Environmental testing - Part 2-38: Tests - Test Z/AD: Composite temperature/humidity cyclic test

IEC 60068-2-38:2021 is available as IEC 60068-2-38:2021 RLV which contains the International Standard and its Redline version, showing all changes of the technical content compared to the previous edition.
IEC 60068-2-38:2021 specifies a composite test procedure, primarily intended for component type specimens, to determine, in an accelerated manner, the resistance of specimens to the deteriorative effects of high temperature/humidity and cold conditions. This test standard does not apply to specimens that are energized during the complete test. Specimens can be energized during the constant phases of the tests. Measurements on energized specimens are typically carried out during constant phases of the test unless specified otherwise. This third edition cancels and replaces the second edition, published in 2009. This edition constitutes a technical revision. This edition includes the following significant technical changes with respect to the previous edition:
- the figures have been updated;
- changes to the wording has been made for clarification purposes.

Essais d'environnement - Partie 2-38: Essais - Essai Z/AD: Essai cyclique composite de température et d'humidité

IEC 60068-2-38:2021 est disponible sous forme de IEC 60068-2-38:2021 RLV qui contient la Norme internationale et sa version Redline, illustrant les modifications du contenu technique depuis l'édition précédente.
L'IEC 60068-2-38:2021 spécifie une procédure d'essai composite, essentiellement destinée aux spécimens de type composant, dans le but de déterminer d'une manière accélérée la résistance des spécimens aux effets destructifs dus à des séjours dans des conditions de température/d'humidité élevées, alternées avec des conditions de froid. La présente norme d'essai ne s'applique pas aux spécimens qui sont mis sous tension durant toute la durée de l'essai. Les spécimens peuvent être mis sous tension durant les phases constantes des essais. Les mesures réalisées sur des spécimens sous tension ont généralement lieu durant les phases constantes de l'essai, sauf spécification contraire. Cette troisième édition annule et remplace la deuxième édition parue en 2009. Cette édition constitue une révision technique. Cette édition inclut les modifications techniques majeures suivantes par rapport à l'édition précédente
- les figures ont été mises à jour;
- la formulation a été modifiée à des fins de clarification.

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Status
Published
Publication Date
24-Mar-2021
Current Stage
PPUB - Publication issued
Completion Date
25-Mar-2021
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IEC 60068-2-38
Edition 3.0 2021-03
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Environmental testing –
Part 2-38: Tests – Test Z/AD: Composite temperature/humidity cyclic test
Essais d'environnement –
Partie 2-38: Essais – Essai Z/AD: Essai cyclique composite de température
et d'humidité
IEC 60068-2-38:2021-03(en-fr)
---------------------- Page: 1 ----------------------
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---------------------- Page: 2 ----------------------
IEC 60068-2-38
Edition 3.0 2021-03
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Environmental testing –
Part 2-38: Tests – Test Z/AD: Composite temperature/humidity cyclic test
Essais d'environnement –
Partie 2-38: Essais – Essai Z/AD: Essai cyclique composite de température
et d'humidité
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 19.040 ISBN 978-2-8322-9586-1

Warning! Make sure that you obtained this publication from an authorized distributor.

Attention! Veuillez vous assurer que vous avez obtenu cette publication via un distributeur agréé.

® Registered trademark of the International Electrotechnical Commission
Marque déposée de la Commission Electrotechnique Internationale
---------------------- Page: 3 ----------------------
– 2 – IEC 60068-2-38:2021 © IEC 2021
CONTENTS

FOREWORD ........................................................................................................................... 4

1 Scope .............................................................................................................................. 6

2 Normative references ...................................................................................................... 6

3 Terms and definitions ...................................................................................................... 6

4 General ........................................................................................................................... 6

4.1 Description of the test ............................................................................................. 6

4.2 Application of the test ............................................................................................. 7

5 Description of test chamber ............................................................................................. 8

5.1 General ................................................................................................................... 8

5.2 Chamber for exposure to moisture .......................................................................... 8

5.3 Chamber for exposure to cold ................................................................................. 8

6 Severities ........................................................................................................................ 9

7 Testing procedure ............................................................................................................ 9

7.1 Preconditioning ....................................................................................................... 9

7.2 Initial measurements ............................................................................................. 10

7.3 Conditioning .......................................................................................................... 10

7.4 Test cycle ............................................................................................................. 13

