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Simulating maintenance work in an engineering firm: a case study
418
World Abstracts on Microelectronics and Reliability
rate for remote electronic equipment facilities. The major assumption of the model is that a facility, prior to failure, will give an observable indication that it is about to fail. In order for the model to predict the failure rate for a change in technician visitation rate, three parameters, obtained from facility maintenance logs, are used to initialize the model. These are the number of technicians preventive maintenance visits, the number of pending-failures corrected as logged by the technician, and the number of hard failures. An upper bound failure rate prediction, for a decrease in facility visits, results from the optimistic assumption that the number of logged pending failures, if not corrected by the technicians, would have resulted in failures. The application of the model to two navigation-facility types indicates that changes in the visitation rate would moderately change the failure rate. Hence, the utility of the upper bound estimate is justified. Since the model is based upon a number of simplifying assumptions, it requires validation from a field test where the actual visitation rate would be varied, and the resulting failure rate would be analyzed. At present, a statistical design for the validation has been developed and is being seriously considered for implementation,
Simulating maintenance work in an engineering firm: a case study. B. A. BASKER,A. MANAN and T. M. HUSBAND. Microelectron. Reliab. 16, 571 (1977). This paper presents the results of a case study carried out in the maintenance department of a medium-sized British engineering firm. Monte Carlo simulation was used to determine the optimal size of maintenance crew under two separate organizational conditions. First the estimation of the optimal number of repair m e n to service a key production department on a decentralized basis. Second, the determination of the centralized maintenance crew size to service the entire factory. The paper seeks to show how simulation can be applied under difficult conditions, in particular the lack of full and formal downtime records. Its objective is to demonstrate the potential of simulation techniques in an industry where maintenance is typically practiced in an unsophisticated fashion,
Selecting the prior distribution in Bayesian estimation. R. V. CANFIELD and J. C. TEED. IEEE Trans. Reliab. R-26, (4) 283 (October 1977). A major problem associated with Bayesian estimation is selecting the prior distribution. Fisher's information measure is extended to cover prior distributions so that a comparative measure of the amount of information in the sample and in the prior is obtained. The amount of information is used as an intuitive measure of the relative value or weight of experimental data and prior information. By determining the relative weights of both types of information beforehand, it is possible to select a prior which has a known and controlled influence on the estimation process.
bate the problem: they will be more complex and tougher to test. As if that were not enough, there is also pressure on LSI vendors and users to keep testing costs in line with the plummeting selling prices of the devices, just as the price of LSI systems and software supports are climbing. Such pressure may mean that the sophisticated testers for screening and qualifying LS1 circuits are not being used to their full capability, reducing the quality and reliability of the devices tested.
Optimum redundancy of repairable modules. J. M. KONTDLEON. IEEE Trans. Reliab. R-26, (4) 277 (October 1977). The design of modules to have some redundant functions in order to minimize module production cost is analysed. U p o n production modules with failed functions are either discarded or repaired. If some functions have 2 elements in parallel, the production cost of a module can be minimized if modules are discarded or repaired, depending on the number of redundant functions, number of functions per module, element costs and element quality. The number of failed functions above which the module is discarded rather than repaired is calculated using a simple computer algorithm.
Random point processes applied to availability analysis of redundant systems with repair. K. ARNDT and P. FRANKEN. IEEE Trans. Reliab. R-26, (4) 266 (October 1977). An approach to calculate the stationary state probabilities and in particular the stationary point availability of redundant systems with repair is presented. The approach is based on the theory of random marked point processes. The tractibility of the results is demonstrated by an example.
A decomposition method for computing system reliability by a Boolean expression. H. NAKAZAWA. IEEE Trans. Reliab. R-26, (4) 250 (October 1977). A substitutionary decomposition method for computing the reliability of a redundant system S given by a Boolean expression is proposed. System S is decomposed into two subsystems S(x) and S(,~) according to up- and down-states of its keystone variable x. This is repeated until all terms become s-independent in each decomposed subsystem. A criterion for choosing the keystone variable and a property which saves computation time are obtained.
