IEC 61207-2:2019

Expression of performance of gas analyzers - Part 2: Measuring oxygen in gas utilizing high-temperature electrochemical sensors

IEC 61207-2:2019 applies to all aspects of analyzers using high-temperature electro¬chemical sensors for the measurement of oxygen in gas. It applies to in-situ and extractive analyzers and to analyzers installed indoors and outdoors.
The object of this part is:
– to specify the terminology and definitions related to the functional performance of gas analyzers, utilizing a high-temperature electrochemical sensor, for the continuous measurement of oxygen concentration in a sample of gas;
– to unify methods used in making and verifying statements on the functional performance of such analyzers;
– to specify what tests are performed to determine the functional performance and how such tests are carried out;
– to provide basic documents to support the application of internationally recognized quality management standards. This second edition cancels and replaces the first edition published in 1994. This edition constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous edition.
a) all the terms and definitions relating to the document have been updated where appropriate;
b) the description of the principle of the galvanic cell has been expanded and clarified;
c) new definitions and illustrations have been added for different measurement methods for oxygen using solid electrolytes for galvanic cells;
d) new illustrations have been added for existing descriptions for ion pump cells;
e) a more detailed description of the effect of the presence of oxidizable gases has been added;
f) all references to “errors” have been replaced by “uncertainties” and appropriate updated definitions applied.

Expression des qualités de fonctionnement des analyseurs de gaz - Partie 2: Mesure de l'oxygène contenu dans le gaz en utilisant des capteurs électrochimiques à haute température

IEC 61207-2:2019 s’applique à tous les aspects des analyseurs utilisant des capteurs électrochimiques à haute température pour la mesure de l’oxygène contenu dans le gaz. Elle s’applique aux analyseurs in situ et extractifs, ainsi qu’aux analyseurs installés à l’intérieur et à l’extérieur.
La présente partie a pour objet:
– de spécifier la terminologie et les définitions relatives aux caractéristiques fonctionnelles des analyseurs de gaz utilisant un capteur électrochimique à haute température pour mesurer en continu la concentration d’oxygène dans un échantillon de gaz;
– d’unifier les méthodes utilisées pour établir et vérifier les spécifications relatives aux caractéristiques fonctionnelles de tels analyseurs;
– de spécifier les essais à effectuer afin de déterminer les caractéristiques fonctionnelles et la manière d’effectuer ces essais;
– fournir des documents de base appuyant l'application des normes de gestion de la qualité reconnues sur le plan international. Cette deuxième édition annule et remplace la première édition parue en 1994. Cette édition constitue une révision technique.
Cette édition inclut les modifications techniques majeures suivantes par rapport à l'édition précédente:
a) tous les termes et définitions concernant le document ont été actualisés le cas échéant;
b) la description du principe du générateur électrochimique a été étendue et clarifiée;
c) de nouvelles définitions et figures ont été ajoutées pour les différentes méthodes de mesure de l’oxygène, en utilisant des électrolytes solides pour les générateurs électrochimiques;
d) de nouvelles figures ont été ajoutées pour les descriptions existantes des cellules à pompe ionique;
e) une description plus détaillée des effets de la présence de gaz oxydants a été ajoutée;
f) toutes les références à des «erreurs» ont été remplacées par des «incertitudes» et l’actualisation des définitions a été effectuée en fonction.

General Information

• Status: Published
• Publication Date: 17-Jun-2019
• ICS: 71.040.20 - Laboratory ware and related apparatus
• ICS: 71.040.40 - Chemical analysis
• Technical Committee: SC 65B - Measurement and control devices
• Drafting Committee: WG 14 - TC 65/SC 65B/WG 14
• Current Stage: PPUB - Publication issued
• Start Date: 18-Jun-2019
• Completion Date: 05-Jul-2019

Relations

• Revises: IEC 61207-2:1994 - Expression of performance of gas analyzers - Part 2: Oxygen in gas (utilizing high-temperature electrochemical sensors)
• Effective Date: 05-Sep-2023

Standards Content (Sample)

IEC 61207-2 ®
Edition 2.0 2019-06
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Expression of performance of gas analyzers –
Part 2: Measuring oxygen in gas utilizing high-temperature electrochemical
sensors
Expression des qualités de fonctionnement des analyseurs de gaz –
Partie 2: Mesure de l'oxygène contenu dans le gaz en utilisant des capteurs
électrochimiques à haute température
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 IEC or IEC's member National Committee in the country of the requester. If you have any questions about IEC
copyright or have an enquiry about obtaining additional rights to this publication, please contact the address below or
your local IEC member National Committee for further information.

