EN 60068-2-81:2003

SLOVENSKI SIST EN 60068-2-81:2004

STANDARD
februar 2004
Environmental testing - Part 2-81: Tests - Test Ei: Shock - Shock response
spectrum synthesis (IEC 60068-2-81:2003)
ICS 19.040 Referenčna številka
©  Standard je založil in izdal Slovenski inštitut za standardizacijo. Razmnoževanje ali kopiranje celote ali delov tega dokumenta ni dovoljeno

EUROPEAN STANDARD EN 60068-2-81
NORME EUROPÉENNE
EUROPÄISCHE NORM October 2003

ICS 19.040
English version
Environmental testing
Part 2-81: Tests –
Test Ei: Shock –
Shock response spectrum synthesis
(IEC 60068-2-81:2003)
Essais d'environnement Umweltprüfungen
Partie 2-81: Essais – Teil 2-81: Prüfungen –
Essai Ei: Chocs – Prüfung Ei: Schocken –
Synthèse du spectre de réponse au choc Synthese des Schockantwortspektrums
(CEI 60068-2-81:2003) (IEC 60068-2-81:2003)

This European Standard was approved by CENELEC on 2003-10-01. 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, Czech Republic,
Denmark, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Lithuania, Luxembourg, Malta,
Netherlands, Norway, Portugal, Slovakia, Spain, Sweden, Switzerland and United Kingdom.

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

© 2003 CENELEC - All rights of exploitation in any form and by any means reserved worldwide for CENELEC members.

Ref. No. EN 60068-2-81:2003 E
Foreword
The text of document 104/306/FDIS, future edition 1 of IEC 60068-2-81, prepared by IEC TC 104,
Environmental conditions, classification and methods of test, was submitted to the IEC-CENELEC
parallel vote and was approved by CENELEC as EN 60068-2-81 on 2003-10-01.
The following dates were fixed:
– latest date by which the EN has to be implemented
at national level by publication of an identical
national standard or by endorsement (dop) 2004-07-01
– latest date by which the national standards conflicting
with the EN have to be withdrawn (dow) 2006-10-01

Annexes designated "normative" are part of the body of the standard.
Annexes designated "informative" are given for information only.
In this standard, annex ZA is normative and annexes A, B, C and D are informative.
Annex ZA has been added by CENELEC.
__________
Endorsement notice
The text of the International Standard IEC 60068-2-81:2003 was approved by CENELEC as a
European Standard without any modification.
__________
- 3 - EN 60068-2-81:2003
Annex ZA
(normative)
Normative references to international publications
with their corresponding European publications
This European Standard incorporates by dated or undated reference, provisions from other
publications. These normative references are cited at the appropriate places in the text and the
publications are listed hereafter. For dated references, subsequent amendments to or revisions of any
of these publications apply to this European Standard only when incorporated in it by amendment or
revision. For undated references the latest edition of the publication referred to applies (including
amendments).
NOTE When an international publication has been modified by common modifications, indicated by (mod), the relevant
EN/HD applies.
Publication Year Title EN/HD Year
1)
IEC 60068-1 1988 Environmental testing EN 60068-1 1994
Part 1: General and guidance
IEC 60068-2-6 1995 Part 2: Tests - Test Fc: Vibration EN 60068-2-6 1995
+ corr. March 1995 (sinusoidal)

IEC 60068-2-27 1987 Part 2: Tests - Test Ea and guidance: EN 60068-2-27 1993
Shock
IEC 60068-2-47 1999 Part 2-47: Test methods - Mounting of EN 60068-2-47 1999
components, equipment and other + corr. June 2000
articles for vibration, impact and similar
dynamic tests
IEC 60068-2-57 1999 Part 2-57: Tests - Test Ff: Vibration - EN 60068-2-57 2000
Time-history method
IEC 60068-2-64 1993 Part 2: Test methods - Test Fh: EN 60068-2-64 1994
+ corr. October 1993 Vibration, broad-band random (digital
control) and guidance
ISO 266 1997 Acoustics - Preferred frequencies - -

ISO 2041 1990 Vibration and shock - Vocabulary - -

1)
EN 60068-1 includes corrigendum October 1988 + A1:1992 to IEC 60068-1.

