VIBRASI_SE~3 (Level2)

Vibra ibration tion Analysis Analysis – Le Leve vell 2 forr assessi fo assessing ng ma m achi chine ne pot pote ent ntial ial fail failur ure e mo modes des

Copyright 2005 2005-- PT. Putranata Putranata Adi Mandiri Mandiri – sole agent agent Prüftechnik Prüftechnik AG, Germa Germany ny

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ANA A NAL L YSIS TECHNIQUES • • • • • • • • • • • • • •

Broad Band Vibration Analysis Bearing Co Condition An Analysis Frequency Analysis (FFT) Time Sync ynchron hronou ous s Ave Averragi aging Anal Analys ysis is Time Waveform Analysis Multispectrum Envelope Analysis Cons onstant tant Per Percent centag age e Ban Bandw dwiidth dth Ana Anallysis ysis Cepstrum Shaft Orbit Tracking Analysis Vector Analysis (Amp. & Phase) Startup / Coastdown Analysis Impact Test


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ANA A NAL L YSIS TECHNIQUES • • • • • • • • • • • • • •

Broad Band Vibration Analysis Bearing Co Condition An Analysis Frequency Analysis (FFT) Time Sync ynchron hronou ous s Ave Averragi aging Anal Analys ysis is Time Waveform Analysis Multispectrum Envelope Analysis Cons onstant tant Per Percent centag age e Ban Bandw dwiidth dth Ana Anallysis ysis Cepstrum Shaft Orbit Tracking Analysis Vector Analysis (Amp. & Phase) Startup / Coastdown Analysis Impact Test


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Broa Bro ad Ba B and Vibra ibr ation tio n Ana A nalysi lysis s

Also know as Overall vibration vibration measurement Typically...

Velo loci city ty me m easu sureme rement nt mm/s, RMS from 2 Hz to 1000 Hz

ISO 10816-3

Displacement measurement um, RMS from 2 Hz to 1000 Hz Can be overall acceleration measurement eg. Gear box monitoring


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Copyright 2005- PT. Putranata Adi Mandiri – sole agent Prüftechnik AG, Germany

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Vibration Monitoring v mm/s 0.45 0.40

Effect of Machine speed variation on Vibration measurement

0.35 0.30 0.25 0.20 0.15 0.10 0.05 0.00 0.05 0.10

v mm/s

0.15

.0

0.20

3 .8

0.25

3 .6

0.30

3 .4

0.35

3 .2 0.40

3 .0 0.45

.8 1500

2000

2500

3000

Time Signal

3500

4000

4500

5000

.6

5500

6000

6500

7000 t ms

.4 .2 .0 1 .8 1 .6 1 .4 1 .2

rms

1 .0 .8 .6 .4 .2

07/02/2001

07/02/2001

07/02/2001

07/02/2001

07/02/2001

4:59:00 PM

4:59:10 PM

4:59:20 PM

4:59:30 PM

4:59:40 PM date


Overall Vibration Level

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Bandpass Measurement

Peak RMS (0.707xPeak) Avg

(0.637xPeak)

Peak to Peak

Freq. = 1/Time

Freq. = Hz = rev. per secon d

Always ask.... Are you measuring RMS or Peak , etc ?? What is the frequency r ange ?? How much averaging?

Machine Freq are functi on of RPM ie. rev. per minu te


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Frequency Analysis

Machine Vibrations

Time Signal

Time, s = Frequency, Hz

Time = 1 / Frequency


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Frequency Analysis

How to make a frequency analysis? FFT - Fast Fourier Transform is merely an efficient means of calculating a DFT (Discrete Fourier Transform). Basically, it transform a time signal into a frequency spectrum.

Time

F

F (Hz)

T

Time = 1 / Frequency


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Frequency Analysis

How to make a frequency analysis? Frequency analysis can be made using frequency selective devices called filters

dB

dB

B

0

B = Bandwidth

f 1

f c

f 2

f

An ideal filter will only signals to pass within its bandwidth

-3

f 1

f c

f 2

f

Practical filter have roll-off, express as half-power (-3dB) For good filters the two will be very similar.

In FFT analysis, the bandwidth = Frequency span / no. lines Copyright 2005- PT. Putranata Adi Mandiri – sole agent Prüftechnik AG, Germany

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Types of Bandwidth Constant Percentage Bandwidth (CPB)

Vibration Am pl it ud e

0.1 1

2

3

Constant Bandwidth (FFT)

4

5

7

8

y

frequency

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b

a x

6

a=b=c

10 kHz

c z

x, y, z are constant % of their center frequency


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Frequency Analysis

Types of fi lters: f

High-Pass filters

- As the name imply, a high pass filter allows high frequencies to pass. (lower frequency limit)

Low-Pass filters

- Allow low frequencies to pass through (upper limit)

Bandpass filters

- Allows only frequencies within the band f

Anti-aliasing filters

- Low pass filter at half the sampling frequencies


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FFT (D (DFT) - Pitfalls it falls Discr ete Four Fourier ier Transfor Transfor m (DF (DFT) - Pitfa itf alls FFT - Fast Fourier Transform is is an efficient means of calculating calculating a DFT DFT (Discrete Fourier Transform). Transform). Basically, it transform a time signal into a frequency spectrum.

