Transcript Sample Testability Requirements

Testability Analysis
Last revised 08/11/2005
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:
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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
Recommended Methodology
Testability Screen Layout
Hint:
Refer to the
FMECA
Manager
online help.
Refer to the
‘Performing
Testability
Analyses’
help book.
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.
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 all failures to 4 or fewer parts, 95% of all failures to 8 or fewer parts
and 99% of all failures to 10 or fewer parts..
Here, the SRA TEST group is
defined with isolation group
sizes that match customer
requirements.
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 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 Data
Note:
All of the failure rate fields are
calculated by ASENT.
Here, we document that
test point J1-92 isolates an
Improper Config Resistor
failure to the R0004
component.
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.
Editing Isolation Lists
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 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 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
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
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 all failures to 4 or fewer parts, 95% of all failures to 8 or fewer
parts and 99% of all failures to 10 or fewer parts.
Test Coverage Exceeds Requirements