Droits de reproduction réservés. Sauf indication contraire, aucune partie de cette publication ne peut être reproduite
ni utilisée sous quelque forme que ce soit et par aucun procédé, électronique ou mécanique, y compris la photocopie
et les microfilms, sans l'accord écrit de l'IEC ou du Comité national de l'IEC du pays du demandeur. Si vous avez des
questions sur le copyright de l'IEC ou si vous désirez obtenir des droits supplémentaires sur cette publication, utilisez
les coordonnées ci-après ou contactez le Comité national de l'IEC de votre pays de résidence.

IEC Central Office Tel.: [phone]
3, rue de Varembé [e-mail]
CH-1211 Geneva 20 www.iec.ch
Switzerland
About the IEC
The International Electrotechnical Commission (IEC) is the leading global organization that prepares and publishes
International Standards for all electrical, electronic and related technologies.

About IEC publications
The technical content of IEC publications is kept under constant review by the IEC. Please make sure that you have the
latest edition, a corrigendum or an amendment might have been published.

IEC publications search - webstore.iec.ch/advsearchform Electropedia - www.electropedia.org
The advanced search enables to find IEC publications by a The world's leading online dictionary on electrotechnology,
variety of criteria (reference number, text, technical containing more than 22 000 terminological entries in English
committee,…). It also gives information on projects, replaced and French, with equivalent terms in 16 additional languages.
and withdrawn publications. Also known as the International Electrotechnical Vocabulary

(IEV) online.
IEC Just Published - webstore.iec.ch/justpublished
Stay up to date on all new IEC publications. Just Published IEC Glossary - std.iec.ch/glossary
details all new publications released. Available online and 67 000 electrotechnical terminology entries in English and
once a month by email. French extracted from the Terms and Definitions clause of
IEC publications issued since 2002. Some entries have been
IEC Customer Service Centre - webstore.iec.ch/csc collected from earlier publications of IEC TC 37, 77, 86 and
If you wish to give us your feedback on this publication or CISPR.

need further assistance, please contact the Customer Service

Centre: [e-mail].
A propos de l'IEC
La Commission Electrotechnique Internationale (IEC) est la première organisation mondiale qui élabore et publie des
Normes internationales pour tout ce qui a trait à l'électricité, à l'électronique et aux technologies apparentées.

A propos des publications IEC
Le contenu technique des publications IEC est constamment revu. Veuillez vous assurer que vous possédez l’édition la
plus récente, un corrigendum ou amendement peut avoir été publié.

Recherche de publications IEC - Electropedia - www.electropedia.org
webstore.iec.ch/advsearchform Le premier dictionnaire d'électrotechnologie en ligne au
La recherche avancée permet de trouver des publications IEC monde, avec plus de 22 000 articles terminologiques en
en utilisant différents critères (numéro de référence, texte, anglais et en français, ainsi que les termes équivalents dans
comité d’études,…). Elle donne aussi des informations sur les 16 langues additionnelles. Egalement appelé Vocabulaire
projets et les publications remplacées ou retirées. Electrotechnique International (IEV) en ligne.

IEC Just Published - webstore.iec.ch/justpublished Glossaire IEC - std.iec.ch/glossary
Restez informé sur les nouvelles publications IEC. Just 67 000 entrées terminologiques électrotechniques, en anglais
Published détaille les nouvelles publications parues. et en français, extraites des articles Termes et Définitions des
Disponible en ligne et une fois par mois par email. publications IEC parues depuis 2002. Plus certaines entrées
antérieures extraites des publications des CE 37, 77, 86 et
Service Clients - webstore.iec.ch/csc CISPR de l'IEC.

Si vous désirez nous donner des commentaires sur cette
publication ou si vous avez des questions contactez-nous:
[e-mail].
IEC 61207-2 ®
Edition 2.0 2019-06
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Expression of performance of gas analyzers –

Part 2: Measuring oxygen in gas utilizing high-temperature electrochemical

sensors
Expression des qualités de fonctionnement des analyseurs de gaz –

Partie 2: Mesure de l'oxygène contenu dans le gaz en utilisant des capteurs

électrochimiques à haute température

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 71.040.20; 71.040.40 ISBN 978-2-8322-7045-5

