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The effect of preventive maintenance on a two-dissimilar unit standby system
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World Abstracts on Microelectronics and Reliabiht5
testing and select the best data mixture for integration testing. The models are based upon software failure data that are collected during testing. These decision models can be valuable not only for the project manager but for the group responsible for generating the appropriate test data.
System comparisons can simplify selection of parametric tester. MICHAEL LEVIS. Electronics 127 (January 1984). Defining user needs and comparing like configurations help when evaluating expensive parametric-test systems. Worst case reliability bounds. SURESr~GOVINDACHAR.Microelectron Reliab. 23 (5), 855 (1983). This paper gives a method for estimating reliability bounds for the reliability of a component, given the confidence intervals for the parameters in the stress and strength distributions. The method considers the smallest and the largest interference area between the distribution functions for the stress and strength random variables and hence the name. The method is explained via an illustrative example. Fuzzy-network planning F N E T . IGOR GAZDiK. IEEE Trans. Reliab. R-32 (3), 304 (August 1983). Currently used network planning techniques, such as P E R T / C P M and their derivatives, assume that, in a graph of known structure, the duration of its activities is known either with certitude or at least with some probability. However, in m a n y applications the structure of the graph and the duration of its activities are imprecise. This paper shows how the application of fuzzy sets to such problems can yield quasi-deterministic results obtained from imprecise input data. Interval reliability for initiating and enabling events. COLIN DUNGLINSON and HOWARD LAMBERT. IEEE Trans. Reliab. R-32 (2), 150 (June 1983). This paper describes generation and evaluation of logic models such as fault trees for interval reliability. Interval reliability assesses the ability of a system to operate over a specific time interval without failure. The analysis requires that the sequence of events leading to system failure be identified. Two types of events are described: (1) initiating events (cause disturbances or perturbations in system variables) that cause system failure and (2) enabling events (permit initiating events to cause system failure). Control-system failures are treated. The engineering and mathematical concepts are described in terms of a simplified example of a pressure-tank system. Later these same concepts are used in an actual industrial application in which an existing chlorine vaporizer system was modified to improve safety without compromising system availability. Computer codes that are capable of performing the calculations, and pitfalls in computing accident frequency in fault tree analysis, are discussed. Fault tree synthesis from a directed graph model for a power distribution network. DANIEL L. CUMMINGS,STEVEN A. LAPP and GARY J. POWERS. IEEE Trans. Reliab. R-32 (2), 140 (June 1983). The L a p p - P o w e r s fault tree synthesis algorithm is applied to an electrical power distribution network and the cut sets are derived for a sustained loss of power on one busbar. This algorithm is based on a directed graph (digraph) representation of the system, in contrast with the method of C a m a r d a et al. which is based on a reliability graph. The digraph model forces an explicit evaluation of the corrective actions (negative feedback and negative feed forward) that are taken to counteract disturbances which enter the network. The presentation is tutorial and shows the disciplined application of fault-tree synthesis operators. A variance expression for a security-of-supply model. OLE PLATZ. IEEE Trans. Reliab. R-32 (2), 191 (June 1983). This note considers a security-of-supply model for energy; it is composed of a demand model which is a deterministic periodic function of time, and a supply model which is a
continuous time Markov chain. Expressions are derived for the mean and variance of the a m o u n t of energy not supplied and of the time the demand is not met within a time interval. Parallel/series dependency and equivalence in generalized Markov's chains. FARRIZIO LOMBARDLMicroelectron. Reliab. 23 (3), 501 (1983). In this paper the analytical solutions to generalized Parallel and Series Markov's Chains are presented. The states dependencies are derived and the condition of equivalence is considered. The results are analyzed with respect to fault tolerant computing system applications.
