4 Vibration Analysis Basics
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Transcript of 4 Vibration Analysis Basics
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Peru, Au gu st 2015
SIXTO SARMIENTO CHIPANA
Vibration Analyst Level III
Machinery Lubricant Analyst Level II
VIBRATION ANALYSIS
INTRODUCTION
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Vibratión Analysis basics
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Vibration Analysis
Why?
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Vibration Analysis provides us with early warnings ofmany potentially serious problems in rotating machinery
Worn/Damaged Bearings
Worn/Damaged Gears
Lubrication Problems
Misalignment
UnbalanceLoose Fittings/Foundation
Why use Vibration Analy
sis?
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Vibration waveforms Vibration amplitude
Time Domain
Frequency Domain
Vibration Analysis
Basic Concepts
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Examples of Vibration
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The Simple Harmonic Oscillator
What is Vibration?
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Mass-Spring Systems with Damping
What is Vibration?
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The simplest possible vibratory motion that can
exist is the movement in one direction of a masscontrolled by a single spring.
Such a mechanical system is called a single degree
of freedom spring-mass system
What is Vibration?
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What is Vibration?
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The machine turns to 1800 RPMThe machine has a large number of frequencies
For example:Line frequency: 60 Hz – 3600 CPM
Fundamental frequency: 1800CPM
The fundamental frequency coincides with the frequency of rotation
What is Vibration?
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VIBRATION CHARACTERISTICS
AMPLITUDE
Displacement
Velocity
Aceleration
FRECUENCYFASE
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wtsinAx
Displacement
Aceleration
Velocity
wtcosAwx
wtsinAw-x2
Desplacement
Aceleration
Velocity
How do we measure amplitude?
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Choose a point
to measure
C h o
o s e
a
d i r e c
t i o n
l
b
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Measurement locations - vibration
measurement
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We can measure...
DISPLACEMENT
VELOCITY
orACCELERATION
A i i i
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DISPLACEMENT = Distance
traveled (miles)
At any point in time...
VELOCITY =
Speedometer reading (mph)
ACCELERATION =
How far your foot is down.
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• Actual physical movement of a
vibrating object• Emphasizes lower frequency
components
•
Measured in mils or microns
Displacement
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• Measuring total mass trajectory.
• It is used for low frequencies (from 0 to 1.200CPM)
•
Is related to stress.
• It uses an accelerometer and the signal isintegrated doubly to obtain displacement
Displacement
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Time
A m p l i t u d e
This is a time domain recording
of vibration displacement
Displacementis the easiest to visualize
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• Measure of the speed at which the
mass is moving
• Preferred unit of measurement as iteffective over over a wide range,
from low frequency to high
frequency• Measured in inches / sec or mm / sec
Velocity
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• Measuring the rate at which the mass ismoving during its oscillations.
• It is used to frequency ranges between600 and 60,000 CPM and is related tofatigue.
• It is measured directly with a "pick up"speed or an accelerometer where thesignal is integrated to obtain velocity.
Velocity
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Velocity or speed is zero as the object
comes to a stop before moving in the
opposite directionSpeed or velocity is greatest
here
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•
Rate of change of Velocity• Emphasizes high-frequency peaks in
a spectrum
•Measured in “g’s”
Acceleration
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• It is the optimum for high frequencies, greater
than 60,000 CPM and is related to the force.
• Acceleration is more difficult to measure the
amplitude of vibration, but more often is the
parameter directly measured in the field using an
accelerometer.
Acceleration
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Acceleration is greatest where velocity is at a
minimum
Object has decelerated and stopped and is about
to begin accelerating again
Comparison of Velocity Displacement & Acceleration
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Comparison of Velocity, Displacement & Acceleration
Acceleration is usedfor measuring high
frequencies:
Bearing FrequenciesVelocity is best over a wide
frequency range
Displacement is used for
measuring low frequencies:
Low RPM
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Simple Harmonic Motion
This displacement waveform is sinusoidal.
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Simple Harmonic Motion - The Simplest Vibration
ANY vibration can be expressed as a sum of individual simple
vibrations.
=
++
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The Frequency Domain
= + + + ...
Frequency
A m p l i t u d eUse a graph to
show how the
complex signal isbroken down into
simple ones....
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Time & Frequency Domain
Time Domain waveform shown as many different frequencies
and amplitudes
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Sinusoidal time domain
Single peak in frequency
domain.
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Noise in time domain
Noise in frequency domain
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• Vibration measurement
– Point & Direction
• Displacement, velocity, acceleration
• Time domain waveforms
• Complex vibration
= sum of simple vibrations
• Frequency domain
Review
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Review:
GIRDHAR, P. (2004). Practical Machinery Vibration
Analysis and Predictive Maintenance. Third Edition. USA:
Elsevier Practical .
https://www.youtube.com/watch?v=DUznmZvSQOU
https://www.youtube.com/watch?v=DUznmZvSQOUhttps://www.youtube.com/watch?v=DUznmZvSQOU