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**Relex Reliability Software “the intuitive solution**

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

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**What is Relex? A Powerful Reliability Software Tool…**

performs efficient reliability analysis uses multiple analysis techniques provides advanced features

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**Relex Is Uniquely Qualified**

Reliability Engineering Experience Commercial Military Software Development Experience

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**Relex Reliability Software “the intuitive solution**

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

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**Introduction to Reliability Prediction**

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**Reliability Predictions**

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

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**Sample Relex Reliability Prediction calculation results**

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

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**Failure Rate Defined As: Units: Rate of Occurrence of Failures**

Number of Failure in Specified Time Period Units: Failures per Million Hours Failures per Billion Hours (FIT Rate)

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**MTBF Defined As: Units: 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

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**Reliability Defined As: Units:**

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)

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**Availability Defined As: Units: The probability that an item is in an**

operable state at any time Units: Probability Value (0-1)

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**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

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**The Bathtub Curve and Reliability**

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

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**Three Phases of Life Infant Mortality Region Wear-Out Region**

Constant Failure Rate Region

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**Bathtub Curve Graph of Failure Rate vs. Time**

Considers three phases of life Represents lifespan of item (i.e. 15 years for a car)

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**Bathtub Curve –Illustration–**

Infant Mortality Wear Out Constant Failure Rate Failure Rate Time 17

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Reliability Models

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**Influences to reliability / Model-parameters**

Production maturity Design & construction Storage conditions Production factors Transport conditions Material- selection Electronic component Application- temperature Operating conditions Application factors electrical stress mechanical stress Climatic environment

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**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.)

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**MIL-HDBK-217 Original standard for reliability**

Reliability math models electronic devices Used commercially & in the defense industry Currently at Revision F Notice 2

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**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

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**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

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

New model with new feature Account for “real data” Burn-in, Field, Laboratory testing data Popular standard for commercial companies

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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

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**CNET & HRD5 Used in Europe Reliability models for telecommunications**

Current Versions: HRD - 5 CNET - 93

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**Bellcore vs. 217 Recognition & Acceptance Concentration**

Calculations & Equations Consideration of Test Data Multiplier Parts Environments Quality Levels

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**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

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**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

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

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**Primary Causes of Failure**

(Nominal Values)

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**PRISM Process Grade Factor Types**

Design Manufacturing Parts Quality System Management CND (Can Not Duplicate) Induced Wearout Growth Infant Mortality

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**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

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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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1 Product Reliability Chris Nabavi BSc SMIEEE © 2006 PCE Systems Ltd.

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