EN 60068-2-47:2005

STANDARDOkoljsko preskušanje – 2-47. del: Preskusi – Pritrjevanje preskušancev pri preskusih vibracij, udarcev in pri podobnih dinamičnih preskusih (IEC 60068-2-47:2005)Environmental testing – Part 2-47: Tests – Mounting of specimens for vibration, impact and similar dynamic tests (IEC 60068-2-47:2005)©
Standard je založil in izdal Slovenski inštitut za standardizacijo. Razmnoževanje ali kopiranje celote ali delov tega dokumenta ni dovoljenoReferenčna številkaSIST EN 60068-2-47:2005(en)ICS19.040

EUROPEAN STANDARD
EN 60068-2-47 NORME EUROPÉENNE EUROPÄISCHE NORM
June 2005 CENELEC European Committee for Electrotechnical Standardization Comité Européen de Normalisation Electrotechnique Europäisches Komitee für Elektrotechnische Normung
Central Secretariat: rue de Stassart 35, B - 1050 Brussels
© 2005 CENELEC - All rights of exploitation in any form and by any means reserved worldwide for CENELEC members.
Ref. No. EN 60068-2-47:2005 E
ICS 19.040 Supersedes EN 60068-2-47:1999
English version
Environmental testing Part 2-47: Tests - Mounting of specimens for vibration,
impact and similar dynamic tests (IEC 60068-2-47:2005)
Essais d'environnment Partie 2-47: Essais –
Fixation de spécimens pour essais
de vibrations, d'impacts et autres essais dynamiques (CEI 60068-2-47:2005)
Umgebungseinflüsse Teil 2-47: Prüfverfahren –
Befestigung von Prüflingen zur Schwing-, Stoß- und ähnlichen dynamischen Prüfungen (IEC 60068-2-47:2005)
This European Standard was approved by CENELEC on 2005-05-01. CENELEC members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European Standard the status of a national standard without any alteration.
Up-to-date lists and bibliographical references concerning such national standards may be obtained on application to the Central Secretariat or to any CENELEC member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by translation under the responsibility of a CENELEC member into its own language and notified to the Central Secretariat has the same status as the official versions.
CENELEC members are the national electrotechnical committees of Austria, Belgium, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Slovakia, Slovenia, Spain, Sweden, Switzerland and United Kingdom.

at national level by publication of an identical
national standard or by endorsement
(dop)
2006-02-01 – latest date by which the national standards conflicting
with the EN have to be withdrawn
(dow)
2008-05-01 Annex ZA has been added by CENELEC. __________ Endorsement notice The text of the International Standard IEC 60068-2-47:2005 was approved by CENELEC as a European Standard without any modification. In the official version, for Bibliography, the following notes have to be added for the standards indicated:
IEC 60068-2-6 NOTE Harmonized as EN 60068-2-6:1995 (not modified).
IEC 60068-2-7 NOTE Harmonized as EN 60068-2-7:1993 (not modified).
IEC 60068-2-21 NOTE Harmonized as EN 60068-2-21:1999 (not modified).
IEC 60068-2-27 NOTE Harmonized as EN 60068-2-27:1993 (not modified).
IEC 60068-2-29 NOTE Harmonized as EN 60068-2-29:1993 (not modified).
IEC 60068-2-31 NOTE Harmonized as EN 60068-2-31:1993 (not modified).
IEC 60068-2-32 NOTE Harmonized as EN 60068-2-32:1993 (not modified).
IEC 60068-2-57 NOTE Harmonized as EN 60068-2-57:2000 (not modified).
IEC 60068-2-59 NOTE Harmonized as EN 60068-2-59:1993 (not modified).
IEC 60068-2-64 NOTE Harmonized as EN 60068-2-64:1994 (not modified).
IEC 60068-2-65 NOTE Harmonized as EN 60068-2-65:1994 (not modified).
IEC 60068-2-75 NOTE Harmonized as EN 60068-2-75:1997 (not modified).
IEC 60068-2-81 NOTE Harmonized as EN 60068-2-81:2003 (not modified). __________

