# 4/28/05Ray: ELEC7250 1 Fault Diagnosis Using Fault Dictionaries and Probability Adam Ray April 28, 2005.

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4/28/05Ray: ELEC7250 1 Fault Diagnosis Using Fault Dictionaries and Probability Adam Ray April 28, 2005

4/28/05Ray: ELEC7250 2 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: ELEC7250 3 The Likelihood Function Likelihood of fault i, time t Faults 0,…,m failed at time t-1 N(t)=total # of remaining faults Test1Test2Test3Test4Test5Test6 Fault1010000 Fault2100000 Fault3100000 Fault4010100 Fault5000100 Fault6001000 Fault7000001 Likelihood 0.140.20.330.511

4/28/05Ray: ELEC7250 4 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)0.220.270.56 Fault2 (1 0 0)0.11000 Fault3 (1 0 0)0.11000 Fault4 (0 1 0)0.110.160.45 Fault5 (0 0 0)0.110.1600 Fault6 (0 0 1)0.220.2700 Fault7 (0 0 0)0.110.1600

4/28/05Ray: ELEC7250 5 Results on 4-Bit ALU After Tests 1 & 2 After Tests 5 & 6 After All Tests

4/28/05Ray: ELEC7250 6 More Results Fault 22-1-1 found with several wrong faults

4/28/05Ray: ELEC7250 7 Add beginning likelihoods Faults (EQUIV)Beginning LikelihoodsEnding Likelihoods 1 0 10.0060.073 20 1 10.0120.136 22 1 10.0120.136 24 1 10.0120.136 26 1 10.0060.073 28 1 10.0060.073 30 1 10.0060.073 32 1 10.0030.06 34 1 10.0030.06 56 5 10.0030.06 59 5 10.0030.06 64 4 10.0030.06 ALL OTHER FAULTS{0.003, 0.006, 0.012}0

4/28/05Ray: ELEC7250 8 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

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