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A new approach to memory testing
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World Abstracts on Microclectronics and Reliability
3. CIRCUIT AND SYSTEMS RELIABILITY, MAINTENANCE AND REDUNDANCY The importance of considering test needs in circuit design. BRIAN CHILDS. Electron. Fngnq. p. 50 (October 1976). The situation has arisen where capital equipment d~igned for production test can also be used bc design staff to ensure the design of easily tested products. Cmnputer design helps predict the ease with which a device can be tested while powerful test systems advise engineers of potential pitfalls. The ability of the engineer to design economical equipment with in built test capabilities is influenced by every physical parameter "affecting other design aspects. This ability for test is affected by size, shape, layout, reliability considerations, complexity, ease of servicing, cost and marketability'. A new approach to m e m o o testing. M. K. M. MORGAN. Microelectron. and Reliab. 15, 351 (1976). As the 4 K RAM has now arrived and the 16 K RAM just around the corner we need to find the most economical way of testing them. What test patterns should we use in order to adequately test these devices? Search for reliability. Jolly Hc.xr. Electronics Wkly. p. 17. (November 17 1976). Traditionally, most asscssments of the reliability of a minicomputer or minicomputer-based system are not measured in terms of MTBF (mean time between failures)---an ill-used term which can be misleading. Of cot, rse, the user wants his machine to be reliable, but his main ore-occupation is in thct that of availability. He needs to know that when he wants to use his minicomputer it will work. first time; and to be reassured that if it does eventually fail--and all equipment is liable to do so sometime it will incur the minimum of downtime before the fault is rectified.
Quality assurance in the nuclear industry. Moving on to a new stage of maturity. WAL'n!R M. VANNOY. Qual. Prog. p. 28. (October 1976). Quality assurance has been an integral part of the nuclear industry for many years. However, only five years have passed since quality assurance 10CFR50, Appendix B--- became a part of the regulatory process for nuclear power plants and fuel cycle facilities. Much progress has been made and the industry is now read), to move to the next stage of maturity and capitalize on the QA base that has been built. On reliability prediction of repairable redundant digital structures. J. C. LAPRIE. IEEE Trans. Reliab. R-25 (4), 256 (October 1976). Taking into account the real characteristics of redtmdant digital structures leads to neglect of failures occurring during the repair instants. The formal definition of the corresponding hypotheses leads to a simplifiexl Markov model which (a) is homogenous and (b) has instantaneous repairs. At last, the paper describes the way by which the validity of the hypotheses can be judged. Analysis of 7 models for the 2-dimimilar-unit, warm standby, redundant system. MASAYORI KODAMA, HtROSHI NAKA3tICII[ and StFUNRO TAI,AMA'ISU.IEEE Trans. Reliab. R-25 (4), 273 (October 1976). The paper is in 2 parts. In all models tile failure rates are constam, but repair rates need not be constant. The method of supplementary variables is used for solving the models. Part I considers the effect of priorities oq reliability and availability for 4 basic models; (1) priority in both repair and operation; (2) priority in repair; (3) priority in operation: (4) no priority. Models 1 and 2 treat 2 repair disciplines: (a) preemptive-repeat, (b) preemptive-resume. We obtain (I) Laplace transforms of availability and (2) explicit
expressions for steady state availability and for mean time to system failure. The effect of priority assigalment to maximize steady state availability is discussed. Part II considers the effect of having different repair rates, depending on whether the failure was from standby or fiom operation. We obtain (1) Laplace transforms of availability and reliability and (2) explicit expressions for mean time to system failure. Analy~s of two difference 1-server systems. M. N. GOPALA.X. IEEE Trans. Reliab. R-25 (4), 280 (October 1976). In tbis paper, the availability and the reliability of two I-server systems with redundancy have been obtained. System 1 consists of n subsystems in series; each subsystem consists of two redundant i.i.d, components in "parallel" (cold standby) and one server. The times to failure of the components arc exponentially distributed; their repair time distributions ,are arbitrary and different. System 2 consists of n dissimilar units and one server. The times to faihlre of the units are arbitrarily distributed: the repair rates are constant but all different. Explicit expressions for the Laplace trans[brm of the mean down-time of the system in (0, t) and for the mean time to system failure have been obtained. A few particular cases are disct,ssed.