- 3 - EN 60068-2-47:2005
Annex ZA
(normative)
Normative references to international publications
with their corresponding European publications The following referenced documents are indispensable for the application 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. NOTE Where an international publication has been modified by common modifications, indicated by (mod), the relevant EN/HD applies. Publication Year Title EN/HD Year IEC 60068-1 1988 Environmental testing Part 1: General and guidance
EN 60068-1 1) 1994 IEC 60068-2-55 1987 Part 2: Tests - Test Ee and guidance: Bounce
EN 60068-2-55 1993 ISO 2041 1990 Vibration and shock - Vocabulary
- -
1) EN 60068-1 includes corrigendum October 1988 + A1:1992 to IEC 60068-1.

NORMEINTERNATIONALECEIIECINTERNATIONALSTANDARD60068-2-47Troisième éditionThird edition2005-04Essais d'environnement – Partie 2-47: Essais – Fixation de spécimens pour essais de vibrations, d'impacts et autres essais dynamiques Environmental testing – Part 2-47: Tests – Mounting of specimens for vibration, impact and similar dynamic tests Pour prix, voir catalogue en vigueur For price, see current catalogue© IEC 2005
Droits de reproduction réservés
⎯
Copyright - all rights reservedAucune partie de cette publication ne peut être reproduite ni utilisée sous quelque forme que ce soit et par aucun procédé, électronique ou mécanique, y compris la photocopie et les microfilms, sans l'accord écrit de l'éditeur. No part of this publication may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from the publisher. International Electrotechnical Commission,
3, rue de Varembé, PO Box 131, CH-1211 Geneva 20, SwitzerlandTelephone: +41 22 919 02 11 Telefax: +41 22 919 03 00 E-mail: inmail@iec.ch
Web: www.iec.ch CODE PRIX PRICE CODE VCommission Electrotechnique InternationaleInternational Electrotechnical Commission

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CONTENTSFOREWORD.5INTRODUCTION.91Scope.112Normative references.113Terms and definitions.114General.115Mounting, where the specimen is a component.136Mounting, where the specimen is equipment and other articles.137Mounting, where the specimen is a packaged product.157.1Packaging available (see also Clause B.2).157.2Product normally packaged but packaging not available (see also Clause B.3).178Information to be given in the relevant specification.17Annex A (informative)
General guidance.29Annex B (informative)
Guidance on packaged products.43Annex C (informative)
Response of a single degree of freedom (SDOF) system
to a half-sine shock pulse.59Bibliography.69Figure 1 – Examples of obvious means of mounting components.19Figure 2 – Examples of mounting of components by the leads only.21Figure 3 – Examples of mounting of components by the body only.23Figure 4 – Examples of mounting of components by the body and the leads.25Figure 5 – Examples of mounting of electronic cabinets.27Figure B.1 – Generalized transmissibility factors for packaging materials.51Figure C.1 – Typical characteristics of half sine pulse.63Figure C.2 – Typical single degree of freedom (SDOF) transmissibility characteristics.63Figure C.3 – Peak Acceleration Responses SRS.65Figure C.4 – Relative Amplitude of Secondary Response Peaks.67Figure C.5 – Notation of Response Characteristics.67

