1、 Reference number ISO/TR 8550-2:2007(E) ISO 2007TECHNICAL REPORT ISO/TR 8550-2 First edition 2007-10-15 Guidance on the selection and usage of acceptance sampling systems for inspection of discrete items in lots Part 2: Sampling by attributes Lignes directrices pour la slection dun systme, dun progr
2、amme ou dun plan dchantillonnage pour acceptation pour le contrle dunits discrtes en lots Partie 2: chantillonnage par attributs ISO/TR 8550-2:2007(E) PDF disclaimer This PDF file may contain embedded typefaces. In accordance with Adobes licensing policy, this file may be printed or viewed but shall
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7、47 E-mail copyrightiso.org Web www.iso.org Published in Switzerland ii ISO 2007 All rights reservedISO/TR 8550-2:2007(E) ISO 2007 All rights reserved iiiContents Page Foreword iv Introduction v 1 Scope 1 2 Normative references 1 3 Selection process 2 4 International Standards for acceptance sampling
8、 of lots by attributes.2 5 Effect on the selection process of market and production conditions6 Bibliography 14 ISO/TR 8550-2:2007(E) iv ISO 2007 All rights reservedForeword ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies (ISO member bo
9、dies). The work of preparing International Standards is normally carried out through ISO technical committees. Each member body interested in a subject for which a technical committee has been established has the right to be represented on that committee. International organizations, governmental an
10、d non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization. International Standards are drafted in accordance with the rules given in the ISO/IEC Directives,
11、 Part 2. The main task of technical committees is to prepare International Standards. Draft International Standards adopted by the technical committees are circulated to the member bodies for voting. Publication as an International Standard requires approval by at least 75 % of the member bodies cas
12、ting a vote. In exceptional circumstances, when a technical committee has collected data of a different kind from that which is normally published as an International Standard (“state of the art”, for example), it may decide by a simple majority vote of its participating members to publish a Technic
13、al Report. A Technical Report is entirely informative in nature and does not have to be reviewed until the data it provides are considered to be no longer valid or useful. Attention is drawn to the possibility that some of the elements of this document may be the subject of patent rights. ISO shall
14、not be held responsible for identifying any or all such patent rights. ISO/TR 8550-2 was prepared by Technical Committee ISO/TC 69, Applications of statistical methods, Subcommittee SC 5, Acceptance sampling. This first edition of ISO/TR 8550-2, together with ISO/TR 8550-1 and ISO/TR 8550-3, cancels
15、 and replaces ISO/TR 8550:1994. ISO/TR 8550 consists of the following parts, under the general title Guidance on the selection and usage of acceptance sampling systems for inspection of discrete items in lots: Part 1: Acceptance sampling Part 2: Sampling by attributes Part 3: Sampling by variables I
16、SO/TR 8550-2:2007(E) ISO 2007 All rights reserved vIntroduction This part of ISO/TR 8550 gives guidance on the selection of a generic acceptance sampling system, scheme or plan for inspection by attributes from those developed by ISO/TC 69. It does this principally by reviewing the available systems
17、 specified by various standards and by showing ways in which these can be compared to assess their suitability for an intended application. It is assumed that the choice has already been made to use sampling by attributes in preference to sampling by variables. A corresponding guidance document on t
18、he selection of a generic acceptance sampling system, scheme or plan for inspection by variables is given in ISO/TR 8550-3. TECHNICAL REPORT ISO/TR 8550-2:2007(E) ISO 2007 All rights reserved 1 Guidance on the selection and usage of acceptance sampling systems for inspection of discrete items in lot
19、s Part 2: Sampling by attributes 1 Scope The guidance given in this part of ISO/TR 8550 is confined to acceptance sampling of products that are supplied in lots and that can be classified as consisting of discrete items (i.e. discrete articles of product). Each item in a lot can be identified and se
20、gregated from the other items in the lot and has an equal chance of being included in the sample. Each item of product is countable and has specific characteristics that are measurable or classifiable as being conforming or nonconforming (to a given specification). Standards on acceptance sampling b
21、y attributes are applicable to a wide variety of inspection situations. These include, but are not limited to, the following: a) end items, such as complete products or sub-assemblies; b) components and raw materials; c) services; d) materials in process; e) supplies in storage; f) maintenance opera
22、tions; g) data or records; h) administrative procedures. Although this part of ISO/TR 8550 is written principally in terms of manufacture and production, it is applicable to the selection of sampling systems, schemes and plans for all types of product and processes as defined in ISO 9000. 2 Normativ
23、e references The following referenced documents are indispensable for the application of this document. For dated references, only the edition listed applies. For undated references, the latest edition of the referenced document (including any amendment) applies. ISO/TR 8550-1:2007, Guidance on the
24、selection and usage of acceptance sampling systems for inspection of discrete items in lots Part 1: Acceptance sampling ISO/TR 8550-2:2007(E) 2 ISO 2007 All rights reserved3 Selection process The task of selecting a suitable sampling system, scheme or plan is influenced by production and marketing c
25、onditions. In addition, the economics of the sampling system, the resources of the inspection organization and other aspects need to be considered. Therefore, the selection process becomes complex and rarely is there one method of acceptance sampling that fits all situations even though they might a
26、ppear to be similar. Tables 1, 2 and 3, together with Figures 1 and 2, illustrate the process of selecting a sampling system, scheme or plan. The tables provide “candidate” sampling systems, schemes and plans to fit given inspection situations, production conditions and market conditions, respective
27、ly. The method suggested is to review Tables 1, 2 and 3 and to select as many “candidate plans” as fit the situation. These candidates should then be reviewed through Figure 1 or 2 so that the user finally arrives at a system, scheme or plan that is most feasible and economical for the situation. Th