11.. AAlliiaassiinngg -- high hig hhfrequ frfreque equenc encies ies aappea ppeari aring nggas frequen uencie cies s high hig fre quenci ncies esappe ap pearin ring aslow lowfreq low frequenc frequ encies ies 22.. LLeeaakkaaggee-- Memory Mem ory con tents tstsforc forced ed to to bbe pe riodic dic.c. . Memory Mem oryconten conten con tents forced for ced tobe beeperio periodi peri odic. Can Cangive givediscontinuities whenends endsjoined joined discontinuitieswhen

sampl ed at 33.. PPicke ic tt fenc fe eeeeffe ffff eect icket icke ket fence fenc nce ffe ct – –Actual Actualspectrum spectrumsampled sampled sampled atdiscrete discrete frequencies. frequencies.Peaks Peaksmay maybe bemissing missing

Copyright 2005 2005-- PT. PT. Putrana Putranata ta Adi Mandiri Mandiri – sole agent agent Prüftechnik AG, Germa Germany ny

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FFT pitfalls pitfalls - Aliasing Effe Effect ct

Sampling mpl ing ra r ate too slow s low High frequency f requency analysis analysis re r esults sul ts in fa f alse low frequency frequency signal

Solution: Use Anti-aliasing filter Typically a 1K (1024 point) transform, 512 frequency components are calculated and 400 lines displayed. Similarly a 2K transform 800 lines are displayed.


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FFT pitfa pit falls lls - Lea Leakage kage +ve +v e 1st Sample

-ve -v e

2n d Sample

…..give discontinuities when ends joined

+ve +v e

-ve -v e Copyright 2005 2005-- PT. PT. Putrana Putranata ta Adi Mandiri Mandiri – sole agent agent Prüftechnik AG, Germa Germany ny

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FFT pitfalls - Picket Fence Effect

Actual Spectrum

Measured Spectrum


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Frequency Analysis

Basic law of frequency analysis

BT > 1 Bandwidth

Analysis Time

T Time

min. analysis time must allow the measured freq. to complete it’s cycle / period


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Fungsi window


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FFT Spectrum 400 lines FFT

1X

2x

3X

1 kHz

IF Freq. Span is 1 KHz then resolution = 1000 / 400 lines = 2.5 Hz 2.5 Hz 5 Hz 7.5Hz

(eg. 2 - IF Span is 40Khz then resol uti on= 100Hz)


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Measurement time

• Harmonic signals can be measured in short time • Random and Pulsed signals

B B ** TT == C C

BB==Highest Highestresolution resolutionofofAnalysis Analysis TT==The TheShortest Shortestmeasurement measurementtime time CC==Constant. Constant.

need longer time • For FFT spectra C Theoretical Theoretical CC==33for Signals forHarmonic Harmonic Signals = 1 pr. average. C = 30 For Random Signals C = 30 For Random Signals

In In Practice Practice

CC==55for forHarmonic HarmonicSignals Signals CC==100 For Random 100 For RandomSignals Signals


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FFT - Fast Fourier Transformation

Sampl e 1

Sampl e 2

Filtering

Filtering

Window Function

Window Function

Detectors

Detectors

FFT

+

FFT

Raw Machine Time Signal

/n = Av g

FFT Spectrum 1

FFT Spectrum

FFT Spectr um 2


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Time Synchronous Averaging Analysis Tacho

Sampl e 1

Sampl e 2

Filtering

Filtering

Raw Machine Time Signal Sample trigg ered by tacho (measured wrt speed)

+ Window Function Detectors

FFT Averaged Time Signal

Spectrum

Non synchronous signal will be averaged out. Reduced vibration effect– fr omagent nearby machine Copyright 2005PT. Putranata Adi Mandiri sole Prüftechnik AG, Germany

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FFT - How to select Freq. Ranges, lines, Averages

Shaft Rotating Speed Journal Bearings instability

Blades 2x

Rolling Element Bearings

Gear 3x

1 KHz

3KHz

40KHz


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Monitoring Techniques Types of Bearings

Journal Journal Bearings Bearings

••Stationary StationarySignals Signals ••Relative RelativeLow LowFrequency Frequency ••Displacement Displacementtransducer t ransducer

Use Proximity probes Rolling Rolling Element Element Bearings Bearings ••Modulated ModulatedRandom RandomNoise Noise ••Pulsating Pulsatingsignals signals ••High HighFrequency Frequency •• Accelerometers Accelerometers

Use Accelerometers Copyright 2005- PT. Putranata Adi Mandiri – sole agent Prüftechnik AG, Germany

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Informasi penting tentang mesin

Amplitudo vibrasi

frekuensi

Apa saja yang mungkin menyebabkan vibrasi ? Copyright 2005- PT. Putranata Adi Mandiri – sole agent Prüftechnik AG, Germany

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Analisa Amplitudo, Frekuensi dan Fase - 1 PENYEBAB

AMPLITUDO

FREKUENSI

FASE

KETERANGAN

GAMBAR SPECTRUM

1. Unbalance

Sebanding dgn ketidak balance, dominan pd radial (2x aksial)

1 x rpm

Single reference mark

Kondisi sering

A

ditemui f 1x

Ve = 15

Vf = 15

Pengukuran getaran : A e = 8

A f = 8

Va = 4 Vb = 3

Vc = 4 He = 15

A a = 3

A b = 4

Hf = 15

A c = 5 A d = 5

Ha = 4

Hb = 5 Hc = 3 Hd = 2

Vd = 4


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AMPLITUDO

FREKUENSI

FASE

KETERANGAN

2. Misalignment kopling atau poros bengkok

Dominan pd aksial, 50% atau lebih dari arah radial

Sering 1 x & 2 x rpm. Kadang 3 x rpm

Single

Ditandai timbulnya vibrasi A aksial. Gunakan alat laseralignment. Apabila mesin baru dipasang terjadi vibrasi, maka kemungkinan besar karena misalignment.

double triple

Ve = 3

GAMBAR SPECTRUM

f 1x

2x

Vf = 4


A f = 5

Va = 4 Vb = 10

Vc = 10 He = 4

A a = 7

A b = 15

Hf = 3

A c = 15 A d = 7

Ha = 5

Hb = 10 Hc = 10 Hd = 5

Vd = 4


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AMPLITUDO

3. Anti friction bearing buruk

FREKUENSI

Tidak stabil, ukur percepatan, gunakan acceleration probe

FASE

KETERANGAN

Sangat tinggi, beberapa kali

Tdk tentu,

Rpm, 1x, 2x, 3x,

rubah

Berubah-

GAMBAR SPECTRUM

Vibrasi akan timbul apabila bearing sdh parah. Gunakan vibrotip / shockpulse u deteksi awal