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INTERNATIONAL ELECTROTECHNICAL COMMISSION ____________ENVIRONMENTAL TESTING – Part 2-47: Tests –
Mounting of specimens for vibration,
impact and similar dynamic 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, Technical Reports, Publicly Available Specifications (PAS) and Guides (hereafter referred to as “IEC Publication(s)”). Their 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.
3) IEC Publications have the form of recommendations for international use and are accepted by IEC National Committees in that sense. While all reasonable efforts are made to ensure that the technical content of IEC Publications is accurate, IEC cannot be held responsible for the way in which they are used or for any misinterpretation by any end user. 4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications transparently to the maximum extent possible in their national and regional publications. Any divergence between any IEC Publication and the corresponding national or regional publication shall be clearly indicated in the latter. 5) IEC provides no marking procedure to indicate its approval and cannot be rendered responsible for any equipment declared to be in conformity with an IEC Publication. 6) All users should ensure that they have the latest edition of this publication. 7) No liability shall attach to IEC or its directors, employees, servants or agents including individual experts and members of its technical committees and IEC National Committees for any personal injury, property damage or other damage of any nature whatsoever, whether direct or indirect, or for costs (including legal fees) and expenses arising out of the publication, use of, or reliance upon, this IEC Publication or any other IEC 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 60068-2-47 has been prepared by IEC technical committee 104: Environmental conditions, classification and methods of test. This third edition cancels and replaces the second edition, published in 1999, and constitutes a technical revision.
The major technical changes with regard to the second edition are related to specific guidance on the testing of packaged products.

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The text of this standard is based on the following documents: FDIS Report on voting 104/359/FDIS 104/366/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. This standard forms Part 2-47 of IEC 60068 which consists of the following major parts, under the general title Environmental testing: Part 1: General and guidance Part 2: Tests Part 3: Supporting documentation and guidance Part 4: Information for specification writers Part 5: Guide to drafting of test methods The committee has decided that the contents of this publication will remain unchanged until the maintenance result 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.

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INTRODUCTION This part of IEC 60068 defines the requirements and gives information regarding the mounting of components, equipment and other articles and packaged products, referred to as "specimens", when they are subjected to vibration, impact and similar dynamic tests. In all cases, component-type specimens are mounted as stated in the relevant specification. Where these details are not specified, a number of standardized methods of mounting are given in this standard. Equipment-type specimens should be mounted by their normal means of attachment unless otherwise stated in the relevant specification. An attempt is made, in the first instance, to categorize specimens into either component or equipment types and then to proceed to test accordingly. If this is not possible, for example for packaged items, this standard may still be relevant, but relates to the packaging and not to the contents. It should be noted that this standard does not apply to the testing of empty packaging. General guidance is provided in Annex A, as appropriate for both the specification writer and the test engineer. Specific guidance on the testing of packaged products is given in Annex B. Annex C provides guidance on the methodology for modifying a half sine pulse test, used as input to a packaged specimen, when the packaging is not available. In some instances, requirements and guidance on mounting are included, partly or wholly, in the individual standards of the IEC 60068 series, for example, Test Fh. Where such a standard is called up by the relevant specification, it will need to be studied as well as this standard.

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ENVIRONMENTAL TESTING – Part 2-47: Tests –
Mounting of specimens for vibration,
impact and similar dynamic tests 1 Scope This part of IEC 60068 provides methods for mounting products, whether packaged or unpackaged, as well as mounting requirements for equipment and other articles, for the series of dynamic tests in IEC 60068-2, that is impact (Test E), vibration (Test F) and acceleration, steady-state (Test G). When they are fastened to the test apparatus and subjected to these tests, whether packaged or unpackaged, they are referred to as specimens. 2 Normative references The following referenced documents are indispensable for the application 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 60068-1:1988, Environmental testing – Part 1: General and guidanceIEC 60068-2-55:1987, Environmental testing – Part 2-55: Tests – Test Ee and guidance: Bounce ISO 2041:1990, Vibration and shock – Vocabulary3 Terms and definitions For the purposes of this document, the terms and definitions used in ISO 2041 and IEC 60068-1 apply. 3.1package
result of the packing operation, consisting of the packaging and its contents, for example, electronic devices prepared for transport 3.2packaging product made of any material of any nature to be used for the containment, protection, handling and delivery, for example, a corrugated fibreboard box 4 General The relevant specification shall state whether the effect of gravitational force is important. If so, the specimen shall be mounted in such a way that the gravitational force acts in the same direction as it would in use. Where the effect of gravitational force is not important, the specimen may be mounted in any attitude.

