计量抽样检验程序.第4部分:声明质量水平的评定程序

[中文适用范围]： 本部分ISO 3951建立了通过变量抽样的抽样计划和程序，可用于评估实体（批次、过程等）的质量水平是否符合声明的值。抽样计划的设计使其操作特性曲线尽可能接近ISO 2859-4中相应属性计划的曲线，因此选择使用属性抽样还是变量抽样不会受到试图增加接受错误声明质量水平的机会的影响。在本部分ISO 3951中，存在1.4%至82%的风险来反驳正确的声明质量水平。存在10%的风险未能反驳错误的声明质量水平，这与限制质量比相关（见第4条）。提供了对应于三种辨别能力水平的抽样计划，以及过程标准差未知和已知的情况。 [外文原描述]： ISO 3951-4:2011 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. 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 ISO 3951-4:2011 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. ISO 3951-4:2011 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 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; 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.