– 2 – IEC 61207-2:2019 © IEC 2019
CONTENTS
FOREWORD . 3
INTRODUCTION . 5
1 Scope . 6
2 Normative references . 6
3 Terms, definitions, and concepts . 6
3.1 Terms and definitions . 6
3.2 Concepts . 7
3.2.1 High-temperature electrochemical sensor . 7
3.2.2 Reference gas . 10
3.2.3 In situ analyzer . 10
3.2.4 Extractive analyzer . 11
3.2.5 Hazardous area . 11
3.2.6 Flame trap . 11
3.2.7 Essential ancillary units . 11
4 Procedures for specification . 11
4.1 General . 11
4.2 Specification of essential units and ancillary services . 11
4.2.1 General . 11
4.2.2 Rated range of reference gas pressure . 11
4.2.3 Rated range of calibration gas pressure. 12
4.2.4 Rated range of aspirator gas pressure . 12
4.3 Additional terms related to the specification of performance . 12
4.4 Important terms related to the specification of performance . 12
4.4.1 General . 12
4.4.2 Rated range of sample gas temperature . 12
4.4.3 Rated range of sample gas pressure . 12
4.4.4 Rated range of interfering components . 12
5 Procedures for compliance testing . 13
5.1 General . 13
5.2 Testing procedures . 14
5.3 Output fluctuation . 14
5.4 Delay time, rise time and fall time . 15
Bibliography . 21

Figure 1 – Flow through tube sensor . 15
Figure 2 – Test tube sensor . 16
Figure 3 – Disc sensor . 16
Figure 4 – Twin chamber design . 16
Figure 5 – Sealed reference design . 17
Figure 6 – Limiting current design . 17
Figure 7 – Fixed volume design . 18
Figure 8 – General test arrangement: In situ analyzer . 19
Figure 9 – General test arrangement: Extractive analyzer . 20

INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
EXPRESSION OF PERFORMANCE OF GAS ANALYZERS –

Part 2: Measuring oxygen in gas
utilizing high-temperature electrochemical sensors

FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of IEC is to promote
international co-operation on all questions concerning standardization in the electrical and electronic fields. To
this end and in addition to other activities, IEC publishes International Standards, Technical Specifications,
Technical Reports, Publicly Available Specifications (PAS) and Guides (hereafter referred to as “IEC
Publication(s)”). Their preparation is entrusted to technical committees; any IEC National Committee interested
in the subject dealt with may participate in this preparatory work. International, governmental and non-
governmental organizations liaising with the IEC also participate in this preparation. IEC collaborates closely
with the International Organization for Standardization (ISO) in accordance with conditions determined by
agreement between the two organizations.
2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international
consensus of opinion on the relevant subjects since each technical committee has representation from all
interested IEC National Committees.
3) IEC Publications have the form of recommendations for international use and are accepted by IEC National
Committees in that sense. While all reasonable efforts are made to ensure that the technical content of IEC
Publications is accurate, IEC cannot be held responsible for the way in which they are used or for any
misinterpretation by any end user.
4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications
transparently to the maximum extent possible in their national and regional publications. Any divergence
between any IEC Publication and the corresponding national or regional publication shall be clearly indicated in
the latter.
5) IEC itself does not provide any attestation of conformity. Independent certification bodies provide conformity
assessment services and, in some areas, access to IEC marks of conformity. IEC is not responsible for any
services carried out by independent certification bodies.
6) All users should ensure that they have the latest edition of this publication.
7) No liability shall attach to IEC or its directors, employees, servants or agents including individual experts and
members of its technical committees and IEC National Committees for any personal injury, property damage or
other damage of any nature whatsoever, whether direct or indirect, or for costs (including legal fees) and
expenses arising out of the publication, use of, or reliance upon, this IEC Publication or any other IEC
Publications.
8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
indispensable for the correct application of this publication.
9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of
patent rights. IEC shall not be held responsible for identifying any or all such patent rights.
International Standard IEC 61207-2 has been prepared by sub-committee 65B: Measurement
and control devices of IEC technical committee 65: Industrial-process measurement, control
and automation.
This second edition cancels and replaces the first edition published in 1994. This edition
constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous
edition.
a) all the terms and definitions relating to the document have been updated where
appropriate;
b) the description of the principle of the galvanic cell has been expanded and clarified;

