305575138-VIBRASI-SE-3-Level2.pdf

Copyright 2005- PT. Putranata Adi Mandiri – sole agent Prüftechnik AG, Germany 1
Vibration Analysis – Level 2
for assessing machine potential failure modes

• Broad Band Vibration Analysis
• Bearing Condition Analysis
• Frequency Analysis (FFT)
• Time Synchronous Averaging Analysis
• Time Waveform Analysis
• Multispectrum
• Envelope Analysis
• Constant Percentage Bandwidth Analysis
• Cepstrum
• Shaft Orbit
• Tracking Analysis
• Vector Analysis (Amp. & Phase)
• Startup / Coastdown Analysis
• Impact Test
ANALYSIS TECHNIQUES

Broad Band Vibration Analysis
Also know as Overall vibration measurement
Typically...
Velocity measurement
mm/s, RMS from 2 Hz to 1000 Hz
Displacement measurement
um, RMS from 2 Hz to 1000 Hz
Can be overall acceleration measurement
eg. Gear box monitoring
ISO 10816-3

Effect of Machine speed variation
on
Vibration measurement
1500 2000 2500 3000 3500 4000 4500 5000 5500 6000 6500 7000
t ms
0.45
0.40
0.35
0.30
0.25
0.20
0.15
0.10
0.05
0.00
0.05
0.10
0.15
0.20
0.25
0.30
0.35
0.40
0.45
v mm/s
0 7 /0 2 /2 0 0 1
4 :5 9 :0 0 PM
0 7 /0 2 /2 0 0 1
4 :5 9 :1 0 PM
0 7 /0 2 /2 0 0 1
4 :5 9 :2 0 PM
0 7 /0 2 /2 0 0 1
4 :5 9 :3 0 PM
0 7 /0 2 /2 0 0 1
4 :5 9 :4 0 PM
d a te
0 .2
0 .4
0 .6
0 .8
1 .0
1 .2
1 .4
1 .6
1 .8
2 .0
2 .2
2 .4
2 .6
2 .8
3 .0
3 .2
3 .4
3 .6
3 .8
4 .0
v m m /s
r m s
Time Signal
Overall Vibration Level
Vibration Monitoring

Bandpass Measurement
Peak
Peak
to
Peak
RMS (0.707xPeak)
Avg (0.637xPeak)
Always ask.... Are you measuring RMS or Peak , etc ??
What is the frequency range ??
How much averaging?
Freq. = 1/Time
Freq. = Hz
= rev. per second
Machine Freq are function of RPM
ie. rev. per minute

Frequency Analysis
Machine Vibrations
Time Signal
Time, s = Frequency, Hz
Time = 1 / Frequency

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.
Frequency Analysis
T
Time F (Hz)
Time = 1 / Frequency
F

Frequency Analysis
How to make a frequency analysis?
Frequency analysis can be made using frequency selective devices called filters
An ideal filter will only signals to pass within its bandwidth
f
dB
Practical filter have roll-off, express as half-power (-3dB)
For good filters the two will be very similar.
f
dB
0
-3
f2
f1 fc
f2
f1 fc
B
B = Bandwidth
In FFT analysis, the bandwidth = Frequency span / no. lines

Types of Bandwidth
0.1
frequency
Constant
Bandwidth a=b=c
(FFT)
Constant
Percentage
Bandwidth
(CPB)
Vibration
Amplitude
1 2 3 4 5 6 7 8 9 10 kHz
a
z
b
c
y
x
x, y, z are constant % of their center frequency

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
Anti-aliasing filters - Low pass filter at half the sampling frequencies
Frequency Analysis
Types of filters:
f
f

Discrete Fourier Transform (DFT) - Pitfalls
FFT - Fast Fourier Transform is an efficient means of calculating a DFT
(Discrete Fourier Transform). Basically, it transform a time signal into a
frequency spectrum.
FFT (DFT) - Pitfalls
1. Aliasing - high frequencies appearing as low frequencies
2. Leakage - Memory contents forced to be periodic.
Can give discontinuities when ends joined
3. Picket fence effect – Actual spectrum sampled at discrete
frequencies. Peaks may be missing
1. Aliasing - high frequencies appearing as low frequencies
2. Leakage - Memory contents forced to be periodic.
Can give discontinuities when ends joined
3. Picket fence effect – Actual spectrum sampled at discrete
frequencies. Peaks may be missing

FFT pitfalls - Aliasing Effect
Sampling rate too slow
High frequency analysis results in false
low 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.