NORME CEI
INTERNATIONALE
IEC
60068-2-81
INTERNATIONAL
Première édition
STANDARD
First edition
2003-07
BASIC SAFETY PUBLICATION
PUBLICATION FONDAMENTALE DE SÉCURITÉ
Essais d’environnement –
Partie 2-81:
Essais – Essai Ei: Chocs –
Synthèse du spectre de réponse au choc

Environmental testing –
Part 2-81:
Tests – Test Ei: Shock –
Shock response spectrum synthesis

CODE PRIX
W
Commission Electrotechnique Internationale
PRICE CODE
International Electrotechnical Commission
МеждународнаяЭлектротехническаяКомиссия
For price, see current catalogue
Pour prix, voir catalogue en vigueur

60068-2-81  IEC:2003 – 3 –
CONTENTS
FOREWORD . 7
INTRODUCTION .11
1 Scope .13
2 Normative references.13
3 Terms and definitions.13
4 Requirements for test apparatus .23
4.1 Basic motion .23
4.2 Cross-motion .23
4.3 Signal tolerance .23
4.4 Measuring system .23
5 Requirements for testing .25
5.1 Test control.25
5.2 Tolerances on SRS .25
5.3 Calculation of test SRS .25
5.4 Algorithms for calculation of SRS .27
5.5 Test frequency range .27
5.6 Mounting.27
6 Severities.29
6.1 Required SRS.29
6.2 Duration of the synthesized time-history .29
6.3 Number of repetitions.31
6.4 Test frequency range .31
6.5 Number of high peaks in a calculated response time-history of a single-
degree-of-freedom system .31
7 Preconditioning .31
8 Initial measurements .33
9 Testing .33
9.1 General .33
9.2 Vibration response investigation.33
9.3 Synthesis of the test time-history.35
9.4 Testing with synthesized test time-histories .37
10 Intermediate measurements .39
11 Recovery .39
12 Final measurements.39
13 Information to be given in the relevant specification.39
14 Information to be given in the test report.41
Annex A (informative) Test time history – General background information.49
Annex B (informative) Parameters for use in synthesizing a test time-history.55
Annex C (informative) How to synthesize a test time-history.63
Annex D (informative)  Recommended frequency ranges for test SRS.71
Bibliography .73

60068-2-81  IEC:2003 – 5 –
Figure 1 – Example of a typical response of an oscillator excited by a specific time-
history (specified threshold value of 70 %) .43
Figure 2 – Example of identification of the peaks of the response higher than a specified
(70 %) threshold value.43
Figure 3 – Typical logarithmic plot of a required response spectrum.45
Figure 4 – Typical time-history.45
Figure 5 – Flow chart for testing with synthesized test time-histories 9.4 .47
Figure B.1 – Strong part of the SRS .61
Table D.1 – Examples of test frequency ranges .71

60068-2-81 © IEC:2003 – 7 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
ENVIRONMENTAL TESTING –
Part 2-81: Tests – Test Ei: Shock –
Shock response spectrum synthesis

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, 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 60068-2-81 has been prepared by IEC technical committee 104:
Environmental conditions, classification and methods of test.
The text of this standard is based on the following documents:
FDIS Report on voting
104/306/FDIS 104/310/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.
It has the status of a basic safety publication in accordance with IEC Guide 104.

