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Posted by: don miller
Date posted: Sat Dec 8 18:38:35 US/Eastern 2001
Subject: random geneic hardware failure rate
30 +years at Boeing. first 10 big hero in OR. logistic analysis , Otimum spares provisioning. I did it all. I had 3 years at TRW 1969 -1972. had the chance to review the basic notion of random failures. Back to Boeing. worked MM AWACS B1 guess what never found a ransom failure which met the criteria for inclusion into MTBF prediction effort. Finally (like Einsten who took 7 years to get rid of wrong ideas)I wised up. Have sound data which shows that any notion of predicting frequency of hardware failures is absurd. Wearout is ok. Failures occur (big time in early MM). However they are virtually always related to design problems, human error, manufacturing problems ect. Please help us rid the aerospace industry of this triva. Or any other foolish folks .I have seen a few MTBF statements on PC. Not many.
Posted by: Leroy Meyers
Date posted: Tue Nov 13 15:24:50 US/Eastern 2001
Subject: Making Sense of Prism
I just completed my first Prism reliability prediction. I used the same piece of equipment for which I used MIL-HDBK-217F previously. I was very interested in comparing the results, so I used a 100% duty cycle in Prism so that calendar hours would equal operating hours.
Using 217, the failure rate of the equipment is 83 failures per million hours. I inserted all the same parts into Prism, and came up with a failure rate of 6.
I'm thinking that 6 is a very low number; will anyone believe it? But then I realized that I forgot to put the software failure rate into Prism. That's understandable, because software is something that I never considered in a prediction before.
So I entered in the software parameters. That alone gave me a failure rate of 17,071!! Now I'm at the other extreme - this failure rate is way too high, I can't use this!
Has anyone else gone through this? How can I make sense of this? If you want to know the details of what I entered into Prism, you can contact me directly at email@example.com
Posted by: Laura Brown
Organization:Northrop Grumman Electronic Systems
Date posted: Tue Nov 6 11:49:14 US/Eastern 2001
Subject: Status of Additional RACRates Models
The 2001 AR&MS tutorial notes on PRISM includes a statement "additional RACRates models are under development". Can you provide the status? What specific models are in process and are there estimated completion dates? I prefer to use RACRates models (rather than the fixed failure rates from the EPRD/NPRD databases) to more accurately reflect the thermal and operating conditions unique to our applications. However, a significant number of parts used in our designs are not covered by the existing RACRates models. This is considered a limitation of PRISM vs. MIL-HDBK-217FN2 which includes more models, albeit outdated. Appreciate the update!
Posted by: Mark Medlin
Date posted: Thu Sep 20 18:27:21 US/Eastern 2001
Subject: Saving a system to a new location
I created a system and have been saving it on my local drive. Now that I am done with it, I am trying to save it to our shared network drive. When I do a File, Save As and select the network folder, Prism responds with a message "Could not create New System. Error code 47." I click OK, and another error message come up saying "Unknown database. Unable to complete network request to host. Failed to establish connection. The system cannot find the file specified." I click OK, and now I cannot close this window or exit Prism by any means because this message keeps coming back. I have to go to Taskmanager and End Task. What is going on, and how do I save this system database to our network folder?
Posted by: Fred Levesque
Date posted: Thu Aug 9 14:35:56 US/Eastern 2001
Subject: Windows 2000
Within a few months we will be moving from NT to Windows 2000. Will there be any compatibility problems for PRISM?
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