EN 60068-2-33:1999

SLOVENSKI STANDARD
01-september-2001
Environmental testing - Part 2: Tests - Guidance on change of temperature tests
Environmental testing -- Part 2: Tests - Guidance on change of temperature tests
Umweltprüfungen -- Teil 2: Prüfungen - Leitfaden zur Prüfgruppe N: Temperaturwechsel
Essais d'environnement -- Partie 2: Essais - Guide pour les essais de variations de
température
Ta slovenski standard je istoveten z: EN 60068-2-33:1999
ICS:
19.040 Preskušanje v zvezi z Environmental testing
okoljem
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

CEI
NORME
INTERNATIONALE IEC
68-2-33
INTERNATIONAL
Première édition
STANDARD
First edition
Essais fondamentaux climatiques
et de robustesse mécanique
Deuxième partie:
Essais
Guide pour les essais de variations de température
Basic environmental testing procedures
Part 2:
Tests
Guidance on change of temperature tests
© CEI 1971 Droits de reproduction réservés — Copyright - all rights reserved
Aucune parte de cette publication ne peut être reproduite ni No part of this publication may be reproduced or utilized in
utilisée sous quelque forme que ce soit et par aucun pro- any form or by any means, electronic or mechanical,
cédé, électronique ou mécanique, y compris la photocopie et including photocopying and microfilm, without permission
les microfilms, sans l'accord écrit de l'éditeur. in writing from the publisher.
Bureau Central de la Commission Electrotechnique Internationale 3, rue de Varembé
Genève, Suisse
Commission Electrotechnique Internationale CODE PRIX
International Electrotechnical Commission PRICE CODE
IEC MewayHapoaHaa 3neKrporexHHVecKaa HoMHCCHa
• • Pour prix, voir catalogue en vigueur
For price, see current catalogue

