Downloaded from https://www.everyspec.com ADS-79D-HDBK sources of failure, such as vibration, heat, or power quality, and from those sensors detect the onset of incipient failures. Electronic components have other attributes that influence the requirements for diagnosis, prognosis, and health management. Aside from the failure modes of the individual elements its failure has an effect on adjoining components that can generate additional failure modes and cause increases in data or power loads on individual elements. The path of propagation can be variable, causing the estimation of MTBF/MTTR to be more complex and probabilistic.
A typical electronic system frequently is upgraded in capability or performance, making it difficult to manage the development of diagnostic and prognostic processes for these coexisting, multiply-variant configurations. A possible framework to model system behavior and detect faults and predict the onset of incipient failures useful life in electronics may include the following tools: Embedded life modes. Failure models derived from reliability studies, OEM data, etc. Such models express in a probabilistic sense the remaining life estimate of electronic components. Operational Environmental information. Sensors can be distributed to measure temperature, humidity, and vibration.
From test data, models can be developed that estimate the life impact to exposures of various levels of environmental stressors and estimate the useful life remaining. Operational data. The number of power-on cycles and run time can be an important factor in wiring and PCB failures. Tracking the operational data per serial number, as well as the power quality feeding the system during operation, can be used to update MTBF/MTTR. H.3.3 Current Diagnostic Test Methods. There are generally two types of test: closed loop test and open loop test. H.3.3.1 Closed loop tests Closed loop tests are tests that do not require operator interaction to complete successfully.
A loopback path from the actuator (or data source) to a sensor (or data sink) which is used to verify correct operation. Because no human interaction is required in the test loop, the loop is said to be ―closed.‖ Examples of a closed loop test include communications interface loopback tests, discrete and analog output loopback tests (where hardware support is available), and other special purpose electronic interfaces where diagnostic loopback paths have been designed into the hardware. Closed loop tests can affect the operation of the system during their execution and may not be comprehensive.
For example, a closed loop test may not verify end-stage hardware such as line drivers/receivers, lamps, and attached instrumentation. H.3.3.2 Open Loop Tests Open loop tests are tests that require some kind of operator interaction to complete and determine whether the test succeeded or failed. With an open loop test, there is no loopback path from the source to the sink that does not include an operator. A human is part of the test 139