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Schemes of dynamic redundancy for fault tolerance in random access memories
1098
World Abstracts on Microelectronics and Reliability
is proposed for selecting near optimal configurations for larger systems.
Reliability evaluation in power-system transmission planning: practical considerations. TAREK A. M. SHARAF and GUNNAR J. BERG. IE E E Trans. Reliab. R-37, 274 (1988). In the reliability algorithm based on the maximum-flow, minimum-cut technique together with the decomposition principle, the generation of the state space for purposes of classification requires a large amount of memory. This paper presents a state-space truncation algorithm which reduces the number of states while maintaining accuracy within specified limits. The reliability algorithm is developed further to produce: (l) all possible loss-of-load levels and their associated probabilities, and (2) the system reliability indexes and their sensitivities with respect to element capacities. Our new algorithm has been applied to a small test system, and to the IEEE reliability test system. Network reliability with are failures and repairs. P. SIMIN PULAT. IEEE Trans. Reliab. R-37, 268 (1988). Arc repair probabilities are incorporated into network reliability calcuhttions for directed networks with independent arc failures. A discrete-time Markov chain with one absorbing state is constructed for the problem. The transition probability matrix is used to determine probability of source-to-sink connectivity in a given time interval, mean time to source-to-sink connectivity, fraction of time a node is blocked, and fraction of time the network is blocked (disconnected). Blockage probabilities aid in repair-crew allocation to the nodes of the network. A practical implementation of the factoring theorem for network reliability. LAVON B. PAGE and Jo ELLEN PERRY. IEEE 7)'ans. Reliah. R-37, 259, (1988). The factoring theorem is a simple and elegant pedagogical tool for determining the Kterminal reliability of a network, ie, the probability that a given set K of terminals in the network are connected to each other by a path of working edges. While numerous recent papers treat theoretical aspects of combining the factoring theorem with various network reductions, it is not widely appreciated that straightforward and relatively simple algorithms work very well. A portable microcomputer implementation is described which outperforms many recently published results obtained using more complicated algorithms on mainframe computers. A simple model for fatigue life. STURE HOLM and JACQUES I)E MARE. I E E E Trans. Reliab. R-37, 314 (1988). There are m a n y methods to predict life lengths. However, the relationship between the life lengths of components exposed to regular oscillating stresses and the life lengths of components exposed to more irregular loads is not clear. A c o m m o n assumption is the Palmgren-Miner linear damage accumulation rule. This rule states that a component fails when the total damage exceeds a prescribed value. The total damage is the sum of the damages caused by each load, independent of the order in which the different loads are applied to the COi'llpon en t. ,\ dmc invariance assumption, commonly used, states that the damage caused by a load depends only on the sequence of extremes of the load and not on the particular form of the load flmction between its extreme values. One instance where this second assumption is used is in the rain flow count of load cycles. This paper shows that these two assumptions together imply the existence of a simple model which determines the life length of a component completely. The main feature of the model is the existence of an exhaustion function which is determined by the damage caused by periodically oscillating loads. This function connects the damages caused by periodically oscillating loads to the damages caused by a load varying in an arbitrary way. Simple deterministic examples
where the damages caused by oscillating loads are determined by the loglinear W f h l e r curve, are discussed in detail. Since different components have different strengths, models for random strengths are suggested. When the load is a random function and the strength is random as well, the randomness of the life length is caused by the randomness of the strength rather than by the randomness of the load.
Reliability analysis using Weibull lifetime data and expert opinion. NOZER D. SINGPURWALLA and MAO Sm SONG. I E E E Trans. Reliab. R-37, 340 (1988). We present a new approach for the analysis of failure data from a Weibull distribution. The novel feature here is the incorporation of expert opinion and of our opinion on the expertise of the experts, into the analysis. A use of the Laplace approximation results in formulae which are easy to compute. New method calculates failure rates. DON DENTON. Semiconductor int., 145 (September 1988). A new technique, based on multiple activation energies, allows you to estimate failure rates from burn-in data.
