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Effect of standby redundancy on system reliability
376
World Abstracts on Microelectronics and Reliability
Placard procurement costs are minimized by photoengraving the placards on adhesive backed aluminum. The computer print-out serves as the master, thereby eliminating drafting costs normally associated with placard development. The need to update is minimized because of the functional organization of the placards. Further, the time and cost to update is only a fraction of that normally expected. The excellent visibility into the mechanization of the system provided by the computer print-outs was useful in the development of the technical manuals and training courses and in the performance of failure modes and effects analysis.
A method for calculation of network reliability. J. DE MERCADO, N. SPYRATOSand B. A. BOWEN. IEEE Trans. Reliab. R-25 (2), 71 (1976). The calculation of the probability that communication between two nodes in a given network is disrupted is difficult when the number of channels is large or when the network configuration is complex. This paper presents an efficient method, formalized as an algorithm, for calculating this probability using subnetworks that are smaller than the original one. This algorithm should prove useful in practice since it permits the possibility of choosing the subnetwork decomposition that one considers best suited for a specific problem. A review of fault detection methods for large system. STEPHEN SHIELDS. Radio and Electronic Engineer. 46 (6), 276 (1976). A critique is made of current research into practical fault finding procedures for the maintenance of complex engineering systems. The half split and other methods currently in practice are analysed and their main weakness shown to be that no account is taken of the various costs involved. Also analysed are cost conscious methods which are useful in diagnosis training or in designing fault detection guides. A brief look is taken at advanced diagnostic techniques which are aided by an on-line computer in selecting the next test to be made. Distribution of a random variable defined through a constitutive equation. A. V. FERRIS-PRABHU. Microelectron. and Reliab. 15, 153 (1976). This paper illustrates how to obtain the distribution of a random variable such as the time to failure, which is itself a function of other random variables whose distributions are known or assumed. Availability of repairable units when failure and restoration rates age in real time. S. GARRIBBA, G. REINA and G. VOLTA. IEEE Trans. Reliab. R-25 (2), 88 (1976). In reliability engineering and practice an important role is played by those units whose life characteristics change with time. The case is herewith considered where change underlies a nonhomogeneous Markov model. Simple repair processes then deal with a 2-state alternating policy resulting from the superposition of failure and restoration, both showing a continuous aging with time. Availability can be expressed through linear differential equations or by means of integral equations; the approaches are equivalent. A computer code is then described which calculates (i) availability, and (it) transition densities for any continuous time dependence of failure and restoration rates. Numerical results are shown for a few examples. Failure rate analysis of Goddard Space Flight Center spacecraft performance during orbital life. H. P. NORRIS and A. R. TIMMINS. Proc. A. Reliability and Maintainability Syrup. p. 120. 2(~22 Jan. 1976. Nevada, U.S.A. Space life performance data of 57 Goddard Space Flight Center spacecraft have been analyzed from the standpoint of determining an appropriate reliability model and the associated reliability parameters. Data from published NASA reports, which cover the space performance of GSFC spacecraft launched in the 1960,1970 decade, form the basis of the analyses. The results of the analyses show that the time distribution of 449 malfunctions, of which 248
were classified as failures (not necessarily catastrophic), follow a reliability growth pattern that can be described with either the Duane Model (represented by the accumulated failure rate, 2~ = F / N T = K T - ~ ) , or a Weibull distribution. The advantages of both mathematical models are used in order to (1) identify space failure rates, (2) observe chronological trends, and (3) compare failure rates with those experienced during the pre-launch environmental tests of the flight model spacecraft. The space performance as described by the Duane growth model shows two characteristic slopes; one for the first 30 days in space, and another for the time period 30300 days in space. The results to date show that the exponential relationship for describing the reliability of spacecraft is not appropriate. The parameters for the Weibull distribution function were developed from both the thermal-vacuum test data and the space data. This made possible a comparison of the terminal failure rates from test with the failure rates in space. The preliminary results show promise for having a basis for comparison of the effectiveness of future test programs, and as a measure of space performance. A six-state system model. BALBIR S. DHILLON. Microelectron. and Reliab. 15, 139 (1976). The six states considered in this short paper relates to a system with normal and open short, intermittent, out-of-tolerance and maladjustment failure modes. A Markov model is developed to obtain the state probabilities.
