MMC Predictive & Preventive Maintenance 3 ā Questions and Answers
Question 1: Motor current signature analysis (MCSA) is primarily used to detect:
- Transformer insulation breakdown
- Mechanical faults such as broken rotor bars and bearing defects (Correct answer)
- Power factor imbalance in distribution panels
- Static electricity buildup on motor shafts
Correct answer: Mechanical faults such as broken rotor bars and bearing defects
MCSA analyzes current waveform signatures to identify mechanical anomalies like broken rotor bars, eccentricity, and bearing faults without physical contact.
Question 2: Which vibration frequency is generated by a rolling element bearing with a defective outer race?
- Shaft rotational frequency (1X)
- Ball pass frequency outer race (BPFO) (Correct answer)
- Gear mesh frequency
- Vane pass frequency
Correct answer: Ball pass frequency outer race (BPFO)
A defect on the outer race produces impacts at the ball pass frequency outer race (BPFO), a calculable frequency based on bearing geometry and shaft speed.
Question 3: What is the key advantage of thermographic surveys conducted during peak electrical load conditions?
- Reduced cost of the survey
- Thermal anomalies are more pronounced under higher current flow (Correct answer)
- Safety regulations require peak-load surveys only
- Cooler ambient temperatures improve camera accuracy
Correct answer: Thermal anomalies are more pronounced under higher current flow
Resistance-related heating (IĀ²R losses) increases with current, making loose connections and overloaded components easier to detect at higher loads.
Question 4: A preventive maintenance program shows high PM compliance but equipment failures have not decreased. The most likely root cause is:
- Maintenance technicians are undertrained
- PM tasks are not matched to actual failure modes (Correct answer)
- CMMS software is outdated
- Spare parts inventory is insufficient
Correct answer: PM tasks are not matched to actual failure modes
If PM tasks do not address the dominant failure modes of the equipment, completing them on schedule will not reduce failure frequency.
Question 5: In oil analysis, a high total base number (TBN) depletion rate in engine oil indicates:
- Oil is over-filtered and too clean
- Acid neutralization capacity is being consumed rapidly, suggesting contamination (Correct answer)
- Viscosity is increasing due to oxidation
- Water contamination from a cooling system leak
Correct answer: Acid neutralization capacity is being consumed rapidly, suggesting contamination
TBN measures the oil's remaining alkaline reserve to neutralize acids; rapid depletion signals acid production from combustion by-products or contamination.
Question 6: Which PM optimization approach uses failure mode and effects analysis (FMEA) to justify maintenance task selection?
- Total Productive Maintenance (TPM)
- Reliability-Centered Maintenance (RCM) (Correct answer)
- Planned Preventive Maintenance (PPM)
- Condition-Based Maintenance (CBM)
Correct answer: Reliability-Centered Maintenance (RCM)
RCM uses FMEA to identify failure modes, their effects, and consequences, then selects tasks that are technically and economically justified for each failure mode.
Question 7: An equipment operator notices a new high-pitched squeal from a conveyor drive motor. This is best categorized as:
- A corrective maintenance trigger requiring immediate repair
- Operator-based condition monitoring that should be documented and reported (Correct answer)
- Normal operational noise requiring no action
- A safety violation requiring line shutdown
Correct answer: Operator-based condition monitoring that should be documented and reported
Operators are a critical sensing resource in condition monitoring; unusual sounds should be documented and reported to maintenance for evaluation.
MMC Predictive & Preventive Maintenance 3
Motor current signature analysis (MCSA) is primarily used to detect: