SIST EN ISO 6145-1:2019

Gas analysis - Preparation of calibration gas mixtures using dynamic methods - Part 1: General aspects (ISO 6145-1:2019)

This document gives a brief overview of each of the dynamic techniques which are described in detail in the subsequent parts of ISO 6145. This document provides basic information to support an informed choice for one or another method for the preparation of calibration gas mixtures. It also describes how these methods can be linked to national measurement standards to establish metrological traceability for the composition of the prepared gas mixtures.
Since all techniques are dynamic and rely on flow rates, this document describes the calibration process by measurement of each individual flow rate generated by the device.
Methods are also provided for assessing the composition of the generated gas mixtures by comparison with an already validated calibration gas mixture.
This document provides general requirements for the use and operation of dynamic methods for gas mixture preparation. It also includes the necessary expressions for calculating the calibration gas composition and its associated uncertainty.
Gas mixtures obtained by these dynamic methods can be used to calibrate or control gas analysers.
The storage of dynamically prepared gas mixtures into bags or cylinders is beyond the scope of this document.

Gasanalyse - Herstellung von Kalibriergasgemischen mit Hilfe von dynamische Verfahren - Teil 1: Kalibrierverfahren (ISO 6145-1:2019)

Dieses Dokument gibt eine kurze Übersicht über jedes der dynamischen Verfahren, die in den nachfolgenden Teilen von ISO 6145 ausführlich beschrieben werden. Dieses Dokument enthält grundlegende Informationen, um eine fundierte Auswahl des einen oder anderen Verfahrens zur Herstellung von Kalibriergasgemischen zu unterstützen. Es beschreibt auch, wie diese Verfahren mit nationalen Normalen in Verbindung gebracht werden können, um die metrologische Rückführbarkeit der Zusammensetzung der hergestellten Gasgemische zu erreichen.
Da alle Verfahren dynamisch sind und auf Durchflussraten beruhen, beschreibt dieses Dokument den Kalibrierprozess durch Messung jedes einzelnen durch das Gerät erzeugten Durchflusses.
Es werden auch Verfahren zur Bewertung der Zusammensetzung der erzeugten Gasgemische durch den Vergleich mit einem bereits validierten Kalibriergasgemisch zur Verfügung gestellt.
Dieses Dokument enthält allgemeine Anforderungen für die Anwendung und den Betrieb dynamischer Verfahren für die Gasgemischherstellung. Es enthält auch die erforderlichen Ausdrücke zur Berechnung der Kalibriergaszusammensetzung und der damit verbundenen Unsicherheit.
Gasgemische, die durch diese dynamischen Verfahren erhalten werden, können verwendet werden, um Gasanalysegeräte zu kalibrieren oder zu überprüfen.
Die Speicherung von dynamisch hergestellten Gasgemischen in Beuteln oder Flaschen geht über den Anwendungsbereich dieses Dokuments hinaus.

Analyse des gaz - Préparation des mélanges de gaz pour étalonnage à l'aide de méthodes dynamiques - Partie 1 : Aspects généraux (ISO 6145-1:2019)

Le présent document donne un rapide aperçu de chacune des techniques dynamiques décrites en détail dans les parties ultérieures de l'ISO 6145. Le présent document fournit des informations de base pour permettre un choix informé de l'une des méthodes pour la préparation de mélanges de gaz pour étalonnage. Il décrit également comment ces méthodes peuvent être liées à des étalons de mesure nationaux pour établir une traçabilité métrologique de la composition des mélanges de gaz préparés.
Comme toutes les techniques sont dynamiques et reposent sur les débits, le présent document décrit le processus d'étalonnage par mesurage de chaque débit individuel généré par le dispositif.
Des méthodes sont également fournies pour évaluer la composition des mélanges de gaz générés par comparaison avec un mélange de gaz pour étalonnage déjà validé.
Le présent document fournit des exigences générales pour l'utilisation et l'application des méthodes dynamiques pour la préparation des mélanges de gaz. Il comprend également les expressions nécessaires pour le calcul de la composition du gaz d'étalonnage et de son incertitude associée.
Les mélanges de gaz obtenus par ces méthodes dynamiques peuvent être utilisés pour étalonner ou contrôler les analyseurs de gaz.
Le stockage des mélanges de gaz préparés dynamiquement dans des sacs ou des bouteilles n'appartient pas au domaine d'application du présent document.

