IEC 60068-2-38:2021

IEC 60068-2-38 ®
Edition 3.0 2021-03
REDLINE VERSION
INTERNATIONAL
STANDARD
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inside
Environmental testing –
Part 2-38: Tests – Test Z/AD: Composite temperature/humidity cyclic test
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IEC 60068-2-38 ®
Edition 3.0 2021-03
REDLINE VERSION
INTERNATIONAL
STANDARD
colour
inside
Environmental testing –
Part 2-38: Tests – Test Z/AD: Composite temperature/humidity cyclic test
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 19.040 ISBN 978-2-8322-9633-2

– 2 – IEC 60068-2-38:2021 RLV © IEC 2021
CONTENTS
FOREWORD . 4
1 Scope . 6
2 Normative references . 6
3 Terms and definitions . 6
4 General . 7
4.1 Description of the test . 7
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 . 9
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 . 21
A.1 General . 21
A.2 Preconditioning . 21
A.3 Exposure to humidity followed by exposure to cold . 22
A.4 Exposure to humidity not followed by exposure to cold. 23
Bibliography . 24
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

Table A.1 – Relative humidity tolerances . 21
Table A.2 – Temperature tolerances . 21
Table A.3 – Tolerances of relative humidity and temperature during exposure to
humidity followed by exposure to cold . 22
Table A.4 – Tolerances of relative humidity and temperature during exposure to

humidity not followed by exposure to cold . 23

– 4 – IEC 60068-2-38:2021 RLV © 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
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8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
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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 IEC 60068-2-38:2009. A vertical bar appears in the margin wherever a change
has been made. Additions are in green text, deletions are in strikethrough red text.

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.
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.
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 document using a colour printer.

– 6 – IEC 60068-2-38:2021 RLV © IEC 2021
ENVIRONMENTAL TESTING –
Part 2-38: Tests –
Test Z/AD: Composite temperature/humidity cyclic test

1 Scope
This part of IEC 60068 provides 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 60068-2-30, Environmental testing – Part 2-30: Tests – Test Db: Damp heat, cyclic (12 h +
12 h cycle)
IEC 60068-2-78, Environmental testing – Part 2-78: Tests – Test Cab: Damp heat, steady state
IEC Guide 104, The preparation of safety publications and the use of basic safety publications
and group safety publications
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.
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 "pumping 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

– 8 – IEC 60068-2-38:2021 RLV © IEC 2021
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.
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;
+3
b) the relative humidity can be maintained at 93 % during the periods of constant or rising
( )
−3
temperature and between 80 % RH and 96 % RH 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) water used for the maintenance of chamber humidity shall have a resistivity of not less than
500 Ωm 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 shall should be taken that the thermal capacity of the specimen under test does not
appreciably influence conditions within the chamber.
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 (see Figure 1)
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.

– 10 – IEC 60068-2-38:2021 RLV © 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.
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 ±0,5 K
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
(points a) to f) 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.

– 12 – IEC 60068-2-38:2021 RLV © 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 prescribed specified are the same in all cases.

Figure 3 – Exposure to humidity not followed by exposure to cold
7.4 Test cycle
7.4.1 Description of temperature/humidity subcycle
The description of the temperature/humidity subcycles is applicable to all cycles (see Figure 2
and Figure 3).
NOTE 1 The dotted lines in Figure 2 and Figure 3 are for orientation purposes only, aiming to give a better
understanding of the test cycle. They place no indication for the order of the set points for the test.
At "zero time" of every 24 h cycle, the chamber condition shall be controlled to a temperature
+3
of 25 °C ± 2 K and relative humidity at %.
( −3 )
– 14 – IEC 60068-2-38:2021 RLV © IEC 2021
A The temperature of the chamber shall be continuously raised to 65 °C ± 2 K in a period of
between 1,5 h and 2,5 h.
+3
During this period, the relative humidity shall remain within the limits of %.
( −3 )
B The temperature and relative humidity in the chamber shall be maintained at 65 °C ± 2 K
+3
and 93 % respectively, until 5,5 h after the start of the cycle.
( )
−3
C The temperature shall then be allowed to fall to 25 °C ± 2 K in a period of between 1,5 h
and 2,5 h.
During this period, the relative humidity shall remain within the limits of 80 % to 96 %.
D Beginning 7 h after the start of the cycle, the relative humidity shall remain within the limits
of 80 % to 98 %.
E Beginning 8 h after the start of the cycle, the temperature shall again be raised to 65 °C ±
2 K in a period of between 1,5 h and 2,5 h. During this period, the relative humidity shall be
+5
(93 ± 3) 93 %.
( −3 )
F Beginning 9,5 h after the start of the cycle, the relative humidity shall remain within the limits
+3
of %.
( −3 )
The temperature and relative humidity in the chamber shall be maintained at 65 °C ± 2 K
+3
and % respectively, until 13,5 h after the start of the cycle.
( −3 )
G The temperature shall then be drop allowed to fall to 25 °C ± 2 K in a period of between
1,5 h and 2,5 h.
During this period, the relative humidity in the chamber shall remain within the limits of 80 %
to 96 %.
H Beginning 15 h after the start of the cycle, the relative humidity shall remain within the limits
of 80 % to 98 %.
I The chamber shall then continue to run at a stabilized temperature of 25 °C ± 2 K and
relative humidity of (93 ±3) % until the start of the cold subcycle or until the end of the 24 h
+5
cycle as appropriate %.
( −3 )
7.4.2 Description of cold subcycle
This description is applicable to any five of the first nine cycles (see Figure 2).
I Following the completion of the temperature/humidity subcycle (points a) to f) areas A to H
in Figure 2), the chamber is maintained at a temperature of 25 °C ± 2 K and a relative
+5
humidity of (93 ± 3) 93 % for a period of at least 1 h but not more than 2 h.
( −3 )
K The specimen shall then be exposed to cold by lowering the temperature of the chamber or
transferring to a second chamber.
If the specimen is transferred from one chamber to another, the transfer should be
completed within a period of 5 min. Beginning 17,5 h after the start of the cycle, the ambient
2 K. This temperature shall be
temperature of the chamber shall be reduced to –10 °C ±
reached 18 h after the start of the cycle.
Beginning 18 h after the start of the cycle, the temperature shall be maintained at
−10 °C ± 2 K for a period of 3 h.
No requirement for humidity is prescribed specified during the entire cold subcycle.
L Beginning 21 h after the start of the cycle, the temperature shall be raised to 25 °C ± 2 K.
This temperature shall be reached 22,5 h after the start of the cycle (see Figure 2).
If the specimen is transferred from one chamber to another, the transfer shall be completed
within a period of 10 min to 15 min.

M The temperature of the chamber shall be maintained at 25 °C ± 2 K until the 24 h cycle is
+5
completed. During this period, the relative humidity shall be (93 ± 3) %.
( −3 )
7.4.3 Description of 24 h cycles with no exposure to cold
This description is applicable to the remaining four of the first nine cycles (Figure 3).
Cycles which do not include a cold subcycle following the humidity/temperature subcycle are
the same as described in 7.4.1, except that under point g) the chamber shall be maintained at
a temperature of 25 °C ±2 K and relative humidity of (93 ± 3) % until the 24 h cycle is completed
from A to H.
I Following the completion of the temperature/humidity subcycle (areas A to H in Figure 2),
the chamber shall be maintained at a temperature of 25 °C ± 2 K and, beginning 16 h after
+5
the start of the cycle, the relative humidity shall be %.
( −3 )
J Beginning 17,5 h after the start of the cycle, the chamber shall then continue to run at a
stabilized temperature of 25 °C ± 2 K and the relative humidity shall be kept within the limits
+3
of 93 % until the end of the 24 h cycle.
( −3 )
NOTE This description is valid for Figure 3 (exposure to humidity not followed by exposure to cold) only.
7.4.4 Description of final cycle
In the final cycle, following the completion of the temperature and humidity subcycle, the
+3
chamber is maintained at a temperature of 25 °C ± 2 K and relative humidity of 93 % for a
( )
−3
period of 3,5 h after which the final measurements are made.
7.4.5 Intermediate measurements
In order to carry out measurements on energized specimen, the following parts of the constant
phases of the test cycles shown in Figure 2 and Figure 3 can be used:
– area beginning 2,5 h after the test has started until 5,5 h after the test has started (time
indicated by end of area B in Figure 2 and Figure 3);
– area beginning 10,5 h after the test has started until 18 h after the test has started (time
indicated by end of area F in Figure 2 and Figure 3)
During operation, functional checks only should be carried out, as permanent operation of the
specimen could interfere with the severity of the climatic stress applied to the specimen.
Figure 4 and Figure 5 indicate the areas where these measurements can be carried out.