1st Sample
2nd Sample
-ve
+ve
+ve
-ve
FFT pitfalls - Leakage
…..give discontinuities
when ends joined

Actual
Spectrum
Measured
Spectrum
FFT pitfalls - Picket Fence Effect

Frequency Analysis
Basic law of frequency analysis
min. analysis time must allow
the measured freq. to complete
it’s cycle / period
BT > 1
Analysis Time
Bandwidth
T
Time
T

Fungsi window

FFT Spectrum
400 lines FFT
1X 2x 3X 1 kHz
IF Freq. Span is 1 KHz then resolution
= 1000 / 400 lines
= 2.5 Hz
(eg. 2 - IF Span is 40Khz then resolution= 100Hz)
2.5 Hz 5 Hz 7.5Hz

Measurement time
• Harmonic signals
can be measured in
short time
• Random and Pulsed
signals
need longer time
• For FFT spectra C
= 1 pr. average.
B * T = C
B = Highest resolution of Analysis
T = The Shortest measurement time
C = Constant.
B * T = C
B = Highest resolution of Analysis
T = The Shortest measurement time
C = Constant.
Theoretical
C = 3 for Harmonic Signals
C = 30 For Random Signals
Theoretical
In Practice
In Practice

Filtering
Window Function
Detectors
FFT
Sample 1
FFT Spectrum 1
+
Sample 2
Window Function
Detectors
FFT
Filtering
FFT Spectrum 2
/n =
Avg FFT Spectrum
FFT - Fast Fourier Transformation
Raw Machine
Time Signal

+
Sample 2
Filtering
Time Synchronous Averaging Analysis
Non synchronous signal will be averaged out.
Reduced vibration effect from nearby machine
Window Function
Detectors
FFT
Spectrum
Averaged Time Signal
Sample 1
Filtering
Sample triggered by tacho
(measured wrt speed)
Raw Machine
Time Signal
Tacho

Gear
Blades
Rolling Element
Bearings
Shaft
Rotating
Speed
2x
3x
Journal
Bearings
instability
1 KHz 3KHz 40KHz
FFT - How to select Freq. Ranges, lines, Averages

Types of Bearings
Journal Bearings
• Stationary Signals
• Relative Low Frequency
• Displacement transducer
Journal Bearings
• Stationary Signals
• Relative Low Frequency
• Displacement transducer
Rolling Element Bearings
• Modulated Random Noise
• Pulsating signals
• High Frequency
• Accelerometers
Rolling Element Bearings
• Modulated Random Noise
• Pulsating signals
• High Frequency
• Accelerometers
Use Proximity probes
Use Accelerometers
Monitoring Techniques

Informasi penting
tentang mesin
Amplitudo
vibrasi
frekuensi
Apa saja yang mungkin menyebabkan vibrasi ?

Analisa Amplitudo, Frekuensi dan Fase - 1
KETERANGAN
FASE
FREKUENSI
AMPLITUDO
PENYEBAB GAMBAR SPECTRUM
Kondisi sering
ditemui
Single
reference
mark
1 x rpm
Sebanding dgn
ketidak balance,
dominan pd
radial (2x aksial)
1. Unbalance A
f
1x
Pengukuran getaran :
Ha = 4
Aa = 3
Va = 4
Hb = 5
Vb = 3 Vc = 4
Ae = 8
Hc = 3
Hd = 2 Vd = 4
Ad = 5
Ab = 4 Ac = 5
He = 15
Ve = 15 Vf = 15
Af = 8
Hf = 15

KETERANGAN
FASE
FREKUENSI
AMPLITUDO
Ha = 5
Aa = 7
Va = 4
Hb = 10
Vb = 10 Vc = 10
Ae = 4
Hc = 10
Hd = 5 Vd = 4
Ad = 7
Ab = 15 Ac = 15
He = 4
Ve = 3 Vf = 4
Af = 5
Hf = 3
Ditandai timbulnya vibrasi
aksial. Gunakan alat laser-
alignment. Apabila mesin
baru dipasang terjadi
vibrasi, maka kemungkinan
besar karena misalignment.
Single
double
triple
Sering 1 x & 2 x
rpm. Kadang 3 x
rpm
Dominan pd
aksial, 50%
atau lebih dari
arah radial
2. Misalignment
kopling atau
poros bengkok
A
f
1x 2x