Analiza plinov - Priprava kalibracijskih plinskih zmesi z uporabo dinamičnih metod - 1. del: Splošni vidiki (ISO 6145-1:2019)

V tem dokumentu je kratek pregled posameznih dinamičnih tehnik, ki so podrobno opisane v poznejših delih standarda ISO 6145. Ta dokument vsebuje osnovne informacije za podporo utemeljene odločitve glede uporabe ene ali druge odločitve za pripravo kalibracijskih plinskih zmesi. Opisuje tudi, kako je mogoče s povezavo teh metod in nacionalnih standardov merjenja vzpostaviti meroslovno sledljivost za sestavo pripravljenih plinskih zmesi. Ker so vse tehnike dinamične in temeljijo na stopnjah pretoka, ta dokument opisuje postopek kalibracije z merjenjem vsake posamezne stopnje pretoka, ki jo proizvede naprava. Podane so tudi metode za ocenjevanje sestave proizvedenih plinskih zmesi s primerjavo že potrjene kalibracijske plinske zmesi. Ta dokument podaja splošne zahteve za uporabo in delovanje dinamičnih metod za pripravo plinskih zmesi. Vključuje tudi potrebne izraze za izračun sestave kalibracijskega plina in povezane negotovosti. Plinske zmesi, pridobljene s temi dinamičnimi metodami, je mogoče uporabiti za kalibriranje oziroma nadzorovanje analizatorjev plinov. Shranjevanje dinamično pripravljenih plinskih zmesi v vrečke ali jeklenke presega področje uporabe tega dokumenta.

General Information

• Status: Published
• Public Enquiry End Date: 02-Dec-2018
• Publication Date: 06-Nov-2019
• ICS: 71.040.40 - Chemical analysis
• Technical Committee: NAD - Petroleum products, lubricants and related products
• Current Stage: 6060 - National Implementation/Publication (Adopted Project)
• Start Date: 04-Nov-2019
• Due Date: 09-Jan-2020
• Completion Date: 07-Nov-2019
• Ref Project: EN ISO 6145-1:2019 - Gas analysis - Preparation of calibration gas mixtures using dynamic methods - Part 1: General aspects (ISO 6145-1:2019)

Relations

• Replaces: SIST EN ISO 6145-1:2008 - Gas analysis - Preparation of calibration gas mixtures using dynamic volumetric methods - Part 1: Methods of calibration (ISO 6145-1:2003)
• Effective Date: 01-Dec-2019

Overview

EN ISO 6145-1:2019 - "Gas analysis - Preparation of calibration gas mixtures using dynamic methods - Part 1: General aspects" provides a consolidated, practical introduction to the dynamic techniques used to prepare calibration gas mixtures. Part 1 summarizes each dynamic method (described in detail in subsequent parts of the ISO 6145 series), explains how to link dynamic methods to national measurement standards for metrological traceability, and defines general requirements for operation, calculation and uncertainty assessment. Storage of prepared mixtures (bags or cylinders) is explicitly out of scope.

Key topics and requirements

• Dynamic techniques overview: concise descriptions of piston pumps, continuous (syringe) injection, capillaries, critical flow orifices, thermal mass flow controllers, diffusion, saturation, permeation and electrochemical generation.
• Flow-rate centric calibration: because methods are dynamic, the standard focuses on calibrating and measuring each individual flow rate element of the system.
• Composition assessment: methods for verifying generated mixtures by comparison with validated reference gas mixtures.
• Calculations and uncertainty: required expressions for computing mixture composition and associated uncertainty for both volumetric and gravimetric mixing approaches.
• Calibration and verification: guidance on calibrating system elements (flow devices), preparing calibration certificates, verification criteria and recalibration intervals.
• Handling and quality: recommendations on safety, materials compatibility, parent gas purity, and good gas-handling practices to avoid reactions or contamination.
• Scope limits: does not cover storage of dynamically prepared mixtures.

Practical applications

• Calibration and quality control of gas analysers used in environmental monitoring, industrial process control, emissions testing and laboratory instrumentation.
• Production of low-uncertainty calibration gases for metrology institutes and accredited calibration laboratories.
• Method selection and system design for gas mixture suppliers and instrument manufacturers who need traceable, documented calibration standards.
• Establishing measurement traceability chains to national standards for regulatory compliance and proficiency testing.

Who should use this standard

• Metrologists and calibration laboratory managers
• Gas analysis and gas mixture suppliers
• Instrument manufacturers and service engineers
• Environmental and emissions monitoring teams
• Quality managers in laboratories requiring traceable calibration gases

Related standards

• This document is Part 1 of the ISO 6145 series; see subsequent parts for detailed procedures and specifications for individual dynamic preparation techniques.
• Use alongside relevant national metrology and accreditation guides for implementing traceability and uncertainty evaluation.