– 16 – IEC 60068-2-38:2021 RLV © IEC 2021

Figure 4 – Test times for intermediate operation of specimen –
Exposure to humidity followed by exposure to cold

Figure 5 – Test times for intermediate operation of specimen –
Exposure to humidity not followed by exposure to cold
7.5 Final measurements
7.5.1 Introductory remarks
Electrical and mechanical measurements may be made
a) at high humidity,
b) immediately upon removal from the chamber,
c) after a drying period, or
d) as required by the relevant specification.
It should be realized that many measurements taken under high humidity conditions are not
directly comparable with those taken initially or after removal from the chamber.

– 18 – IEC 60068-2-38:2021 RLV © IEC 2021
7.5.2 At high humidity
The measurements shall be made during the last two hours of the 3,5 h period referred to in
6.4.4 Figure 3.
The relevant specification shall specify the particular precautions to be followed in making
measurements under conditions of high relative humidity, including the means to be adopted
for the removal of surface water if this is necessary.
The specimen shall be removed from the chamber after all measurements have been completed.
7.5.3 Immediately upon removal from the chamber
On completion of the final cycle, the specimen shall be removed from the chamber and be kept
at the laboratory ambient temperature.
If the initial measurements were made under conditions different from the laboratory ambient
temperature, the same conditions shall be used for both sets of measurements.
Electrical and mechanical measurements, as specified, shall be made within a period of
between 1 h and 2 h after removal from the chamber.
Measurements taken early in this time period may be repeated once only, later in the time
period. The later reading will be used for failure determination.
7.5.4 After final drying
On completion of the final cycle, the specimen shall be removed from the chamber and shall be
kept under standard atmospheric conditions for testing for a period of 24 h before the specified
final measurements are made.
If the initial measurements were made under conditions other than standard atmospheric
conditions for testing, the same conditions shall be used for both sets of measurements.
Measurements may be made during the 24 h period, but only measurements made at the end
of the 24 h period shall be used for failure determination.
8 Information to be given in the relevant specification
When this test is included in the relevant specification, the following details shall be given as
far as they are applicable:
a) type of test (subcycle);
b) preconditioning;
c) initial measurements;
d) details of mounting and supports;
e) number of cycles;
f) position of cold subcycles;
g) measurements and/or loading during conditioning;
h) recovery;
i) final measurements;
j) any deviation in procedure as agreed upon between customer and supplier.

9 Information to be given in the test report
As a minimum, the test report shall show the following information:
a) Customer (name and address)
b) Test laboratory (name and address and details of
accreditation - if any)
c) Test dates (dates when test was run)
d) Type of test (Z/AD)
e) Purpose of test (development, qualification, etc.)
f) Test standard, edition (IEC 60068-2-38, edition used)
g) Relevant laboratory test procedure (code and issue)
h) Test specimen description (drawing, photo, quantity build status, etc.)
i) Test chamber identity (manufacturer, model number, unique
identity, etc.)
j) Performance of test apparatus (set point temperature control, air flow, etc.)
k) Air velocity and direction (air velocity and direction of incident air to
the specimen)
l) Uncertainties of measuring system (uncertainties data)
m) Calibration data (last and next due date)
n) Initial, intermediate and final (initial, intermediate and final
measurements measurements)
o) Required severities (from relevant specification)
p) Test severities (measuring points, data, etc.)
q) Performance of test specimens (results of functional tests, etc.)
r) Observations during testing and actions (any pertinent observations)
taken
s) Summary of test (test summary)
t) Distribution (distribution list)
NOTE A test log should be written for the testing which can be attached to the report.
a) Customer (name and address);
b) Test laboratory (name and address and details of
accreditation – if any);
c) Test dates (dates when test was run);
d) Type of test (Z/AD);
e) Test standard, edition (IEC 60068-2-38, edition used);
f) Test specimen description (drawing, photo, quantity build status, etc.);
g) Test chamber identity (unique identity of the chamber, e.g.
internal Laboratory Identification
number/code);
h) Initial, intermediate and final (if performed by the test laboratory);
measurements
i) Required severities (from relevant specification);
j) Test severities (measuring points, data, etc.);
k) Performance of test specimens (results of functional tests, etc.);
l) Observations during testing and (any pertinent observations);
actions taken
m) Test results (test summary, e.g. pass/fail decision).

