ISO 3951-1:2022
Sampling procedures for inspection by variables — Part 1: Specification for single sampling plans indexed by acceptance quality limit (AQL) for lot-by-lot inspection for a single quality characteristic and a single AQL
Sampling procedures for inspection by variables — Part 1: Specification for single sampling plans indexed by acceptance quality limit (AQL) for lot-by-lot inspection for a single quality characteristic and a single AQL
- Статус документа:
- Действующий
- Формат:
- Электронный (PDF)
- Количество страниц:
- 114
- Дата публикации:
- 18 августа 2022 г.
- Издание:
- ISO IS 3951 edition 3 version 1
- ICS:
- 03.120.30
This document specifies single sampling plans for lot-by-lot inspection under the following conditions: a) where the inspection procedure is applied to a continuing series of lots of discrete products, all supplied by one producer using one production process; b) where only a single quality characteristic, x, of these products is taken into consideration, which is measurable on a continuous scale; c) where production is under statistical control and the quality characteristic, x, is distributed according to a normal distribution or a close approximation to the normal distribution; d) where a contract or standard defines a lower specification limit, L, an upper specification limit, U, or both. An item is qualified as conforming if its measured quality characteristic, x, satisfies as appropriate one of the following inequalities: 1) x ≥ L (i.e. the lower specification limit is not violated); 2) x ≤ U (i.e. the upper specification limit is not violated); 3) x ≥ L and x ≤ U (i.e. neither the lower nor the upper specification limit is violated). Inequalities 1) and 2) are cases with a single specification limit, and 3) is a case with double specification limits. Where double specification limits apply, it is assumed in this document that conformity to both specification limits is equally important to the integrity of the product. In such cases, it is appropriate to apply a single AQL to the combined percentage of a product outside the two specification limits. This is referred to as combined control.
Abstract
Overview
ISO 3951-1:2022 - Sampling procedures for inspection by variables specifies single sampling plans indexed by the Acceptance Quality Limit (AQL) for lot‑by‑lot inspection of a single measurable quality characteristic. It applies when production is continuous under statistical control and the quality characteristic is (approximately) normally distributed. The standard defines how to decide lot acceptance using measured variable data and covers single and double specification limits (combined control).
Keywords: ISO 3951-1:2022, sampling procedures, inspection by variables, AQL, single sampling plans, lot-by-lot inspection, normal distribution, specification limits.
Key topics and technical requirements
- Scope conditions: a continuing series of lots from one producer/process; one continuous quality characteristic; normal (or near‑normal) distribution; defined lower and/or upper specification limits.
- Acceptance criterion: an item conforms if x ≥ L, x ≤ U, or L ≤ x ≤ U (single or double limits). For double limits, combined control treats out‑of‑spec at either tail as part of one AQL.
- Sampling plan families:
- s‑method - unknown process standard deviation estimated from sample (sample standard deviation s).
- σ‑method - assumed known process standard deviation σ.
- p*‑method - alternative approach provided in the standard.
- Switching rules: rules to move between normal, tightened, and reduced inspection based on recent inspection history - protecting consumers and incentivizing suppliers.
- Measurement uncertainty: procedures to accommodate and record measurement variability (Annex B and Clause 11).
- Normality, data transformations, outliers: guidance on assessing and handling deviations from normality (Clause 12).
- Tables and examples: comprehensive tables (Clause 14) and worked examples (Clause 15) for practical implementation.
- Monitoring and recording: requirements for process monitoring, capability assessment, and inspection recordkeeping (Clause 13).
Practical applications and users
ISO 3951-1:2022 is used to design and implement variable‑based sampling inspection programs where continuous measurements are available. Practical applications include:
- Incoming inspection and lot acceptance for manufactured parts
- Production quality control and process monitoring
- Supplier quality agreements and contractual AQL specification
- Quality audits and conformity assessment
Primary users:
- Quality engineers and statisticians
- Supplier quality and procurement teams
- Manufacturing process owners
- Compliance officers and regulatory auditors
Related standards
- ISO 3951-2 - more technical treatment of the AQL scheme (complements this part).
- ISO 2859-1 - attributes sampling standard; ISO 3951-1 includes comparisons and guidance on relations/differences.
- ISO 10576-1 - referenced for measurement error considerations.
ISO 3951-1:2022 helps organizations replace attributes sampling with statistically efficient variables sampling where appropriate, enabling smaller sample sizes, better process insight, and well‑defined consumer/producer risk control.
Технические детали
- Технический комитет
- ISO/TC 69/SC 5 - Acceptance sampling
- SKU
- ISO 3951-1:2022
Похожие стандарты
Стандарты, упомянутые в описании