BS-2011-2.1Z-AD-1977 IEC-60068-2-38-1974.pdf
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1、BRITISH STANDARD BS 2011-2.1Z/AD: 1977 IEC 68-2-38: 1974 Basic environmental testing procedures Part 2.1 Tests Tests Z/AD: Composite temperature/humidity cyclic test (This Part should be read in conjunction with Part 1.1 General) UDC 621.37/.39.001.4:620.169.1:620.193.94 + 620.193.24 Licensed Copy:
2、sheffieldun sheffieldun, na, Tue Nov 28 13:47:06 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS2011-2.1Z/AD:1977 This British Standard, having been prepared under the direction of the General Electrotechnical Engineering Standards Committee, was published under the authority of the Executive Board on
3、 31 August 1977 BSI 03-1999 The following BSI references relate to the work on this standard: Committee reference GEL/15 Draft for approval 76/26488 ISBN 0 580 09992 X Amendments issued since publication Amd. No.DateComments Licensed Copy: sheffieldun sheffieldun, na, Tue Nov 28 13:47:06 GMT+00:00 2
4、006, Uncontrolled Copy, (c) BSI BS2011-2.1Z/AD:1977 BSI 03-1999i Contents Page Forewordii 1Introduction1 2Object1 3General description of the test1 4Description of test apparatus1 5Severities2 6Testing procedure2 7Information to be given in the relevant specification4 Figure 1 Pre-conditioning5 Figu
5、re 2a Exposure to humidity followed by exposure to cold6 Figure 2b Exposure to humidity not followed by exposure to cold7 Licensed Copy: sheffieldun sheffieldun, na, Tue Nov 28 13:47:06 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS2011-2.1Z/AD:1977 ii BSI 03-1999 Foreword This British Standard has b
6、een prepared under the direction of the General Electrotechnical Engineering Standards Committee. It is identical with IEC Publication 68-2-38:1974 “Basic environmental testing procedures. Part 2: Tests Test Z/AD: Composite temperature/humidity cyclic test”. Conventions. The text of the IEC Publicat
7、ion has been accepted as suitable for publication, without deviation, as a British Standard. Certain conventions are used, however, that are not identical with those used in British Standards. Attention is therefore drawn to the following. The comma has been used in the figures as a decimal marker.
8、In British Standards it is current practice to use a full point (a full stop on the baseline) as the decimal marker. Wherever page numbers are quoted in connection with references to figures in this publication, they are IEC page numbers. Cross reference. For the following reference to another IEC P
9、ublication that is given in the text, there is an equivalent British Standard, given below. A British Standard does not purport to include all the necessary provisions of a contract. Users of British Standards are responsible for their correct application. Compliance with a British Standard does not
10、 of itself confer immunity from legal obligations. Reference to IEC PublicationEquivalent British Standard IEC 68-1 Basic environmental testing procedures Part 1 General BS 2011-1.1 Basic environmental testing procedures Part 1.1 General Summary of pages This document comprises a front cover, an ins
11、ide front cover, pages i and ii, pages 1 to 7 and a back cover. This standard has been updated (see copyright date) and may have had amendments incorporated. This will be indicated in the amendment table on the inside front cover. Licensed Copy: sheffieldun sheffieldun, na, Tue Nov 28 13:47:06 GMT+0
12、0:00 2006, Uncontrolled Copy, (c) BSI BS2011-2.1Z/AD:1977 BSI 03-19991 1 Introduction 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 test differs from other cyclic damp heat
13、 tests in that it derives its increased severity from: a) A greater number of temperature variations or “pumping” 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
14、 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
15、 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 larg
16、e 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. Application of the test For the reasons given a
17、bove, 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
18、 Z/AD. For solid type specimens, e.g. 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 is preferred for investigating these effects. For larger specimens such as equipment
19、or when it is essential for components to ensure thermal stability during the various phases of the cycle, test Db should be employed, although due to the reduced number of cycles in a given period the degree of acceleration may not be so great. In this case, test Db should normally form part of a s
20、equence such as that defined in Clause 7 of IEC Publication 68-1. 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 t
21、he chamber conditions. From the above, it is therefore evident that 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 c
22、haracteristics of the test specimens and the types of failure mechanisms which are significant for each particular case. 2 Object To provide a composite test procedure, primarily intended for component type specimen, to determine in an accelerated manner the resistance of specimens to the deteriorat
23、ive effects of high temperature/humidity and cold conditions. 3 General description of the test The test employs temperature cycling at high-relative humidity and will produce a “breathing” action of moisture into partially sealed containers. The test includes exposure to low temperatures to determi
24、ne the effects of periodic icing. 4 Description of test apparatus The exposure to moisture, followed by cold, can either be performed in one chamber or in two separate chambers. 4.1 The chamber for the exposure to moisture shall be so constructed that: a) The temperature can be varied between 25 2 C
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