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1、BRITISH STANDARD BS 2011-2.1Fdc: 1973 Incorporating Amendment Nos. 1 and 2 Methods for Basic environmental testing procedures Part 2.1: Tests Test Fdc Random vibration wide band reproducibility low (This part should be read in conjunction with Part 1.1: General and it is recommended that reference b
2、e made to Part 2.1Fd) UDC 621.37/.39.001.4:620.169.1:620.178.53:539.433 Licensed Copy: sheffieldun sheffieldun, na, Tue Nov 28 13:49:33 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 2011-2.1Fdc:1973 BSI 03-2000 Draft for comment 69/23643 ISBN 0 580 07537 0 Amendments issued since publication Amd. No
3、.Date of issueComments 2339September 1977 4469June 1984Indicated by a sideline in the margin Licensed Copy: sheffieldun sheffieldun, na, Tue Nov 28 13:49:33 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 2011-2.1Fdc:1973 BSI 03-2000i Contents Page Forewordii 1Object1 2Mounting and control1 2.1Mountin
4、g1 2.2Text deleted1 2.3Text deleted1 2.4Reference and control points1 3Resonance searches1 3.1Sinusoidal amplitude1 3.2Resonance search procedure1 4Vibration motion requirements2 4.1Basic motion2 4.2Distribution2 4.3Acceleration spectral density spectrum and total r.m.s. acceleration requirements2 4
5、.4Total r.m.s. acceleration values within the specified frequency range2 4.5Displacement limitations2 5Initial measurements2 6Excitation prior to conditioning3 7Conditioning3 8Final measurements3 Appendix A Confirmation method8 Figure 1 Tolerance band for distribution of instantaneous acceleration v
6、alues6 Figure 2 Acceleration spectral density spectrum and tolerance limits7 Table 1 Acceleration spectral density and related sinusoidal amplitude1 Table 2 Tolerance limits for indicated acceleration spectral density and true total r.m.s. acceleration2 Table 3a Total r.m.s. acceleration values4 Tab
7、le 3b Total r.m.s. acceleration values5 Licensed Copy: sheffieldun sheffieldun, na, Tue Nov 28 13:49:33 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 2011-2.1Fdc:1973 ii BSI 03-2000 Foreword The basic requirements for the random vibration test, wide band, are given in BS 2011-2.1, Test Fd Electrotec
8、hnical Commission. The basic requirements for the random vibration test, wide band, are given in BS 2011, Part 2 Tests, Test Fd Random vibration: wide band, general requirements. In addition, three possible degrees of reproducibility have been specified called High, Medium and Low and designated Tes
9、t Fda, Fdb and Fdc respectively. Each of these forms a separate test method complete with its recommended confirmation procedures: BS 2011-2.1, Test Fda Random vibration: wide band, reproducibility high. BS 2011-2.1, Test Fdb Random vibration: wide band, reproducibility medium. BS 2011-2.1, Test Fdc
10、 Random vibration: wide band, reproducibility low. All the information required by the relevant specification writer is, therefore, contained in Test Fd, General requirements, whilst that needed by the test engineer is contained in Tests Fda, Fdb or Fdc, whichever is specified. Whilst the relevant s
11、pecification writer need only read Test Fd General requirements, and the test engineer the specified test Fda, Fdb or Fdc, it is strongly recommended that all users read BS 2011-2.1Fd and that part of BS 2011, Test Fd, containing the reproducibility required. It should be noted that two terms of par
12、ticular importance to the subject of random vibration testing are referred to frequently throughout the text of this publication. They are defined here to ensure that the text is made as clear as possible to the reader. Acceleration spectral density (hereinafter abbreviated to A.S.D.) is the spectra
13、l density of an acceleration variable and is given in units of acceleration squared per unit frequency. A.S.D. spectrum defines the way the A.S.D. varies within the frequency range. This British Standard, incorporating Amendment No. 1 published in 1977 and Amendment No. 2 published in 1984, is techn
14、ically equivalent to IEC Publication 68-2-37:1973 “Basic environmental testing procedures, Part 2: Tests Test Fdc: Random vibration wide band Reproducibility Low”, published by the International Electrotechnical Commission (IEC). A British Standard does not purport to include all the necessary provi
15、sions of a contract. Users of British Standards are responsible for their correct application. Compliance with a British Standard does not of itself confer immunity from legal obligations. Summary of pages This document comprises a front cover, an inside front cover, pages i and ii, pages 1 to 8 and
16、 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 13:49:33 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 2011-2.1
17、Fdc:1973 BSI 03-20001 1 Object The object of this test method is to determine the ability of components and equipments to withstand specified severities of random vibration. This random vibration test is applicable to components and equipments which may in service be subjected to conditions involvin
