Modified:
Let’s take a look at the new ISO 3951-1 and ISO 3951-2 revisions for Sampling Procedures for Inspection by Variables today. These two standards were just revised so a new 2nd Edition is available for each of them. They are part of a 5-part series on the topic. We’ll review each new revision separately.
ISO 3951-1, 2nd Edition, 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
The new ISO 3951-1 2013 Edition is a minor revision of the previous ISO 3951-1 2006 publication. Measurement uncertainty is now accommodated by new procedures. And sampling plans have been adjusted to better match the operating characteristic curves of the corresponding ISO 2859-1 sampling by attributes standard.
ISO 3951-2, 2nd Edition, Sampling procedures for inspection by variables – Part 2: General specification for single sampling plans indexed by acceptance quality limit (AQL) for lot-by-lot inspection of independent quality characteristics
Again, this 2013 Edition replaces the ISO 3951-2 2006 Edition (plus the Amendment 1) which is now obsolete. And the changes are based on the same issues — measurement uncertainty and harmonization with ISO 2859-1.
The ISO 3951 series defines a sampling system using inspection by variables. This is a schema with fairly simple requirements, using a “switching rules” methodology to ensure that lots of acceptable quality are likely to pass QC and inferior lots are not. Lot quality is determined by estimating the percentage of nonconforming material by random sampling of item from the lot. The trick is to move to a tightened form of inspection should any deterioration of quality be found.
Part 1 deals with just one producer using one production process, for a single quality characteristic measurable on a continuous scale. Part 2 covers two or more such quality characteristics.
The other parts of the series are:
- ISO 3951-3, 1st Edition, Sampling Procedures for Inspection by Variables – Part 3: Double Sampling Schemes Indexed by Acceptance Quality Limit (AQL) for Lot-By-Lot Inspection
- ISO 3951-4, 1st Edition, Sampling Procedures for Inspection by Variables – Part 4: Procedures for Assessment of Declared Quality Levels
- ISO 3951-5, 1st Edition, Sampling Procedures for Inspection by Variables – Part 5: Sequential Sampling Plans Indexed by Acceptance Quality Limit (AQL) for Inspection by Variables (Known Standard Deviation)
Because there is no draft activity for Parts 3, 4 or 5, I believe that they are stable for the time being.
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