IEC 60068-3-6:2018
(Main)Environmental testing - Part 3-6: Supporting documentation and guidance - Confirmation of the performance of temperature/ humidity chambers
Environmental testing - Part 3-6: Supporting documentation and guidance - Confirmation of the performance of temperature/ humidity chambers
IEC 60068-3-6:2018 provides a uniform and reproducible method of confirming that temperature and humidity test chambers, without specimens, conform to the requirements specified in climatic test procedures of IEC 60068-2 (all parts). This document is intended for users when conducting regular chamber performance monitoring. This second edition cancels and replaces the first edition published in 2001. This edition constitutes a technical revision. This edition includes the following significant technical changes with respect to the previous edition:
- Confirmation procedures are clarified.
The French version of this standard has not been voted upon.
Essais d'environnement - Partie 3-6: Documentation d'accompagnement et recommandations – Confirmation des performances des chambres d'essai en température/humidité
L'IEC 60068-3-6:2018 fournit une méthode uniforme et reproductible pour confirmer que les chambres d'essai en température et humidité, sans spécimens, respectent les exigences spécifiées dans les procédures d'essai climatique de l'IEC 60068-2 (toutes les parties). Le présent document s'adresse aux utilisateurs qui effectuent une surveillance régulière des performances des chambres.
La présente version bilingue (2019-07) correspond à la version anglaise monolingue publiée en 2018-01.
Cette deuxième édition annule et remplace la première édition parue en 2001. Cette édition constitue une révision technique.
Cette édition inclut les modifications techniques majeures suivantes par rapport à l'édition précédente:
- Les procédures de confirmation ont été clarifiées.
La version française de cette norme n'a pas été soumise au vote.
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Standards Content (Sample)
IEC 60068-3-6 ®
Edition 2.0 2018-01
INTERNATIONAL
STANDARD
Environmental testing –
Part 3-6: Supporting documentation and guidance – Confirmation of the
performance of temperature/humidity chambers
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.
IEC Central Office Tel.: +41 22 919 02 11
3, rue de Varembé info@iec.ch
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 corrigenda or an amendment might have been published.
IEC Catalogue - webstore.iec.ch/catalogue Electropedia - www.electropedia.org
The stand-alone application for consulting the entire The world's leading online dictionary of electronic and
bibliographical information on IEC International Standards, electrical terms containing 21 000 terms and definitions in
Technical Specifications, Technical Reports and other English and French, with equivalent terms in 16 additional
documents. Available for PC, Mac OS, Android Tablets and languages. Also known as the International Electrotechnical
iPad. Vocabulary (IEV) online.
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The advanced search enables to find IEC publications by a 67 000 electrotechnical terminology entries in English and
variety of criteria (reference number, text, technical French extracted from the Terms and Definitions clause of
committee,…). It also gives information on projects, replaced IEC publications issued since 2002. Some entries have been
and withdrawn publications. collected from earlier publications of IEC TC 37, 77, 86 and
CISPR.
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IEC 60068-3-6 ®
Edition 2.0 2018-01
INTERNATIONAL
STANDARD
Environmental testing –
Part 3-6: Supporting documentation and guidance – Confirmation of the
performance of temperature/humidity chambers
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 19.040 ISBN 978-2-8322-5208-6
– 2 – IEC 60068-3-6:2018 © IEC 2018
CONTENTS
FOREWORD . 3
INTRODUCTION . 5
1 Scope . 6
2 Normative references . 6
3 Terms and definitions . 6
4 Measuring of performances . 9
4.1 Test area environment . 9
4.2 Measurement system . 9
4.3 Temperature measurement system . 9
4.4 Humidity measurement system . 9
4.5 Temperature/humidity chamber test specimens . 10
4.6 Specified location of temperature sensors and humidity sensor in working
space . 10
4.6.1 General . 10
4.6.2 Temperature sensors . 11
4.6.3 Humidity sensor . 11
4.7 Measurement method . 11
4.7.1 General . 11
4.7.2 Achieved humidity . 11
4.7.3 Temperature/humidity stabilization . 12
4.7.4 Humidity fluctuation . 12
4.7.5 Humidity gradient. 13
4.7.6 Humidity variation in space . 14
4.8 Standard humidity sequence . 15
5 Information to be given in the performance test report . 16
Bibliography . 17
Figure 1 – Example of humidity differences . 8
Figure 2 – Working space . 8
Figure 3 – Location sensors for temperature/humidity chambers up to 2 000 l. 10
Figure 4 – Location of minimal additional sensors for temperature/humidity chambers
over 2 000 l . 11
Figure 5 – Example of achieved humidity . 12
Figure 6 – Example of temperature/humidity stabilization . 12
Figure 7 – Example of humidity fluctuation . 13
Figure 8 – Example of humidity gradient for chambers up to 2 000 l . 14
Figure 9 – Example of humidity variation in space for chambers up to 2000 l . 15
Figure 10 – Example of climatogram . 16
Table 1 – Practical dimensions . 9
Table 2 – Example of test sequence . 15
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
ENVIRONMENTAL TESTING –
Part 3-6: Supporting documentation and guidance –
Confirmation of the performance of temperature/humidity chambers
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 60068-3-6 has been prepared by IEC technical committee 104:
Environmental conditions, classification and methods of test.
