IEC 60068-3-1:2011

Environmental testing - Part 3-1: Supporting documentation and guidance - Cold and dry heat tests

IEC 60068-3-1:2011 provides guidance regarding the performance of cold and dry heat tests. This second edition cancels and replaces the first edition, published in 1974, and constitutes a technical revision. The main changes with regard to the previous edition are as follows:
- removal of guidance regarding thermal characteristics of chamber walls;
- revision of sections that address environmental chambers that do not use movement of air for temperature control.

Essais d'environnement - Partie 3-1: Documentation d'accompagnement et guide - Essais de froid et de chaleur sèche

La CEI 60068-3-1:2011 fournit des lignes directrices relatives aux performances des essais de froid et de chaleur sèche. Cette deuxième édition annule et remplace la première édition parue en 1974, dont elle constitue une révision technique. Les modifications principales par rapport à l'édition précédente sont les suivantes:
- retrait du guide concernant les caractéristiques thermiques des parois de la chambre;
- révision des sections traitant des chambres environnementales qui n'utilisent pas le mouvement de l'air pour le contrôle de la température.

General Information

• Status: Published
• Publication Date: 18-Aug-2011
• ICS: 19.040 - Environmental testing
• Technical Committee: TC 104 - Environmental conditions, classification and methods of test
• Drafting Committee: MT 16 - TC 104/MT 16
• Current Stage: DELPUB - Deleted Publication
• Start Date: 29-Jun-2023
• Completion Date: 13-Aug-2021

Relations

• Revised: IEC 60068-3-1:2023 - Environmental testing - Part 3-1: Supporting documentation and guidance - Cold and dry heat tests
• Effective Date: 05-Sep-2023

Standards Content (Sample)

IEC 60068-3-1 ®
Edition 2.0 2011-08
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Environmental testing –
Part 3-1: Supporting documentation and guidance – Cold and dry heat tests

Essais d’environnement –
Partie 3-1: Documentation d’accompagnement et guide – Essais de froid et de
chaleur sèche
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IEC 60068-3-1 ®
Edition 2.0 2011-08
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Environmental testing –
Part 3-1: Supporting documentation and guidance – Cold and dry heat tests

Essais d’environnement –
Partie 3-1: Documentation d’accompagnement et guide – Essais de froid et de
chaleur sèche
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
PRICE CODE
INTERNATIONALE
CODE PRIX M
ICS 19.040 ISBN 978-2-88912-626-2

– 2 – 60068-3-1 © IEC:2011
CONTENTS
FOREWORD . 3
1 Scope . 5
2 Normative references . 5
3 Terms and definitions . 5
4 Selection of test procedures . 5
4.1 General background . 5
4.1.1 General . 5
4.1.2 Ambient temperature . 6
4.1.3 Specimen temperatures . 6
4.1.4 Specimens without heat dissipation . 6
4.1.5 Specimens with heat dissipation . 6
4.2 Mechanisms of heat transfer . 6
4.2.1 Convection . 6
4.2.2 Radiation . 9
4.2.3 Thermal conduction . 10
4.2.4 Forced air circulation . 10
4.3 Test chambers . 10
4.3.1 General . 10
4.3.2 Methods of achieving the required conditions in the test chamber. 11
4.4 Measurements . 11
4.4.1 Temperature . 11
4.4.2 Air velocity . 11
Annex A (informative) Effect of airflow on chamber conditions and on surface
temperatures of test specimens . 12

Figure 1 – Experimental data on the effect of airflow on surface temperature of a wire-
wound resistor – Radial airflow . 7
Figure 2 – Experimental data on the effect of airflow on surface temperature of a wire-
wound resistor – Axial airflow . 8
Figure 3 – Temperature distribution on a cylinder with homogeneous heat generation in
–1
.................................................................................... 9
airflow of velocities 0,5, 1 and 2 m⋅s

Table 1 – Influence parameters when testing heat-dissipating specimens . 11

60068-3-1 © IEC:2011 – 3 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
ENVIRONMENTAL TESTING –
Part 3-1: Supporting documentation and guidance –
Cold and dry heat tests
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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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 60068-3-1 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 1974, and constitutes
a technical revision.
The main changes with regard to the previous edition are as follows:
– removal of guidance regarding thermal characteristics of chamber walls;
– revision of sections that address environmental chambers that do not use movement of air
for temperature control.
– 4 – 60068-3-1 © IEC:2011
The text of this standard is based on the following documents:
FDIS Report on voting
104/555/FDIS 104/558/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.
A list of all parts in the IEC 60068 series, under the general title Environmental testing 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 web site 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.
60068-3-1 © IEC:2011 – 5 –
ENVIRONMENTAL TESTING –
Part 3-1: Supporting documentation and guidance –
Cold and dry heat tests
1 Scope
This part of IEC 60068 provides guidance regarding the performance of cold and dry heat
tests.
2 Normative references
The following referenced documents are indispensable for the application 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 60068-1, Environmental testing – Part 1: General and guidance
IEC 60068-2-1, Environmental testing – Part 2-1: Tests – Test A: Cold
IEC 60068-2-2, Environmental testing – Part 2-2: Tests – Test B: Dry heat
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
heat-dissipating specimen
specimen on which the hottest point on its surface, measured in free-air conditions and under
the air pressure as specified in IEC 60068-1, is more than 5 K above the ambient temperature
of the surrounding atmosphere after thermal stability has been reached
3.2
non heat-dissipating specimen
specimen that does not produce heat to a level that can affect the air temperature surrounding
the specimen or those specimens located nearby
3.3
free-air conditions
conditions within an infinite space where the movement of the air is affected only by the heat-
dissipating specimen
4 Selection of test procedures
4.1 General background
4.1.1 General
Specimen performance may be influenced or limited by the temperatures in which the
specimen is operated. The level of influence may be affected by test gradients that exist
within the test system (climatic or environmental chamber) and internal temperatures within

