Forum: Reliability & Maintainability Questions and Answers
Posted by: David Vermeis (dvv@Ingersoll.com )
Organization:Ingersoll Milling Machine Co.
Date posted: Wed Jan 26 10:45:28 US/Eastern 2000
Subject: Reliability Prediction Software and Database
I am looking for a software package that will perform R&M analysis for mechanical and electrical components and have an integral database for storing component data gathered from testing and field data. Also is there a source for commercial componet R&M data? Thanks in advance.
Posted by: Sheila Prather (firstname.lastname@example.org )
Organization:Northrop Grumman Corporation
Date posted: Thu Jan 13 13:51:21 US/Eastern 2000
Subject: 217 Model for GaAs FET for high power, high frequency
MIL-HDBK-217 currently provides the high frequency GaAs FET model in section 6.8, but for that device type operating in the 1GHz range with power dissipations above 0.1W as well as for any other frequency level with high power dissipations, the model renders unrealistic results.
As well, the piT factor for the devices addressed in section 6.8 have a great impact on the resulting failure rate, even for those items operating at a power level within the range of the model. These results are unrealistic since these devices typically have rated junction/channel temperatures around 175degC. To compare, the piT values for both the low noise/high frequency (section 6.6) and high power/high frequency (section 6.7) bipolar transistors are extremely smaller in comparison; despite comparable maximum junction/channel ratings. Using these models, as is, the high power/high frequency GaAs FET f.r. is unusable and obviously worst than that of the RF microwave bipolar devices. I furthered reviewed the results published in EPRD97 for the following device types. The published f.r.s for the GaAs devices were lower than those for the bipolar RF transistors for comparable packaging and type; which is totally contradictory to the results if using the model. So, my questions follow; a) what is the recommended model for the high power + high frequency GaAs devices (vs. just high frequency GaAs), and b) what, if any, modifications should be made to the piT values when using the model in section 6.8 where the frequency and power level is within the acceptable range as dictated. Thanks for your response.
Posted by: Dave Fetters (email@example.com )
Date posted: Thu Jan 13 12:00:16 US/Eastern 2000
Subject: MIL STD 471 - M. Demo
I'm planning a Maintainability Demonstration. There are MTTR and MaxTTR requirements at each of 3 levels of maintenance. I wanted to use Test Method 8 in MIL-STD-471A in hopes of avoiding 50 observations on 6 different specifications (which the other methods seem to require). However, the DS-level MTTR spec. is 2 hours (greater than the 100 minute limitation called out in the second paragraph of the method). I can't figure out how important that 100 minute limitation is. In other words, is it possible to "cheat" by 20 minutes, or is there a workaround for longer MTTRs? Anybody know?
Posted by: Serge CRUZEL (firstname.lastname@example.org )
Organization:CNES (French Space Agency)
Date posted: Mon Jan 10 9:26:07 US/Eastern 2000
Subject: PRISM tool
The RAC products catalog indicates the avaibility of the PRISM tool that performs reliability assessments. Does this tool replace the old data handbook such as the MIL 217 ?
Is it possible to have a demo version, in the RAC web site for example ?
Posted by: Xiangping,Wu (email@example.com )
Date posted: Fri Jan 7 2:26:06 US/Eastern 2000
Subject: LCC Analysis
I'm trying to do a LCC analysis.I have established the LCC breakdown structure,but I don't know how to calculate the cost of every subitem by mathematics models.In other words,how to establish the math models of every item'cost?
Does anyone could give me some references? An example is better.Thanks.