– 4 – IEC 61207-2:2019 © IEC 2019
c) new definitions and illustrations have been added for different measurement methods for
oxygen using solid electrolytes for galvanic cells;
d) new illustrations have been added for existing descriptions for ion pump cells;
e) a more detailed description of the effect of the presence of oxidizable gases has been
added;
f) all references to “errors” have been replaced by “uncertainties” and appropriate updated
definitions applied.
The text of this International Standard is based on the following documents:
FDIS Report on voting
65B/1156/FDIS 65B/1158/RVD
Full information on the voting for the approval of this standard can be found in the report on
voting indicated in the above table.
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.
This International Standard is to be used in conjunction with IEC 61207-1:2010.
A list of all parts in the IEC 61207 series under the general title Expression of performance of
gas analyzers, can be found on the IEC website.
The committee has decided that the contents of this publication will remain unchanged until
the stability date indicated on the IEC website under "http://webstore.iec.ch" in the data
related to the specific publication. At this date, the publication will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
INTRODUCTION
This part of IEC 61207 includes the terminology, definitions, statements and tests that are
specific to oxygen analyzers, which utilise high-temperature electrochemical sensors.
Oxygen analyzers employing high-temperature electrochemical sensors operating at tem-
peratures usually in excess of 500 °C, have a wide range of applications for the measurement
of oxygen in gas samples. Such samples are typically the result of a combustion process or
oxygen impurity measurements.
Two main types of analyzer exist, the in situ analyzer, where the sensor is positioned within
the process duct work, and the "extractive" analyzer, where the sample is drawn from the duct
via a simple sample system and presented to the sensor.
An analyzer will typically comprise a sensor head, mounted on the process duct, and a control
unit remotely mounted, with interconnecting cable.

– 6 – IEC 61207-2:2019 © IEC 2019
EXPRESSION OF PERFORMANCE OF GAS ANALYZERS –

Part 2: Measuring oxygen in gas
utilizing high-temperature electrochemical sensors

1 Scope
This part of IEC 61207 applies to all aspects of analyzers using high-temperature electro-
chemical sensors for the measurement of oxygen in gas.
It applies to in-situ and extractive analyzers and to analyzers installed indoors and outdoors.
The object of this part is:
– to specify the terminology and definitions related to the functional performance of gas
analyzers, utilizing a high-temperature electrochemical sensor, for the continuous
measurement of oxygen concentration in a sample of gas;
– to unify methods used in making and verifying statements on the functional performance of
such analyzers;
– to specify what tests are performed to determine the functional performance and how such
tests are carried out;
– to provide basic documents to support the application of internationally recognized quality
management standards.
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.
IEC 61207-1:2010, Expression of performance of gas analyzers – Part 1: General
3 Terms, definitions, and concepts
3.1 Terms and definitions
No terms and definitions are listed in this document.
ISO and IEC maintain terminological databases for use in standardization at the following
addresses:
• IEC Electropedia: available at http://www.electropedia.org/
• ISO Online browsing platform: available at http://www.iso.org/obp

