RAM System Reliability Analysis 2 — Questions and Answers
Question 1: In a reliability block diagram (RBD), what does a parallel configuration represent?
- All components must work for system success
- At least one component must work for system success (Correct answer)
- Components are tested sequentially for failures
- Redundant components share the load equally at all times
Correct answer: At least one component must work for system success
A parallel configuration in an RBD means the system succeeds if at least one of its parallel paths is functioning.
Question 2: Which reliability metric directly measures the probability that a component will NOT fail during a specified mission time?
- Mean Time Between Failures (MTBF)
- Failure rate (λ)
- Reliability R(t) (Correct answer)
- Availability A
Correct answer: Reliability R(t)
Reliability R(t) is defined as the probability that a component or system performs its required function without failure over a specified time interval.
Question 3: A system has three components in series with individual reliabilities of 0.95, 0.90, and 0.85. What is the system reliability?
- 0.726 (Correct answer)
- 0.900
- 0.950
- 0.583
Correct answer: 0.726
For series systems, system reliability equals the product of individual reliabilities: 0.95 × 0.90 × 0.85 = 0.726.
Question 4: What is the primary purpose of a Failure Mode and Effects Analysis (FMEA)?
- To schedule preventive maintenance intervals
- To identify potential failure modes and assess their impact on system performance (Correct answer)
- To calculate the MTBF of individual components
- To determine the optimal redundancy level for a system
Correct answer: To identify potential failure modes and assess their impact on system performance
FMEA systematically identifies potential failure modes, their causes, and the effects they have on system operation to prioritize corrective actions.
Question 5: The Weibull distribution's shape parameter (β) equals exactly 1. What does this indicate about the failure behavior?
- Failures are increasing (wear-out phase)
- Failures are decreasing (infant mortality phase)
- Failures are constant (random/chance failures) (Correct answer)
- Failures follow a normal distribution
Correct answer: Failures are constant (random/chance failures)
When β = 1, the Weibull distribution reduces to the exponential distribution, indicating a constant failure rate characteristic of the useful life period.
Question 6: In fault tree analysis (FTA), what does an AND gate indicate?
- The top event occurs if any one input event occurs
- The top event occurs only if all input events occur simultaneously (Correct answer)
- The top event is independent of the input events
- The top event occurs when a majority of input events occur
Correct answer: The top event occurs only if all input events occur simultaneously
An AND gate in FTA indicates that the output event (top event) occurs only when all input events occur simultaneously.
Question 7: Which analysis technique identifies the minimum sets of basic events that are sufficient to cause the top (undesired) event in a fault tree?
- Minimal cut sets (Correct answer)
- Minimal path sets
- Common cause failure groups
- Success space analysis
Correct answer: Minimal cut sets
Minimal cut sets are the smallest combinations of basic events whose simultaneous occurrence causes the top event in a fault tree.
RAM System Reliability Analysis 2
In a reliability block diagram (RBD), what does a parallel configuration represent?