4x … 10x

Ve = 5

A

f 1x

2x

3x

Vf = 3


A f = 2

Va = 2 Vb = 4

Vc = 5-10 He = 4

A a = 4

A b = 3

Hf = 4

A c = 10-15 A d = 5

Ha = 3

Hb = 3 Hc = 5-10 Hd = 4

Vd = 3


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4x

Frekuensi bearing karakteristik


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Dimensi bearing


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Kalkulasi frekuensi dari elemen bearing BD ⎞ ( Hz ) β ⋅ fr ⋅ ⎛ 1 − ⋅ cos ⎜ ⎟ 2 PD ⎠ ⎝ n ⎛ BD ⋅ cos β ⎞ ( Hz ) Kerusakan di inner race = ⋅ fr ⋅ ⎜1 + ⎟ 2 ⎝ PD ⎠ 2 ⎛ ⎛ BD ⎞ PD ⎞ ⎜ ⋅ fr ⋅ ⎜1 − ⎜ ⋅ cos β ⎟ ⎟⎟ ( Hz ) Kerusakan pada elemen berputar = BD ⎠ ⎠ ⎝ ⎝ PD fr ⎛ BD ⋅ ⎜1 − ⋅ cos β ⎞⎟ ( Hz ) Kerusakan pada cage = 2 ⎝ PD ⎠ Kerusakan di outer race =

n

dimana: BD &PD : lihat gambar fr : Frekuensi rotasi dari inner race n : jumlah elemen berputar

β : sudut kontak Copyright 2005- PT. Putranata Adi Mandiri – sole agent Prüftechnik AG, Germany

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Why sho ck pul ses for rolling bearing n oise ? c

f nat =

(

m

x

1 m

∼

1 l

,

1 d

,

1 a

c = stiffness

) m = Mass

Material crack Shock pulse range rolling bearing

Machine vibration

plastical / elastical deformation

Natural frequencies rolling bearing pieces f nat,O

f nat,B

f nat, 2 1

Example

l

1

d

⋅m f ≈ x ⋅ 1 / 1 m f nat ≈ x ⋅ 30 Hz

l = n

1 000

2

⋅ 1 mm f ≈ x ⋅ 1/1 000 m f nat ≈ x ⋅ 30 000 Hz

a

d = n

10 000

⋅ μm f ≈ x ⋅ 1 / 1 00 000 m f nat ≈ x ⋅ 3 00 000 Hz a

36 000

100 000

=n

f log / Hz

ultra sound emissi on Copyright 2005- PT. Putranata Adi Mandiri – sole shock agent Prüftechnik 31 velocity acceleration pulsesAG, Germany

Overall values for Bearing condition

Acceleration - Crest Factor Spike Energy Value BCU - Value Kurtosis Factor gSE - Value SEE - Value

Shock Pulse Measurement Normalising with… • Shaft speed (rpm) • Shaft Diameter (Bearing Size)

? ?

? Time

Time Copyright 2005- PT. Putranata Adi Mandiri – sole agent Prüftechnik AG, Germany

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Normalising of shock pulse signals dBsv

dBsv 90

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90 ideal measurement

dBn

measurement location with signal damping

P dBn

25 15

dBm

C

dB m

10 dBc

dB c

dBi

dBia 0

0

-9

-9 dB sv = absolute shock pulse value

dB n = normalised shock pulse value

dBi = initial value

dBia = adjusted inital value

→

→ →

Basic value of the normalised shock pulse values

signal damping of real measurement location influencing factors like load condition

Copyright 2005PT. Putranata Mandiri – sole agent Prüftechnik AG, Germany → determined throughAdi RPM and lubrication and bearing type

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Fungsi envelope


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Signature Rolling Bearing Defects No rolling track defect:

Rolling track defect:

Time signal:

Time signal: a in m/s2

a in m/s2

Envelope

Enveiope

t in s

t in s

Ta

Envelope spectrum:

Envelope spectrum:

a in m/s2

a in m/s2

f in Hz

f RPOF

2•f RPOF 3 •f RPO F 4 •f RPOF

f in

Hz

• f RPOF=

1 TRPOF

Defect frequency


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Enve nv elope lo pe Spectru Spectrum m be b earing ri ng Loc ation :PT. Caltex\Wa Caltex\Water ter Plant\Fresh Water Pump\Centrifugal Pump\Coupling Side\rolling bearing >120 >120

am /s² 2.0

#

X

Y

0

0.63

0.96

1

25.00

0.21

2

50.00

0.14

Alarm

3

176.88

0.10

W arn rn

4

151.88

0.10

0.6

5

126.88

0.08

0.4

6

4.38

0.08

7

20.63

0.07

8

29.38

0.07

1000 fHz 9

15.00

0.06

1.8 1.6 1.4 1.2 1.0 0.8

0.2 0.0

0

100

200

300

400

500

600

700

800

900


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An A n ali al i s a A m p l i t u d o , Frek Fr eku u ens en s i d an Fase Fas e - 4 PENYEBAB