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If significant for the test results, the relevant specification shall also state a)
the temperature limits within which the specimen shall be tested, b) the maximum level of magnetic interference which may be imposed on the specimen and/or the orientation of the specimen in relation to the direction of the magnetic field (for example, near an electrodynamic vibration generator), c)
the relative humidity limits within which the specimen shall be tested. 5 Mounting, where the specimen is a component The mounting method to be used shall be as stated in the relevant specification. Where the method of mounting is not specified but is obvious from the design, as in Figure 1, this method shall be used. Where it is not obvious, the mounting methods shall, whenever possible, be chosen in accordance with the principles shown in Figures 2, 3 or 4,bearing in mind whether the intention is to load dynamically the leads and/or the body or to determine the internal robustness. When the specimen is to be tested with additional leads attached, these shall be so arranged that they impose similar restraint and mass to those when the specimen is used in its normal manner. In all cases, components shall be fastened to a rigid test fixture or directly to the mounting surface of the test apparatus. The most common failure mode for electronic components as shown in Figures 1, 2 and 3 is not failure of the component itself but of the solder connection due to flexure of the printed circuit board. Testing of the complete printed circuit board is essential. NOTEA "rigid test fixture" is one where there are no resonances within the test range or where the requirements of the test tolerances can be met at all fixing points. 6 Mounting, where the specimen is equipment and other articles The specimen shall be mechanically connected to the mounting surface of the test apparatus either directly or by means of a rigid test fixture (see note above), as shown in Figure 5, or as stated in the relevant specification.
NOTE In the case of acoustically induced vibration, the mounting technique is quite different and reference should be made to IEC 60068-2-65.In cases where the normal mounting structure for the equipment is available, the relevant specification shall state if it shall be used (see also Clause A.2). Any additional stays or straps shall be avoided. Any connections to the specimen such as cables, pipes, etc. shall be so arranged that they impose similar restraint and mass to those when the specimen is installed in its operational position. In order to achieve this, it may be necessary to fasten the cables, pipes, etc., to the fixture. The relevant specification shall specify the size, mounting torque and associated tolerance of the fixing bolts.

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Specimens intended for use with isolators shall normally be tested with their isolators. If it is not practicable to carry out the test with the appropriate isolators, the specimen may be tested without the isolators at a different severity, as stated in the relevant specification. The relevant specification may require an additional test on a specimen with the external isolators removed or blocked, in order to demonstrate that minimum acceptable structural resistance has been achieved. In this case, the severity to be applied shall be given in the relevant specification. Where, operationally, any heating effect on the isolators is likely to be of significance, this shall be taken into account during testing. 7 Mounting, where the specimen is a packaged product All the relevant requirements in Clauses 5 and 6 above shall be met. Generally, in order to reproduce the effects of the transportation phase, a product, if normally packaged for that phase, shall be tested in its packaging. However, there are a number of situations to consider, as follows: 7.1 Packaging available (see also Clause B.2)Unless otherwise stated in the relevant specification, the packaging, if available, shall be used during the testing. If the method of fastening the packaged product to a transportation vehicle is known, that method shall, where practicable, be replicated and details of this shall be specified in the relevant specification and stated in the test report. The relevant specification shall specify the size, mounting torque and associated tolerance of the fixing bolts. If the specimen is capable of being fastened to a transportation vehicle in a number of known ways then, from engineering knowledge of the dynamic behaviour of the product, the worst case(s) shall be selected so that faults are most likely to be revealed. Where the specimen is fastened to a transportation vehicle but the method varies in an unpredictable way, it shall be mechanically connected to the test apparatus as detailed in the relevant specification. This may be in a manner which only engineering judgement can decide and shall be based upon faults considered most likely to be revealed. If the specimen is intended, or is likely, to be carried in a transportation vehicle without being fastened down, or with some degree of freedom, it shall be tested in accordance with IEC 60068-2-55. See also B.4.3. If the packaged product is intended to be fastened to a transportation vehicle but it is considered likely that, in practice, it might not be fastened down, the relevant specification may require the test method stated in the previous paragraph to be applied. This may be in addition to the appropriate test where the product is fastened down.

