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Standardizing test data formats
1096
World Abstracts on Microelectronics and Reliability
turbances considered are unit step and linear trend disturbances to the process average. The evaluation is based on the determination of the Average Run Lengths (ARLs) resulting from computer simulations. Estimation of system reliability for independent series components with Weibull life distributions. DIPAK K. DE¥ and LLOYD R. JAIS1NGH. IEEE Trans. Reliab. R-37, 401 (1988). The reliability of a series system with independent components is estimated based on random samples from Weibull failure distributions with parameters 0~ and [~. It is assumed that the fl/s are known, which reduces the reliability of the system to a function, 7(0), of 0 = (0~..... 0p). An estimate of ?,(0) which is better than the M V U E of 7(0) in terms of mean square error is determined. The predicted reliability and the percentage improvement for this estimator is computed and compared with the usual M V U E of ),(0). The predicted reliability using the improved estimator is numerically closer to the true system reliability. Selection of a checkpoint interval in a critical-task environment. ROBERTGEIST, ROBERT REYNOLDSand JAMESWESTALL. IEEE Trans. Reliab. R-37, 395 (1988). The selection of an optimal checkpointing strategy has most often been considered in the transaction processing environment where systems are allowed unlimited repairs. In this environment an optimal strategy maximizes the time spent in the normal operating state and consequently the rate of transaction processing. This paper seeks a checkpoint strategy which maximizes the probability of critical-task completion on a system with limited repairs. These systems can undergo failure and repair only until a repair time exceeds a specified threshold, at which time the system is deemed to have failed completely. For such systems a model is derived which yields the probability of completing the critical task when each checkpoint operation has fixed cost. The optimal number of checkpoints can increase as system reliability improves. The model is extended to include a constraint which enforces timely completion of the critical task. Characterizations of gamma and negative binomial distributions. SHUNJ| OSAKI and XIN-XIAN(-? LI. IEEE Trans. Reliab. R-37, 379 (1988). Characterizations of g a m m a and negative binomial distributions are presented by using the conditional expectation. A necessary and sufficient condition is given in terms of the failure rate for each distribution. For illustrating the usefulness of our results, we discuss the mean residuaMife of the g a m m a distribution. A new R & M measure and its estimation. J. MARCUS JOBE. IEEE Trans. Reliab. R-37, 413 (1988). The reliability & maintainability measure is referred to as M T U T . It is the mean time to restore an equipment and its maintenance system to its original working status; it is expressed as a proportion of the mean time to failure for any given equipment. This measure integrates maintenance and repair time expenditures of all types from three levels of maintenance. Other measures discussed in the literature such as availability, mean time to repair, and average queue length are compared to M T U T . A testing program for the demonstration phase of equipment development is presented. Fstimarion and discrimination procedures are derived fur M T U T using data from the outlined testing program. Largesample theory is used to construct both interval estimates and discrimination procedures for the M T U T , using data acquired from the assessment phase of equipment development. Transient-fault analysis for retry techniques. ABDALLAH M. SALEH and JANAK H. PATEL. IEEE Trans. Reliab. R-37, 323 (1988). This paper addresses the problem of system recovery from transient fauhs using retry techniques. A probabilistic model for the activity of faulty periods and a fault analysis to
derive the optimum retry period are presented. Distribution functions are derived to represent the case of false alarm, where a transient fault is flagged as permanent, and the case of a miss, where too many faults coexist thus overcoming the checker's capability to detect them. These derivations are compared with the results of a simulation program representing the model. Other factors influencing the value of the retry period are also discussed. Moment estimators for the 3-parameter Weibull distribution. G. W. CRAN. IEEE Trans. Reliab. R-37, 360 (1988). Weibull moments are defined generally and then calculated for the 3parameter Weibull distribution with non-negative location parameter. Sample estimates for these moments are given and used to estimate the parameters. The results of a simulation investigation of the properties of the parameter estimates are discussed briefly. A simple method of deciding whether the location parameter can be considered zero is described. The influence for MTTR of maintenance engineers and maintenance support