Machine Vib Measurement Presentation

7/24/2019 Machine Vib Measurement Presentation

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Machine Vibration MeasurementPresented by Joko Ismiyanto

PT. NUSANTARA TURBIN & PROPULSI Joko Ismiyanto


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Pendahuluan

Principles of vibration

Vibration measurement (how to measure correct data for

analysis)

Time waveform

Spectrum FFT

Time waveform vs Spectrum FFT

Interpreting Pattern of spectrum and TWF



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Vibration and Mechanical Vibration

Getaran adalah gerakan bolak-balik suatu benda disekitar satu posisi

referensi.

Getaran mekanis adalah getaran yg dapat dirasakan dan diukur pada

permukaan mesin, pondasi dll, dirambatkan melalui benda padat

Terjadi jika ada massa yang bergerak (berputar, berosilasi dan lain-lain).

Dalam batas tertentu diperbolehkan,

Tidak boleh melebihi batas yang diijinkan. Sesuatu yang inherent (bagian yang melekat) pada sistem yang memiliki

komponen yang bergerak



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What cause vibration

Repeating forces (gaya yang berulang)

Looseness (kendor)

Resonance (resonansi)

Repeating Forces

Almost all machine vibration caused by repeating forces



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Imbalanced

Repeating forces :



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Misalignment

Repeating forces :

Worn (aus)



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Improperly driven machines

Repeating forces :



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Looseness (kendor)

Resonance (resonansi) Play



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Why monitor machine vibration Give understanding about health condition of a machine

The information from monitoring can be used to detect theproblem that might be develop, and can be prevent before the

problem getting worst.

These problem below will appears if the monitoring program is not

implemented and the consequences cost will raise even bigger

than monitoring program:

- Severe machine damage

- High power consumption

- Machine unavailability

- Unnecessary maintenance

- Quality problem



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How is machine vibration described ?



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Waveform



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Waveform



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Spectrum



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How is machine vibration measured ?

The keys to answer the question above are :



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Time Waveform - Spectrum Frekuensi



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Vibration Measurement


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Vibration MeasurementLebar frekuensi pengukuran

Design of equipment (bearing type)

Nature of vibration (frekuensi danamplitude) frekuensi komponen danfrekuensi operasi

Tujuan pengukuran: periodicmonitoring, fault analysis, conditionevaluation, acceptance testing,

parameter identification



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Perpindahan (Displacement): Jarak benda dari titik referensi, mils peak to peakatau mm

peak to peak. Displacement menunjukkan tingkat stress.

Kecepatan (Velocity) Menunjukkan besarnya perubahan jarak persatuan waktu.

inches per second peakatau mm per second RMS. Velocity menunjukkan energi getaran.

Percepatan (Acceleration) Menunjukkan perubahan kecepatan per satuan waktu. Percepatan umumnya diukur dalam G RMS. Percepatan sebanding dengan gaya getaran.


Vib i M


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Type / jenis sensor (transducer) getaran : Relative shaft vibration - displacement type Absolute vibration accelerometer & velocity types



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Vibration Transducer/Pickup



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Vibration Transducer/Pickup



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Vib i M


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Skema Vibration Analyzer


Vib i M


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Four (4) Keys Measurement Setting

(1) Fmax = Maximum Frequency This dictates the highest frequency that can be displayed in the spectrum It aslo effects the actual resolution A higher fmax reduces actual resolution and shorten measurement time

(2) LOR = Line of Resolution

This effect the detail you can see in the spectrum

Example: 800, 1600, 3200 lines A higher fmax reduces actual resolution and shorten measurement time

(3) Number of Averages

Reduces the effect of noise Ensure that you can compares the data between measurement

(4) Unit : Displacement, velocity, acceleration

Displacement : Journal bearing machines and low speed machines Velocity : General fault diagnosis Acceleration : high frequency analysis, bearing, gear mesh



Vib i M


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(1) Fmax = Maximum Frequency

Make sure that you know what is important about the machine :type of the machine, speed, configuration, what is the important of

source of the vibration, when there is a fault condition.

Its often useful to take two measurement, 1st measurement is

intended on zoom in measurement to area that you know it will be

any interesting information and 2nd measurement is back to zoom out

measurement and getting more information.

Make sure to listening all important information the machine will

generate




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Component Span

Shaft vibration 10 x RPM

Gearbox 3 x GM

Rolling element bearings 10 x BPFI

Pumps 3 x VP

Fans 3 x BP

Motors/Generators 3 x 2LF

Sleeve Bearings 10 x RPM

Engines 12 x RPM

FREQUENCY SPANS / FMAX (lebar frekuensi)


Vib ti M t


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Averages




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Vibration MeasurementHow many averages to use

Do a test on your machine :

Set the analyzer to free run watch the live data

Set the averages as long as possible, but it will be

limited by the long of average time and memory, more

average more time taken.The most important from averages are that we get

good representation of the vibration on the machine

and get a good repeatability.




