Overview
ISO 13909-7:2016 - Hard coal and coke - Mechanical sampling - Part 7 - specifies methods for determining the precision of mechanical sampling, sample preparation and testing for hard coal and coke. The standard develops formulae that link the variables contributing to overall sampling precision and describes practical procedures to estimate precision, derive primary increment variance, and check the variance introduced during sample preparation and laboratory testing.
Key topics
- Precision concept and index: Defines precision as an index related to the sample estimate of population standard deviation (commonly expressed as two times the sample standard deviation).
- Formulae relating precision factors: Mathematical relationships linking primary increment variance, number and mass of increments, and preparation/testing variances to overall sampling precision.
- Estimation of primary increment variance:
- Direct determination from individual primary increments
- Indirect determination using precision estimates
- Methods for estimating precision:
- Replicate sampling and duplicate sampling approaches
- Duplicate sampling during routine operations and alternatives when capacity is limited
- Precision adjustment procedures to modify sampling schemes
- Calculation procedures:
- How to compute precision for replicate and normal sampling schemes
- Checking sample preparation and testing:
- Procedures for on-line and off-line preparation
- Target variance criteria and staged checking methods (including obtaining parallel samples with riffles or mechanical dividers)
- Informative methods: Annex A (variogram method) and Annex B (Grubbs’ estimators) provide additional techniques for variance determination.
Applications and users
ISO 13909-7:2016 is intended for organizations and professionals involved in coal and coke sampling and quality assurance:
- Sampling engineers and designers - to design or modify sampling schemes to meet required precision.
- Quality control managers and laboratory analysts - to evaluate and verify precision of sample preparation and testing.
- Operations and production teams - to implement duplicate or replicate sampling for routine checks.
- Regulatory bodies, auditors and traders - to assess the reliability of reported fuel quality data.
Practical uses include estimating expected variability of results, determining the number/mass of increments needed, setting target variances for preparation and analysis, and diagnosing where precision losses occur (sampling vs. preparation vs. testing).
Related standards
ISO 13909-7 is part of the ISO 13909 series on mechanical sampling of hard coal and coke. Relevant companion parts include:
- ISO 13909-1 to ISO 13909-6 and ISO 13909-8 (general introduction, sampling from moving streams and stationary lots, preparation of test samples, and methods for testing for bias).
Keywords: ISO 13909-7:2016, mechanical sampling, hard coal and coke, sampling precision, primary increment variance, duplicate sampling, replicate sampling, sample preparation variance, testing variance.