Keywords: EN ISO 6145-1:2019, gas analysis, calibration gas mixtures, dynamic methods, flow rate calibration, metrological traceability, uncertainty, gas analysers calibration.

Standards Content (Sample)

SLOVENSKI STANDARD
01-december-2019
Nadomešča:
SIST EN ISO 6145-1:2008
Analiza plinov - Priprava kalibracijskih plinskih zmesi z uporabo dinamičnih metod
- 1. del: Splošni vidiki (ISO 6145-1:2019)
Gas analysis - Preparation of calibration gas mixtures using dynamic methods - Part 1:
General aspects (ISO 6145-1:2019)
Gasanalyse - Herstellung von Kalibriergasgemischen mit Hilfe von dynamische
Verfahren - Teil 1: Kalibrierverfahren (ISO 6145-1:2019)
Analyse des gaz - Préparation des mélanges de gaz pour étalonnage à l'aide de
méthodes dynamiques - Partie 1 : Aspects généraux (ISO 6145-1:2019)
Ta slovenski standard je istoveten z: EN ISO 6145-1:2019
ICS:
71.040.40 Kemijska analiza Chemical analysis
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EN ISO 6145-1
EUROPEAN STANDARD
NORME EUROPÉENNE
October 2019
EUROPÄISCHE NORM
ICS 71.040.40 Supersedes EN ISO 6145-1:2008
English Version
Gas analysis - Preparation of calibration gas mixtures
using dynamic methods - Part 1: General aspects (ISO
6145-1:2019)
Analyse des gaz - Préparation des mélanges de gaz Gasanalyse - Herstellung von Kalibriergasgemischen
pour étalonnage à l'aide de méthodes dynamiques - mit Hilfe von dynamische Verfahren - Teil 1:
Partie 1 : Aspects généraux (ISO 6145-1:2019) Kalibrierverfahren (ISO 6145-1:2019)
This European Standard was approved by CEN on 1 September 2019.

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, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and
United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION

EUROPÄISCHES KOMITEE FÜR NORMUNG

CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2019 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 6145-1:2019 E
worldwide for CEN national Members.

Contents Page
European foreword . 3

European foreword
This document (EN ISO 6145-1:2019) has been prepared by Technical Committee ISO/TC 158 "Analysis
of gases" in collaboration with Technical Committee CEN/SS N21 “Gaseous fuels and combustible gas”
the secretariat of which is held by CCMC.
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 April 2020, and conflicting national standards shall be
withdrawn at the latest by April 2020.
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CEN shall not be held responsible for identifying any or all such patent rights.
This document supersedes EN ISO 6145-1:2008.
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, Republic of
North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and the
United Kingdom.
Endorsement notice
The text of ISO 6145-1:2019 has been approved by CEN as EN ISO 6145-1:2019 without any
modification.
INTERNATIONAL ISO
STANDARD 6145-1
Third edition
2019-09
Gas analysis — Preparation of
calibration gas mixtures using
dynamic methods —
Part 1:
General aspects
Analyse des gaz — Préparation des mélanges de gaz pour étalonnage
à l'aide de méthodes dynamiques —
Partie 1: Aspects généraux
Reference number
ISO 6145-1:2019(E)
©
ISO 2019
ISO 6145-1:2019(E)
© ISO 2019
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’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: [phone]
Fax: [phone]
Email: [e-mail]
Website: www.iso.org
Published in Switzerland
ii © ISO 2019 – All rights reserved