KETERANGAN
FASE
FREKUENSI
AMPLITUDO
Vibrasi akan timbul
apabila bearing sdh
parah. Gunakan
vibrotip / shockpulse u
deteksi awal
Tdk tentu,
Berubah-
rubah
Sangat tinggi,
beberapa kali
Rpm, 1x, 2x, 3x,
4x … 10x
Tidak stabil,
ukur percepatan,
gunakan
acceleration
probe
3. Anti friction
bearing buruk
A
f
1x 2x 3x 4x
Ha = 3
Aa = 4
Va = 2
Hb = 3
Vb = 4 Vc = 5-10
Ae = 4
Hc = 5-10
Hd = 4 Vd = 3
Ad = 5
Ab = 3 Ac = 10-15
He = 4
Ve = 5 Vf = 3
Af = 2
Hf = 4

Frekuensi bearing karakteristik

Dimensi bearing

Kalkulasi frekuensi dari elemen bearing
kontak
sudut
berputar
elemen
jumlah
n
race
inner
dari
rotasi
Frekuensi
fr
gambar
lihat
PD
BD
dimana:
Hz
PD
BD
fr
cage
pada
Kerusakan
Hz
PD
BD
fr
BD
PD
berputar
elemen
pada
Kerusakan
Hz
PD
BD
fr
n
race
inner
di
Kerusakan
Hz
PD
BD
fr
n
race
outer
di
Kerusakan
:
:
:
:
&
)
(
cos
1
2
)
(
cos
1
)
(
cos
1
2
)
(
cos
1
2
2
β
β
β
β
β
⎟
⎠
⎞
⎜
⎝
⎛
⋅
−
⋅
=
⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛
⎟
⎠
⎞
⎜
⎝
⎛
⋅
−
⋅
⋅
=
⎟
⎠
⎞
⎜
⎝
⎛
⋅
+
⋅
⋅
=
⎟
⎠
⎞
⎜
⎝
⎛
⋅
−
⋅
⋅
=

Why shock pulses for rolling bearing noise ?
Machine vibration Shock pulse range rolling bearing
Material crack
plastical / elastical
deformation
1 000 10 000 100 000
36 000 flog / Hz
velocity acceleration shock pulses ultra sound emission
Natural frequencies rolling bearing pieces
l = n ⋅ m
f ≈ x ⋅ 1 / 1 m
fnat
≈ x ⋅ 30 Hz
Example
d = n ⋅ 1 mm
f ≈ x ⋅ 1/1 000 m
fnat
≈ x ⋅ 30 000 Hz
a = n ⋅ μm
f ≈ x ⋅ 1 / 1 00 000 m
fnat
≈ x ⋅ 300 000 Hz
d a
fnat,O fnat,Ι fnat,B
l
fnat =
x
c
m
( ∼ , , )
1
m
1
l
1
d
1
a m = Mass
c = stiffness
1
2
1 2

Overall values for Bearing condition
Shock Pulse
Measurement
Acceleration - Crest Factor
Spike Energy Value
BCU - Value
Kurtosis Factor
gSE - Value
SEE - Value
Normalising with…
• Shaft speed (rpm)
• Shaft Diameter (Bearing Size)
Time
?
?
Time
?

Normalising of shock pulse signals
dBi = initial value
→ Basic value of the normalised
shock pulse values
→ determined through RPM and
diameter of the bearing
dBia = adjusted inital value
→ signal damping of real measurement location
→ influencing factors like load condition
lubrication and bearing type
ideal
measurement
measurement location
with signal damping
dBsv
dBi
dBsv
0
90
-9
-9
0
dBn
90
dBia
dBm
dBc
dBm
dBc
dBn
dBsv = absolute shock pulse value dBn = normalised shock pulse value
35
25
15
10
P
C

Fungsi envelope

Signature Rolling Bearing Defects
Time signal:
Time signal:
a in
m/s2
Envelope
Enveiope
a in
m/s2
t in s
t in s
Ta
f in Hz
a in
m/s2
Envelope spectrum: Envelope spectrum:
a in
m/s2
fRPOF 2•fRPOF 3•fRPO F 4•fRPOF f in
Hz
• fRPOF= Defect frequency
1
TRPOF
No rolling track defect: Rolling track defect:

