CRE CRE Statistical Methods and Reliability Modeling

Question 1

Which probability distribution is most commonly used to model the time between failures for electronic components during their useful life period?

Accepted Answer

Exponential distribution

Answer

During the useful life phase, the exponential distribution is used because it assumes a constant failure rate (λ).

Question 2

A Weibull shape parameter (β) equal to 1 indicates which type of failure behavior?

Accepted Answer

Constant failure rate (random failures)

Answer

When β = 1, the Weibull distribution reduces to the exponential distribution, indicating a constant failure rate.

Question 3

Mean Time Between Failures (MTBF) is mathematically the reciprocal of which reliability parameter?

Accepted Answer

Failure rate λ

Answer

MTBF = 1/λ, where λ is the constant failure rate under the exponential distribution assumption.

Question 4

A component has an MTBF of 500 hours. What is its reliability at t = 500 hours assuming an exponential distribution?

Accepted Answer

36.8%

Answer

R(t) = e^(-t/MTBF) = e^(-500/500) = e^(-1) ≈ 0.368 or 36.8%.

Question 5

Which reliability system model assumes that the system fails when any single component fails?

Accepted Answer

Series system

Answer

In a series reliability model, all components must function for the system to function, so failure of any one causes system failure.

(CRE) Certified Reliability Engineer Practice Test