ISO 6145-1:2019(E)
Contents Page
Foreword .v
Introduction .vi
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Symbols . 2
5 Principle . 2
5.1 General . 2
5.2 Suitability of the method to the application . 3
5.3 Piston pumps . 3
5.4 Continuous (syringe) injection . 4
5.5 Capillary . 4
5.6 Critical flow orifices . 4
5.7 Thermal mass flow controller . 5
5.8 Diffusion . 5
5.9 Saturation . 5
5.10 Permeation method . 6
5.11 Electrochemical generation . 6
5.12 Summary . 6
6 Recommendations for handling the dynamic system . 7
6.1 Safety considerations . 7
6.1.1 Reactions between mixture components . 7
6.1.2 Reactions with dynamic system materials . 8
6.2 Quality considerations . 8
6.2.1 Purity of parent gas standards or "zero" gas . 8
6.2.2 Gas handling . 8
7 Calibration methods of a dynamic system . 8
7.1 Generalities on the calibration . 8
7.2 Calibration of each element . 9
7.2.1 General. 9
7.2.2 Calibration devices for flow rate: Principle and uncertainty .10
7.3 Single point calibration of a dynamic system by comparison with reference gas
mixtures .13
7.4 Calibration certificate .13
8 Calculation of the composition and its uncertainty .13
8.1 General .13
8.2 Calculations for volumetric methods . .14
8.2.1 General.14
8.2.2 Formulae .14
8.3 Calculations for gravimetric methods .15
8.3.1 General.15
8.3.2 Formula .15
9 Sources of uncertainty and uncertainty of the final mixture .15
10 Verification .16
10.1 Principle .16
10.2 Verification criteria .16
10.3 Recalibration criteria .16
Annex A (normative) Calculation details .17
Annex B (informative) Atomic weights and molar masses .21
ISO 6145-1:2019(E)
Bibliography .23
iv © ISO 2019 – All rights reserved

ISO 6145-1:2019(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.
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).
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. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www .iso .org/patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation on 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 the following
URL: www .iso .org/iso/foreword .html.
This document was prepared by Technical Committee ISO/TC 158, Gas analysis.
This third edition cancels and replaces the second edition (ISO 6145-1:2003), which has been technically
revised. The main changes compared to the previous edition are as follows.
— The techniques for the preparation of gas mixtures are described in an abbreviated manner since
there is no need to repeat the text and formulae from each of the different parts of the ISO 6145
series. However, a summary table (Table 1) presenting the advantages and limitations of each
method has been introduced.
— Recommendations regarding the handling of the dynamic mixing systems and quality considerations
have been added.
— The methods and instruments to calibrate a dynamic system have changed and are better described.
— The calculations to obtain composition and uncertainties are more detailed, and the different ways
of mixing gases (volume flow rates or mass flow rates) have been taken into account.
— Clauses on certificates (7.4) and verification (Clause 10) have been added.
A list of all parts in the ISO 6145 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.
ISO 6145-1:2019(E)
Introduction
This document is one of a series of standards which describes the various dynamic methods for the
preparation of calibration gas mixtures.
Several techniques are available and the choice between them is decided based on the desired gas
composition range, the consistency of equipment with the application and the required level of
uncertainty. This document aids with making an informed choice by listing all the advantages and
limitations of the methods.
The main techniques used for the preparation of gas mixtures are:
a) piston pumps;
b) continuous injection;
c) capillary;
d) critical orifices;
e) thermal mass-flow controllers;
f) diffusion;
g) saturation;
h) permeation;
i) electrochemical generation.
In dynamic methods, a gas A is introduced at a known constant volume or mass flow rate into a known
constant flow rate of a complementary gas B. Gases A and B can be either pure gases or gas mixtures.
The preparation process can be continuous (such as mass flow controllers, permeation tube) or pseudo-
continuous (such as piston pump).
The dynamic preparation techniques produce a continuous flow of calibration gas mixtures into the
analyser but do not generally allow the build-up of a reserve by storage under pressure.
vi © ISO 2019 – All rights reserved