This second edition cancels and replaces the first edition published in 2001. This edition
constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
a) Confirmation procedures are clarified.
– 4 – IEC 60068-3-6:2018 © IEC 2018
The text of this International Standard is based on the following documents:
FDIS Report on voting
104/760/FDIS 104/779/RVD
Full information on the voting for the approval of this International Standard can be found in
the report on voting indicated in the above table.
This document has been drafted in accordance with the ISO/IEC Directives, Part 2.
IEC 60068-3-6 is to be read in conjunction with IEC 60068-3-5:2001 and IEC 60068-3-7:2001.
A list of all parts in the IEC 60068 series, published under the general title Environmental
testing, can be found on the IEC website.
The committee has decided that the contents of this document will remain unchanged until the
stability date indicated on the IEC website under "http://webstore.iec.ch" in the data related to
the specific document. At this date, the document will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
A bilingual version of this publication may be issued at a later date.
INTRODUCTION
IEC 60068 (all parts) contains fundamental information on environmental testing procedures
and severities.
The expression "environmental conditioning" or "environmental testing" covers the natural and
artificial environments to which components or equipment may be exposed so that an
assessment can be made of their performance under conditions of use, transport and storage
to which they may be exposed in practice.
Temperature and humidity chambers used for "environmental conditioning" or "environmental
testing" are not described in any publication, although the method of maintaining and
measuring temperature and/or humidity has a great influence on test results. The physical
characteristics of temperature and humidity chambers can also influence test results.
– 6 – IEC 60068-3-6:2018 © IEC 2018
ENVIRONMENTAL TESTING –
Part 3-6: Supporting documentation and guidance –
Confirmation of the performance of temperature/humidity chambers
1 Scope
This part of IEC 60068 provides a uniform and reproducible method of confirming that
temperature and humidity test chambers, without specimens, conform to the requirements
specified in climatic test procedures of IEC 60068-2 (all parts). This document is intended for
users when conducting regular chamber performance monitoring.
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. Fo
...
IEC 60068-3-6 ®
Edition 2.0 2018-01
REDLINE VERSION
INTERNATIONAL
STANDARD
colour
inside
Environmental testing –
Part 3-6: Supporting documentation and guidance – Confirmation of the
performance of temperature/humidity chambers
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.
IEC Central Office Tel.: +41 22 919 02 11
3, rue de Varembé info@iec.ch
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 corrigenda or an amendment might have been published.
IEC Catalogue - webstore.iec.ch/catalogue Electropedia - www.electropedia.org
The stand-alone application for consulting the entire The world's leading online dictionary of electronic and
bibliographical information on IEC International Standards, electrical terms containing 21 000 terms and definitions in
Technical Specifications, Technical Reports and other English and French, with equivalent terms in 16 additional
documents. Available for PC, Mac OS, Android Tablets and languages. Also known as the International Electrotechnical
iPad. Vocabulary (IEV) online.
IEC publications search - webstore.iec.ch/advsearchform IEC Glossary - std.iec.ch/glossary
The advanced search enables to find IEC publications by a 67 000 electrotechnical terminology entries in English and
variety of criteria (reference number, text, technical French extracted from the Terms and Definitions clause of
committee,…). It also gives information on projects, replaced IEC publications issued since 2002. Some entries have been
and withdrawn publications. collected from earlier publications of IEC TC 37, 77, 86 and
CISPR.
IEC Just Published - webstore.iec.ch/justpublished
Stay up to date on all new IEC publications. Just Published IEC Customer Service Centre - webstore.iec.ch/csc
details all new publications released. Available online and If you wish to give us your feedback on this publication or
also once a month by email. need further assistance, please contact the Customer Service
Centre: sales@iec.ch.
IEC 60068-3-6 ®
Edition 2.0 2018-01
REDLINE VERSION
INTERNATIONAL
STANDARD
colour
inside
Environmental testing –
Part 3-6: Supporting documentation and guidance – Confirmation of the
performance of temperature/humidity chambers
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 19.040 ISBN 978-2-8322-5325-0
– 2 – IEC 60068-3-6:2018 RLV © IEC 2018
CONTENTS
FOREWORD . 3
INTRODUCTION . 5
1 Scope . 6
2 Normative references . 6
3 Terms and definitions . 6
4 Measuring of performances . 9
4.1 Test area environment . 9
4.2 Measurement system . 9
4.3 Temperature measurement system . 9
4.4 Humidity measurement system . 10
4.5 Temperature/humidity chamber test specimens . 10
4.6 Specified location of temperature sensors and humidity sensor in working
space . 10
4.6.1 General . 10
Installation of sensors .
4.6.2 Temperature sensors . 11
4.6.3 Humidity sensor . 12
4.7 Measurement method . 12
4.7.1 General . 12
4.7.2 Achieved humidity . 12
4.7.3 Temperature/humidity stabilization . 13
4.7.4 Humidity fluctuation . 13
4.7.5 Humidity gradient. 14
4.7.6 Humidity variation in space . 15
4.8 Standard humidity sequence . 16
5 Information to be given in the performance test report . 18
Determination of humidity performance.
Evaluation criteria .
