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Vibration monitoring and analysis for rotating machine
Introduction to mechanical vibration
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Outline
Introduction
Vibration monitoring and analysis
Vibration : Measurement
Data Acquisition
Types of transducer
Mounting method
FFT analysis
Example
Unbalance
Misalignment
Spur gear
Centrifugal pump
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Introduction
Static equipment
Ex. Pressure vessel, Tank
Rotating equipment
Pump, Compressor, turbine
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Vibration monitoring and analysis
Raw Data
Time domain
Analysis data
Frequency domain
FFT analyzer Sensor
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Vibration : Measurement Amplitude Units
Displacement, D Micrometer peak to peak
Velocity, V mm/s - peak or rms
Acceleration, A mm/s2 - peak or rms
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Types of transducer
Proximity Probe Seismic Velocity
Probe Acceleration Probe
Relative displacement Velocity Acceleration
0 1,500 Hz 8 1,500 Hz 1 20,000 Hz
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Mounting method
Method Frequency limit (Hz)
Hand held 500 Magnet 2,000
Adhesive 2,500 4,000
Bees wax 5,000
Stud 6,000 10,000
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FFT analysis
Fast fourier
transform (FFT)
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Vibration monitoring and analysis
Raw Data
Time domain
Analysis data
Frequency domain
FFT analyzer Sensor
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Example Unbalance
Misalignment
Spur gear
Centrifugal pump
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Type of unbalance 1. Static unbalance 2. Couple unbalance 3. Dynamic unbalance
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12
Static Unbalances
Corrected
balance weight in one plane at rotor centre of gravity (CG).
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Couple Unbalances
180
Corrected
balancerequires correction in two planes at 180.
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Dynamics Unbalances
static couple Static unbalance Couple
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Special case of Dynamics Unbalances
Corrected
Overhung rotors often have both static and couple unbalance each of which may require correction.
Overhung Rotor Unbalance
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Balancing cooling tower
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Cooling Tower
1. (transducer) (Tachoprobe)
2. 1 - (Magnitude :mm/sec) - (phase angle)
3. (trial weight) Rotor
4. 2 - (Magnitude :mm/sec) - (phase angle)
5. Polar graph
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(Trail weight) Wt = 30 x Wr / r
Wr Static weight : g r (radius of trial weight : mm)
(correct weight) Vc = Vo x Wt / Vt
Vo Unbalance : mm/sec Vt : mm/sec
Reference by : Machinery vibration & Balancing /Victor Wowk.
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spectrum cooling #4 1X rpm Amplitude Unbalancing
Frequency : 355.3
Amplitude: 4.379
Phase : 84 degree
( )
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Vector correct & angle phase on Polar graph
Data: 1.Rotor & Fan weight : 26 kg ,(4x32 kg)
2. Radius of trial : 220 mm.
Vector unbalance Vo: 4.379 mm/sec
Phase Vo: 84 degree.
Trial weight : 25 g (21 g)
Vector unbalance +weight V1: 7.4 mm/sec
Phase V1: 215 degree.
Vector from trial weight Vt: 10.8 mm/sec
Phase : 329 degree. (Vt-Vc)
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Position of point to correct (Balancing)
Trial weight : 25 g (21 g)
Phase : 84 degree.
Correct weight ,Mc : 10.1 g
Correct phase : 31 degree.
Before..
After..
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Amplitude: 1.684 mm/sec
4.375
()
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Misalignment
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Misalignment
Introductio
n
What is it ?
Misalignment is a condition
where the centerlines of
coupled shafts do not coincide.
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EX.
Introductio
n Misalignment
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Introductio
n
Bearing, Coupling, Seal and Shaft failure
Lost time to repair machine
Lost opportunity to run process
Lost Maintenance Cost
Misalignment
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Type of
misalignmen
t Misalignment
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Detection
method Misalignment
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Introductio
n Misalignment
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Misalignment Detection
method
Time- Frequency Domain
Fast fourier
transform (FFT)
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Type of
misalignmen
t Misalignment
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Type of
misalignmen
t Misalignment
Shear force
Bending moment
2X component will be higher than 1X.
Depend on the coupling type
Axial 1X and 2X levels will be low
Symptoms: 2X radial, smaller 1X
radial
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Type of
misalignmen
t Misalignment
Bending moment
Also be fairly
strong radial
1X and 2X levels
Symptoms: High axial vibration: 1X
strong (but 2X and 3X can also be
strong)
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Type of
misalignmen
t Misalignment
Can be 3X, 4X all the
way up to 8X peaks
The noise floor is
not raised(unlike
rotating looseness)
Frequency: 1X and 2X (and 3X and
4X) axial and radial
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Spur Gear
Failure Mode : Backlash, Tooth wear and Broken teeth etc.
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Normal
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Backlash
Normal
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Tooth wear
Normal
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Tooth load
Normal
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Broken Tooth
Normal
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Broken Tooth
Normal
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Vibration in centrifugal pump
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Loosen components
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Gap between blade vanes and case is too small
-the BPF will increase
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Turbulence flow
-random amplitude
at low frequency
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Cavitation
-random amplitude
at high frequency