#### Read ReliaSoft's Reliability Edge, Volume 4 Issue 1 text version

```ReliaSoft's Reliability EdgeVolume 4, Issue 1Fault Tree Analysis, Reliability Block Diagrams and BlockSim FTI EditionFault trees and reliability block diagrams are both symbolic analytical logic techniques that can be applied to analyze system reliability and related characteristics. Although the symbols and structures of the two diagram types differ, most of the logical constructs in a fault tree diagram (FTD) can also be modeled with a reliability block diagram (RBD). Given this similarity, ReliaSoft is expanding the BlockSim software family by introducing the BlockSim FTI edition (Fault Tree Interface edition) in August of this year. The FTI edition is a complete and integrated package in which you can use fault trees or RBDs or combinations of both in your analyses. This article presents a brief introduction to fault tree analysis concepts, illustrates the similarities between fault tree diagrams and reliability block diagrams and introduces some of the capabilities of BlockSim FTI. Fault Tree Analysis: Brief Introduction Bell Telephone Laboratories developed the concept of fault tree analysis in 1962 for the U.S. Air Force for use with the Minuteman system. It was later adopted and extensively applied by the Boeing Company. A fault tree diagram follows a top-down structure and represents a graphical model of the pathways within a system that can lead to a foreseeable, undesirable loss event (or a failure). The pathways interconnect contributory events and conditions using standard logic symbols (AND, OR etc). Fault tree diagrams consist of gates and events connected with lines. The AND and OR gates are the two most commonly used gates in a fault tree. To illustrate the use of these gates, consider two events (called &quot;input events&quot;) that can lead to another event (called the &quot;output event&quot;). If the occurrence of either input event causes the output event to occur, then these input events are connected using an OR gate. Alternatively, if both input events must occur in order for the output event to occur, then they are connected by an AND gate. Figure 1 shows a simple fault tree diagram in which either A or B must occur in order for the output event to occur. In this diagram, the two events are connected to an OR gate.Please Turn to Page 8Figure 1: Fault tree where either A or B can occurExamining Risk Priority Numbers in FMEAThe Risk Priority Number (RPN) methodology is a technique for analyzing the risk associated with potential problems identified during a Failure Mode and Effects Analysis (FMEA). This article presents a brief overview of the basic RPN method and then examines some additional and alternative ways to use RPN ratings to evaluate the risk associated with a product or process design and to prioritize problems for corrective action. Note that this article discusses RPNs calculated at the level of the potential causes of failure (Severity x Occurrence x Detection). However, there is a great deal of variation among FMEA practitioners as to the specific analysis procedure and some analyses may include alternative calculation methods. Overview of Risk Priority Numbers An FMEA can be performed to identify the potential failure modes for a product or process. The RPN method then requires the analysis team to use past experience and engineering judgment to rate each potential problem according to three rating scales: Severity, which rates the severity of the potential effect of the failure. Occurrence, which rates the likelihood that the failure will occur. Detection, which rates the likelihood that the problem will be detected before it reaches the end-user/customer.Please Turn to Page 14Also Inside... Reliability Growth Analysis and Plots  Reliability and Maintainability Analysis for a Remote Telecommunications System And much more...Page 2Volume 4, Issue 1In this IssuePage 1 Fault Tree Analysis, Reliability Block Diagrams and BlockSim FTI Edition Examining Risk Priority Numbers in FMEA Theoretical Resources for the Reliability Professional From the Editor's Desk Reliability Growth Analysis and Plots Criticality Analysis Reliability and Maintainability Analysis for a Remote Telecommunications System For Your Information Bulletin BoardTheoretical Resources for the Reliability ProfessionalIn addition to world-class software for performing reliability analysis, plotting and reporting, ReliaSoft also provides an extensive array of theoretical resources for the reliability professional in a variety of formats. Training Seminars ReliaSoft provides reliability training seminars, both public and on-site, in a variety of locations throughout the year. These seminars provide instruction in reliability engineering principles and theory, as well as hands-on experience with the software tools designed to put that theory into practice. Theoretical Textbooks Whenever applicable, ReliaSoft's standard software products are shipped with theoretical reference textbooks that describe the principles and theory that underlie the analyses performed by the software. These textbooks include numerous demonstration examples. Online versions are published on www.weibull.com and additional printed copies of each reference can be purchased from ReliaSoft. Available references include: Life Data Analysis Reference Accelerated Life Testing Reference System Analysis Reference Reliability Growth Reference Knowledgeable Technical Support ReliaSoft provides free technical support for registered software users via phone, fax or e-mail. Support personnel are knowledgeable about both the software and the underlying principles and theory. Professional Consulting Services ReliaSoft Consulting Services (RCS) provides professional consulting services on an as-needed basis. Areas of expertise include reliability program development; test/experiment design; data analysis; developing, evaluating and communicating reliability requirements; equipment reliability, maintainability and availability assessment and theoretical development. weibull.com In addition to the on-line theoretical textbooks on life data analysis and other important topics, the weibull.com Web site provides thousands of pages of free resources that are updated and expanded on a continual basis. Available resources include: Quick Subject Guides and Glossary Web Links and Recommended Books Case Studies and Training Guides Discussion Forums Free Reliability Software Tools Probability Plotting Papers RS RGA 6 supports the analysis of data from reliability growth tests (both continuous times-to-failure and discrete success/failure results) using all of the major reliability growth analysis models. This includes the Crow (AMSAA) model and variations that can also be used for reliability growth projections and repairable systems analysis. Beginning on page 3, we present a brief overview of some of RGA's capabilities and introduce some of the results and plots that can be generated for your reliability growth analyses. As always, we welcome your feedback on these and other articles and appreciate your ideas for other subjects of interest. --Lisa HackerPage 2  Page 3 Page 16 Page 19Page 23 Reliability Edge is published up to four times a year. To obtain a free subscription, to send comments or to submit articles for consideration: ReliaSoft Publishing ReliaSoft Plaza 115 S. Sherwood Village Drive Tucson, AZ 85710 USA Telephone: +1.520.886.0366 Fax: +1.520.886.0399 E-mail: [email protected]
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Correspondence with the editor may be published, in whole or in part, in future issues of ReliaSoft publications. An electronic copy of this document can be viewed or downloaded from: www.ReliaSoft.com/newsletter For information about products and services: ReliaSoft Sales ReliaSoft Plaza 115 S. Sherwood Village Drive Tucson, AZ 85710 USA Telephone: +1.520.886.0410 Fax: +1.520.886.0399 E-mail: [email protected]
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Maintenance Program Creator http://MPC.ReliaSoft.com Failure Modes and Effects Analysis http://Xfmea.ReliaSoft.com Reliability Growth Analysis http://RGA.ReliaSoft.comReliaSoft SalesToll Free: 1.888.886.0410 (U.S. and Canada) Phone: +1.520.886.0410 Fax: +1.520.886.0399 E-mail: [email protected]
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Reliability software tools Free downloads and on-line utilities Probability plotting papers On-line eTextbooks, including: Life Data Analysis Reference Accelerated Life Testing Reference System Analysis Reference Reliability Growth Reference HotWire eMagazine Subject indexes, glossaries, guides, links Research papers, case studies, examples Discussion forumweibull.com is a free service for the reliability community, provided by ReliaSoft Corporation.ReliaSoft Corporation ReliaSoft Plaza 115 S. Sherwood Village Drive Tucson, AZ 85710Prst Std U.S. Postage PAID Tucson, AZ Permit #541Volume 4, Issue 1```

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ReliaSoft's Reliability Edge, Volume 4 Issue 1