Natural gas - Determination of composition and associated uncertainty by gas chromatography - Part 2: Uncertainty calculations (ISO 6974-2:2012)

This part of ISO 6974 describes the process required to determine the uncertainty associated with the mole
fraction for each component from a natural gas analysis in accordance with ISO 6974‑1.

Erdgas - Bestimmung der Zusammensetzung und der zugehörigen Unsicherheit durch Gaschromatographie - Teil 2: Unsicherheitsberechnungen (ISO 6974-2:2012)

Dieser Teil von ISO 6974 beschreibt den erforderlichen Prozess zur Bestimmung der mit der Mol¬fraktion jeder Komponente verbundenen Unsicherheit bei einer Erdgasanalyse nach ISO 6974 1.

Gaz naturel - Détermination de la composition et de l'incertitude associée par chromatographie en phase gazeuse - Partie 2: Calculs d'incertitude (ISO 6974-2:2012)

La présente partie de l'ISO 6974 décrit le processus nécessaire pour déterminer l'incertitude associée à la
fraction molaire de chaque constituant d'une analyse de gaz naturel conformément à l'ISO 6974-1.

Zemeljski plin - Določevanje sestave in pripadajoče negotovosti s plinsko kromatografijo - 2. del: Računanje negotovosti (ISO 6974-2:2012)

Ta del standarda ISO 6974 opisuje postopek za določevanje pripadajoče negotovosti z molsko frakcijo za vsako sestavino iz analize zemeljskega plina v skladu s standardom ISO 6974-1.

General Information

Status
Published
Publication Date
14-May-2012
Current Stage
6060 - Definitive text made available (DAV) - Publishing
Due Date
15-May-2012
Completion Date
15-May-2012

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SLOVENSKI STANDARD
SIST EN ISO 6974-2:2012
01-julij-2012
1DGRPHãþD
SIST EN ISO 6974-2:2002
=HPHOMVNLSOLQ'RORþHYDQMHVHVWDYHLQSULSDGDMRþHQHJRWRYRVWLVSOLQVNR
NURPDWRJUDILMRGHO5DþXQDQMHQHJRWRYRVWL ,62
Natural gas - Determination of composition and associated uncertainty by gas
chromatography - Part 2: Uncertainty calculations (ISO 6974-2:2012)
Erdgas - Bestimmung der Zusammensetzung und der zugehörigen Unsicherheit durch
Gaschromatographie - Teil 2: Unsicherheitsberechnungen (ISO 6974-2:2012)
Gaz naturel - Détermination de la composition avec une incertitude définie par

chromatographie en phase gazeuse - Partie 2: Calculs d'incertitude (ISO 6974-2:2012)

Ta slovenski standard je istoveten z: EN ISO 6974-2:2012
ICS:
75.060 Zemeljski plin Natural gas
SIST EN ISO 6974-2:2012 en

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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SIST EN ISO 6974-2:2012
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SIST EN ISO 6974-2:2012
EUROPEAN STANDARD
EN ISO 6974-2
NORME EUROPÉENNE
EUROPÄISCHE NORM
May 2012
ICS 75.060 Supersedes EN ISO 6974-2:2002
English Version
Natural gas - Determination of composition and associated
uncertainty by gas chromatography - Part 2: Uncertainty
calculations (ISO 6974-2:2012)

Gaz naturel - Détermination de la composition et de Erdgas - Bestimmung der Zusammensetzung und der

l'incertitude associée par chromatographie en phase zugehörigen Unsicherheit durch Gaschromatographie - Teil

gazeuse - Partie 2: Calculs d'incertitude (ISO 6974-2:2012) 2: Unsicherheitsberechnungen (ISO 6974-2:2012)

This European Standard was approved by CEN on 14 May 2012.

CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European

Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references concerning such national

standards may be obtained on application to the CEN-CENELEC Management Centre or to any CEN member.

This European Standard exists in three official versions (English, French, German). A version in any other language made by translation

under the responsibility of a CEN member into its own language and notified to the CEN-CENELEC Management Centre has the same

status as the official versions.

CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,

Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland,

Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and United Kingdom.

EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
Management Centre: Avenue Marnix 17, B-1000 Brussels

© 2012 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 6974-2:2012: E

worldwide for CEN national Members.
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SIST EN ISO 6974-2:2012
EN ISO 6974-2:2012 (E)
Contents Page

Foreword ..............................................................................................................................................................3

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SIST EN ISO 6974-2:2012
EN ISO 6974-2:2012 (E)
Foreword

This document (EN ISO 6974-2:2012) has been prepared by Technical Committee ISO/TC 193 "Natural gas".