Envelope Spectrum bearing
0 1
0
0 2
0
0 3
0
0 4
0
0 5
0
0 6
0
0 7
0
0 8
0
0 9
0
0 1
0
0
0
fH
z
0
.0
0
.2
0
.4
0
.6
0
.8
1
.0
1
.2
1
.4
1
.6
1
.8
2
.0
am
/s
²
W
a
rn
A
la
rm
Location :PT. CaltexWater PlantFresh Water
PumpCentrifugal PumpCoupling Siderolling
bearing >120
# X Y
0 0.63 0.96
1 25.00 0.21
2 50.00 0.14
3 176.88 0.10
4 151.88 0.10
5 126.88 0.08
6 4.38 0.08
7 20.63 0.07
8 29.38 0.07
9 15.00 0.06

KETERANGAN
FASE
FREKUENSI
AMPLITUDO
pd rodagigi vibrasi segaris
dengan pusat kontak. pd
motor/gen vibrasi hilang
bila mesin dimatikan. pd
pompa/blower
kemungkinan unbalance
Single
1 x rpm, seolah-
olah seperti
unbalance
Tidak besar,
aksial
lebih tinggi
4. Sleeve, metal,
Jurnal bearing
(friction
bearing) /
eksentrik
A
f
1x
Ha = 3
Aa = 7
Va = 4
Hb = 8
Vb = 7 Vc = 3
Ae = 4
Hc = 5
Hd = 3 Vd = 5
Ad = 4
Ab = 15 Ac = 4
He = 4
Ve = 4 Vf = 4
Af = 5
Hf = 3

KETERANGAN
FASE
FREKUENSI
AMPLITUDO
Ha = 3
Aa = 3
Va = 4
Hb = 2
Vb = 3 Vc = 7
Ae = 8
Hc = 7
Hd = 7 Vd = 7
Ad = 9
Ab = 4 Ac = 8
He = 6
Ve = 7 Vf = 3
Af = 5
Hf = 4
Tdk tentu
Sangat tinggi
Jumlah gigi x
rpm
Rendah, ukur
kecepatan &
percepatan,
gunakan
acceleration
5. Rodagigi
buruk atau
bersuara
A
f
1x 2x 3x 4x
tooth
Awal rusak
bersuara, semakin
lama keras.
Vibrasi biasanya
dalam toleransi.

KETERANGAN
FASE
FREKUENSI
AMPLITUDO
Ha = 3
Aa = 3
Va = 4
Hb = 2
Vb = 3 Vc = 7
Ae = 8
Hc = 7
Hd = 7 Vd = 7
Ad = 9
Ab = 4 Ac = 8
He = 6
Ve = 7 Vf = 3
Af = 5
Hf = 4
tooth
Sering terjadi
pada saat
pemasangan
Tdk tentu
Sangat tinggi
Jumlah gigi x
rpm
Rendah, ukur
kecepatan &
percepatan,
gunakan accel.
6. Gear mesh
buruk atau
bersuara
(pada saat
start / stop)
A
f
1x 2x 3x 4x

Gear frequencies for Parallel Offset Gear
• Number of teeth on the pinion...................(Np)
• Pinion speed, rpm.......................................(Rp)
• Number of teeth on gear.............................(Ng)
• Gear speed, rpm.........................................(Rg)
• Gear rotational frequency, Hz...................(frg)
• Pinion rotational frequency, Hz.................(frp)
• Mesh frequency, H................................(fm)
• Tooth repeat frequency, Hz......................(ftr)
• Assembly phase passage frequency, Hz.....(fa)
Data
needed
from
the
gear
Info
calculated
from
the
data

• 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

Air Compressor

Centrifugal Compressor

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

Generator

Generators
• Generators are generally well-behaved dynamically, 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 loading (vars)
• Power factor
• Coolant gas temperature and pressure
• Winding temperatures
• Field current

Gas Turbine

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.

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
• Gross generation (kW) or shaft speed and torque
• Reheat steam conditions (if applicable)
• Kvars (generator drive applications)

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

Trending

Shaft Crack

Rubs

Shaft Structure

Shaft balancingShaft mode
shape

Location of fluid-induced
instability

Rotational & Mesh Gear Frequencies
)
(
:
)
(
60
),
(
60
:
&
Hz
N
f
N
f
f
frequency
Mesh
Hz
R
f
Hz
R
f
s
frequencie
rotational
Pinion
Gear
g
rg
p
rp
m
p
rp
g
rg
×
=
×
=
=
=

Assembly phase passage gear frequency (1)
Ng = 15 Np = 9
Gear tooth Q Pinion Tooth
1-10-4-13-7 1-7-4
2-11-5-14-8 2-8-5
3-12-6-15-9 3-9-6