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sepe k hold ver ging




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Averaging Process

Record twf average Windowing process

Do FFT process Do FFT averaging




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The keys is we have to listening

machine long enough to get

legitimate data by decreasing the

overlap average and increasing the

number of average




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Amplitude ModulationThe carrier is the original sinewave. The modulating frequency is

typically a lower amplitude and frequency.

The modulating frequency is always related to the carrier frequency.The amplitude of the sinewave is change periodically Forming sideband on spectrum




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Amplitude Modulation

Sideband can vary in a number of ways :

Around different carrierAround harmonics Different number of sideband Different amplitude relative to the center/carrier frequency




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Frequency ModulationThe frequency of the sinewave is change periodically.

Imagine the machine very slightly slowing down and speeding up

periodically.As gear mesh together, and there is any eccentricity and gear teeth

mess, then there is will be any variation on the speed. When gear

teeth mess at eccentricity the speed will be slightly slowing down and

then back to the normal speed.

Variation in speed mean variation in frequency




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Demodulation (enveloping) technique

Assume we have have ball bearing with a fault on the outer race, Every time the ball

hit the fault, its creates a ring. The timewave form of the bearing is more like below :

The process of demodulation focuses on the

frequency being

rung and the rate at which it rings louder. It

removes the frequency or sound of the ringing

itself (high

frequency) and returns the rate at which it is

getting rung.




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Demodulation (enveloping) technique




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Vibration MeasurementP kV


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PeakVue

PeakVue is technology unique to CSI and means Peak Value use for

detecting bearing fault at earlier stage Such as the Peak Value of an impact generated by a bearing defect in a

timewave form (True Peak Value)

The True Peak value is obtained by focusing on Stress Wave Analysis

rather than conventional vibration data

The stress wave accompany with metal to metal impacting. These stress waves

are short term (a fraction of few millisecond) transient event which

introduce a ripple effect on machinery surface (Like the effect of the stonebeing dropped in the water)

If a bearing has a early bearing wear, when a rolling element passes over the

defect it bend the race slightly and then as the rolling element passes it

restores back to its natural state.

This event causes a high frequency (1-50KHz) short duration stress wave


Pengukuran Getaran

PeakVue How Does It Work?


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PeakVueHow Does It Work?


Pengukuran Getaran


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Pengukuran Getaran


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Vibration MeasurementPeak Hold (coast down run up) Resonance Meas


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Peak Hold (coast downrun up) Resonance Meas.

Resonance is a very common cause of excessive machine vibration.

Resonance is the result of an external force vibrating at the same frequency

as the natural frequency of a system.

Its therefore important that the running speed of equipment be out of the

resonance range.

Technique used to confirm a resonance

It is very important to confirm a resonance phenomenon by at least 2 different type

of technique before trying to correct it.

Impact Test

Strike the equipment with a mass and measure the response. This type of test must

performed with equipment off. This way you can easily identify the natural

frequency of the equipment.




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Peak Hold (coast down run up) Resonance Meas.

Impact Test Using an Instrumented Hammer

Basically the same as regular impact test, but the hammer equipped with

accelerometer at the end, and is used in tandem with the sensor used to measure

the vibration. A two channel analyzer needed to measure force induced to the

system by hammer and response at different frequencies.

When the phase shifted 90, the frequency at which is occurs is the natural

frequency.

Coast down / Run Up Peak Hold Function

Another method used is to monitor the vibration level usingpeak hold function,

that can only be done using smart modern machinery analyzer. The idea behind this

function is to capture peak vibration during decrement or increment of speed.

On case of coast down peak hold, peak vibration captured during down time

process. If the vibration levels start rising at any time while equipment is being shutdown, the speed at which the amplitude increase is a possible natural frequency




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Peak Hold (coast down run up) Resonance Meas.

Coast down / Run Up Peak Hold Phase Function

Its same method with coast down/run up peak hold, but with addition of installingphoto tach and reflecting tape on the rotating shaft of equipment. Then you can

monitor the peak vibration and the phase. This will allow you to see the amplitude

and phase shift at all running speed. If no resonance, the vibration should drop at

steady state. If the vibration peak at a certain speed and the phase shift by 180 this

indicate natural frequency of equipment or structure. The actual natural frequency

is the frequency situated in the middle of the phase shfit (90).


Pengukuran Getaran


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Pengukuran Getaran


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Pengukuran Getaran


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Pengukuran Getaran


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Pengukuran Getaran


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Pengukuran Getaran


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Pengukuran Getaran


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Terminology


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Terminology

FTF - FundamentalTrain Frequency


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FTF - Fundamental Train Frequency

Frekuensi dimana cage/retainer berputar bersama dengan

rolling element

BSF - Ball Spin Frequency

Frekuensi putaran rolling element.