AMPLITUDO

FREKUENSI

FASE

KETERANGAN

4. Sleeve, metal, Jurnal bearing (friction bearing) / eksentrik

Tida Tidak k besa besar, r, aksial

1 x rpm, seolaholah olah sepe sepert rtii unbalance

Single

pd rodagigi vibrasi segaris dengan dengan pusat pusat kontak kontak.. pd motor/ motor/gen gen vibrasi vibrasi hilang hilang bila mesin dimatikan. pd pompa/blower kemungkina kemungkinan n unbalance unbalance

lebi lebih h ting tinggi gi

Ve = 4

GAMBAR SPECTRUM

A

f 1x

Vf = 4

Pengukur ngukura an geta getara ran n: A e = 4

A f = 5

Va = 4 Vb = 7

Vc = 3 He = 4

A a = 7

A b = 15

Hf = 3

A c = 4 A d = 4

Ha = 3

Hb = 8 Hc = 5 Hd = 3

Vd = 5


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An A n ali al i s a A m p l i t u d o , Frek Fr eku u ens en s i d an Fase Fas e - 5 PENYEBAB

AMPLITUDO

5. Rodagigi buruk atau bersuara

Rendah, ukur kece kecepa pata tan n& percepatan, gunakan acceleration

FREKUENSI

FASE

KETERANGAN

Sangat Sangat tinggi tinggi

Tdk Tdk tent tentu u

GAMBAR SPECTRUM

Awal Awal rusa rusak k bersuara, semakin lama keras. Vibras Vibrasii biasan biasanya ya dalam dalam toleran toleransi. si.

Jumlah gigi x rpm

Ve = 7

A

f 1x

2x

3x

tooth

Vf = 3

Pengukur ngukura an geta getara ran n: A e = 8

A f = 5

Va = 4 Vb = 3

Vc = 7 He = 6

A a = 3

A b = 4

Hf = 4

A c = 8 A d = 9

Ha = 3

Hb = 2 Hc = 7 Hd = 7

Vd = 7


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4x


AMPLITUDO

FREKUENSI

FASE

KETERANGAN

6. Gear mesh buruk atau bersuara (pada saat start / stop)

Rendah, ukur kecepatan &

Sangat tinggi

Tdk tentu

percepatan, gunakan accel.

rpm

GAMBAR SPECTRUM

Sering terjadi pada saat pemasangan

Jumlah gigi x

A

f 1x

2x

3x

tooth

Ve = 7

Vf = 3


A f = 5

Va = 4 Vb = 3

Vc = 7 He = 6

A a = 3

A b = 4

Hf = 4

A c = 8 A d = 9

Ha = 3

Hb = 2 Hc = 7 Hd = 7

Vd = 7


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4x

Gear frequencies for Parallel Offset Gear • Number of teeth on the pinion...................(N p ) • Pinion speed, rpm.......................................(R p ) • Number of teeth on gear.............................(N g )

f r D o a m t a n t h e e e g d e e a d r

• Gear speed, rpm.........................................(R g ) • Gear rotational frequency, Hz...................(f rg ) • Pinion rotational frequency, Hz.................(f rp ) • Mesh frequency, H................................(f m ) • Tooth repeat frequency, Hz......................(f tr )

f n r I o f m o c t h a l e c d u l a a t a t e d

• Assembly phase passage frequency, Hz.....(f a) Copyright 2005- PT. Putranata Adi Mandiri – sole agent Prüftechnik AG, Germany

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• Pumps are found in nearly every industry in a wide array of sizes and capacities. Larger pumps, such as boiler feed pumps and reactor recirculation/coolant pumps, are often permanently monitored, though many smaller units are not. Regardless, the following parameters are necessary to effectively evaluate process-related phenomena: • Speed • Suction pressure and temperature • Discharge pressure and temperature • Flow • Bearing metal and oil drain temperatures • Driver power Copyright 2005- PT. Putranata Adi Mandiri – sole agent Prüftechnik AG, Germany

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Air Compressor


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Air Compressor


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Centrifugal Compressor


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Centrifugal Compressor

•

• • • • • • •

The compressor is one of the petrochemical industry's most durable and dependable machines. In general, there is a more limited set of variables to be monitored in compressors than in gas and steam turbines, which helps when you are analyzing and troubleshooting. However, rotational speeds tend to be much higher. The following process parameters are considered key items: Suction pressure and temperature Discharge pressure and temperature Product (gas) flow rate Gas analysis (mole weight) Compressor speed Driver power Bearing metal and oil drain temperatures


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Generator


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Generators

• Gene Genera rato tors rs are are gen gener eral ally ly wel welll-be beha have ved d dyna dynami mica call lly, y, due due to their less complicated construction, compared to gas and steam turbines. Unbalance, thermal bows, and seal rubs comprise the majority of problems seen. The process variable list reflects this: • Output (kW or MW) • Reactive lo loading (v (vars) • Power factor • Cool Coolan antt gas gas temp temper erat atur uree and and pres pressu sure re • Winding temperatures • Field current • Bear Bearin ing g met metal al and and oil oil drai drain n tem tempe pera ratu ture ress Copyright 2005 2005-- PT. PT. Putrana Putranata ta Adi Mandiri Mandiri – sole agent agent Prüftechnik AG, Germa Germany ny

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Gas Turbine


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gas turbines

•

It is easy to see the interaction of process and vibration characteristics by studying industrial and aeroderivative gas turbines, because they are really three machines in one. They are a compressor that pressurizes ambient air, a combustor that introduces fuel and burns the air/fuel mixture, and an expansion (or power) turbine through which the hot, high pressure combustion gases expand, driving the compressor and any other connected machinery. Gas turbines are subject to wide performance and vibration variations when ambient air, fuel, or load values change. For example, high inlet air temperature reduces gas turbine performance, requiring higher fuel consumption for a specific power level. Conversely, low air temperature causes the power to increase. If humidity is high, ice can form on the inlet filters, inlet ducting, and inlet casing of the compressor. Large accumulations of ice reduce and distort the airflow, which may cause compressor stall and surge.


