IEC 60068-2-39:2015

IEC 60068-2-39 ®
Edition 2.0 2015-09
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Environmental testing –
Part 2-39: Tests – Tests and guidance: Combined temperature or temperature
and humidity with low air pressure tests

Essais d'environnement –
Partie 2-39: Essais – Essais et lignes directrices: Essais combinés de
température ou de température et d’humidité à basse pression atmosphérique

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IEC 60068-2-39 ®
Edition 2.0 2015-09
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Environmental testing –
Part 2-39: Tests – Tests and guidance: Combined temperature or temperature

and humidity with low air pressure tests

Essais d'environnement –
Partie 2-39: Essais – Essais et lignes directrices: Essais combinés de

température ou de température et d’humidité à basse pression atmosphérique

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 19.040 ISBN 978-2-8322-2897-5

– 2 – IEC 60068-2-39:2015 © IEC 2015
CONTENTS
FOREWORD . 3
INTRODUCTION . 5
1 Scope and object . 6
2 Normative references . 6
3 Terms and definitions . 6
4 Testing . 6
4.1 General . 6
4.2 Preferred combinations . 6
4.3 Initial measurement and functional performance test . 7
4.4 Test procedure . 7
4.4.1 Preconditioning . 7
4.4.2 Test with temperature and low air pressure . 7
4.4.3 Test with temperature, humidity and low air pressure . 9
5 Final measurements . 12
6 Information to be given in the relevant specification . 12
7 Information to be given in the test report. 12
Annex A (informative) Guidance on combined temperature or temperature and
humidity with low air pressure testing . 14
A.1 General . 14
A.2 Environmental effects . 14
A.3 Measurement of temperature . 14
Bibliography . 16

Figure 1 – Example of test sequence with cold temperature and low air pressure . 8
Figure 2 – Example of test sequence with dry heat and low air pressure . 9
Figure 3 – Example of test sequence of temperature and humidity with low air
pressure . 11

Table 1 – Test severities . 7

INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
ENVIRONMENTAL TESTING –
Part 2-39: Tests –
Tests and guidance: Combined temperature or
temperature and humidity with low air pressure 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
this end and in addition to other activities, IEC publishes International Standards, Technical Specifications,
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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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Publications is accurate, IEC cannot be held responsible for the way in which they are used or for any
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6) All users should ensure that they have the latest edition of this publication.
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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 60068-2-39 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 1976 and constitutes a
technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
a) preferred severities of the IEC 60068 series;
b) combined temperature, humidity and low air pressure

– 4 – IEC 60068-2-39:2015 © IEC 2015
The text of this standard is based on the following documents:
FDIS Report on voting
104/657/FDIS 104/661/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, published 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.
INTRODUCTION
Equipment and components are required to function without significant reduction in
performance when subjected to different environmental parameters. The combination of
temperature, humidity and low air pressure may have certain effects on components and
gaskets, for example.
The type and severity of the environmental parameters depend on the operational, transport
and storage environments to which the equipment and components are subjected. The
environmental effects on the performance of equipment in the tropics and subtropics are
totally different from those in arctic regions. Individual environmental parameters cause a
variety of different and overlapping effects on the equipment and components.
The manufacturer attempts to ensure, and the user expects, that equipment and components
will survive the environments to which they will be subjected throughout their useful life. This
expectation can be assessed by exposure of the specimen to a range of simulated
environmental parameters controlled in the laboratory. The severity of the environmental
parameters is often increased to obtain meaningful results in a relatively short period of time.
This allows assessment of the likely effects of applied environmental conditions.

– 6 – IEC 60068-2-39:2015 © IEC 2015
ENVIRONMENTAL TESTING –
Part 2-39: Tests –
Tests and guidance: Combined temperature or
temperature and humidity with low air pressure tests

