Automatic (Automated) Test Equipment
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(ATE) -
Equipment that is used to automatically conduct analysis of functional or static parameters and to evaluate the degree of UUT performance degradation; may be used to perform fault isolation of UUT malfunctions. The decision making, control, or evaluative functions are conducted with a minimum reliance on human intervention and usually done under computer control.
Source: McDonnal Douglas Aerospace
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Automatic Test Equipment
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(ATE) -
Equipment designed to automatically analyze functional or static parameters in order to evaluate performance degradation. It may also be designed to perform fault isolation.
Source: SMTA
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Common Cause Isolation
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Also called Single Fault Isolation. A method of fault isolation that proceeds under the assumption that all "failed" tests in a diagnostic session are due to a single malfunction or fault. Although frequently used as the basis for diagnostic analyses (such as testability) during the design phase, common cause isolation cannot consistency produce accurate results when multiple components are simultaneously malfunctioning during diagnosis. The degree to which diagnostic accuracy suffers depends on the likelihood of multiple failures (taking into consideration the possibility of dependent failures and the length of the interval between diagnostic sessions) and the extent to which single failures can produce the same test signature as multiple failures.(Compare with Multiple Failure Isolation).
Source: Testability.com
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Equivalent Fault
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Two or more faults which create the same response for all possible tests. It is usually difficult to distinguish these faults for fault isolation purposes.
Source: A.T.E. Solutions, Inc.
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Fault Isolation
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(FI) -
The process of identifying the faulty replaceable unit or group of units, whose replacement will repair the system. The replaceable unit in a system is the module(s); in a module, the board(s); on a board, the component(s). FI is expressed as Fault Isolation to n number of replaceable units in p percentage of cases, where n is an integer and p is a percentage. The percentages are often derived from and weighted by the failure rate of the items isolated.
Source: A.T.E. Soutions, Inc.
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Once a fault has been detected, it needs to be isolated from other possible faults. A diagnoser does this by examining the elements of ambiguity set and by using some reasoning technique to prune the set down to the actual fault. During the process of diagnosis, more evidence may come in, causing the ambiguity set to shrink or grow. The goal is that at the end of diagnosis, the ambiguity set should contain only the fault that actually occurred, i.e., there should be no ambiguity in the diagnosis. In case of multiple faults, the set should contain all the faults that actually occurred and only the faults that actually occurred. The time needed for the resolution of ambiguity between faults may vary depending on the dynamics of the system and sensor coverage which determines the available evidence at a given time.
Source: Institute for Software Integrated Systems
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Fault Isolation Time
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The elapsed time between the detection and isolation of a fault; a component of repair time.
Source: MIL-STD-2165
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Fault Localization
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The process designed to identify the location of a fault known to exist within a general area of equipment. Fault localization may be less specific than fault isolation.
Source: A.T.E. Solutions, Inc.
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Fault Masking
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Fault Resolution
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The degree to which a test program or procedure can isolate a fault within an item; generally expressed as the percent of the cases for which the isolation procedure results in a given ambiguity group size. Same as Fault Isolation.
Source: MIL-STD-2165
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Hierarchical Built-In Self Test
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Hierarchical BIST involves fault detection and fault isolation where BIST capabilities exist at System Level, Board or Subsystem Level and perhaps even at Component Level. With System Level BIST at the top of the hierarchy, if System Level BIST reports a failure and accuses a SubSystem of causing the failure, that SubSystem BIST is interrogated to confirm or deny the accusation. Similarly the SubSystem BIST can call on Component Level BIST to assist with further fault isolation. When successfully implemented, Hierarchical BIST can save on fault isolation costs, eliminate false removals and false alarms.
Source: A.T.E. Solutions, Inc.
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Lambda Search
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A method for prioritizing the replacement of repair items in an isolated ambiguity group, based on isolated failure probability. Testability analyses often include both fault isolation metrics (based on testing only, without the use of lambda search) and fault resolution metrics (which take into consideration both testing and serial replacement prioritized using a technique like lambda search).
Source: Testability.com
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Mean Time To Repair
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(MTTR) -
The reliability weighted mean of repair times for an operational end item This includes test time, access time, fault isolation time, remove and replace or repair time, checkout time, and access secure time.
Source: Testability.com
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(MTTR) -
The reliability weighted mean of repair times for an operational end item This includes test time, access time, fault isolation time, remove and replace or repair time, checkout time, and access secure time.
Source: Prognostics and Health Management
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Multiple Failure Isolation
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A method of fault isolation that takes into consideration the possibility of multiple, simultaneous malfunctions during diagnostics. The likelihood of multiple faults existing during diagnostics is influenced by several criteria: the failure rates associated with individual faults, the likelihood of dependent failures, and the length of the time interval between diagnostic sessions. The diagnostic accuracy of procedures that incorporate multiple-failure isolation is generally higher than those based on common cause isolation. Although multiple-failure isolation can result in greater diagnostic ambiguity than does common cause isolation, the ambiguity groups that result from multiple-failure isolation often lend themselves to prioritized replacement, thereby negating or reducing the effect of multiple-failure isolation upon diagnostic performance.
Source: Testability.com
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Test Effectiveness
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Measures which include consideration of hardware design, BIT design, test equipment design, and test program set (TPS) design. Test effectiveness measures include, but are not limited to, fault coverage, fault resolution, fault detection time, fault isolation time, and false alarm rate.
Source: MIL-STD-2165
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Testability Prediction
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