3.2 Concepts
3.2.1 High-temperature electrochemical sensor
3.2.1.1 General
°
The sensor is usually controlled at a stable, high temperature, typically in excess of 500 C.
This high temperature is normally maintained by an electric heater, however, in some high-
temperature in-situ applications, the sensor may require cooling to be applied. The sensor
may also be run in passive mode with temperature sensing, where the heating is provided by
the sample environment and the measured temperature is used in the calculation of the
oxygen concentration. The high-temperature electrochemical sensor can be constructed in
two basic forms:
a) galvanic concentration cell;
b) ion pump cell.
3.2.1.2 Galvanic concentration cell (gauge cell)
3.2.1.2.1 General
Most commercially available analyzers employ the galvanic concentration cell consisting of
two gas volumes or chambers, separated by an oxygen ion conducting solid electrolyte, and
provided with a porous electrode on each side. The two sides are filled with sample gas on
the one side and a fixed oxygen partial pressure reference gas on the other side. The
reference gas shall contain some oxygen. The reference gas is usually air, but could be
another constant oxygen partial pressure mixture or even a sealed reference where the
oxygen partial pressure is maintained by a metal/metal oxide mixture.
The electrodes are catalytic and the electrode/solid electrolyte interface at elevated
2-
temperature allows the formation of oxygen ions (O ) which can then diffuse across the solid
electrolyte interface. This interface remains an impenetrable barrier for the other gases
present and thus provides a selective means of determining the partial pressure of oxygen
present in the sample gas. The solid electrolyte is typically yttrium oxide (yttria)-stabilized
zirconium oxide (zirconia), and the porous electrode is platinum based, although other
materials may be used. The signal magnitude is temperature dependent and thus requires a
low uncertainty of temperature measurement of the solid electrolyte interface by employing
IEC 60751, and stability of heating provided
temperature sensors as given in IEC 60584 and
to achieve the high temperatures required for efficient and sensitive operation.
When the sensor is brought to a temperature at which the solid electrolyte conducts oxygen
ions, and the e.m.f. between the two electrodes is measured, the output will be related to the
logarithm of the ratio of the partial pressures of oxygen at each of the electrodes in
accordance with the Nernst formula:
RT P
E= ln
(1)
4FP
P
E= k log
(2)
P
P
ET()mV = 0,0496 log
(3)
P
– 8 – IEC 61207-2:2019 © IEC 2019
where
P is the partial pressure of oxygen in the reference gas;
P is the partial pressure of oxygen in the sample gas;
E is the electromotive force output from the cell in mV;
-1 -1
R is the gas constant (8,314 4 J K mol );
T is the absolute temperature (K);
4 -1
F is the Faraday constant (9,648 53 x 10 C mol );
k is the Nernstian coefficient (slope factor).
Thus, provided the oxygen partial pressure is known at one electrode (P ), then the potential
difference between the two electrodes will enable the unknown oxygen pressure to be
determined at the other electrode (P ).
Note that in the above formulae, it is the partial pressure of oxygen on the two sides which is
important, not the fractional component of the oxygen. Therefore, if equal component mixtures
containing oxygen (e.g. air), but at different absolute pressures, are applied to either side of
the solid electrolyte barrier, the signal will not be 0 mV, but proportional to the logarithm of the
ratio of the absolute pressures of the gases on each side.
The Nernstian response of the high-temperature electrochemical ceramic sensor holds over a
very wide range of oxygen partial pressures differences, and the sensor output increases
logarithmically with linear reduction of the oxygen's partial pressure at a given temperature.
The sensor output is directly proportional to temperature, and hence for quantitative analysis,
the temperature of the cell should be closely controlled and/or measured, and the necessary
corrections applied in Formula (1).
Theoretically, the output e.m.f. of the sensor, when the partial pressures of the sample gas
and reference gas are equal, is 0 V. However, in some sensors, a zero offset is measured and
is considered as being largely due to thermo-electric effects and thermal gradients across the
electrodes. This offset can be considered theoretically as an extra constant (asymmetry
potential).
P
Ek(mV) log+U
10 a
(4)
P
P
EU()mV 0,0496 log+
10 a
(5)
P
where
U is the asymmetry potential (mV).
a
Non-ideal oxygen ion conduction can also be compensated for by introducing modifications to
the slope factor k.
In practice, manufacturers whose sensors exhibit zero offset may supply practical average
values of U to help in calibration. Modern equipment can automatically compensate the
a
asymmetry potential during air point calibration (i.e. air in both chambers).
Typical applications are in combustion control, which measures the oxygen level which can be
in the order of a few percentage points under normal working conditions or in oxygen
contamination, for example in nitrogen production and purification using ASUs (air separation
units), where the oxygen level is in the region of a few parts per million. Therefore, it can be
seen that this technique provides a very wide potential measuring range of the oxygen level
from 100 % down to sub parts per million. In practice, the ultimate lower quantitative
=
=
measurement limit depends on the leak integrity of the device and the limitations of the
electronics. The solid electrolyte sensors may have the gases actively flow fed or diffusionally
fed to the sample and reference sides of the solid electrolyte interface.
Some examples in 3.2.1.2.2 to 3.2.1.2.6 are given of generic sensor designs. For
simplification, the temperature sensors in these illustrations have been shown as being
positioned at the solid electrolyte interface, however, the practical implementation of a generic
design may limit the actual physical location of the temperature sensor. Any non-ideal location
may give rise to a voltage offset (U ) as illustrated in Formulae (4) and (5).
a
NOTE Platinum is frequently used for the electrodes, and the ceramic electrolyte is usually zirconium oxide, fully
or partially stabilized with yttrium oxide, calcium oxide or thorium oxide, which, when heated above 500 °C, allows
the charge transfer mechanism to be predominantly oxygen ion conduction.
3.2.1.2.2 Flow through tube sensor
The solid electrolyte tube is given porous electrodes on the inner and outer surfaces. The
tube is hermetically sealed to inlet and outlet pipes and sample gas flows through the inner
tube, whilst the reference gas (air) surrounds the outer surface. This is shown schematically
in Figure 1.
3.2.1.2.3 Test tube sensor
A solid electrolyte tube is sealed at one end and porous electrodes placed on the inner and
outer surfaces. The sample either flows past or diffuses around the outside of the tube. A
reference gas (air) is in the middle of the tube. External heating provides the high temperature
required. This is shown schematically in Figure 2.
3.2.1.2.4 Disc sensor
A solid electrolyte disc with porous electrodes on each face is sealed into a tube with matched
coefficient of thermal expansion. The outside surface is exposed to sample gas and the inside
surface to a reference gas (air). The high temperature is provided by an internal heater on the
reference side. This configuration is suitable for use as part of an in situ probe for oxygen
measurements. This is shown schematically in Figure 3.
3.2.1.2.5 Twin chamber design
In this design, the sample and reference gases are either flowed or diffusionally fed into two
chambers separated by a solid electrolyte interface. The high working temperature required is
provided by a band heater or equivalent around the outer surface of the solid electrolyte tube,
which gives a relatively wide area of flat thermal gradient leading to a highly stable reading.
This arrangement is best suited for an extractive or close coupled extractive arrangement.
This is shown schematically in Figure 4.
3.2.1.2.6 Sealed reference design
This has similarities to the above generic configurations, however, instead of using a
continuously replenished reference gas (air), a sealed reference volume is used. It is
important to retain a constant partial pressure of oxygen within this volume, and this is
normally achieved by using a mixture of metal and metal oxide powders which maintains an
equilibrium within the reference cavity and acts both as a source and sink for oxygen. This
has the advantage of not requiring a reference gas; however it is more susceptible to the
influence of any breach of the hermetic seal on the reference side. This equilibrium is shown
in Formula (6) where a and b are constants and M and O represent a metal and oxygen. This
arrangement is illustrated schematically in Figure 5. This type of sensor may have a limited
lifetime, depending on working conditions.
b
aM+ O ↔ M O
(6)
2 ab
– 10 – IEC 61207-2:2019 © IEC 2019
3.2.1.3 Ion pump cell
If a direct current is made to flow between the electrodes of a cell, with reference gas (air) in
one chamber and an inert gas in the other chamber, the current flow will cause a pumping of
oxygen molecules from one side to the other. The action obeys Faraday's laws and the
quantity of oxygen pumped by diffusion into the inert gas is given by:
I
Q= (7)
4F
where
-1
Q is the quantity of oxygen pumped, in mol s ;
I is the current (A);
4 -1
F is the Faraday constant (9,648 53 x 10 C mol ).
This is used generally in two basic configurations.
3.2.1.4 Limiting current
A diffusion restriction such as a pinhole limits the rate of arrival of oxygen molecules at the
measuring electrode, and a constant voltage across the electrodes ensures that all the
oxygen arriving at the measuring electrode is pumped to the other side. This reduces the
partial pressure of oxygen at the cathode close to zero. In this limiting condition, the current
flowing is determined by the rate of diffusion of oxygen through the restriction, which in turn is
proportional to the oxygen concentration in the sample gas. The current generated is
quantitatively related to the number of oxygen molecules transferred. An example is shown in
Figure 6.
3.2.1.5 Fixed volume (pump-gauge devices)
This configuration consists of two sets of electrodes arranged across a small fixed volume.
The first set comprises a concentration (gauge) cell, the second set the ion pump. The volume
is initially swept free of oxygen molecules by the ion pump to a predetermined low level as
determined by the concentration cell. Pump action is then initiated in the opposite direction
until the concentration cell reading shows that the oxygen concentration in the volume and
that outside at the sample side, are the same. The current and time required to achieve this
are related to the oxygen concentration of the sample gas. An example is shown in Figure 7.
3.2.2 Reference gas
All analyzers using the high-temperature electrochemical concentration cell require some form
of reference. This could be an applied reference gas of known and constant partial pressure –
for convenience usually air is employed – although in principle it could be any known, stable
oxygen partial pressure. In some instances, a sealed reference is used, where the oxygen
partial pressure is maintained at a constant level (see 3.2.1.2.6).
NOTE The sensor output is a function of the partial pressure of oxygen in the sample, provided the reference has
a constant partial pressure of oxygen.
3.2.3 In situ analyzer
The in situ analyzer has the high-temperature electrochemical sensor situated in the sample;
however the sensor may require a filter to remove particulates.
One version of the in situ analyzer controls the temperature of the sensor in the range
of 500 °C to 900 °C. In this case the sample temperature cannot exceed the control
temperature. The second version relies on the temperature of the sample to attain the
operating temperature. It is then necessary to measure the sensor temperature to enable the
oxygen value to be calculated.

