CEN/TR 14547:2005
(Main)Sampling schemes for third party conformity assessment of fineness in precious metal articles
Sampling schemes for third party conformity assessment of fineness in precious metal articles
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....
Probenahmeverfahren für die Konformitätsbewertung des Feingehaltes von Gegenständen aus Edelmetall durch Dritte
Programmes d'échantillonnage pour une évaluation de la conformité du titre des ouvrages en métaux précieux par une tierce partie
Le présent Rapport technique spécifie un système d’acceptation basé sur des plans d’échantillonnage simples pour contrôle à la fois par attributs et par variables. Les plans par attributs sont de la forme zéro défaut, c’est-à-dire qu’aucun lot n’est accepté si le prélèvement contient un ou plusieurs produits non conformes. (Pour les besoins du présent Rapport technique, un produit non conforme est un ouvrage en métal précieux qui contient moins que la proportion nominale en masse du métal précieux). Les plans par variables nécessitent généralement des effectifs d’échantillon plus petits que ceux des plans par attributs, mais imposent que le titre en métal précieux de tous les ouvrages prélevés excède le titre nominal d’une quantité spécifiée minimale.
L’objectif de ce Rapport technique est de fournir des programmes et des procédures zéro-défaut permettant de garantir une limite supérieure au pourcentage à long terme d’ouvrages en métal précieux non conformes mis sur le marché (c’est-à-dire le pourcentage d’ouvrages arrivant sur le marché qui contiennent moins que la proportion nominale de métal précieux), en utilisant des effectifs d’échantillon aussi réduits que possible. La limite supérieure fournie par ce Rapport technique est un taux de non-conformité de 1,47 %. L’objectif est atteint de trois manières :
a) l’effectif d’échantillon diminue au fur et à mesure que le nombre total d’ouvrages acceptés dans l’ensemble des lots depuis le dernier rejet augmente ;
b) si la qualité est régulièrement élevée, il est possible, sous certaines conditions, de passer de l’échantillonnage par attributs à l’échantillonnage par variables ;
c) dans le cas de l’échantillonnage par variables, des réductions supplémentaires de l’effectif d’échantillon peuvent être obtenues en passant de la méthode de l’écart-type inconnu (méthode "s") à la méthode de l’écart-type connu (méthode "s") s’il existe des preuves suffisantes que l’écart-type du processus est constant.
Sheme vzorčenja za potrjevanje skladnosti čistine izdelkov iz plemenitih kovin pri tretji stranki
General Information
Standards Content (Sample)
SLOVENSKI STANDARD
01-februar-2006
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Sampling schemes for third party conformity assessment of fineness in precious metal
articles
Probenahmeverfahren für die Konformitätsbewertung des Feingehaltes von
Gegenständen aus Edelmetall durch Dritte
Programmes d'échantillonnage pour une évaluation de la conformité du titre des
ouvrages en métaux précieux par une tierce partie
Ta slovenski standard je istoveten z: CEN/TR 14547:2005
ICS:
39.060 Nakit Jewellery
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
TECHNICAL REPORT
CEN/TR 14547
RAPPORT TECHNIQUE
TECHNISCHER BERICHT
November 2005
ICS 39.060
English Version
Sampling schemes for third party conformity assessment of
fineness in precious metal articles
Méthodes d'échantillonnage pour une évaluation de Probenahmeverfahren für die Konformitätsbewertung des
conformité du titre des articles en métaux précieux par une Feingehaltes von Gegenständen aus Edelmetall durch
tierce personne Dritte
This Technical Report was approved by CEN on 8 August 2005. It has been drawn up by the Technical Committee CEN/TC 283.
CEN members are the national standards bodies of Austria, Belgium, Cyprus, Czech Republic, Denmark, Estonia, Finland, France,
Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Slovakia,
Slovenia, Spain, Sweden, Switzerland and United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
Management Centre: rue de Stassart, 36 B-1050 Brussels
© 2005 CEN All rights of exploitation in any form and by any means reserved Ref. No. CEN/TR 14547:2005: E
worldwide for CEN national Members.
