National foreword

This British Standard is the UK implementation of ISO 13909‑7:2016. It supersedes BS ISO 13909‑7:2001 which is withdrawn.

The UK participation in its preparation was entrusted to Technical Committee PTI/16, Solid mineral fuels.

A list of organizations represented on this committee can be obtained on request to its secretary.

This publication does not purport to include all the necessary provisions of a contract. Users are responsible for its correct application.

Compliance with a British Standard cannot confer immunity from legal obligations.

Foreword

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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 documents 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).

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The committee responsible for this document is ISO/TC 27, Solid mineral fuels, Subcommittee SC 4, Sampling.

This second edition cancels and replaces the first edition (ISO 13909‑7:2001), which has been technically revised.

ISO 13909 consists of the following parts, under the general title Hard coal and coke — Mechanical sampling:

Part 1: General introduction
Part 2: Coal — Sampling from moving streams
Part 3: Coal — Sampling from stationary lots
Part 4: Coal — Preparation of test samples
Part 5: Coke — Sampling from moving streams
Part 6: Coke — Preparation of test samples
Part 7: Methods for determining the precision of sampling, sample preparation and testing
Part 8: Methods of testing for bias

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 part of ISO 13909 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 is 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.

NOTE In the text, the term “fuel” is used where both coal and coke would be applicable in the context and either “coal” or “coke” where that term is exclusively applicable.

1 Scope

In this part of ISO 13909, 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.

2 Normative references

3 Terms and definitions

4 General

5 Formulae relating to factors affecting precision

5.1 General

5.2 Sampling

6 Estimation of primary increment variance

6.1 Direct determination of individual primary increments

6.2 Determination using the estimate of precision

7 Methods for estimating precision

7.1 General

7.2 Duplicate sampling with twice the number of increments

7.3 Duplicate sampling during routine sampling

7.4 Alternatives to duplicate sampling

7.5 Precision adjustment procedure

8 Calculation of precision

8.1 Replicate sampling

8.2 Normal sampling scheme

9 Methods of checking sample preparation and testing errors

9.1 General

9.2 Target value for variance of sample preparation and analysis

9.3 Checking procedure as a whole

9.4 Checking stages separately

9.5 Procedure for obtaining two samples at each stage

9.6 Example

Bibliography

BS ISO 13909-7:2016

Hard coal and coke. Mechanical sampling - Methods for determining the precision of sampling, sample preparation and testing

Published:

30 Jun 2016

Withdrawn:

25 Jul 2025