ISO 3951-2:20 13规定了单个抽样计划的验收抽样系统，用于按变量进行检查。它根据验收质量限值（AQL）进行索引，具有技术性质，针对已经熟悉变量抽样或有复杂要求的用户。（在ISO 3951-1中给出了更多的介绍性处理。） ISO 3951-2:20 13中规定的方法的目的是确保质量可接受的批次具有较高的可接受概率，并且不接受劣质批次的概率尽可能高。这通过提供以下内容的切换规则来实现: 如果检测到质量恶化，对消费者的自动保护（通过切换到更严格的检查或停止抽样检查）；降低检验成本（通过改用较小的样本量）的激励措施（由主管当局自行决定）应始终实现良好的质量。 在ISO 3951-2:20 13中，一个批次的可接受性是根据该批次中项目的随机样本，根据工艺中不合格项目的百分比估计值隐含或明确确定的。 ISO 3951-2:20 13旨在应用于所有由一个生产商使用一种生产工艺提供的一系列连续批次的离散产品。如果有不同的生产商或生产工艺，ISO 3951-2:20 13分别适用于每个生产商或生产工艺。

ISO 3951-2:2013 specifies an acceptance sampling system of single sampling plans for inspection by variables. It is indexed in terms of the acceptance quality limit (AQL) and is of a technical nature, aimed at users who are already familiar with sampling by variables or who have complicated requirements. (A more introductory treatment is given in ISO 3951-1.) The objectives of the methods laid down in ISO 3951-2:2013 are to ensure that lots of an acceptable quality have a high probability of acceptance and that the probability of not accepting inferior lots is as high as practicable. This is achieved by means of the switching rules, which provide the following:

• automatic protection to the consumer (by means of a switch to tightened inspection or discontinuation of sampling inspection) should a deterioration in quality be detected;
• an incentive (at the discretion of the responsible authority) to reduce inspection costs (by means of a switch to a smaller sample size) should consistently good quality be achieved.

In ISO 3951-2:2013, the acceptability of a lot is either implicitly or explicitly determined from an estimate of the percentage of nonconforming items in the process, based on a random sample of items from the lot. ISO 3951-2:2013 is intended for application to a continuing series of lots of discrete products all supplied by one producer using one production process. If there are different producers or production processes, ISO 3951-2:2013 is applied to each one separately.