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Vibration Analysis 1

Level 1 Certification Chapter 3

QuestionAnswer
In order to become an expert in the field of vibration what does a person need to know? How to take a measurement. What you are measuring. What the signal looks like. How to interpret the final data graphically.
What is vibration? vibration is a result of the forces within a machine. These forces are transferred to the bearings. The response of the bearing housing to the forces generated inside the machine.
What is the most basic form of vibration called? Simple harmonic motion
Simple harmonic waveforms result in what? Sine wave
What is amplitude in reference to a vibration waveform? The height of the vibration waveform and it is proportional to the severity of the vibration.
Simple harmonic motion results in what? A sine wave.
The height of the vibration waveform is called what? Amplitude
The total distance of amplitude is called Peak to peak
The total distance the mass moves from rest or 0 is ? Peak amplitude
RMS stands for? What is its meaning Root Mean Squared and it describes the amount of energy contained in the waveform.
In a sine wave and only a sine wave RMS amplitude is equal to? .707
True/False: Most real life vibration is not in the form of a sine wave. True
Calculating either the period or the frequency is accomplished by? Dividing either by 1.
If fan speed increases then the period_______. Decreases.
What type of phase measurement occurs when using a tachometer as the phase reference? Absolute phase
What type of phase measurement occurs when using to channels on a data collector to determine phase? Relative phase
Why is phase useful in vibration analysis? It can be used in diagnosing certain faults in machines.
Circles with lines coming out of them that describe the phase relationship between axial readings on both sides of the coupling are called what? Bubble diagrams
Phase readings are used in many applications including Balancing, diagnosing common machine faults, verifying resonance, understanding how structures move.
Displacement describes The distance traveled by the mass.
Velocity describes How fast the mass is moving at any point.
Acceleration The rate of change of velocity.
Describe the phase relationship between acceleration, velocity, and displacement. Acceleration leads velocity by 90 degrees, velocity leads displacement by 90 degrees.
The sensor we use and the way we display the data will depend on the __________. Application
Typical displacement units are? Metric= micron pk-pk, Imperial= mils pk-pk
1 micron =? 1000th of a mm = .04 mils
True/False At low frequencies displacement can be high. True
At high frequencies displacement will be? Low
Below 600 RPM is best suited for what type of vibration measurement? Displacement
Proximity probes are typically used to measure what? Displacement
When performing balancing what units are commonly used. Units of displacement
Displacement is proportional to? Stress
What is Velocity? The rate of change of displacement
Typical units for velocity are? Metric= mm/sec RMS Imperial= in/sec pk 1mm = .04 inch
True or False: Velocity is the most commonly used measure of vibration for general rotating machinery with rolling element bearings. True
Velocity is best used to measure frequencies between ______________________. 2 and 2000 Hz.
Velocity is proportional to Fatigue. Note velocity is a measure of the severity of fatigue.
Acceleration is the rate ______________. of change of velocity.
Typical units for acceleration are? Metric= g's or mm/sec^2RMS or m/s^ RMS Imperial= g's RMS in/s^2 and Adb
When is acceleration most sensitive? High frequencies
When is acceleration generally used? On high speed machinery greater than 10,000 RPM
Other than high speed machinery, what can acceleration be used for? Bearings and gearbox analysis.
Acceleration is proportional to what? The forces in the machine.
Most analysts use ___________ to measure vibration but then they convert the data to units of velocity before analyzing it. accelerometers
To perform the conversion of units what must be known? Frequency
It is common to capture and trend velocity readings and compare the readings to __________. ISO alarm chart.
True/False: According to ISO standard for RMS overall readings, they are only taken in the limited frequency range between 3 and 1500 Hz. False. 3-1000 Hz.
What are three negative characteristics of measuring RMS values? Limited frequency range, Only gives us a single value, overall is not universal (some meters do not measure in the same frequency of the ISO standard 3-1000 Hz.
The ratio of the peak value to the RMS value is called? Crest Factor
A signal from an out of balance machine will give us close to what crest factor? 1.4 or 1.41 for a pure sine wave. But with bearing faults there will be more impacting so the crest factor will be much higher.
The _____ tells us the source of the vibration, and the _______ tells us about the severity of the vibration. Frequency, Amplitude
In a spectra the X and Y axis represent what? X axis represents frequency, CPM, or orders. The Y axis represents the amplitude.
The term for expressing frequency in multiples of running speed is? Orders
True/False:Working in orders allows us to trend a vibration patterns. True. It allows us to overlay and compare graphs that have been normalized.
Forcing frequencies may also be referred to as? Fault frequencies or defect frequencies.
Examples of forcing frequencies are? Blade pass rate, vane pass rate, bearing frequencies, ball spin, cage rate, ball pass inner race, ball pass outer race, belt frequency, gearmesh, rotor bar passing rate.
How do we calculate forcing frequencies of belt driven machines? Output speed = Input speed(Input sheave diameter/output sheave diameter)
How do we calculate forcing frequencies of the belt rate? BR= (Pi X Sd X Srpm)/Belt Length (Sd= shaft diameter, Srpm= shaft RPM).
What is the gear mesh formula? GM= #teeth X shaft rate (the number of teeth and the shaft rate are for the shaft the gear is mounted to.
How do we calculate the shaft rate of a gear driven shaft? S2=S1X(T1/T2) S1= Input shaft rate, T1= teeth on the input gear, T2= teeth on the output gear.
If we plot two waveforms against each other 90 degrees apart we get? Orbit or orbit plot (Lissojous figure)
What are orbital plots used for? Large journals or sleeve bearings using proximity probes.
Created by: davidkintner
 

 



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