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7.2 Product normally packaged but packaging not available (see also Clause B.3)If a product is normally packaged but the packaging is not available, it is generally not possible to mount the product on the test apparatus in a truly representative manner and the test becomes one of an empirical nature. However, it is possible to adjust the test severity in order to allow for an element of the protection provided when the packaging is otherwise present. Great care is needed in interpreting the results in this case and such a test should be considered as a development test, not an approval test. It is strongly recommended to test again with the specimen in the packaging.
Two situations exist; firstly, where the packaging performance is known and secondly, where it is not known. These are dealt with separately below. 7.2.1 Packaging performance known If the packaging performance is known, or can be calculated, this will often enable the applied severity to be modified. Knowledge of the transfer function or transmissibility of the packaging provides the ability to adjust the vibration or shock test levels, see also Annex C. Where the design of the packaging defines its attitude during transportation, then the attitude of the internal product is also known. It shall be fastened to the mounting surface of the test apparatus in a manner representative of that attitude. Unless otherwise stated by the relevant specification, the modified severity shall be applied (see previous paragraph). Where the attitude of the package during transportation is variable and hence the attitude of the product can vary, the test shall be conducted in the attitude considered to represent the worst case(s). If engineering judgement does not enable this choice to be made, a number of possible worst case attitudes shall be stated in the relevant specification. Unless otherwise stated in the relevant specification, the modified test severity (see above) shall be applied. Although the packaging performance may be known and the package is, or might be, carried in an unfastened manner in a transportation vehicle, the absence of the packaging prevents a practicable test from being performed. See Clause B.3 and B.4.3. 7.2.2 Packaging performance not knownWhere the packaging is not available and its performance is not known, generalized transmissibility curves are provided in Figure B.1 for use in modifying the applied vibration test severity. The relevant specification should state which transmissibility curve shall be used. Annex C provides a method for adjusting the half-sine shock severity. 8 Information to be given in the relevant specification When this part of IEC 60068-2 is referred to in a relevant specification, the following details shall be given as far as they are applicable. a) Mounting and attitude for testing, gravitational effect (Clause 4) b) Maximum or minimum temperature (Clause 4) c) Maximum magnetic interference (Clause 4) d) Maximum or minimum relative humidity (Clause 4) e) Mounting of specimens (components) (Clause 5)

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f) Mounting of specimens (equipment and other articles) (Clause 6) g) Mounting of package (stacking) h) Transmissibility curve used to modify test severity (Clause 7) Methods of mounting Examples Components provided with obvious means
of mounting, for example diodes, electrolytic capacitors, rectifiers, switches, connectors, relays, transformers, power transistors Figure 1 – Examples of obvious means of mounting components

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Methods of mounting Examples Components such as transistors, integrated circuits, relays and others where the distance to the fixture is limited by design Resistors, capacitors Resistors, capacitors, inductors, diodes Resistors, capacitors, inductors,
diodes, transistors NOTEIt is important that the relevant specification states whether or not the component is in contact with the mounting surface. Figure 2 – Examples of mounting of components by the leads only

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Methods of mounting Examples Tubular components, the coating of which is fragile, such as high-power resistors Transistors, diodes Integrated circuits Figure 3 – Examples of mounting of components by the body only

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Methods of mounting Examples Capacitors, relays. Additional body fastening, for example with extra bracket, necessary by reason of weight or severity Transistors mounted on a heat-sink Transformers, chokes Relays Figure 4 – Examples of mounting of components by the body and the leads

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Fixing pointsTesting axesIIEC
1285/99Figure 5 – Examples of mounting of electronic cabinets

