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Verification & Validation Using Diagnostician in Simulate Mode
In addition to reducing TPS development time and cost, the model-based diagnostics reasoning approach can be used to verify the effectiveness of the test program. This verification can be done earlier in the process than is done today, and the verification can be accomplished without physical insertion of faults. The net effect is better quality test programs at a lower cost. For years, many commercial tools (e.g. LASAR) have existed which support the automatic generation of test programs for digital printed circuit boards. These tools use a software model of a digital unit to generate a series of tests which provide fault detection and fault isolation. They also provide metrics on the effectiveness of the test program. For many years, the government has accepted these automated tools and techniques as a valid approach to TPS verification: physical fault insertion of digital circuit cards is not required because the software model is accepted as an accurate representation of fault detection / fault isolation capability of a digital test program. The ability to use automated tools for test program development and verification has saved the government significant, untold dollars. Unfortunately, the technology and supporting tools have not existed to expand this capability beyond digital circuit boards to analog and mixed signal boards and up to the weapons replaceable assembly level. Today, the increasing complexity of digital circuit boards is rapidly rendering traditional digital test development tools unusable. In the past, test engineers tasked with developing fault isolation tests for analog or very complex digital circuit boards or line replaceable units have had no tools to help them develop the fault isolation portions of test programs. Manually, they have had to determine what faults are caught by each test (test coverage), use the test coverage data to determine what additional functional and diagnostic tests need to be made, use the test coverage of the expanded set of tests to generate a diagnostic fault tree, and translate the diagnostic fault tree into test implementation language "IF...THEN" structures. The process is laborious and error prone, and the underlying test coverage information is eventually lost. Further, the only way to verify the fault isolation capability of these test programs is physical insertion of faults, which is a very time-consuming and resource-consuming process, as it requires time on the test station. The verification also cannot be performed until after final integration of the tester, the test program and the interface device. A new technology is emerging which enables the automation of test program development and verification that has so long been enjoyed in the digital area to be implemented in the analog, hybrid and complex digital areas: model-based reasoning. Model-based reasoning implies that the diagnostic logic is independent of the test program or sequence of tests that are being run. The application of this technology to automatic test systems is being spearheaded by Giordano Automation Corp. Most other implementations of model-based reasoning are being applied to field service testing using manual instruments, as opposed to computer-controlled, high speed test systems. Giordano Automation has developed the only model-based reasoning software which uses a dynamic model as opposed to pre-computed fault trees. Our reasoning software is available as an off-the-shelf, commercial product: the Diagnostician. Giordano Automation has developed the capability and supporting software tools to apply model-based reasoning to the verification of test programs, thereby eliminating the need to perform physical fault insertion to verify test program capability. The Diagnostician contains a diagnostic model in the form of a connectivity matrix which represents the propagation of faults (rows in the matrix) to observable measurement locations and the coverage of tests that Pass or Fail (columns in the matrix). When used in run-time, the software algorithms and knowledge base (matrix) operate to isolate faults without troubleshooting sequences and without hard-coded diagnostic test programs. TPS V&V Software Module The CETS tool set currently includes a software module that can be utilized to verify/validate the fault localization capability (to a component or ambiguity group) within a test program set. The Fault Propagation Simulator (FPSIM) allows the user to simulate the insertion of a faulty condition at any physical location in the subject UUT and subsequently calculate simulated test results which would be generated in response to the simulated fault. The simulated faulty test results are outputted to ASCII test results file(s) which are interpreted by the run-time Diagnostician. The Diagnostician correlates the test results, generated from the fault propagation simulator, to the UUT Diagnostic Knowledge Base to determine the specific faulty component or components (ambiguity group). This diagnosis is predicated upon the simulated test results, the UUT Diagnostic Knowledge Base, and the reasoning process conducted by the inference engine. Thus, a total diagnostic simulation/validation process is effected: (1) insertion of a fault and the generation of simulated pass/fail test results, (2) simulation of the diagnostic reasoning process (diagnostic logic) in response to the pass/fail data, and (3) declaration of a fault call-out (i.e. which component or components caused the simulated failure). If run in the interactive mode, the user is able to trace through, and view details associated with individual test sessions, such as which test results were required for diagnostics, the resultant fault call-out or ambiguity group, the linkages to Automated Technical Information routines, and the specific test results (Pass/Fail) at each test location. The statistical information to be maintained for V&V analysis includes data such as: total number of possible faults, number of faults simulated, percentage of faults isolated to ambiguity group levels, comparison of test results to signature, total tests available vs. tests used for each fault simulated, percent of tests used, approximate test time (if test time parameter are including during profiling) and diagnostic resolution for critical vs. non-critical faults. The software produces information/file(s) which can be logged and stored for further analysis or V&V documentation. The results of each individual fault simulation session, as well as cumulative statistics for all fault insertion sessions can be saved to a standard ASCII text file which can be viewed on-line or imported to any word processor.  For a demo disk on Windows 3.1 please E-mail Mary Nolan at mary@giordano.com
Show me Tool Set for Generation of Knowledge Bases CETS Advantages / Users / Questions and Answers
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