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Improve the Diagnostic Capability of a System or Design

Address the Four Main Goals of Diagnostic Engineering

While data interoperability between heterogeneous reliability assessment tools & products remains a challenge from and between subsystem designs, the goals at the “integrated system” or fielded product level (Availability, Cost of Ownership, Mission/Operational Success and Safety) remain unchanged.

1) Increased Availability
2) Reduced Cost of Ownership
3) Mission or Operational Success (Reliability)
4) Improved Safety

These four (4) goals may not be specifically identified in a Design or Sustainment Requirements document. But nonetheless, the “trading” or “balancing” of these objectives would be sought by the end-user or customer. The product manufacturer must consider to what extent it can develop a product that can meet or exceed such needs of the customer without increasing product development or sustainment costs.

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Diagnostic Impact on False Alarms and System Aborts

What is a “False Alarm”?

The definition of a False Alarm, unfortunately is dependent upon your specific perspective. In a very general sense, it is the improper reporting of a failure to the operator of the equipment or system. In addressing the universe of possibilities that could compromise the proper reporting of a failure, DSI has conquered one specific cause and the primary contributor to the experience of False Alarms, which is the “Diagnostic-Induced” False Alarms, or more simply “Diagnostic False Alarms”.

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The Pioneering of DFT

Testability, as a concept, was created in 1964 based on a concept formulated by Ralph A. De Paul Jr. during the prior decade, then formally authored by William Keiner, certified by the U.S Congress, and published as MIL-STD-2165. This was before acronyms such as Designing-for-Testability (DFT), Design-for-Test (DfT), or Design-to-Test (DTT) were established to describe specific segmented activities within the fully intended scope of designing for testability. The objective was to influence the design so that it could be used for testing, any and all testing and, concurrently, to influence the design for effective sustainment, or as DSI terms it, Design-for-Sustainment (DFS).

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Synchronizing Reliability and Diagnostic Engineering for IVHM

When designing for any diagnostic paradigm or any combinations of diagnostic paradigms, or most specifically when coordinating on-board operational run-time diagnostics (typically performed by Health Monitoring Systems and Health Management Systems by using on-board BIT sensing technologies) with off-board maintenance activities, the eXpress approach will facilitate the coordination, integration and cross-validation of the design assessment products from each design discipline.

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Capturing of Expert Knowledge within Diagnostic Design

There are two (2) general approaches to capturing the IVHM (or “ISHM”) design within the eXpress environment – either using a “Top-Down” or a “Bottom-Up” approach. In either approach, capturing the IVHM design in eXpress will enable the IVHM to be influenced for more inclusive and holistic “integrated systems” diagnostic capabilities that will continue to benefit both the operational run-time diagnostic capability of the IVHM and then continue into any off-board diagnostic paradigm throughout the sustainment lifecycle(s)…..

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Impact of BIT on HM – ISHM, IVHM and PHM

The eXpress diagnostic modeling environment is essential for determining the diagnostic designs’ ability to “Uniquely Isolate” any failures (or loss of function). This capability, designated as “FUI” in eXpress, enables the assessment to determine if the design is able to isolate between the sensor and any of the functions contained on the object that is being sensed.

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Diagnostic Assessment of BIT and Sensors

Design for Test (DFT) and Designing for Testability (DFT):

These are two related but separate endeavors. The Design for Test (DFT) and Design for Testability (DFT)processes and objectives are very often confused among experts in the two separate design discipline(s).

Design for Test is typically performed solely for electronic design components (chips, circuit boards, sets of circuit boards) at the lowest levels of design. As a result, Design for Test is inadvertently performed at the expense of the broader vision of the test effectiveness or value at the fielded product (Integrated Systems’ Level). Whereas Design for Testability can reuse the investment into Design for Test to validate the test coverage effectiveness at the higher and highest levels of the fielded design.