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Annex A
(informative) General guidance A.1 Mounting, where the specimen is a component When the test is to determine the suitability of a component for its operational environment, the relevant specification should ensure that the component is held in a manner that simulates that used in service. It cannot be emphasized too strongly that components above a certain mass, which should be given in the relevant specification, will also require the body to be supported both for the test and for the operational environment. It is important that the method of mounting is in accordance with the requirements of the manufacturer. The detailed information given in Figures 1 to 4should be used only when such requirements are not available. Some components having special geometrical shapes, for instance discs, spheres, bulbs, and those requiring special fastening devices are not shown in the figures. For these, it is essential that the relevant specification gives detailed information. If a specimen is designed for a number of methods of mounting, all of these should be considered. It is recommended that new components should be used for each test. Whichever method is specified or chosen it is important that the fastening to the test fixture or apparatus be rigid. This can be achieved by clamping, soldering, embedding or bonding the component body and/or its leads, as appropriate. A normal size printed wiring board to which components are fastened does not, generally, give sufficient rigidity, and it may not be possible to achieve the requirements of the test in this manner. In addition, reproducibility will probably be impaired. Small portions of a board may prove to be satisfactory, provided that attention is paid to their dynamic characteristics. When an internal robustness test is to be performed, it is important to note that the mounting method is rarely that which will be used in the operational environment. It is then essential that the dynamic stress be transmitted to the internal structure. This is generally obtained by mounting the component both by its body and by its leads. Should it be necessary to subject a component to a ‘robustness of terminations test’ (see IEC 60068-2-21), after the dynamic tests, the leads should not be bent for the dynamic tests, nor should they be displaced relative to the body of the components. If, however, this cannot be avoided, the relevant specification should specify that separate components are to be used for each test. In addition, it may be necessary for the velocity of sound in the fixture material to be considered. Care should be taken to ensure, as far as is practicable, that the propagation path is well below a quarter wavelength. Test fixtures for large components or for the simultaneous testing of several components will need special consideration and the general principles given for equipment fixtures are applicable (see Clause A.3).
For guidance related to packaged products, see Annex B.

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A.2 Mounting, where the specimen is equipment and other articles It is important that the specimen is mounted in a manner representative of that used in its operational position. For example, a specimen normally held by its front panel alone should be so mounted for the test (see Figure 5). If it is practical to use part of the real mounting structure as the fixture, it should be utilized as this represents operational conditions. The fixing points are then taken as those of the mount-ing structure and not of the specimen. The relevant specification should state whether to use the mounting structure and which fixing points to use as control points for controlling the test. If the normal mounting structure is not available or, in special cases even when it is available but where it is known that it does not influence the behaviour of the equipment, the test fixture, designed so that the appropriate test requirements can be met, should be used. Specimens intended for use with isolators may sometimes have to be tested without them, for example if the specimen is mounted with others on a common mounting system, or if the dynamic characteristics of the isolators are very variable (for example if they are temperature dependent). As a result, the test level will then need to be modified. For vibration testing, this new level should be determined by considering the envelope of the transmissibility curve of the isolator system in each axis. Where the severity is known to vary with the direction of the applied test/excitation, this should be taken into account.If no transmissibility characteristics are available, the new severity will need to be chosen arbitrarily but preferably after discussion between the supplier and the purchaser.
NOTEIn the case of the sinusoidal vibration test (see IEC 60068-2-6), some general transmissibility curves are given in A.5.1 of Annex A of that standard. These general curves may also be appropriate for other IEC 60068-2 vibration tests. It should be noted that, for a steady-state acceleration test, there may, under certain circum-stances, be a safety hazard if the specimen is tested with its isolators. The use of stays or straps may then be unavoidable. It is particularly important for this test that the stresses to be experienced by the attachment bolts be calculated in order to avoid a safety hazard. For guidance related to packaged products see Annex B. A.3 Test fixture A test fixture will invariably be required for mounting and for orientation purposes. Therefore, it is considered desirable to highlight possible problem areas associated with the fixture design that could prevent the achievement of the test requirements and thus affect reproducibility. However, it should be noted that it is not the function of this annex to offer solutions; these can usually be found in the technical literature. The fundamental purpose of the test fixture is to transmit faithfully the mechanical stimulation from the test apparatus to the specimen, and to ensure that the specification requirements can be met at the fixing points of the specimen.
The physical shape and mass of the specimen, the severity of the test requirements and the capabilities of the test apparatus will govern the design of the test fixture. These last two parameters are dependent on the test under consideration. In addition, for the impact and steady-state acceleration tests, the design may be further complicated by the need to test in the "plus" and "minus" directions of each test axis. Additionally some of the parameters, which need to be considered in the fixture design, are given in A.3.5 and in Clause A.4.