60068-2-81  IEC:2003 – 9 –
The committee has decided that the contents of this publication will remain unchanged until
2010. At this date, the publication will be
• reconfirmed;
• withdrawn;
• replaced by a revised edition, or
• amended.
60068-2-81  IEC:2003 – 11 –
INTRODUCTION
This part of IEC 60068, designed for testing with a synthesized shock response spectrum
(SRS) is intended for general application for components, equipment and other products,
hereinafter referred to as “specimens”, when simulation of transient responses of a complex
nature is required. The test method centres on the use of SRS and techniques associated
with SRS.
The purpose of the test is to demonstrate the adequacy of the test specimen to resist the
specified transient excitation, without unacceptable degradation of its functional and/or
structural performance. It is particularly useful for tailoring shock responses where measured
data are available from the operational environment. However, the test is applicable to any
transient excitation within the limits of the testing apparatus.
The test method is based primarily on the use of an electrodynamic or a servo-hydraulic
vibration generator with an associated computer-based control system used as a shock testing
system.
Other shock testing machines may be used, provided they fulfil the requirements of this
standard.
It is emphasized that SRS synthesis testing always demands a certain degree of engineering
judgement. Both supplier and purchaser should be fully aware of this fact. The writer of the
relevant specification is expected to select the testing procedure and the values of severity
appropriate to the specimen and its use.

60068-2-81  IEC:2003 – 13 –
ENVIRONMENTAL TESTING –
Part 2-81: Tests – Test Ei: Shock –
Shock response spectrum synthesis
1 Scope
This part of IEC 60068 specifies tests using a synthesized shock response spectrum (SRS).
It is intended for general application to specimens when simulation of transient excitation of a
complex nature is required.
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 guidance
IEC 60068-2-6:1995, Environmental testing – Part 2: Tests – Test Fc: Vibration (sinusoidal)
IEC 60068-2-27:1987, Basic environmental testing procedures – Part 2: Tests – Test Ea and
guidance: Shock
IEC 60068-2-47:1999, Environmental testing – Part 2-47: Test methods – Mounting of
components, equipment and other articles for vibration, impact and similar dynamic tests
IEC 60068-2-57:1999, Environmental testing – Part 2-57: Tests – Test Ff: Vibration − Time-
history method
IEC 60068-2-64:1993, Environmental testing – Part 2: Test methods – Test Fh: Vibration,
broad-band random (digital control) and guidance
ISO 266:1997, Acoustics – Preferred frequencies
ISO 2041:1990, Vibration and shock – Vocabulary
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 2041, IEC 60068-1,
IEC 60068-2-6, IEC 60068-2-27, IEC 60068-2-57 and IEC 60068-2-64, together with the
following definitions, apply.
3.1
–3 dB bandwidth
frequency bandwidth between two points in a frequency response function which is 0,707 of
the maximum response when associated with a single resonance peak

60068-2-81  IEC:2003 – 15 –
3.2
critical damping
minimum viscous damping that will allow a displaced system to return to its initial position
without oscillation in the shortest time possible
3.3
critical frequency
frequencies at which
– malfunctioning and/or deterioration of performance of the specimen which are dependent
on vibration are exhibited, and/or
– mechanical resonances and/or other response effects occur, for example chatter
3.4
damping
generic term ascribed to the numerous energy dissipation mechanisms in a system. In practice,
damping depends on many parameters, such as the structural system, mode of vibration,
strain, applied forces, velocity, materials, joint slippage, etc.
3.5
damping ratio
ratio of actual damping to critical damping in a system with viscous damping
3.6
decibel
dB
relation between magnitudes written in a logarithmic form:
 
X
 
L = 20log10 (dB)
 
 
X
 0
where
L is the logarithmic value in dB;
X/X is the relation between magnitudes X and X
0 0
3.7
fixing point
part of the specimen in contact with the fixture or vibration table at a point where the specimen
is normally fastened in service
NOTE If a part of the real mounting structure is used as the fixture, the fixing points are taken as those of the
mounting structure and not of the specimen.
3.8
g
n
standard acceleration due to the earth's gravity, which itself varies with altitude and
geographical latitude
NOTE For the purposes of this standard, the value of g is rounded up to the nearest whole number, that is,
n
10 m/s².
3.9
Hanning window
weighting function for time-histories that forces the start and the end of the time-history to
a zero value in the selected time window. It has the shape of a cosine bell
NOTE See ISO 18431-2 for a more detailed definition.