Effect of standby redundancy on system reliability. P. K. KAPUR and K. R. KAPOOR. IEEE Trans. Reliab. R-25 (2), 120 (1976). Two reliability models for a 2-unit cold-standby intermittently available system, whose units are subject to repair and preventive maintenance, have been studied. In Model I, the Laplace Transform of the pdf of 'Disappointment time' and in Model II, the Laplace Transform of the 'Interference time' are derived. Disappointment time and the interference time definitions include the demand pattern. Interface between maintainability and commercial aircraft spares support. JOHN E. LOSSEE. Proc. A. Reliability and Maintainability Syrup. p. 500. 20-22 Jan. 1976. Nevada, U.S.A. The spares support of commercially operated aircraft is big business. As such, planning for spares support needs to be a major consideration by Maintainability from conception through the service life of a commercial liner. This paper presents the general methodology used by Douglas Aircraft to develop the spares support program for the DC-10. Steady-state profit in a 2-unit standby system, ASHOK KUMAR. IEEE Trans. Reliab. R-25 (2), 105 (1976). Three models arc presented for a 2-unit standby system, Models l and 2 deal with a 2-unit warm-standby system with and without preventive maintenance (pm) to standby unit. Model 3 is a 2-unit cold-standby system with pm to operative unit. An income structure has been superimposed on the semi-Markov processes generated by the systems to obtain s-expected profit. For models 2 and 3, s-expected profit is suggested as the measure of maintenance effectiveness. Numerical examples are included to illustrate the results. Reliability calculation of redundant systems with non-identical units. E. BALAGURUSAMYand K. B. MISRA. Mieroeleetron. and Reliab. 15, 135 (1976). The present paper develops mathematical models for evaluating the exact reliability and mean time to failure of k-out-of-m:G systems with different unit failure probabilities. The ith unit is assumed to be characterised by a general hazard rate hi(t) - ~.ith. The models are based on the concepts of tie sets: they are faMy simple and can be used for any values of m and
World Abstracts on Microelectronics and Reliability
Placard procurement costs are minimized by photoengraving the placards on adhesive backed aluminum. The computer print-out serves as the master, thereby eliminating drafting costs normally associated with placard development. The need to update is minimized because of the functional organization of the placards. Further, the time and cost to update is only a fraction of that normally expected. The excellent visibility into the mechanization of the system provided by the computer print-outs was useful in the development of the technical manuals and training courses and in the performance of failure modes and effects analysis.
A method for calculation of network reliability. J. DE MERCADO, N. SPYRATOSand B. A. BOWEN. IEEE Trans. Reliab. R-25 (2), 71 (1976). The calculation of the probability that communication between two nodes in a given network is disrupted is difficult when the number of channels is large or when the network configuration is complex. This paper presents an efficient method, formalized as an algorithm, for calculating this probability using subnetworks that are smaller than the original one. This algorithm should prove useful in practice since it permits the possibility of choosing the subnetwork decomposition that one considers best suited for a specific problem. A review of fault detection methods for large system. STEPHEN SHIELDS. Radio and Electronic Engineer. 46 (6), 276 (1976). A critique is made of current research into practical fault finding procedures for the maintenance of complex engineering systems. The half split and other methods currently in practice are analysed and their main weakness shown to be that no account is taken of the various costs involved. Also analysed are cost conscious methods which are useful in diagnosis training or in designing fault detection guides. A brief look is taken at advanced diagnostic techniques which are aided by an on-line computer in selecting the next test to be made. Distribution of a random variable defined through a constitutive equation. A. V. FERRIS-PRABHU. Microelectron. and Reliab. 