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A.3.1 Shock and bump The manufacturer will normally specify the total mass and maximum severity permitted for the test apparatus. For a given specimen mass, the design of the test fixture will generally be easier if the capability of the test apparatus is significantly greater than that strictly necessary, since the fixture can then be heavier and less complex. It is still important to consider the effect of stiffness and dimensions (see A.3.5). A.3.2 Vibration The main parameter limiting the total mass of the specimen and its test fixture is the thrust capability of the vibration generator. The manufacturer normally specifies this. In terms of severity, the most important features are the frequency range and displacement and/or acceleration required. However, in terms of the test apparatus performance, large thrust and a wide frequency range are normally incompatible. Thus, unlike the shock and bump situation, it may not be appropriate to use the largest vibration generator available. As a result, test fixtures are normally more complex than those required for other tests, and extensive experience is needed in order to achieve satisfactory results. Also, the frequency response may well be affected when the fixture and specimen are fastened to the vibration generator. It needs to be remembered that the dynamic mass may well be of greater significance than the static mass. A.3.3 Vibration, acoustically induced The type and design of test fixtures to mount specimens for vibration tests that are acoustically induced depend very much on the size and mass of the test specimens. In the simplest case of an electronic box to be tested in a reverberation chamber, the specimen should be elastically suspended so that it becomes located in the central area of the chamber.
The suspension device, such as rubber cords, should be attached to the fixing points of the electronic box. Larger test specimens such as reflectors or solar arrays should, wherever practicable, use the same fixing mechanisms as in the operational case. Generally the test fixtures should be as transparent as possible, with respect to the acoustic environment. However, in special cases it may be desirable to simulate the shielding or reflecting conditions to which the specimen is subjected in its operational environment. Such cases include solar arrays for satellites that are often mounted on a satellite sidewall simulator for acoustic tests. Very large specimens, such as complete satellites, generally use their real payload attachment fitting as a test fixture. In all cases, the total assembly should be isolated against vibration from the floor or ceiling of the reverberation chamber. The suspension frequency should be less than 25 Hz or 25 % of the lowest frequency of interest of the specimen. A.3.4 Acceleration, steady-state The fixture design is simplest for this case since the acceleration is applied progressively and the dynamic behaviour of the fixture and the specimen can be ignored. Thus the fixture need only be rigid enough to withstand the static forces involved and sufficiently versatile to accommodate the orientation of the specimen. It should be remembered, however, that normally a maximum force for the test apparatus would be specified by the manufacturer. It should not be overlooked that the ratio of specimen to centrifuge radius is important because of the acceleration gradient across the specimen. Attention is drawn to the difficulties which may arise when testing components at very high values of acceleration, particularly those above 10 000 ms–2.

