Reliability Maintenance and Managing Risk Conference 2019 Can Fault Tree Analysis Technique Resolve Fault Isolation Ambiguity? Alpana Gangopadhyaya Supportability Systems Engineer Northrop Grumman Alpana.Gangopadhyaya@ngc.com Phone Number 630 853-9974 RMMR 2019, Oct. 15 - 16, San Antonio, TX 1
Reliability Maintenance and Managing Risk Conference 2019 Outline of Abstract We propose an advanced methodology for resolving fault isolation (FI) ambiguity by applying Fault Tree Analysis (FTA) technique in conjunction with Built-In Test (BIT). FI ambiguity occurs whenever any fault is associated with multiple replaceable units, which can cause false replace and remove maintenance activities. As a result, we experience substantial and unnecessary support cost along with reduced system availability. BIT is considered to be a potential technique for fault detection and fault isolation (FDFI) that is inherent in system design. However, for many systems, BIT by itself cannot isolate the fault to a single unit without additional external diagnostic efforts. FTA is a deductive technique where a top-level undesired system failure is analyzed logically to find the basic cause of that failure. FTA generates a graphical representation of the logical relationship between an undesired system failure and the basic fault events associated with it. This presentation will describe how to resolve FI ambiguity by combining FTA technique with BIT information as a diagnostic instrument. RMMR 2019, Oct. 15 - 16, San Antonio, TX 2
Reliability Maintenance and Managing Risk Conference 2019 Agenda • Problem Description / Challenge • Built-In-Test (BIT) Design Background • An Affordable Methodology For FI Diagnosis: Apply Fault Tree Analysis (FTA) in Conjunction With BIT • How To Develop A Fault Diagnosis Methodology ? : FTA + BIT • A Case Study for A Sample Hypothetical System • Case Study Conclusion: Is Unambiguous Fault Isolation Possible? • Benefits And Drawbacks of FTA + BIT Methodology • Summary RMMR 2019, Oct. 15 - 16, San Antonio, TX 3
Reliability Maintenance and Managing Risk Conference 2019 Problem Description / Challenge Fault Isolation (FI) Ambiguity: FI Ambiguity occurs when: • A fault is associated with multiple replaceable units • When fault occurs on interface of units FI Ambiguity Consequences: • Maintenance events ““No Fault Found” / “Cannot Duplicate” occurs • Increases in Support cost • Decreases in System availability. The Challenge : Significant Demand for Unambiguous Fault Isolation in Maintenance Technology RMMR 2019, Oct. 15 - 16, San Antonio, TX 4
Reliability Maintenance and Managing Risk Conference 2019 Built-In Test Design Background • Built-In Test (BIT) – A potential technique for fault detection and fault isolation (FDFI) integrated within system design – Designed to detects potential failures using Failure Mode Effect And Criticality Analysis (FMECA) • BIT Coverage Limitation – Does not always guarantee a capability to identify the cause of a fault – Does not alone accurately fault isolate to a single unit • BIT limitation – FMECA process may have different potential failures with very different risk priority numbers ▪ Discrepancy makes it difficult to identify and prioritize failures ▪ Lacks reliability and validity when used in isolation Require an Additional Diagnostic Implementation to Resolve FI Ambiguity RMMR 2019, Oct. 15 - 16, San Antonio, TX
Reliability Maintenance and Managing Risk Conference 2019 Apply Fault Tree Analysis (FTA) in Conjunction With BIT • Fault Tree Analysis (FTA) – FTA is a top-down approach, which provides a logical framework for understanding the ways a system can fail for an undesired system failure – FTA is a deductive technique where a top-level undesired system failure is analyzed logically to find the basic cause / event • New FI Diagnosis Methodology – BIT design uses Failure Mode Effect and Criticality Analysis (FMECA) to capture potential fault detection – FMECA is bottom-up inductive analytical approach, whereas FTA is a top- down – Apply FTA in conjunction with BIT during preliminary design phase – Provides an opportunity to overcome any BIT deficiencies – Is extremely effective and affordable Apply “FTA + BIT” Method During Design Phase to Reduce FI Ambiguity RMMR 2019, Oct. 15 - 16, San Antonio, TX