3.2.4 Extractive analyzer
This can be subdivided into two groups: close coupled and extractive. In the "extractive"
analyzer the sensor head is installed outside the gas stream to be measured, and the sample
is drawn through a sample probe and presented to the sensor which is maintained at a
controlled temperature to ensure ionic conduction (typically in the range of 500 °C to 900 °C).
Additionally, the extractive analyzer may require sample conditioning. The extractive analyzer
may require a filter to remove particulates, and a driving force (often an aspirator) to move the
sample. The pipework involved should be minimized and maintained above the dew-point of
any condensable species to prevent formation of any condensation.
3.2.5 Hazardous area
Area in which an explosive gas atmosphere is present, or may be expected to be present, in
quantities such as to require special precautions for the construction, installation and use of
devices
3.2.6 Flame trap
A device used to prevent a flame, resulting from the ignition of a flammable gas mixture, from
propagating.
3.2.7 Essential ancillary units
Essential ancillary units are those without which the analyzer will not operate (e.g., pumps for
aspirators, calibration systems, etc.).
4 Procedures for specification
4.1 General
The procedures for specification are detailed in IEC 61207-1. They cover:
– operation and storage requirements;
– specification of ranges of measurement and output signals;
– limits of uncertainties;
– recommended reference values and rated ranges of influence quantities.
In this part of IEC 61207, specifications of ranges for ancillary equipment are given. Additional
terms for specification of performance and important aspects of performance relevant to high-
temperature electrochemical sensors are also detailed.
4.2 Specification of essential units and ancillary services
4.2.1 General
All oxygen analyzers utilizing high-temperature electrochemical concentration cells require a
reference gas supply. This is usually air, filtered to remove moisture and oil. Analyzers require
facilities for calibration after installation. Bottled calibration gases and pressure regulation
facilities are generally required.
4.2.2 Rated range of reference gas pressure
Reference gas pressure in practice may have small effects on uncertainty.
The reference gas pressure will also affect the reference gas flow. High flows can cause
cooling of electrodes and subsequent uncertainties.