INTERNATIONAL STANDARD ISO 6145-1:2019(E)
Gas analysis — Preparation of calibration gas mixtures
using dynamic methods —
Part 1:
General aspects
1 Scope
This document gives a brief overview of each of the dynamic techniques which are described in detail
in the subsequent parts of ISO 6145. This document provides basic information to support an informed
choice for one or another method for the preparation of calibration gas mixtures. It also describes how
these methods can be linked to national measurement standards to establish metrological traceability
for the composition of the prepared gas mixtures.
Since all techniques are dynamic and rely on flow rates, this document describes the calibration process
by measurement of each individual flow rate generated by the device.
Methods are also provided for assessing the composition of the generated gas mixtures by comparison
with an already validated calibration gas mixture.
This document provides general requirements for the use and operation of dynamic methods for gas
mixture preparation. It also includes the necessary expressions for calculating the calibration gas
composition and its associated uncertainty.
Gas mixtures obtained by these dynamic methods can be used to calibrate or control gas analysers.
The storage of dynamically prepared gas mixtures into bags or cylinders is beyond the scope of this
document.
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 6143, Gas analysis — Comparison methods for determining and checking the composition of calibration
gas mixtures
ISO 7504, Gas analysis — Vocabulary
ISO 12963, Gas analysis — Comparison methods for the determination of the composition of gas mixtures
based on one- and two-point calibration
ISO 14912, Gas analysis — Conversion of gas mixture composition data
ISO 19229, Gas analysis — Purity analysis and the treatment of purity data
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 7504 and the following apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https: //www .iso .org/obp
ISO 6145-1:2019(E)
— IEC Electropedia: available at http: //www .electropedia .org/
3.1
mass flow rate
q
m
mass of gas per unit of time
3.2
volume flow rate
q
v
volume of gas per unit of time
4 Symbols
Symbol Definition
i, k Indices for components in a gas or gas mixture
j Index for a parent gas
K Conversion factor between two gases
m Mass of a component
M Molar mass of a component
p Pressure
q Number of components in the gas mixture
q Mass flow rate
m
q Amount-of-substance flow rate
n
R Ideal gas constant
r Number of parent gases
T Temperature
V Volume
q Volume flow rate
v
u(x) Standard uncertainty of a quantity x
v Mass fraction of a component in a parent gas
w Mass fraction of a component in a gas mixture
x Amount-of-substance fraction of a component in a parent gas
y Amount-of-substance fraction of a component in a gas mixture
Z Compressibility factor
φ Volume fraction of a component in a parent gas
ϕ Volume fraction of a component in a gas mixture
5 Principle
5.1 General
All preparation techniques described in ISO 6145 (all parts) are based on the combination of gas flows.
These flow rates can be measured on a volume or mass basis. The composition is calculated from the
flow rate data and the composition of the parent gases.
It is applicable only to
— pure gases,
— gas mixtures, or
2 © ISO 2019 – All rights reserved

ISO 6145-1:2019(E)
— totally vaporized components at ambient pressure,
which do not react with each other or with any surfaces of the mixing device.
For the calculation of the composition, it is essential to appreciate the composition of the parent gases
used for preparing the calibration gas mixture. Even if such gases are considered “pure”, their purity
shall be verified in accordance with ISO 19229. The corresponding compositional data of these parent
gases shall be used in the calculation of the composition, as described in Clause 7.
Practically, all preparation systems are furthermore sensitive to changes or fluctuations in the
conditions under which the calibration gas mixture is prepared. These conditions typically include
the pressure and temperature of the gases, as well as the dynamic effects of combining flows and
homogenization of the calibration gas mixture, among others. In the subsequent parts of ISO 6145,
attention is drawn to these effects, and care shall be taken to follow these instructions.
Several techniques are available and the choice between them should be decided based on the desired
composition range, the availability of equipment and the required uncertainty.
The principles of gas mixing systems are described in each part of ISO 6145.
Depending on its principle, each dynamic method will generate gas mixtures of composition based
on either volume fraction, mass fraction, amount-of-substance fraction or mass concentration. The
calibration procedure will also affect the expression of gas mixture composition (mass, volume or
amount-of-substance fraction). The final fraction and its associated uncertainty depend both on the