organization (case study of makers' maintenance practice on industrial computer systems). SHUICHI NITTA. Proc. 18th Syrup. Reliab. Maintainah. (Condensed Version), 56 (1988). In order to improve maintainability (reduction of repair time), a variety of considerations to reduce the h u m a n factor have been taken: for example, structure design to practice easy maintenance, completeness of maintenance manuals, education for engineers, completeness of RASIS functions, development of experts systems and so on. And, it may be clear that the above items are effective for maintainability improvement. However, repair time varies much, depending on the h u m a n factor, that is, the maintenance engineers'. Somehow or other, M T B F can be calculated by specified formula, but in many cases. MTTR may be calculated on the basis of maintenance trial operation, as the human factor :nay be dominant to MTTR. This paper clarifies which factors in maintenance engineers' ability and maintenance support organization dominate M T T R , on the basis of actual corrective maintenance time practiced by seventy-nine maintenance engineers (working at seven service centers) who did maintenance at the users' sites. These studies may be useful to the education of engineers and the making up service centers' organization. Standardizing test data formats. BRADt.EVJ. TttOMPSON. I'est Measuremt Wld, 123 (October 1988). A proposed software standard can help PC-based test systems users transfer mcompatible data files fiom acquisition programs to postprocessing software. Two properties of mixtures of exponential distributions. M. M. NASSAR. IEEE Trans. Reliab. R-37, 383 (1988). Two properties characterizing mixtures of exponential distributions are obtained. The first result, suggested by Puri, is improved in the case of a mixture of two exponentials. A result generalizing that of Nassar & M a h m o u d is considered. Bayes estimation of the parameters and reliability lunction of the 3-parameter Weibnll distribution. S. K. SINHA and J. A. SLOAN. IEEE Trans. Reliab. R-37, 364 (1988). In this paper we obtain Bayes estimates of the parameters and reliability function of a 3-parameter Weibull distribution and compare posterior standard-deviation estimates with the corresponding asymptotic standard-deviation estimates of their m a x i m u m likelihood counterparts. Numerical examples are given. Queueing model of a bi-level Markov service system and its solution using recursion, MANSOORAt, AM and V. MAN1. IEEE Trans. Reliab. R-37, 427 0988). This paper presents a closed
World Abstracts on Microelectronics and Reliability
turbances considered are unit step and linear trend disturbances to the process average. The evaluation is based on the determination of the Average Run Lengths (ARLs) resulting from computer simulations. Estimation of system reliability for independent series components with Weibull life distributions. DIPAK K. DE¥ and LLOYD R. JAIS1NGH. IEEE Trans. Reliab. R-37, 401 (1988). The reliability of a series system with independent components is estimated based on random samples from Weibull failure distributions with parameters 0~ and [~. It is assumed that the fl/s are known, which reduces the reliability of the system to a function, 7(0), of 0 = (0~..... 0p). An estimate of ?,(0) which is better than the M V U E of 7(0) in terms of mean square error is determined. The predicted reliability and the percentage improvement for this estimator is computed and compared with the usual M V U E of ),(0). The predicted reliability using the improved estimator is numerically closer to the true system reliability. Selection of a checkpoint interval in a critical-task environment. ROBERTGEIST, ROBERT REYNOLDSand JAMESWESTALL. IEEE Trans. Reliab. R-37, 395 (1988). The selection of an optimal checkpointing strategy has most often been considered in the transaction processing environment where systems are allowed unlimited repairs. In this environment an optimal strategy maximizes the time spent in the normal operating state and consequently the rate of transaction processing. This paper seeks a checkpoint strategy which maximizes the probability of critical-task completion on a system with limited repairs. These systems can undergo failure and repair only until a repair time exceeds a specified threshold, at which time the system is deemed to have failed completely. For such systems a model is derived which yields the probability of completing the critical task when each checkpoint operation has fixed cost. The optimal number of checkpoints can increase as system reliability improves. The model is extended to include a constraint which enforces timely completion of the critical task. Characterizations of gamma and negative binomial distributions. SHUNJ| OSAKI and XIN-XIAN(-? LI. IEEE Trans. Reliab. R-37, 379 (1988). Characterizations of g a m m a and negative binomial distributions are presented by using the conditional expectation. A necessary and sufficient condition is given in terms of the failure