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Relex Reliability Software “the intuitive solution!” Relex Software Corporation 1.

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Presentation on theme: "Relex Reliability Software “the intuitive solution!” Relex Software Corporation 1."— Presentation transcript:

1 Relex Reliability Software “the intuitive solution!” Relex Software Corporation 1

2 2 What is Relex? A Powerful Reliability Software Tool…   performs efficient reliability analysis   uses multiple analysis techniques   provides advanced features

3 3 Relex Is Uniquely Qualified  Reliability Engineering Experience  Commercial  Military  Software Development Experience

4 Relex Reliability Software “the intuitive solution!” Relex Software Corporation

5 Introduction to Reliability Prediction

6 6 Reliability Predictions What is a Reliability Prediction?  Calculation of failure rate (MTBF) How is it Calculated?  Based on established reliability model

7 Reliability Measures  Failure Rate ( )  Mean Time Between Failures (MTBF)  Reliability  Availability Sample Relex Reliability Prediction calculation results

8 8 Failure Rate Defined As:  Rate of Occurrence of Failures  Number of Failure in Specified Time Period Time PeriodUnits:  Failures per Million Hours  Failures per Billion Hours (FIT Rate)

9 9 MTBF Defined As:  Mean Time Between Failures  Number of Hours to Pass Before a Failure Occurs Before a Failure Occurs  Inverse of Failure Rate* Units:  Typically expressed in Hours *Constant Failure Rate Systems *Constant Failure Rate Systems

10 10 Reliability Defined As:  The probability 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 time timeUnits:  Probability Value (0-1)

11 11 Availability Defined As:  The probability that an item is in an operable state at any time operable state at any timeUnits:  Probability Value (0-1)

12 12 Reliability “Summary”  Failure Rate -- number of failures in time  MTBF -- average time between failures  Reliability -- takes into account mission time  Availability -- accounts for repairs (MTTR) and downtime and downtime

13 The Bathtub Curve and Reliability

14 14 The Bathtub Curve  Represents failure rate tendencies for the lifespan of an item  Failure rate varies in different phases of life

15 15 Three Phases of Life  Infant Mortality Region  Wear-Out Region  Constant Failure Rate Region

16 16 Bathtub Curve  Graph of Failure Rate vs. Time  Considers three phases of life  Represents lifespan of item (i.e. 15 years for a car)

17 Time Failure Rate Infant Mortality Wear Out Constant Failure Rate Bathtub Curve –Illustration– 17

18 Reliability Models

19 Influences to reliability / Model-parameters Production maturity Storage conditions Transport conditions Design & construction Material- selection Application- temperature mechanical stress Climatic environment electrical stress Operating conditions Electronic component Production factors Application factors

20 Relex Prediction Models  MIL-HDBK-217 (FN1, FN2 )  Telcordia (Telcordia 1, Bellcore 4,5,6)  Prism: RAC model (Process Grades, Bayesian)  NSWC-98/LE1: mechanical model  HRD5: British telecomm model  CNET 93: French telecomm model  299B: 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.)

21 21 MIL-HDBK-217  Original standard for reliability  Reliability math models electronic devices  Used commercially & in the defense industry  Currently at Revision F Notice 2

22 22 Parts Count  A section of MIL-HDBK-217  Provides simpler reliability math  Typical Uses:  Used early in the design process  Used to acquire a rough estimate of reliability

23 23 Telcordia (Bellcore)  Originally developed at AT&T Bell Labs  “Modified” MIL-HDBK-217 equations  New equations represented what their equipment was experiencing in the field

24 24 Telcordia (Bellcore) (cont.)  New model with new feature  Account for “real data”  Burn-in, Field, Laboratory testing data  Popular standard for commercial companies

25 25 Mechanical  Based on the Handbook of Reliability Prediction Procedures for Mechanical Equipment, NSWC-98/LE1  Provides models for various types of mechanical devices including springs, bearings, seals, etc.  New and unique standard

26 26 CNET & HRD5  Used in Europe  Reliability models for telecommunications  Current Versions:  HRD - 5  CNET - 93

27 27 Bellcore vs. 217  Recognition & Acceptance  Concentration  Calculations & Equations  Consideration of Test Data  Multiplier  Parts  Environments  Quality Levels

28 Accuracy of MTBF Assessments 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

29 PRISM Reliability Model  Developed by the Reliability Analysis Center (RAC)  Accounts for the effect of process related variability on system failure rate  Inherent failure rate based on base failure rate and environmental conditions (RAC Rates model)  Failure rate may then be modified by:  Process Grade Factors, and/or  Bayesian Analysis, and/or  Predecessor Data

30 PRISM 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

31 Primary Causes of Failure (Nominal Values)

32 PRISM Process Grade Factor Types  Design  Manufacturing  Parts Quality  System Management  CND (Can Not Duplicate)  Induced  Wearout  Growth  Infant Mortality

33 Other PRISM Adjustments  Bayesian  Uses test and field data to enhance predicted failure rate  Predecessor  Uses previous history data to further refine predicted failure rate

34 PRISM Note  Although PRISM contains RAC Rate models for many part types, it does not include the following:  Rotating devicesRelays  Switching devicesTubes  ConnectionsLasers  Miscellaneous parts  Relex can solve this problem by allowing the user to apply PRISM concepts (Process Grade, Bayesian, Predecessor) to a failure rate calculated by all other models.


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