This reliability model is the most widely used prediction method available. Its original use was in the defence industry but it is also used by commercial companies, particularly in high value applications. It contains failure rate models for numerous electronic components such as integrated circuits, transistors, diodes, resistors, capacitors, relays, switches, and connectors, etc.
The military standard is a little harsher in the calculation of failure rate data than the commercial standards. Typically, but not always, the calculated results will show a higher failure rate for the same system. This difference in the standards stems from the original intended use of MIL-217 for aerospace and military, or mission critical applications
The standard 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 reliability, a more conservative result than the Parts Stress Method would produce.
The failure rate formulas include a base failure rate for every component. That base rate is then multiplied according to various factors known as 'Pi factors' to simulate the actual operating conditions. This includes the physical environment, the ambient temperature, power stress levels and component quality levels. The factors combine to form the overall failure rate for the part. Unless there are redundant parts present, the system failure rate will be the summation of the individual component failure rates.
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