This European Standard shall be given the status of a national standard, either by publication of an identical

text or by endorsement, at the latest by November 2012, and conflicting national standards shall be withdrawn

at the latest by November 2012.

Attention is drawn to the possibility that some of the elements of this document may be the subject of patent

rights. CEN [and/or CENELEC] shall not be held responsible for identifying any or all such patent rights.

This document supersedes EN ISO 6974-2:2002.

According to the CEN/CENELEC Internal Regulations, the national standards organizations of the following

countries are bound to implement this European Standard: Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech

Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia,

Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain,

Sweden, Switzerland, Turkey and the United Kingdom.
Endorsement notice

The text of ISO 6974-2:2012 has been approved by CEN as a EN ISO 6974-2:2012 without any modification.

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SIST EN ISO 6974-2:2012
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SIST EN ISO 6974-2:2012
INTERNATIONAL ISO
STANDARD 6974-2
Second edition
2012-05-15
Natural gas — Determination of
composition and associated uncertainty
by gas chromatography —
Part 2:
Uncertainty calculations
Gaz naturel — Détermination de la composition et de l’incertitude
associée par chromatographie en phase gazeuse — Partie 2: Calculs
d’incertitude
Reference number
ISO 6974-2:2012(E)
ISO 2012
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SIST EN ISO 6974-2:2012
ISO 6974-2:2012(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2012

All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by any means,

electronic or mechanical, including photocopying and microfilm, without permission in writing from either ISO at the address below or ISO’s

member body in the country of the requester.
ISO copyright office
Case postale 56 • CH-1211 Geneva 20
Tel. + 41 22 749 01 11
Fax + 41 22 749 09 47
E-mail copyright@iso.org
Web www.iso.org
Published in Switzerland
ii © ISO 2012 – All rights reserved
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SIST EN ISO 6974-2:2012
ISO 6974-2:2012(E)
Contents Page

Foreword ............................................................................................................................................................................iv

Introduction ........................................................................................................................................................................ v

1 Scope ...................................................................................................................................................................... 1

2 Normative references ......................................................................................................................................... 1

3 Terms and definitions ......................................................................................................................................... 1

4 Symbols ................................................................................................................................................................. 1

4.1 Symbols ................................................................................................................................................................. 1

4.2 Subscripts ............................................................................................................................................................. 2

5 Calculation of uncertainty ................................................................................................................................. 2

5.1 General considerations ..................................................................................................................................... 2

5.2 Principles ............................................................................................................................................................... 5

5.3 Step 9 — Calculation of uncertainty of mole fractions ............................................................................. 5

5.4 Step 10 — Calculation of the expanded uncertainty of mole fractions .............................................. 11

Annex A (informative) Calculation of processed component uncertainties for

the methane-by-difference approach ...........................................................................................................12

Annex B (normative) Uncertainties of relative response factors ........................................................................13

Annex C (informative) Alternative calculation of the uncertainty of the value of the unknown ..................14

Bibliography .....................................................................................................................................................................16

© ISO 2012 – All rights reserved iii
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SIST EN ISO 6974-2:2012
ISO 6974-2:2012(E)
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.

International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.

The main task of technical committees is to prepare International Standards. Draft International Standards

adopted by the technical committees are circulated to the member bodies for voting. Publication as an

International Standard requires approval by at least 75 % of the member bodies casting a vote.

Attention is drawn to the possibility that some of the elements of this document may be the subject of patent

rights. ISO shall not be held responsible for identifying any or all such patent rights.

ISO 6974-2 was prepared by Technical Committee ISO/TC 193, Natural Gas, Subcommittee SC 1, Analysis

of natural gas.

This second edition of ISO 6974-2, together with ISO 6974-1:2012, cancels and replaces ISO 6974-1:2000 and

ISO 6974-2:2001, which have been technically revised.