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Steam turbines

•

• • • • • • •

Steam turbines are used in almost every industry for driving compressors, generators, pumps, and other equipment. Sizes vary from small, single stage units of less than 100 hp to large power generation units capable of over 1,000 MW in a single machine train. However, despite these size variations, steam conditions generally provide significant insight into any rotor response changes, such as rubs and shaft bow. Process variables that should be monitored on each driver include: Steam supply and exhaust conditions - temperature, pressure, flow, quality Extraction conditions (if applicable) Condenser vacuum Bearing metal and oil drain temperatures Gross generation (kW) or shaft speed and torque Reheat steam conditions (if applicable) Kvars (generator drive applications)


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Phase Analysis

• Trending for Acceptance Regions • Shaft crack detection • Rub detection • Shaft balancing • Shaft/structural resonance detection • Shaft mode shape • Location of a fluid-induced instability Copyright 2005- PT. Putranata Adi Mandiri – sole agent Prüftechnik AG, Germany

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Trending


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Shaft Crack


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Rubs


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Shaft Structure


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Shaft balancingShaft mode shape


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Location of flui d-induced instability


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Rotational & Mesh Gear Frequencies

Gear & Pinion rotational frequencies : f rg

=

Rg

60

( Hz ),

f rp

=

R p

60

( Hz )

Mesh frequency : f m

= f rp × N p = f rg × N g ( Hz )


84

Assembly phase passage gear frequency (1)

Ng = 15 Gear tooth 1-10-4-13-7 2-11-5-14-8 3-12-6-15-9

Np = 9 Pinion Tooth 1-7-4 2-8-5 3-9-6


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Ng = 15 Gear tooth 1-10-4-13-7 2-11-5-14-8 3-12-6-15-9

Np = 9 Pinion Tooth 1-7-4 2-8-5 3-9-6


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Assembly phase passage frequency : f m f a = ( Hz ) N a N a

= Pr oduct of common prime factors

example : F g = 1,3,5,15 F p = 1,3,3,9 N a = 1× 3 = 3

Ng = 15 Gear tooth 1-10-4-13-7 2-11-5-14-8 3-12-6-15-9

Np = 9 Pinion Tooth 1-7-4 2-8-5 3-9-6


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Tooth repeat gear frequencies

Tooth repeat frequency : f tr =

f m × N a N g × N p

( Hz )

or for a true hunting tooth combination

( when N a f tr =

f rg N p

= 1) : ( Hz )


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Summary gear frequencies for parallel offset gear To obtain

f tr

f rg

f rp

N a /N g

1/M g

1

N a /N p

1

Mg

f a

f m

multiply

f rp f rg

f m

by

N a /(N g × 1/N g 1/N p Np )

N p /N a N p N g /N a

Ng

1/N a

1

N a = Number of assembly phases, N p = Number of teeth on pinion N g = Number of teeth on gear, M g = Ratio gear, f tr = Tooth repeat freq (Hz) f rg = Gear rotational freq (Hz), f rp = Pinion rotational freq (Hz) f a = Assembly phase passage freq (Hz), f m = Mesh frequency (Hz) Copyright 2005- PT. Putranata Adi Mandiri – sole agent Prüftechnik AG, Germany

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Gear frequencies for Planetary Gear


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Application mill drive - cement industry

[bar] [m/s²] [bar]

4x [°C]

Machine speed Alarm status

[m/s²]

[m/s²]

[m/s²] [m/s²]

PCS

External expert

Data backup LAN / WAN

Internal expert

Interne t Copyright 2005- PT. Putranata Adi Mandiri – sole agent Prüftechnik AG, Germany

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Gear frequencies for Planetary Gear Planetary Gear : Ts x Tr ⎞ ⎛ Tooth Mesh Freq = ⎜ ⎟ x Ns = Tr x Nc (Hz) ⎝ Ts + Tr ⎠ ⎛ np x Tr ⎞ x Ns = np x Tr x Nc (Hz) Defect on Sun = ⎜ ⎟ Ts ⎝ Ts + Tr ⎠ Defect on Planet = 2 x Nc x

Tr Tp

(Hz)

Defect on Ring = np x Nc (Hz) where : Ns = speed of sun gear (output), Nc = speed of carrier (input) Ts = number of teeth on sun, Tr = number of teeth on ring np = number of planets Copyright 2005- PT. Putranata Adi Mandiri – sole agent Prüftechnik AG, Germany

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Comparison of Sinusoi dal and Impact Gear Tooth Contact


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AMPLITUDO

FREKUENSI

FASE

KETERANGAN

7. Mechanical looseness (Housing bearing aus)

Tinggi pada aksial

2 x rpm

2 referensi Sering agak kacau bersamaan dgn unbalance / misalignment

Ve = 3

GAMBAR SPECTRUM

A

f 2x

Vf = 3


A f = 4

Va = 4 Vb = 12

Vc = 5 He = 4

A a = 3

A b = 15

Hf = 2

A c = 5 A d = 3

Ha = 3

Hb = 12 Hc = 5 Hd = 4

Vd = 5


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AMPLITUDO

FREKUENSI

FASE

KETERANGAN

GAMBAR SPECTRUM

8. Mechanical Looseness (Pondasi kendor – dudukan lemah/karatan – baut kendor)

Tinggi pada vertikal

Kurang dari 1 x rpm

Tdk tentu

Kencangkan baut Untuk memastikan

A

f <1x

Ve = 3

Vf = 2


A f = 3

Va = 9 Vb = 10

Vc = 5 He = 3

A a = 3

A b = 4

Hf = 4

A c = 2 A d = 2

Ha = 2

Hb = 4 Hc = 2 Hd = 4

Vd = 3


96


AMPLITUDO

FREKUENSI

FASE

KETERANGAN

9. Mechanical looseness (Pondasi melengkung)

Tinggi pada vertikal, horizontal & aksial

2 x rpm


Ve = 3

GAMBAR SPECTRUM

A

f 2x

Vf = 3


A f = 4

Va = 9 Vb = 12

Vc = 5 He = 4

A a = 7

A b = 6

Hf = 2

A c = 5 A d = 3

Ha = 13

Hb = 14 Hc = 5 Hd = 4

Vd = 5


97


AMPLITUDO

FREKUENSI

FASE

10. Drive belt buruk

Tdk tentu/berpulsa

1,2,3 atau 4 x rpm belt

1 atau 2 tergantung frekuensi, tdk tetap

Belt

KETERANGAN

GAMBAR SPECTRUM

Biasanya terjadi karena belt tdk berada pada tempatnya secara sempurna.

