1、 STD.ASQ Db1078-ENGL 1997 m 075950b 0002180 LB8 ANSUIEC/ASQ D61078-1997 Analysis techniques for dependabilty-reliability block diagram method Approved as an American National Standard by: American Society for Quality COPYRIGHT American Society for QualityLicensed by Information Handling ServicesANSI
2、/I EC/ASQ D61078-1997 AMERICAN NATIONAL STANDARD Analysis Techniques for Dependability- Reliability Block Diagram Method Approved as an American National Standard by: American Society for Quality An American National Standard Approved on September 16, 1997 American National Standards: An American Na
3、tional Standard implies a consensus of those substantially concerned with its scope and provisions. An American National Standard is intended as a guide to aid the manufacturer, the consumer, and the general public. The existence of an American National Standard does not in any respect preclude anyo
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8、ote: As used in the document, the term “International Standard” refers to the American National Standard adoption of this and other International Standards. ASQ Mission: To facilitate continuous improvement and increase customer satisfac- tion by identifying, communicating, and promoting the use of
9、quality principles, con- cepts, and technologies; and thereby be recognized throughout the world as the leading authority on, and champion for, quality. 1098 76543 2 1 Printed in the United States of America Printed on acid-free paper Published by: American Societv for Qualitv Quality Press 61 1 Eas
10、t Wisconsin Avenue Milwaukee, Wisconsin 53201 -3005 Web site http:/w.asq.org 800-248-1 946 COPYRIGHT American Society for QualityLicensed by Information Handling ServicesANSI/IEC/ASQ D61078-1997 Contents Page Foreword. 1 Introduction 2 Clause Scope 3 Normative references . 3 Definitions . 3 Symbols
11、. 3 . 3 System fault definitions and reliability requirements 4 6.1 General considerations . 4 6.2 Detailed considerations . 4 Elementary models . 5 . . 7.1 Developing the model 5 7.2 Evaluating the model 8 More complex models . 8.1 General procedures . 11 8.2 Models with common bl . 16 8.3 rn out o
12、f n models (non-identical items). 19 8.4 Method of reduction 19 Extension of reliability block diagram methods to availability calculations . 21 9.1 Introduction 9.2 Assumptions . . 21 9.3 Examples. . 21 9.4 Conclusions and general remarks . 22 11 Annexes A B Symbols and abbreviations . 23 Summary o
13、f formulae 25 iii COPYRIGHT American Society for QualityLicensed by Information Handling ServicesANSI/IEC/ASQ D61078-1997 56( C0)137 Analysis Techniques for Dependability- Reliability Block Diagram Method 56(C0)145 Foreword 1) The formal decisions or agreements of the IEC on technical matters, prepa
14、red by Technical Committees on which all the National Committees having a special interest therein are represented, express, as nearly as possible, an international consensus of opinion on the subjects dealt with. 2) They have the form of recommendations for international use and they are accepted b
15、y the National Committees in that sense. 3) In order to promote international unification, the IEC expresses the wish that all National Committees should adopt the text of the IEC recommendation for their national rules in so far as national condi- tions will permit. Any divergence between the IEC r
16、ecommendation and the corresponding national rules should, as far as possible, be clearly indicated in the latter. This International Standard has been prepared by IEC Technical Committee No. 56: Dependability. The text of this standard is based on the following documents: I Six Months Rule 1 Report
17、 on Voting 1 Full information on the voting for the approval of this standard can be found in the Voting Report indi- cated in the above table. Annex A forms an integral part of this International Standard. Annex B is for information only, 1 COPYRIGHT American Society for QualityLicensed by Informat
18、ion Handling ServicesANSI/IEC/ASQ D61078-I997 Introduction Different analytical methods of dependability analysis are available, of which the Reliability Block Diagram (RBD) is one. The purposes of each method and their individual or combined applicability in evaluating the reliability and availabil
19、ity of a given system or component should be examined by the ana- lyst prior to starting work on the RBD. Consideration should also be given to the results obtainable from each method, data required to perform the analysis, complexity of analysis, and other factors identified in this standard. 2 COP
20、YRIGHT American Society for QualityLicensed by Information Handling ServicesANSI/IEC/ASQ D61078-1997 Analysis Techniques for Dependability- Reliability Block Diagram Method 1 Scope This International Standard describes procedures for modelling the dependability of a system and for using the model in
21、 order to calculate reliability and availability measures. A standard set of symbols related to reliability parameters is given in annex A. Some formulae are given in Annex B. 2 Normative references The following normative document contains provisions which, through reference in this text, constitut
22、e provisions of this International Standard. At the time of publication, the edition indicated was valid. All normative documents are subject to revision, and parties to agreements based on this International Standard are encouraged to investigate the possibility of applying the most recent edition
23、of the norma- tive document listed below. Members of IEC and IS0 maintain registers of currently valid International Standards. IEC 60050 (1 91): 1990, International Electrotechnical Vocabulary (IEV), Chapter 191: Dependability and quality of service. 3 Definitions Terms and definitions are in accor
24、dance with the International Electrotechnical Vocabulary (IEV), Chapter 191. 4 Symbols Symbols and abbreviations are given in annex A. 5 Applicability An RBD is a pictorial representation of a systems reliability performance. It shows the logical connection of (functioning) components needed for sys
25、tem success. The modelling techniques described are intended to be applied primarily to systems without repair and where the order in which failures occur does not matter. For systems where the order of failures must be taken into account or where repairs are to be carried out, other modelling techn
26、iques, such as Markov analysis, are more suitable. At any instant in time, an item is considered to be in only one of two possi- ble states: operational or faulty. 3 COPYRIGHT American Society for QualityLicensed by Information Handling ServicesSTD-ASQ Dbl078-ENGL 1777 075750b 0002187 532 ANSI/IEC/A
27、SQ D61078-1997 In the symbolic representation, no distinction is made between open circuit, short circuit or other fault modes; however, in the numerical evaluation this is possible. 6 System fault definitions and reliability requirements 6.1 General considerations A prerequisite for constructing sy
