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

Relex Reliability Software “the intuitive solution!” Relex Software Corporation. 1. What is Relex ?. A Powerful Reliability Software Tool… performs efficient reliability analysis uses multiple analysis techniques provides advanced features. Relex Is Uniquely Qualified.

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

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

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

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

  4. RelexReliability Software“the intuitive solution!”Relex Software Corporation

  5. Introduction to Reliability Prediction

  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. Failure Rate Defined As: • Rate of Occurrence of Failures • Number of Failure in Specified Time Period Units: • Failures per Million Hours • Failures per Billion Hours (FIT Rate)

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

  10. Reliability Defined As: • The probability that an item will perform a required function without failure under stated conditions for a stated period of time Units: • Probability Value (0-1)

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

  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

  13. The Bathtub Curve and Reliability

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

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

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

  18. Reliability Models

  19. Production maturity Design & construction Storageconditions Transportconditions Material-selection Electronic component Application-temperature Operating conditions electricalstress mechanicalstress Climatic environment Influences to reliability /Model-parameters 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. 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. 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. 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. Telcordia (Bellcore) (cont.) • New model with new feature • Account for “real data” • Burn-in, Field, Laboratory testing data • Popular standard for commercial companies

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

  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 Operational Profile, Environmental and Electrical Stresses Process Assessments RAC ComponentModels Test Data RAC Failure Rate Databases System Reliability Assessment Model Bayesian Data Combination Historical Data on Similar Systems System Reliability Estimate Software Model

  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 devices Relays • Switching devices Tubes • Connections Lasers • 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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