Ve = 8

A

f 1x

2x

3x

Vf = 4


A f = 3

Va = 3 Vb = 2

Vc = 10 He = 7

A a = 2

A b = 3

Hf = 2

A c = 10 A d = 10

Ha = 2

Hb = 4 Hc = 10 Hd = 8

Vd = 10


98

4x


AMPLITUDO

11. Elektrikal

Tidak tinggi, ada suara berdengung, lebih terasa bila dimatikan

FREKUENSI

FASE

KETERANGAN

2 x rpm lebih tinggi daripd

Single/

Vibrasi & suara hilang bila mesin dimatikan

rotate double mark

1 x rpm.

GAMBAR SPECTRUM

A

f 1x

Ve = 3

2x

Vf = 2


A f = 3

Va = 7 Vb = 6

Vc = 4 He = 3

A a = 6

A b = 7

Hf = 1

A c = 5 A d = 5

Ha = 8

Hb = 8 Hc = 5 Hd = 3

Vd = 3


99

Jenis-jenis motor listrik

- Motor induksi (induction / asynchronous motor) - Synchronous motor - DC motor


100

Permasalahan pada motor listrik - Electrical

- Eccentric rotor - Uneven airgap (penyebab : softfoot / frame distortion) - Broken rotor bars - Shorted rotor lamination - Phasing problem


101

Istilah-istilah motor listrik

- Line frequency (frekuensi jala-jala) = FL (di Indonesia : 50 Hz, USA : 60 Hz) - Poles (P) = stator conductors = 2FL / RPM (FL dlm CPM) - Slots (S) = stator winding containers - Bars (B) = rotor field conductors


102

Frequencies of electric motors

• Magnetic field speed, RPM (Ns) = 120 x FL / (# poles) • Slip frequency (SF) = Ns – actual speed • Pole pass frequency (Fp) = SF x (# poles) • Rotor bar pass freq. (RBPF) = (# bars) x RPM • Stator slot pass freq. (SSPF) = (# stator slot) x RPM Example : Info on Name plate of electric motor : Speed = 1480 RPM, # rotor bars = 40 -> # poles = (2 x 3000) / 1480 = 4 -> Ns = 120 x 50 / 4 = 1500 RPM -> SF = 1500 – 1480 = 20 RPM = 0.33 Hz -> Fp = 4 x 20 RPM = 80 RPM = 1.33 Hz -> RBPF = 40 x 1480 RPM = 59200 RPM = 986.67 Hz Copyright 2005- PT. Putranata Adi Mandiri – sole agent Prüftechnik AG, Germany

103

Analisa vibrasi pada motor listrik – 1 / 4

- Stator eccentricity, loose iron, shorted laminations : 1x

e d u t i l p m A

2FL

FL = Line Frequency (3000 CPM, for 50 Hz Li ne Freq.)

2x Frequency

- Uneven air gap (variable air gap) / Eccentric rotor : e d u t i l p m A

1x

2FL

FL = Lin e Frequenc y (3000 CPM, for 50 Hz Lin e Freq.) Fp Sidebands around FL

Fp Frequency • Pole pass f requency (Fp) = SF x (# poles) • Slip fr equency (SF) = Ns – actual speed • Magneti c fi eld s peed, RPM (Ns) = 120 x FL / (# pol es)


104


- Rotor problems 1 (broken/cracked rotor bars / shorting rings, shorted rotor laminations) : 1x

e d u t i l p m A

3x 2x

* Fp Sidebands around 1x for broken rotor bars * Fp Sidebands aroun d 1x, 2x, 3x, …. for cracked rotor bars

Frequency

- Rotor problems 2 (loose/broken rotor bars) : RBPF e d u t i l p m A

1x

2FL Sidebands around RBPF or its harmonic freq. 2x

RBPF = Roto r Bar Pass Frequenc y = # Bars x RPM

Frequency


105


- Phasing problems (motor beroperasi hanya 2 dari 3 phasa, disebabkan oleh loose / broken connectors) : 2FL 1/3 FL Sidebands arou nd 2FL

e d u t i l p m A

Frequency

Loose stator coils pada synchronous motors : CPF e d u t i l p m A

1x RPM Sidebands aro und CPF = Coil Pass Freq. 1x 2x CPF = # stator c oils x RPM

Frequency


106


- DC motor problems 1 (broken field winding, bad SCR and loose connection) : 6FL = SCR Firing Freq. or its h armon ic freq. e d u t i l p m A

1x 2x

Frequency

- DC motor problems 2 (loose/blown fuses, shorted control card) : FL e d u t i l p m A

Am pl itu de ting gi pad a 1x h ing ga 5x L ine Fr eq. 2FL 3FL

4FL

5FL

Frequency


107

Rekommendasi untuk analisa vibrasi motor listrik

Untuk mendeteksi uneven airgap, eccentric rotor :

-> 3 titik “ resolusi tinggi” (diambil 1x setahun) * HOH : high resolution, motor outboard horizontal * HIH : high resolution, motor inboard horizontal * HOA (or HIA) : high resolution, motor outboard (or inboard) axial -> Fmax = 200 Hz, 1600 lines -> Resolusi = 0.125 Hz


108

Rekommendasi untuk analisa vibrasi motor listrik

Untuk mendeteksi munculnya rotor bar pass frequency atau stator slot pass frequency :