18、g vibration of a stochastic nature. The purpose of the test is to determine mechanical weakness and/or degradation in specified performance and to use this information in conjunction with the relevant specification to decide whether a specimen complies with the requirements of that specification. Du
19、ring the application of the environmental stress (conditioning) specified by this test, the specimen is subjected to random vibration of a given level within a wide frequency band. Due to complex mechanical reactions from the specimen and its fixture, this test requires particular care in the prepar
20、ation and performance, and in the confirmation of the specified requirements. 2 Mounting and control 2.1 Mounting. The specimen shall be mounted on the test apparatus in accordance with BS 2011-4.1. 2.2 Test deleted 2.3 Test deleted 2.4 Reference and control points. The test requirements are confirm
21、ed by measurements made at the reference point and in certain cases at control points, all related to fixing points of the specimen. Measurements at the control points are only necessary when a fictitious reference point is specified. In the case of a large number of small specimens mounted on one f
22、ixture, the reference and/or the control points may be related to the fixture rather than to the specimens when the lowest resonance mode of the loaded fixture is above the upper test frequency limit f2. 2.4.1 Fixing point. A fixing point is defined as a part of the specimen in contact with the fixt
23、ure or vibration table at a point where the specimen is normally fastened in service. If a part of the real mounting structure is used as the fixture, the fixing points shall be taken as those of the mounting structure and not of the specimen. 2.4.2 Control point. A control point is normally a fixin
24、g point. It shall be as close as possible to the fixing point and in any case shall be rigidly connected to the fixing point. If a fictitious reference point is specified, and four or less fixing points exist, each shall be used as a control point. If more than four fixing points exist, four represe
25、ntative ones shall be defined in the relevant specification, these to be used as control points. NOTEFor large and/or complex specimens it is important that the control points are defined in the relevant specification. 2.4.3 Reference point. The reference point is the single point from which the ref
26、erence signal is obtained to confirm the test requirements and is taken to represent the motion of the specimen. It may be a control point or a fictitious point created by manual or automatic processing of the signals from the control points. If a fictitious point is used, the spectrum of the refere
27、nce signal is defined as the arithmetic mean at each frequency of the A.S.D. values of the signals from all control points. In this case the total r.m.s. value of the reference signal is equivalent to the root mean square of the r.m.s. value of the signals from the control points. The relevant speci
28、fication shall state the point to be used or how it should be chosen. It is recommended that for large and/or complex specimens a fictitious point be used. 3 Resonance searches If the relevant specification calls for resonance searches, the tolerances given in the sinusoidal vibration test in BS 201
29、1-2, Test F Vibration, shall apply during the following sinusoidal test phase. 3.1 Sinusoidal amplitude. Unless otherwise stated in the relevant specification, the sinusoidal amplitude to be used for resonance searches is determined by the specified A.S.D. level. (See Table 1.) This amplitude shall
30、be applied at the reference point. Where a fictitious reference point is to be used during the random vibration conditioning this sinusoidal amplitude shall be applied at a control point. Table 1 A.S.D. and related sinusoidal amplitude 3.2 Resonance search procedure. A complete sinusoidal sweep (up
31、and down) of the frequency range shall be carried out for both the initial and final resonance searches. Specified A.S.D. level Sinusoidal amplitude (peak values) (m/s2)2/Hz 19.2 Equivalent g2/Hz 0.2 m/s2 9.8 14.7 19.6 Equivalent g 1.0 1.5 2.0 Licensed Copy: sheffieldun sheffieldun, na, Tue Nov 28 1
32、3:49:33 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 2011-2.1Fdc:1973 2 BSI 03-2000 During the searches, the specimen shall be examined in order to determine frequencies at which: 1) specimen malfunctioning and/or deterioration of performance are exhibited which are dependent on vibration; 2) mecha
33、nical resonances occur. The sweep may be interrupted in order to examine the effects more carefully and to find the exact frequencies. During the initial resonance search, all frequencies and amplitudes at which these effects occur shall be noted for comparison with those found in the final search.
