4/28/05Ray: ELEC Fault Diagnosis Using Fault Dictionaries and Probability Adam Ray April 28, 2005

4/28/05Ray: ELEC Problem Statement Identify which fault occurred in a failing circuit Need a way to quantify inherent uncertainties – Equivalent faults – Truncated test sets Assumptions – Single stuck-at faults – Stuck-at fault is lowest replaceable unit (LRU)

4/28/05Ray: ELEC The Likelihood Function Likelihood of fault i, time t Faults 0,…,m failed at time t-1 N(t)=total # of remaining faults Test1Test2Test3Test4Test5Test6 Fault Fault Fault Fault Fault Fault Fault Likelihood

4/28/05Ray: ELEC Diagnostic Algorithm START LOOP END Assign beginning likelihoods to each fault Apply next test vector to faulty circuit If outputs are faulty (i.e. Test yields “1”) Assign zero likelihood to faults that show “0” for current test vector Else Assign zero likelihood to faults that show “1” for current test vector Redistribute likelihoods using Likelihood Function Repeat LOOP Output final fault likelihoods BeginTest 1Test2Finish Fault1 (0 1 0) Fault2 (1 0 0) Fault3 (1 0 0) Fault4 (0 1 0) Fault5 (0 0 0) Fault6 (0 0 1) Fault7 (0 0 0)

4/28/05Ray: ELEC Results on 4-Bit ALU After Tests 1 & 2 After Tests 5 & 6 After All Tests

4/28/05Ray: ELEC More Results Fault found with several wrong faults

4/28/05Ray: ELEC Add beginning likelihoods Faults (EQUIV)Beginning LikelihoodsEnding Likelihoods ALL OTHER FAULTS{0.003, 0.006, 0.012}0

4/28/05Ray: ELEC Conclusions Algorithm correctly identifies the fault – Equivalent faults are incorrectly identified Likelihood makes results more conclusive Algorithm can be halted at any point New Algorithm for multiple faults