Fault Diagnosis Using Fault Dictionaries and Probability Adam
Fault Diagnosis Using Fault Dictionaries and Probability Adam Ray April 28, 2005 1 4/28/05 Ray: ELEC 7250
Problem Statement l Identify which fault occurred in a failing circuit l Need a way to quantify inherent uncertainties – – l Assumptions – 2 Equivalent faults Truncated test sets – Single stuck-at faults Stuck-at fault is lowest replaceable unit (LRU) 4/28/05 Ray: ELEC 7250
The Likelihood Function Likelihood of fault i, time t Faults 0, …, m failed at time t-1 N(t)=total # of remaining faults Test 1 Test 2 Test 3 Test 4 Test 5 Test 6 Fault 1 0 0 0 0 Fault 2 1 0 0 0 Fault 3 1 0 0 0 Fault 4 0 1 0 0 Fault 5 0 0 0 1 0 0 Fault 6 0 0 1 0 0 0 Fault 7 0 0 0 1 Likelihood 3 0. 14 0. 2 4/28/05 0. 33 0. 5 1 1 Ray: ELEC 7250
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 4 Begin Test 1 Test 2 Finish Fault 1 (0 1 0) 0. 22 0. 27 0. 56 Fault 2 (1 0 0) 0. 11 0 0 0 Fault 3 (1 0 0) 0. 11 0 0 0 Fault 4 (0 1 0) 0. 11 0. 16 0. 45 Fault 5 (0 0 0) 0. 11 0. 16 0 0 Fault 6 (0 0 1) 0. 22 0. 27 0 0 Fault 7 (0 0 0) 0. 11 0. 16 0 0 4/28/05 Ray: ELEC 7250
Results on 4 -Bit ALU After Tests 1 & 2 After Tests 5 & 6 After All Tests 5 4/28/05 Ray: ELEC 7250
More Results Fault 22 -1 -1 found with several wrong faults 6 4/28/05 Ray: ELEC 7250
Add beginning likelihoods 7 Faults (EQUIV) Beginning Likelihoods Ending Likelihoods 1 0. 006 0. 073 20 1 1 0. 012 0. 136 22 1 1 0. 012 0. 136 24 1 1 0. 012 0. 136 26 1 1 0. 006 0. 073 28 1 1 0. 006 0. 073 30 1 1 0. 006 0. 073 32 1 1 0. 003 0. 06 34 1 1 0. 003 0. 06 56 5 1 0. 003 0. 06 59 5 1 0. 003 0. 06 64 4 1 0. 003 0. 06 ALL OTHER FAULTS {0. 003, 0. 006, 0. 012} 0 4/28/05 Ray: ELEC 7250
Conclusions l Algorithm correctly identifies the fault – 8 Equivalent faults are incorrectly identified l Likelihood makes results more conclusive l Algorithm can be halted at any point l New Algorithm for multiple faults 4/28/05 Ray: ELEC 7250
- Slides: 8