7.4.1 Description of temperature/humidity subcycle ................................................ 13

7.4.2 Description of cold subcycle .......................................................................... 14

7.4.3 Description of 24 h cycles with no exposure to cold ....................................... 15

7.4.4 Description of final cycle ................................................................................ 15

7.4.5 Intermediate measurements........................................................................... 15

7.5 Final measurements .............................................................................................. 17

7.5.1 Introductory remarks ...................................................................................... 17

7.5.2 At high humidity ............................................................................................. 18

7.5.3 Immediately upon removal from the chamber ................................................. 18

7.5.4 After final drying ............................................................................................ 18

8 Information to be given in the relevant specification ....................................................... 18

9 Information to be given in the test report........................................................................ 19

Annex A (informative) Supporting documentation for test sequence ..................................... 20

A.1 General ................................................................................................................. 20

A.2 Preconditioning ..................................................................................................... 20

A.3 Exposure to humidity followed by exposure to cold ............................................... 21

A.4 Exposure to humidity not followed by exposure to cold.......................................... 22

Bibliography .......................................................................................................................... 23

Figure 1 – Preconditioning .................................................................................................... 10

Figure 2 – Exposure to humidity followed by exposure to cold............................................... 12

Figure 3 – Exposure to humidity not followed by exposure to cold ......................................... 13

Figure 4 – Test times for intermediate operation of specimen – Exposure to humidity

followed by exposure to cold ................................................................................................. 16

Figure 5 – Test times for intermediate operation of specimen – Exposure to humidity

not followed by exposure to cold ........................................................................................... 17

---------------------- Page: 4 ----------------------
IEC 60068-2-38:2021 © IEC 2021 – 3 –

Table A.1 – Relative humidity tolerances .............................................................................. 20

Table A.2 – Temperature tolerances ..................................................................................... 20

Table A.3 – Tolerances of relative humidity and temperature during exposure to

humidity followed by exposure to cold ................................................................................... 21

Table A.4 – Tolerances of relative humidity and temperature during exposure to

humidity not followed by exposure to cold ............................................................................. 22

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– 4 – IEC 60068-2-38:2021 © IEC 2021
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
ENVIRONMENTAL TESTING –
Part 2-38: Tests –
Test Z/AD: Composite temperature/humidity cyclic test
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,

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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.

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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.

IEC 60068-2-38 has been prepared by IEC technical committee 104: Environmental conditions,

classification and methods of test. It is an International Standard.

This third edition cancels and replaces the second edition, published in 2009. This edition

constitutes a technical revision.

This edition includes the following significant technical changes with respect to the previous

edition:
a) the figures have been updated;
b) changes to the wording has been made for clarification purposes.
---------------------- Page: 6 ----------------------
IEC 60068-2-38:2021 © IEC 2021 – 5 –
The text of this International Standard is based on the following documents:
Draft Report on voting
104/891/FDIS 104/896/RVD

Full information on the voting for its approval can be found in the report on voting indicated in

the above table.
The language used for the development of this International Standard is English.

This document was drafted in accordance with ISO/IEC Directives, Part 2, and developed in

accordance with ISO/IEC Directives, Part 1 and ISO/IEC Directives, IEC Supplement, available

at www.iec.ch/members_experts/refdocs. The main document types developed by IEC are

described in greater detail at www.iec.ch/standardsdev/publications.

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.
---------------------- Page: 7 ----------------------
– 6 – IEC 60068-2-38:2021 © IEC 2021
ENVIRONMENTAL TESTING –
Part 2-38: Tests –
Test Z/AD: Composite temperature/humidity cyclic test
1 Scope

This part of IEC 60068 specifies a composite test procedure, primarily intended for component

type specimens, to determine, in an accelerated manner, the resistance of specimens to the

deteriorative effects of high temperature/humidity and cold conditions.

This test standard does not apply to specimens that are energized during the complete test.

Specimens can be energized during the constant phases of the tests. Measurements on

energized specimens are typically carried out during constant phases of the test unless

specified otherwise.
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 60068-1, Environmental testing – Part 1: General and guidance

IEC 60068-2-67, Environmental testing – Part 2-67: Tests – Test Cy: Damp heat, steady state,

accelerated test primarily intended for components
3 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
4 General
4.1 Description of the test

Test Z/AD is a cyclic temperature/humidity test which is designed to reveal defects in test

specimens caused by "breathing" as distinct from the absorption of moisture.