Bibliography . 19
Figure 1 – Example of humidity differences . 8
Figure 2 – Working space . 9
Figure 3 – Location sensors for temperature/humidity chambers up to 2 000 l. 11
Figure 4 – Location of minimal additional sensors for temperature/humidity chambers
over 2 000 l . 11
Figure 5 – Example of achieved humidity . 12
Figure 6 – Example of temperature/humidity stabilization . 13
Figure 7 – Example of humidity fluctuation . 14
Figure 8 – Example of humidity gradient for chambers up to 2 000 l . 15
Figure 9 – Example of humidity variation in space for chambers up to 2000 l . 16
Figure 10 – Example of climatogram . 17
Table 1 – Practical dimensions . 9
Table 2 – Example of test sequence . 17
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
ENVIRONMENTAL TESTING –
Part 3-6: Supporting documentation and guidance –
Confirmation of the performance of temperature/humidity chambers
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.
This redline version of the official IEC Standard allows the user to identify the changes
made to the previous edition. A vertical bar appears in the margin wherever a change
has been made. Additions are in green text, deletions are in strikethrough red text.
– 4 – IEC 60068-3-6:2018 RLV © IEC 2018
International Standard IEC 60068-3-6 has been prepared by IEC technical committee 104:
Environmental conditions, classification and methods of test.
This second edition cancels and replaces the first edition published in 2001. This edition
constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
a) Confirmation procedures are clarified.
The text of this International Standard is based on the following documents:
FDIS Report on voting
104/760/FDIS 104/779/RVD
Full information on the voting for the approval of this International Standard can be found in
the report on voting indicated in the above table.
This document has been drafted in accordance with the ISO/IEC Directives, Part 2.
IEC 60068-3-6 is to be read in conjunction with IEC 60068-3-5:2001 and IEC 60068-3-7:2001.
A list of all parts in the IEC 60068 series, published under the general title Environmental
testing, can be found on the IEC website.
The committee has decided that the contents of this document will remain unchanged until the
stability date indicated on the IEC website under "http://webstore.iec.ch" in the data related to
the specific document. At this date, the document will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
IMPORTANT – The “colour inside” logo on the cover page of this publication indicates
that it contains colours which are considered to be useful for the correct understanding
of its contents. Users should therefore print this publication using a colour printer.
INTRODUCTION
IEC 60068 (all parts) contains fundamental information on environmental testing procedures
and severities.
The expression "environmental conditioning" or "environmental testing" covers the natural and
artificial environments to which components or equipment may be exposed so that an
assessment can be made of their performance under conditions of use, transport and storage
to which they may be exposed in practice.
Temperature and humidity chambers used for "environmental conditioning" or "environmental
testing" are not described in any publication, although the method of maintaining and
measuring temperature and/or humidity has a great influence on test results. The physical
characteristics of temperature and humidity chambers can also influence test results.
– 6 – IEC 60068-3-6:2018 RLV © IEC 2018
ENVIRONMENTAL TESTING –
Part 3-6: Supporting documentation and guidance –
Confirmation of the performance of temperature/humidity chambers
1 Scope
This part of IEC 60068 provides a uniform and reproducible method of confirming that
temperature and humidity test chambers, without load specimens, conform to the
requirements specified in climatic test procedures contained in of IEC 60068-2 (all parts). This
document is destined intended for users when conducting regular chamber performance
monitoring.
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 60068-3-4, Environmental testing – Part 3-4: Supporting documentation and guidance –
Damp heat tests
IEC 60068-3-5:2001, Environmental testing – Part 3-5: Supporting documentation and
guidance – Confirmation of the performance of temperature chambers
IEC 60068-3-7:2001, Environmental testing – Part 3-7: Supporting documentation and
guidance – Measurements in temperature chambers for tests A and B (with load)
IEC 60068-3-11, Environmental testing – Part 3-11: Supporting documentation and guidance
– Calculation of uncertainty of conditions in climatic test chambers
IEC 60584-1, Thermocouples – Part 1: Reference tables
IEC 60751, Industrial platinum resistance, thermometer sensors
ISO 10012-1, Quality assurance requirements for measuring equipment – Part 1: Metrological
confirmation system for measuring equipment
ISO 10012-2, Quality assurance for measuring equipment – Part 2: Guidelines for control of
measurement processes
ISO 4677-1, Atmospheres for conditioning and testing – Determination of relative humidity –
Part 1: Aspirated psychrometer method
ISO (unnumbered), Guide to the Expression of Uncertainty in Measurement
3 Terms and definitions
For the purpose of this document, the following terms and definitions apply.
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
NOTE 1 For terms and definitions regarding temperature testing, refer to IEC 60068-3-5.
NOTE 2 Unless otherwise specified, "humidity" is relative humidity (RH).
3.1
temperature/humidity chamber
enclosure or space in some parts of which the temperature/humidity conditions specified in
IEC 60068-2 (all parts) can be achieved
Note 1 to entry: See IEC 60068-3-4.
3.2
generation of humidity
see clause 3 of IEC 60068-3-4
3.2
absolute humidity
mass of water vapour present in a unit volume of moist air
Note 1 to entry: Typical units of measure are g/m3.
