Advanced Analysis Beyond Waveform And Spectrum
This quiz is to help with understanding and applying tools that are included in many portable vibration instruments. Topics dealing with coastdown, bump test, cross-channel phase, and long time waveform functionality are covered.
- 1.
What tool can be used to determine natural frequencies on a machine?
- A.
Coastdown
- B.
Bump Test
- C.
Long Time Waveform
- D.
All of the above
Correct Answer
D. All of the aboveExplanation
All three tools are effective to detect resonance and natural frequency. Coastdown can show a cascade spectral display or Bode plot. Bump test provides a peak hold of excited frequencies. Long time waveforms can be panned and zoomed for frequency content.Rate this question:
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- 2.
What tool can be used to determine relative motion of machine components?
- A.
Coastdown
- B.
Bump Test
- C.
Cross-channel Phase
- D.
Long Time Waveform
Correct Answer
C. Cross-channel PhaseExplanation
Cross-channel phase shows amplitude and relative phase of two components with simultaneous measurement. Phase provides relative motion.Rate this question:
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- 3.
Cross-channel phase measurement requires a reference signal (tachometer) input.
- A.
True
- B.
False
Correct Answer
B. FalseExplanation
The beauty of cross-channel is that it does not require a reference input, just two simultaneous measurements of vibration.Rate this question:
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- 4.
Bump testing requires a calibrated modal hammer.
- A.
True
- B.
False
Correct Answer
B. FalseExplanation
Bump testing is not a calibrated force and response function, as required for modal analysis. It is simply an impact force exciting natural frequencies.Rate this question:
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- 5.
Cross-channel phase measurement can detect the following problem.
- A.
Soft foot
- B.
Misalignment
- C.
Couple unbalance
- D.
All of the above
Correct Answer
D. All of the aboveExplanation
All types of problems can be determined from relative motion of machine components including the three noted in the answers.Rate this question:
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- 6.
What is a plot type that is commonly used with a coastdown for resonance detection?
- A.
Orbit
- B.
Time waveform
- C.
Single point spectrum
- D.
Bode
Correct Answer
D. BodeExplanation
It is the Bode plot that shows both vibration amplitude and phase data versus speed. An amplitude peak and a phase change of 180 degrees pinpoints a natural frequency.Rate this question:
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- 7.
A Bode plot provides both the vibration magnitude and phase display for each speed measurement and requires a reference input.
- A.
True
- B.
False
Correct Answer
A. TrueExplanation
A Bode plot does take some time to set up, as it requires and accurate reference for speed and phase on each sample of vibration amplitude.Rate this question:
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- 8.
A Bump test cannot be performed for any analysis work while the machine is running.
- A.
True
- B.
False
Correct Answer
B. FalseExplanation
It will take some care, but one can excite a machine structure with a bump even while it is running, and by taking a before and after spectral plot and overlay, responsive natural frequencies will be displayed.Rate this question:
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- 9.
In trying to capture an event on a machine that is really hard to catch with one sample, one would use:
- A.
Coastdown
- B.
Cross-channel phase
- C.
Long Time Waveform
- D.
Bump Test
Correct Answer
C. Long Time WaveformExplanation
Long Time Waveform is the tool of choice to capture a short-term event. By looking over the waveform and panning and zooming until the event is noted, the spectrum of that area only can be displayed and analyzed.Rate this question:
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- 10.
Bump testing typically uses the following type of averaging on the spectral processing.
- A.
Linear
- B.
Logarithmic
- C.
Exponential
- D.
Peak Hold
Correct Answer
D. Peak HoldExplanation
Peak hold spectral data is typically most effective in capturing and displaying an excited natural frequency. It will show a raised noise floor and skirts on both sides of the resonance condition excited by the bump.Rate this question:
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Current Version
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Mar 14, 2024Quiz Edited by
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Jun 28, 2012Quiz Created by
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