Schemes of dynamic redundancy for fault tolerance in random access memories. KARL E. GROSSPIETSCH. I E E E Trans. Reliab. R-37, 331 (1988). This paper presents two methods of implementing fault tolerance by means of dynamic redundancy in random access memories which allow the treatment of memory-chip faults at the interface of the memory. I. A stand-by rcconfiguration system. If the access to a word cell in a faulty memory-block is required, the I/0 lines of the memory can be dynamically switched to spare bit-slices. This is performed by a switching network implemented at the memory interface. For every memory access, the network is controlled by a fault-status table which memorizes the fault conditions of each memory block; this fault-status table also is implemented outside the memory-chip array. A major advantage is that it can be added to an existing memory. It was implemented by one VLSI chip that can be added modularly to the memory interface. The basic properties of the method and a prototype VLSI implementation are described. 2. Memory reconfiguration by means of graceful degradation. The memory reliability implied by both approaches is estimated by a simple memory-reliability model. These methods improve the reliability considerably compared to conventional memory fault-tolerance methods, and the size of the units of reconfiguration can be tailored to the demands of the system user. On computing M T B F for a k-out-of-n:G repairable system. JOHN E. ANGUS. I E E E Trans. Reliab. R-37, 312 (1988). It is often necessary to calculate M T B F (mean time between failures) quickly in order to make timely design decisions. An important system for which such calculations must be made is a k-out-of-n:G parallel system with unlimited repair and exponential interfailure and repair times at the unit level. Although a general formula is known, it is not easily remembered nor derived. This paper presents a method for deriving a formula for M T B F in this situation that is easily reproduced quickly by remembering a few simple concepts.
Optimization of spare provisioning for a periodically operated system. YUICHI YATOUMARU, MASAFUM1 SASAKI a n d SH1GERU YANAGL Proc. 18th Syrup. Reliab. Maintainab. (Condensed Version), 62 (1988). In this paper, the optimal spare allocation model for a periodically operated system is considered. Firstly, a reliability evaluation model is built. Then the optimization problem of spare allocation for this system is discussed. The optimization problem is the determination of a spare allocation which minimizes the total system cost
World Abstracts on Microelectronics and Reliability
is proposed for selecting near optimal configurations for larger systems.
Reliability evaluation in power-system transmission planning: practical considerations. TAREK A. M. SHARAF and GUNNAR J. BERG. IE E E Trans. Reliab. R-37, 274 (1988). In the reliability algorithm based on the maximum-flow, minimum-cut technique together with the decomposition principle, the generation of the state space for purposes of classification requires a large amount of memory. This paper presents a state-space truncation algorithm which reduces the number of states while maintaining accuracy within specified limits. The reliability algorithm is developed further to produce: (l) all possible loss-of-load levels and their associated probabilities, and (2) the system reliability indexes and their sensitivities with respect to element capacities. Our new algorithm has been applied to a small test system, and to the IEEE reliability test system. Network reliability with are failures and repairs. P. SIMIN PULAT. IEEE Trans. Reliab. R-37, 268 (1988). Arc repair probabilities are incorporated into network reliability calcuhttions for directed networks with independent arc failures. A discrete-time Markov chain with one absorbing state is constructed for the problem. The transition probability matrix is used to determine probability of source-to-sink connectivity in a given time interval, mean time to source-to-sink connectivity, fraction of time a node is blocked, and fraction of time the network is blocked (disconnected). Blockage probabilities aid in repair-crew allocation to the nodes of the network. A practical implementation of the factoring theorem for network reliability. LAVON B. PAGE and Jo ELLEN PERRY. IEEE 7)'ans. Reliah. R-37, 259, (1988). The factoring theorem is a simple and elegant pedagogical tool for determining the Kterminal reliability of a network, ie, the probability that a given set K of terminals in the network are connected to each other by a path of working edges. While numerous recent papers treat theoretical aspects of combining the factoring theorem with various network reductions, it is not widely appreciated that straightforward and relatively simple algorithms work very well. A portable microcomputer implementation is described which outperforms many recently published results obtained using more complicated algorithms on mainframe computers. A simple model for fatigue life. STURE