28、e initial selection decisions are for long and short production runs, isolated lots, and attribute or variables sampling; these decisions will point to one or more possible sampling schemes specified in standards. Figures 1 and 2 are not flow charts. They show, in summary form, the procedures contai
29、ned within each standard for arriving at a sampling system, scheme or plan. The summaries are listed side by side, which allows direct comparison between them. The solid connecting lines indicate the primary course to be followed in choosing and operating a standard; the broken lines indicate altern
30、atives. These alternatives are applicable only under certain conditions. Text references and notes to the figures are given for guidance in following these procedures. The standards and procedures given below the horizontal line in each of the two figures are for use when economy of average sample s
31、ize is an important consideration. The procedure presented in Figure 1 is applicable when production is continuous and there are more than 10 lots of product undergoing inspection. International Standards from the ISO 2859 series are included here as “candidate systems”. Figure 2 is applicable when
32、other conditions prevail, e.g. when there is no continuity of production, when the number of lots is 10 or fewer, when the product warranty does not survive acceptance and/or when the presence of a small number of nonconforming items can result in a large loss. A final selection should be based on b
33、oth the requirements of the situation and the resources of the inspection organization. When selecting a sampling system, scheme or plan, it may become apparent that it has one or more deficiencies. The cases in which only one method is appropriate are few. Iterative investigations usually identify
34、two or more methods. The most economical and appropriate method should be chosen. 4 International Standards for acceptance sampling of lots by attributes 4.1 General This clause summarizes the salient features of each of the current standards concerned with acceptance sampling methods by attributes.
35、 The summaries of the scope and application of the available standards should enable a user to select those standards which are most likely to suit a given purpose. The comparisons between the various standard acceptance sampling systems in these summaries are not enough to allow a final selection o
36、f a sampling system, scheme or plan to be made in a particular situation. Before this can be done, a number of factors need to be understood and considered. These factors are reviewed in Clause 5. ISO/TR 8550-2:2007(E) ISO 2007 All rights reserved 3 4.2 ISO 2859 1: Sampling procedures for inspection
37、 by attributes Part 1: Sampling schemes indexed by acceptance quality limit (AQL) for lot-by-lot inspection This presents a sampling system indexed by lot-size ranges, inspection levels and AQLs, and specifies sampling plans and procedures for inspection by attributes of discrete items. It contains
38、sampling plans for single, double and multiple sampling indexed by percent nonconforming and nonconformities per 100 items. The sampling system specified in ISO 2859-1 is intended to employ tightened, normal and reduced inspection on a continuing series of lots to achieve customer protection while a
39、ssuring the producer that, if quality is better than the AQL, acceptance will occur most of the time. The objective is to maintain a process average quality at least as good as the AQL that has been agreed between the producer and the consumer, while at the same time providing an upper limit for the
40、 risk to the consumer of accepting the occasional lot of poor quality. The sampling plans in ISO 2859-1 may also be used for the inspection of lots in isolation, but in this case the user is strongly advised to consult the operating characteristic curves (in Table 12 of ISO 2859-1:1999) to find a pl
41、an which will yield the desired protection. A much simpler procedure to follow in this type of situation is presented in ISO 2859-2. 4.3 ISO 2859-2: Sampling procedures for inspection by attributes Part 2: Sampling plans indexed by limiting quality (LQ) for isolated lot inspection This establishes s
42、ampling plans indexed by limiting quality (LQ) and procedures for inspection that can be used when the switching rules of ISO 2859-1 cannot be applied. The LQ is used to indicate the customer protection. Procedure A is used for single lots and procedure B for lots isolated from a continuing series.
43、Both procedures treat the LQ as an indicator of the actual percentage nonconforming in the lots submitted, though they can also be used in cases where quality is expressed in non-conformities per 100 items. Procedure A is used when both the supplier and the customer wish to regard the lot in isolati
44、on, but it is also used as the default procedure where there is no specific instruction to use procedure B. Procedure B is used when the supplier regards the lot as one of a continuing series, but the customer considers the lot received in isolation. The sampling plans employed permit a producer to
45、maintain consistent procedures for customers, irrespective of whether the customers receive individual lots or a continuing series of lots. The manufacturer is concerned with all of the production but the individual customer only with the particular lot received. For procedure A, sampling plans are
46、identified by their lot size and LQ; for procedure B, they are identified by lot size, LQ and inspection level. Procedure A includes sampling plans with an acceptance number of zero, but these are excluded from procedure B. Double and multiple sampling plans can be used as alternatives to single sam
47、pling plans in procedure B and for the non-zero acceptance number plans in procedure A. 4.4 ISO 2859-3: Sampling procedures for inspection by attributes Part 3: Skip-lot sampling procedures This specifies a sampling system that extends the procedures specified in ISO 2859-1. It provides generic attr
48、ibute skip-lot sampling procedures, for reducing the inspection effort on products submitted by suppliers who have demonstrated their ability to control, in an effective manner, all facets of product quality and to produce superior quality material consistently. However, the standard proscribes thes
49、e procedures for the inspection of product characteristics that involve the safety of personnel. The skip-lot programme uses the acceptance sampling plans specified in ISO 2859-1 and is intended only for a continuing series of lots; it is not appropriate for isolated lots. All lots in a series are expected to be of a similar quality and there should be no reason to believe that lots that have not been inspected are of a poorer quality than those that have. ISO/TR 8550-2:2007(E) 4 ISO 2007 All rights reservedIn a skip-lo