3.3
dewpoint
T
d
temperature at which the saturation vapour pressure over water or ice is equal to the partial
pressure of the water vapour in the air
3.4
saturation vapour pressure
when a given volume of air, at a constant temperature, has water present and is incapable of
holding any more water it is said to be saturated
maximum possible pressure exerted by a water vapour in equilibrium with its solid or liquid
phase, such that any increase will initiate within the vapour a change to a more condensed
state
3.5
partial vapour pressure
contribution of water vapour in a given volume of air at a constant pressure and temperature
to the pressure exerted by of the atmosphere
3.6
relative humidity
RH
ratio of the partial vapour pressure, divided by the saturation vapour pressure of a given
volume of air at a constant temperature, expressed as percentage
Note 1 to entry: The most popular method to express the water vapour content in air is relative humidity.
3.7
temperature/humidity stabilization
temperature/humidity in the chamber can be considered stable when all points in the working
space have reached and have maintained the setpoint temperature/humidity within a given
tolerance
state of maintaining temperature/humidity within specified tolerance for a specified time at
specified points in the working space
– 8 – IEC 60068-3-6:2018 RLV © IEC 2018
3.8
achieved humidity
humidity in the chamber at any point within the working space after stabilization
stabilized humidity which desired humidity at the centre of the working space achieves within
specified tolerance
3.9
climatogram
graphic display of combined temperature with relative humidity
Note 1 to entry: See Figure 9.
3.10
relative humidity fluctuation
fluctuation calculated with the temperature sensor which has the largest fluctuation
difference, after stabilization, between the maximum and minimum humidity at specified points
in the working space during a specified interval of time
Note 1 to entry: For calibration, the centre point of working space may be used.
3.11
relative humidity gradient
gradient whose predominant contribution is caused by the temperature gradient in the working
space
maximum difference in mean humidity value, after stabilization, at any moment in time
between two separate points in the working space
Note 1 to entry: The absolute humidity of the air can be considered to be the same throughout the working space.
Note 2 to entry: See Figure 1.
3.12
relative humidity variation in space
difference in mean value, after stabilization, at any moment in time between the humidity at
the centre of the working space and at any other point in the working space
Note 1 to entry: See Figure 1.
Humidity fluctuation
outside the centre of
working space
Humidity fluctuation
in the centre of
working space
Humidity fluctuation
outside the centre of
working space
Time
IEC
Figure 1 – Example of humidity differences
Humidity
Variation
Gradient
3.13
working space
part of the chamber in which the specified conditions can be maintained within the specified
tolerances
Note 1 to entry: See Figure 2 and Table 1.
X
L
X
X
X
X X
1 2
L L
1 2
IEC
NOTE Practical dimensions of working space see Table 1.
Figure 2 – Working space
Table 1 – Practical dimensions
Size Volume Distance X X (min.)
l mm mm
Small Up to 1 000 L/10 50
Medium 1 000 to 2 000 L/10 100
Large More than 2 000 L/10 150
NOTE Not all chambers are cubic in construction.
4 Measuring of performances
4.1 Test area environment
The environment around a temperature/humidity test chamber may influence the conditions
inside the test chamber.
The confirmation of performance of a temperature/humidity chamber should be carried out
under standard atmospheric conditions specified in IEC 60068-1.
4.2 Measurement system
When performing an assessment of a temperature/humidity chamber, a temperature/humidity
measuring system, which is independent of the chamber’s control system should be used.
4.3 Temperature measurement system
In accordance with See IEC 60068-3-5.
– 10 – IEC 60068-3-6:2018 RLV © IEC 2018
4.4 Humidity measurement system
The uncertainty of measurement of the output of the measurement system should be
determined by calibration of the system, traceable to international standards (see ISO 10012-
1 and ISO 10012-2).The measurement system should have a calibration at the test conditions,
traceable to international standards (see ISO 10012-1 and ISO 10012-2) and the overall
measurement uncertainty should be established using the ISO/IEC Guide 98-3 related to the
expression of uncertainty in measurement.
Some examples of humidity measurement systems include, but are not limited to, those listed
below.
a) Wet and dry bulb method
This method (see ISO 4677-1) uses the cooling effect of water evaporation from a wet
sock. The temperature of the sock is measured with a temperature sensor whilst
simultaneously measuring the temperature of the air with a second temperature sensor.
b) Dewpoint mirror method
This method cools the surface of the mirror until condensation occurs on it. The
temperature indicated is the dewpoint temperature.
c) Lithium chloride sensor
This method gives absolute humidity values (dewpoint temperature).
d) Capacitive sensor
Permeation of humidity changes the dielectric properties of certain materials and this is
used for direct measurement of relative humidity.
4.5 Temperature/humidity chamber test specimens
All measurements described below are performed with an empty working space. For
measuring with test specimens (with or without heat dissipation), see IEC 60068-3-7.
4.6 Specified location of temperature sensors and humidity sensor in working space
4.6.1 General
Temperature measuring sensors are located in each corner and in the centre of the working
space (see Figure 3, minimum 9 sensors). Humidity measuring sensor is located in the centre
of the working space. For temperature/humidity chambers over 2 000 l, additional temperature
sensors should be located in front of the centre of each wall (see Figure 4, minimum
15 sensors).