ISO 6974 consists of the following parts, under the general title Natural Gas — Determination of composition

and associated uncertainty by gas chromatography:
— Part 1: General guidelines and calculation of composition
— Part 2: Uncertainty calculations

— Part 3: Determination of hydrogen, helium, oxygen, nitrogen, carbon dioxide and hydrocarbons up to C

using two packed columns

— Part 4: Determination of nitrogen, carbon dioxide and C to C and C hydrocarbons for a laboratory and

1 5 6+
on-line measuring system using two columns

— Part 5: Determination of nitrogen, carbon dioxide and C to C and C hydrocarbons for a laboratory and

1 5 6+
on-line process application using three columns

— Part 6: Determination of hydrogen, helium, oxygen, nitrogen, carbon dioxide and C to C hydrocarbons

1 8
using three capillary columns
Future subsequent parts of ISO 6974 are planned.
iv © ISO 2012 – All rights reserved
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SIST EN ISO 6974-2:2012
ISO 6974-2:2012(E)
Introduction

ISO 6974 describes methods of analysis of natural gas and methods for calculating component mole fractions and

uncertainties. ISO 6974 (all parts) is intended for the measurement of H , He, O , N , CO and hydrocarbons, either

2 2 2 2

as individual components or as a group, for example all hydrocarbons above C , defined as C . This approach is

5 6+

suitable for a range of end applications, including calibrating gas mixtures and providing natural gas composition

and uncertainty data to be used in the calculation of calorific value and other additive physical properties of the

gas. Details of these end applications are provided in ISO 6974-3 and subsequent parts of ISO 6974.

ISO 6974-1 gives guidelines for calculating the mole composition of natural gas, determined using one of the

gas chromatographic methods described in ISO 6974-3 and subsequent parts of ISO 6974. ISO 6974-1 also

describes all the essential steps for setting up an analysis, including outlining the structure of the analysis,

defining the working ranges and establishing the analytical procedure.

This part of ISO 6974 describes the steps required to calculate the uncertainty of the component mole fractions

of natural gas determined using gas chromatography.

ISO 6974-3 and subsequent parts of ISO 6974 describe different gas chromatographic methods. These

methods cover both daily practice in the laboratory and on-line field applications. ISO 6974-1:2012, Annex A,

provides a comparison of the characteristics of the analytical methods described in ISO 6974-3 and subsequent

parts of ISO 6974.

It is intended that this part of ISO 6974 be used in conjunction with ISO 6974-1 and a method of analysis, e.g.

ISO 6974-3 or subsequent parts of ISO 6974.

ISO 6974-1:2012, 5.5, describes the conventional normalization approach for calculating processed mole

fractions from raw mole fractions. When conventional normalization is used for multiple operation methods

without bridging, the uncertainties of the calculated mole fractions will be conservative. If a more accurate

assessment of uncertainty is required, an alternative approach to normalization, using the generalized least

squares (GLS) method, can be used; this is described in ISO 6974-1:2012, Annex B. Further alternative

approaches are available for calculating processed mole fractions, including methane-by-difference (see

ISO 6974-1:2012, Annex C) and data harmonization (see Reference [1]).
© ISO 2012 – All rights reserved v
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SIST EN ISO 6974-2:2012
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SIST EN ISO 6974-2:2012
INTERNATIONAL STANDARD ISO 6974-2:2012(E)
Natural gas — Determination of composition and associated
uncertainty by gas chromatography —
Part 2:
Uncertainty calculations
1 Scope

This part of ISO 6974 describes the process required to determine the uncertainty associated with the mole

fraction for each component from a natural gas analysis in accordance with ISO 6974-1.

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 6974-1:2012, Natural gas — Determination of composition and associated uncertainty by gas

chromatography — Part 1: General guidelines and calculation of composition

ISO/IEC Guide 98-3, Uncertainty of measurement — Part 3: Guide to the expression of uncertainty in

measurement (GUM:1995)
3 Terms and definitions

For the purposes of this document, the terms and definitions given in ISO 6974-1 apply.

4 Symbols
4.1 Symbols
b parameters of the regression function (z = 0, 1, 2 or 3)
mean parameters of the regression function (in “mean normalization” method)
C sensitivity coefficient
k coverage factor
K relative response factor with respect to the reference component

total number of components (direct plus indirect, but excluding “other components”)

total number of gas standards or mixtures
total number of injections (and therefore total number of responses)
standard deviation
total mole fraction of all raw components
© ISO 2012 – All rights reserved 1
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SIST EN ISO 6974-2:2012
ISO 6974-2:2012(E)
u(…) standard uncertainty (of the quantity in parentheses)
U(…) expanded uncertainty (of the quantity in parentheses)
x normalized mole fraction
x raw mole fraction
x′ mole fraction calculated using the methane-by-difference approach [Annex A]
xˆ adjusted mole fraction [Annex C]
y instrumental response of the specified analyte
y mean instrumental response (in “mean normalization” method)
ˆy adjusted instrumental response [Annex C]
Y instrumental response [Annex C]
α intercept of a first-order calibration function [Annex C]
β gradient of a first-order calibration function [Annex C]
γ gradient of the calibration curve [Annex C]
mean of the distribution of non-linearity errors
4.2 Subscripts
cal calibration [Annex A]
i component
ind components or groups of components to be analysed by indirect measurement
j gas standard/mixture
l injection
oc other components
p, q indices defining a regression coefficient
ref reference (component or pressure)
s index defining a component
wms working measurement standard
5 Calculation of uncertainty
5.1 General considerations

