Downloaded from https://www.everyspec.com ADS-79D-HDBK Failure rate data for electronic components refers commonly to the phase with constant failure rate (useful life period on the classical bathtub curve). It is recognized that the constant failure rate assumption for electronic is sometimes not justified. The design can be less than perfect or not every failure of every part will cause the equipment to fail (error correction circuitry, memory, redundant/fault-tolerant circuitry etc.) But such an assumption provides suitable values for comparative analysis. H.3.2 Diagnostic framework for electrical/electronic systems.
Figure 1 illustrates the typical configuration of an electrical subsystem as part of the overarching LRU. Line Replaceble Unit Mechanical Structual Electrical Software Power supplies Power distribution Power Bus output input Processing cards Backplane bus ... FIGURE H-1 LRU electrical subsystems The elements of a typical electronic component, such as solder joints, wires, and printed circuit boards (PCBs), accumulate damage at rates depending on their environment and operational conditions. Therefore, the time between repair/removal is a function of environmental history, design tolerances, material properties, and operational conditions including software.
Software controls how the embedded electronic system operates, speed, duty-cycle, etc and therefore effect to internal temperature of the system. Parameters that accelerate failure most significantly in electronics, and in turn should be monitored by the health monitoring system, are • Temperature and humidity • Temperature variation • Vibrations • Shock • Power quality • Extreme operating conditions Electrical system health monitoring relies on thermal monitor, impedance measurement (contact and breakdown), and visual inspection.
Many systems include built-in test, either integrated in the system or as an external device that performs tests of the system to ensure proper operation which can be used to identify system faults as they occur. This approach can result in a large number of false positives. These false positives often result in Can Not Duplicate (CND) failures within the electronic modules. High level of CND failures limits the ability to transition from diagnostics to prognostics for electronics. However, there are few systems that use distributed sensors to continuously monitor the 138