34、The relevant specification shall state what action should be taken if any change of resonance frequency occurs. The specimen should be functioning during the resonance search, if appropriate. Where the mechanical vibration characteristics cannot be assessed because the unit is functioning, an additi
35、onal resonance search with the specimen not functioning shall be carried out. Any arrangement made to detect the effect upon internal parts shall not substantially change the dynamic behaviour of the specimen as a whole. It may be necessary to provide a period of time after the conditioning in which
36、 to allow the specimen to attain the same condition as existed at the commencement of the initial resonance search, e.g. as regards temperature. 4 Vibration motion requirements 4.1 Basic motion. The basic motion of the fixing points of the specimen shall be rectilinear and of a stochastic nature wit
37、h a normal (gaussian) distribution of instantaneous acceleration values. They shall also have substantially identical motions. 4.2 Distribution. The distribution of instantaneous acceleration values at the reference point shall be normal within the tolerance band given in Figure 1. If a fictitious p
38、oint is used, the distribution applies to a control point. NOTEFor most random vibration testing, the distribution falls within the tolerance band, therefore confirmation need only be done in exceptional circumstances. Nevertheless, where possible, it is recommended that the acceleration waveform be
39、 visually examined to ensure that peaks of at least 2“ times the r.m.s. value of the signal are present. 4.3 A.S.D. spectrum and total r.m.s. acceleration requirements. The A.S.D. level and frequency range are stated in the relevant specification. The A.S.D. shall be as shown in Figure 2. These quan
40、tities together determine the nominal total r.m.s. value of the acceleration. This value can be found in Table 3a and Table 3b. The tolerance on the indicated values of the A.S.D. as read from the analysing equipment and the true total r.m.s. acceleration values are given in Table 2. As seen from th
41、e table the tolerances on the true total r.m.s. value are tighter than the tolerance on the indicated values of the A.S.D. Acceleration measurements for confirmation of the motion requirements need only be made in the intended direction at the reference point. Table 2 Tolerance limits for indicated
42、A.S.D. and true total r.m.s. acceleration Confirmation of the A.S.D. tolerances may be performed with any method appropriate to the tolerances given. However, it is recommended that the confirmation method given in the Appendix A be used. NOTEIn the special case where a shaped spectrum is specified,
43、 the confirmation method given in Appendix A may still be used. 4.4 Total r.m.s. acceleration values within the specified frequency range. The required total r.m.s. acceleration values are given in Table 3a and Table 3b. In order to confirm these values a low pass filter shall be used. This low pass
44、 filter shall have its cut-off frequency (3 dB point) at the frequency f2. If the 3 dB bandwidth differs by more than 2 % from the equivalent noise bandwidth obtained when measuring the output from the filter with a white noise input signal, this should be taken into consideration when using the cal
45、culated r.m.s. values of the table. 4.5 Displacement limitations. All vibrators have displacement limitations. It may be necessary to insert a high pass filter before the power amplifier in order to limit the peak displacements. NOTEIf the A.S.D. has to be reduced in the low frequency region due to
46、the displacement limits of the vibrator, the reduction is to be noted and agreed between the customer and the supplier. 5 Initial measurements The specimen shall be electrically and mechanically checked as required by the relevant specification. If the relevant specification calls for resonance sear
47、ches before and after conditioning, the complete test sequence including resonance search should be performed in one axis and repeated for the other axes. The resonance search procedure is given in 3.2. Tolerance limits in dB for: Indicated value of A.S.D. True total r.m.s. acceleration (f1 to f2) 3
48、 2.0 Licensed Copy: sheffieldun sheffieldun, na, Tue Nov 28 13:49:33 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 2011-2.1Fdc:1973 BSI 03-20003 6 Excitation prior to conditioning When applying sinusoidal vibration for resonance searches the time should be kept to a minimum. The amplitude to be used
49、 is given in 3.1. The complete test sequence, including any resonance searches and the conditioning shall be carried out in one axis without removing the specimen from the vibrator. The complete test sequence is then repeated in each of the other axes. Prior to the application of the random vibration conditioning at the specified level, a preliminary random excitation of the actual test specimen may be necessary at a lower level for equalization and preliminary analysis. It is important that, at this time the level and time of application