15, 153 (1976). This paper illustrates how to obtain the distribution of a random variable such as the time to failure, which is itself a function of other random variables whose distributions are known or assumed. Availability of repairable units when failure and restoration rates age in real time. S. GARRIBBA, G. REINA and G. VOLTA. IEEE Trans. Reliab. R-25 (2), 88 (1976). In reliability engineering and practice an important role is played by those units whose life characteristics change with time. The case is herewith considered where change underlies a nonhomogeneous Markov model. Simple repair processes then deal with a 2-state alternating policy resulting from the superposition of failure and restoration, both showing a continuous aging with time. Availability can be expressed through linear differential equations or by means of integral equations; the approaches are equivalent. A computer code is then described which calculates (i) availability, and (it) transition densities for any continuous time dependence of failure and restoration rates. Numerical results are shown for a few examples. Failure rate analysis of Goddard Space Flight Center spacecraft performance during orbital life. H. P. NORRIS and A. R. TIMMINS. Proc. A. Reliability and Maintainability Syrup. p. 120. 2(~22 Jan. 1976. Nevada, U.S.A. Space life performance data of 57 Goddard Space Flight Center spacecraft have been analyzed from the standpoint of determining an appropriate reliability model and the associated reliability parameters. Data from published NASA reports, which cover the space performance of GSFC spacecraft launched in the 1960,1970 decade, form the basis of the analyses. The results of the analyses show that the time distribution of 449 malfunctions, of which 248
were classified as failures (not necessarily catastrophic), follow a reliability growth pattern that can be described with either the Duane Model (represented by the accumulated failure rate, 2~ = F / N T = K T - ~ ) , or a Weibull distribution. The advantages of both mathematical models are used in order to (1) identify space failure rates, (2) observe chronological trends, and (3) compare failure rates with those experienced during the pre-launch environmental tests of the flight model spacecraft. The space performance as described by the Duane growth model shows two characteristic slopes; one for the first 30 days in space, and another for the time period 30300 days in space. The results to date show that the exponential relationship for describing the reliability of spacecraft is not appropriate. The parameters for the Weibull distribution function were developed from both the thermal-vacuum test data and the space data. This made possible a comparison of the terminal failure rates from test with the failure rates in space. The preliminary results show promise for having a basis for comparison of the effectiveness of future test programs, and as a measure of space performance. A six-state system model. BALBIR S. DHILLON. Microelectron. and Reliab. 15, 139 (1976). The six states considered in this short paper relates to a system with normal and open short, intermittent, out-of-tolerance and maladjustment failure modes. A Markov model is developed to obtain the state probabilities.
Effect of standby redundancy on system reliability. P. K. KAPUR and K. R. KAPOOR. IEEE Trans. Reliab. R-25 (2), 120 (1976). Two reliability models for a 2-unit cold-standby intermittently available system, whose units are subject to repair and preventive maintenance, have been studied. In Model I, the Laplace Transform of the pdf of 'Disappointment time' and in Model II, the Laplace Transform of the 'Interference time' are derived. Disappointment time and the interference time definitions include the demand pattern. Interface between maintainability and commercial aircraft spares support. JOHN E. LOSSEE. Proc. A. Reliability and Maintainability Syrup. p. 500. 20-22 Jan. 1976. Nevada, U.S.A. The spares support of commercially operated aircraft is big business. As such, planning for spares support needs to be a major consideration by Maintainability from conception through the service life of a commercial liner. This paper presents the general methodology used by Douglas Aircraft to develop the spares support program for the DC-10. Steady-state profit in a 2-unit standby system, ASHOK KUMAR. IEEE Trans. Reliab. R-25 (2), 105 (1976). Three models arc presented for a 2-unit standby system, Models l and 2 deal with a 2-unit warm-standby system with and without preventive maintenance (pm) to standby unit. Model 3 is a 2-unit cold-standby system with pm to operative unit. An income structure has been superimposed on the semi-Markov processes generated by the systems to obtain s-expected profit. For models 2 and 3, s-expected profit is suggested as the measure of maintenance effectiveness. Numerical examples are included to illustrate the results. Reliability calculation of redundant systems with non-identical units. E. BALAGURUSAMYand K. B. MISRA. Mieroeleetron. and Reliab. 15, 135 (1976). The present paper develops mathematical models for evaluating the exact reliability and mean time to failure of k-out-of-m:G systems with different unit failure probabilities. The ith unit is assumed to be characterised by a general hazard rate hi(t) - ~.ith. The models are based on the concepts of tie sets: they are faMy simple and can be used for any values of m and