ISO/FDIS 13909-7
(Main)Coal and coke — Mechanical sampling — Part 7: Methods for determining the precision of sampling, sample preparation and testing
Coal and coke — Mechanical sampling — Part 7: Methods for determining the precision of sampling, sample preparation and testing
In ISO 13909-7:2016, formulae are developed which link the variables that contribute to overall sampling precision. Methods are described for estimating overall precision and for deriving values for primary increment variance which can be used to modify the sampling scheme to change the precision. Methods for checking the variance of sample preparation and testing are also described.
Charbon et coke — Échantillonnage mécanique — Partie 7: Méthodes pour la détermination de la fidélité de l'échantillonnage, de la préparation de l'échantillon et de l'essai
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ISO/TC 27/SC 4
Coal and coke — Mechanical
Secretariat: SABS
sampling —
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2025-04-21
Part 7:
Methods for determining the
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precision of sampling, sample
preparation and testing
Charbon et coke — Échantillonnage mécanique —
Partie 7: Méthodes pour la détermination de la fidélité de
l'échantillonnage, de la préparation de l'échantillon et de l'essai
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FINAL DRAFT
International
Standard
ISO/TC 27/SC 4
Coal and coke — Mechanical
Secretariat: SABS
sampling —
Voting begins on:
Part 7:
Methods for determining the
Voting terminates on:
precision of sampling, sample
preparation and testing
Charbon et coke — Échantillonnage mécanique —
Partie 7: Méthodes pour la détermination de la fidélité de
l'échantillonnage, de la préparation de l'échantillon et de l'essai
RECIPIENTS OF THIS DRAFT ARE INVITED TO SUBMIT,
WITH THEIR COMMENTS, NOTIFICATION OF ANY
RELEVANT PATENT RIGHTS OF WHICH THEY ARE AWARE
AND TO PROVIDE SUPPOR TING DOCUMENTATION.
© ISO 2025
IN ADDITION TO THEIR EVALUATION AS
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BEING ACCEPTABLE FOR INDUSTRIAL, TECHNO-
LOGICAL, COMMERCIAL AND USER PURPOSES, DRAFT
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
INTERNATIONAL STANDARDS MAY ON OCCASION HAVE
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TO BE CONSIDERED IN THE LIGHT OF THEIR POTENTIAL
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TO BECOME STAN DARDS TO WHICH REFERENCE MAY BE
MADE IN NATIONAL REGULATIONS.
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Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland Reference number
ii
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 General . 1
5 Formulae relating to factors affecting precision. 2
5.1 General .2
5.2 Sampling .3
6 Estimation of primary increment variance . 4
6.1 Direct determination of individual primary increments .4
6.2 Determination using the estimate of precision .5
7 Methods for estimating precision . 5
7.1 General .5
7.2 Duplicate sampling with twice the number of increments .5
7.3 Duplicate sampling during routine sampling.8
7.4 Alternatives to duplicate sampling .9
7.5 Precision adjustment procedure .9
8 Calculation of precision . 10
8.1 Replicate sampling .10
8.2 Normal sampling scheme .11
9 Methods of checking sample preparation and testing errors .12
9.1 General . 12
9.2 Target value for variance of sample preparation and analysis . 12
9.2.1 General . 12
9.2.2 Off-line preparation . 13
9.2.3 On-line preparation . 13
9.3 Checking procedure as a whole . 13
9.4 Checking stages separately .14
9.4.1 General .14
9.4.2 Procedure 1 . 15
9.4.3 Procedure 2 .18
9.4.4 Interpretation of results .21
9.5 Procedure for obtaining two samples at each stage . 22
9.5.1 With a riffle . 22
9.5.2 With a mechanical sample divider . 22
9.6 Example . 22
Annex A (informative) Variogram method for determining variance .26
[2]
Annex B (informative) Grubbs' estimators method for determining sampling precision.33
Bibliography .42
iii
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out through
ISO technical committees. Each member body interested in a subject for which a technical committee
has been established has the right to be represented on that committee. International organizations,
governmental and non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely
with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are described
in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the different types
of ISO document should be noted. This document was drafted in accordance with the editorial rules of the
ISO/IEC Directives, Part 2 (see www.iso.org/directives).
ISO draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed patent
rights in respect thereof. As of the date of publication of this document, ISO had not received notice of (a)
patent(s) which may be required to implement this document. However, implementers are cautioned that
this may not represent the latest information, which may be obtained from the patent database available at
www.iso.org/patents. ISO shall not be held responsible for identifying any or all such patent rights.
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and expressions
related to conformity assessment, as well as information about ISO's adherence to the World Trade
Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 27, Coal and coke, Subcommittee SC 4, Sampling.
