Vibration monitoring and analysis for rotating machine
Introduction to mechanical vibration
Outline
Introduction
Vibration monitoring and analysis
Vibration : Measurement
Data Acquisition
Types of transducer
Mounting method
FFT analysis
Example
Unbalance
Misalignment
Spur gear
Centrifugal pump
Introduction
Static equipment
Ex. Pressure vessel, Tank
Rotating equipment
Pump, Compressor, turbine
Vibration monitoring and analysis
Raw Data
Time domain
Analysis data
Frequency domain
FFT analyzer Sensor
Vibration : Measurement Amplitude Units
Displacement, D Micrometer peak to peak
Velocity, V mm/s - peak or rms
Acceleration, A mm/s2 - peak or rms
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
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
FFT analysis
Fast fourier
transform (FFT)
Vibration monitoring and analysis
Raw Data
Time domain
Analysis data
Frequency domain
FFT analyzer Sensor
Example Unbalance
Misalignment
Spur gear
Centrifugal pump
Type of unbalance 1. Static unbalance 2. Couple unbalance 3. Dynamic unbalance
12
Static Unbalances
Corrected
balance weight in one plane at rotor centre of gravity (CG).
Couple Unbalances
180
Corrected
balancerequires correction in two planes at 180.
Dynamics Unbalances
static couple Static unbalance Couple
Special case of Dynamics Unbalances
Corrected
Overhung rotors often have both static and couple unbalance each of which may require correction.
Overhung Rotor Unbalance
Balancing cooling tower
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
(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.
spectrum cooling #4 1X rpm Amplitude Unbalancing
Frequency : 355.3
Amplitude: 4.379
Phase : 84 degree
( )
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)
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..
Amplitude: 1.684 mm/sec
4.375
()
Misalignment
Misalignment
Introductio
n
What is it ?
Misalignment is a condition
where the centerlines of
coupled shafts do not coincide.
EX.
Introductio
n Misalignment
Introductio
n
Bearing, Coupling, Seal and Shaft failure
Lost time to repair machine
Lost opportunity to run process
Lost Maintenance Cost
Misalignment
Type of
misalignmen
t Misalignment
Detection
method Misalignment
Introductio
n Misalignment
Misalignment Detection
method
Time- Frequency Domain
Fast fourier
transform (FFT)
Type of
misalignmen
t Misalignment
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
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)
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
Spur Gear
Failure Mode : Backlash, Tooth wear and Broken teeth etc.
Normal
Backlash
Normal
Tooth wear
Normal
Tooth load
Normal
Broken Tooth
Normal
Broken Tooth
Normal
Vibration in centrifugal pump
Loosen components
Gap between blade vanes and case is too small
-the BPF will increase
Turbulence flow
-random amplitude
at low frequency
Cavitation
-random amplitude
at high frequency
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