1 Scope and object
This part of IEC 60068 provides a description of test methods and guidance for testing of
equipment or components under combined temperature or temperature and humidity with low
air pressure tests.
The object of combined testing is to investigate to what extent the equipment or components
are affected by combined temperature or temperature and humidity with low air pressure tests.
The method of combined tests detects electrical, mechanical or other physical variations.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and
are indispensable for its application. 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 60068-2-78, Environmental testing – Part 2-78: Tests – Test Cab: Damp heat, steady
state
3 Terms and definitions
None.
4 Testing
4.1 General
All values of test parameters such as cold, dry heat, low air pressure, humidity, exposure time
and conditions such as state of operation and so on, should be selected from the IEC 60068-2
series or the relevant specification.
The duration of exposure shall be measured from the time when temperature stability of the
specimen has been reached under conditions of low air pressure. Temperature stability shall
be according to IEC 60068-1.
It should preferably be tested with low air velocity.
4.2 Preferred combinations
Preferred combinations of temperature, low air pressure and duration shall be selected from
Table 1.
Table 1 – Test severities
Temperature Low air pressure Duration
°C kPa h
–55 5 2
–55 15 2
–55 25 2
–55 40 2
–40 55 2 or 16
–40 70 2 or 16
–25 55 2 or 16
40 55 2
55 15 2
55 25 2
55 40 2
55 55 2 or 16
55 70 2 or 16
85 5 2
85 15 2
155 5 2
155 15 2
4.3 Initial measurement and functional performance test
The specimen shall be submitted to the visual, dimensional and functional checks specified by
the relevant specification.
4.4 Test procedure
4.4.1 Preconditioning
The relevant specification may require preconditioning of specimen.
4.4.2 Test with temperature and low air pressure
Figure 1 and Figure 2 show examples of test sequence with temperature and low air pressure.
The specimen shall be introduced in the chamber as required (unpacked, switched on or off,
etc.).
The temperature within the chamber shall be adjusted to the required temperature as
determined in 4.1. The rate of temperature change should not exceed 1 K/min. The specimen
shall be allowed to reach temperature stability.
In the case of electrically-operated specimens, a function check shall be made in accordance
with the relevant specification. Intermediate measurements shall be performed as required or
specified in the relevant specification.
The pressure in the chamber shall then be reduced to the required value as determined in 4.1.
The rate of change of pressure should not exceed 15 kPa/min.

– 8 – IEC 60068-2-39:2015 © IEC 2015
The conditions of temperature and low air pressure shall be maintained for the required
duration as determined in 4.1.
The low air pressure shall then be restored to normal pressure, at a rate not exceeding
15 kPa/min. During the increase of pressure, the temperature does not need to be controlled.
The specimen remains within the chamber until the temperature reaches standard
atmospheric conditions. The rate of temperature change should not exceed 1 K/min.
The specimen shall then be subjected to the recovery procedure as required.
T
L
T
R
t
P
L
P
R
t t t t t t t t t t
1 2 3 4 5 6 7 8 9
IEC
Key
P pressure at laboratory
L
P pressure required
R
T temperature at laboratory
L
T temperature required
R
t duration of preconditioning at P and T
1 L L
t duration of temperature change from T to T
2 L R
t duration to reach required temperature stability T
3 R
t duration of pressure change from P to P
4 L R
t test duration as defined in Table 1
t plus t  duration of pressure change from P to P
6 7 R L
t plus t  duration of temperature change from T to T
7 8 R L
t duration of recovery at P and T
9 L L
Figure 1 – Example of test sequence with cold temperature and low air pressure
Pressure Temperature
T
R
T
L
t
P
L
P
R
t t t t t t t t t t
1 2 3 4 5 6 7 8 9
IEC
Key
P pressure at laboratory
L
P pressure required
R
T temperature at laboratory
L
T temperature required
R
t duration of preconditioning at P and T
1 L L
t duration of temperature change from T to T
2 L R
t duration to reach required temperature stability T
3 R
t duration of pressure change from P to P
4 L R
t test duration as defined in Table 1
t plus t  duration of pressure change from P to P
6 7 R L
t plus t  duration of temperature change from T to T
7 8 R L
t duration of recovery at P and T
9 L L
Figure 2 – Example of test sequence with dry heat and low air pressure
4.4.3 Test with temperature, humidity and low air pressure
Figure 3 shows an example of test sequence of temperature and humidity with low air
pressure.
The specimen shall be introduced in the chamber as required (unpacked, switched on or off,
etc.)
The temperature within the chamber shall be adjusted to the required temperature as
determined in 4.1. The rate of temperature change should not exceed 1 K/min. The specimen
shall be allowed to reach temperature stability.
A functional test shall be carried out in accordance with the relevant specification.
Intermediate measurements shall be performed as required or specified in the relevant
specification.
With the temperature still maintained at the required value as determined in 4.1, the air
pressure in the chamber shall then be reduced to the required value as determined in 4.1. The
rate of change of pressure should not exceed 15 kPa/min.
Pressure Temperature
– 10 – IEC 60068-2-39:2015 © IEC 2015
The conditions of temperature and low air pressure shall be maintained for the required
duration as determined in 4.1.
Water vapour shall then be injected at a rate sufficient to cause frost to form on the specimen.
After that, the temperature shall be raised to laboratory temperature, while the low air
pressure is constant.
When the rising temperature has reached a value between 0 °C and 5 °C, the low air pressure
shall be restored to normal pressure with a rate not exceeding 15 kPa/min. During the
increase of pressure, the temperature does not need to be controlled. The temperature and
humidity shall be stabilized at the required values; refer to the relevant specification or
IEC 60068-2-78. The conditions of temperature and humidity shall be maintained for the
required duration as determined in 4.1.
The specimen shall then be subjected to the recovery procedure as required.