This third edition cancels and replaces the second edition (ISO 13909-7:2016), which has been technically
revised.
The main changes are as follows:
— references have been updated;
— the results discussed in Clause B.4 have been clarified.
A list of all parts in the ISO 13909 series can be found on the ISO website.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.
iv
Introduction
Two different situations are considered when a measure of precision is required. In the first, an estimate is
made of the precision that can be expected from an existing sampling scheme and, if this is different from that
desired, adjustments are made to correct it. In the second, the precision that is achieved on a particular lot
is estimated from the experimental results actually obtained using a specifically designed sampling scheme.
The formulae developed in this document are based on the assumption that the quality of the fuel varies
in a random manner throughout the mass being sampled and that the observations will follow a normal
distribution. Neither of these assumptions are strictly correct. Although the assumption that observations
will follow a normal distribution is not strictly correct for some fuel parameters, this deviation from assumed
conditions will not materially affect the validity of the formulae developed for precision checking since the
statistics used are not very sensitive to non-normality. Strictly speaking, however, confidence limits will
not always be symmetrically distributed about the mean. For most practical uses of precision, however, the
errors are not significant.
In this document, the term “fuel” is used where t
...
Date: 2025-02-20
ISO/TC 27/SC 4
Secretariat: SABS
Date: 2025-04-04
Coal and coke — Mechanical sampling — —
Part 7:
Methods for determining the precision of sampling, sample
preparation and testing
HouilleCharbon et coke — Échantillonnage mécanique —
Partie 7: Méthodes pour la détermination de la fidélité de l'échantillonnage, de la préparation de l'échantillon
et de l'essai
FDIS stage
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication
may be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying,
or posting on the internet or an intranet, without prior written permission. Permission can be requested from either ISO
at the address below or ISO'sISO’s member body in the country of the requester.
ISO Copyright Officecopyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: + 41 22 749 01 11
Email: E-mail: copyright@iso.org
Website: www.iso.org
Published in Switzerland.
ii
Contents Page
Foreword . iv
Introduction . vi
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 General. 2
5 Formulae relating to factors affecting precision . 3
6 Estimation of primary increment variance . 4
7 Methods for estimating precision . 5
8 Calculation of precision . 12
9 Methods of checking sample preparation and testing errors . 14
Annex A (informative) Variogram method for determining variance . 32
[ ]
Annex B (informative) Grubbs' estimators method 2 for determining sampling precision . 41
Bibliography . 50
iii
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out through
ISO technical committees. Each member body interested in a subject for which a technical committee has been
established has the right to be represented on that committee. International organizations, governmental and
non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the
International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are described
in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the different types of
ISO document should be noted. This document was drafted in accordance with the editorial rules of the
ISO/IEC Directives, Part 2 (see www.iso.org/directives).
ISO draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed patent rights
in respect thereof. As of the date of publication of this document, ISO had not received notice of (a) patent(s)
which may be required to implement this document. However, implementers are cautioned that this may not
represent the latest information, which may be obtained from the patent database available at
www.iso.org/patents. ISO shall not be held responsible for identifying any or all such patent rights.
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and expressions
related to conformity assessment, as well as information about ISO's adherence to the World Trade
Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 27, Coal and coke, Subcommittee SC 4, Sampling.
This third edition cancels and replaces the second edition (ISO 13909--7:2016), which has been technically
revised.
The main changes are as follows:
—
— — references have been updated;
— — the results discussed in Clause B.4Clause B.4 have been clarified.
— —
A list of all parts in the ISO 13909 series can be found on the ISO website.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.
iv
fIntroduction
v
Introduction
Two different situations are considered when a measure of precision is required. In the first, an estimate is
made of the precision that can be expected from an existing sampling scheme and, if this is different from that
desired, adjustments are made to correct it. In the second, the precision that is achieved on a particular lot is
estimated from the experimental results actually obtained using a specifically designed sampling scheme.
The formulae developed in this document are based on the assumption that the quality of the fuel varies in a
random manner throughout the mass being sampled and that the observations will follow a normal
distribution. Neither of these assumptions isare strictly correct. Although the assumption that observations
will follow a normal distribution is not strictly correct for some fuel parameters, this deviation from assumed
conditions will not materially affect the validity of the formulae developed for precision checking since the
statistics used are not very sensitive to non-normality. Strictly speaking, however, confidence limits will not
always be symmetrically distributed about the mean. For most practical uses of precision, however, the errors
are not significant.
n the textIn this document, the term “fuel” is used where the method is applicable to both coal and coke and
either “coal” or “coke” where the method is exclusively applicable to that commodity.
vi
FINAL DRAFT International Standard ISO/FDIS 13909-7:2025(en)
Coal and coke- — Mechanical sampling – —
Part 7:
Methods for determining the precision of sampling, sample
preparation and testing
1 Scope
This document defines methods for estimating overall precision and for deriving values for primary increment
variance which can be used to modify the sampling scheme to change the precision. Methods for checking the
variance of sample preparation and testing are also described.
