RelexRelexReliability SoftwareReliability Software

“the intuitive solution!”“the intuitive solution!”

Relex Software Relex Software CorporationCorporation

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What is What is RelexRelex??

A Powerful Reliability Software Tool… performs efficient reliability analysis uses multiple analysis techniques provides advanced features

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Relex Is Relex Is Uniquely QualifiedUniquely Qualified

Reliability Engineering ExperienceReliability Engineering Experience CommercialCommercial MilitaryMilitary

Software Development ExperienceSoftware Development Experience

RelexRelexReliability SoftwareReliability Software

“the intuitive solution!”“the intuitive solution!”

Relex Software Relex Software CorporationCorporation

Introduction to Introduction to Reliability PredictionReliability Prediction

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Reliability PredictionsReliability Predictions

What is a Reliability Prediction?What is a Reliability Prediction? Calculation of failure rate (MTBF)Calculation of failure rate (MTBF)

How is it Calculated?How is it Calculated? Based on established reliability modelBased on established reliability model

Reliability MeasuresReliability Measures

Failure Rate (Failure Rate ()) Mean Time Between Failures (MTBF)Mean Time Between Failures (MTBF) ReliabilityReliability AvailabilityAvailability

Sample Relex Reliability Prediction calculation results

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Failure RateFailure Rate

Defined As:Defined As: Rate of Occurrence of FailuresRate of Occurrence of Failures Number of Failure in Specified Number of Failure in Specified

Time PeriodTime Period

Units:Units: Failures per Million HoursFailures per Million Hours Failures per Billion Hours (FIT Rate)Failures per Billion Hours (FIT Rate)

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MTBFMTBF

Defined As:Defined As: Mean Time Between FailuresMean Time Between Failures Number of Hours to Pass Number of Hours to Pass

Before a Failure Occurs Before a Failure Occurs Inverse of Failure Rate*Inverse of Failure Rate*

Units:Units: Typically expressed in HoursTypically expressed in Hours *Constant Failure Rate Systems*Constant Failure Rate Systems

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ReliabilityReliability

Defined As:Defined As: The The probabilityprobability that an item will perform a that an item will perform a

required function without failure under required function without failure under

stated conditions for a stated period of stated conditions for a stated period of

timetime

Units:Units: Probability Value (0-1)Probability Value (0-1)

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AvailabilityAvailability

Defined As:Defined As: The The probabilityprobability that an item is in an that an item is in an

operable state at any timeoperable state at any time

Units:Units: Probability Value (0-1)Probability Value (0-1)

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Reliability “Summary”Reliability “Summary”

Failure Rate -- number of failures in timeFailure Rate -- number of failures in time

MTBF -- average time between failuresMTBF -- average time between failures

Reliability -- takes into account mission timeReliability -- takes into account mission time

Availability -- accounts for repairs (MTTR) Availability -- accounts for repairs (MTTR) and downtimeand downtime

The Bathtub Curve The Bathtub Curve and Reliabilityand Reliability

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The Bathtub CurveThe Bathtub Curve

Represents failure rate tendencies for Represents failure rate tendencies for the lifespan of an itemthe lifespan of an item

Failure rate varies in different phases of Failure rate varies in different phases of lifelife

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Three Phases of LifeThree Phases of Life

Infant Mortality RegionInfant Mortality Region

Wear-Out RegionWear-Out Region

Constant Failure Rate RegionConstant Failure Rate Region

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Bathtub CurveBathtub Curve

Graph of Failure Rate vs. TimeGraph of Failure Rate vs. Time

Considers three phases of lifeConsiders three phases of life

Represents lifespan of itemRepresents lifespan of item

(i.e. 15 years for a car)(i.e. 15 years for a car)

TimeTime

Fai

lure

Rat

eF

ailu

re R

ate

Infant Infant MortalityMortalityWear Wear OutOutConstant Failure Constant Failure

RateRate

Bathtub CurveBathtub Curve–Illustration––Illustration–

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Reliability ModelsReliability Models

Influences to reliability /Influences to reliability /Model-parametersModel-parameters

Production maturity

Storageconditions

Transportconditions

Design &construction

Material-selection

Application-temperature

mechanicalstress

Climatic environment

electricalstress

Operatingconditions

Electronic component

Pro

du

ctio

n f

acto

rsA

pp

lica

tio

n f

acto

rs

Relex Prediction ModelsRelex Prediction Models MIL-HDBK-217 (FN1, FN2 )MIL-HDBK-217 (FN1, FN2 ) Telcordia (Telcordia 1, Bellcore 4,5,6) Telcordia (Telcordia 1, Bellcore 4,5,6) Prism: RAC model (Process Grades, Bayesian)Prism: RAC model (Process Grades, Bayesian) NSWC-98/LE1: mechanical modelNSWC-98/LE1: mechanical model HRD5: British telecomm modelHRD5: British telecomm model CNET 93: French telecomm modelCNET 93: French telecomm model 299B: Chinese standard299B: Chinese standard

Relex allows the user to use multiple models within one project and use functionality across models (i.e. use Prism process grade factors

on 217 predicted failure rates, use Bellcore methods on 217 calculations, etc.)