The effect of preventive maintenance on a system with imperfect switchover. M. I. MAHMOUDand M. A. W. MAHMOUD. Microelectron. Reliab. 23 (5), 821 (1983). A two-unit standby redundant system with repair, preventive maintenance and imperfect switchover is considered. The Laplace-Stieltjes transform (LST) of the survivor function (sf) of the time to the first system failure (TFSF) and the mean are derived. Finally a theorem about the effect of preventive maintenance is proved. Shifting shape-parameter in life tests: a Bayes analysis. G. S. LINGAPPAIAH. IEEE Trans. Reliab. R-32 (3), 317 (August 1983). A problem related to prediction of an order statistic in a future sample based on earlier samples is analysed here. The basis for this analysis is a predictive distribution. The problem is that, during a life test while sampling, the shape parameter shifts from an exponential to a gamma. Under this situation, the effects on the Bayes prediction region and on the variance of the predictive distribution are analysed. The discussion includes change in prior degree of belief as well. Selection of Weibull shape parameter, based on adaptive estimation. M. PANDEY and S. K. UPADHYAY. IEEE Trans. Reliab. R-32 (2), 205 (June 1983). The paper provides a modified likelihood ratio criterion for deciding where or not the Weibull shape parameter is unity. The analysis is based on a Monte Carlo study of 1000 samples of simulated life-test data. The method has been used as a preliminary test for estimating u n k n o w n parameters. Thus two sets of adaptive estimators of the scale and the shape parameters are proposed and their s-efficiency studied by a Monte Carlo simulation. The adaptive estimators are better. The effect of preventive maintenance on a two-dissimilar unit standby system. M. I. MAHMOUD and M. A. W. MAHMOUD. Microelectron. Reliab. 23 (3), 485 (1983). A system which consists of two dissimilar units, one as a main unit the other as a standby, is considered, taking account of repair and preventive maintenance (PM). The standby unit cannot fail and the switch is perfect. The Laplace transform (LT) of the survivor function of the time to the first system failure (TFSF) and the mean are derived. Finally, a theorem about the effect of maintenance is proved. Shrunken estimators of Weibull shape parameter in censored samples. M. PANDEY. IEEE Trans. Reliab. R-32 (2), 200 (June 1983). This paper suggests some shrunken estimators of the shape parameter of the Weibull distribution for failure-censored samples. They are compared with the approximately unbiased estimators derived from Bain & Engelhardt's estimator. Two estimators are s-efficient if the guess value is near the true value. Of the two 2-stage shrunken estimators discussed here, one is based on a 1-sided preliminary test while the other is based on a 2-sided preliminary test. Prediction intervals using exceedances for an additional thirdstage sample. D. B. OWEN and YOuN-MIN CHOU. IEEE Trans. Reliab. R-32 (3), 314 (August 1983). Prediction intervals are extended to a third sampling stage involving the
World Abstracts on Microelectronics and Reliabiht5
testing and select the best data mixture for integration testing. The models are based upon software failure data that are collected during testing. These decision models can be valuable not only for the project manager but for the group responsible for generating the appropriate test data.
System comparisons can simplify selection of parametric tester. MICHAEL LEVIS. Electronics 127 (January 1984). Defining user needs and comparing like configurations help when evaluating expensive parametric-test systems. Worst case reliability bounds. SURESr~GOVINDACHAR.Microelectron Reliab. 23 (5), 855 (1983). This paper gives a method for estimating reliability bounds for the reliability of a component, given the confidence intervals for the parameters in the stress and strength distributions. The method considers the smallest and the largest interference area between the distribution functions for the stress and strength random variables and hence the name. The method is explained via an illustrative example. Fuzzy-network planning F N E T . IGOR GAZDiK. IEEE Trans. Reliab. R-32 (3), 304 (August 1983). Currently used network planning techniques, such as P E R T / C P M and their derivatives, assume that, in a graph of known structure, the duration of its activities is known either with certitude or at least with some probability. However, in m a n y applications the structure of the graph and the duration of its activities are imprecise. This paper shows how the application of fuzzy sets to such problems can yield quasi-deterministic results obtained from imprecise input data. Interval reliability for initiating and enabling events. COLIN DUNGLINSON and HOWARD LAMBERT. IEEE Trans. Reliab. R-32 (2), 150 (June 1983). This paper describes generation and evaluation of logic models such as fault trees for interval reliability. Interval reliability assesses the ability of a system to operate over a specific time interval without failure. The analysis requires that the sequence of events leading to system failure be identified. Two types of events are described: (1) initiating events (cause disturbances or perturbations in system variables) that cause system failure and (2) enabling events (permit initiating events to cause system failure). Control-system failures are treated. The engineering and mathematical concepts are described in terms of a simplified example of a pressure-tank system. Later these same concepts are used in an actual industrial application in which an existing chlorine vaporizer system was modified to improve safety without compromising system availability. Computer codes that are capable of performing the calculations, and pitfalls in computing accident frequency in fault tree analysis, are discussed. Fault tree synthesis from a directed graph model for a power distribution network. DANIEL L. CUMMINGS,STEVEN A. LAPP and GARY J. POWERS. IEEE Trans. Reliab. R-32 (2), 140 (June 1983). The L a p p - P o w e r s fault tree synthesis algorithm is applied to an electrical power distribution network and the cut sets are derived for a sustained loss of power on one busbar. This algorithm is based on a directed graph (digraph) representation of the system, in contrast with the method of C a m a r d a et al. which is based on a reliability graph. The digraph model forces an explicit evaluation of the corrective actions (negative feedback and negative feed forward) that are taken to counteract disturbances which enter the network. The presentation is tutorial and shows the disciplined application of fault-tree synthesis operators. A variance expression for a security-of-supply model. OLE PLATZ. IEEE Trans. Reliab. R-32 (2), 191 (June 1983). This note considers a security-of-supply model for energy; it is composed of a demand model which is a deterministic periodic function of time, and a supply model which is a
continuous time Markov chain. Expressions are derived for the mean and variance of the a m o u n t of energy not supplied and of the time the demand is not met within a time interval. Parallel/series dependency and equivalence in generalized Markov's chains. FARRIZIO LOMBARDLMicroelectron. Reliab. 23 (3), 501 (1983). In this paper the analytical solutions to generalized Parallel and Series Markov's Chains are presented. The states dependencies are derived and the condition of equivalence is considered. The results are analyzed with respect to fault tolerant computing system applications.
The effect of preventive maintenance on a system with imperfect switchover. M. I. MAHMOUDand M. A. W. MAHMOUD. Microelectron. Reliab. 23 (5), 821 (1983). A two-unit standby redundant system with repair, preventive maintenance and imperfect switchover is considered. The Laplace-Stieltjes transform (LST) of the survivor function (sf) of the time to the first system failure (TFSF) and the mean are derived. Finally a theorem about the effect of preventive maintenance is proved. Shifting shape-parameter in life tests: a Bayes analysis. G. S. LINGAPPAIAH. IEEE Trans. Reliab. R-32 (3), 317 (August 1983). A problem related to prediction of an order statistic in a future sample based on earlier samples is analysed here. The basis for this analysis is a predictive distribution. The problem is that, during a life test while sampling, the shape parameter shifts from an exponential to a gamma. Under this situation, the effects on the Bayes prediction region and on the variance of the predictive distribution are analysed. The discussion includes change in prior degree of belief as well. Selection of Weibull shape parameter, based on adaptive estimation. M. PANDEY and S. K. UPADHYAY. IEEE Trans. Reliab. R-32 (2), 205 (June 1983). The paper provides a modified likelihood ratio criterion for deciding where or not the Weibull shape parameter is unity. The analysis is based on a Monte Carlo study of 1000 samples of simulated life-test data. The method has been used as a preliminary test for estimating u n k n o w n parameters. Thus two sets of adaptive estimators of the scale and the shape parameters are proposed and their s-efficiency studied by a Monte Carlo simulation. The adaptive estimators are better. The effect of preventive maintenance on a two-dissimilar unit standby system. M. I. MAHMOUD and M. A. W. MAHMOUD. Microelectron. Reliab. 23 (3), 485 (1983). A system which consists of two dissimilar units, one as a main unit the other as a standby, is considered, taking account of repair and preventive maintenance (PM). The standby unit cannot fail and the switch is perfect. The Laplace transform (LT) of the survivor function of the time to the first system failure (TFSF) and the mean are derived. Finally, a theorem about the effect of maintenance is proved. Shrunken estimators of Weibull shape parameter in censored samples. M. PANDEY. IEEE Trans. Reliab. R-32 (2), 200 (June 1983). This paper suggests some shrunken estimators of the shape parameter of the Weibull distribution for failure-censored samples. They are compared with the approximately unbiased estimators derived from Bain & Engelhardt's estimator. Two estimators are s-efficient if the guess value is near the true value. Of the two 2-stage shrunken estimators discussed here, one is based on a 1-sided preliminary test while the other is based on a 2-sided preliminary test. Prediction intervals using exceedances for an additional thirdstage sample. D. B. OWEN and YOuN-MIN CHOU. IEEE Trans. Reliab. R-32 (3), 314 (August 1983). Prediction intervals are extended to a third sampling stage involving the