ISO 3951-6:2023
Sampling procedures for inspection by variables — Part 6: Specification for single sampling plans for isolated lot inspection indexed by limiting quality (LQ)
Sampling procedures for inspection by variables — Part 6: Specification for single sampling plans for isolated lot inspection indexed by limiting quality (LQ)
- Статус документа:
- Действующий
- Формат:
- Электронный (PDF)
- Количество страниц:
- 80
- Дата публикации:
- 1 декабря 2023 г.
- Издание:
- ISO IS 3951 edition 1 version 1
- ICS:
- 03.120.30
This document specifies an acceptance sampling system of single sampling plans for inspection by variables, primarily designed for use under the following conditions: a) where the inspection procedure is applied to an isolated lot of discrete products all supplied by one producer using one production process; b) where only a single quality characteristic, x, of this process is taken into consideration, which is measurable on a continuous scale; c) where the quality characteristic, x, is distributed according to a normal distribution or a close approximation to a normal distribution; d) where the quality characteristic can be measured without error or with moderate measurement error; e) 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 and only if its measured quality characteristic, x, satisfies the 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, whereas inequality 3) is a case with double specification limits. Where double specification limits apply, it is assumed in this document that conformance to both specification limits is equally important to the integrity of the product. In such cases, it is appropriate to apply a single LQ to the combined fraction of a product outside the two specification limits. This is referred to as combined control.
Abstract
Overview - ISO 3951-6:2023 (Sampling procedures for inspection by variables)
ISO 3951-6:2023 specifies single sampling plans for inspection by variables indexed by limiting quality (LQ), intended for isolated lot inspection. It provides an acceptance sampling system where a single, continuous quality characteristic x is measured and assumed to follow a normal (or near-normal) distribution. The standard covers cases with a single specification limit (lower or upper) or double specification limits (combined control), and is designed for situations where the switching rules of ongoing inspection (ISO 3951-1) are not applicable - for example, isolated lots or short production runs.
Key topics and technical requirements
- Scope and assumptions
- One quality characteristic measurable on a continuous scale.
- Normality assumption (or close approximation).
- Measurement error negligible or moderate (Annex B addresses measurement uncertainty).
- Plan types
- s-method (unknown standard deviation estimated from sample).
- σ-method (presumed known process standard deviation).
- p-method* for approximations and specific operational needs.
- Indexing and objective
- Plans are indexed by Limiting Quality (LQ) - designed so lots at LQ have ~10% probability of acceptance.
- Acceptance is based on an estimate of the fraction nonconforming from the sample.
- Practical procedures and tools
- Tables for plan selection (Clause 12) and worked examples (Clause 13).
- Guidance on choice between variables vs attributes, data transformations, handling outliers, and constructing acceptance diagrams (Annex H).
- Operating characteristic (OC) curves and relations to attributes plans (ISO 2859-2).
- Software support: R package “ISO 3951” (Annex I) to implement plans and compute OC curves.
- Risk and quality analysis
- Annexes with operating characteristics, consumer’s risk, producer’s risk quality and strategies for sampling.
Applications and who uses it
- Quality engineers, statisticians, and inspectors performing acceptance sampling on isolated lots (e.g., one-off shipments, pilot batches).
- Procurement, suppliers, and conformity assessment bodies needing objective single-lot acceptance criteria indexed by LQ.
- Laboratories and manufacturers measuring a continuous quality attribute (dimension, strength, content) where normality holds.
- Useful when switching rules for ongoing inspection are not possible or not desired.
Related standards
- ISO 3951-1 (variables plans with switching rules)
- ISO 2859-2 (attributes plans indexed by LQ for isolated lots) - OC curve comparisons
- ISO 2859-1 and ISO 3534 (statistical vocabulary and symbols)
Keywords: ISO 3951-6:2023, sampling procedures, inspection by variables, limiting quality LQ, single sampling plans, isolated lot inspection, s-method, σ-method, p*-method, acceptance sampling, OC curves, measurement uncertainty.
Технические детали
- Технический комитет
- ISO/TC 69/SC 5 - Acceptance sampling
- SKU
- ISO 3951-6:2023
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