rate for each distribution. For illustrating the usefulness of our results, we discuss the mean residuaMife of the g a m m a distribution. A new R & M measure and its estimation. J. MARCUS JOBE. IEEE Trans. Reliab. R-37, 413 (1988). The reliability & maintainability measure is referred to as M T U T . It is the mean time to restore an equipment and its maintenance system to its original working status; it is expressed as a proportion of the mean time to failure for any given equipment. This measure integrates maintenance and repair time expenditures of all types from three levels of maintenance. Other measures discussed in the literature such as availability, mean time to repair, and average queue length are compared to M T U T . A testing program for the demonstration phase of equipment development is presented. Fstimarion and discrimination procedures are derived fur M T U T using data from the outlined testing program. Largesample theory is used to construct both interval estimates and discrimination procedures for the M T U T , using data acquired from the assessment phase of equipment development. Transient-fault analysis for retry techniques. ABDALLAH M. SALEH and JANAK H. PATEL. IEEE Trans. Reliab. R-37, 323 (1988). This paper addresses the problem of system recovery from transient fauhs using retry techniques. A probabilistic model for the activity of faulty periods and a fault analysis to
derive the optimum retry period are presented. Distribution functions are derived to represent the case of false alarm, where a transient fault is flagged as permanent, and the case of a miss, where too many faults coexist thus overcoming the checker's capability to detect them. These derivations are compared with the results of a simulation program representing the model. Other factors influencing the value of the retry period are also discussed. Moment estimators for the 3-parameter Weibull distribution. G. W. CRAN. IEEE Trans. Reliab. R-37, 360 (1988). Weibull moments are defined generally and then calculated for the 3parameter Weibull distribution with non-negative location parameter. Sample estimates for these moments are given and used to estimate the parameters. The results of a simulation investigation of the properties of the parameter estimates are discussed briefly. A simple method of deciding whether the location parameter can be considered zero is described. The influence for MTTR of maintenance engineers and maintenance support organization (case study of makers' maintenance practice on industrial computer systems). SHUICHI NITTA. Proc. 18th Syrup. Reliab. Maintainah. (Condensed Version), 56 (1988). In order to improve maintainability (reduction of repair time), a variety of considerations to reduce the h u m a n factor have been taken: for example, structure design to practice easy maintenance, completeness of maintenance manuals, education for engineers, completeness of RASIS functions, development of experts systems and so on. And, it may be clear that the above items are effective for maintainability improvement. However, repair time varies much, depending on the h u m a n factor, that is, the maintenance engineers'. Somehow or other, M T B F can be calculated by specified formula, but in many cases. MTTR may be calculated on the basis of maintenance trial operation, as the human factor :nay be dominant to MTTR. This paper clarifies which factors in maintenance engineers' ability and maintenance support organization dominate M T T R , on the basis of actual corrective maintenance time practiced by seventy-nine maintenance engineers (working at seven service centers) who did maintenance at the users' sites. These studies may be useful to the education of engineers and the making up service centers' organization. Standardizing test data formats. BRADt.EVJ. TttOMPSON. I'est Measuremt Wld, 123 (October 1988). A proposed software standard can help PC-based test systems users transfer mcompatible data files fiom acquisition programs to postprocessing software. Two properties of mixtures of exponential distributions. M. M. NASSAR. IEEE Trans. Reliab. R-37, 383 (1988). Two properties characterizing mixtures of exponential distributions are obtained. The first result, suggested by Puri, is improved in the case of a mixture of two exponentials. A result generalizing that of Nassar & M a h m o u d is considered. Bayes estimation of the parameters and reliability lunction of the 3-parameter Weibnll distribution. S. K. SINHA and J. A. SLOAN. IEEE Trans. Reliab. R-37, 364 (1988). In this paper we obtain Bayes estimates of the parameters and reliability function of a 3-parameter Weibull distribution and compare posterior standard-deviation estimates with the corresponding asymptotic standard-deviation estimates of their m a x i m u m likelihood counterparts. Numerical examples are given. Queueing model of a bi-level Markov service system and its solution using recursion, MANSOORAt, AM and V. MAN1. IEEE Trans. Reliab. R-37, 427 0988). This paper presents a closed