BPFO - Ball Pass Frequency of Outer Race

Frekuensi dimana rolling element melewati suatu titikpada outer race.

BPFI - Ball Pass Frequency of Inner Race

Frekuensi dimana rolling element melewati suatu titik

pada outer race.


Terminology

Ball pass frequency inner race


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xRPM

P

BNBPFI

d

dbcos1

2

Dimana:

Pd = Diameter Pitch

Bd = Diameter bola

Nd = jumlah bola= sudut kontak

Asumsi umum Bd/Pd cos =2

sehingga:

BPFI = 0.6 x Nb x RPM


Terminology


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Terminology

CRITICAL SPEED


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Putaran operasional suatu mesin yang pas sama atau

dekat dengan frekuensi natural dari mesin tersebut.Mesin yang beroperasi pada kondisi critical speed-

nya akan bergetar berlebihan karena resonansi.

Untuk menghindari mesin rusak, jangan

mengoperasikan mesin pada kondisi critical speednya

terlalu lama. Ketika melewati kondisi tersebut, putaran

mesin harus secepatnya dinaikkan atau diturunkan.


Terminology

Fi O d Vib i 1X Vib i


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First Order Vibration atau 1X Vibration

Getaran mesin yang berputar yang disebabkan olehunbalance shaft. Frekuensi dalam Hz dihitung dengan cara

RPM/60

Resolution

(FMAXFMIN)/Number of Lines of Resolution

FMAX = Limit frekuensi maximum dari spectrum yg dievaluasi

FMIN = Limit frekuensi minimum dari spectrum yg dievaluasi


TerminologyGear Mesh Frequency (GMF)


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Frekuensi getaran dari setiap mesin yang mempunyai gear,

sama dengan jumlah gigi gear x frekuensi putar gearGear Mesh = jumlah gigi gear x putaran shaft

2625 rpm8 teeth

GMF= 21k CPM

1500 rpm

14 teeth


TerminologyHigh-Pass Filter

P l t i i hk k


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Peralatan penyaring yang memisahkan komponen-

komponen dari suatu sinyal dan hanya mengijinkan

sinyal dengan frekuensi diatas frekuensi yang dipilih

Natural FrequencyFrekuensi dari getaran bebas suatu benda/system

saat dieksitasi dengan impact force. (Frekuensi alami

benda/system tersebut)


TerminologyHarmonics

Frekuensi dari komponen yang merupakan hasil kali


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Frekuensi dari komponen yang merupakan hasil kali

bilangan bulat (integer) dari fundamental frequency

Orders

Unit dari frekuensi yang unik pada rotating machine

dimana first order (1X) sama dengan rotational speed.

Berbeda dengan harmonics yang merupakan

perkalian bilangan bulat dari fundamental frequency,

order tidak selalu bil. bulat (bisa) pecahan, contoh :

1.2X, 6.3X dsb.



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TerminologyOrbit

Pola pergerakan centerline shaft selama berputar. Bisa dilihat menggunakan

oscilloscope yang dihubungkan dengan tranducer yang dipasang secara X


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oscilloscope yang dihubungkan dengan tranducer yang dipasang secara Xdan Y berbeda 90. Beberapa vibration analyzer memiliki kapabilitas untuk

menyajikan orbit.


TerminologyOverall LevelNilai pengukuran dari total amplitudo getaran pada range


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Nilai pengukuran dari total amplitudo getaran pada range

frekuensi yang telah ditentukan. Nilai ini dapat diukur

menggunakan meter analog getaran atau dihitung dari

spectrum getaran dengan cara menjumlah semua nilai

amplitudo yang berada dalam range frekuensi yang telah

ditentukan


TerminologyPhasePerbedaan waktu relatif antara dua sinyal diukur dalam


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Perbedaan waktu relatif antara dua sinyal diukur dalam

unit sudut (angle). Dan hanya berarti jika dua sinyal yang

diukur mempunyai frekuensi sama. Diukur dengan cara

two channel measurement.


TerminologySidebandsKomponen spektrum yang dihasilkan dari modulasi amplitudo


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atau modulasi frekuensi. Jarak frekuensi dari sideband sama

dengan besarnya modulasi frekuensi, digunakan untukmendiagnosa mesin. Sebagai contoh, gear yang rusak akan

muncul sideband pada frekuensi putaran gear.


TerminologySynchronousKomponen spektrum yang berasal dari perkalian bilangan bulat


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p p y g p g

atau harmonics dari frekuensi fundamental.


TerminologySub-SynchronousKomponen dari sinyal getaran yang mempunyai


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p y g y g p y

frekuensi kurang dari frekuensi putaran shaft (1X RPM)



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Terminology


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Time Waveform (TWF) vs FFT


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Interpreting spectrum & TWF pattern


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Documents

Machine Vib Measurement Presentation