calibration method and on the preparation technique.
5.2 Suitability of the method to the application
Before preparing a gas mixture, it is necessary to consider the suitability of the dynamic system to
the application. Pressure and flow rates should be consistent with the analyser to which the dynamic
system will be linked.
Users shall comply with the manufacturers' recommendations. Check if the dynamic method is sensitive
to external parameters, such as temperature or atmospheric pressure, and follow the recommendations
given in each part of ISO 6145.
Depending on the principle used by the dynamic system, the achievable range of concentration in
the final mixture will differ. In order to compare the capabilities of each method, a dilution ratio is
estimated as follows:
— use of pure components as parent components (for example: in cylinders, or permeation tubes or by
syringe injection);
— only one step dilution is considered.
This dilution ratio could be extended for some dynamic systems by two step dilution.
When choosing the type of the dynamic method, the user shall take into consideration the advantages
and limitations of each method.
5.3 Piston pumps
ISO 6145-2 specifies a volumetric method for the dynamic preparation of calibration gas mixture using
piston pumps. Two or more piston pumps, combined in a gas-mixing pump, are driven with a defined
ratio of strokes. The stroke volume of each piston pump is individually determined by the geometry
(cross-section) of the cylinder and the height of stroke of the piston. The composition is rapidly
changed by the mechanical changing of the ratio of strokes. Suitable peripherals for gas feeding and
homogenization of the final mixture are recommended.
ISO 6145-1:2019(E)
The calibration of the stroke volume is made by dimensional measurements in the SI base unit of length.
Uncertainty evaluation of the gas mixture composition and an assessment of potential sources with
quantification of significant sources of uncertainty are out lined in detail in ISO 6145-2.
The merits of the method are that the composition and the associated uncertainty of the calibration gas
mixture are calculated from the geometric stroke volume and the ratio of strokes of the piston pumps.
The content of each component is directly expressed in volume fractions and in amount-of-substance
fractions.
Final mixture flow rates from 5 l/h to 500 l/h can be prepared depending on the equipment used.
Using this method, dilution ratios from 1:1 up to 1:10 can be prepared from initial amount-of-substance
fraction. Higher dilution ratios can be prepared by a two-stage dilution.
5.4 Continuous (syringe) injection
ISO 6145-4 specifies a method for preparation of calibration gas mixtures using continuous injection.
The calibration component, either in the gaseous or liquid phase, is displaced from a reservoir through
a capillary into a complementary inert gas stream. The system may contain a syringe, whose plunger
is continuously driven by a suitable variable-speed motor. Alternatively, the component may be forced
through the capillary by controlled pressurization of the reservoir.
This method applies also to multi-component mixtures of known composition. In the case of liquids, the
calibration component is vaporized while mixing with the complementary gas.
The flow rate of the calibration component is determined by the geometry (cross-section) of the syringe
and the linear velocity of the plunger or by the continuous weighing of the reservoir.
4 7
Using this method, dilution ratios from 1:10 up to 1:10 can be prepared from initial amount-of-
substance fraction.
5.5 Capillary
ISO 6145-5 specifies a method for the continuous preparation of calibration gas mixtures from pure
gases or gas mixtures using capillary tubes in single or multiple combinations.
A constant flow of gas from a capillary tube under conditions of constant pressure drop is added
to a controlled flow of complementary gas. The complementary gas may be derived from another
capillary tube.
This application is used in industrial gas mixing panels for the production of specific gas atmospheres.
Gas dividers can be used to divide gas mixtures prepared from pure gases or gas mixtures into
controlled proportions by volume.
Using this method, dilution ratios from 1:1 up to 1:10 can be prepared from initial amount-of-substance
fraction.
5.6 Critical flow orifices
ISO 6145-6 specifies a method for the continuous preparation of calibration gas mixtures by use of
critical flow orifice systems.
When passed through a critical orifice at increasing upstream pressure P , the volume flow rate of gas
in
passing through the orifice will increase. When the ratio of the gas pressure downstream P and the
out
gas pressure upstream P of the orifice has reached the critical value, the volume flow rate of the gas
in
becomes independent with respect to P and is proportional to P .
out in
4 © ISO 2019 – All rights reserved

