Comparison of MTBF in the parallel string configuration and the quad configuration systems

In this study, four redundant systems having the parallel string configuration and the quad configuration consisting of 2n identical units are considered and the reliability of each system and MTBF (Mean Time Between Failures) are evaluated. Next, as the special case of the systems in this study, the case of four units corresponds to the Keene's system and MTBF of each system agreed with his results. Further, as the results evaluated MTBF relating to each system consisting of 6, 8 and 10 units, the large and small relations of the MTBF between systems are made clear.     

Approximated reliability of r-out-of-n(F) system with common cause failure and maintenance

In modern industries very high reliability system are needed. To improve the reliability of system, the component redundancy and maintenance of component or system play an impotant role and must be studied. This paper presents a reliability model of a r-out-of-n(F) redundant system with maintenance and Common Cause Failure. Failed component repair times are arbitrarily distributed. The system is in a failed state when r units failed because of the combination of single element failure or CCF(Common Cause Failure). Laplace transformation of reliability is derived by using analysis of Markov state transition graph. By using the analyzed MTBF, we compute MTBF of r-out-of-n(F) system. The MTBF with CCF is saturable even if repair rate is large.Approximated reliability of the r-out-of-n(F) system with maintenance and Common Cause Failure O.SummaryThe paper presents a reliability model of a r-out-of-n(F) redundant system with maintenance and Common Cause Failure. Failed component repair times are arbitrarily distributed. The system is in a failed state when r units failed because of the combination of single element failure or Common Cause Failure. Laplace transformation of reliability is derived by using analysis of Markov state transition graph. By analyzing this mean visiting time equations, we compute MTBF and shows computational example. The MTBF with CCF is saturable even if repair rate is large. In general the maintenance overcomes MTBF bounds, But the repair method not overcome the MTBF saturation when the system has Common Cause Failure.     

Survey of reliability and availability evaluation of complex networks using Monte Carlo techniques

Generally there are four main difficulties in evaluating complex large-scale system reliability, availability and MTBF: the system structure may be very complex; subsystems may follow various failure distributions; subsystems may conform to arbitrary failure and repair distributions for maintained systems; the failure data of subsystems are sometimes not sufficient, reliability test sample sizes tend to be small. It is difficult and often impossible to obtain s-confidence limits of them by classical statistics. Monte Carlo technique combined with Bayes method is a powerful tool to solve this kind of problems. In this survey, the typical existing Monte Carlo reliability, availability and MTBF simulation procedures, variance reduction methods, and random variate generation algorithms are analyzed and summarized. The advantages, drawbacks, accuracy and computer time of Monte Carlo simulation in evaluating reliability, availability and MTBF of a complex network are discussed. Finally, some conclusions are drawn and a general Monte Carlo reliability and MTTF assessment procedure is recommended.     

Reliability analysis of a 2-out-of-n:F system with repairable primary and degradation units

In this paper we consider a 2-out-of-n:F system composed of repairable primary and degradation units. Two stochastic models are proposed depending upon the policies of the repair discipline. We derive the availability, the expected number of visits to system failure per unit time and the MTBF by applying an extended Markov renewal process for each model. We finally show the numerical examples and investigate the impacts of introducing degradation units on the reliability measures obtained above.     

Relcomp: A Computer Program for Calculating System Reliability and MTBF

A conversational time-sharing computer program called Relcomp can be used for rapid and economical calculation of the reliability and mean time between failures (MTBF) of systems consisting of serial and redundant units. Relcomp is simple to use and does not require any special knowledge of programming. A copy of the complete Relcomp program listing is provided in Tymshare Super Basic language. Use of the program to calculate the reliability and MTBF of a system, its subsystems, and blocks is illustrated by examples.     