This process can be initiated by the forming of condensation on the specimen's surface. As the

temperature on parts or the whole of the specimen's surface might be lower than the

corresponding dew point at the humidity value, water can accumulate in small cracks or gaps

on the specimen's surface.
---------------------- Page: 8 ----------------------
IEC 60068-2-38:2021 © IEC 2021 – 7 –

Once the air temperature is reduced, the air in internal voids of specimen is contracted which

results in a drop of pressure and drawing-in either wet air or condensed water through cracks

or other leaks inside the specimen. The wet air will condense on inner walls of a void and may

gradually fill it. During the temperature rising phase, the air in the void is expanded, this time

with a lower dew point than during drawing-in, and partially escape out. This cycle is repeated,

and water can be accumulated inside the specimen and may gradually fill its voids.

This so-called "breathing" effect is caused by changing the temperature inside the specimen in

an atmosphere with high humidity. During the excursion to sub-zero temperature phase of the

test, the water trapped in cracks and other voids freezes and due to the expansion of ice volume

the cracks extend, and new cracks can form.

This test differs from other cyclic damp heat tests in that it derives its increased severity from:

a) a greater number of temperature variations or "breathing" actions in a given time;

b) a greater cyclic temperature range;
c) a higher cyclic rate of change of temperature;
d) the inclusion of a number of excursions to sub-zero temperatures.

The accelerated breathing and the effect of the freezing of trapped water in cracks and fissures

are the essential features of this composite test.

It is emphasized, however, that the freezing effect will occur only if the fissure dimensions are

large enough to allow the penetration of a coherent mass of water as is normally the case in

fissures between seals and metal assemblies, or between seals and wire terminations.

The degree of condensation will depend mainly upon the thermal time constant of the surface

of the test specimens and may be negligible for very small specimens but copious for large

specimens.

Similarly, the breathing effect will be more apparent on specimens which contain relatively large

air-filled or gas-filled voids, but again, the severity of the test will depend to some extent on the

thermal characteristics of the specimens.

The condensation effect and the temperature distribution could be disturbed by functional

checks, therefore the checks should be carried out during the constant phases of the

temperature profiles (Figure 2 and Figure 3, areas B and F).

To simply the programming of the test sequences, the set points are given in Annex A.

4.2 Application of the test

For the reasons given above, it is recommended that this test procedure be limited to component

type specimens when the construction of the specimens suggests a "breathing" type of damp

heat test combined with icing and where the thermal characteristics are compatible with the

rates of change of temperature, etc., of test Z/AD.

For solid type specimens, for example plastic encapsulated, where there may be small hairline

cracks or porous material, the absorption or diffusion mechanisms will predominate and a

steady damp heat such as test C of IEC 60068-2-78 is preferred for investigating these effects.

For larger specimens such as equipment or when it is essential for components to ensure

thermal stability during the various phases of the cycle, test Db of IEC 60068-2-30 should be

employed, although due to the reduced number of cycles in a given period, the degree of

acceleration may not be as fast. In this case, test Db should normally form part of a sequence

such as that defined in IEC 60068-1.
---------------------- Page: 9 ----------------------
– 8 – IEC 60068-2-38:2021 © IEC 2021

As in other damp heat tests, a polarizing voltage or electrical loading may be applied to the

specimens. In the case of electrical loading, the loading should be such that the temperature

rise of the specimens does not unduly affect the chamber conditions.

From the above, test Z/AD should not be considered to be interchangeable with, or an

alternative to, either steady-state or other cyclic damp heat tests, but the choice of test

procedure should be made with due regard for the physical and thermal characteristics of the

test specimens and the types of failure mechanisms which are significant for each particular

case.
5 Description of test chamber
5.1 General

The exposure to moisture, followed by cold, can either be performed in one chamber or in two

separate chambers.

NOTE All temperatures and humidity values measured refer to a supply air measurement of the test chamber.

5.2 Chamber for exposure to moisture
The chamber for the exposure to moisture shall be so constructed that:

a) the temperature can be varied between 25 °C ± 2 K and 65 °C ± 2 K in a period of between

1,5 h and 2,5 h for both rising and falling temperatures;

b) the relative humidity can be maintained at % during the periods of constant or rising

( −3)
temperature and between 80 % and 96 % during the falling temperature periods;

c) the conditions prevailing at any point in the working space are uniform and are as similar as

possible to those prevailing in the immediate vicinity of suitably located temperature- and

humidity-sensing devices;

The air in the chamber shall therefore be continuously stirred at a rate necessary to maintain

the specified conditions of temperature and humidity.

d) the specimens under test shall not be subjected to radiant heat from the chamber

conditioning processes;

e) the water used for the chamber humidity system shall comply with the limits given in

IEC 60068-2-67;

f) condensed water shall be continuously drained from the chamber and not used again unless

it has been re-purified.