– 12 – IEC 61207-2:2019 © IEC 2019
4.2.3 Rated range of calibration gas pressure
Calibration gas pressure may have small effects on uncertainty. Calibration gas pressure will
also affect calibration gas flow in a similar manner as described in 4.2.2.
4.2.4 Rated range of aspirator gas pressure
For analyzers employing aspirators, the rated range of aspirator gas pressure is required to
ensure correct sample flow (and sometimes reference air flow).
4.3 Additional terms related to the specification of performance
4.3.1 The following additional statements may be required to define the performance of the
analyzer. Depending on the design details, some of these additional terms may be omitted.
4.3.2 Hazardous classification of the area in which the sensor head and electronic unit are
to be located. General purpose analyzers will not be suitable for location in hazardous areas.
4.3.3 As the high-temperature electrochemical sensor is a potential ignition source, an
additional statement on the permissible level of flammable gas in the sample is required.
NOTE Many analyzers are designed to prevent ignition of the sample gas, for example by using flame traps.
4.3.4 The high-temperature electrochemical sensor has a finite life expectancy and will
require occasional replacement. The actual cell life will be dependent on the sample.
4.4 Important terms related to the specification of performance
4.4.1 General
Although covered in IEC 61207-1, the following terms are particularly relevant.
4.4.2 Rated range of sample gas temperature
In an in situ analyzer, operation will only be satisfactory within the rated range of sample gas
temperatures. In an extractive analyzer the extraction probe will only be suitable within the
rated range of the sample gas temperature.
4.4.3 Rated range of sample gas pressure
In certain analyzer designs of the extractive type, sample pressure is important if the sample
is vented to the atmosphere. The sample gas pressure shall be within the rated range to
ensure sample flow.
4.4.4 Rated range of interfering components
If a high-temperature electrochemical sensor is used to measure the oxygen content of a
gaseous mixture which contains moisture and gases capable of being oxidized at the
operating temperature of the sensor, then the oxygen content figures obtained using a high-
temperature electrochemical sensor will always be lower than those obtained when using an
analyzer based on measuring a preconditioned dry sample (e.g., a paramagnetic oxygen
analyzer).
This is due to two facts:
a) Oxygen is consumed at the high-temperature cell surface in accordance with the oxidation
reaction associated with the oxidizable gas. An illustration of this is given in Formula (8)
for a hydrocarbon present in an oxygen containing mixture:

yy
C H + ()x+ O → xCO + H O
(8)
xy 2 22
where C H is a hydrocarbon molecule comprising x atoms of carbon and y atoms of
x y
hydrogen. In this example, every molecule of hydrocarbon present would reduce the

