CEN/TR 14547:2005

Foreword
Section one: General
1 Scope
2 Normative references
3 Terms and definitions
4 Symbols and abbreviations
5 Average outgoing quality limit
6 Switching between attributes and variables inspection
7 The credit principle
8 Classification by weight range
9 Role and use of 100% inspection of non-accepted lots
Section two: Choice of sampling plan
10 Choice between attributes and variables
11 Choice between the "s" method and the "sigma" method
12 Choice of constant, c, for sampling by variables
13 Choice of sampling plan
Section three: Operation of a sampling scheme
14 Preliminary operations
15 Standard procedure for sampling by attributes
16 Standard procedure for the "s" method
17 Standard procedure for the "sigma" method
18 Procedure during continuing inspection
19 Normality and outliers
   19.1 Normality
   19.2 Outliers
20 Records
   20.1 Measures of location and variation
   20.2 Results of tests for outliers and departure from normality
   20.3 Results of tests for heterogeneity and inconsistency of
        sample standard deviations
   20.4 Significant test results
21 Operation of switching rules
   21.1 The start of inspection operations
   21.2 Switching to sampling by variables
   21.3 Switching from variables inspection to attributes inspection
   21.4 Switching between preferred values of c
   21.5 Discontinuation of inspection
22 Switching between "s" method and "sigma" method
   22.1 Switching from the "s" method to the "sigma" method
   22.2 Switching from the "sigma" method to the "s" method
Section four: Tables
Annex A (normative) Procedures for obtaining s and sigma
      A.1 Procedure for obtaining s
      A.2 Procedure for obtaining sigma
Annex B (normative) Likelihood ratio tests for heterogeneity
        and inconsistency of standard deviations
Bibliography

This Technical Report specifies an acceptance sampling system of single sampling plans both for inspection by attributes and for inspection by variables. The attributes plans are of the accept-zero form, i.e. no lot is accepted if the sample from it contains one or more nonconforming articles. (For the purposes of this Technical Report, a nonconforming article is a precious metal article containing less than the nominal proportion by weight of the precious metal). The variables plans generally require smaller sample sizes than the attributes plans, but require the precious metal content of all the sampled articles to exceed the nominal content by at least a specified amount.The objective of this Technical Report is to provide accept-zero schemes and procedures for assuring an upper limit to the long-term percentage of nonconforming precious metal articles in the market place (i.e. the percentage of articles reaching the market place that contain less than the nominal proportion of precious metal) by means of the lowest practicable sample sizes. The upper limit provided by this Technical Report is 1,47% nonconforming. The objective is achieved in three ways:a)the sample size reduces as the total number of articles accepted in all the lots since the last non-acceptance increases;b)if quality is consistently high, then subject to certain conditions it will be possible to switch from sampling by attributes to sampling by variables;c)under sampling by variables, further reductions in sample size may be achieved by switching from the unknown standard deviation method (the "s" method) to the known standard deviation method (the "s" method) if there is sufficient evidence that the process standard deviation is constant....