28、stem reliability models is a sound understanding of the ways in which the system can operate. Systems often require more than one fault definition. These should be defined and listed. In addition there should be clear statements concerning: -functions to be performed; - performance parameters and pe
29、rmissible limits on such parameters; - environmental and operating conditions. Various qualitative analysis techniques may be employed in the construction of an RBD. Therefore the systems fault definition has to be established. The system success is dependent on one or more system failures. For each
30、 system fault definition the next step is to divide the system into logical blocks appro- priate to the purpose of the reliability analysis. Particular blocks may represent system substructures, which in turn may each be represented by other RBDs (system reduction). For the quantitative evaluation o
31、f an RBD, various methods are available. Depending on the type of structure, simple Boolean techniques and/or path and cut set analyses may be employed. Calculations may be made using basic component reliabilitylavailability data. It should be noted that a reliability block diagram does not necessar
32、ily represent the way the hardware is physically connected. While this is obvious to experienced reliability engineers, it may not be so to others. 6.2 Detailed considerations 6.2.1 System operation It may be possible to use a system for more than one functional mode. If separate systems were used f
33、or each mode, such modes should be treated independently of the rest, and separate reliability models should be used accordingly. If the same system were used to perform all these functions, then separate diagrams should be used for each type of operation. Clear statements of the reliability require
34、ments associated with each aspect of system operation is a prerequisite. 6.2.2 Environmental conditions The system performance specifications should be accompanied by a description of the environmental conditions under which the system is designed to operate. This should include a description of all
35、 the conditions to which the system will be subjected during transportation, storage and use. 4 COPYRIGHT American Society for QualityLicensed by Information Handling ServicesSTD-ASQ DbL078-ENGL 1997 075750b OUO2LB8 479 Ip ANSI/IEC/ASQ D61078-1997 A particular piece of equipment is often used in mor
36、e than one environment, for example on board ship, in an aircraft or on the ground. When this is so, reliability evaluations may be carried out using the same reliability block diagram each time but using the appropriate failure rates for each environment. 6.2.3 Duty cycles The relationship between
37、calendar time, operating time and on/off cycles should be established. When it can be assumed that the process of switching equipment on and off does not in itself promote failures, and that the failure rate of equipment in storage can be negligible, then only the actual operational time of the equi
38、pment need be considered. However, in some instances the process of switching on and off is in itself the prime cause of equipment failure, and equipment may have a higher failure rate in storage than when operational. In complex cases where only parts of the system are switched on and off, modellin
39、g techniques other than reliability block diagrams (e.g. Markov analysis) may be more suitable. 7 Elementary models 7.1 Developing the model The first step is to select a system success definition. If more than one definition is possible a separate reliability block diagram may be required for each.
40、 The next step is to divide the system into blocks of equipment to reflect its logical behaviour of the system so that each block is statistically independent and as large as possible. At the same time each block should contain (where possible) no redundancy. For ease of numerical evaluation, each b
41、lock should contain only those items which follow the same sta- tistical distributions for times to failure. In practice it may be necessary to make repeated attempts at constructing the block diagram (each time bearing in mind the steps referred to above) before a suitable block diagram is finalize
42、d. The next step is to refer to the system fault definition and construct a diagram that connects the blocks to form a “success path.” As indicated in the diagrams that follow, the various paths, between the input and output ports of the diagram, pass through those combinations of blocks which must
43、function in order that the system functions. If all the blocks are required to function for the system to function then the corresponding block diagram will be one in which all the blocks are joined in series as illustrated in figure 1. Figure 1 5 COPYRIGHT American Society for QualityLicensed by In
44、formation Handling ServicesSTD-ASQ Db3078-ENGL I777 075750b 0002387 305 ANSI/IEC/ASQ D61078-I997 In this diagram “I” is the input port, “O” the output port and A, B, C . . . Z are the blocks which together constitute the system. Diagrams of this type are known as “series reliability block diagrams.”
45、 A different type of block diagram is needed when failure of one component or “block” does not affect system performance as far as the system fault definition is concerned. If in the above instance the entire link is duplicated (made redundant), then the block diagram is as illustrated by figure 2.
46、If, however, each block within the link is duplicated the block diagram is as illustrated by figure 3. Diagrams of this type are known as parallel reliability block diagrams. Block diagrams used for model- ling system reliability are often mixtures of series and parallel diagrams. Such a diagram wou
47、ld arise if we were to consider an example consisting of a duplicated communication link comprising three repeaters A, B and C, and a common power supply item (D). The resulting diagram would become as illustrated in figures 4 and 5. Figure 2 Figure 3 I -do A2 82 C2 Figure 4 6 COPYRIGHT American Soc
48、iety for QualityLicensed by Information Handling ServicesSTD.ASQ DbL07-ENGL 1777 075750b 0002L70 027 I- D ANSI/IEC/ASQ D61078-1997 - - -0 Figure 5 On account of the statistical independence stated above, failure of any block must not give rise to change in the probability of failure of ANY other blo
49、ck within the system. In particular, failure of a dupli- cated block must not affect system power supplies or signal sources. The need frequently arises to model systems where the success definition is that rn or more of n items connected in parallel are required for system success. The block diagram then takes the form of figure 6 or figure 7. X I* X O X X X X X Figure 6 Figure 7 Thus, in figure 6, the failure of one item is tolerated but two or more are not. O Most reliability block diagrams are easily understood and the requirements for system success are evi- dent. Not all