T
RH
T
L
0 °C to 5 °C
T
RL
t
P
L
P
R
t
rh
R
rh
U
t
t t t t t t t t t
1 2 3 4 5 6 7 8 9
t
IEC
Key
P pressure at laboratory
L
P pressure required
R
rh relative humidity required
R
rh relative humidity uncontrolled
U
T temperature at laboratory
L
T temperature required according to IEC 60068-2-78 or relevant specification
RH
T temperature required causing frost on the specimen
RL
t duration of preconditioning at P , T and rh
1 L L U
t duration of temperature change from T to T
2 L RL
t duration to reach required temperature stability at T
3 RL
t duration of pressure change from P to P
4 L R
t test duration as defined in Table 1
t plus t  duration of temperature change from T to T
6 7 RL L
t duration of pressure change from P to P
7 R L
t duration to reach required T and rh
8 rh R
t duration at T , P and rh
9 rh L R
NOTE Humidity will not stay constant while temperature is changing.
Figure 3 – Example of test sequence of temperature
and humidity with low air pressure
Injection of water vapour Humidity Pressure Temperature

– 12 – IEC 60068-2-39:2015 © IEC 2015
5 Final measurements
The specimen shall be submitted to the visual, dimensional and functional checks prescribed
by the relevant specification.
The relevant specification shall provide the criteria upon which the acceptance or rejection of
the specimen is to be based.
6 Information to be given in the relevant specification
The relevant specification shall contain the following details as far as they are applicable:
a) duration of exposure;
b) temperature for low air pressure;
c) value of low air pressure;
d) value of temperature for humidity;
e) value of humidity;
f) type of test procedure;
g) preconditioning;
h) type and scope of initial measurement;
i) type and scope of intermediate measurement;
j) recovery;
k) type and scope of final measurement;
l) criteria for evaluation;
m) type and scope of test report.
7 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 procedure (e.g. temperature, humidity and low air
pressure)
e) Required values (temperature, low air pressure etc.)
f) Purpose of test (development, qualification, etc.)
g) Test standard, edition (IEC 60068-2-39, edition used)
h) Relevant laboratory test procedure (code and issue)
i) Test specimen description (drawing, photo, quantity, build status, etc.)
j) Test chamber (manufacturer, model number, unique id, etc.)
k) Performance of test apparatus (set point temperature control, air flow etc.)
l) Air velocity and direction (air velocity and direction of incident air to the
specimen)
m) Uncertainties of measurement system (uncertainties data, including temperature
stability of transducer sensitivities)

n) Calibration data (last and next due date)
o) Initial, intermediate and final (initial, intermediate and final measurements)
measurements
p) Required severities (from relevant specification)
q) Test severities (measuring points, data, etc.)
r) Performance of test specimens (results of functional tests etc.)
s) Observations during testing and (any pertinent observations)
actions taken
t) Summary of test (test summary)
u) Distribution (distribution list)
NOTE Text in brackets serves as explanations.

– 14 – IEC 60068-2-39:2015 © IEC 2015
Annex A
(informative)
Guidance on combined temperature or temperature
and humidity with low air pressure testing
A.1 General
Annex A furnishes fundamental comments for applying combined tests of temperature or
temperature and humidity and low air pressure based on different parts within the
IEC 60068-2 series.
For the purposes of combined testing, IEC 60068-1 shall be used together with the relevant
preferred values described in the IEC 60068-2 series.
A.2 Environmental effects
A.2.1 The following effects on the specimen are considered to be due to the combination of
temperature and low air pressure:
a) Increase of surface temperature and changes of temperature gradients of heat dissipating
specimens in comparison with the specified values are due to the decrease of the
convection coefficient, at low air pressure. Although the increase of surface temperatures
can be achieved by using a higher test temperature at normal air pressure, this test
temperature value cannot be properly established and the correct temperature gradients
cannot be achieved without combining with low air pressure.
b) Changes in functional or safety characteristics of specimen due to changes with low air
pressure and temperature of dielectric properties of air. At low air pressure, particularly
when combined with high temperature, there is a marked reduction of air dielectric
strength with the consequent increased risk of arc, surface or corona discharges.
c) Changes in material characteristics due to cold or heat increase the risk that sealed
equipment or component will be deformed or cracked at low air pressure.
A.2.2 Other effects due essentially to temperature but remarkably accelerated by low air
pressure are:
a) volatilization of plasticizers and of degradation products from plastics, with changes in the
mechanical and electrical characteristics of individual parts of the specimen. These
evaporated products can conden
...