SIST EN ISO 6145-7:2019

SLOVENSKI STANDARD
01-marec-2019
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SIST EN ISO 6145-7:2011
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Gas analysis - Preparation of calibration gas mixtures using dynamic methods - Part 7:
Thermal mass-flow controllers (ISO 6145-7:2018)
Gasanalyse - Herstellung von Kalibriergasgemischen mit Hilfe von dynamisch-
volumetrischen Verfahren - Teil 7: Thermische Massendurchflussregler (ISO 6145-
7:2018)
Analyse des gaz - Préparation des mélanges de gaz pour étalonnage à l'aide de
méthodes dynamiques - Partie 7: Régulateurs thermiques de débit massique (ISO 6145-
7:2018)
Ta slovenski standard je istoveten z: EN ISO 6145-7:2018
ICS:
71.040.40 Kemijska analiza Chemical analysis
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EN ISO 6145-7
EUROPEAN STANDARD
NORME EUROPÉENNE
December 2018
EUROPÄISCHE NORM
ICS 71.040.40 Supersedes EN ISO 6145-7:2010
English Version
Gas analysis - Preparation of calibration gas mixtures
using dynamic methods - Part 7: Thermal mass-flow
controllers (ISO 6145-7:2018)
Analyse des gaz - Préparation des mélanges de gaz Gasanalyse - Herstellung von Kalibriergasgemischen
pour étalonnage à l'aide de méthodes dynamiques - mit Hilfe von dynamisch-volumetrischen Verfahren -
Partie 7: Régulateurs thermiques de débit massique Teil 7: Thermische Massendurchflussregler (ISO 6145-
(ISO 6145-7:2018) 7:2018)
This European Standard was approved by CEN on 16 October 2018.

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, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania,
Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, 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
© 2018 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 6145-7:2018 E
worldwide for CEN national Members.

Contents Page
European foreword . 3

European foreword
This document (EN ISO 6145-7:2018) has been prepared by Technical Committee ISO/TC 158 "Analysis
of gases" in collaboration with 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 June 2019, and conflicting national standards shall be
withdrawn at the latest by June 2019.
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 6145-7:2010.
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, Former Yugoslav Republic of Macedonia,
France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta,
Netherlands, Norway, Poland, Portugal, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland,
Turkey and the United Kingdom.
Endorsement notice
The text of ISO 6145-7:2018 has been approved by CEN as EN ISO 6145-7:2018 without any
modification.
INTERNATIONAL ISO
STANDARD 6145-7
Third edition
2018-12
Gas analysis — Preparation of
calibration gas mixtures using
dynamic methods —
Part 7:
Thermal mass-flow controllers
Analyse des gaz — Préparation des mélanges de gaz pour étalonnage
à l'aide de méthodes dynamiques —
Partie 7: Régulateurs thermiques de débit massique
Reference number
ISO 6145-7:2018(E)
©
ISO 2018
ISO 6145-7:2018(E)
© ISO 2018
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
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Phone: +41 22 749 01 11
Fax: +41 22 749 09 47
Email: copyright@iso.org
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Published in Switzerland
ii © ISO 2018 – All rights reserved

ISO 6145-7:2018(E)
Contents Page
Foreword .iv
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Symbols . 2
5 Principle . 2
6 Set-up . 2
6.1 General . 2
6.2 Thermal mass-flow controller using a constant current supply . 3
6.3 Thermal mass-flow controller under constant temperature control . 3
7 Preparation of gas mixtures . 4
7.1 Description of the experimental procedure . . 4
7.2 Range of validity . 6
7.3 Operating conditions . 6
8 Calculations. 7
8.1 Volume fraction . 7
8.2 Sources of uncertainty . 7
8.3 Uncertainty of measurement . 8
Annex A (informative) Pre-mixed gases for the preparation of mixtures of high dilution .9
Annex B (informative) Practical hints .10
Annex C (informative) Calculation of uncertainties .12
Bibliography .14
ISO 6145-7:2018(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 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 158, Analysis of gases.
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.
This third edition cancels and replaces the second edition (ISO 6145-7:2009), which has been technically
revised. The main changes compared to the previous edition are as follows:
— correction of some errors in the formulae in Annexes A and C;
— minor editorial corrections.
A list of all parts in the ISO 6145 series can be found on the ISO website.
iv © ISO 2018 – All rights reserved

