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Testability Analysis Last revised 08/11/2005

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Testability Analysis Last revised 08/11/2005. Introduction.

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Testability Analysis

Last revised 08/11/2005

introduction
Introduction

Normally, a FMECA must be conducted in order to perform Testability Analysis. Since these two analyses share much of the same information, ASENT includes its Testability tool as part of the FMECA Manager. Some of the key features associated with the Testability tool are listed below:

  • Leverage the existing FMECA data
  • Define and Edit Detection/Isolation Groups
  • Define and Edit Test Categories and Codes
  • Testability Data Editor
  • Perform trade-offs using Alternate Testability Data
  • Calculate fault detection / fault isolation
  • Calculate False Alarm Rate
  • Generate a wide range of Testability reports
testability screen layout
Testability Screen Layout

Hint:Refer to the FMECA Manager online help. Refer to the‘Performing Testability Analyses’help book.

defining groups and test codes
Defining Groups and Test Codes

To define ambiguity groups and test codes select the Library Editor option.

From the Library Editor, click on the Detection/Isolation Groups tab and the Detection Codes tab to define ambiguity groups and test codes.

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Sample Test Coverage Requirements

Component Isolation - SRA Test Points

Test points shall be provided which shall enable detection of 90% SRA failures and isolation of 80% of allfailures to 4 or fewer parts, 95% of all failures to 8 or fewer parts and 99% of all failures to 10 or fewerparts..

Here, the SRA TEST group is defined with isolation group sizes that match customer requirements.

entering testability data
Entering Testability Data

The Testability Analysis leverages off of FMECA data. From the FMECA Manager, select a failure mode and then click on the Testability tab to begin entering Testability data.

entering testability data8
Entering Testability Data

Note: Testability data is typically only entered for failure modes at the lowest level in the tree. All intermediate values are calculated when you select the Calculate Testability option from the system node.

entering testability data9
Entering Testability Data

Note: All of the failure rate fields are calculated by ASENT.

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Here, we document that test point J1-92 isolates an Improper Config Resistor failure to the R0004 component.
assigning assembly types
Assigning Assembly Types

The ‘Assy Type’ field allows you to assign the types that correspond to your isolation categories (i.e. LRU, SRU, LRM, WRA, SRA, etc..). This is a field you can use to create your own types. All the other types you have created on this FMECA are also available in the drop down list. This can also be used with reports to report only on a selected set of assemblies. The Assy Type field is available in both the Reliability Manager and the FMECA Manager.

Note: initially this picklist may be empty. If so, merely type in the value you want, save it, and it now has been added to the list.

linking functions or signals to parts
Linking Functions or Signals to Parts

ASENT allows you to link FMECA functions or signals to parts on the Reliability tree so that these functions or signals get the benefit of any updates to the reliability prediction. This can save you quite a bit of time in cases where you do not have the time or budget to do a piece-part level FMECA. In the FMECA Manager, right-click on the function or signal, select Link Node | To Parts and the Reliability tree will be displayed. Select the board that contains the parts you wish to link to.

Reliability Tree

linking functions or signals to parts14
Linking Functions or Signals to Parts

Once you have selected the board in the reliability tree, then ASENT will display the part list for that board. Use the button to move selected parts over to the Linked Parts list. If you leave the failure rate ratio (FR Ratio) blank it will default to 1. In this example we are saying that our function consists of 100% of C0001 and C0002, and 50% of J0001.

alternate tests trade offs
Alternate Tests - Trade-offs

Alternate Tests can be defined in order to perform tradeoffs. Below, a failure mode, Bad Memory, has two detection/isolation methods defined.

Note: This option is accessed by selecting the BIT Detail button when entering Testability Data.

testability reports
Testability Reports

Generate reports by right-clicking on an item. Then select the Reports, Testability option and a list of Testability reports will be displayed.

ASENT’s Test Coverage Summary report shows the calculated Fault Detection / Fault Isolation percentages for each group. The user also has the ability to combine multiple groups and see how this affects their test coverage.

sample test coverage summary report
Sample Test Coverage Summary Report

The Test Coverage Summary report verifies that test coverage exceeds customer requirements.

Customer Requirements:

Component Isolation - SRA Test Points

Test points shall be provided which shall enable detection of 90% SRA failures and isolation of 80% of allfailures to 4 or fewer parts, 95% of all failures to 8 or fewer parts and 99% of all failures to 10 or fewerparts.

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