ISO 6145-1:2019(E)
To prepare calibration gas mixtures, the gas blender mixes the complementary gas flowing at a known
rate out of one or several critical flow orifice(s) and the gas to be diluted flowing out of one or several
critical flow orifice(s). The resulting mixture is generally homogenized in a mixing chamber.
Although it is more particularly applicable to the preparation of gas mixtures at atmospheric pressure,
the method also offers the possibility of preparing calibration gas mixtures at pressures greater
than atmospheric. The upstream pressure should be at least two times higher than the downstream
pressure. The range of flow rates covered by this document extends from 1 ml/min to 10 l/min.
It has the merit of allowing multi-component mixtures to be prepared as readily as binary mixtures if
an appropriate number of critical flow orifices are used.
Using this method, dilution ratios from 1:1 up to 1:10 can be prepared from initial amount-of-substance
fraction. Higher dilution ratios can be prepared by a two-stage dilution.
5.7 Thermal mass flow controller
ISO 6145-7 specifies a method for continuous preparation of calibration gas mixtures using thermal
mass flow controllers. By adjustment of the set-points on the flow controllers, it is possible to change
the composition of the gas mixture rapidly and in a continuously variable manner.
The range of flow rates covered by this document extends from 1 ml/min to 10 l/min.
The advantages of the method are that a large quantity of the gas mixture can be prepared on a
continuous basis and that multi-component mixtures can be prepared as readily as binary mixtures if
the appropriate number of thermal mass-flow controllers is utilized.
Using this method, dilution ratios from 1:1 up to 1:10 can be prepared from initial amount-of-substance
fraction. Higher dilution ratio can be prepared by two stage dilution.
5.8 Diffusion
ISO 6145-8 describes a method, which applies to components that are liquids or solids that can produce
a vapour. The vapour of the pure component migrates by diffusion through a diffusion cell of suitable
dimensions (length, diameter) into a flow of a complementary gas. The rate of diffusion should remain
constant, if the system is kept at constant temperature and the pure component is still present as liquid
or solid.
The substance, of a known high purity, is contained in a reservoir that acts as the source of the
component vapour. The reservoir is provided with a vertically placed diffusion cell. This assembly (the
diffusion cell) is placed in a temperature-controlled enclosure that is purged at a constant flow rate by
a high-purity and inert complementary gas. The diffusion rate is measured by periodic weighing of the
diffusion cell.
Using this method, dilution ratios from 1:10 up to 1:10 can be prepared from initial amount-of-
substance fraction.
5.9 Saturation
ISO 6145-9 specifies a method for the dynamic preparation of calibration gas mixture based upon
the vapour saturation pressure of liquid and solid substances. The complementary gas flow is passed
through a temperature-controlled saturator in which the vapour of the calibration component is
maintained in equilibrium with their liquid or solid phases.
The amount-of-substance fraction of the calibration component in the gas flow is approximately equal
to the ratio of the vapour pressure of the component and the total pressure of the mixture at that
temperature. The saturation pressure values for very many components as a function of temperature
are given in reference books.
ISO 6145-1:2019(E)
This method applies to all pure components that are in a stable equilibrium with their vaporized
and liquid phase. The vapour pressure in equilibrium with its condensate phase depends only on
temperature. Variation of volume fraction is achieved by variation of temperature and pressure in the
saturator.
Two procedures are described for the application of this method. Calculation of composition and
uncertainty evaluation are given based on vapour pressure data.
The merits of the method are that calibration gases with condensable components can be dynamically
prepared and used at ambient conditions near the individual component condensation point. In
combination with other volumetric dynamic methods a small flow of saturated calibration gas can be
easily diluted by a large flow of complementary gas to very small volume fractions.
3 6
Using this method, dilution ratios from 1:10 up to 1:10 can be prepared from initial amount-of-
substance fraction .
5.10 Permeation method
ISO 6145-10 describes a method in which the calibration component is contained in a sealed tube
or container, which consists either wholly or partly of a polymer through which the component can
permeate. The component is usually contained as a liquid or solid in equilibrium with its own vapour
but can be contained as a gas. In the former case, the rate of permeation should remain constant while
the liquid is still present. In the latter case, the rate decays with the pressure of the gas. In either case,
the rate of permeation is dependent on temperature.
The vessel containing the calibration component is put into an enclosure. The diluent gas is passed
through the enclosure at a fixed flow rate. The entire housing is placed in a temperature-controlled
chamber.
The permeation rate can be measured by weighing the tube periodically. This procedure is described in
ISO 6145-10.
Using this method, gas mixtures of dilution ratios from 1:10 up to 1:10 can be prepared from the
permeation rate.
5.11 Electrochemical generation
ISO 6145-11 describes a method based on electrochemical generation of one pure component which is
diluted in a complementary gas. The composition of the gas mixture is controlled by the magnitude of
the electrical charge passed through the electrolyte in the cell and by the flowrate of the complementary
gas and is dependent on the efficiency of the cell.
An advantage of the method is that a stable gas mixture can be established rapidly within a few minutes.
However, in ISO 6145-11, a list indicates that the number of different gases that can be produced by
electrochemical generation is limited to those which follow: oxygen, nitrogen, hydrogen, hydrogen
cyanide, hydrogen sulphide, chlorine, bromine, chlorine dioxide, ammonia, phosphine, arsine, nitric
oxide, carbon dioxide and ozone.
4 7
Using this method, dilution ratios from 1:10 up to 1:10 can be prepared from initial amount-of-
substance fraction.
5.12 Summary
Table 1 gives a summary of the preparation techniques.
6 © ISO 2019 – All rights reserved