N
N
L
N
10 N
Centre
N
L
N
N
N
L
N
L
L
2 L
L
L
L
IEC
Figure 3 – Location of sensors for temperature/humidity chambers up to 2 000 l
X
X
IEC
Figure 4 – Location of minimal additional sensors for
temperature/humidity chambers over 2 000 l
4.4 Installation of sensors
4.6.2 Temperature sensors
Normally sensors should be either the resistance type (in accordance with IEC 60751) or the
thermocouple type (in accordance with IEC 60584-1). The 50 % response time in air of the
sensor shall be between 10 s and 40 s. The response time of the overall system should be
less than 40 s.
In a temperature range from –200 °C to +200 °C the sensor measurement uncertainty should
be in accordance with class A of IEC 60751.
See IEC 60068-3-5, 4.2.
X
– 12 – IEC 60068-3-6:2018 RLV © IEC 2018
4.6.3 Humidity sensor
A single humidity sensor should shall be positioned at the centre of the working space. The
relative humidity is then calculated (by Pernter’s or Sprung’s psychrometric formula) at each
point in the working space where a temperature sensor is located by using the temperature
difference. This assumes that the absolute humidity remains the same throughout the working
space.
For confirmation monitoring, data should be recorded at least once a minute. The device
utilised for recording data from the chamber monitoring sensors should be independent of the
chamber control system.
Sensor measurement uncertainty should not exceed ±3 % RH.
4.7 Measurement method
4.7.1 General
The confirmation of temperature performance of temperature/humidity chamber shall be
carried out by IEC 60068-3-5. Humidity measurement point is at the centre of the working
space only. The output of the temperature/humidity measuring system (see Figure 3 or
Figure 4) determine, after chamber stabilization, the achieved humidity, humidity fluctuation
and humidity gradient of the working space. For tolerance, the specification of the
temperature/humidity chamber or, as necessary, tolerance specified in IEC 60068-2 (all
parts), is required to maintain at the centre of the working space. Location of sensor is
minimum 9 points or 15 points. This depends on the test chamber size. Measurement method
is explained based on 9 points.
Uncertainty of measurement of the temperature/humidity measuring system shall be according
to IEC 60068-3-11.
4.7.2 Achieved humidity
Humidity at the centre of the working space, shown in Figure 5, has reached and maintained
the set humidity within tolerance.
t
N
Tolerance
Setting
humidity
IEC
t should be minimum 30 min. N is the humidity at the centre of the working space.
1 5
Figure 5 – Example of achieved humidity
4.7.3 Temperature/humidity stabilization
Humidity reached and maintained at the centre of the working space within the tolerance of
the chamber specification or the requirement of the relevant part of the IEC 60068-2 series.
An example is shown in Figure 6. Specified time t is minimum 30 min.
T
N
Allowable
range
N
IEC
Figure 6 – Example of temperature/humidity stabilization
4.7.4 Humidity fluctuation
The fluctuation during a specified interval of time at a measuring point is shown in Figure 7.
After the temperature and humidity has stabilized, the humidity at the centre of the working
space shall be measured at least 10 times at evenly spaced time intervals over a period of at
least 30 min. At the same time, temperature shall be measured in 9 points at least 10 times at
evenly spaced time intervals over a period of at least 30 min. Humidity shall be calculated
assuming a uniform humidity mixing ratio, using the humidity value at the centre and
temperature values measurement at 9 points. Measurements are actually made at a certain
sampling interval. It is not guaranteed that that data captures the fluctuation peak. For that
reason, the sample standard deviation, σ , shall be obtained from the data measured in
n – 1
each measurement point after temperature has stabilized. Values ±2σ shall be obtained in
n – 1
all 9 measurement points, and the highest value within that shall be annotated as the humidity
fluctuation.
The calculated values shall be indicated as N , N , … , N , … N (n≧10).
1 2 i n
The mean of N shall be N
ave.
The sample standard deviation,σ , shall be defined as follows.
n – 1
– 14 – IEC 60068-3-6:2018 RLV © IEC 2018
N
Max
+2σ
n–1
+1σ
n–1
–1σ
n–1
Average humidity
N
Ave
σ
n–1
Sample standard
deviation
–2σ
n–1
N
Min
0 5 10 15 20 25 30
Time (min)
IEC
Figure 7 – Example of humidity fluctuation
4.7.5 Humidity gradient
As shown in Figure 8, the maximum difference in average humidity in all measurement points
of the working space shall be the humidity gradient.
Humidity (% RH)
N
AveMax
N
AveMin
0 5 10 15 20 25 30
Time (min)
IEC
N : Mean highest humidity in each of 9 measurement points
AveMax
N : Mean lowest humidity in each of 9 measurement points
AveMin
Humidity gradient = N – N
AveMax AveMin
Figure 8 – Example of humidity gradient for chambers up to 2 000 l
4.7.6 Humidity variation in space
As shown in Figure 9, humidity variation in space is the difference between the mean humidity
at the centre of the working space and the mean humidity from all other measurement points.
The maximum difference between the centre of the working space and each measuring point
shall be stated.
Humidity (% RH)
Humidity gardient
--------
...