60068-2-81  IEC:2003 – 17 –
3.10
high-frequency asymptote
HFA
high-frequency asymptotic value of the SRS curve (see Figure 3)
NOTE 1 The SRS high-frequency asymptote is of practical significance as it represents the largest peak value of
the excitation time-history. This is not to be confused with the peak value in the SRS.
NOTE 2 Another name of the SRS high-frequency asymptote is zero-period acceleration (ZPA).
3.11
measuring points
specific points at which data are gathered when conducting the test. These points are of three
types, as defined below
3.11.1
check point
point located on the fixture, on the vibration table or on the specimen as close as possible
to, or combined with, one of its fixing points, and in any case rigidly connected to it
NOTE 1 A number of check points are used as a means of ensuring that the test requirements are satisfied.
NOTE 2 If four or fewer fixing points exist, each is used as a check point. If more than four fixing points exist,
four representative fixing points will be defined in the relevant specification to be used as check points.
NOTE 3 In special cases, for example, for large or complex specimens, the check points will be prescribed by
the relevant specification if not close to the fixing points.
NOTE 4 Where a large number of small specimens are mounted on one fixture, or in the case of a small
specimen where there are a number of fixing points, a single check point (that is the reference point) may be
selected for the derivation of the control signal. This signal is then related to the fixture rather than to the fixing
points of the specimen(s). This procedure is only valid when the lowest resonance frequency of the loaded
fixture is well above the upper frequency of the test.
3.11.2
reference point
point, chosen from the check points, whose signal is used to control the test
3.11.3
response point
point on the specimen used for measurement of the response during vibration response
investigation or during testing. This point is not a check or a reference point
NOTE More than one response point can be used.
3.12
natural frequency
frequency of damped or undamped free vibration of a structure depending only on its own
physical characteristics (mass, stiffness and damping)
3.13
number of high peaks of the response time-history
measured number of peaks at the response point or number of peaks of the calculated
response time-history of one single-degree-of-freedom system (oscillator), excited by a time-
history, exceeding a specified threshold value (see Figure 1)
NOTE 1 In practice, reference is made to high peaks of the response time-history since it is difficult to identify
complete response cycles due to a transient excitation.
NOTE 2 The peak is a positive or a negative maximum deviation from the zero-line between two consecutive zero-
crossing points (see Figure 2).
NOTE 3 Calculated peaks instead of measured peaks are preferred in this standard, as it is not always possible
to obtain measured peaks of response time-histories.

60068-2-81  IEC:2003 – 19 –
3.14
oscillator
single-degree-of-freedom system intended to produce, or be capable of maintaining,
mechanical oscillations
3.15
pause
interval between two consecutive time-histories
NOTE A pause should be such as to result in no significant superposition of the response motion of the specimen
and can be obtained from
1 100
T > ×
f d
where
T is the duration in seconds (s);
f is the lowest undamped natural frequency in hertz (Hz);
d is the damping ratio at the lowest natural frequency (in per cent).
3.16
preferred testing axes
three orthogonal axes which correspond to the most vulnerable axes of the specimen
3.17
Q-factor
quantity, which is a measure of the sharpness of resonance, or frequency selectivity of a
resonant oscillatory mechanical system having a single degree of freedom. The Q-factor is
one-half the reciprocal of the damping ratio
3.18
required SRS
SRS specified in the relevant specification (see Figure 3)
NOTE The relevant specification can contain more than one SRS with different Q-factors for a certain test case.
3.19
shock response spectrum
SRS
plot of the maximum response (displacement, velocity or acceleration) of a base-excited series
of single-degree-of-freedom systems to a defined input motion as a function of their undamped
natural frequencies and at a specified Q-factor
NOTE 1 For calculation purposes, linear fixed-base single-degree-of-freedom systems and viscous damping are
assumed, if not otherwise defined.
NOTE 2 The relevant specification can contain several SRS with different Q-factors for a given test case, from
which the required SRS shall be selected depending on the Q-factor of the test specimen.
3.20
sampling frequency
number of discrete magnitude values taken per second to record or represent a time-history
in digital form
3.21
signal tolerance
signal tolerance S in per cent is defined as
t
60068-2-81  IEC:2003 – 21 –
NF
 