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

3
3
1
9
,
3
,
3
,
1
15
,
5
,
3
,
1
:
)
(
:
=
×
=
=
=
=
=
a
p
g
a
a
m
a
N
F
F
example
factors
prime
common
of
oduct
Pr
N
Hz
N
f
f
frequency
passage
phase
Assembly
Ng = 15 Np = 9
1-10-4-13-7 1-7-4
2-11-5-14-8 2-8-5
3-12-6-15-9 3-9-6

Tooth repeat gear frequencies
)
(
:
)
1
(
)
(
:
Hz
N
f
f
N
when
n
combinatio
tooth
hunting
true
a
for
or
Hz
N
N
N
f
f
frequency
repeat
Tooth
p
rg
tr
a
p
g
a
m
tr
=
=
×
×
=

Summary gear frequencies for parallel offset gear
To
obtain
multiply
by
tr
f rg
f rp
f a
f m
f
rp
f
rg
f
m
f
)
N
/(N
N
p
g
a
g
a/N
N
p
a/N
N
×
g
1/M
1
g
1/N p
1/N a
1/N 1
(Hz)
frequency
Mesh
f
(Hz),
freq
passage
phase
Assembly
f
(Hz)
freq
rotational
Pinion
f
(Hz),
freq
rotational
Gear
f
(Hz)
freq
repeat
Tooth
f
gear,
Ratio
M
gear,
on
teeth
of
Number
N
pinion
on
teeth
of
Number
N
phases,
assembly
of
Number
N
m
a
rp
rg
tr
g
g
p
a
=
=
=
=
=
=
=
1
g
M
a
p/N
N
a
g/N
N g
N
p
N
=
=

Gear frequencies for Planetary Gear

Application mill drive - cement industry
[m/s²]
4x [°C]
[m/s²]
[m/s²]
[m/s²]
[m/s²]
[bar]
[bar]
Machine speed
Alarm status
LAN / WAN
Internal
expert
Data backup
External
expert
Interne
t
PCS

Gear frequencies for
Planetary Gear
planets
of
number
np
ring
on
teeth
of
number
Tr
sun,
on
teeth
of
number
Ts
(input)
carrier
of
speed
Nc
(output),
gear
sun
of
speed
Ns
:
where
(Hz)
Nc
x
np
Ring
on
Defect
(Hz)
Tp
Tr
x
Nc
x
2
Planet
on
Defect
(Hz)
Nc
x
Ts
Tr
x
np
Ns
x
Tr
Ts
Tr
x
np
Sun
on
Defect
(Hz)
Nc
Tr x
Ns
x
Tr
Ts
Tr
x
Ts
Freq
Mesh
Tooth
:
Gear
Planetary
=
=
=
=
=
=
=
=
⎟
⎠
⎞
⎜
⎝
⎛
+
=
=
⎟
⎠
⎞
⎜
⎝
⎛
+
=

Comparison of Sinusoidal and
Impact Gear Tooth Contact

KETERANGAN
FASE
FREKUENSI
AMPLITUDO
Sering
bersamaan dgn
unbalance /
misalignment
2 referensi
agak kacau
2 x rpm
Tinggi pada
aksial
7. Mechanical
looseness
(Housing
bearing aus)
A
f
2x
Ha = 3
Aa = 3
Va = 4
Hb = 12
Vb = 12 Vc = 5
Ae = 4
Hc = 5
Hd = 4 Vd = 5
Ad = 3
Ab = 15 Ac = 5
He = 4
Ve = 3 Vf = 3
Af = 4
Hf = 2

KETERANGAN
FASE
FREKUENSI
AMPLITUDO
Kurang dari
1 x rpm
Tinggi pada
vertikal
8. Mechanical
Looseness (Pondasi
kendor – dudukan
lemah/karatan –
baut kendor)
A
f
<1x
Ha = 2
Aa = 3
Va = 9
Hb = 4
Vb = 10 Vc = 5
Ae = 4
Hc = 2
Hd = 4 Vd = 3
Ad = 2
Ab = 4 Ac = 2
He = 3
Ve = 3 Vf = 2
Af = 3
Hf = 4
Tdk tentu Kencangkan baut
Untuk memastikan

KETERANGAN
FASE
FREKUENSI
AMPLITUDO
Sering
bersamaan dgn
unbalance /
misalignment
2 referensi
agak kacau
2 x rpm
Tinggi pada
vertikal,
horizontal &
aksial
9. Mechanical
looseness
(Pondasi
melengkung)
A
f
2x
Ha = 13
Aa = 7
Va = 9
Hb = 14
Vb = 12 Vc = 5
Ae = 4
Hc = 5
Hd = 4 Vd = 5
Ad = 3
Ab = 6 Ac = 5
He = 4
Ve = 3 Vf = 3
Af = 4
Hf = 2