IEC 60068-3-6 ®
Edition 2.0 2018-01
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Environmental testing –
Part 3-6: Supporting documentation and guidance – Confirmation of the
performance of temperature/humidity chambers
Essais d'environnement –
Partie 3-6: Documentation d'accompagnement et guide – Confirmation des
performances des chambres d'essai en température/humidité
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IEC 60068-3-6 ®
Edition 2.0 2018-01
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Environmental testing –
Part 3-6: Supporting documentation and guidance – Confirmation of the
performance of temperature/humidity chambers
Essais d'environnement –
Partie 3-6: Documentation d'accompagnement et guide – Confirmation des
performances des chambres d'essai en température/humidité
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 19.040 ISBN 978-2-8322-7180-3
– 2 – IEC 60068-3-6:2018 © IEC 2018
CONTENTS
FOREWORD . 3
INTRODUCTION . 5
1 Scope . 6
2 Normative references . 6
3 Terms and definitions . 6
4 Measuring of performances . 9
4.1 Test area environment . 9
4.2 Measurement system . 9
4.3 Temperature measurement system . 9
4.4 Humidity measurement system . 9
4.5 Temperature/humidity chamber test specimens . 10
4.6 Specified location of temperature sensors and humidity sensor in working
space . 10
4.6.1 General . 10
4.6.2 Temperature sensors . 11
4.6.3 Humidity sensor . 11
4.7 Measurement method . 11
4.7.1 General . 11
4.7.2 Achieved humidity . 11
4.7.3 Temperature/humidity stabilization . 12
4.7.4 Humidity fluctuation . 12
4.7.5 Humidity gradient. 13
4.7.6 Humidity variation in space . 14
4.8 Standard humidity sequence . 15
5 Information to be given in the performance test report . 16
Bibliography . 17
Figure 1 – Example of humidity differences . 8
Figure 2 – Working space . 8
Figure 3 – Location of sensors for temperature/humidity chambers up to 2 000 l . 10
Figure 4 – Location of minimal additional sensors for temperature/humidity chambers
over 2 000 l . 10
Figure 5 – Example of achieved humidity . 11
Figure 6 – Example of temperature/humidity stabilization . 12
Figure 7 – Example of humidity fluctuation . 13
Figure 8 – Example of humidity gradient for chambers up to 2 000 l . 14
Figure 9 – Example of humidity variation in space for chambers up to 2000 l . 15
Figure 10 – Example of climatogram . 16
Table 1 – Practical dimensions . 9
Table 2 – Example of test sequence . 15
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
ENVIRONMENTAL TESTING –
Part 3-6: Supporting documentation and guidance –
Confirmation of the performance of temperature/humidity chambers
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
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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
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3) IEC Publications have the form of recommendations for international use and are accepted by IEC National
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4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications
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between any IEC Publication and the corresponding national or regional publication shall be clearly indicated in
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5) IEC itself does not provide any attestation of conformity. Independent certification bodies provide conformity
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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
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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 60068-3-6 has been prepared by IEC technical committee 104:
Environmental conditions, classification and methods of test.
This bilingual version (2019-07) corresponds to the monolingual English version, published in
2018-01.
This second edition cancels and replaces the first edition published in 2001. This edition
constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
a) Confirmation procedures are clarified.
– 4 – IEC 60068-3-6:2018 © IEC 2018
The text of this International Standard is based on the following documents:
FDIS Report on voting
104/760/FDIS 104/779/RVD
Full information on the voting for the approval of this International Standard can be found in
the report on voting indicated in the above table.
The French version of this standard has not been voted upon.
This document has been drafted in accordance with the ISO/IEC Directives, Part 2.
IEC 60068-3-6 is to be read in conjunction with IEC 60068-3-5:2001 and IEC 60068-3-7:2001.
A list of all parts in the IEC 60068 series, published under the general title Environmental
testing, can be found on the IEC website.
The committee has decided that the contents of this document will remain unchanged until the
stability date indicated on the IEC website under "http://webstore.iec.ch" in the data related to
the specific document. At this date, the document will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
INTRODUCTION
IEC 60068 (all parts) contains fundamental information on environmental testing procedures
and severities.
The expression "environmental conditioning" or "environmental testing" covers the natural and
artificial environments to which components or equipment may be exposed so that an
assessment can be made of their performance under conditions of use, transport and storage
to which they may be exposed in practice.
Temperature and humidity chambers used for "environmental conditioning" or "environmental
testing" are not described in any publication, although the method of maintaining and
measuring temperature and/or humidity has a great influence on test results. The physical
characteristics of temperature and humidity chambers can also influence test results.
– 6 – IEC 60068-3-6:2018 © IEC 2018
ENVIRONMENTAL TESTING –
Part 3-6: Supporting documentation and guidance –
Confirmation of the performance of temperature/humidity chambers
1 Scope
This part of IEC 60068 provides a uniform and reproducible method of confirming that
temperature and humidity test chambers, without specimens, conform to the requirements
specified in climatic test procedures of IEC 60068-2 (all parts). This document is intended for
users when conducting regular chamber performance monitoring.
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 60068-3-5:2001, Environmental testing – Part 3-5: Supporting documentation and
guidance – Confirmation of the performance of temperature chambers
IEC 60068-3-7:2001, Environmental testing – Part 3-7: Supporting documentation and
guidance – Measurements in temperature chambers for tests A and B (with load)
IEC 60068-3-11, Environmental testing – Part 3-11: Supporting documentation and guidance
– Calculation of uncertainty of conditions in climatic test chambers
3 Terms and definitions
For the purpose of this document, the following terms and definitions apply.
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
NOTE 1 For terms and definitions regarding temperature testing, refer to IEC 60068-3-5.