Reliability Maintenance and Managing Risk Conference 2019 “FTA + BIT” Method Flow Chart FTA + BIT Incorporate BIT with each cause Top Event FTA Construct Fault Tree Associate BIT with respective component Determine a set of Basic events that Causes the top event Is Basic cause NO associated with a single component? YES Unambiguous FI achieved RMMR 2019, Oct. 15 - 16, San Antonio, TX
Reliability Maintenance and Managing Risk Conference 2019 “FTA + BIT” Method Steps: Top- • Select Top-level event and set physical boundary Event • Perform FTA and construct fault tree for top-level event FTA • Transform the generated fault tree knowledge into BIT Preliminary Design FTA + BIT • Unambiguous FI occurred? FI • If not, then find all hidden faults to mitigate design RMMR 2019, Oct. 15 - 16, San Antonio, TX
Reliability Maintenance and Managing Risk Conference 2019 A Case Study for A Hypothetical System LRU3 LRU2 Thermal Imaging Sensor Image Video Image Assembly Processor Assembly Comm_2 LRU Controller Comm_1 Sensor LRU1 Camera System Processor Infrared Sensor Imaging Process RMMR 2019, Oct. 15 - 16, San Antonio, TX
Reliability Maintenance and Managing Risk Conference 2019 A Case Study (Cont.) Preliminary BIT Design and Definition for IR Sensor Using FMECA BIT Error BIT Test Name BIT Test Description PFL MFL Code Fault in receiving Sensor T1 Sensor_Comm_Err IR_Sensor_Fail LRU 1, LRU2 image from LRU2 to LRU1 Fault in receiving Video image T2 Video_Image_Fail IR_Sensor_Fail LRU2, LRU 3 from LRU 3 to LRU2 LRU1 to LRU2 Interface T3 Comm1_Err IR_Sensor_Fail LRU1, LRU2 Communication fault LRU3 to LRU2 Interface T4 Comm2_Err IR_Sensor_Fail LRU2, LRU 3 Communication fault Sensor_Ctl_Comm_E Fault in Sensor Camera and T5 IR_Sensor_Fail LRU 3 rr Sensor Controller interface T6 Carousel_Err Fault in Carousel IR_Sensor_Fail LRU2, LRU 3 Thermal_Image_Com Fault in Thermal Image T7 IR_Sensor_Fail LRU2, LRU 3 m_Err processing T8 Sensor_Motor_Err Fault in Sensor Motor IR_Sensor_Fail LRU2, LRU 3 T9 Sensor_Temp_Err Temperature fault in sensor IR_Sensor_Fail LRU2, LRU 3 Fault in communication T10 Loop_back_Comm1 IR_Sensor_Fail LRU1 interface loopback check Fault in communication T11 Comm1_Intrf_Err IR_Sensor_Fail LRU2 interface in LRU2 T12 Sensor_Init_Fail Fault in sensor initialization IR_Sensor_Fail LRU 3 Fault in Image processor T13 Image_Proc_Init_Err IR_Sensor_Fail LRU2 initialization BIT Definition For IR Sensor Process Developed with use of FMECA RMMR 2019, Oct. 15 - 16, San Antonio, TX
Reliability Maintenance and Managing Risk Conference 2019 A Case Study (Cont.): Fault Tree for Top Event “IR Sensor Fail” Basic Events RMMR 2019, Oct. 15 - 16, San Antonio, TX
Reliability Maintenance and Managing Risk Conference 2019 A Case Study (Cont.): Fault Tree for Top Event “IR Sensor Fail” Ambiguity in Basic Event BIT Preliminary Design has Ambiguity in Fault Isolation RMMR 2019, Oct. 15 - 16, San Antonio, TX
Reliability Maintenance and Managing Risk Conference 2019 A Case Study (Cont.): Captured Hidden Faults Fault check for carousel T14 Carousel_BIT_Err controller Fault check for carousel T15 Carousel_FDBK_Err feedback message Sensor_Motor_BIT_ Fault check for sensor T16 Fail controller Sensor_Motor_FDB Fault check for Senosr motor T17 K_Err feedback message Fautl check for cooler T18 Cooler_Ctl_BIT controller Fault check for cooler T19 Cooler_FDBK_Err feedback message Unambiguous Fault Isolation RMMR 2019, Oct. 15 - 16, San Antonio, TX
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