Failure Modes, Effects and Diagnostic Analysis

Appendix E FAILURE MODES EFFECTS AND DIAGNOSTIC ANALYSIS (FMEDA) 303... 

A hardware analysis called a Failure Modes Effects and Diagnostics Analysis (FMEDA) can be done to determine the failure rates and failure modes of an instrument (Ref. 4). This is done to provide the safety design engineer with the data needed to more accurately perform probabilistic analysis. 

Fortunately, several instrumentation manufacturers are providing detailed analysis of their products to determine a more accurate set of numbers useful for safety verification purposes. A Failure Modes Effects and Diagnostic Analysis (FMEDA) will provide specific failure rates for each failure mode of an instrumentation product. The percentage of failures that are safe versus dangerous is clear and relatively precise for each specific product. The diagnostic ability of the instrument is precisely measured. Overall, the numbers from such an analysis are indeed product specific and provide a much higher level of accuracy when compared to industry database numbers and experience based estimates. 

Failure Modes, Effects and Diagnostic Analysis, R0S02/11-07 ROOl, PA Sellersville, exida, Eeb. 2004. 

Failure Modes Effects and Diagnostics Analysis (FMEDA)... 

FAILURE MODES, EFFECTS, AND DIAGNOSTIC ANALYSIS AND SYSTEM INTEGRATION ISSUES... 

Manufacturing controls to ensure to the desired safety requirements Control of management of change (MOC) to meet the requirements Failure modes, effects and diagnostic analysis (FMEDA) to determine SFF, PHF Details of proof test requirements... 

FMEDA Failure Modes, Effects and Diagnostic Coverage Analysis... 

Since diagnostics are such a critical variable in the calculations, the ability to measure and evaluate the effectiveness of the diagnostics is important. This is done using an extended failure modes and effects analysis technique (Ref. 9) and verified with fault injection testing (Ref. 10 and 11). The techniques were refined to include multiple failure modes (Ref. 12) and today are commonly used to evaluate diagnostic capability and failure mode split (Ref. 13). 

This is a detailed analysis of the different failure modes and diagnostic capabilities for a piece of equipment. It is an effective method for determining failure modes and failure rates, a requirement for certification against lEC 61508 in most certification agencies. 

The optimal approach to select devices is to collect information regarding field experience and the device s compliance to specific IEC 61508 requirements. For example, a manufacturer may provide a failure-modes-and-effects analysis for the device based on IEC 61508 criteria. This analysis may include the failure-modes listing, failure rate, and diagnostic coverage assumptions for the device as manufactured. 

Failure Mode and Effects Analysis Another method is failure mode and effects analysis. It considers what may go wrong and what the consequences will be. Most people are familiar with this method through diagnostic charts that aid in trouble shooting automobiles or other equipment. By locating the failure or symptom in the chart, one can locate possible causes and solutions for the problem. In failure mode and effects analysis for safety, one is trying to identify what controls will prevent or reduce the danger of some hazard. 

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