In this document, formulae are developed which link the variables that contribute to overall sampling
precision.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content constitutes
requirements 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 13909--1, Coal and coke — Mechanical sampling — Part 1: General introduction
1)
ISO 13909--2,:— , Coal and coke — Mechanical sampling — Part 2: Sampling of coal from moving streams
ISO 13909--3, Coal and coke — Mechanical sampling — Part 3: Sampling of coal from stationary lots
ISO 13909--4, Coal and coke — Mechanical sampling — Part 4: Preparation of test samples of coal
ISO 13909--5, Coal and coke — Mechanical sampling — Part 5: Sampling of coke from moving streams
ISO 13909--6, Coal and coke — Mechanical sampling — Part 6: Preparation of test samples of coke
ISO 13909--8, Coal and coke — Mechanical sampling — Part 8: Methods of testing for bias
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 13909--1 apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— — ISO Online browsing platform: available at https://www.iso.org/obp
— — IEC Electropedia: available at https://www.electropedia.org/
1)
Under preparation. Stage at the time of publication: ISO/FDIS 13909-2:2025.
4 General
When designing a sampling scheme in order to meet a required precision of results, formulae that link certain
fuel and sampling characteristics to that precision are necessary. The main factors to be considered are the
variability of primary increments, preparation and testing errors, the number of increments and samples
taken to represent the lot, and the mass of the samples. These formulae are derived in Clause 5Clause 5.
Methods for estimating the parameters used in those formulae are given in Clause 6Clause 6.
Once a sampling system has been designed and installed, the precision which is being achieved on a routine
basis should be checked. An estimate of the precision can be obtained from the primary increment variance,
V , the numbers of increments, n, and sub-lots, m, (see Clause 5Clause 5)) and the preparation and testing
I
variance, V . The preparation component of V is made up of on-line sample processing and off-line sample
PT PT
preparation.
Sampling variance is a function of product variability, so the same number of increments, sub-lots, and
preparation and testing errors will yield different precision with fuels that exhibit different product
variability.
Depending on the extent to which serial correlation exists and which method of estimating primary increment
variance is used, such an estimate can represent a considerable overestimate of the numerical value of the
precision (i.e. indicate that it is worse than is really the case). In addition, in order for the results to be
meaningful, large numbers of increments (in duplicate) would need to be prepared and analysed for the
estimation of V and V .
I PT
Quality variations obtained in the form of primary increment variances on existing systems are not absolute
and, therefore, designers should exercise caution when using such results in a different situation. The
estimated value of the primary increment variance, V , should be derived experimentally for each fuel and at
I
each sampling location.
Whenever a sampling scheme is used for determining increment variance, the operating conditions should be
as similar as possible to the conditions known, or anticipated, to prevail during the sampling for which the
increment variance is needed, whether it be carried out by the same or by a different sampling system.
An estimate of the precision actually achieved can be obtained by taking the sample in a number of parts and
comparing the results obtained from these parts. There are several methods of doing this, depending on:
a) a) the purpose of the test,; and
b) b) the practical limitations imposed by the available sampling procedures and equipment.
Where a sampling system is in existence, the purpose of the test is to check that the scheme is in fact achieving
the desired precision (see Clause 7Clause 7).). If it is not, it may need to be modified and rechecked until it
meets the precision required. In order to do this, a special check scheme should be devised which may be
different from the regular scheme but which measures the precision of the regular scheme.
For regular sampling schemes, the most rigorous approach is that of duplicate sampling of sub-lots. In many
existing mechanical sampling systems, however, the capacity of individual components and the interval
between increments in the regular scheme is insufficient to allow the taking of extra increments. In such cases,
duplicate samples can be constituted from the normal number of increments and the result adjusted for the
smaller number of increments in each sample (see 7.37.3).).
The need to sample a particular lot and to know the precision of the result obtained (see Clause 8Clause 8))
can arise. Once again, a special check scheme needs to be devised, but in this case, it is the precision achieved
by that scheme on that lot which is required. For the measurement of the precision achieved for a particular
lot, replicate sampling is the best method.
Methods for detailed checking of preparation and testing errors are given in Clause 9Clause 9. The results
may also be used to provide data for the formulae used in Clause 5Clause 5.
5 Formulae relating to factors affecting precision
5.1 General
Precision is a measure of the closeness of agreement between the results obtained by repeating a
measurement procedure several times under specified conditions and is a characteristic of the method used.
The smaller the random errors of a method, the more precise the method is.
...
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