ISO 6145-2:2014
(Main)Gas analysis — Preparation of calibration gas mixtures using dynamic methods — Part 2: Piston pumps
Gas analysis — Preparation of calibration gas mixtures using dynamic methods — Part 2: Piston pumps
ISO 6145 comprises a series of International Standards dealing with various dynamic methods used for the preparation of calibration gas mixtures. ISO 6145-2:2014 describes a method and preparation system using piston pumps. The mixture composition and its associated uncertainty are based on calibration of the piston pumps by dimensional measurements. The calibration gas mixtures prepared using this method consist of two or more components, prepared from pure gases or other gas mixtures using gas-mixing pumps. Such gas-mixing pumps contain at least two piston pumps, each driven with a defined ratio of strokes, and appropriate accessories for gas feeding and mixture homogenization. ISO 6145-2:2014 is applicable only to mixtures of gaseous or totally vaporized components including corrosive gases, as long as these components neither react with each other nor with the wetted surfaces of the mixing pump. The use of gas mixtures as parent gases is covered as well. Multi-component gas mixtures and multi-step dilution procedures are included in this International Standard as they are considered to be special cases of the preparation of two-component mixtures. ISO 6145-2:2014 describes a method of preparing calibration gas mixtures whose composition is expressed in volume fractions. The necessary equations and associated uncertainty evaluation to express the gas composition in amount?of?substance fractions are given in Annex A. With this method, provided that sufficient quality assurance and control measures are taken, calibration gas mixtures can be prepared with a relative expanded uncertainty of 0,5 % (coverage factor k = 2) in the volume fraction. Numerical examples showing that under specified conditions smaller uncertainties are attainable are given in Annexes B through D. Using this method, dilution ratios of 1:10 000 can be achieved in discrete increments. Lower fractions (down to 1 × 10−8) can be achieved by multi-stage dilution or by the use of gas mixtures as input gases. Final mixture flow rates of 5 l/h to 500 l/h can be realized depending on the equipment used.
Analyse des gaz — Préparation des mélanges de gaz pour étalonnage à l'aide de méthodes volumétriques dynamiques — Partie 2: Pompes à piston
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Standards Content (Sample)
INTERNATIONAL ISO
STANDARD 6145-2
Second edition
2014-08-15
Gas analysis — Preparation of
calibration gas mixtures using
dynamic methods —
Part 2:
Piston pumps
Analyse des gaz — Préparation des mélanges de gaz pour étalonnage
à l’aide de méthodes volumétriques dynamiques —
Partie 2: Pompes à piston
Reference number
©
ISO 2014
© ISO 2014
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ii © ISO 2014 – All rights reserved
Contents Page
Foreword .iv
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 2
4 Symbols . 2
5 Principle and equipment . 3
5.1 Principle . 3
5.2 Equipment . 3
6 Calibration gas mixture preparation . 5
6.1 Safety issues . 5
6.2 Mixture feasibility . 6
6.3 Preparation system and setting-up of mixture composition . 7
6.4 Input pressure control . 7
6.5 Temperature control . 7
6.6 Homogenization . 7
6.7 Stability . 8
6.8 Output pressure and flow pulsation . 8
6.9 Composition of the parent gases . 8
7 Calculation of volume fractions and associated uncertainty evaluation .9
7.1 Calculation method A . 9
7.2 Calculation method B .10
8 Gas mixture composition verification .12
Annex A (normative) Amount-of-substance fractions .13
Annex B (informative) Uncertainty evaluation of the gas mixture composition .15
Annex C (informative) Gas mixture verification .21
Annex D (informative) Numerical example .25
Bibliography
.............................................................................................................................................................................................................................30
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. 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. 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 meaning of ISO specific terms and expressions related to conformity
assessment, as well as information about ISO’s adherence to the WTO principles in the Technical Barriers
to Trade (TBT) see the following URL: Foreword - Supplementary information
The committee responsible for this document is ISO/TC 158, Analysis of gases.
This second edition cancels and replaces the first edition (ISO 6145-2:2001), which has been technically
revised. The main objective of this revision is to extend the first edition for calculating the composition
in volume and amount–of–substance fractions from the displacement volumes of piston pumps.
Appropriate measurement functions and guidance on uncertainty evaluation are given for the mixing of
real gases at unequal operational conditions of the piston pumps.