– 6 – 60068-3-1 © IEC:2011
the specimen itself. In order to determine the level of influence that exists and to ensure that
the specimen is designed appropriately, cold and/or dry heat tests are performed.
4.1.2 Ambient temperature
The maximum and minimum values of the ambient temperature where the specimen will be
subjected to should be known. Preferred values for testing purposes are provided in
IEC 60068-2-1 and/or IEC 60068-2-2.
Difficulties can arise due to the fact that heat transfer causes temperature variations in the
area surrounding the specimen. Consequently, the affect from the transfer of heat to the
ambient temperature of the surrounding atmosphere should be considered. Air flow related to
spacing between specimens should also be considered when performing a test.
4.1.3 Specimen temperatures
The performance of the specimen can be affected by its own temperature in the case of heat-
dissipating specimens. Because of this, when controlling the test environment, it may be
necessary to measure the temperature of the specimen under test at different locations, both
internally and externally.
4.1.4 Specimens without heat dissipation
lf the ambient temperature is uniform and constant and there is no generation of heat within
the specimen, heat will flow from the ambient atmosphere into the specimen if the ambient
atmosphere is at a higher temperature. Conversely, heat will flow from the specimen into the
ambient atmosphere if the specimen is at a higher temperature. This heat transfer will
continue until the specimen has completely reached thermal equilibrium with the surrounding
atmosphere. From that moment on, the heat transfer ceases and will not start again unless
the ambient temperature changes.
4.1.5 Specimens with heat dissipation
If heat is generated within the specimen the temperature of the specimen will rise to a
stabilization point above the ambient temperature. It follows that if a steady temperature is
reached, heat will flow continuously from the specimen by convection, radiation, and/or
conduction into the atmosphere whereby the specimen is cooled.
If more than one specimen is subjected to a dry heat test in the same chamber, it is
necessary to ensure that all specimens are in the same ambient temperature and have
identical mounting conditions. It has not, however, been found necessary to differentiate
between testing of single specimens and multiple specimens when the cold test is being
performed.
4.2 Mechanisms of heat transfer
4.2.1 Convection
Heat transfer through convection is an important factor when testing heat-dissipating
specimens. The coefficient of heat transfer from the surface of the test specimen to the
ambient air is affected by the velocity of the surrounding air. The greater the air velocity, the
more efficient the heat transfer is. Therefore, the higher the air velocity, the lower the surface
temperature of the test specimen will be with the same temperature of the ambient air. This
effect is illustrated in Figures 1 and 2.

60068-3-1 © IEC:2011 – 7 –
Full size vitreous enamel
wirewound resistor
Airflow
9 W
6 W
4,5 W
3 W
1,5 W
1 W
0,5 W
0,25 W
0,5 1,0 1,5 2,0 2,5 3,0
–1
Airflow  (m ⋅ s )
IEC  1811/11
Figure 1 – Experimental data on the effect of airflow on surface temperature
of a wire-wound resistor – Radial airflow
Temperature rise  (K)
– 8 – 60068-3-1 © IEC:2011
Full size vitreous enamel
wirewound resistor
Airflow
9 W
6 W
4,5 W
3 W
1,5 W
50 1 W
0,5 W
0,25 W
0,5 1,0 1,5 2,0 2,5 3,0
–1
Airflow  (m ⋅ s )
IEC  1812/11
Figure 2 – Experimental data on the effect of airflow on surface temperature
of a wire-wound resistor – Axial airflow
In addition to the influence on the surface temperature of the test specimen, the airflow within
the chamber will also affect the temperature distribution over the surface of the specimen
under test. This effect is illustrated in Figure 3.
Temperature rise  (K)
60068-3-1 © IEC:2011 – 9 –
90°
When calculating the curves, the thermal
conductance in the specimen has been
neglected (worst case)
ΔT = 100 K
90 K
80 K
70 K
60 K
50 K
40 K
30 K
20 K
10 K
Flow
0° 180°
direction
––11
VV = 2= 2 m m ⋅⋅ ss
–1
V = 1 m ⋅ s
–1
V = 0,5 m ⋅ s
270°
ΔT is the rise in surface temperature of the specimen above ambient
–1
V air velocity m ⋅ s
Air temperature 70 °C
Cylinder diameter 6 mm
–1
Heat-dissipation per unit of surface area 1,5 kW m ⋅ s
IEC  1813/11
Figure 3 – Temperature distribution on a cylinder with homogeneous heat generation
–1
in airflow of velocities 0,5, 1 and 2 m⋅s
Therefore, when testing heat-dissipating specimens, the effects of air flow around or over the
specimen should be known to ensure that the conditions approximate as close as possible
typical free air conditions or those conditions expected when the specimen is in use.
4.2.2 Radiation
Heat transfer by thermal radiation cannot be neglected when test chamber conditions for
testing of heat-dissipating specimens are discussed. In a "free air" condition, the heat
transferred from the test specimen is absorbed by its surroundings.