HOLM and JACQUES I)E MARE. I E E E Trans. Reliab. R-37, 314 (1988). There are m a n y methods to predict life lengths. However, the relationship between the life lengths of components exposed to regular oscillating stresses and the life lengths of components exposed to more irregular loads is not clear. A c o m m o n assumption is the Palmgren-Miner linear damage accumulation rule. This rule states that a component fails when the total damage exceeds a prescribed value. The total damage is the sum of the damages caused by each load, independent of the order in which the different loads are applied to the COi'llpon en t. ,\ dmc invariance assumption, commonly used, states that the damage caused by a load depends only on the sequence of extremes of the load and not on the particular form of the load flmction between its extreme values. One instance where this second assumption is used is in the rain flow count of load cycles. This paper shows that these two assumptions together imply the existence of a simple model which determines the life length of a component completely. The main feature of the model is the existence of an exhaustion function which is determined by the damage caused by periodically oscillating loads. This function connects the damages caused by periodically oscillating loads to the damages caused by a load varying in an arbitrary way. Simple deterministic examples
where the damages caused by oscillating loads are determined by the loglinear W f h l e r curve, are discussed in detail. Since different components have different strengths, models for random strengths are suggested. When the load is a random function and the strength is random as well, the randomness of the life length is caused by the randomness of the strength rather than by the randomness of the load.
Reliability analysis using Weibull lifetime data and expert opinion. NOZER D. SINGPURWALLA and MAO Sm SONG. I E E E Trans. Reliab. R-37, 340 (1988). We present a new approach for the analysis of failure data from a Weibull distribution. The novel feature here is the incorporation of expert opinion and of our opinion on the expertise of the experts, into the analysis. A use of the Laplace approximation results in formulae which are easy to compute. New method calculates failure rates. DON DENTON. Semiconductor int., 145 (September 1988). A new technique, based on multiple activation energies, allows you to estimate failure rates from burn-in data.
Schemes of dynamic redundancy for fault tolerance in random access memories. KARL E. GROSSPIETSCH. I E E E Trans. Reliab. R-37, 331 (1988). This paper presents two methods of implementing fault tolerance by means of dynamic redundancy in random access memories which allow the treatment of memory-chip faults at the interface of the memory. I. A stand-by rcconfiguration system. If the access to a word cell in a faulty memory-block is required, the I/0 lines of the memory can be dynamically switched to spare bit-slices. This is performed by a switching network implemented at the memory interface. For every memory access, the network is controlled by a fault-status table which memorizes the fault conditions of each memory block; this fault-status table also is implemented outside the memory-chip array. A major advantage is that it can be added to an existing memory. It was implemented by one VLSI chip that can be added modularly to the memory interface. The basic properties of the method and a prototype VLSI implementation are described. 2. Memory reconfiguration by means of graceful degradation. The memory reliability implied by both approaches is estimated by a simple memory-reliability model. These methods improve the reliability considerably compared to conventional memory fault-tolerance methods, and the size of the units of reconfiguration can be tailored to the demands of the system user. On computing M T B F for a k-out-of-n:G repairable system. JOHN E. ANGUS. I E E E Trans. Reliab. R-37, 312 (1988). It is often necessary to calculate M T B F (mean time between failures) quickly in order to make timely design decisions. An important system for which such calculations must be made is a k-out-of-n:G parallel system with unlimited repair and exponential interfailure and repair times at the unit level. Although a general formula is known, it is not easily remembered nor derived. This paper presents a method for deriving a formula for M T B F in this situation that is easily reproduced quickly by remembering a few simple concepts.
Optimization of spare provisioning for a periodically operated system. YUICHI YATOUMARU, MASAFUM1 SASAKI a n d SH1GERU YANAGL Proc. 18th Syrup. Reliab. Maintainab. (Condensed Version), 62 (1988). In this paper, the optimal spare allocation model for a periodically operated system is considered. Firstly, a reliability evaluation model is built. Then the optimization problem of spare allocation for this system is discussed. The optimization problem is the determination of a spare allocation which minimizes the total system cost