ISO 6145-1:2019(E)
Table 1 — Preparation techniques — Summary
Preparation Range of dilution
Advantages Limitations
technique ratio in one-step
— Outlet flow stability
ISO 6145-2: Two-step dilution pos-
1:1 to 1:10
Piston pumps sible, down to 1:10
— Atmospheric pressure
Stability of the flow of gas A and
ISO 6145-4: Starting from a liquid
4 7
1:10 to 1:10 duration limitation due to the sy-
Continuous injection or a gas
ringe volume
— High sensitivity to pressure and
temperature
ISO 6145-5: Two-step dilution
1:1 to 1:10
Capillary possible
— Calibration for each gas or use of
conversion factor
ISO 6145-6: Two-step dilution pos- Calibration for each gas or use of
1:1 to 1:10
Critical flow orifices sible, down to 1:10 conversion factor
ISO 6145-7: Thermal Two-step dilution pos- Calibration of MFC according to each
1:1 to 1:10
mass flow controllers sible, down to 1:10 gas or use of conversion factor
Large range of compo-
ISO 6145-8: High sensitivity to pressure and
1:10 to 1:10 nents available (gas,
Diffusion temperature
liquid or solid)
Large range of compo-
ISO 6145-9: High sensitivity to pressure and
3 6
1:10 to 1:10 nents available (gas,
Saturation temperature
liquid or solid)
— High sensitivity to pressure and
Large range of compo-
temperature
ISO 6145-10:
1:10 to 1:10 nents available (gas,
Permeation
— Not recommended above
liquid or solid)
10 µmol/mol
ISO 6145-11: Stable gas mixtures
4 7
Electrochemical 1:10 to 1:10 can be established Restricted to 14 gases at present
generation within a few minutes
6 Recommendations for handling the dynamic system
6.1 Safety considerations
6.1.1 Reactions between mixture components
Before preparing a gas mixture, it is necessary to consider possible chemical reactions between the
components of the mixture. The method cannot be used to prepare mixtures:
— containing potentially chemically interactive substances (such as hydrochloric acid and ammonia);
— producing other possible dangerous reactions including explosions (such as mixtures containing
flammable gases and oxygen);
— producing strong exothermic polymerizations (such as high concentrations of hydrogen cyanide); and
— containing gases which can decompose (such as acetylene).
A comprehensive compilation of reactive combinations is not available. Therefore, chemical expertise is
required to assess the possible hazards or stability of a gas mixture.
For dangerous reactions and dangerous combinations, to be excluded for safety reasons, some
information can be found in regulations on dangerous goods and in gas supplier handbooks.
ISO 6145-1:2019(E)
6.1.2 Reactions with dynamic system materials
Before preparing a gas mixture, it is necessary to consider possible chemical reactions of mixture
components with materials of the dynamic system. Special consideration shall be given to adsorption
and attack by corrosive gases with metals or elastomers used in the dynamic systems. Such reactions
should be prevented by using only materials that are inert to all components of the mixture. If this is
not possible, measures shall be taken to minimize corrosive attack on the materials with which the
gases make contact to prevent any significant effect on mixture composition.
Information on the compatibility of gases with container materials is given in gas sampling guidelines,
in ISO 16664, ISO 11114-1 and ISO 11114-2, corrosion tables and gas supplier handbooks.
6.2 Quality considerations
6.2.1 Purity of parent gas standards or "zero" gas
The accuracy of the final concentration will depend significantly on the purity of the parent gases and
the zero gas used for the preparation of the calibration gas mixture. Impurities in the parent gases
are often one of the most critical contributors to the uncertainty of the final mixture composition. The
uncertainty contributions depend on the amount of impurities present in the pure, parent gases and
upon the accuracy with which these impurities have been measured. In many cases, the purity of the
complementary gas is of most importance. This is especially true when the amount-of-substance fraction
of the minor component is low, and this component is likely to be an impurity in the complementary
gas. It is also important to evaluate critical impurities that may react with the minor component (for
example, oxygen present in pure nitrogen will react with NO to form NO ). The result of purity analysis
of parent gases shall be incorporated into a purity table containing the amount (or mass) fractions of all
components with accompanying uncertainties derived from analysis.
A gas generator can be used as a source of a complementary gas. A gas generator refers to a device
that produces pure gases from air purification (N O , or air) or by water electrolysis (H ). When a gas
2, 2 2
generator is used, special attention should be drawn to the purity of the gas delivered. For instance, a
nitrogen generator can concentrate argon and hydrocarbons to a significant amount.
ISO 19229 describes the process to follow for performing a purity analysis.
6.2.2 Gas handling
In all cases, and most particularly if very dilute mixtures are concerned, the materials used for the
apparatus are chosen as a function of their resistance to corrosion and low adsorption capacity.
The pressure regulators and the pipework shall be purged before use.
It should be pointed out that the surface adsorption phenomena have a lower impact for dynamic
methods than for static methods.
ISO 16664 gives recommendations for good practice in gas handling.
7 Calibration methods of a dynamic system
7.1 Generalities on the calibration
Any dynamic system should be calibrated either by flow rate or by concentration before the first use.
There are two approaches to calibrate a dynamic system.
— Considering each element of the dynamic system and calibrating each of them; in that case, the
flow rates of each element are calibrated either by volume or by mass. The concentration in the
generated mixture is obtained by calculation, using flow rates.
8 © ISO 2019 – All rights reserved
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