Weibull analysis

Illustrated explanation

Distinguish a failure study from a safety-function claim

3Weibull analysis
Distinguish a failure study from a safety-function claimCallout 1: FMEA / FMEDA. Callout 2: Demand / continuous duty. Callout 3: Failure-data model. Failure-mode analysis follows effects and diagnostics. Safety integrity concerns a defined safety function and operating mode, while Weibull analysis models stated failure-time or strength data. Current term: Weibull analysis, callout 3. 1ModeEffectSystemFMEDA adds rates + diagnosticsFMEA / FMEDA 2Defined safety functionPFDavg: probability on demandPFH: dangerous failures per hourDemand / continuous duty 3Time or strengthFailure fractionExample curveFailure-data model
  1. FMEA / FMEDA

    FMEA examines failure modes and their effects. FMEDA adds the relevant failure-rate and diagnostic information for the defined analysis.

  2. SIL / PFDavg / PFH

    The measures apply to different stated operating modes of a safety function. SIL is not a standalone material or cable-gland grade.

  3. Weibull analysisThis term

    Fit a statistical model to relevant data with stated assumptions and censoring. An example curve is not a measured life prediction.

Failure-mode analysis follows effects and diagnostics. Safety integrity concerns a defined safety function and operating mode, while Weibull analysis models stated failure-time or strength data.

Conceptual analysis relationships and an illustrative distribution. No SIL level, failure rate, probability estimate or cable-gland functional-safety approval is claimed.

ReferencesIEC 60812:2018 — Failure modes and effects analysisIEC 61508-1:2010 — Functional safety — General requirementsIEC 61649:2008 — Weibull analysis