Forum: Reliability & Maintainability Questions and Answers
Posted by: IC
Date posted: Thu Sep 13 9:33:01 US/Eastern 2001
Subject: Modem Failure Rates
Does anybody have a generic failure rate for a standard Modem.
Thanks In Advance
Posted by: Rob Johnson (email@example.com )
Date posted: Tue Sep 11 11:11:47 US/Eastern 2001
Subject: Weibull Beta Tables for Zero Failure Testing
Where can I locate tables of beta values for various materials and failure modes. I wish to perform zero failure testing (Weibayes) and thought I could select an approximate beta value rather than guessing or performing a costly preliminary study.
Posted by: Chris Wright (firstname.lastname@example.org )
Date posted: Mon Sep 10 15:18:41 US/Eastern 2001
Subject: PRISM - Software or Methodology? Why so secret?
I have installed the PRISM Demo and it hasn't helped me at all to decide to purchase it. I see input forms for models with a whole bunch of Pi-factors aka MIL-HDBK-217. But what are they? Where are the technical papers that describe these models in detail? When folks ask for detailed info, all I see for responses is quotes from the brochure. It is not acceptable to me to use something because "it has gained wide acceptance". Maybe they have only gained acceptance because they result in lower failure rates. I don't know. If these models were developed under an Air Force contract, why are they being treated as proprietary? I wouldn't mind buying a technical book that describes them. But why can I only get the models if I buy your software? I am thinking of putting in a request under the Freedom of Information Act.
A frustrated Reliability Engineer (16+ years experience)
Posted by: Shi Ke (email@example.com )
Date posted: Mon Sep 10 11:45:46 US/Eastern 2001
Subject: temperature for Arrenius law
In Bellcore TR-332, we consider the temperature factor. We use the Arrenius law to relate 2 temperatures. For the temperature, it refers to the operating ambient temperature. If the temperature around the device has a very big difference. What temperature should we use. By the way, is it more reasonable to use the junction temperature of transistor or chip? Thanks
Posted by: John (firstname.lastname@example.org )
Date posted: Sun Sep 9 21:40:53 US/Eastern 2001
Subject: Plotting Reliability
When plotting cumulative MTBF vs. Time for multiple units, (sample size is 12, with 2000 hours on each unit)what rules of thumb should be used for selecting the time interval to calculate the MTBF. The shape of the curve will change depending on this time interval (t = 100, 500, 1000, ... vs. t = 50, 100, 150, 200, ...)? t = 100 means each of the 12 units has 100 hours on it, so the total hours is 1200 hours.
I have seen the term instantaneous MTBF, what is this used for and can this be calculated from my data? Thank you. John