NOTE 2 Unless otherwise specified, "humidity" is relative humidity (RH).
3.1
temperature/humidity chamber
enclosure or space in some parts of which the temperature/humidity conditions specified in
IEC 60068-2 (all parts) can be achieved
Note 1 to entry: See IEC 60068-3-4.
3.2
absolute humidity
mass of water vapour present in a unit volume of moist air
Note 1 to entry: Typical units of measure are g/m3.
3.3
dewpoint
T
d
temperature at which the saturation vapour pressure over water is equal to the partial
pressure of the water vapour in the air
3.4
saturation vapour pressure
maximum possible pressure exerted by a water vapour in equilibrium with its solid or liquid
phase, such that any increase will initiate within the vapour a change to a more condensed
state
3.5
partial vapour pressure
contribution of water vapour in a given volume of air at a constant pressure and temperature
of the atmosphere
3.6
relative humidity
RH
ratio of the partial vapour pressure, divided by the saturation vapour pressure of a given
volume of air at a constant temperature, expressed as percentage
Note 1 to entry: The most popular method to express the water vapour content in air is relative humidity.
3.7
temperature/humidity stabilization
state of maintaining temperature/humidity within specified tolerance for a specified time at
specified points in the working space
3.8
achieved humidity
stabilized humidity which desired humidity at the centre of the working space achieves within
specified tolerance
3.9
climatogram
graphic display of combined temperature with relative humidity
Note 1 to entry: See Figure 9.
3.10
relative humidity fluctuation
difference, after stabilization, between the maximum and minimum humidity at specified points
in the working space during a specified interval of time
Note 1 to entry: For calibration, the centre point of working space may be used.
3.11
relative humidity gradient
maximum difference in mean humidity value, after stabilization, at any moment in time
between two separate points in the working space
Note 1 to entry: The absolute humidity of the air can be considered to be the same throughout the working space.
Note 2 to entry: See Figure 1.
3.12
relative humidity variation in space
difference in mean value, after stabilization, at any moment in time between the humidity at
the centre of the working space and at any other point in the working space
Note 1 to entry: See Figure 1.
– 8 – IEC 60068-3-6:2018 © IEC 2018
Humidity fluctuation
outside the centre of
working space
Humidity fluctuation
in the centre of
working space
Humidity fluctuation
outside the centre of
working space
Time
IEC
Figure 1 – Example of humidity differences
3.13
working space
part of the chamber in which the specified conditions can be maintained within the specified
tolerances
Note 1 to entry: See Figure 2 and Table 1.
X
L
X
X
X
X X
1 2
L
L
IEC
NOTE Practical dimensions of working space see Table 1.
Figure 2 – Working space
Humidity
Variation
Gradient
Table 1 – Practical dimensions
Size Volume Distance X X (min.)
l mm mm
Small Up to 1 000 L/10 50
Medium 1 000 to 2 000 L/10 100
Large More than 2 000 L/10 150
NOTE Not all chambers are cubic in construction.
4 Measuring of performances
4.1 Test area environment
The environment around a temperature/humidity test chamber may influence the conditions
inside the test chamber.
The confirmation of performance of a temperature/humidity chamber should be carried out
under standard atmospheric conditions specified in IEC 60068-1.
4.2 Measurement system
When performing an assessment of a temperature/humidity chamber, a temperature/humidity
measuring system which is independent of the chamber’s control system should be used.
4.3 Temperature measurement system
See IEC 60068-3-5.
4.4 Humidity measurement system
The uncertainty of measurement of the output of the measurement system should be
determined by calibration of the system, traceable to international standards (see ISO 10012),
and the overall measurement uncertainty should be established using ISO/IEC Guide 98-3
related to the expression of uncertainty in measurement.
Some examples of humidity measurement systems include, but are not limited to, those listed
below.
a) Wet and dry bulb method
This method uses the cooling effect of water evaporation from a wet sock. The
temperature of the sock is measured with a temperature sensor whilst simultaneously
measuring the temperature of the air with a second temperature sensor.
b) Dewpoint mirror method
This method cools the surface of the mirror until condensation occurs on it. The
temperature indicated is the dewpoint temperature.
c) Lithium chloride sensor
This method gives absolute humidity values (dewpoint temperature).
d) Capacitive sensor
Permeation of humidity changes the dielectric properties of certain materials and this is
used for direct measurement of relative humidity.
– 10 – IEC 60068-3-6:2018 © IEC 2018
4.5 Temperature/humidity chamber test specimens
All measurements described below are performed with an empty working space. For
measuring with test specimens (with or without heat dissipation), see IEC 60068-3-7.
4.6 Specified location of temperature sensors and humidity sensor in working space
4.6.1 General
Temperature measuring sensors are located in each corner and in the centre of the working
space (see Figure 3, minimum 9 sensors). Humidity measuring sensor is located in the centre
of the working space. For temperature/humidity chambers over 2 000 l, additional temperature
sensors should be located in front of the centre of each wall (see Figure 4, minimum
15 sensors).
N
N
L
N
10 N
Centre
N
L
N
N
N
L
N
L
L
L
L
L
10 1
L
IEC
Figure 3 – Location of sensors for temperature/humidity chambers up to 2 000 l
X
X
IEC
Figure 4 – Location of minimal additional sensors for
temperature/humidity chambers over 2 000 l
X
4.6.2 Temperature sensors
See IEC 60068-3-5, 4.2.