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MIL-HDBK-217MIL-HDBK-217

Original standard for reliabilityOriginal standard for reliability

Reliability math models electronic devicesReliability math models electronic devices

Used commercially & in the defense industryUsed commercially & in the defense industry

Currently at Revision F Notice 2Currently at Revision F Notice 2

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Parts CountParts Count

A section of MIL-HDBK-217A section of MIL-HDBK-217

Provides simpler reliability mathProvides simpler reliability math

Typical Uses:Typical Uses:

Used early in the design processUsed early in the design process

Used to acquire a rough estimate of reliabilityUsed to acquire a rough estimate of reliability

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Telcordia (Bellcore)Telcordia (Bellcore)

Originally developed at AT&T Bell LabsOriginally developed at AT&T Bell Labs

““Modified” MIL-HDBK-217 equationsModified” MIL-HDBK-217 equations

New equations represented what their New equations represented what their

equipment was experiencing in the fieldequipment was experiencing in the field

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Telcordia (Bellcore) (cont.)Telcordia (Bellcore) (cont.)

New model with new featureNew model with new feature

Account for “real data”Account for “real data”

Burn-in, Field, Laboratory testing dataBurn-in, Field, Laboratory testing data

Popular standard for commercial Popular standard for commercial

companiescompanies

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MechanicalMechanical

Based on the Handbook of Reliability Based on the Handbook of Reliability Prediction Procedures for Mechanical Prediction Procedures for Mechanical Equipment, NSWC-98/LE1Equipment, NSWC-98/LE1

Provides models for various types of Provides models for various types of mechanical devices including springs, mechanical devices including springs, bearings, seals, etc.bearings, seals, etc.

New and unique standardNew and unique standard

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CNET & HRD5CNET & HRD5

Used in EuropeUsed in Europe Reliability models for telecommunicationsReliability models for telecommunications Current Versions:Current Versions:

HRD - 5 HRD - 5 CNET - 93 CNET - 93

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Bellcore vs. 217Bellcore vs. 217 Recognition & AcceptanceRecognition & Acceptance ConcentrationConcentration Calculations & EquationsCalculations & Equations Consideration of Test DataConsideration of Test Data MultiplierMultiplier PartsParts EnvironmentsEnvironments Quality LevelsQuality Levels

Accuracy of MTBF Accuracy of MTBF AssessmentsAssessments

Stage I:Parts count method, assuming constant failure rates

Stage II:Variation of failure rates according to part families

Stage III:Taking into account of operational parameters

Stage IV:Consideration of failure modes, time influences, different failure distribution for each part, etc.

Accuracy

Time spent for the analysis

PRISM Reliability PRISM Reliability ModelModel

Developed by the Reliability Analysis Center (RAC)Developed by the Reliability Analysis Center (RAC)

Accounts for the effect of process related variability Accounts for the effect of process related variability

on system failure rateon system failure rate

Inherent failure rate based on base failure rate and Inherent failure rate based on base failure rate and

environmental conditions (RAC Rates model)environmental conditions (RAC Rates model)

Failure rate may then be modified by:Failure rate may then be modified by: Process Grade Factors, and/orProcess Grade Factors, and/or

Bayesian Analysis, and/orBayesian Analysis, and/or

Predecessor DataPredecessor Data

PRISM MethodologyPRISM Methodology

RAC Component

Models

System Reliability Assessment

Model

RAC Failure Rate Databases

Historical Data on Similar Systems

Process Assessments

Software Model

Test Data

Bayesian Data

Combination

System Reliability Estimate

Operational Profile, Environmental and Electrical Stresses

Primary Causes of FailurePrimary Causes of Failure

(Nominal Values)

PRISM Process Grade PRISM Process Grade Factor TypesFactor Types

DesignDesign ManufacturingManufacturing Parts QualityParts Quality System ManagementSystem Management CND (Can Not Duplicate)CND (Can Not Duplicate) InducedInduced WearoutWearout GrowthGrowth Infant MortalityInfant Mortality

Other PRISM AdjustmentsOther PRISM Adjustments

BayesianBayesian Uses test and field data to enhance Uses test and field data to enhance

predicted failure ratepredicted failure rate

PredecessorPredecessor Uses previous history data to further refine Uses previous history data to further refine

predicted failure ratepredicted failure rate

PRISM NotePRISM Note

Although PRISM contains RAC Rate models for Although PRISM contains RAC Rate models for many part types, it does not include the following:many part types, it does not include the following: Rotating devicesRotating devices RelaysRelays Switching devicesSwitching devices TubesTubes ConnectionsConnections LasersLasers Miscellaneous partsMiscellaneous parts

Relex can solve this problem by allowing the user to Relex can solve this problem by allowing the user to apply PRISM concepts (Process Grade, Bayesian, apply PRISM concepts (Process Grade, Bayesian, Predecessor) to a failure rate calculated by all other Predecessor) to a failure rate calculated by all other models.models.