The process of setting up a gas chromatograph for the analysis of natural gas consists of the steps outlined in

the flowcharts in Figures 1 and 2.

Steps 1 to 8 are covered in ISO 6974-1. This part of ISO 6974 covers steps 9 and 10.

2 © ISO 2012 – All rights reserved
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SIST EN ISO 6974-2:2012
ISO 6974-2:2012(E)
START
Step 1: Define the working range
[ISO 6974-1:2012, 6.2]
Step 2: Define the requirements of
the analytical method
[ISO 6974-1:2012, 6.3]
Step 3: Select equipment and
working conditions
[ISO 6974-1:2012, 6.4]
Step 4 [ISO 6974-1:2012, 6.5]
Is primary calibration or
Type 1 or Type 2
performance evaluation
Yes
Type 2
analysis?
required?
Type 1
Primary calibration Performance evaluation
Determine analysis function: Determine initial analysis function
(a) Selection of reference gases (a) Selection of reference gases
(b) Measurement of reference gases (b) Measurement of reference gases
(c) Regression analysis (c) Regression analysis
(d) Selection of regression function
Are there any
No indirect
components?
Yes
Step 5: Assign relative response
factors
[ISO 6974-1:2012, 6.6]
FLOWCHART B

Figure 1 — Procedure for determining mole fraction and uncertainty — Steps 1 to 5

© ISO 2012 – All rights reserved 3
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SIST EN ISO 6974-2:2012
ISO 6974-2:2012(E)
START FROM
FLOWCHART A
Will the analyser be
used for routine
operation?
Yes
Step 6
[ISO 6974-1:2012, 6.7]
Quality assurance
(QA) check or routine QA check
calibration (RC)?
RC with a WMS QA with a WMS
[ISO 6974-1:2012, 6.7.3.2] [ISO 6974-1:2012, 6.7.3.3]
Step 7: Analysis of samples
[ISO 6974-1:2012, 6.8]
Step 8: Calculation of component mole fractions
[ISO 6974-1:2012, 6.9]
Are uncertainties of
component mole FINISH
fractions required?
Yes
Step 9: Calculation of uncertainty in mole fractions
[ISO 6974-2:2012, 5.3]
Step 10: Calculation of the expanded
uncertainty in mole fractions
[ISO 6974-2:2012, 5.4]
FINISH

Figure 2 — Procedure for determining mole fraction and uncertainty — Steps 6 to 10

4 © ISO 2012 – All rights reserved
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SIST EN ISO 6974-2:2012
ISO 6974-2:2012(E)
5.2 Principles

Uncertainties associated with the component mole fractions shall be calculated in accordance with

ISO/IEC Guide 98-3.

For Type 1 analyses in accordance with ISO 6974-1, the uncertainty calculation includes random and systematic

uncertainties from three main sources: uncertainty of the certified reference mixtures, uncertainty of analysis

and uncertainty of the data fitting procedure.

For Type 2 analyses in accordance with ISO 6974-1, the uncertainty calculation includes both random elements

and systematic errors introduced by the assumption of a linear response through the origin, the systematic

errors being calculated from the results of the initial performance evaluation.

Subclause 5.3 describes methods for estimating the uncertainties of processed mole fractions calculated from

raw mole fractions using the conventional normalization method. Annex A provides a method for use when the

methane-by-difference approach (see ISO 6974-1:2012, Annex C) is employed.

ISO 6974-1 recommends the use of the generalized least squares (GLS) approach for calculation of the

processed mole fraction. However, in some circumstances, an alternative approach using ordinary least

squares may be acceptable and calculation of uncertainty in processed mole fractions in this situation is

described in Annex C.
5.3 Step 9 — Calculation of uncertainty of mole fractions
5.3.1 Determining the equations to be used
5.3.1.1 General considerations
The equations to be used in t
...

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