Precautions shall be taken to ensure that no condensed water from the walls and roof of the

test chamber can fall on the specimens.
5.3 Chamber for exposure to cold
The chamber for exposure to cold shall be so constructed that
a) the temperature can be maintained at –10 °C ± 2 K,

b) the conditions prevailing at any point in the working space are uniform and are as similar as

possible to those prevailing in the immediate vicinity of suitably located temperature-sensing

devices.
The air in the chamber shall therefore be continuously moving.

Care should be taken that the thermal capacity of the specimen under test does not appreciably

influence conditions within the chamber.
---------------------- Page: 10 ----------------------
IEC 60068-2-38:2021 © IEC 2021 – 9 –

The humidity chamber may be used for exposure to cold, in which case it shall meet the

requirements of 4.1 and, in addition, shall be so constructed that

1) the temperature can be lowered from 25 °C ± 2 K to −10 °C ± 2 K in a period of not more

than 30 min,

2) the specimen can be held at a temperature of −10 °C ± 2 K for a period of 3 h,

3) the temperature can be raised from −10 °C ± 2 K to 25 °C ± 2 K in a period of not more than

90 min.
6 Severities

The number of 24 h cycles shall be 10, unless otherwise specified. If other than 10, the relevant

specification shall define the number.
7 Testing procedure
7.1 Preconditioning

Unless otherwise specified, the specimens in the unpacked, switched-off, ready-for-use state

shall be subjected to the conditions for "assisted drying" specified in IEC 60068-1 (55 °C ± 2 K

with a relative humidity not exceeding 20 %) for a period of 24 h prior to the first cycle of the

damp heat test.

The specimens shall then be allowed to attain thermal stability at standard atmospheric

conditions for testing or, as otherwise specified, before the initial measurements are made.

Figure 1 gives an overview about the preconditioning phase. During the stabilizing period no

specific rate of cooling is specified, however it shall not exceed 1 K/min.
---------------------- Page: 11 ----------------------
– 10 – IEC 60068-2-38:2021 © IEC 2021
Figure 1 – Preconditioning
7.2 Initial measurements

The specimens shall be visually inspected and electrically and mechanically checked as

required by the relevant specification.
7.3 Conditioning

The total temperature tolerance of ±2 K given in this document is intended to take account of

absolute errors in the measurement, slow changes of temperature and temperature variations

of the working space.
---------------------- Page: 12 ----------------------
IEC 60068-2-38:2021 © IEC 2021 – 11 –

NOTE This tolerance is valid for an empty test space during stabilized temperature/humidity conditions of the test.

In some conditions, where the specimen has a negligible impact on the chamber control, the tolerances can still be

valid for the chamber with specimen(s).

However, in order to maintain the relative humidity within the required tolerances, it is necessary

to keep the temperature difference between any two points in the working space at any moment

within narrower limits. The required humidity conditions will not be achieved if such temperature

differences exceed 1 K. It may also be necessary to keep short-term fluctuations within these

limits to maintain the required humidity.

The specimens shall be introduced into the humidity chamber, in the unpacked, switched-off,

ready-for-use state, and mounted in the normal orientation, if this is known, or as otherwise

specified and shall be subjected to 10 temperature/humidity cycles, each of 24 h duration.

During any five of the first nine of the above cycles after exposure to the humidity subcycle

(areas A to H in Figure 2), the specimens shall be subjected to cold. The position of the cold

subcycles should be defined in the relevant specification.
---------------------- Page: 13 ----------------------
– 12 – IEC 60068-2-38:2021 © IEC 2021
Figure 2 – Exposure to humidity followed by exposure to cold

This exposure may be performed either in the same chamber or in separate chambers. If

separate chambers are used for the high-temperature/high-humidity and low-temperature

subcycles of the test, the specimens should not be subjected to thermal shock conditions unless

it is known that they are insensitive to this degree of thermal shock.

If a batch of specimens is subjected to thermal shock using the two chamber method and

significant failures occur, a further batch shall be retested with gradual change of temperatures

and shall be considered to have passed the test successfully if no significant failures occur

under these conditions.

The remaining four of the first nine cycles shall be run without exposure to cold (see 7.4.3 and

Figure 3). The humidity cycles specified are the same in all cases.
---------------------- Page: 14 ---------------------
...

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