INTERNATIONAL STANDARD ISO 6145-7:2018(E)
Gas analysis — Preparation of calibration gas mixtures
using dynamic methods —
Part 7:
Thermal mass-flow controllers
1 Scope
ISO 6145 is a series of documents dealing with various dynamic methods used for the preparation of
calibration gas mixtures. This document specifies a method for continuous preparation of calibration
gas mixtures, from nominally pure gases or gas mixtures by use of thermal mass-flow controllers. The
method is applicable to preparation of mixtures of non-reacting species, i.e. those which do not react
with any material of construction of the flow path in the thermal mass-flow controller or the ancillary
equipment.
If this method is employed for preparation of calibration gas mixtures the optimum performance is
as follows: the relative expanded measurement uncertainty U, obtained by multiplying the standard
uncertainty by a coverage factor k = 2, is not greater than 2 %.
−6
If pre-mixed gases are used instead of pure gases, mole fractions below 10 can be obtained. The
measurement of mass flow is not absolute and the flow controller requires independent calibration.
The merits of the method are that a large quantity of the calibration 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.
NOTE Gas blending systems, based upon thermal mass-flow controllers, and some including the facility of
computerization and automatic control, are commercially available.
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 6145-1, Gas analysis — Preparation of calibration gas mixtures using dynamic volumetric methods —
Part 1: Methods of calibration
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 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 apply.
ISO 6145-7:2018(E)
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
— IEC Electropedia: available at: http: //www .electropedia .org/
4 Symbols
C Heat capacity (at constant pressure)
p
i,k Indices for components in a gas or gas mixture
j Index for a parent gas
m Mass
p Pressure
q Number of components in the gas mixture
q Mass flow rate
m
q Volume flow rate
V
T Temperature
V Volume
Φ Heat flux
ϕ Volume fraction of a component in a parent gas
φ Volume fraction of a component in a gas mixture
ρ Density
5 Principle
The continuous preparation of calibration gas mixtures from nominally pure gases or other gas
mixtures by the use of commercially available thermal mass-flow controllers is described. By
adjustment of the set-points on the mass flow controllers to pre-determined values, it is possible to
change the composition of the gas mixture rapidly and in a continuously variable manner. By selection
of appropriate combinations of thermal mass-flow controllers and with use of pure gases, the volume
fraction of the component of interest in the matrix gas can be varied by a factor of 1 000.
6 Set-up
6.1 General
To prepare a gas mixture, each gaseous component is passed through a calibrated thermal mass flow
controller (TMC) at a known and controlled flow rate and at constant pressure. Accurate flow meters
are used to measure the relevant flow rates in order to achieve an acceptable level of uncertainty
regardless of the setting of the mass flow controller (see also ISO 6145-1).
A TMC consists of a measuring unit for mass flow and a proportioning valve which is controlled by an
electronic unit (see also Reference [1] and [2]).
2 © ISO 2018 – All rights reserved

ISO 6145-7:2018(E)
6.2 Thermal mass-flow controller using a constant current supply
The flowing gas is passed through a heater connected to a constant current supply and the temperature
is sensed upstream and downstream from the heater.
Figure 1 shows the working principle of a TMC and its key parts: heater, temperature sensors and
associated circuitry. The two temperature sensors, one upstream and one downstream from the heater
form two arms of a Wheatstone bridge circuit, which is balanced to give zero reading when there is
no gas flow. When there is a gas flow through the system a temperature difference, ΔT, is established
between the two sensors such that the heat flux, Φ, is given by Formula (1):
ΦΔ=CTq (1)
pm
Key
1 temperature sensor 1 5 current supply
2 heater 6 wheatstone bridge
3 temperature sensor 2 7 differential amplifier
4 gas supply 8 signal readout
Figure 1 — Principle of a thermal mass-flow controller with constant current supply
The difference in temperature between sensors results in a potential difference across the Wheatstone
bridge circuit and thus a signal. The signal is compared with an adjustable reference voltage in a
differential amplifier. The resulting output signal is in turn used for operating a control valve to
regulate the flow of gas.
6.3 Thermal mass-flow controller under constant temperature control
In the system, shown in Figure 2, the parent gas passes through three heaters in sequence, each of
which is connected into an arm of a self-regulating Wheatstone bridge. Instead of the difference in
temperature being measured, the input to each heater is such that the temperature distribution along
the flow path is uniformly maintained. The Wheatstone bridge current is proportional to the heat loss
and therefore proportional also to the mass flow of the gas. The output signal is again used to operate a
solenoid valve to control the mass flow rate.
ISO 6145-7:2018(E)
Key
1 heater 1 5 current supply
2 heater 2 6 wheatstone bridge
3 heater 3 7 differential amplifier
4 gas supply 8 signal readout
Figure 2 — Thermal mass-flow controller under constant temperature control
In the preparation of multicomponent mixtures, it is generally necessary to use one mass-flow controller
for each component. Dual-channel controllers are available and may be used in the preparation of
binary mixtures or, for example, preparation of mixtures of a given gas in air.
7 Preparation of gas mixtures
7.1 Description of the experimental procedure
A schematic diagram of the arrangement for preparation of binary mixtures is shown in Figure 3.
The pressure and temperature at the time of the calibration shall be recorded. Depending on the gases
to be mixed and their departure from ideality, the volume fraction can be somewhat influenced by the
ambient pressure and temperature. The pressure and temperature at the time of calibration of the
analyser should be as near as possible to those prevalent at the time the TMCs were checked by the
comparison method ISO 6143 or ISO 12963 (see 7.3).
Compositions of calibration gas mixtures are normally expressed by volume fractions but
manufacturers’ accuracy specifications for thermal mass-flow controllers are usually expressed in
terms of percentage of the full scale of the instrument. The relative expanded uncertainty of 2 %, which
is quoted in the Scope of this document, is 2 % of the volume fraction of the calibration component of
the mixture. This value assumes optimum use of each TMC in the system, which means that each is
operated at, or very near to, its maximum flow rate. Thus, if a TMC is operated at 10 % of full scale, th
...