Tools And Applications For Pdm
This quiz is intended to test your knowledge on some basic terms and subject matter related to good predictive maintenance practices. Several areas are covered just to stimulate your thinking and to encourage you to look into available training materials and courses.
Questions and Answers
- 1.
With modern-day FFT displays of frequency data, there is not much value in a raw time waveform.
- A.
True
- B.
False
Correct Answer
B. FalseExplanation
Time Waveform shapes and signatures are just as important as spectral displays for finding classical problems such as unbalance, misalignment, impacting, binding, etc.Rate this question:
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- 2.
A machine must be stopped in order to perform any impact tests to determine natural resonance frequencies.
- A.
True
- B.
False
Correct Answer
B. FalseExplanation
Bump tests can be made during machine running conditions as long as data can be filtered in terms of the normal running signature.Rate this question:
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- 3.
One of the best time waveform tools to determine the amount of impacting in the collected data is Crest Factor.
- A.
True
- B.
False
Correct Answer
A. TrueExplanation
There are two very valuable tools for time waveform analysis. One is Crest Factor (max. peak value divided by RMS) and true peak-to-peak measurement.Rate this question:
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- 4.
A rotor to be balanced is considered “rigid” if it is operating at less than 70% of its first critical frequency.
- A.
True
- B.
False
Correct Answer
A. TrueExplanation
This is the main criteria to make certain that the rotor is not going through its first critical, where there is bowing in the center.Rate this question:
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- 5.
In order to reproduce a good time waveform, the raw signal needs to be sampled at a rate greater than twice the highest frequency content.
- A.
True
- B.
False
Correct Answer
A. TrueExplanation
This is a mathematical term called Nyquist criteria. Digital sampling is actually conducted at a rate of 2.56 times the Fmax value.Rate this question:
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- 6.
An 800-line spectral display can be made from 1024 samples of the raw time waveform.
- A.
True
- B.
False
Correct Answer
B. FalseExplanation
In order to get 800 lines of spectral data, it is necessary to get 2.56 samples for each line. 1024 samples produce a 400-line spectrum. For 800 lines, it takes 2048 samples.Rate this question:
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- 7.
When measuring machines running between 600 and 60,000 RPM, acceleration is the best choice for the vibration measurement.
- A.
True
- B.
False
Correct Answer
B. FalseExplanation
As a general rule, displacement is good for speeds under 600 RPM. Acceleration is used for speeds above 120,000 CPM. Velocity is flat, and the best choice between 600 and 60,000 RPM.Rate this question:
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- 8.
Demodulation is a good tool for discovering rolling element defects, but it is not effective on machines running less than 120 RPM.
- A.
True
- B.
False
Correct Answer
B. FalseExplanation
As we are really looking at bearing faults exciting higher natural resonance frequencies in a machine structure, Demodulation techniques actually work well at low frequencies also, with some success all the way down to 5 RPM.Rate this question:
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- 9.
Two-plane dynamic balancing takes the static and couple effects of the unbalance condition into account.
- A.
True
- B.
False
Correct Answer
A. TrueExplanation
Dynamic balancing involves the use of trial (calibration) weights in two planes to determine the machine characteristics and cross effects; and therefore, it handles static and couple components.Rate this question:
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- 10.
Cross-channel phase measurements are good for visualizing the relative motion between machine components and structure.
- A.
True
- B.
False
Correct Answer
A. TrueExplanation
This is a field-proven tool to decide the direction of vibratory forces from foundation to frame or across couplings and side-to-side motion.Rate this question:
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