Forum: Reliability & Maintainability Questions and Answers
Posted by: Daniel Mahoney (email@example.com )
Date posted: Fri Aug 20 10:01:26 US/Eastern 1999
Subject: Turn on/turn of effects on parts
Can anyone supply some insight into the effects of turn on/turn off to electronic parts? Specifically, which is better? If I have some very low power electronics (1 millivolt level) should I turn them on for a tenth of a second, then off for 10 seconds or just leave them on (GB environment)?
Posted by: Ray (firstname.lastname@example.org )
Date posted: Fri Aug 13 17:29:06 US/Eastern 1999
Subject: Spurious Trip Rate
I am using Fault-Tree based reliability analysis programs to calculate the Probability of Failure on Demand (PFD) of a process model. I am interested in calculating the spurious trip rate (STR), that is safe trips or false trips. None of the programs I have are able to perform STR. Anyone who knows how to model the voting of redundant devices (especially 2-out-of-2 and 2-out-of-3) to calculate the STR? Any available resources on the internet? Your input is appreciated.
Posted by: Wee Teck Hoon (email@example.com )
Organization:DSO National Laboratories
Date posted: Thu Aug 12 3:21:01 US/Eastern 1999
Subject: SMART BIT
Have read the Final Technical Report on SMART BIT/TSMD Integration (RL-TR-91-353) and but could not find any follow-up on this issue. Would like to know whether SMART BIT technology has been field proven on avionics systems. Beside temperature and vibration, are there other stresses affecting intermittent failure in avionics system. Would like to know if there are any relevent data that relates environmental stresses to intermittent failures, which I can reference to. Thanks
Posted by: Jon Ilseng (firstname.lastname@example.org )
Organization:Schlumberger Oilfield Services
Date posted: Mon Aug 9 15:54:12 US/Eastern 1999
Subject: MIl-HDBK-217F Stress Analysis Predictions
I have a question concerning the MIL-HDBK-217F Stress Analysis Predictions for Commercial Fixed Film Resistors (Style RN) vs. Commercial Resistor Networks containg Fixed Film Resistors. The PCB I am doing a MIL-HDBK-217F stress analysis prediction contains these parts. The PCB operates in a Ground Mobile environment at 40 Degrees C ambient temperature. For a 0.125W Fixed Film Resistor operating at 2% of its rated power, the predicted failure rate is 0.0984. For a resistor network containing 9 Fixed Film Resistors, the predicted failure rate is 0.037. Why does a resistor network containing 9 Fixed Film Resistors have a smaller failure rate than one Fixed Film Resistor? My only guess is because of the difference in quality factor values. For a resistor network with commercial resistors, the quality factor value is 3.0. For a commercial Fixed Film Resistor, the quality factor value is 15.0. I would appreciate anyone's help.
Posted by: Ty Pollak (email@example.com )
Date posted: Thu Aug 5 15:10:19 US/Eastern 1999
Subject: Use of Reliability predictions to supplement flight test data
I am analyzing reliability for a missile weapon system and basing my point estimate on flight test data. Due to the limited data, however, I'd like to incorporate contractor-provided reliability estimates to decrease my confidence interval about the pt estimate. The contractor solution is based on HALT and other developmental tests. My solution is to develop a distribution for Pr (system reliability) based on flight tests only, and another for the contractor's Pr. Then sample from these distributions according to a "scale factor" determined by my confidence in the contractor estimates, methodology, and correlation w/ flt test data. This scale factor is subjective. By sampling from the 2 distributions, I will generate a "total" Pr distribution, which I can pick off confidence bounds from. Any comments, suggestions, insights?