 100 150 200

0

2000

4000

6000

8000

10000

Four

ier

Ampl

itude

Frequency (Hz)

Figure 28- Velocity waveform (geophone data)

Case 3

0 50 100 150 200

0.00

0.05

0.10

0.15

0.20

0.25

0.30

Four

ier

Am

plitu

de

Frequency (Hz)

Figure 29- Velocity waveform obtained by multiplying


0 50 100 150 200

0.0

0.1

0.2

0.3

0.4

0.5

Four

ier A

mpl

itude

Frequency

Figure 30- Integrated Acceleration waveform

(acceleration data)



0 50 100 150 200

0

1000

2000

3000

4000

5000

Four

ier

Am

plitud

e

Frequency (Hz)

Figure 31 -Velocity waveform (geophone data)

In order to obtain the result, three graphs

[Velocity waveform obtained by multiplying

transfer function with geophone data, Integrated

acceleration waveform (acceleration data) and

Velocity waveform (geophone data)] are

compared. After comparison of first two graphs

for all the three cases (improved velocity

waveform and integrated acceleration

waveform), it can concluded that the peaks and

valleys of both the graphs almost look alike.

Noticeable waveform occurs between the

frequency ranges 0 to 200 Hz for all the cases

.Thus while generating graphs waveform

generated between 0 to 200 Hz is only

considered for the final analysis. When the three

waveforms in all the three cases are closely

studied, the main thing which can be noticed is

that the occurrence of peak amplitude .In all the

cases the peak amplitude occurs between the

range of 0 to 50 Hz. For the first case the value

of the highest peak in integrated acceleration

waveform is 1.7 times the value of highest peak

in accuracy improved velocity waveform and for

the second case the value of the highest peak in

integrated acceleration waveform is 1.5 times the

value of highest peak in accuracy improved

velocity waveform. Finally for the third case the

value of the highest peak in integrated

acceleration waveform is 1.25 times the value of

highest peak in accuracy improved velocity

waveform. Thus from three cases it can be

concluded that the average range will be 1.48

times. This value will change if more results are

considered. Thus the project objective of

improving the accuracy of velocity waveform

using transfer function, obtained by geophone

and accelerometer, is achieved.

5 CONCLUSIONS AND RECOMMENDATIONS

After obtaining the result suitable conclusions

should be derived. The research project as a

whole is dependent on geophone and

accelerometer .The primary aim of the research

project was to improve the accuracy of velocity

waveform using transfer function. So the transfer

function between geophone and accelerometer is

obtained .Obtaining the transfer function was the

secondary aim of the research project. Thus the

main conclusions obtained in the research

project are summarized below.



5.1 CONCLUSIONS

(1) As already stated that the objective of this

research project was to improve the accuracy of

velocity waveform using transfer function

obtained by geophone and accelerometer. This is

considered as the primary objective.

(2) In order to achieve this primary objective

transfer function has to be obtained. So obtaining

transfer function was set as the secondary

objective. In order to obtain transfer function

almost twenty blast vibration measurements

were taken and it was followed by subsequent

necessary calculations .Finally the transfer

function was obtained. Transfer function for

twenty results was obtained. Then the final

transfer function was obtained by taking the

average of all the twenty transfer functions.

(3) In order to apply these transfer function three

additional blast vibrational measurements were

taken. Then the transfer function is multiplied

with the corresponding geophone data for all the

three cases .This resulted in the improvement of

accuracy of velocity waveform. After that all the

three waveforms are compared.

(4) After comparison of first two graphs for all

the three cases (improved velocity waveform and

integrated acceleration waveform), it can be

stated that the peaks and valleys of both the

graphs almost look alike.

(5) From the comparison of three waveforms, it

can be concluded that noticeable waveform

always occurs between the frequency ranges 0 to

200 Hz for all the cases.

(6) By the careful study of all the three

waveforms a conclusion can derived that the

peak amplitude occurs between the ranges of 0

to 50 Hz.

(7) From the observation and analysis of three

graphs the variation of amplitude between the

accuracy improved velocity waveform and

integrated acceleration waveform is noticeable

.For the first case the amplitude of the highest

peak in integrated acceleration waveform is 1.7

times the value of highest peak in accuracy

improved velocity waveform. For the second and

third case it is 1.5 and 1.25 times respectively.

Thus from three cases it can be concluded that

the average range will be 1.48 times.

(8) For this research project almost twenty six

blast vibration measurements were taken. The

accuracy of the final result depends on the

transfer function. Transfer function was obtained

from average of twenty readings The degree of

accuracy depends upon the number of readings.

The accuracy of the final result would have been

improved if more readings were taken (such as

50 or 100 readings).

5.2 RECOMMENDATIONS FOR FURTHER WORK

This research project entirely depends on

transfer function .But the transfer function

between geophone and accelerometer depends

on the recorded blast vibration waves.

Sometimes the results will cause some ambiguity



.It is due to the presence of some existing errors

in the instruments .So it is always recommended

to collect as many blast vibration data to

minimize the error. And it can maximize the

degree of accuracy of final result.

Through this research project it can be shown

that the obtained transfer function can improve

the accuracy of geophone. Thus the final result

will be a much more precise velocity waveform

from a geophone. Thus the application of

transfer function is not only limited to this

research project but also can be employed in

large scale blast vibration measurements so that

geophones can be used effectively and

economically. Thus this research project will

result in precise vibration measurement at low

cost in mines.

ACKNOWLEDGEMENTS

I would like to thank and extend my sincere

gratitude to all the academic staff of Mining

Engineering Department, Western Australian

School of Mines (WASM) Curtin University

Western Australia.I am deeply thankful to my

supervisor Dr. Youhei Kawamura without whom

this project would never happen. His instructive

advice and valuable suggestions helped me a lot

for the completion of this thesis. Support from

the supervisor for the completion of this research

project was outstanding.

I would also like to thank Prof .Erkan Topal ,

Head of Mining Engineering Department , for

his full support for me as an international student

during the last one and half year. I am deeply

grateful to Mr .Mahroof for granting me

permission to use the Geology department lab.

Finally I would like to thank the almighty god,

my parents and my brother for their

unconditional love and support. Once again I

would like to thank each and every one who has

helped me in my entire work.

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