oxygen content by (x+ y / ) molecules.
Carbon monoxide (CO) is a common background gas present in a typical combustion flue
gas mixture. The effect is illustrated in Formula (9) and in this case every two molecules of
carbon monoxide reduce the oxygen content by one molecule.
(9)
22CO+ O → CO
The consumption of oxygen by these oxidation reactions will reduce the final measured
oxygen reading. The impact of this reduction will depend on the application.
If a well-controlled combustion process is being measured with a few per cent oxygen
present, then the net reduction in the oxygen content will typically be less than 0,01% and
so the induced uncertainty will be less than 0,5 % of the reading, which is a small
uncertainty and can be ignored for most practical purposes. Under the condition of low
oxygen level, which results in incomplete combustion of the fuel present and increased
levels of carbon monoxide, the uncertainty will be much greater and may give a
significantly lower than expected oxygen reading. However, since a commercial
combustion system will typically have active feedback adjustment, a low oxygen reading
will normally result in extra oxygen (air) being added to the fuel mix to increase combustion
efficiency and therefore, the impact of this effect is normally acceptable in this application.
If the application involves measuring low level (ppm) oxygen impurity in nitrogen (or other
inert background), then any cross sensitivity to oxidizable gases present could be very
significant. In some instances, the oxidizable gases could potentially consume all of the
oxygen present. In order to minimize the effect of this consumption of oxygen, the
measurement may be optimized by adjusting the operating temperature, the choice of
electrode catalyst and selective deactivation of particular activation pathways on the
catalyst associated with oxidation reactions. By these means, the cross sensitivity to
oxidizable gases can be reduced considerably and allows the application of the solid
electrolyte in these high purity applications. These advantages should be considered in
combination with the potential disadvantages of the resultant reduction in sensitivity if the
working temperature is significantly lowered, and possible heightened susceptibility to
catalyst poisoning.
b) There are sample volume differences: the electrochemical cell uses the wet gas basis
whilst the paramagnetic analyzer often uses the dry gas basis because water vapour in
the source gas is removed prior to measurement.
NOTE 1 It is understood that the inherent selectivity of the zirconium oxide, based on the property of oxygen ion
mobility, makes direct interferences not possible. Indirect interferences can occur of the type in a) above, or by
screening effects, or by parasitic chemical reactions. Also oxygen-based substances which thermally decompose at
the cell operating temperature would obviously interfere with the O determination.
NOTE 2 Some substances can poison the high-temperature electrochemical cell in a permanent manner, thereby
reducing the sensitivity of the cell to oxygen. The poisoning can be a result of decomposition products formed
and/or other chemicals present in the sample coating or permanently adhering to the catalytic surfaces. For
example, free halogens, certain sulphur compounds, silicones, and lead are commonly recognized poisons.
5 Procedures for compliance testing
5.1 General
In order for a high-temperature electrochemical sensor to be used for the quantitative analysis
of oxygen in a sample, the sensor unit shall be maintained at a constant temperature, or the
analyzer should measure the temperature of the sensor and carry out the necessary
correction for any variation in the temperature.

– 14 – IEC 61207-2:2019 © IEC 2019
The tests given in Clause 5 apply to the complete analyzer as supplied by the manufacturer
and include all necessary ancillary equipment to ensure its correct functioning. It will be set
up by the manufacturer, or in accordance with his instructions, prior to testing.
The calibration of the sensor head can usually be carried out using two methods.
The first method utilizes a calibration chamber in which the sensor is enclosed and the
calibration gas is then passed into the chamber. This represents the sampling of calibration
gases as if they were the sample.
The second method utilizes the normal calibration facility, as designed into the analyzer,
whereby the calibration gas is injected on to the sensor without removing it from its working
environment. Figure 8 shows the general test arrangements for the in situ analyzer and Figure
9 for the extractive analyzer.
Both calibration methods should be used initially. Providing the results obtained by each
method are within acceptable limits, the normal calibration facility should be used for all other
tests except the response time test.
Instrument air or some other oxygen-containing gas mixture of known partial pressure is used
. Three
as the reference gas and as the sample gas in order to measure and calibrate for U
a
other calibration gases representing approximately 10 %, 50 %, and 90 % of the measuring
range of oxygen shall be used. The composition of the calibration gases should be traceable
to an accepted standard or checked by independent means. (See IEC 61207-1 for relevant
standards.)
5.2 Testing procedures
The following relevant testing procedures and definitions are detailed in IEC 61207-1:
– intrinsic uncertainty;
– linearity uncertainty;
– repeatability uncertainty;
– output fluctuation;
– drift;
– delay time, rise time and fall time;
– interference uncertainty;
– variation (influence uncertainty);
– warm-up time.
The ancillary equipment, necessary for the correct functioning of the analyzer, will be
maintained under reference conditions.
Additional test details for analyzers utilizing high-temperature electrochemical sensors are
given below.
Due to the nature of the signal, the sample and reference gases shall always contain some
oxygen.
5.3 Output fluctuation
The output fluctuation depends on the level of oxygen to be measured. The analyzer is
presented with an agreed test ga
...