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Reliability
Chapter Ten
Reliability
Reliability

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Definitions
Reliability: The ability of a product, part, or system to perform its intended function under a prescribed set of conditions
Failure: Situation in which a product, part, or system does not perform as intended
Normal operating conditions: The set of conditions under which an item’s reliability is specified
Reliability
Reliability

3. Reliability Example Determine the reliability of the system shown .92
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Reliability Example
Determine the reliability of the system shown
.98
.90
.92
.95
Reliability
Reliability

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Solution
The system can be reduced to a series of three components
.98
(1-.90)
(1-.95)
.98 x .99 x .996 = .966
Reliability
Reliability

5. Failure Rate Curve Infant mortality Failures due to wear-out
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Failure Rate Curve
Infant
mortality
Failures due
to wear-out
Few (random) failures
Time, T
Reliability
Reliability

6. Failure Rate as an Exponential Function
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Failure Rate as an Exponential Function
Reliability = e -T/MTBF
1- e -T/MTBF T
Time
Reliability
Reliability

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Normal Approximation
Reliability z
Reliability
Reliability

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Availability
The fraction of time a piece of equipment is expected to be available for operation
MTBF = mean time between failures
MTR = mean time to repair
Reliability
Reliability

9. Improving Reliability
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Improving Reliability
Component design
Production/assembly techniques
Testing
Redundancy
Preventive maintenance procedures
User education
System design
Reliability
Reliability