ISO INTERNATIONAL STANDARD 3951-3 First edition 2007-05-01 Sampling procedures for inspection by variables Part 3: Double sampling schemes indexed by acceptance quality limit (AQL) for lot-by-lot inspection Regles d'échantillonnage pour les controles parmesures Partie 3: Plans d'échantillonnage doubles pour le controle lot par lot, indexés d'apres le niveau de qualité acceptable (NQA) Reference number ISO 3951-3:2007(E) @ ISO 2007 ISO 3951-3:2007(E) Contents Page Foreword Introduction vi 1 Scope 2 Normative references 3 Terms and definitions 4 Symbols and abbreviations... 5 Acceptance quality limit (AQL).. 6 Switching rules for normal, tightened and reduced inspection 10 7 Relation to ISO 2859-1. 10 8 Limiting quality protection. 11 9 Planning. 12 10 Choice between variables and attributes ... 12 11 Choice of method... 12 Choice between single and double sampling plans . 13 Choice of inspection level and AQL 14 14 Choice of sampling scheme 14 15 Preliminary operations.. 15 16 Standard univariate "'s" method procedures.... 17 Standard univariate “"" method procedures.. 25 18 Procedure during continuing inspection .... 19 Normality and outliers.... 20 Records. 21 Operation of switching rules. 33 22 Discontinuation and resumption of inspection . 23 Switching between the “"s" and "" methods.. Annex A (informative) Standard multivariate “"s" method procedures for double sampling with independentqualitycharacteristics... Annex B (informative) Standard multivariate “" method procedures for double sampling with independent quality characteristics ..... .74 Annex C (informative) Standard multivariate combined “"s" and “"" method procedures for double sampling with independent quality characteristics .... Annex D (informative) Location of text on key features. 78 Annex E (normative) Estimating the process fraction nonconforming.. Annex F (informative) Form k “s" method single sampling plans matched to the corresponding single sampling plans by attributes. .87 ii ISO 3951-3:2007(E) single sampling plans by attributes.. ..91 Annex H (informative) Average sample sizes for double sampling by variables: “"s" method... ....95. Annex I (informative) Producer's risks for the “"s" method ... ....98 Annex J (informative) Tabulated operating characteristics for double sampling plans with known process standard deviation .... Annex K (informative) Ratios of Assls of double sampling plans under normal inspection to the sample size of the corresponding single sampling plan by variables .. Annex L (informative) Ratios of the AsSls of double sampling plans by variables to the AsSls of corresponding plans by attributes... Annex M (informative) Design methodology . Bibliography ... iv @ Is0 2007-All rights reserved ISO3951-3:2007(E) Foreword IsO (the International Organization for Standardization) is a worldwide federation of national standards bodies technicalcommittees.Eachmemberbodyinterestedinasubjectforwhichatechnicalcommitteehasbeer International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization. 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 casting a vote. Attentionisdrawntothepossibilitythatsomeoftheelementsofthisdocumentmaybethesubjectofpatent rights. IsO shall not be held responsible for identifying any or all such patent rights. ISO 3951-3 was prepared by Technical Committee ISO/TC 69, Applications of statistical methods, Subcommittee sc 5, Acceptance sampling. Iso 3951 consists of the following parts, under the general title Sampling procedures for inspection by variables: inspection for a single quality characteristic and a single AQL Part 2: General specification for single sampling plans indexed by acceptance quality limit (AQL) for lot by-lot inspection of independen