1.
With modern-day FFT displays of frequency data, there is not much value in a raw time waveform.
Correct Answer
B. False
Explanation
In machinery diagnostics, time waveform shapes and signatures hold equal significance to spectral displays in identifying classical issues like unbalance, misalignment, impacting, binding, etc. Analyzing these time-based patterns provides crucial insights into equipment health, enabling early detection and preventive action. By scrutinizing waveform characteristics alongside spectral data, maintenance professionals can effectively pinpoint and address potential problems, ensuring optimal machinery performance and reliability.
2.
A machine must be stopped in order to perform any impact tests to determine natural resonance frequencies.
Correct Answer
B. False
Explanation
Bump tests conducted during machine operation are viable if data can be filtered based on the typical running signature. Filtering ensures that the bump test results are accurately interpreted within the context of normal machine operation, facilitating effective diagnosis and maintenance actions.
3.
One of the best time waveform tools to determine the amount of impacting in the collected data is Crest Factor.
Correct Answer
A. True
Explanation
Two invaluable tools for time waveform analysis are Crest Factor (the ratio of maximum peak value to RMS) and true peak-to-peak measurement. These metrics provide critical insights into waveform characteristics, aiding in the identification of anomalies and potential machinery issues for effective maintenance strategies.
4.
A rotor to be balanced is considered “rigid” if it is operating at less than 70% of its first critical frequency.
Correct Answer
A. True
Explanation
This criterion is crucial to ensure that the rotor is not approaching its first critical speed, where central bowing may occur. Monitoring this parameter helps prevent potential rotor instability issues, ensuring safe and optimal operation of rotating machinery.
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.
Correct Answer
A. True
Explanation
The Nyquist criterion is a mathematical principle dictating that digital sampling should occur at a rate of at least 2.56 times the maximum frequency (Fmax) value. Adhering to this guideline ensures accurate representation of analog signals in digital form, minimizing aliasing and preserving signal fidelity.
6.
An 800-line spectral display can be made from 1024 samples of the raw time waveform.
Correct Answer
B. False
Explanation
False. An 800-line spectral display typically requires a greater number of samples than 1024 from the raw time waveform. The number of lines or frequency bins in a spectral display corresponds to the resolution or frequency range that can be represented. In general, higher-resolution displays, such as an 800-line display, require more samples to accurately represent the frequency content of the signal. Therefore, to create an 800-line spectral display, more than 1024 samples of the raw time waveform would be needed to provide sufficient detail and resolution in the frequency domain.
7.
When measuring machines running between 600 and 60,000 RPM, acceleration is the best choice for the vibration measurement.
Correct Answer
A. True
Explanation
True. When measuring machines running between 600 and 60,000 RPM, acceleration is typically the preferred choice for vibration measurement. This is because acceleration measurements are more sensitive to high-frequency vibrations, which are common in high-speed rotating machinery. Additionally, acceleration measurements provide better resolution and accuracy in detecting and diagnosing vibration-related issues in such machinery.
8.
Demodulation is a good tool for discovering rolling element defects, but it is not effective on machines running less than 120 RPM.
Correct Answer
B. False
Explanation
False. Demodulation can be an effective tool for discovering rolling element defects regardless of the machine's operating speed. While demodulation techniques may be more commonly used on machines operating at higher speeds where vibration signals contain higher frequency components, they can still be useful for detecting rolling element defects on machines running at speeds lower than 120 RPM. The effectiveness of demodulation depends on various factors such as the type of defect, the signal-to-noise ratio, and the specific characteristics of the vibration signal. Therefore, demodulation can be applied to machines operating at a wide range of speeds to detect rolling element defects.
9.
Two-plane dynamic balancing takes the static and couple effects of the unbalance condition into account.
Correct Answer
A. True
Explanation
True. Two-plane dynamic balancing does indeed take into account both the static and couple effects of the unbalance condition. This balancing method involves correcting unbalance in two different planes simultaneously, addressing both the primary unbalance (static) and the secondary unbalance (couple) to ensure optimal balance conditions across multiple planes. By accounting for both static and couple effects, two-plane dynamic balancing helps minimize vibration and ensures smooth operation of rotating machinery.
10.
Cross-channel phase measurements are good for visualizing the relative motion between machine components and structure.
Correct Answer
A. True
Explanation
True. Cross-channel phase measurements are indeed useful for visualizing the relative motion between machine components and structure. By comparing the phase relationship between vibration signals from different measurement points or channels, engineers can gain insights into the synchronization or relative displacement of machine components. This information is valuable for diagnosing issues such as misalignment, looseness, or bearing faults, as variations in phase can indicate differences in the timing or direction of motion between components. Therefore, cross-channel phase measurements play a crucial role in vibration analysis and condition monitoring, helping to identify potential problems and optimize machinery performance.