S = −1 ×100 (per cent)
t
F
 
where
NF is the r.m.s. value of the unfiltered signal;
F is the r.m.s. value of the filtered signal
NOTE 1 This parameter applies to whichever signal, i.e. acceleration, velocity or displacement, is being used
to control the test.
NOTE 2 This parameter applies only to excitation with sinusoidal vibration.
3.22
strong part of the time-history
part of the time-history from the time when the plot first reaches 25 % of the maximum value to
the time when it falls for the last time to the 25 % level (see Figure 4)
3.23
synthesized time-history
artificially generated time-history such that its SRS envelops the required SRS
3.24
test frequency range
frequency range chosen for testing depending on the synthesizing of the required SRS and on
the capabilities of the test apparatus with the test specimen attached. It has a lower (f ) and
an upper (f ) frequency limit, corresponding to the lowest and highest wavelet frequency that
may be used
NOTE  The frequency range of the SRS is larger than the test frequency range and extends to infinite frequency
(see definition 3.10).
3.25
test SRS
SRS derived from the real motion of the reference point on the vibration generator table, either
analytically or by using SRS analysis equipment (see Figure 3)
3.26
time-history
recording, as a function of time, of acceleration, velocity or displacement
NOTE A definition of the mathematical term “time-history” is given in ISO 2041 and relates to the magnitude of
a quantity expressed as a function of time.
3.27
time window
duration of synthesis of the test time-history in which all the wavelets are contained
NOTE In some test control systems, this time window is doubled in duration and the synthesized time-history
centred in the middle of the new time frame.
3.28
wavelet
time-history with a single frequency that is a component of the synthesized time-history for
SRS testing
NOTE The term ‘wavelet’ as used in this standard should not be mixed up with wavelet as used in wavelet theory
and wavelet analysis.
60068-2-81  IEC:2003 – 23 –
4 Requirements for test apparatus
The required characteristics apply to the complete test apparatus, which for an electrodynamic
testing system includes the control system, power amplifier, vibrator, test fixture and specimen
when loaded for testing. The components are similar for a servo-hydraulic testing system.
The requirements for the test apparatus according to 4.1 to 4.3 shall be verified by means of
sinusoidal vibration excitation.
4.1 Basic motion
The basic motion during verification shall be a sinusoidal function of time and such that the
fixing points of the specimen move substantially in phase and straight parallel lines, subject to
the limitation of 4.2 and 4.3.
4.2 Cross-motion
The maximum vibration amplitude of acceleration or displacement at the check points in any
axis perpendicular to the specified axis shall not exceed 50 % of the vibration amplitude of the
basic motion up to 1 000 Hz and is allowed to go up to 100 % above 1 000 Hz. The
measurements need only cover the specified test frequency range. In special cases, for
example small specimens, the maximum permissible cross-motion may be limited to 25 %
if required by the relevant specification.
Where rotational motion of the vibration table is likely to be important, a tolerable level shall be
prescribed by the relevant specification and then be stated in the test report.
In some cases, for example with large-size or high-mass specimens or at certain frequencies,
it may be difficult to achieve the figures quoted above. In such cases the relevant specification
shall state which of the following requirements applies:
a) cross-motion in excess of that specified above shall be stated in the test report; or
b) cross-motion which is known to offer no hazard to the specimen need not be monitored.
4.3 Signal tolerance
Unless otherwise stated in the relevant specification, acceleration signal tolerance
measurements shall be performed. They shall be carried out at the reference point and shall
cover the frequencies up to 5 000 Hz, or five times the upper test frequency (f ), whichever is
the lesser value. However, this maximum analysing frequency may be extended to the upper
test frequency, or beyond if specified by the relevant specification. Unless otherwise stated in
the relevant specification, the signal tolerance shall not exceed 5 %.
In the case of large or complex specimens, where the specified signal tolerance values cannot
be satisfied at some parts of the frequency range the signal tolerance shall be stated in the test
report.
4.4 Measuring system
The characteristics of the measuring system shall be such that it can be determined that the
true value of the time-history, as measured in the intended axis at the reference point, is within
the tolerances required for the test.

