CMRT Equipment Reliability 2 — Questions and Answers
Question 1: A pump has an MTBF of 2,000 hours and an MTTR of 8 hours. What is its inherent availability?
- 99.6% (Correct answer)
- 98.4%
- 97.2%
- 95.0%
Correct answer: 99.6%
Inherent availability = MTBF / (MTBF + MTTR) = 2000 / 2008 ≈ 99.6%.
Question 2: Which reliability metric measures the average time a system operates before failing?
- MTTR
- MTBF (Correct answer)
- MTTF
- OEE
Correct answer: MTBF
MTBF (Mean Time Between Failures) measures average operating time between consecutive failures for repairable systems.
Question 3: If a component has a constant failure rate of 0.0005 failures/hour, what is its reliability after 1,000 hours?
- 60.7% (Correct answer)
- 50.0%
- 36.8%
- 13.5%
Correct answer: 60.7%
R(t) = e^(-λt) = e^(-0.0005 × 1000) = e^(-0.5) ≈ 0.607 or 60.7%.
Question 4: A system has three components in series with reliabilities of 0.95, 0.90, and 0.98. What is the system reliability?
- 0.837 (Correct answer)
- 0.943
- 0.997
- 0.610
Correct answer: 0.837
Series system reliability = R1 × R2 × R3 = 0.95 × 0.90 × 0.98 ≈ 0.837.
Question 5: What does the 'bathtub curve' infant mortality region indicate about equipment failure?
- Failures decrease over time due to early defect elimination (Correct answer)
- Failures increase steadily due to wear
- Failures are random and unpredictable
- Failures spike due to overloading
Correct answer: Failures decrease over time due to early defect elimination
The infant mortality region shows a decreasing failure rate as weak components fail early and are removed from service.
Question 6: Which measure describes the probability that a failed system will be restored to operating condition within a specified time?
- Availability
- Reliability
- Maintainability (Correct answer)
- Dependability
Correct answer: Maintainability
Maintainability is the probability that a failed item will be restored to a specified condition within a given time when maintenance is performed.
Question 7: When two identical components are placed in active parallel redundancy with individual reliability of 0.80, what is the system reliability?
- 0.96 (Correct answer)
- 0.80
- 0.64
- 0.90
Correct answer: 0.96
Parallel redundancy: R_system = 1 – (1–0.80)(1–0.80) = 1 – 0.04 = 0.96.
CMRT Equipment Reliability 2
A pump has an MTBF of 2,000 hours and an MTTR of 8 hours.
What is its inherent availability?