Date post: | 21-Feb-2017 |
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VIBRATION ANALYSIS FOR CBMBASIC CONCEPTS – UNIT 1
BY DIBYENDU DE
ALL MACHINES VIBRATE
Because of: Inertia
Stiffness Imposed forces
VIBRATION MONITORING
What causes Vibration ?
INDUCED FORCE
&
FREEDOM FOR MOVEMENT
VIBRATION MONITORING
Types of Forces ?
Inertia ForcesAcceleration & Deceleration
Looseness & Impacts
MACHINE VIBRATION IS COMPLEX
• Behaviour of each component creates their own frequencies
• Frequency tells us about a possible problem. • Amplitude tells us about the severity of the
problem. • Multiple frequencies combine to produce the
overall vibration• Vibration from 1 Hz to 1000 Hz captures
overall amplitude
ONE CYCLE OF VIBRATION
• Movement of weight from neutral position to upper limit
• Upper limit back through neutral position to lower limit
• Lower limit to neutral position• The movement of the weight
plotted against time is a sine wave
•
FREE & FORCED VIBRATION
• With sudden impulse the system will vibrate at its natural frequency
• Free vibrations die out with time if the system is stable. (Bump test)
• Forced vibration are periodically imposed on the system (like motor). The response is also periodic
FORCE, MOBILITY & VIBRATION
• Response to forced vibration is not uniform at all frequencies.
• Response depends on the mobility of the structure
• Mobility varies with frequencies. High at resonance. Low where damping is present.
MEASUREMENT OF AMPLITUDE & FREQUENCYPeak for velocity and acceleration (used for algorithms)
Peak to Peak Displacement
RMS Velocity & acceleration (Europe) Energy content (only for sine wave)
Average Not used in vibration analysis
Frequency = 1/Period (Hz/CPM)
MEASUREMENT OF AMPLITUDE
Peak for velocity and acceleration
Peak to Peak Displacement
RMS Velocity & acceleration (Europe) Energy content (only for sine wave)
Average Not used in vibration analysis
DISPLACEMENT, VELOCITY & ACCELERATION
What?• Displacement = d = x = A sin (wt)
• Velocity = v = dx / dt = Aw cos wt = Aw sin (wt + 90o)
• Acceleration = a = dv /dt = - Aw2 sin wt = Aw2 sin (wt + 180o)
Why?• Strain Energy ∝ to d2
• Kinetic Energy ∝ to v2
• Acoustic Pressure ∝ to a2
• Force
VIBRATION - CAR ANALOGY
Low FrequencyLong period (T)High displacementAverage VelocityLow Acceleration
Medium FrequencyMedium period (T)Average displacementAverage VelocityAverage Acceleration
High FrequencyShort period (T)Low displacementAverage VelocityHigh Acceleration
THANK YOU FOR COMPLETING UNIT 1 CONTACT: FOR FACILITATED TRAINING
DIBYENDU DE, EMAIL ID: [email protected]