A Bayesian scheme for sequentially testing a muhi-component system. DAVH) V. MAS'rRAN. IEEE Trans. Reliab. R-25 (4), 270 (October 1976). Althot, gh the literature on reliability theory is filled with methods for optimally designing multi-component systems subject to various constraints, very little is available in the literature on methods for optimally testing such systems. Both capabilities are needed, because after a system is assembled, periodic t~ting is required to insure against degradation of component rcliabilities. Some components in the system should be tested more than others, because of their reliability, cost of testing, or placement in the system. This paper providc~ Bayesian decision rules for testing components sequentially to minimize the sum of the cost of testing and the cost of misestimation. Approximate confidence intervals for reliability of a series system. R, L. RACICor. IEEE Trans. Reliab. R-25 (4), 265 (October 1976). Two solutions arc proposed for estimating s-confidence intervals for reliability of a repairable series system comprised of non-constant failure rate components: (1) the system is treated as a st,m of renew',d processes with the mean and variance of total number of system failures being computed fiom the moments of failure times of the components; and (2) a pseudo-Bayesian solution is derived for the mean and variance of the log-reliability of a system of Weibull components. In both solution approaches, the central limit theorem is invoked for a sum of component random variables determined from test data such as number of failures or log-reliabilities..s-Confidence limits are then approximated using Gaussian probability tables. The intervals derived yield close-to-exact frequency limits, depending on such variables as number of test failures, number of components, and component parameters. On the behaviuur of some quantities used in Bayesian reliability demonstration tests. J. J. HIG(nxS and C. P. T~)KOS. IEEE Trans. Reliab. R-25 (4), 261 (October 1976). Equiprnent mean time between failures (MTBI-) is assumed to be a frequency random variable. The goodness of lit of the uniform prior as a probability model for the MTBF is compared to the goodness of fit of the inverted gamma prior for actual failure data. 'Ihcse distributions can both be adequately fitted to the same failure data when the
World Abstracts on Microclectronics and Reliability
3. CIRCUIT AND SYSTEMS RELIABILITY, MAINTENANCE AND REDUNDANCY The importance of considering test needs in circuit design. BRIAN CHILDS. Electron. Fngnq. p. 50 (October 1976). The situation has arisen where capital equipment d~igned for production test can also be used bc design staff to ensure the design of easily tested products. Cmnputer design helps predict the ease with which a device can be tested while powerful test systems advise engineers of potential pitfalls. The ability of the engineer to design economical equipment with in built test capabilities is influenced by every physical parameter "affecting other design aspects. This ability for test is affected by size, shape, layout, reliability considerations, complexity, ease of servicing, cost and marketability'. A new approach to m e m o o testing. M. K. M. MORGAN. Microelectron. and Reliab. 15, 351 (1976). As the 4 K RAM has now arrived and the 16 K RAM just around the corner we need to find the most economical way of testing them. What test patterns should we use in order to adequately test these devices? Search for reliability. Jolly Hc.xr. Electronics Wkly. p. 17. (November 17 1976). Traditionally, most asscssments of the reliability of a minicomputer or minicomputer-based system are not measured in terms of MTBF (mean time between failures)---an ill-used term which can be misleading. Of cot, rse, the user wants his machine to be reliable, but his main ore-occupation is in thct that of availability. He needs to know that when he wants to use his minicomputer it will work. first time; and to be reassured that if it does eventually fail--and all equipment is liable to do so sometime it will incur the minimum of downtime before the fault is rectified.