KETERANGAN
FASE
FREKUENSI
AMPLITUDO
1 atau 2
tergantung
frekuensi,
tdk tetap
1,2,3
atau 4 x
rpm belt
Tdk
tentu/berpulsa
10. Drive belt
buruk
A
f
1x 2x 3x 4x
Ha = 2
Aa = 2
Va = 3
Hb = 4
Vb = 2 Vc = 10
Ae = 8
Hc = 10
Hd = 8 Vd = 10
Ad = 10
Ab = 3 Ac = 10
He = 7
Ve = 8 Vf = 4
Af = 3
Hf = 2
Belt
Biasanya terjadi
karena belt tdk berada
pada tempatnya secara
sempurna.

KETERANGAN
FASE
FREKUENSI
AMPLITUDO
Ha = 8
Aa = 6
Va = 7
Hb = 8
Vb = 6 Vc = 4
Ae = 3
Hc = 5
Hd = 3 Vd = 3
Ad = 5
Ab = 7 Ac = 5
He = 3
Ve = 3 Vf = 2
Af = 3
Hf = 1
Vibrasi & suara
hilang bila
mesin dimatikan
Single/
rotate
double
mark
2 x rpm lebih
tinggi daripd
1 x rpm.
Tidak tinggi, ada
suara
berdengung,
lebih terasa bila
dimatikan
11. Elektrikal A
f
1x 2x

Jenis-jenis motor listrik
- Motor induksi (induction / asynchronous motor)
- Synchronous motor
- DC motor

Permasalahan pada motor listrik - Electrical
- Eccentric rotor
- Uneven airgap
(penyebab : softfoot / frame distortion)
- Broken rotor bars
- Shorted rotor lamination
- Phasing problem

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

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

Analisa vibrasi pada motor listrik – 1 / 4
- Stator eccentricity, loose iron, shorted laminations :
- Uneven air gap (variable air gap) / Eccentric rotor :
2FL
2x
1x
Frequency
Amplitude
FL = Line Frequency (3000 CPM, for 50 Hz Line Freq.)
2FL
Fp Sidebands around FL
1x
Frequency
Amplitude
Fp
FL = Line Frequency (3000 CPM, for 50 Hz Line Freq.)
• Pole pass frequency (Fp) = SF x (# poles)
• Slip frequency (SF) = Ns – actual speed
• Magnetic field speed, RPM (Ns) = 120 x FL / (# poles)

- Rotor problems 1 (broken/cracked rotor bars /
shorting rings, shorted rotor laminations) :
- Rotor problems 2 (loose/broken rotor bars) :
2x
* Fp Sidebands around 1x for broken rotor bars
* Fp Sidebands around 1x, 2x, 3x, …. for cracked
rotor bars
1x
Frequency
Amplitude
3x
2x
2FL Sidebands around RBPF or its harmonic freq.
RBPF = Rotor Bar Pass Frequency = # Bars x RPM
1x
Amplitude
Frequency
RBPF

- Phasing problems (motor beroperasi hanya 2 dari 3
phasa, disebabkan oleh loose / broken connectors) :
Loose stator coils pada synchronous motors :
1/3 FL Sidebands around 2FL
Frequency
Amplitude
2FL
1x RPM Sidebands around CPF = Coil Pass Freq.
CPF = # stator coils x RPM
Frequency
Amplitude
CPF
2x
1x

- DC motor problems 1 (broken field winding, bad
SCR and loose connection) :
- DC motor problems 2 (loose/blown fuses, shorted
control card) :
Frequency
Amplitude
6FL = SCR Firing Freq. or its harmonic freq.
2x
1x
2FL
Amplitude tinggi pada 1x hingga 5x Line Freq.
FL
Frequency
Amplitude
3FL 4FL 5FL

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

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

KETERANGAN
FASE
FREKUENSI
AMPLITUDO
Ha = 2
Aa = 1
Va = 1
Hb = 2
Vb = 2 Vc = 4
Ae = 7
Hc = 3
Hd = 4 Vd = 4
Ad = 3
Ab = 3 Ac = 5
He = 13
Ve = 14 Vf = 13
Af = 7
Hf = 14
Lebih terasa bila
beban tidak
stabil.
1 x rpm atau
jumlah sudu
atau fan atau
impeler x
rpm
Tinggi pada
vertikal atau
horizontal
12. Gaya
aerodinamik /
hidrolik
A
f
1x Jml x
Tdk tentu

