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Posted by: Barry Ives
Organization:Lockheed Martin System Integration - Owego
Date posted: Thu Apr 18 8:52:35 US/Eastern 2002
Subject: Instantaneous failure time
What does "Instantaneous Failure Time" refer to and how is it used in the calculation of the infant mortality factor?
Posted by: Chris Wright
Date posted: Wed Mar 6 15:32:13 US/Eastern 2002
Subject: RACRates IC Model Questions
I have been evaluating the PRISM IC RACRates model for my company and have a few questions.
First, how is it that the pi-factors tend to go down for non-hermetic devices versus hermetic? This seems counter intuitive, especially for pi-RHT. The overall device failure rate ends up being lower for a non-hermetic part. Is this true?
Second, it appears that pi-TO, pi-RHT, pi-DT and Lambda-SJ all vary with device temperature, but there is nothing in the manual which describes these relationships.
I am also puzzled as to why pi-RHT would change when I add a junction temperature rise, since this is supposed to be a non-operating factor. The junction temperature rise should only apply to operating factors. When non-operating the device should be at its non-operating ambient temperature with no junction temperature rise since it wouldn't be dissipating power at that point.
Posted by: Boutbien Laurent
Organization:MBDAM (Châtillon France)
Date posted: Wed Feb 27 10:21:13 US/Eastern 2002
Subject: similarity between software and paper guide
Using your own example for a system analysis, i was focusing on the study concerning the reliability calculation for the four resistance R1-R4 of A3A2 sub-assembly. The aim of this study was to identify the relation between the software and the tabulated figures within the paper guide. Keeping the original parameters (i.e element temperature calculation is based on ambient temperature and default temperature rise), I was not able to check the default tabulated parameter for the following factors : PiTO , PiTE , Pi DT and lambdaSJ. I am aware that choosing different options for the element temperature calculation will induce different Pi-factors. However I do not understand why selecting the default option is not leading to the selection of the default parameters (these summarised in the tables : table C5 page 192 version 1.2).
Can you please explain why the parameters are not corresponding to the ones expected (for ground stationary, indoors).
Thank you for your help.
Posted by: Boutbien laurent
Organization:MBDAM (Châtillon France)
Date posted: Wed Feb 27 4:59:54 US/Eastern 2002
Subject: query on Process Grade Score
First of all, thank you for your previous answer regarding the PRISM software guide. I am now able to have a better understanding of the PRISM philosophy analysis.
However, I have now a new question concerning the relation between the Process Grade Score query and the corresponding Pi-Factor. Answering the different queries for the Process Grade Score, I have noticed that there is no corresponding between the software true figures and the expected tabulated figures summarised in tables I-4 (page 262) and H-10 (page 247). In order to illustrate this remark , please find herefafter the result of the simulation :
Type Pi (software)Grade Pi (tables)
Design 0,0419 78,3% 0,039
Manufacturing 0,0347 83,6% 0,034
Part Quality 0,0795 89,3% 0,075
Management 0,0020 89,5% 0,002
CND 0,1460 76,2% 0,134
Induced 0,0272 100% 0,009
Wearout 0,0229 100% 0,008
growth 0,927 100% not tabulated
Infant Mortality 0,271 100% not tabulated
Moreover, How can you justify constant value for the growth factor and infant mortality factor despite the existence of mathematical formulae for determining these factors (Pi function of time).
Thank you for your assistance and help.
Posted by: BOUTBIEN
Organization:MBDA (Châtillon FRANCE)
Date posted: Mon Feb 25 8:21:26 US/Eastern 2002
Subject: query for PRISM documentation
My company had just purchased the PRISM toolkit (version 1.2). However, within the package, there is no manual documentation which i consider mandatory for a better understanding of your software. Is it possible to receive a official documentation (not only the on line help !)provided i give you all the detail necessary to proove the purchase ?
Thank you in advance for your help and hoping an quick answer in my E-mail address.
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