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BIT Optimization – Validation- Integration

Traditionally, BIT has been assigned to “test” the presence of the proper functioning at various “testing locations or points”. Such test points have often been selected by the designer or the manufacturer based upon their specific expertise or available resources. If a more careful effort was to be required, then the determining of the BIT would require additional tools, technologies, expertise and then additional resources – meaning more cost and time.

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Synchronization of On-Board BIT and Guided Troubleshooting

Ensure Sensor Corroboration and Explicit Test Coverage

With ISDD, all of the sensors used throughout the subsystems are fully described in the eXpress Diagnostic model. When the eXpress model is “processed” by eXpress, “ALL” of the interdependencies are identified and exposed to elaborate diagnostic design scrutiny, including the ability to determine the confidence or effectiveness of the sensors as used within the design architecture. As such, the Test Coverage for every sensor contained therein is fully represented and extrapolated throughout the integrated design(s), and any constraints (knowingly or unknowingly) reducing or “interfering” with the BIT Test Coverage (as may exist in any operational mode or “state”) is fully considered and reported within eXpress for better-informed design or sustainment decision-making purposes.

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Designing for IVHM or any On-Board Health Management

The eXpress diagnostic modeling environment is essential for determining the diagnostic designs’ ability to “Uniquely Isolate” any failures (or loss of function). This capability, designated as “FUI” in eXpress, enables the assessment to determine if the design is able to isolate between the sensor and any of the functions contained on the object that is being sensed.

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Diagnostics Based on Expert Knowledge of the Diagnostic Design

Ensure Health Management Provides “Diagnostic Conclusions” to the Field

Such Health Management Implementations (IVHM, ISHM, PHM, etc.) have not typically been designed in coordination with the “bridging” of the on-board “diagnostic conclusions” to the off-board diagnostic implementation. This has been a ubiquitous shortcoming of the designing for on-board HM as it is not designed to comingle with the off-board diagnostic activities nearly as diagnostically-conclusive as it would naturally be capable of doing with ISDD.

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Breaking Down of False Alarms; Combining Diagnostics, R&M

The Breaking Down of False Alarms “False Alarms” need to be more succinctly identified as a failure effect at the level of analysis (or lowest level of replacement) and then mapped to the fully-fielded Integrated System Level as a precursor to providing more reliable detection, isolation and corrective action. While describing an failure effect to be alarm-generating as “intended to be” detected by the sensor(s) within a subsystem is a step toward having the alarm be equally discernible at the System Level – that is, in and around any diagnostic or hardware design interference that…

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Predictive Maintenance – Assessment and Alternatives

Predictive Maintenance (PM or “PdM”), in referring to the optimizing of the sustainment approach for a fielded asset, is attempting to facilitate and provide the means to detect and rectify failures of an equipment or system in advance of the failure(s). As such, the approach may consider the development or reliance upon a variety of specialized sensors or maintenance method(s). But determining the diagnostic or prognostic effectiveness of the sensors (BIT location, coverage, diagnostic validation, etc.) is the first step in determining the effectiveness of the sustainment capability for the fielded asset….

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Reducing False Alarms and System Aborts

FA’s and FSA’s and BIT Effectiveness

While there is plenty of leeway for interpretation or the meaning of a False Alarm (FA) as it may pertain to any particular industry or event, we will consider the FA to be the result of an incorrect indication of a “failure” as observed and reported by any sensing device. Furthermore, we will define that sensing device to be a Built-In-Test (BIT) or any other monitoring circuity or sensor. Before we jump ahead to learn about the significant what impact a well-executed diagnostic design process has on either FAs or System Aborts (SA), we will first examine BIT.

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BIT Optimization Availability (“Uptime”)

ISDD: Realizing Interdisciplinary Value Exploiting New Benefits of Corroboration As systems continue to increase in both size and complexity, the ability to drill down and find the root causes to failures continues to be a growing challenge. Many of the traditional methods to compute low level reliability or maintainability statistics in complex designs and bring this data to the system level to address system requirements conformance is becoming increasingly costly and challenging. Competing Among Partnering Design Disciplines? While contributing lower level designs may be developed to satisfy their own specific reliability and maintainability requirements, the…

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