60068-2-81  IEC:2003 – 25 –
The frequency response of the overall measuring system, which includes the transducer, the
signal conditioner and the data acquisition and processing device, has a significant effect on
the accuracy of the measurements.
The frequency range of the measuring system shall extend from at least 0,67 times the lowest
wavelet frequency (f ) to 1,5 times the highest wavelet frequency (f ) of the test frequency
range. (See also 4.2 in IEC 60068-2-27.) The frequency response of the measuring system
shall be flat within ±5 % in this frequency range.
5 Requirements for testing
5.1 Test control
The test time-history shall be a synthesized time-history composed of wavelets included within
the specified time window. This time-history is obtained from the specified SRS in the relevant
specification as shown in 9.3.
A value of the damping ratio of 5 % (Q-factor of 10) shall be used unless otherwise specified in
the relevant specification. Alternative values can be obtained from a vibration response
investigation (see 9.2). A vibration response investigation can also show which Q-factor to use
if several SRS (with different Q-factors) have been specified in the relevant specification.
The spacing of the wavelets by frequency shall be selected depending on the specified Q-factor
for the test as follows:
– in 1/3 octave bands if the Q-factor is lower than, or equal to, 5;
– in 1/6 octave bands if the Q-factor lies between 5 and 25;
– in 1/12 octave bands if the Q-factor is higher than, or equal to, 25.
NOTE Preferred frequencies for octave bands are given in ISO 266.
5.2 Tolerances on SRS
The test SRS, measured at the reference point, shall be within ±1,5 dB of the required SRS
(see Figure 3).
If a small portion of the test SRS, in less than 20 % of the frequency range, lies within the
tolerance band ±3 dB, the test may still be acceptable provided such points do not coincide
with the critical resonance frequencies of the specimen in the test frequency range. The
deviation from the required SRS shall be stated in the test report.
At a minimum, the test SRS shall be checked with the same frequency spacing as stated in 5.1
– selection depending on the Q-factor.
5.3 Calculation of test SRS
In order to keep errors to a minimum when calculating the test SRS, special consideration shall
be given to sampling and filtering of the signal from the reference point.
It is recommended that the sampling frequency of the time-history be at least a factor of 10 or
higher than the upper frequency (f ) for the response calculation if an interpolation algorithm is
not used in the subsequent SRS calculation.