Bounds on MTBF of Systems Subjected to Periodic Maintenance

Mean time between failures (MTBF) is a common reliability measure used to assess the failure behavior of repairable systems. In order to increase MTBF, in most systems, it is a common practice to perform preventive maintenance activities at periodic intervals. In this paper: We first discuss the validity of a commonly used equation for computing MTBF of systems subjected to periodic maintenance. For complex systems where this equation is valid, we propose a simple and better approximation than the exponential approximation proposed in a recent paper. In addition, we prove that for systems with increasing failure rate on average (IFRA) distributions, the exponential approximation proposed in a recent paper always underestimates the MTBF; hence, it is a lower bound at best. The proposed approximation and bounds are applicable for a wide range of systems because systems which contain components with exponential or any increasing failure rate (IFR) distribution (viz., Weibull with$beta≫1$, gamma, Gumbel,$s$-normal, and uniform) follow an IFRA distribution. As a special case, the proposed bounds & approximations provide better results for systems that contain only exponential failure distributions.     

Reliability of a 3-unit cold redundant system with Weibull failure

Redundancy technique is applied to increase the reliability of a system where maintenance or repair is either not possible or is too costly. Reliability of a cold redundant system is always higher than a hot one. Moreover the increase in reliability due to adding of a unit in sequence can always be exactly determined.Literature is full of derivation of reliability expressions of a cold redundant system whose units obey exponential failure density. Due to extreme difficulty in evaluation of integrals involving Weibull density function, few attempts on derivation of reliability of redundant systems have been made. We have here derived reliability of a simple case of a 3-unit cold standby system whose units obey Weibull failure density.     

Reliability of Some Redundant Systems with Repair

A mathematical model is established for the reliability of modularly redundant systems with repair. The model allows different hazard rates for active units and for standby units. The hazard rates are assumed to be constant. The cases of constant repair rate and constant repair time for a two unit system are evaluated using the reliability and mean time between failure. The approach is then extended to systems with more than two units. A system parameter, relating to certain types of sensing, switching, and/or recovery has a very significant impact on system reliability for modularly redundant systems with repair.     

Reliability analysis of component-level redundant topologies for solid-state fault current limiter

Experience shows that semiconductor switches in power electronics systems are the most vulnerable components. One of the most common ways to solve this reliability challenge is component-level redundant design. There are four possible configurations for the redundant design in component level. This article presents a comparative reliability analysis between different component-level redundant designs for solid-state fault current limiter. The aim of the proposed analysis is to determine the more reliable component-level redundant configuration. The mean time to failure (MTTF) is used as the reliability parameter. Considering both fault types (open circuit and short circuit), the MTTFs of different configurations are calculated. It is demonstrated that more reliable configuration depends on the junction temperature of the semiconductor switches in the steady state. That junction temperature is a function of (i) ambient temperature, (ii) power loss of the semiconductor switch and (iii) thermal resistance of heat sink. Also, results’ sensitivity to each parameter is investigated. The results show that in different conditions, various configurations have higher reliability. The experimental results are presented to clarify the theory and feasibility of the proposed approaches. At last, levelised costs of different configurations are analysed for a fair comparison.     

Reliability study of duplex-hybrid systems

Duplex (double modular redundant) systems utilising standby spares are described and the reliability equations of such systems are derived. The system reliability as a function of normalised time is plotted and compared with conventional TMR (triple modular redundant) system. It is shown that the duplex-hybrid system is noticeably more reliable than the TMR-hybrid system with the similar configuration of standby spares. Implementation of a duplex-hybrid system supplemented by an intelligent unit with powerful capabilities is discussed.     

On a compound redundant system without repair

This paper deals with the reliability considerations on a redundant system consist of two subsystems connected in series, in which they have a similar warm-standby subsystem, respectively. And these four subsystems are composed of several identical units in parallel redundancy, respectively and are connected with switching devices each other.The purpose of this paper is to attain the following two subjects; (1) to utilize the surviving units at any switch-over point of time, as many as possible, making use of the switching devices as mensioned above, and (2) to deal with various complex redundant systems with or without switching devices, simultaneously.In these considerations we have obtained the reliability function and mean time to system failure (MTSF) of this system.     