KETERANGAN
FASE
FREKUENSI
AMPLITUDO
Pada mesin
reciprocating
bisa ganti
desain/isolasi
1 x,2 x rpm
atau lebih
13. Gaya
reciprocating
A
f
1x 2x
Ha = 8
Aa = 6
Va = 7
Hb = 7
Vb = 8 Vc = 3
Ae = 3
Hc = 2
Hd = 4 Vd = 3
Ad = 4
Ab = 7 Ac = 4
He = 4
Ve = 2 Vf = 2
Af = 3
Hf = 2
Dominan aksial Single,
double,
triple

Ringkasan Analisa Amplitudo, Frekuensi dan Fase
KETERANGAN
FASE
FREKUENSI
AMPLITUDO
Kondisi sering
ditemui
Single
reference
mark
1 x rpm
Sebanding dgn
ketidak balance,
dominan pd
radial (2x aksial)
1. Unbalance A
f
1x
Ditandai timbulnya vibrasi
aksial. Gunakan alat laser-
alignment. Apabila mesin
baru dipasang terjadi
vibrasi, maka kemungkinan
besar karena misalignment.
Single
double
triple
Sering 1 x & 2 x
rpm. Kadang 3 x
rpm
Dominan pd
aksial, 50%
atau lebih dari
arah radial
2. Misalignment
kopling atau
poros bengkok
A
f
1x 2x
Vibrasi akan timbul
apabila bearing sdh
parah. Gunakan
enveloping &
shockpulse
Tdk tentu,
Berubah-
rubah
Sangat tinggi,
beberapa kali
Rpm, 1x, 2x, 3x,
4x … 10x
Tidak stabil,
ukur acceleration
untuk freq.
tinggi
3. Anti friction
bearing buruk
A
f
1x 2x 3x 4x
pd rodagigi vibrasi segaris
dengan pusat kontak. pd
motor/gen vibrasi hilang
bila mesin dimatikan. pd
pompa/blower
kemungkinan unbalance
Single
1 x rpm, seolah-
olah seperti
unbalance
Tidak besar,
aksial
lebih tinggi
4. Sleeve, metal,
Jurnal bearing
(friction
bearing)
A
f
1x
Tdk tentu
Sangat tinggi
Jumlah gigi x
rpm
Rendah, ukur
kecepatan &
percepatan,
gunakan accel.
5. Rodagigi
buruk atau
bersuara
A
f
1x 2x 3x 4x
Awal rusak bersuara,
semakin lama keras.
Vibrasi biasanya
dalam toleransi.
tooth

KETERANGAN
FASE
FREKUENSI
AMPLITUDO
Sering terjadi
pada saat
pemasangan
Tdk
tentu
Sangat tinggi
Jumlah gigi x
rpm
Rendah, ukur
kecepatan &
percepatan,
gunakan accel.
6. Gear mesh
buruk atau
bersuara pada
saat start/stop
A
1x
f
2x 3x 4x
Sering
bersamaan dgn
unbalance /
misalignment
2 referensi
agak kacau
2 x rpm
Tinggi pada
aksial
7. Mechanical
looseness
(Housing
bearing aus)
A
f
2x
Kurang dari
1 x rpm
Tinggi pada
vertikal
8. Mechanical
Looseness (Pondasi
kendor – dudukan
lemah/karatan –
baut kendor)
A
f
<1x
Tdk tentu Kencangkan baut
Untuk memastikan
Sering
bersamaan dgn
unbalance /
misalignment
2 referensi
agak kacau
2 x rpm
Tinggi pada
vertikal,
horizontal &
aksial
9. Mechanical
looseness
(Pondasi
melengkung)
A
f
2x
1 atau 2
tergantung
frekuensi,
tdk tetap
1,2,3
atau 4 x
rpm belt
Tdk
tentu/berpulsa
10. Drive belt
buruk
A
f
1x 2x 3x 4x
Biasanya terjadi
karena belt tdk berada
pada tempatnya secara
sempurna.