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A.3.5 Choice of material When designing a test fixture, the choice of material will primarily be governed by mass and stiffness considerations. Some problems associated with mass limitations were dealt with above as appropriate to each type of test. Stiffness, which is only of significance where dynamic considerations are involved, can impose severe restrictions on the design of the fixture. The stiffness of a material is a function of its physical properties. It therefore varies over the wide range of metals and plastics available for use. For any given material, the stiffness varies with the dimensions, its means of support (for example single or double encastre beams) and, to a lesser extent, the method of construction. Certain materials have more advantageous stiffness-to-mass ratios, and this enables a fixture to be stiffer for the same mass, which is usually desirable. Another characteristic of a material is its internal damping, which is also a function of its fundamental properties. As an example, the internal damping of aluminium is approximately four times greater than that for steel. Damping has some influence, mainly on the behaviour of vibration fixtures.
The fundamental aim of the design of the test fixture is to permit no resonances to exist within the frequency range specified for the test. If this is impracticable, then the fidelity of the transmission of vibration from the test apparatus to the specimen is affected. The degree to which it is affected is directly related to the damping. It should be borne in mind that the internal damping of most common metals, whilst varying one to another, has a relatively small effect on the overall behaviour of the test fixture, but under certain circumstances it may need to be utilized. A further feature that needs to be considered, particularly in the case of a shock test requiring a fast rise time or a vibration test with a high upper frequency, is the velocity of sound in the material to be chosen. The distance along the propagation path between any fixture point and the vibration generator table should be, whenever possible, well below a quarter of the wavelength in the fixing material.
For calculating the wavelength λ it is necessary to take into account the vibratory mode associated with the lowest velocity of sound. Usually, it is the mode in the transverse direction. Example:
aluminium test fixture for use up to 2 000 Hz. The approximate velocity of sound in aluminium is v1= 5 100 ms–1 for the longitudinal wave,
v2 = 3 200 ms–1 for the transverse wave. The wavelength to be considered is therefore
000220032==fvλ = 1,6 m The maximum length, l, of the propagation path is consequently m4,04==λlTest fixtures need not be made of the same material throughout. It may be necessary, for various reasons, for example, electrical or thermal insulation, or increased damping, to use fixtures made of a combination of materials such as metal and plastics, or even metal and ceramic.

60068-2-47 ¤ IEC:2005 – 37 –
A.4 General recommendations for fixture design There are various methods of construction available. These include bolting, riveting, welding, casting, the use of adhesives and so on. The choice will depend on the difficulties anticipated in meeting the test requirements, the material used, etc. The test fixture should be as simple as possible; for example, a solid block is often all that is necessary. It should be noted that bolted structures will not normally achieve the stiffness obtained with the other forms of construction, and that a riveted structure would be worse than that of the use of a bolted structure. This factor becomes important when dealing with large structures and/or high frequencies. For cheapness, ease of manufacture and due to its relatively high internal damping properties, aluminium alloy is often used. All interfaces should be as square and flat as is necessary to achieve good mechanical contact, especially when conducting frequency tests above, e.g. 500 Hz. In addition, the maximum number of fixing holes on the mounting surface of the test apparatus should be utilized, consistent with the size of the fixture. It is often advantageous to design a fixture which can be used a number of times for different specimens. If threaded holes are used and the material is such that undue wear might occur, the use of steel inserts is recommended. Care should be taken, however, that their fit is adequate and that no deterioration takes place. If bolts are used, they may need to be of the high-tensile type. It is good practice to remove material at the centre of a bolted connection to ensure that the contact surface is well defined and at a large radius (for high rotational stiffness) even if the mating surfaces are not completely flat. It is important that, when fastening the specimen to the fixture, no deformation of either should occur. If it does, this probably indicates that the fixture is insufficiently stiff and might prevent the required test severity from being applied to the fixing points of the specimen. The stiffness of a fixture can be greatly reduced by insufficient pre-load in fasteners or bolt strength. As far as is practicable, all bolts should be tightened to their maximum permitted torque. This value is determined by the weakest link in the system, for example, insert strength, compressive strength of fixture materials or bolt strength.
On fabricated fixtures joints should be welded. If possible, bolted or spot welded connections should be avoided. If this is not possible, the joint line should be filled with suitable adhesive. However, if damping is likely to be of real significance, it should be noted that the damping of a bolted or riveted structure is greater than that of one that has been welded. Where it is difficult to build a fixture whose natural frequency is outside the vibration specification, as much damping as possible needs to be introduced into the design since, above the natural frequency of the fixture, the drop-off rate of transmissibility is significantly reduced. In addition, at the natural frequency, the damping reduces the speed of power decrease to maintain a constant acceleration level and, therefore, the control system and power amplifier responses reduce
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