-> 2 titik “ extended range” (diambil 1x setahun) * EOH : extended range, motor outboard horizontal * EIH : extended range, motor inboard horizontal -> Fmax = 5000 Hz, 3200 lines, jika tidak diketahui jumlah rotor atau stator slot, sebenarnya cukup s/d frekuensi : (2x rotor / stator slot pass freq. + 400 Hz) -> Jika ingin mengambil data ini 1x sebulan, cukup dengan 400 – 800 lines untuk menghemat memori Copyright 2005- PT. Putranata Adi Mandiri – sole agent Prüftechnik AG, Germany

109


AMPLITUDO

12. Gaya aerodinamik / hidrolik

Tinggi pada vertikal atau horizontal

FREKUENSI

FASE

1 x rpm atau jumlah sudu atau fan atau impeler x rpm

KETERANGAN

Tdk tentu

GAMBAR SPECTRUM

Lebih terasa bila beban tidak stabil.

A

f 1x

Ve = 14

Jml x

Vf = 13


A f = 7

Va = 1 Vb = 2

Vc = 4 He = 13

A a = 1

A b = 3

Hf = 14

A c = 5 A d = 3

Ha = 2

Hb = 2 Hc = 3 Hd = 4

Vd = 4


110


AMPLITUDO

FREKUENSI

FASE

13. Gaya reciprocating

Dominan aksial

1 x,2 x rpm

Single, double, triple

atau lebih

KETERANGAN

GAMBAR SPECTRUM

A

Pada mesin reciprocating bisa ganti desain/isolasi

Ve = 2

f 1x

2x

Vf = 2


A f = 3

Va = 7 Vb = 8

Vc = 3 He = 4

A a = 6

A b = 7

Hf = 2

A c = 4 A d = 4

Ha = 8

Hb = 7 Hc = 2 Hd = 4

Vd = 3


111

Ringkasan Analisa Amplitudo, Frekuensi dan Fase PENYEBAB

AMPLITUDO

FREKUENSI

FASE

KETERANGAN

1. Unbalance

Sebanding dgn ketidak balance, dominan pd radial (2x aksial)

1 x rpm

Single reference mark

Kondisi sering

Dominan pd aksial, 50% atau lebih dari arah radial

Sering 1 x & 2 x rpm. Kadang 3 x rpm

2. Misalignment kopling atau poros bengkok

Single double triple Tdk tentu,

4. Sleeve, metal, Jurnal bearing (friction bearing)

Tidak besar, aksial

Single

5. Rodagigi buruk atau bersuara

Rendah, ukur kecepatan & percepatan, gunakan accel.

lebih tinggi

A

ditemui f 1x

Tidak stabil, Sangat tinggi, ukur acceleration beberapa kali untuk freq. Rpm, 1x, 2x, 3x, tinggi 4x … 10x

3. Anti friction bearing buruk

GAMBAR SPECTRUM

1 x rpm, seolaholah seperti unbalance Sangat tinggi Jumlah gigi x rpm

Berubahrubah

Tdk tentu

Ditandai timbulnya vibrasi A aksial. Gunakan alat laseralignment. Apabila mesin baru dipasang terjadi vibrasi, maka kemungkinan besar karena misalignment.

Vibrasi akan timbul apabila bearing sdh parah. Gunakan enveloping & shockpulse

A

pd rodagigi vibrasi segaris dengan pusat kontak. pd motor/gen vibrasi hilang bila mesin dimatikan. pd pompa/blower kemungkinan unbalance

A

Awal rusak bersuara, semakin lama keras. Vibrasi biasanya dalam toleransi.

A

f 1x

2x

1x

2x

f 3x

4x

f 1x

f 1x

2x

3x

tooth Copyright 2005- PT. Putranata Adi Mandiri – sole agent Prüftechnik AG, Germany

112

4x


AMPLITUDO

FREKUENSI

6. Gear mesh buruk atau bersuara pada saat start/stop

Rendah, ukur kecepatan &

Sangat tinggi

Tdk

Jumlah gigi x

tentu

percepatan, gunakan accel.

rpm

7. Mechanical looseness (Housing bearing aus)

Tinggi pada aksial

2 x rpm

8. Mechanical Looseness (Pondasi kendor – dudukan lemah/karatan – baut kendor)

Tinggi pada vertikal

9. Mechanical looseness (Pondasi melengkung)

Tinggi pada vertikal, horizontal & aksial

2 x rpm

10. Drive belt buruk

Tdk tentu/berpulsa

1,2,3 atau 4 x rpm belt

Kurang dari 1 x rpm

FASE

KETERANGAN

Sering terjadi pada saat pemasangan

GAMBAR SPECTRUM

A

f 1x


A

Tdk tentu

A

Kencangkan baut Untuk memastikan

2x

3x

4x

f 2x

f <1x


A

1 atau 2 tergantung frekuensi, tdk tetap

A

Biasanya terjadi karena belt tdk berada pada tempatnya secara sempurna.

f 2x

f 1x


2x

3x

113

4x


AMPLITUDO

FREKUENSI

FASE

KETERANGAN

11. Elektrikal

Tidak tinggi, ada suara dengung, lbh terasa bila dimatikan

2 x rpm lebih tinggi daripd

Single/

Vibrasi & suara hilang bila mesin dimatikan

Tinggi pada vertikal atau horizontal

1 x rpm / jml sudu / fan atau impeler x rpm

Tdk tentu

1 x,2 x rpm

Single, double, triple

12. Gaya aerodinamik / hidrolik 13. Gaya reciprocating

Dominan aksial

1 x rpm.

atau lebih

rotate double mark

GAMBAR SPECTRUM

A

f 1x

Lebih terasa bila beban tidak stabil.