In addition to the mandatory information the test report can include, for example:

– 20 – IEC 60068-2-38:2021 RLV © IEC 2021
n) Purpose of test (development, qualification, etc.);
o) Relevant laboratory test procedure (code and issue);
p) Performance of test apparatus (set point temperature control, air flow,
etc.);
q) Air velocity and/or direction (air velocity and/or direction of incident air
to the specimen);
r) Uncertainties of chamber independent (uncertainties data);
measuring system
s) Calibration data (last and next due date).

A test log should be written for the testing which can be attached to the report.

A.1 General
In order to simplify creating test routines for operating climatic chambers, the test steps for
each test procedure are given in Table A.1 to Table A.4.
A.2 Preconditioning
Table A.1 – Relative humidity tolerances
Test step Time Lower limit Upper limit
h % %
1 0 0 20
2 24 45 75
a
3 45 75
a
Can be extended if necessary.
Table A.2 – Temperature tolerances
Test step Time Lower limit Upper limit
h °C °C
1 0 53 57
2 24 53 57
5 5
f(t) = − 0,000 006 258 71 t f(t) = − 0,000 003 441 6 t
4 4
+ 0,001 255 169 t + 0,000 746 803 t
3 3
− 0,102 362 894 t − 0,066 182 76 t
a
3 48
2 2
+ 4,293 766 092 t + 2,997 420 635 t
− 93,907 963 78 t − 69,342 126 98 t
+ 882,047 291 3 + 689,24
a
Can be extended if necessary.
– 22 – IEC 60068-2-38:2021 RLV © IEC 2021
A.3 Exposure to humidity followed by exposure to cold
Table A.3 – Tolerances of relative humidity and temperature during
exposure to humidity followed by exposure to cold
Humidity tolerances Temperature tolerances Test
Test Test
subsequence
step time
Lower limit Upper limit Lower limit Upper limit
(see 7.4)
h % % °C °C
1 0 90 96 23 27
A
2 1,5 90 96 47 67
3 2,5 90 96 63 67
B
4 5,5 90 96 63 67
5 5,5 80 96 63 67
C
6 7 80 96 23 43
7 7 80 98 23 43
D
8 8 80 98 23 27
9 8 90 98 23 27
E
10 9,5 90 98 47 67
11 9,5 90 96 47 67
12 10,5 90 96 63 67 F
13 13,5 90 96 63 67
14 13,5 80 96 63 67
G
15 15 80 96 23 43
16 15 80 98 23 43
H
17 16 80 98 23 27
18 16 90 98 23 27
I
19 17,5 90 98 23 27
a
20 17,5  −12 27
a
21  −12 −8 K
a
22  −12 −8
a
23 21  −12 27
L
24 22,5 90 98 23 27
25 24 90 98 23 27 M
a
No humidity tolerance given between 17,5 h and 22,5 h.

A.4 Exposure to humidity not followed by exposure to cold
Table A.4 – Tolerances of relative humidity and temperature during
exposure to humidity not followed by exposure to cold
Humidity tolerances Temperature tolerances Test
Test Test
subsequence
step time
Lower limit Upper limit Lower limit Upper limit
(see 7.4)
h % % °C °C
1 0 90 96 23 27
A
2 1,5 90 96 47 67
3 2,5 90 96 63 67
B
4 5,5 90 96 63 67
5 5,5 80 96 63 67
C
6 7 80 96 23 43
7 7 80 98 23 43
D
8 8 80 98 23 27
9 8 90 98 23 27
E
10 9,5 90 98 47 67
11 9,5 90 96 47 67
12 10,5 90 96 63 67 F
13 13,5 90 96 63 67
14 13,5 80 96 63 67
G
15 15 80 96 23 43
16 15 80 98 23 43
H
17 16 80 98 23 27
18 16 90 98 23 27
I
19 17,5 90 98 23 27
20 17,5 90 96 23 27
J
21 24 90 96 23 27
– 24 – IEC 60068-2-38:2021 RLV © IEC 2021
Bibliography
IEC 60068-2-30, Environmental testing – Part 2-30: Tests – Test Db: Damp heat, cyclic
(12 h + 12 h cycle)
IEC 60068-2-78, Environmental testing – Part 2-78: Tests – Test Cab: Damp heat, steady state

___________
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
– 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 .
...