KETERANGAN
FASE
FREKUENSI
AMPLITUDO
Vibrasi & suara
hilang bila
mesin dimatikan
Single/
rotate
double
mark
2 x rpm lebih
tinggi daripd
1 x rpm.
Tidak tinggi, ada
suara dengung,
lbh terasa bila
dimatikan
11. Elektrikal A
f
1x
Lebih terasa bila
beban tidak
stabil.
1 x rpm / jml
sudu / fan
atau impeler
x rpm
Tinggi pada
vertikal atau
horizontal
12. Gaya
aerodinamik /
hidrolik
A
f
1x Jml x
Pada mesin
reciprocating
bisa ganti
desain/isolasi
1 x,2 x rpm
atau lebih
13. Gaya
reciprocating
A
f
1x 2x
Tdk tentu
Single,
double,
triple
Dominan aksial
2x

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)

Phase Analysis
Tanda-tanda “shaft crack” :
- Nilai tinggi pada frekuensi 1x RPM di gambar spectrum
- Perubahan dalam nilai fase yang cukup signifikan
0
1
2
3
4
5
6
0 20 40 60 80 100 120 140 160 180 200 220 240
Time (interval 20 minutes)
A
m
plitudo
0
20
40
60
80
100
120
0 20 40 60 80 100 120 140 160 180 200 220 240
Time (interval 20 minutes)
P
ha
s
e
la
g

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
steady state vibration due to a seal rub
0
2
4
6
8
0
20
40
60
80
100
120
140
160
180
200
220
240
260
280
300
320
340

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

Time Signal
raw
Cepstrum Analysis
Hz
V (dB)
100 200 300 400 500
70
80
90
100
F
FFT
FFT Spectrum
0,1 0,2 0,3
s
28,1 ms (35 Hz)
95,9 ms (10 Hz)
V
F
-1
FFT
Cepstrum
Spectrum Cepstrum
Frequency (Hz) Qerfuency (ms)
Harmonics Rahmonics
Filter Lifter
Magnitude Gamnitude
Sideband patterns easily diagnosed and trended with Cepstrum analysis
Cepstrum is a spectrum of a logarithmic spectrum
Cepstrum is a spectrum of a logarithmic spectrum

Bode Plot
Bode plot involves plotting the vibration amplitude
and phase against rotational speed
Bode plot involves plotting the vibration amplitude
and phase against rotational speed
0o
90o
180o
Phase
Amplitude
Rotational Speed
Critical
Speed
Slow roll
Use for identifying resonance or critical speed. Very sensitive to run-out

Polar Plots (Nyquist plots)
Polar plot - the vibration amplitude is plotted against
Phase on a polar graph paper
Polar plot - the vibration amplitude is plotted against
Phase on a polar graph paper
0o
90o
180o
Amplitude
at critical
speed
Same information as Bode plot – different presentation.
Advantage: Easy to correct for run out by shifting orgin for all vectors.
Origin
Residual
unbalance
Increasing
Shaft speed
Critical Speed
90o Phase shift

AC Signal
DC
Signal
Gap
A proximity probe provides two signal output:
1. Shaft dynamic motion relative to the probe mounting (AC signal)
2. Shaft average position relative to the probe mounting (DC signal)
A proximity probe provides two signal output:
1. Shaft dynamic motion relative to the probe mounting (AC signal)
2. Shaft average position relative to the probe mounting (DC signal)
Proximity probe’s signal

+
+
a
a
b
b
+
+
+
+
+
+
++
Shaft centerline plot
um
um
Plotting X-Y coordinates of Gap (DC signal)
from 2 prox. probe space 90o apart at each bearing
Plotting X-Y coordinates of Gap (DC signal)
from 2 prox. probe space 90o apart at each bearing
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

Orbits (lissajou)
Orbits – Plotting X-Y coordinates of two signals
(shaft displacement) space 90o apart at each bearing
Orbits – Plotting X-Y coordinates of two signals
(shaft displacement) space 90o apart at each bearing
• 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
X, horizontal
Y, vertical

Orbits (lissajou)
X, horizontal
Y, vertical
Orbits – use to display a accurate picture of shaft motion
greatly magnified, and easily understood
Orbits – use to display a accurate picture of shaft motion
greatly magnified, and easily understood
Line of action
External forces reduces amplitude:
Gravity, Preload by pressure dam
bearings, Misalignment of shafts restrain

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)

Order
Amplitude
Phase
Run-up/
Coastdown
Speed

Time Signal:
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
FFT
Fast Fourier
Transformation
Time vs FFT

Predictive Maintenance
Start
Create
Ref.
Regular
Meas.
Input
m/c
specs
Fault
Diagnostics
Fault
correction
Compare
limits
YES
NO
Rules
+
Experi
Create
New Ref. & Limits

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