60068-2-81  IEC:2003 – 27 –
NOTE 1 In this way the response time-history for the highest f oscillator will be calculated with a magnitude error
of less than 5 %. If a sampling frequency of 2,56 f is used, as is common for frequency analysis, an error
exceeding 60 % can be obtained in the maximum response of the highest f oscillator.
If an interpolation algorithm is used in the subsequent SRS calculation, the sampling frequency
can be as low as four times the upper frequency (f ).
A low-pass filter shall always be used prior to digitizing the time-history under evaluation to
avoid aliasing errors. It is recommended that the half-power point cut-off frequency of the anti-
aliasing filter is 1,5 f . The cut-off rate shall be at least –60 dB/octave. Use of these
recommended values ensures that a full response is obtained for the highest f oscillator.
Errors at the highest oscillators, due to phase modifications induced by anti-aliasing filters, are
also suppressed. Filters shall have a linear relation between phase and frequency.
A high-pass filter shall be used if low-frequency errors or d.c. offset influence the test. It is
recommended that the half-power cut-off frequency of such a filter is not higher than 0,1 of the
lower frequency (f ) for the response calculation, or 2 Hz, whichever is higher.
Truncation errors can be obtained if the time-history under evaluation or the response time-
histories of the oscillators do not decay within the time frame for the calculation. This is
particularly critical when calculations are performed for oscillators with low damping.
Truncation errors shall be avoided by using a long time frame.
NOTE 2 A rationale of the problem is reported in Appendix B of IEC 60068-2-27 which gives the definitions of
“initial” and “residual” SRS. For the evaluation of the test SRS, a maximax SRS should be calculated.
5.4 Algorithms for calculation of SRS
There are many ways to calculate the SRS, and the algorithms used can give different results,
especially at low and high frequencies. It is therefore important to use a validated algorithm
that gives a correct calculation of the SRS at least in the test frequency range.
5.5 Test frequency range
The test frequency range chosen is dependent on the maximum frequency content of the shock
environment to be simulated and the frequencies that can be truly generated by the test
apparatus with the specimen attached.
5.6 Mounting
The specimen shall be mounted in accordance with IEC 60068-2-47.
The orientation and mounting of the specimen during testing shall be prescribed by the relevant
specification and constitute the only condition for which the specimen is considered as
complying with the requirements of the standard, unless adequate justification can be given for
extension to an untested condition (for instance, if it is shown that the effects of gravity do not
influence the behaviour of the specimen).
If a specimen is normally mounted on isolators, but it is necessary to carry out a test
without them, the specified excitation level shall be modified to take this into account (see
IEC 60068-2-47).
The influence of connections, cables, piping, etc., shall be taken into account when mounting
the specimen.
60068-2-81  IEC:2003 – 29 –
6 Severities
The test severity shall be a combination of the following parameters:
a) Mandatory parameters
– required SRS including its Q-factor;
– test axes and directions;
– duration of the synthesized time-history;
– number of repetitions;
– test frequency range.
b) Optional parameters
– high-frequency asymptotic value (HFA) of the required SRS;
– duration of the strong part of the synthesized time-history;
– number of high peaks of the response time-history;
– Fourier spectra;
– energy spectral density;
– time domain root mean square of the synthesized time-history (see Clause B.2);
– frequency domain root mean square of the synthesized time-history (see Clause B.4).
NOTE  The list of optional parameters is not complete, see also Annex B.
The relevant specification shall state the values for each parameter on the basis of the
recommendations given in 6.1 to 6.5.
Optional parameters may be needed if the specimen is tested not only for survival of a certain
response but also for low-cycle fatigue (repeated responses).
6.1 Required SRS
The relevant specification shall state the level and shape of the required SRS for each test
case, including its Q-factor, tolerances, and optionally the SRS high-frequency asymptotic
value (HFA). The SRS shall be specified as a maximax spectrum. The relevant specification
shall also state the specimen axes and directions along which each spectrum shall be applied,
when they are not identical for all the axes.
NOTE  The relevant specification can contain several SRS with different Q-factors for a certain test case.
6.2 Duration of the synthesized time-history
The relevant specification shall state the duration of each time-history for which recommended
values in seconds or parts of seconds are given by the following series: . 1; 2; 3; 5; 10.
NOTE The choice of the duration of the synthesized time-history is dependent on the sampling frequency used for
the SRS synthesis and the time window. It is therefore not always possible to get close to the series above.
In some cases, the relevant specification may require the strong part of the time-history to be a
given percentage of the total duration. Otherwise, except when precluded by the requirements
of 6.5, the value of the strong part shall be selected from the following percentages of
the total duration:
25 %, 50 %, 75 %.
60068-2-81  IEC:2003 – 31 –
The selected value shall be stated in the test report.
6.3 Number of repetitions
The relevant specification shall specify the number of repetitions of time-histories to be applied
to the specimen in the axes and directions concerned.
Unless otherwise specified, the number of repetitions to be applied to each test axis and
direction and for each test case shall be selected from the following series: 1; 2; 5; 10; 20; 50.
When more than one time-history test level is used, testing shall always begin with the lowest
and continue with higher levels. Each time-history shall be followed by a pause.
6.4 Test frequency range
The test frequency range shall be given in the relevant specification by selecting the frequency
limits as close as possible to the following series: … 1; 2; 5; 10; 20; 50.…The lower frequency
limit (f ) shall start with 0,1 Hz as its lowest value and the upper frequency limit (f ) shall not
1 2
exceed 5 000 Hz.
NOTE The values of the frequency range are dependent on the sampling frequency used for the SRS synthesis
and of the time window. It is therefore not always possible to get close to the series indicated above.
6.5 Number of high peaks in a calculated response time-history
of a single-degree-of-freedom system
The relevant specification may state the number of high peaks in the calculated response time-
history of a single-degree-of-freedom system leading to values greater than a specified
threshold value.
High peaks of the response time-histories are an optional severity, applicable preferably when
testing for low-cycle fatigue is of interest.
Calculation of high peaks of response shall be made on the complete response time-history
from a selected single-degree-of-freedom system excited by the synthesized time-history. The
undamped natural frequency and Q-factor of this system shall be selected from results of
the vibration response investigation or from an estimate of these parameters.
The high peaks of the response time-histories shall be expressed as a percentage of the
required SRS value at the natural frequency of interest for the test specimen.
Unless otherwise prescribed by the relevant specification, the number of high peaks of
response time-histories shall be within the range of 3 to 20, with reference to a threshold value
of 70 %, for a 2 % to 10 % damping ratio (Q-factor from 5 to 25). The alternate positive
and negative peaks shall be approximately equally distributed.
7 Preconditioning
The relevant specification shall call for preconditioning and shall then prescribe the conditions.

