Reliability

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Reliability Maintainability EngineeringAn
Introduction

• Robert Brown
• Electrical Computer Engineering
• Worcester Polytechnic Institute

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Reliability / Maintainability-ability

• Reliability Probability that a device will
  operate within specifications for the specified
  duration
• Maintainability Amount of resources required to
  remove faults
• Diagnose-ability The ability to locate faults
• Repair-ability The ability to remove faults

Availability Probability that a device is
operationally ready
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Why is it important?Reliability
Maintainability Engineering

• Mission Success - The product correctly operates
  for the duration of the mission
• Customer Satisfaction Perceived product quality
• Brand loyalty, customer loyalty
• Competitive Products Market requirements
• Safety
• Support Legal Contractual Requirements
• Reduce Cost of Ownership
• Reduce Product Cost Warranty
• Reduce Service Cost Service delivery cost
• Insurance

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Bathtub CurveFailures over Time
Warranty Period
l Failure Rate
Time
Infancy
Steady State
Wearout
Workmanship Contamination Burn-In Quality Control
Random Failures Overload Improper Usage
Thermal Fatigue Oxidation Cracking-Shrinking Frict
ion Wear
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Product Life Cycle ActivitiesReliability
Maintainability
Design
Develop
Deploy
Manage

• Identify competitive market requirements
• Design for reliability
• Failure analysis
• Reliability predictions

• Reliability testing
• Maintainability testing
• Develop service strategy

• Ongoing reliability testing
• Engineering changes
• Maintenance releases

• End of product life
• End of service life
• Logistics strategy

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ReliabilityDeveloping reliable products

• Quality materials
• Stability mechanical / electrical
• Design for anticipated load
• Design for operating environment
• Cooling
• Redundancy
• Full functionality
• Reduced functionality
• Self-healing

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Series and ParallelPredicting System Reliability
Series
Parallel
System requires device A AND device B to
operate
System requires device A OR device B to
operate
RS R1 R2 Rn
RS 1 ( 1 - R1 ) ( 1 RN )
RS 0.8 0.9 0.72
RS 1 (1 - 0.8) (1 - 0.9) RS 0.98
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Complex ConfigurationPredicting System
Reliability
System includes series and parallel device
configuration
B
RS 1 ( 1 - R1 ) ( 1 RN ) RBC 1 (1 -
0.8) (1 - 0.9) RBC 0.98
A
C
RS R1 R2 Rn RS RA RBC RS 0.8
0.98 0.78
A
BC
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Reliability MetricsReliability is specified and
measured in several ways
Failure Rate l Count of failures during a time period. Usually 106 hours
MTBF or MTTF Reliability Mean Time Between Failures Mean Time To Fail Stated in hours MTBF 1 / l Usually MTBF 106 / l R(p) e-lt t Mission time
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ReliabilityCalculating MTBF
Component l
Duty Cycle
Component
Failure Rate l
30
100
CPU
30
20
100
Power Supply
20
20
20
Floppy
4
54
Total
1
1
MTBF
18518 hrs


54
l
Note l in 106 Hours
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Maintainability
Resources required to remove faults

• MTTR Mean Time To Repair
• Measured in hours
• Major activities
• Diagnoses
• Repair
• Focus on labor and materials

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Diagnose-abilityDeveloping diagnose-able products
Quickly and Correctly Locate the Fault

• User and service documentation, tools and
  training
• Operator indicators and error messages.
  Preserved state indicators accessed by repair
  depot.
• Test points
• Device error and state change logging
• Environmental measurements
• Diagnostic and failure detection tools
• Local and remote diagnosis
• Call Home
• Designed for technical and non-technical users
• Product labeling and revision management

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Repair-abilityDeveloping repair-able products
Quickly Remove the Fault

• Repair or replace?
• Remote and On-site repair?
• Firmware, software, micro-code
• Limit specialized tools
• Limit adjustments
• Hot-Swap
• Larger, functionally dense sub-assemblies
• Physical layout
• Easier to replace less reliable components
• Minimal disruption to replace a component

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EconomicsReliability Maintainability
Population (units)
20,000
20,000
20,000
20,000
Reliability MTBF Hr
10,000
15,000
10,000
15,000
Repair cost
25.00
25.00
12.50
12.50
Duty Cycle12/24 Day 50
50
50
50
50
Operating Time (1236520000)
87,600,000
87,600,000
87,600,000
87,600,000
Repair Calls(87600000/MTBF)
8,760
5,840
8,760
5,840
Annual
Service Cost (CallsCost)
219,000
146,000
109,500
73,000
Savings
73,000
109,500
146,000
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Resources

• Applied Reliability by Dave Trindade
• Reliability Magazine http//www.reliability-magazi
  ne.com/index.php
• IEEE Reliability Society http//ewh.ieee.org/soc/r
  s/