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McGraw-Hill/IrwinOperations Management, Seventh Edition, by William J. StevensonCopyright © 2002 by The McGraw-Hill Companies, Inc. All rights reserved.

Reliability

Chapter 4 Supplement

Reliability

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McGraw-Hill/IrwinOperations Management, Seventh Edition, by William J. StevensonCopyright © 2002 by The McGraw-Hill Companies, Inc. All rights reserved.

Reliability

Reliability

• 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

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McGraw-Hill/IrwinOperations Management, Seventh Edition, by William J. StevensonCopyright © 2002 by The McGraw-Hill Companies, Inc. All rights reserved.

Reliability

• Probability that the product or system will:– Function when activated– Function for a given length of time

• Independent events

• Redundancy

Reliability is a Probability

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McGraw-Hill/IrwinOperations Management, Seventh Edition, by William J. StevensonCopyright © 2002 by The McGraw-Hill Companies, Inc. All rights reserved.

Reliability

Example 1: Reliability

Determine the reliability of the system shown

.98 .90

.90 .92

.95

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McGraw-Hill/IrwinOperations Management, Seventh Edition, by William J. StevensonCopyright © 2002 by The McGraw-Hill Companies, Inc. All rights reserved.

Reliability

Example 1 Solution

The system can be reduced to a series of three components

.98 .90+.90(1-.90) .95+.92(1-.95)

.98 x .99 x .996 = .966

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McGraw-Hill/IrwinOperations Management, Seventh Edition, by William J. StevensonCopyright © 2002 by The McGraw-Hill Companies, Inc. All rights reserved.

Reliability

Failure Rate

Few (random) failuresInfantmortality

Failures dueto wear-out

Time, T

Figure 4S-1

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McGraw-Hill/IrwinOperations Management, Seventh Edition, by William J. StevensonCopyright © 2002 by The McGraw-Hill Companies, Inc. All rights reserved.

Reliability

Exponential Distribution

Reliability = e -T/MTBF

1- e -T/MTBF

T Time

Figure 4S-2

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McGraw-Hill/IrwinOperations Management, Seventh Edition, by William J. StevensonCopyright © 2002 by The McGraw-Hill Companies, Inc. All rights reserved.

Reliability

Normal Distribution

Reliability

0 z

Figure 4S-3

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McGraw-Hill/IrwinOperations Management, Seventh Edition, by William J. StevensonCopyright © 2002 by The McGraw-Hill Companies, Inc. All rights reserved.

Reliability

Availability

• The fraction of time a piece of equipment is expected to be available for operation

AvailabilityMTBF

MTBF MTR

MTBF = mean time between failuresMTR = mean time to repair

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McGraw-Hill/IrwinOperations Management, Seventh Edition, by William J. StevensonCopyright © 2002 by The McGraw-Hill Companies, Inc. All rights reserved.

Reliability

Improving Reliability

• Component design

• Production/assembly techniques

• Testing

• Redundancy/backups

• Preventive maintenance procedures

• User education

• System design