60068-2-81  IEC:2003 – 33 –
8 Initial measurements
The specimen shall be submitted to visual, dimensional and functional checks as prescribed by
the relevant specification.
An initial response investigation shall be performed, unless otherwise prescribed by the
relevant specification (see 9.2).
9 Testing
9.1 General
The specimen shall be excited in each of three preferred testing axes unless otherwise
prescribed by the relevant specification. The order of testing along these axes is not important
unless prescribed by the relevant specification.
The specimen shall be excited in such a manner that the motion of the vibration generator
fulfils the specified SRS. Almost all suppliers of control systems for electrodynamic vibration
generators provide special software to generate the relevant drive signal.
9.2 Vibration response investigation
An investigation of the dynamic behaviour of the specimen is mandatory if not otherwise
prescribed by the relevant specification.
The response investigation shall be performed with sinusoidal or random excitation in the test
frequency range, or at least five times higher than the first undamped natural frequency,
whichever is the lesser value, and with a test level as prescribed by the relevant specification.
Reference is made to IEC 60068-2-6 for sinusoidal vibration and to IEC 60068-2-64 for random
vibration.
The response investigation shall be carried out with a test level selected so that the response
of the specimen remains smaller than during SRS-testing, but at a sufficiently high level to
detect critical frequencies.
The response investigation with sinusoidal excitation shall be carried out with a logarithmic
sweep rate not higher than one octave per minute, but it may be decreased if more precise
determination of the response characteristics is needed. Undue dwell should be avoided.
The response investigation with random vibration shall be carried out taking into account that
the time of the test shall be long enough to minimi
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