Transcript Introduction to - University of Central Oklahoma

Chapter 4 Supplement
Reliability
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Reliability:
the probability that a manufactured good, piece of
equipment, or system performs its intended function for a stated period of
time under specified operating conditions.
Several ways to looking at reliability:
First view:
Related to the probability of working properly when needed.
Second view:
Related to the life of the product (How long does it work before it breaks)
Probability of a product serving longer than a specified period of time
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RP = 0.98
RL = 0.95
RF = 0.97
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Example of Overhead Projector
RP = 0.98
RL = 0.95
RF = 0.97
RbL = 0.96
Rs = 0.94
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Providing Backups
Rss = Rm + {(1-Rm) x Rb}
Rss =
Probability of
first
component +
working
Probability of
needing
x
second
component
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Probability of
second
component
working
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System Reliability - Components in Series
100
n=1
Reliability of the System (Percent)
80
60
40
20
0
100
99
98
97
Average Reliability of all Components (Percent)
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96
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Basic Rule
.70
Lamp 3 (backup for Lamp 2)
.80
Lamp 2 (backup for Lamp1)
1 – P(all fail)
1-[(1-.90)*(1-.80)*(1-.70)] = .994
.90
Lamp 1
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Availability
The fraction of time a piece of equipment is expected to be
available for operation.
MTBF
Availabili ty 
MTBF  MTR
MTBF = mean time between failures
MTR = mean time to repair
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Failure
rate
Infant
mortality
Regular failure
Wear-out failure
Lifetime
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Improving Reliability
•
•
•
•
•
•
•
Component design
Production/assembly techniques
Testing
Redundancy/backups
Preventive maintenance procedures
User education
System design
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Exponential Distribution
Reliability = e -T/MTBF
1- e -T/MTBF
T
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Time
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Normal Distribution
Reliability
0
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z
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