Check Your Skills In Predictive Maintenance

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Reliaquiz

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Quizzes Created: 10 | Total Attempts: 2,559

Questions: 10 | Attempts: 265 | Updated: Mar 21, 2023

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Check Your Skills In Predictive Maintenance - Quiz

Condition monitoring and predictive maintenance require good data acquisition, root-cause analysis, problem correction, and verification. There are 10 true/false questions offered here to check your knowledge and to stimulate your thinking. The goal is to improve your skills in using the technology and the tools that are available.

Questions and Answers

1.

Having a vibration reading at 1X running speed with amplitude that is 80% or greater than the overall level is a sure sign of unbalance.
- A.
  
  True
- B.
  
  False
Correct Answer
B. False

Explanation
While this is certainly one leading indicator, other areas need to be checked such as amplitude and phase readings in several axes and eliminating structural looseness and resonance as possible faults.

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2.

If I have a VFD and I suspect that there is a resonance condition somewhere in the operating range, I can run a Bump Test to find the problem.
- A.
  
  True
- B.
  
  False
Correct Answer
A. True

Explanation
This is one way to find out, but it usually requires the machine to be stopped. Another good method is to perform a Coastdown and Bode analysis.

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3.

A good way to determine impacting in a captured time waveform is Crest Factor, calculated by true peak value divided by RMS.
- A.
  
  True
- B.
  
  False
Correct Answer
A. True

Explanation
This is one good tool in working with time waveform data. Another way is to assess true peak-to-peak values.

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4.

I cannot find the natural resonance of a machine structure without first turning it off and using a Bump Test or shutting it down and capturing Coastdown data during its coast.
- A.
  
  True
- B.
  
  False
Correct Answer
B. False

Explanation
One way to capture data on a machine in service is to bump it while running and capture a long time waveform. You can then pan and zoom on the data when the structure is excited and when it is in the normal running condition and compare spectral data overlays.

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5.

A sure way to find bearing faults is to use Demodulation and Enveloping techniques, and these will work well without knowing bearing details.
- A.
  
  True
- B.
  
  False
Correct Answer
B. False

Explanation
While the initial data might show a tell-tale sign of problems, the actual bearing fault frequencies need to be overlaid on the spectral plot to confirm the actual bearing with the problem.

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6.

In just looking at high-frequency acceleration data, one can see the early signs of rolling-element bearing problems.
- A.
  
  True
- B.
  
  False
Correct Answer
A. True

Explanation
A raised noise floor and “haystack” will show up in the upper end of the spectral display.

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7.

A rotor that is considered “rigid” does not have to be balanced at running speed. In fact, it can be properly balanced all the way down to 500 RPM.
- A.
  
  True
- B.
  
  False
Correct Answer
A. True

Explanation
In fact, for safety reasons, it is recommended that the rigid rotor be balanced at a lower speed. Its characteristics are linear, and it will remain balanced from the lower speed to its intended operating speed.

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8.

If a machine is a bit unbalanced at a running speed of 1800, the condition with the vibratory forces will be twice as bad when going to 3600 RPM.
- A.
  
  True
- B.
  
  False
Correct Answer
B. False

Explanation
The vibratory forces for unbalance are proportional to the square of the speed change. In this case, it will be a factor of 4!

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9.

In order to do well with the analysis of gearbox issues, it is necessary to calculate the GMF and have data collected to at least 2X GMF.
- A.
  
  True
- B.
  
  False
Correct Answer
B. False

Explanation
As high amplitudes occur at 2X and 3X GMF along with sidebands of shaft speeds, it is necessary to go out to 3.25 GMF with Fmax.

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10.

With an induction motor at 70% load, one can use a current clamp and spectral analysis to pinpoint cracked or broken rotor bar problems.
- A.
  
  True
- B.
  
  False
Correct Answer
A. True

Explanation
In fact, analysis charts exist to pinpoint the severity of the problem when looking at the first pole-pass sideband amplitude relative to the line frequency amplitude.

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Current Version
Mar 21, 2023

Quiz Edited by
ProProfs Editorial Team
Apr 17, 2012

Quiz Created by
Reliaquiz

Check Your Skills In Predictive Maintenance

Having a vibration reading at 1X running speed with amplitude that is 80% or greater than the overall level is a sure sign of unbalance.

If I have a VFD and I suspect that there is a resonance condition somewhere in the operating range, I can run a Bump Test to find the problem.

A good way to determine impacting in a captured time waveform is Crest Factor, calculated by true peak value divided by RMS.

I cannot find the natural resonance of a machine structure without first turning it off and using a Bump Test or shutting it down and capturing Coastdown data during its coast.

A sure way to find bearing faults is to use Demodulation and Enveloping techniques, and these will work well without knowing bearing details.

In just looking at high-frequency acceleration data, one can see the early signs of rolling-element bearing problems.

A rotor that is considered “rigid” does not have to be balanced at running speed. In fact, it can be properly balanced all the way down to 500 RPM.

If a machine is a bit unbalanced at a running speed of 1800, the condition with the vibratory forces will be twice as bad when going to 3600 RPM.

In order to do well with the analysis of gearbox issues, it is necessary to calculate the GMF and have data collected to at least 2X GMF.

With an induction motor at 70% load, one can use a current clamp and spectral analysis to pinpoint cracked or broken rotor bar problems.