— 3 —
INTERNATIONAL ELECTROTECHNICAL COMMISSION
BASIC ENVIRONMENTAL TESTING PROCEDURES
Part 2: Tests — Guidance on change of temperature tests
FOREWORD
1) The formal decisions or agreements of the IEC on technical matters, prepared by Technical Committees on which all the
National Committees having a special interest therein are represented, express, as nearly as possible, an international
consensus of opinion on the subjects dealt with.
2) They have the form of recommendations for international use and they are accepted by the National Committees in that
sense.
3)
In order to promote this international unification, the IEC expresses the wish that all National Committees having as
yet no national rules, when preparing such rules, should use the IEC recommendations as the fundamental basis for these
rules in so far as national conditions will permit.
4) The desirability is recognized of extending international agreement on these matters through an endeavour to harmonize
national standardization rules with these recommendations in so far as national conditions will permit. The National
Committees pledge their influence towards that end.
PREFACE
This Recommendation has been prepared by Sub-Committee 50B, Climatic Tests, of IEC Technical
Committee No. 50, Environmental Testing.
It is intended to give guidance for Test N : Change of Temperature (I EC Publication 68-2-14).
A first draft was discussed at the meeting held in Stockholm in 1968, as a result of which a new draft
was submitted to the National Committees for approval under the Six Months' Rule in January 1969.
The following countries voted explicitly in favour of publication :
Australia Korea (Republic of)
Austria Netherlands
Belgium Norway
Czechoslovakia Romania
Denmark South Africa
Finland Switzerland
Turkey
Germany
Hungary United Kingdom
Israel United States of America
Japan
— 5 —
BASIC ENVIRONMENTAL TESTING PROCEDURES
Part 2: Tests — Guidance on change of temperature tests
1. Introduction
This Recommendation gives guidance to designers and testing personnel on the specification
and use of change of temperature tests.
A change of temperature test is intended to determine the effect on the specimen of a change
of temperature or a succession of changes of temperature.
It is not intended to show effects which are due only to the high or low temperature. For these
effects, the dry heat test or the cold test should be used.
The effect of such tests is determined by :
— values of high and low conditioning temperature between which the change is to be effected ;
— the conditioning times for which the test specimen is kept at these temperatures ;
— the rate of change between these temperatures ;
— the number of cycles of conditioning ;
— the amount of heat transfer into or from the specimen.
2. Field conditions of changing temperature
In electronic equipment and components, only gradual changes of temperature usually occur.
Parts inside an equipment will undergo slower changes of temperature than those on an external
surface of the equipment when it is not switched on.
Rapid changes of temperature may be expected :
—
when equipment is transported from warm indoor environments into cold open air conditions
or vice versa ;
— when equipment is suddenly cooled by rainfall or immersion in cold water ;
in externally mounted airborne equipment ;
— or under certain conditions of transportation and storage.
Components will undergo stresses due to changing temperature when high temperature gradients
build up in an equipment after switching on ; e.g. in the neighbourhood of high wattage resistors,
radiation can cause rise of surface temperature in neighbouring components while other portions
are still cool.
Artificially cooled components may be subjected to rapid temperature changes when the cooling
system is switched on.
Rapid changes of temperature in components may also be induced during manufacturing pro-
cesses of equipment.
The number and amplitude of temperature changes, and the time interval between them, are
important.
When a transfer time of 2 min to 3 min is applied, the magnitude of the thermal stresses expe-
rienced by the specimen will be less for very small items than for large ones. The thermal stresses,
however, will bear a relationship to that which would be experienced by such a specimen when
it was transported within a few minutes from an atmosphere at one extreme of temperature to
one at the other extreme.
The effects on components and equipment of temperature rise and temperature fall may be
different. Dew or frost appearing on components or equipment may cause additional stresses
and, where these additional stresses are not desired, humidity should be suitably controlled to
minimize these effects.
3. Basic philosophy
3.1 Design of change of temperature tests
The change of temperature tests, Tests Na, Nb and Nc (IEC Publication 68-2-14), comprise
alternate periods at a high and at a low temperature with well defined transitions from one
temperature to the other. The conditioning run from room temperature to the first conditioning
temperature, then to the second conditioning temperature, and back to room temperature, is
called one test cycle.
3.1.1 Test parameters
— Room temperature.
— High temperature.
— Low temperature.
— Duration of exposure.
— Interval between exposure to the two extremes of temperature.
— Number of test cycles.
The high and low temperatures are understood to be ambient temperatures which will be
reached by most specimens with a certain time-lag.
Only in exceptional cases may they be specified outside the normal storage or operating tem-
perature range of the object under test.
The test is accelerated because the number of severe changes of temperature in a given period
is greater than that which will occur under field conditions.
3.2 Purpose and choice of the tests
A change of temperature test is not intended to simulate field conditions exactly. The purpose
of a change of temperature test is to stress specimens in order to determine whether they are
properly designed or made.
3.2.1 Change of temperature testing is recommended in the following cases :
3.2.1.1 Evaluation of electrical performance during a change of temperature, Test Nb.
3.2.1.2 Evaluation of mechanical performance during a change of temperature, Test Nb.
3.2.1.3 Evaluation of electrical performance after a specified number of rapid changes of temperature,
Test Na or Test Nc.
3.2.1.4 Evaluation of the suitability of mechanical components, and of materials and combinations of
materials to withstand rapid changes of temperature, Test Na or Test Nc.
3.2.1.5 Evaluation of the suitability of construction of components to withstand artificial stressing, Test
Na or Test Nc.
3.2.2 The change of temperature tests specified in IEC Publication 68 are not intended to evaluate the
difference in material constants or electrical performance when operating under temperature
stability at the two extremes of temperature.
3.3 Choice of the duration of the exposure
The duration of the exposure should be related in such a way to the temperature time constant
of the specimens (or of their critical parts) that they would reach the approximate ambient tem-
perature of the space or of the bath. It is, therefore, important to know the temperature time
constant of the specimen. As the temperature time constant of the outside and inside parts of
large specimens (equipment) may differ considerably from each other, it is preferable to take into
consideration the temperature time constant of the innermost or most critical part.
The time constant depe
...