– 10 – 60068-3-1 © IEC:2011
4.2.3 Thermal conduction
Heat transfer by thermal conduction depends on the thermal characteristics of mounting and
other connections. These should be known in advance of the test.
Many heat-dissipating specimens are intended to be mounted on heat sinks or other well-
conducting elements, with the result that a certain amount of heat is effectively transferred
through thermal conduction.
The relevant specification shall define the thermal characteristics of the mounting and these
characteristics should be reproduced when the test is made.
If a specimen can be mounted in more than one manner with different values of thermal
conduction, the mounting device with the lowest thermal conductivity for dry heat tests on a
specimen with heat dissipation and the mounting device with the highest thermal conductivity
for all the other tests (dry heat tests on specimens without heat dissipation, cold tests on
specimens with or without heat dissipation) should be used.
4.2.4 Forced air circulation
To verify that the temperature at representative points on the surface of the test specimen are
not unduly influenced by the air velocity used in the chamber, measurements should be made
with the specimen inside the chamber, with the chamber operating at standard atmospheric
conditions for measurement and tests (see IEC 60068-1). If the surface temperature at any
point of the test specimen is not reduced by more than 5 K by the influence of the air
circulation used in the chamber, the cooling effect of the forced air circulation may be ignored.
Where the reduction of surface temperature exceeds 5 K, the temperatures from a
representative number of points on the surface of the test specimen should be measured in
order to give a basis for calculation of the surface temperatures at the specified test
conditions. These measurements should be carried out under those load conditions which are
specified for the test temperature by the relevant specification.
For small temperature differences (<5 K) between the ambient temperature and surface
temperature of the specimen, the surface temperature can be assumed to be the same when
tested at different ambient temperatures.
The choice of representative points to be checked should be based on a detailed knowledge
of the test specimen (thermal distribution, thermally critical points, etc.). A single chamber
characterization may cover the chamber performance for a long series of the same type of
tests with similar specimens, whereas in other cases a characterization may need to be made
prior to each test for different types of specimens.
4.3 Test chambers
4.3.1 General
Even in very large chambers, the air circulation and temperature distribution around the test
specimen will not be identical with actual free air conditions. It is not practical for testing
purposes to try to reproduce free air conditions, but it is possible to simulate the effects of
these conditions. Nevertheless, it is established by experimental results and test experience
that a reasonably large chamber with low air flow through the work space will affect the
temperature of the test specimen in approximately the same way as would free air conditions.
Table 1 shows the parameters of a test chamber that should be considered when testing heat-
dissipating specimen.
60068-3-1 © IEC:2011 – 11 –
Table 1 – Influence parameters when testing heat-dissipating specimens
Convection
Transfer
Radiation Conduction
mechanism
Free air Forced air circulation
Chamber Chamber Chamber dimensions, Emissivity of the Thermal characteristic of
parameter dimensions Air velocity chamber wall mounting

4.3.2 Methods of achieving the required conditions in the test chamber
4.3.2.1 Design of chambers for simulating the effect of free air condition
Heating and cooling components used to control the temperature of the working space should
not be placed in the working space.
4.3.2.2 Design of chambers with forced air circulation
The airflow should be as uniform as possible, and should be directed in such a way to
minimize the variation that would occur due to convection. The effects of airflow are given in
more detail in Annex A.
4.4 Measurements
4.4.1 Temperature
Measurement of the temperature at various points on or in a specimen are recommended for
tests involving heat-dissipating specimens in conditions other than "free air". The choice of
representative points should be based on a detailed knowledge of the test specimen (thermal
distribution, thermally critical points, etc.).
4.4.2 Air velocity
The velocity of the air in the test chamber should be known to ensure uniformity of conditions
within the chamber in the case of testing multiple specimens in the same chamber.
Measurements should be made based on the working space within the chamber and the size
and shape of the test specimen.

– 12 – 60068-3-1 © IEC:2011
Annex A
(informative)
Effect of airflow on chamber conditions and
on surface temperatures of test specimens

A.1 Calculation
Calculation of the effect of airflow on a specimen temperature and on temperature gradient in
the chamber uses the following symbols, where:
–1
V is the air velocity (m⋅s );
–2 –1
λ(V) is the heat transfer coefficient (W⋅m ⋅ K );
P is the quantity of heat transferred i
...