# Advanced Analysis Beyond Waveform And Spectrum

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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

D. All of the above
Explanation
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.

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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

C. Cross-channel pHase
Explanation
Cross-channel phase shows amplitude and relative phase of two components with simultaneous measurement. Phase provides relative motion.

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• 3.

### Cross-channel phase measurement requires a reference signal (tachometer) input.

• A.

True

• B.

False

B. False
Explanation
The beauty of cross-channel is that it does not require a reference input, just two simultaneous measurements of vibration.

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• 4.

### Bump testing requires a calibrated modal hammer.

• A.

True

• B.

False

B. False
Explanation
Bump testing is not a calibrated force and response function, as required for modal analysis. It is simply an impact force exciting natural frequencies.

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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

D. All of the above
Explanation
All types of problems can be determined from relative motion of machine components including the three noted in the answers.

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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

D. Bode
Explanation
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.

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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

A. True
Explanation
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.

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• 8.

### A Bump test cannot be performed for any analysis work while the machine is running.

• A.

True

• B.

False

B. False
Explanation
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.

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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

C. Long Time Waveform
Explanation
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.

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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

D. Peak Hold
Explanation
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.

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• Current Version
• Jul 17, 2024
Quiz Edited by
ProProfs Editorial Team
• Jun 28, 2012
Quiz Created by
Reliaquiz