Parts count reliability prediction

Parts count reliability prediction. The MIL-HDBK-217 Parts Count Reliability Prediction is normally used when accurate design data and component specifications are not determined. Typically, this occurs in the proposal and bid process or early in the design process. Minimal information is required for a Parts Count Rehability Prediction. The formula for a parts count analysis is the sum of the base failure rate of all components in the system. MIL-HDBK-217 provides tables for the same component groups in the Parts Stress Analysis, listing generic failure rates and quality factors for different environments. The predicted failure rate results will normally be harsher than those of the Part Stress Analysis approach. 

Military Handbook 217E (MIL 217E) establishes uniform methods for predicting the reliability of military electronic equipment and systems. There are two methods of reliability predictions, namely parts count and parts stress analysis. 

The parts count method is suitable for early design phase reliability prediction. The method uses information on generic types, quality levels, and environment. The latter two effects are considered with the application of specified factors. The failure rates for both methods are calculated using the same generic expressions. 

The handbook contains two methods of reliability prediction Part Stress Analysis and Parts Count Analysis. The two methods vary in the degree of information required to be provided. The Part Stress Analysis Method requires a greater amount of detailed information and is usually more applicable to the later design phase." The Parts Count Method requires less information such as part quantities, quality level, and application environment It is most applicable during early design or proposal phases of a project. The Parts Count Method will usually result in a higher failure rate or lower system rehabUity, a more conservative result than the Parts Stress Method would produce. 

This handbook contains two methods of reliability prediction - Part Stress Analysis (in Sections 5 through 23) and Parts Count (in Appendix A). These methods vary in the degree of information needed to apply them ... 

The handbook includes a series of empirical failure rate models developed using historical piece part failure data for a wide array of component types. There are models for virtually all electrical/ electronic parts and a number of electromechanical parts as well. All models predict reliability in terms of failures per million operating hours and assume an exponential distribution (constant failure rate), which allows the addition of failure rates to determine higher assembly reliability. The handbook contains two prediction approaches, the parts stress technique and the parts count technique, and covers 14 separate operational environments, such as ground fixed, airborne inhabited, etc. 

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