A reduction technique for obtaining a simplified reliability expression. T. CASE. IEEE Trans. Reliab. R-26, (4) 248 (October 1977). A reduction technique is described for obtaining a simplified reliability expression (probability of success) when applied to the canonical form of minterms (having independent variables) such as those generated from a truth table format. The resulting terms are always mutually exclusive, which allows simple, direct transformation to a probability expression.
2-Unit redundant systems with replacement and repair. 16, 587 (1977). In the present paper, a model to evaluate the expected number of non-catastrophic failures in an electronic device, due to noise, has been developed under the assumption that the first time derivative of the amplitude of signal plus noise follows non-Gaussian distribution. The number of failures so obtained enables one to find out the Reliability of the system. For a particular case results seem to correspond to those obtained by Bendat.
J. SKAKALA and B. ROHAL-ILKIV. IEEE Trans. Reliah. R-26, (4) 294 (October 1977). The paper deals with redundant systems consisting of i.i.d, units with repair. There are 2 kinds of spare units (1) warm standby units with instant perfect replacement and (2) cold stock units which can be supplied after a delay only. The replacement mechanism and the derivation of the mean 'time to first system failure' (TFSF) using Markov renewal processes are illustrated on two models. The influence of stock unit replacement time on the mean TFSF is studied.
LSI: the testing nightmare. BRUCE LEBoss. Electronics
Availability of a certain item within a system. E. WOLEr~ER,
p. 65 (December 8, 1977). Makers of LSI testers must sometimes feel like laboratory rats being asked to run ever more complex mazes. And the large-scale integrated circuits now on the drawing board promise only to exacer-
Microeleetron. Reliab. 16, 143 (1977). We assume a set of operating items for which a set of stand-by items is made available in the event of operational failures. The problem to be studied is not the system availability, but rather the
Analysis of non-catastrophic failures in electronic devices due to random noise. C. PRAKASH. Microelectron, Reliab.
World Abstracts on Microelectronics and Reliability
rate for remote electronic equipment facilities. The major assumption of the model is that a facility, prior to failure, will give an observable indication that it is about to fail. In order for the model to predict the failure rate for a change in technician visitation rate, three parameters, obtained from facility maintenance logs, are used to initialize the model. These are the number of technicians preventive maintenance visits, the number of pending-failures corrected as logged by the technician, and the number of hard failures. An upper bound failure rate prediction, for a decrease in facility visits, results from the optimistic assumption that the number of logged pending failures, if not corrected by the technicians, would have resulted in failures. The application of the model to two navigation-facility types indicates that changes in the visitation rate would moderately change the failure rate. Hence, the utility of the upper bound estimate is justified. Since the model is based upon a number of simplifying assumptions, it requires validation from a field test where the actual visitation rate would be varied, and the resulting failure rate would be analyzed. At present, a statistical design for the validation has been developed and is being seriously considered for implementation,
Simulating maintenance work in an engineering firm: a case study. B. A. BASKER,A. MANAN and T. M. HUSBAND. Microelectron. Reliab. 16, 571 (1977). This paper presents the results of a case study carried out in the maintenance department of a medium-sized British engineering firm. Monte Carlo simulation was used to determine the optimal size of maintenance crew under two separate organizational conditions. First the estimation of the optimal number of repair m e n to service a key production department on a decentralized basis. Second, the determination of the centralized maintenance crew size to service the entire factory. The paper seeks to show how simulation can be applied under difficult conditions, in particular the lack of full and formal downtime records. Its objective is to demonstrate the potential of simulation techniques in an industry where maintenance is typically practiced in an unsophisticated fashion,
Selecting the prior distribution in Bayesian estimation. R. V. CANFIELD and J. C. TEED. IEEE Trans. Reliab. R-26, (4) 283 (October 1977). A major problem associated with Bayesian estimation is selecting the prior distribution. Fisher's information measure is extended to cover prior distributions so that a comparative measure of the amount of information in the sample and in the prior is obtained. The amount of information is used as an intuitive measure of the relative value or weight of experimental data and prior information. By determining the relative weights of both types of information beforehand, it is possible to select a prior which has a known and controlled influence on the estimation process.
