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BS ISO 3951-4:2011

BS ISO 3951-4:2011

$167.15

Sampling procedures for inspection by variables – Procedures for assessment of declared quality levels

Published By Publication Date Number of Pages
BSI 2011 36
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This part of ISO 3951 establishes sampling plans and procedures by variables that can be used to assess whether the quality level of an entity (lot, process, etc.) conforms to a declared value. The sampling plans have been devised so that their operating characteristic curves match those of the corresponding attributes plans in ISO 2859-4 as closely as possible, so that the choice between using sampling by attributes and sampling by variables is not influenced by attempts to increase the chance of accepting an incorrectly declared quality level. In this part of ISO 3951, there is a risk of between 1,4 % and 8,2 % of contradicting a correct declared quality level. The risk is 10 % of failing to contradict an incorrect declared quality level which is related to the limiting quality ratio (see Clause 4). Sampling plans are provided corresponding to three levels of discriminatory ability, and for the cases of unknown and known process standard deviation.

In contrast to the procedures in the other parts of ISO 3951, the procedures in this part of ISO 3951 are not applicable to acceptance assessment of lots. Generally, the balancing of the risks of reaching incorrect conclusions in assessment procedures will differ from the balancing in the procedures for acceptance sampling.

This part of ISO 3951 may be used for various forms of quality inspection in situations where objective evidence of conformity to some declared quality level is to be provided by means of inspection of a sample. The procedures are applicable to entities such as lots, process output, etc. that allow random samples of individual items to be taken from the entity.

The sampling plans provided in this part of ISO 3951 are applicable, but not limited, to inspection of a variety of products such as

  • end items,

  • components and raw materials,

  • operations,

  • materials in process,

  • supplies in storage,

  • maintenance operations,

  • data or records, and

  • administrative procedures.

The procedures are intended to be used when the quality characteristics are measurable variables that are independent and normally distributed, and where the quantity of interest is the fraction of items that are nonconforming.

PDF Catalog

PDF Pages PDF Title
9 Scope
10 Normative references
Terms, definitions, symbols and abbreviations
Terms and definitions
Symbols and abbreviated terms
11 Principles
12 Declared quality level (DQL)
13 Sampling plans
LQR (limiting quality ratio) levels
Level I
14 Level II
Level III
15 Selection of an “s” method sampling plan
16 Selection of a “(” method sampling plan
Operating a sampling plan
Sample selection
Rules for contradicting a declared quality level: “s” method
General
Single specification limit
17 Double specification limits under combined control
18 Double specification limits under separate control
Double specification limits under complex control
19 Multivariate “s” method for independent quality characterist

General

20 Single specification limit
Double specification limits under combined control
21 Double specification limits under separate control
Double specification limits under complex control
22
23 Disposition of nonconforming items
Further information
Curves showing approximate probability of contradiction
Tables indicating discriminatory ability

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BS ISO 3951-4:2011
$167.15