CHAPTER 4 Time-Dependent Failure Rate Models 113 (b) Determine the design life if a reliability of 0.90 is desired. (c) Compute the MTTF. (d) Given that the unit has operated for 50 hr, what is the probability that it will survive a second 50 hr of (e) The power unit is also subject to chance failures at a rate of 0.002 failures per operating hour because of the external environment. What is the power unit's reliability for the first 50 hr of operation considering both failure modes? operation? The wear out of a machine part is normally distributed with 90 percent of the fail- 4.9 ures occurring between 200 and 270 hr of use (i.e., 5 percent below 200 hr and 5 percent above 270 hr). (a) Find the MTTF and the standard deviation of failure times. (b) What is the reliability if the part is to be used for 210 hr and then replaced? (c) Determine the design life if no more than a 1 percent probability of failure prior to replacement is to be tolerated. (d) Compute the reliability for a 10-hr use if the part has been operating for 200 hr (i.e., find the conditional reliability). 10 After burn-in, the lifetime of a mechanical valve is known to be lognormal with tmed = 2236 hr and s= 0.41. (a) Determine its design life if specifications call for a reliability of 0.98. (b) The component is to be used in a pumping device that will require 5 weeks %3D Ure What is the probability of a failure occurring because of

Elements Of Electromagnetics
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Q 4.9

CHAPTER 4 Time-Dependent Failure Rate Models
113
(b) Determine the design life if a reliability of 0.90 is desired.
(c) Compute the MTTF.
(d) Given that the unit has operated for 50 hr, what is the probability that it will
survive a second 50 hr of
(e) The power unit is also subject to chance failures at a rate of 0.002 failures per
operating hour because of the external environment. What is the power unit's
reliability for the first 50 hr of operation considering both failure modes?
operation?
The wear out of a machine part is normally distributed with 90 percent of the fail-
4.9
ures occurring between 200 and 270 hr of use (i.e., 5 percent below 200 hr and 5
percent above 270 hr).
(a) Find the MTTF and the standard deviation of failure times.
(b) What is the reliability if the part is to be used for 210 hr and then replaced?
(c) Determine the design life if no more than a 1 percent probability of failure prior
to replacement is to be tolerated.
(d) Compute the reliability for a 10-hr use if the part has been operating for 200 hr
(i.e., find the conditional reliability).
10 After burn-in, the lifetime of a mechanical valve is known to be lognormal with
tmed = 2236 hr and s= 0.41.
(a) Determine its design life if specifications call for a reliability of 0.98.
(b) The component is to be used in a pumping device that will require 5 weeks
%3D
Ure What is the probability of a failure occurring because of
Transcribed Image Text:CHAPTER 4 Time-Dependent Failure Rate Models 113 (b) Determine the design life if a reliability of 0.90 is desired. (c) Compute the MTTF. (d) Given that the unit has operated for 50 hr, what is the probability that it will survive a second 50 hr of (e) The power unit is also subject to chance failures at a rate of 0.002 failures per operating hour because of the external environment. What is the power unit's reliability for the first 50 hr of operation considering both failure modes? operation? The wear out of a machine part is normally distributed with 90 percent of the fail- 4.9 ures occurring between 200 and 270 hr of use (i.e., 5 percent below 200 hr and 5 percent above 270 hr). (a) Find the MTTF and the standard deviation of failure times. (b) What is the reliability if the part is to be used for 210 hr and then replaced? (c) Determine the design life if no more than a 1 percent probability of failure prior to replacement is to be tolerated. (d) Compute the reliability for a 10-hr use if the part has been operating for 200 hr (i.e., find the conditional reliability). 10 After burn-in, the lifetime of a mechanical valve is known to be lognormal with tmed = 2236 hr and s= 0.41. (a) Determine its design life if specifications call for a reliability of 0.98. (b) The component is to be used in a pumping device that will require 5 weeks %3D Ure What is the probability of a failure occurring because of
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