bate the problem: they will be more complex and tougher to test. As if that were not enough, there is also pressure on LSI vendors and users to keep testing costs in line with the plummeting selling prices of the devices, just as the price of LSI systems and software supports are climbing. Such pressure may mean that the sophisticated testers for screening and qualifying LS1 circuits are not being used to their full capability, reducing the quality and reliability of the devices tested.
Optimum redundancy of repairable modules. J. M. KONTDLEON. IEEE Trans. Reliab. R-26, (4) 277 (October 1977). The design of modules to have some redundant functions in order to minimize module production cost is analysed. U p o n production modules with failed functions are either discarded or repaired. If some functions have 2 elements in parallel, the production cost of a module can be minimized if modules are discarded or repaired, depending on the number of redundant functions, number of functions per module, element costs and element quality. The number of failed functions above which the module is discarded rather than repaired is calculated using a simple computer algorithm.
Random point processes applied to availability analysis of redundant systems with repair. K. ARNDT and P. FRANKEN. IEEE Trans. Reliab. R-26, (4) 266 (October 1977). An approach to calculate the stationary state probabilities and in particular the stationary point availability of redundant systems with repair is presented. The approach is based on the theory of random marked point processes. The tractibility of the results is demonstrated by an example.
A decomposition method for computing system reliability by a Boolean expression. H. NAKAZAWA. IEEE Trans. Reliab. R-26, (4) 250 (October 1977). A substitutionary decomposition method for computing the reliability of a redundant system S given by a Boolean expression is proposed. System S is decomposed into two subsystems S(x) and S(,~) according to up- and down-states of its keystone variable x. This is repeated until all terms become s-independent in each decomposed subsystem. A criterion for choosing the keystone variable and a property which saves computation time are obtained.
A reduction technique for obtaining a simplified reliability expression. T. CASE. IEEE Trans. Reliab. R-26, (4) 248 (October 1977). A reduction technique is described for obtaining a simplified reliability expression (probability of success) when applied to the canonical form of minterms (having independent variables) such as those generated from a truth table format. The resulting terms are always mutually exclusive, which allows simple, direct transformation to a probability expression.
2-Unit redundant systems with replacement and repair. 16, 587 (1977). In the present paper, a model to evaluate the expected number of non-catastrophic failures in an electronic device, due to noise, has been developed under the assumption that the first time derivative of the amplitude of signal plus noise follows non-Gaussian distribution. The number of failures so obtained enables one to find out the Reliability of the system. For a particular case results seem to correspond to those obtained by Bendat.
J. SKAKALA and B. ROHAL-ILKIV. IEEE Trans. Reliah. R-26, (4) 294 (October 1977). The paper deals with redundant systems consisting of i.i.d, units with repair. There are 2 kinds of spare units (1) warm standby units with instant perfect replacement and (2) cold stock units which can be supplied after a delay only. The replacement mechanism and the derivation of the mean 'time to first system failure' (TFSF) using Markov renewal processes are illustrated on two models. The influence of stock unit replacement time on the mean TFSF is studied.
LSI: the testing nightmare. BRUCE LEBoss. Electronics
Availability of a certain item within a system. E. WOLEr~ER,
p. 65 (December 8, 1977). Makers of LSI testers must sometimes feel like laboratory rats being asked to run ever more complex mazes. And the large-scale integrated circuits now on the drawing board promise only to exacer-
Microeleetron. Reliab. 16, 143 (1977). We assume a set of operating items for which a set of stand-by items is made available in the event of operational failures. The problem to be studied is not the system availability, but rather the
Analysis of non-catastrophic failures in electronic devices due to random noise. C. PRAKASH. Microelectron, Reliab.