Quality assurance in the nuclear industry. Moving on to a new stage of maturity. WAL'n!R M. VANNOY. Qual. Prog. p. 28. (October 1976). Quality assurance has been an integral part of the nuclear industry for many years. However, only five years have passed since quality assurance 10CFR50, Appendix B--- became a part of the regulatory process for nuclear power plants and fuel cycle facilities. Much progress has been made and the industry is now read), to move to the next stage of maturity and capitalize on the QA base that has been built. On reliability prediction of repairable redundant digital structures. J. C. LAPRIE. IEEE Trans. Reliab. R-25 (4), 256 (October 1976). Taking into account the real characteristics of redtmdant digital structures leads to neglect of failures occurring during the repair instants. The formal definition of the corresponding hypotheses leads to a simplifiexl Markov model which (a) is homogenous and (b) has instantaneous repairs. At last, the paper describes the way by which the validity of the hypotheses can be judged. Analysis of 7 models for the 2-dimimilar-unit, warm standby, redundant system. MASAYORI KODAMA, HtROSHI NAKA3tICII[ and StFUNRO TAI,AMA'ISU.IEEE Trans. Reliab. R-25 (4), 273 (October 1976). The paper is in 2 parts. In all models tile failure rates are constam, but repair rates need not be constant. The method of supplementary variables is used for solving the models. Part I considers the effect of priorities oq reliability and availability for 4 basic models; (1) priority in both repair and operation; (2) priority in repair; (3) priority in operation: (4) no priority. Models 1 and 2 treat 2 repair disciplines: (a) preemptive-repeat, (b) preemptive-resume. We obtain (I) Laplace transforms of availability and (2) explicit
expressions for steady state availability and for mean time to system failure. The effect of priority assigalment to maximize steady state availability is discussed. Part II considers the effect of having different repair rates, depending on whether the failure was from standby or fiom operation. We obtain (1) Laplace transforms of availability and reliability and (2) explicit expressions for mean time to system failure. Analy~s of two difference 1-server systems. M. N. GOPALA.X. IEEE Trans. Reliab. R-25 (4), 280 (October 1976). In tbis paper, the availability and the reliability of two I-server systems with redundancy have been obtained. System 1 consists of n subsystems in series; each subsystem consists of two redundant i.i.d, components in "parallel" (cold standby) and one server. The times to failure of the components arc exponentially distributed; their repair time distributions ,are arbitrary and different. System 2 consists of n dissimilar units and one server. The times to faihlre of the units are arbitrarily distributed: the repair rates are constant but all different. Explicit expressions for the Laplace trans[brm of the mean down-time of the system in (0, t) and for the mean time to system failure have been obtained. A few particular cases are disct,ssed.
A Bayesian scheme for sequentially testing a muhi-component system. DAVH) V. MAS'rRAN. IEEE Trans. Reliab. R-25 (4), 270 (October 1976). Althot, gh the literature on reliability theory is filled with methods for optimally designing multi-component systems subject to various constraints, very little is available in the literature on methods for optimally testing such systems. Both capabilities are needed, because after a system is assembled, periodic t~ting is required to insure against degradation of component rcliabilities. Some components in the system should be tested more than others, because of their reliability, cost of testing, or placement in the system. This paper providc~ Bayesian decision rules for testing components sequentially to minimize the sum of the cost of testing and the cost of misestimation. Approximate confidence intervals for reliability of a series system. R, L. RACICor. IEEE Trans. Reliab. R-25 (4), 265 (October 1976). Two solutions arc proposed for estimating s-confidence intervals for reliability of a repairable series system comprised of non-constant failure rate components: (1) the system is treated as a st,m of renew',d processes with the mean and variance of total number of system failures being computed fiom the moments of failure times of the components; and (2) a pseudo-Bayesian solution is derived for the mean and variance of the log-reliability of a system of Weibull components. In both solution approaches, the central limit theorem is invoked for a sum of component random variables determined from test data such as number of failures or log-reliabilities..s-Confidence limits are then approximated using Gaussian probability tables. The intervals derived yield close-to-exact frequency limits, depending on such variables as number of test failures, number of components, and component parameters. On the behaviuur of some quantities used in Bayesian reliability demonstration tests. J. J. HIG(nxS and C. P. T~)KOS. IEEE Trans. Reliab. R-25 (4), 261 (October 1976). Equiprnent mean time between failures (MTBI-) is assumed to be a frequency random variable. The goodness of lit of the uniform prior as a probability model for the MTBF is compared to the goodness of fit of the inverted gamma prior for actual failure data. 'Ihcse distributions can both be adequately fitted to the same failure data when the