2x

A

f 1x

Pada mesin reciprocating bisa ganti desain/isolasi

Jml x

A

f 1x


2x

114

Phase Analysis

Kegunaan informasi fase untuk analisa masalah mesin :

- Mendeteksi “ shaft crack” - Mendeteksi “ rubbing” - Diperlukan sewaktu Balancing - Mendeteksi resonansi dari shaft atau casing - Mengetahui bentuk gerakan shaft (shaft bending)


115

Phase Analysis

Tanda-tanda “ shaft crack” :

- Nilai tinggi pada frekuensi 1x RPM di gambar spectrum - Perubahan dalam nilai fase yang cukup signifikan 6

o5 d u4 t i l 3 p 2 m1 A 0

0

20

40

60

80

100

120

140

160

180

200

220

240

Time (interval 20 m inutes)

Time (interval 20 minutes) 0

20

40

60

80

100

120

140

160

180

200

220

240

0

g 20 a l 40 e 60 s a 80 h100 P 120


116

Phase Analysis

Tanda-tanda masalah “ rubbing” :

- Nilai amplitudo yang berfluktuasi di frekuensi 1x RPM - Nilai fase yang secara kontinu berubah Polar Vibration Trend Plot of st eady state vibration due to a seal rub

0 340 320

8

20 40

6

300

60

4

2

280

80

0 260

100

240

120

220

140 200

160 180


117

Phase Analysis

Mengetahui bentuk gerakan shaft :

- Untuk menentukan balancing 1 atau 2 plane - Untuk mendeteksi resonansi dari shaft atau struktur 1

2

3

4

1

2

3

4


118

Cepstrum Analysis Cepstrum Cepstrumisisaaspectrum spectrumof ofaalogarithmic logarithmicspectrum spectrum

FFT Spectrum

Time Signal F raw

F

V (dB)

Cepstrum

-1 V

28,1 ms (35 Hz)

100

FFT

95,9 ms (10 Hz)

90

FFT

80 70 100 200

Spectrum Frequency (Hz) Harmonics Filter Magnitude

300 400

500

Hz

0,1

0,2

0,3

Cepstrum Qerf uency (ms) Rahmonics Lif ter Gamnitude

Sideband patterns easily diagnosed and trended with Cepstrum analysis Copyright 2005- PT. Putranata Adi Mandiri – sole agent Prüftechnik AG, Germany

119

s

Bode Plot Bode es plotting Bodeplot plotinvolv invol ves plottingthe thevibration vibrationamplitude amplitude and andphase phaseagainst againstrotational rotationalspeed speed 0o

Phase

90o

180o

Critical Speed Amplitude Slow roll Use for identifying resonance or critical speed. Very sensitive to run-out

Rotational Speed


120

Polar Plots

(Nyquist plots)

Polar Polarplot plot--the thevibration vibrationamplitude amplitudeisisplotted plottedagainst against Phase Phaseon onaapolar polargraph graphpaper paper 90o

Criti cal Speed 90o Phase shift

Amplitude at critical speed Increasing Shaft speed

180o

0o

Origin

Residual unbalance

Same information as Bode plot – different presentation. Advantage: Easy to correct for run out by shifting orgin for all vectors. Copyright 2005- PT. Putranata Adi Mandiri – sole agent Prüftechnik AG, Germany

121


122

Proximity probe’s signal A Aproximity proximityprobe probeprovides providestwo twosignal signaloutput: output: 1. 1. Shaft Shaftdynamic dynamicmotion motionrelative relativeto tothe theprobe probemounting mounting(AC (ACsignal) signal) 2. 2. Shaft Shaftaverage averageposition positionrelative relativeto tothe theprobe probemounting mounting(DC (DCsignal) signal)

AC Signal

Gap

DC Signal


123

Shaft centerline plot Plotting PlottingX-Y X-Ycoordinates coordinatesof ofGap Gap(DC (DCsignal) signal) o from from22prox. prox.probe probespace space90 90oapart apartat ateach eachbearing bearing um

b

+ ++ + + + b + + ++ a

um

Provides exact determination of the average shaft Centerline position relative to the bearing clearance Compared with bearing centerline for measurement of shaft attitude angle = exceeds 90o ~ instability

a Copyright 2005- PT. Putranata Adi Mandiri – sole agent Prüftechnik AG, Germany

124

Orbits

(lissajou)

Orbits Orbits––Plotting PlottingX-Y X-Ycoordinates coord inatesof oftwo twosignals signals o (shaft (shaftdisplacement) displacement)space space90 90oapart apartat ateach eachbearing bearing Y, vertical

X, horizontal • Two pure sine waves of equal amplitude with 90o phase difference = circular orbit • If they have different amplitudes but retain 90o phase = elliptical with the major axis In the direction of the largest amplitude Copyright 2005- PT. Putranata Adi Mandiri – sole agent Prüftechnik AG, Germany

125

Orbits

(lissajou)

Orbits e of Orbits––use useto todisplay displayaaaccurate accuratepictur picture ofshaft shaftmotion motion greatly greatlymagnified, magnified,and andeasily easilyunderstood understood

Line of action Y, vertical

X, horizontal

External forc es reduces ampli tude: Gravity, Preload by pressure dam bearing s, Misalign ment of shafts r estrain


126

Typical misalignment Produce a 180o phase shift across coupling This phase shift can be observed in radial vibration and/or shaft centerline (connecting the trigger points)


127


128


129

Order Amplitude

Phase

Run-up/ Coastdown Speed Copyright 2005- PT. Putranata Adi Mandiri – sole agent Prüftechnik AG, Germany

130


131

Time vs FFT Time Signal:

FFT Fast Fourier Transformation

transient signals, repeat frequencies, beats and sine waveform good visible → but: Individual Frequencies of the Vibration Spectrum almost not visible Amplitude Spectrum: good visibility of the dominant frequencies of the vibration signal → but: transient Signals, shocks with repeat frequency and beat signals almost not visible


132

VIBRASI_SE~3 (Level2)

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