TECH SPOT: SAMPLE CRE QUESTIONS (Part 30)

By Tim Gaens posted 2 hours ago

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to have a constant failure rate. What is the failure rate?

A .0.005 per month

B. 0.004 per month

C. 0.01 per month

D. 0.0009 per month

A one-year guarantee. An electronic device is tested for two months and found to have a reliability of 0.990; the device is also known tee is given based on the assumption that no more than 10% of the items will be returned. Assuming an exponential distribution, what is the maximum failure rate that can be tolerated?

A. 0.091/year

B. 0.0943/year

C. 0.1054/year

D. 0.0231/year

3. A servomechanism has an MTBF of 2000 hr. with a constant failure rate. What is the reliability for a 125- hr mission?

A. 0.939

B. 0.92

C. 0.952

D. 0.965

4. Using 3 above, neglecting repair time, what is the probability that more than one failure will occur during a 125-hr mission?

A. 0.0035

B. 0.0092

C. 0.019

D. 0.0019

5.Suppose that a system consists of two subsystems in active parallel. The reliability of each subsystem is given by the Rayleigh distribution(Weibull with β=2).

Assuming that common-mode failures may be neglected, determine the system MTTF

A . 1.452

B. 1.293

C. 1.154

D. 1.375

6.Using the table below, calculate the reliability of a switchable attenuator consisting of 15 resistors, 2 connectors, and 1 rotary switch operating for 1000 hours.

A.0.991

B. 0.9975

C. 0.9877

D. 0.999

7. Ten identical devices are tested until failure at times(in hours):

170, 350, 500, 650, 800, 960, 1100, 1300, 1800, 2200

Using whatever software you have, decide what Reliability

distribution seems to represent this data.

A. Weibull

B. Log–Normal

C. Gamma

D. Log-logistic

Hint: use the AD(Anderson-Darling) to decide

An engineer designs a system consisting of two subsystems in series. The reliabilities are R1 = 0.98 and R2 = 0.94. The cost of the two subsystems is about equal. Which of the following would be better to do?

A.