ISO 6145 consists of the following parts, under the general title Gas analysis — Preparation of calibration
gas mixtures using dynamic methods:
— Part 1: Methods of calibration
— Part 2: Volumetric pumps
— Part 4: Continuous syringe injection method
— Part 5: Capillary calibration devices
— Part 6: Critical orifices
— Part 7: Thermal mass-flow controllers
— Part 8: Diffusion method
— Part 9: Saturation method
— Part 10: Permeation method
— Part 11: Electrochemical generation
ISO 6145-3, entitled Periodic injections into a flowing gas stream, has been withdrawn.
iv © ISO 2014 – All rights reserved
INTERNATIONAL STANDARD ISO 6145-2:2014(E)
Gas analysis — Preparation of calibration gas mixtures
using dynamic methods —
Part 2:
Piston pumps
1 Scope
ISO 6145 comprises a series of International Standards dealing with various dynamic methods used for
the preparation of calibration gas mixtures. This part of ISO 6145 describes a method and preparation
system using piston pumps. The mixture composition and its associated uncertainty are based on
calibration of the piston pumps by dimensional measurements.
The calibration gas mixtures prepared using this method consist of two or more components, prepared
from pure gases or other gas mixtures using gas-mixing pumps. Such gas-mixing pumps contain at
least two piston pumps, each driven with a defined ratio of strokes, and appropriate accessories for gas
feeding and mixture homogenization.
This part of ISO 6145 is applicable only to mixtures of gaseous or totally vaporized components including
corrosive gases, as long as these components neither react with each other nor with the wetted surfaces
of the mixing pump. The use of gas mixtures as parent gases is covered as well. Multi-component gas
mixtures and multi-step dilution procedures are included in this International Standard as they are
considered to be special cases of the preparation of two-component mixtures.
This part of ISO 6145 describes a method of preparing calibration gas mixtures whose composition
is expressed in volume fractions. The necessary equations and associated uncertainty evaluation to
express the gas composition in amount–of–substance fractions are given in Annex A.
With this method, provided that sufficient quality assurance and control measures are taken, calibration
gas mixtures can be prepared with a relative expanded uncertainty of 0,5 % (coverage factor k = 2) in
the volume fraction. Numerical examples showing that under specified conditions smaller uncertainties
are attainable are given in Annexes B through D.
Using this method, dilution ratios of 1:10 000 can be achieved in discrete increments. Lower fractions
−8
(down to 1 × 10 ) can be achieved by multi-stage dilution or by the use of gas mixtures as input gases.
Final mixture flow rates of 5 l/h to 500 l/h can be realized depending on the equipment used.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and are
indispensable for its application. For dated references, only the edition cited applies. For undated
references, the latest edition of the referenced document (including any amendments) applies.
ISO 7504, Gas analysis — Vocabulary
ISO 14912, Gas analysis — Conversion of gas mixture composition data
ISO/IEC Guide 98-3, Uncertainty of measurement — Part 3: Guide to the expression of uncertainty in
measurement (GUM:1995)
ISO/IEC Guide 99, International vocabulary of metrology — Basic and general concepts and associated
terms (VIM)
3 Terms and definitions
For the purposes of this document, terms and definitions given in ISO/IEC Guide 99, ISO/IEC Guide 98-3,
ISO 14912, ISO 7504, and the following apply.
3.1
operational conditions
pressure and temperature in the piston pumps at which the gas mixture is prepared
3.2
parent gas
pure gas or gas mixture used for preparation of a gas mixture
3.3
piston pump
gas forwarding system comprising cylinder, piston, steering plate, and eccentric driving disk mounted
on a common plate
3.4
reduction gear ratio
quotient of the number of strokes and the maximum number of strokes of the piston pump that can be
set in distinct steps by the switch gear
3.5
reference conditions
pressure and temperature to which volume fractions refer
3.6
stroke volume
forwarding geometric displacement volume per stroke of a piston pump
4 Symbols
Symbol Quantity Unit
−1
B’ second virial coefficient (virial equation–of–state in pressure) Pa
i index of a component
k,l index of a piston pump; index of a parent gas
L gear ratio
N number of strokes (in a given period of time)
N maximum number of strokes (in a given period of time)
max
n amount–of–substance mol
n total amount–of–substance of a mixture mol
mix
p pressure Pa
−1 −1
R ideal gas constant J mol K
T temperature K
u standard uncertainty
V gas volume m
2 © ISO 2014 – All rights reserved
Symbol Quantity Unit
V stroke volume m
geo
x amount–of–substance fraction (of a component in a parent gas) 1
y amount–of–substance fraction (of a component in the prepared gas mixture) 1
Z compressibility 1
ϕ volume fraction (of a component in the prepared gas mixture) 1
φ volume fraction (of a component in a parent gas) 1
5 Principle and equipment
5.1 Principle
The principle of the dynamic preparation method described in this part of ISO 6145 is based on the
displacement volume of piston pumps forwarding defined gas portions that are continuously merged and
homogenized for obtaining the required gas mixture. For pure gases, the volume fraction of component
i in the prepared gas mixture is approximately equal to the volume of component i divided by total
volume of all components, as given by Formula (1):
NV⋅
igeo,i
ϕ (1)
≈
i
NV⋅
∑ kgeo,k
k
where ϕ denotes the volume fraction of component i at the operational cond
...
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