Steady-State Reliability of Systems of Mutually Independent Subsystems

Predicting the reliability of a redundant system with repair is considerably simplified when the system can be subdivided into mutually independent subsystems. Results can be obtained without knowing the failure of repair time distributions of the subsystems. In this paper formulae are developed for the ``steady-state' availability and MTBF of a complex system in terms of the availabilities and MTBF's of its constituent subsystems. The basic concepts required are introduced and discussed in a review of a simplex system. These concepts are then applied to a complex system to obtain the main results of the paper. Finally, two examples are given to illustrate the application of these results.     

A 2-Unit Repairable Redundant System with Switching Failure

The switch has two different failure modes: It switches an operating unit out of operation when it should not, and does not switch the standby in when it should. We consider a 2-unit warm-standby redundant system with two switching failure modes, and derive the stochastic behavior of system failure. Several reliability models are shown as special cases.     

On comparison of MTBF between four redundant systems

In this study we compare the mean time between failures (MTBF) of four series-parallel and parallel-series redundant systems composed of 2n independent components. General ordering relations between the four systems in terms of their MTBF are obtained. These results substantially improve previous ones obtained by Yamashiro etc.     

Reliability evaluation of systems with critical human error

This paper presents four mathematical models to evaluate reliability of redundant systems with critical human error. Equations for system reliability, state probabilities and mean time to failure are developed. System reliability and mean time to failure plots are shown.     

可靠性工程分配法在雷达设计中的应用

在工程设计中经常要评估产品可靠性方面的指标，如失效率、平均无故障时间、平均维修时间等数值的测算和分配。总结了双基地多普勒气象雷达可靠性设计方面的一些具体工作，以及可靠性原理在其中的应用。     

The mean residual life function of a k-out-of-n structure at the system level

In the study of the reliability of technical systems, k-out-of-n systems play an important role. In the present paper, we consider a k-out-of-n system consisting of n identical components with independent lifetimes having a common distribution function F. Under the condition that, at time t, all the components of the system are working, we propose a new definition for the mean residual life (MRL) function of the system, and obtain several properties of that system.     

基于Bellcore标准的电子产品可靠性预计方法及案例研究

介绍了Bellcore标准进行可靠性预计的理论基础,包括元器件失效率与单元失效率模型等。利用Bellcore现行的TelcordiaSR-332标准手册,对某用于商用环境中的单板计算机进行了可靠性预计。给出了该单板计算机MTBF预计的过程和方法,以及失效率和MTBF的预计结果,并与军用标准的预计结果进行了对比,说明了Bellcore标准目前存在的一些问题。     

Time to Failure and Availability of Paralleled Systems with Repair

This paper discusses reliability properties of some simple paralleled or redundant systems, where repair is possible in case of failure. We are assuming here that a ``failure' may always be instantly identified, and the appropriate steps taken. In certain problems such an assumption is not warranted. The ``systems' discussed are composed of two identical ``subsystems,' e.g., computers, or radars, and the system is considered to be in a state of failure when, and only when, both subsystems are simultaneously in such a state. Such system design strategies have been proposed for various applications, but have received little analysis. Two measures of reliability are discussed: 1) the time to system failure, measured from an instant at which both subsystems are operative, and 2) the long-run availability of the system, where the latter means the average fraction of the time during which the system is able to perform its function. Analysis is based on the assumption of ``random' (Poisson-like) failure for the subsystems (for theoretical justification see Drenick [2]), and independent but otherwise arbitrarily distributed repair times. It is of some interest that several of the important operational measures deduced, depend in detail upon the form of the distribution of repair times, as it is summarized in its Laplace transform, and not simply upon certain simple averages or moments of repair time.     

Analysis of a two unit standby redundant fail-safe system

This paper evaluates reliability and fail-safety of a two unit cold standby fail-safe redundant system. Three modes of failure—(1) failure due to human error, (2) failure due to unit faults and (3) failure due to switchover faults—are considered. The complete failure states of the system are divided into two categories, fail-safe state and fail-dangerous state. Several fail-safety measures of interest to a fail-safe system designer are defined and evaluated, such as safety function, safety ratio and danger ratio.