Contents
Foreword .3
Section one: General.4
1 Scope.4
2 Normative references.4
3 Terms and definitions.5
4 Symbols and abbreviations.6
5 Average outgoing quality limit.7
6 Switching between attributes and variables inspection .7
7 The credit principle.8
8 Classification by weight range.8
9 Role and use of 100% inspection of non-accepted lots.8
Section two : Choice of sampling plan .10
10 Choice between attributes and variables.10
11 Choice between the "s" method and the "σ" method .10
12 Choice of constant, c, for sampling by variables .10
13 Choice of sampling plan.11
Section three : Operation of a sampling scheme .12
14 Preliminary operations.12
15 Standard procedure for sampling by attributes .12
16 Standard procedure for the "s" method.13
17 Standard procedure for the "σσσσ" method.14
18 Procedure during continuing inspection.15
19 Normality and outliers.15
19.1 Normality.15
19.2 Outliers.15
20 Records.15
20.1 Measures of location and variation .15
20.2 Results of tests for outliers and departure from normality .16
20.3 Results of tests for heterogeneity and inconsistency of sample standard deviations .16
20.4 Significant test results.16
21 Operation of switching rules.16
21.1 The start of inspection operations.16
21.2 Switching to sampling by variables.16
21.3 Switching from variables inspection to attributes inspection.16
21.4 Switching between preferred values of c.17
21.5 Discontinuation of inspection.17
22 Switching between "s" method and "σσ" method .17
σσ
22.1 Switching from the "s" method to the "σσσσ" method.17
22.2 Switching from the "σσ" method to the "s" method.17
σσ
Section four: Tables .18
Annex A (normative) Procedures for obtaining s and σσσσ.57
A.1 Procedure for obtaining s.57
A.2 Procedure for obtaining σσ .58
σσ
Annex B (normative) Likelihood ratio tests for heterogeneity and inconsistency of standard deviations.59
Bibliography.60
Foreword
This Technical Report (CEN/TR 14547:2005) has been prepared by Technical Committee CEN /TC 283, "Precious
metals - Applications in jewellery and associated products", the secretariat of which is held by UNI.
Section one: General
1 Scope
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 "σσσσ" method) if there
is sufficient evidence that the process standard deviation is constant.
This Technical Report is designed for use under conditions where:
d) articles are of a similar type, weight and nominal precious metal content, all supplied by the same supplier;
NOTE Where any of these factors differ, this Technical Report should be applied to each combination of type, weight
range, nominal precious metal content and supplier separately.
e) the cost to the supplier for marking for fineness increases with the number of articles inspected and the cost of
inspection of each article;
f) for sampling by attributes, it is possible to accurately determine whether the sampled articles are conforming or
nonconforming with regard to precious metal content;
g) for sampling by variables, the precious metal content by weight for each sampled article is measurable on a
continuous scale (usually in parts per thousand, expressed as a real number), and the precious metal content from
article to article is distributed according to a normal distribution, at least to a close approximation;
h) for sampling by variables under the "σσσσ" method, the process standard deviation is stable.
2 Normative references
The following referenced documents are indispensable for the application of this document. For dated references,
only the edition cited applies. For undated references, the latest edition of the referenced document (including any
amendments) applies.
ISO 3534-1:1993, Statistics - Vocabulary and symbols - Part 1: Probability and general statistical terms
ISO 3534-2:1993, Statistics - Vocabulary and symbols - Part 2:Statistical quality control
ISO 5479, Statistical interpretation of data - Tests for departure from the normal distribution
ISO 5725-6, Accuracy (trueness and precision) of measurement methods and results - Part 6: Use in practice of
accuracy values
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 3534-1:1993 and ISO 3534-2:1993 and
the following apply. For ease of reference, the definitions of some of these terms are quoted from these standards
while others are re-defined or newly defined.
3.1
inspection
activity such as measuring or gauging the precious metal content of an article, and comparing the results with
specified requirements in order to establish whether conformity is achieved
3.2
lot
definite collection of precious metal articles of the same type, the same approximate weight, the same nominal
precious metal content and from the same supplier
3.3
sample
a set of one or more articles taken from a lot and intended to provide information on the lot
3.4
sample size
number of articles in the sample
3.5
sampling plan
combination of sample size to be used and associated lot acceptability criteria
NOTE 1 A sampling plan does not contain the rules on how to draw the sample.
NOTE 2 There is a distinction between the terms "sampling plan" (3.5), "sampling scheme" (3.6) and "sampling
system" (3.7).
3.6
sampling scheme
combination of sampling plans with rules for changing from one plan to another
3.7
sampling system
collection of sampling plans, or of sampling schemes, each with its own rules for changing plans, together with
sampling procedures including criteria by which appropriate plans or schemes may be chosen
NOTE This Technical Report is a sampling system indexed by lot size and credit.
3.8
test portion
a quantity of material taken from an article or articles for analysis
3.9
lower specification limit, L
the nominal minimum precious metal content of an article
NOTE L will normally be expressed in terms of parts per thousand by weight.
3.10
inspection by attributes
inspection by means of which each article is classified simply as conforming or nonconforming with
...
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