RAM Preventive & Predictive Maintenance 3 — Questions and Answers
Question 1: In ultrasonic predictive maintenance, what physical phenomenon is being detected when monitoring for compressed air leaks or bearing defects?
- Infrared radiation emitted by turbulent flow or friction
- High-frequency acoustic emissions above 20 kHz generated by turbulence or stress (Correct answer)
- Low-frequency vibration caused by imbalance or misalignment
- Electromagnetic interference from damaged insulation
Correct answer: High-frequency acoustic emissions above 20 kHz generated by turbulence or stress
Ultrasonic testing detects high-frequency sound waves (typically 20–100 kHz) produced by gas turbulence at leak points or stress-wave emissions from bearing defects and electrical arcing.
Question 2: What does a 'fast Fourier transform' (FFT) spectrum analyzer do in a vibration-based predictive maintenance program?
- Converts time-domain vibration waveform data into a frequency-domain spectrum (Correct answer)
- Filters out background noise from vibration signals using a Fourier band-pass filter
- Calculates the overall RMS vibration level for ISO severity comparison
- Predicts remaining useful life using frequency trend analysis
Correct answer: Converts time-domain vibration waveform data into a frequency-domain spectrum
FFT converts a time-domain vibration signal into a frequency-domain spectrum, revealing the amplitude of each frequency component and enabling identification of specific fault frequencies.
Question 3: A predictive maintenance program uses motor current signature analysis (MCSA). Which fault is this technique specifically effective at detecting?
- Bearing outer-race defects from mechanical wear
- Rotor bar cracks or broken rotor bars in induction motors (Correct answer)
- Misalignment between motor and driven equipment
- Soft-foot condition in the motor mounting
Correct answer: Rotor bar cracks or broken rotor bars in induction motors
MCSA detects anomalies in the stator current spectrum; broken or cracked rotor bars produce characteristic sidebands around the supply frequency at specific slip-related intervals.
Question 4: Which parameter is used to define the 'age exploration' strategy in RCM when no historical failure data exists for a component?
- Manufacturer's recommended overhaul interval (OEM TBO)
- Mean Time To Failure estimated from similar equipment populations
- A conservative initial interval that is extended only if no failures are found at inspection (Correct answer)
- The interval at which the first failure has historically occurred in the fleet
Correct answer: A conservative initial interval that is extended only if no failures are found at inspection
When failure data is absent, RCM recommends starting with a conservative (short) interval and extending it incrementally—'age exploration'—based on the condition found at each inspection.
Question 5: ISO 10816-3 vibration severity standards classify machinery vibration based on which measurement?
- Peak vibration velocity in mm/s measured on the bearing housing (Correct answer)
- Peak-to-peak displacement in microns measured on the shaft
- Overall acceleration in g-RMS measured on the machine baseplate
- Crest factor derived from time-waveform analysis
Correct answer: Peak vibration velocity in mm/s measured on the bearing housing
ISO 10816-3 specifies evaluation zones (A through D) for industrial machines based on the broadband RMS vibration velocity (mm/s) measured on non-rotating parts such as bearing housings.
Question 6: A maintenance planner is developing a preventive maintenance task for a centrifugal pump mechanical seal. The task is justified only if it can:
- Reduce the probability of failure to zero over the maintenance interval
- Detect a potential failure before it becomes a functional failure (Correct answer)
- Restore the item to 'as-new' condition regardless of current wear state
- Extend the P-F interval beyond the next scheduled shutdown window
Correct answer: Detect a potential failure before it becomes a functional failure
A scheduled on-condition task (predictive maintenance) is only applicable and effective if it can reliably detect a potential failure condition before functional failure occurs and the P-F interval allows time to act.
Question 7: During a lubrication PM task, a technician notices the grease color has turned black and has a burnt odor. This observation most likely indicates:
- Normal oxidation of the base oil after extended service
- Over-greasing causing excessive churning and heat build-up (Correct answer)
- Contamination from external dust in the environment
- Correct lubrication interval adherence
Correct answer: Over-greasing causing excessive churning and heat build-up
Black, burnt-smelling grease is a classic indicator of thermal degradation caused by over-lubrication, where excess grease churns inside the bearing and generates frictional heat above the grease's thermal limit.
RAM Preventive & Predictive Maintenance 3
In ultrasonic predictive maintenance, what physical phenomenon is being detected when monitoring for compressed air leaks or bearing defects?