4.6.3 Humidity sensor
A single humidity sensor shall be positioned at the centre of the working space. The relative
humidity is calculated (by Pernter’s or Sprung’s psychrometric formula) at each point in the
working space where a temperature sensor is located by using the temperature difference.
This assumes that the absolute humidity remains the same throughout the working space.
4.7 Measurement method
4.7.1 General
The confirmation of temperature performance of temperature/humidity chamber shall be
carried out by IEC 60068-3-5. Humidity measurement point is at the centre of the working
space only. The output of the temperature/humidity measuring system (see Figure 3 or
Figure 4) determine, after chamber stabilization, the achieved humidity, humidity fluctuation
and humidity gradient of the working space. For tolerance, the specification of the
temperature/humidity chamber or, as necessary, tolerance specified in IEC 60068-2 (all
parts), is required to maintain at the centre of the working space. Location of sensor is
minimum 9 points or 15 points. This depends on the test chamber size. Measurement method
is explained based on 9 points.
Uncertainty of measurement of the temperature/humidity measuring system shall be according
to IEC 60068-3-11.
4.7.2 Achieved humidity
Humidity at the centre of the working space, shown in Figure 5, has reached and maintained
the set humidity within tolerance.
t
N
Tolerance 5
Setting
humidity
IEC
t should be minimum 30 min. N is the humidity at the centre of the working space.
1 5
Figure 5 – Example of achieved humidity
– 12 – IEC 60068-3-6:2018 © IEC 2018
4.7.3 Temperature/humidity stabilization
Humidity reached and maintained at the centre of the working space within the tolerance of
the chamber specification or the requirement of the relevant part of the IEC 60068-2 series.
An example is shown in Figure 6. Specified time t is minimum 30 min.
T
N
Allowable
range
N
IEC
Figure 6 – Example of temperature/humidity stabilization
4.7.4 Humidity fluctuation
The fluctuation during a specified interval of time at a measuring point is shown in Figure 7.
After the temperature and humidity has stabilized, the humidity at the centre of the working
space shall be measured at least 10 times at evenly spaced time intervals over a period of at
least 30 min. At the same time, temperature shall be measured in 9 points at least 10 times at
evenly spaced time intervals over a period of at least 30 min. Humidity shall be calculated
assuming a uniform humidity mixing ratio, using the humidity value at the centre and
temperature values measurement at 9 points. Measurements are actually made at a certain
sampling interval. It is not guaranteed that that data captures the fluctuation peak. For that
reason, the sample standard deviation, σ , shall be obtained from the data measured in
n – 1
each measurement point after temperature has stabilized. Values ±2σ shall be obtained in
n – 1
all 9 measurement points, and the highest value within that shall be annotated as the humidity
fluctuation.
The calculated values shall be indicated as N , N , … , N , … N (n≧10).
1 2 i n
The mean of N shall be N
ave.
The sample standard deviation,σ , shall be defined as follows.
n – 1
N
Max
+2σ
n–1
+1σ
n–1
–1σ
n–1
Average humidity
N
Ave
σ
n–1
Sample standard
deviation
–2σ
n–1
N
Min
0 5 10 15 20 25 30
Time (min)
IEC
Figure 7 – Example of humidity fluctuation
4.7.5 Humidity gradient
As shown in Figure 8, the maximum difference in average humidity in all measurement points
of the working space shall be the humidity gradient.
Humidity (% RH)
– 14 – IEC 60068-3-6:2018 © IEC 2018
N
AveMax
N
AveMin
0 5 10 15 20 25 30
Time (min)
IEC
N : Mean highest humidity in each of 9 measurement points
AveMax
N : Mean lowest humidity in each of 9 measurement points
AveMin
Humidity gradient = N – N
AveMax AveMin
Figure 8 – Example of humidity gradient for chambers up to 2 000 l
4.7.6 Humidity variation in space
As shown in Figure 9, humidity variation in space is the difference between the mean humidity
at the centre of the working space and the mean humidity from all other measurement points.
The maximum difference between the centre of the working space and each measuring point
shall be stated.
Humidity (% RH)
Humidity gardient
N
CornerAve
N
CenterAve
N
CornerAve
0 5 10 15 20 25 30
Time (min)
IEC
N : Mean humidity at centre of working space
centreAve
N j = 1 to 8: Mean humidity at corner of working space
CornerAve(j)
Humidity variation in space =｜Max(N – N )｜
cornerAve[j] CentreAve
The value obtained as the humidity variation in space shall be (N – N ), and the absolute value of
CornerAve(j) CentrerAve
the highest difference obtained for the all measurement points shall be annotated as the humidity variation in
space.
Figure 9 – Example of humidity variation in space for chambers up to 2000 l
4.8 Standard humidity sequence
The following test sequence is considered to obtain the necessary data for confirming the
range of operation of a temperature/humidity chamber.
An example of a test sequence is given in Table 2.
Table 2 – Example of test sequence
Step Temperature Relative humidity
°C %
1 23 50
2 23 U
3 t (min.) U
3 3
4 t (min.) U (max.)
4 4
5 t (max.) U (min.)
5 5
6 t (max.) U
...
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