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1、BRITISH STANDARD CONFIRMED DECEMBER 1984 BS 2011-2.1 Fdb:1973 Incorporating Amendment Nos. 1 and 2 Basic environmental testing procedures Part 2.1: Tests Test Fdb Random vibration wide band reproducibility medium (This part should be read in conjunction with Part 1.1 General and it is recommended th
2、at reference be 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 13:45:28 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 2011-2.1 Fdb:1973 BSI 03-1999 Draft for comment 69/23643 ISBN 0 580 07527 3 Amendments issued since publ
3、ication Amd. No.Date of issueComments 2340September 1977 4468June 1984Indicated by a sideline in the margin Licensed Copy: sheffieldun sheffieldun, na, Tue Nov 28 13:45:28 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 2011-2.1 Fdb:1973 BSI 03-1999i Contents Page Foreword3 1 Object1 2 Mounting and co
4、ntrol1 2.1 Mounting1 2.2Text deleted1 2.3Text deleted1 2.4 Reference and control points1 3 Frequency response measurements and resonance searches1 3.1 Sinusoidal amplitude1 3.2 Frequency response measurement procedure2 3.3 Resonance search procedure2 4 Vibration motion requirements2 4.1 Basic motion
5、2 4.2 Distribution2 4.3 Acceleration spectral density spectrum and total r.m.s. acceleration requirements3 4.4 Total r.m.s. acceleration values within the specified frequency range3 4.5 Displacement limitations3 5 Choice of confirmation method3 5.1 Criteria for choice3 5.2 Applicability of the recom
6、mended confirmation methods3 5.3 Mixed confirmation methods4 6 Initial measurements4 7 Excitation prior to conditioning4 8 Conditioning4 9 Final measurements5 Appendix A Confirmation method by swept filter technique11 Appendix B Confirmation method by fixed filter technique14 Appendix C Confirmation
7、 method by swept sinusoidal technique16 Figure 1 Determination of peak-notch amplitude ratio Ap/An8 Figure 2 Peak-notch pairs8 Figure 3 Tolerance band for distribution of instantaneous acceleration values9 Figure 4 Acceleration spectral density spectrum and tolerance limits10 Figure 5 Illustration o
8、f accumulation of errors12 Figure 6 Analyser error in notch region13 Figure 7 Analyser error in peak region13 Figure 8 Remaining ripple after equalization15 Table 1 Acceleration spectral density and related sinusoidal amplitude1 Table 2 Tolerance limits for true acceleration spectral density and tru
9、e total r.m.s. acceleration3 Table 3 Total r.m.s. acceleration values6 Table 4 Variation in acceleration spectral density plus instrumentation errors16 Licensed Copy: sheffieldun sheffieldun, na, Tue Nov 28 13:45:28 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 2011-2.1 Fdb:1973 ii BSI 03-1999 Forew
10、ord This British Standard, incorporating Amendment No. 1 published in 1977 and Amendment No. 2 published in 1984, is technically equivalent to IEC Publication 68-2-36:1973 “Basic environmental testing procedures, Part 2: Tests Test Fdb: Random vibration wide band Reproducibility Medium”, published b
11、y the International Electrotechnical Commission (IEC). The basic requirements for the random vibration test, wide band, are given in BS 2011-2.1 Test Fd: Random vibration wide band General requirements. In addition, three possible degrees of Reproducibility have been specified called High, Medium an
12、d Low, and designated Test 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 medi
13、um. BS 2011-2.1, Test Fdc 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.
14、 Whilst the relevant specification 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 2011-2.1 Fd and that part of BS 2011 Test Fd containing the reproducibility required. It should be noted t
15、hat two terms of particular 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.
16、S.D.) is the spectral 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. A British Standard does not purport to include all the necessary provisions of a contract. Users o
17、f 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 16 and a back cover. This standar
18、d 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 13:45:28 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 2011-2.1 Fdb:1973 BSI 03-19991 1 Ob
19、ject The object of this test method is to determine the ability of components and equipment to withstand specified severities of random vibration. This random vibration test is applicable to components and equipment which may in service be subjected to conditions involving vibration of a stochastic
20、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. During the application of the
21、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 fixtures, this test requires particular care in its preparation and performance, and
22、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 Text deleted. 2.3 Text deleted. 2.4 Reference and control points. The test requirements are confirmed by measurements made a
23、t 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 fixture, the reference a
24、nd/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 fixture or vibration table
25、 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 fixing point. It shall be a
26、s 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 representative ones shall be
27、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 reference signal is obtai
28、ned 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 signal from the control points. If a fictitious point is used, the spectrum of the reference signal is defined a
29、s 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. values of the signals from the control points. The relevant specification shall state
30、 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 Frequency response measurements and resonance searches The tolerances given in the sinusoidal vibration test in BS 2011-2F, Vibration, shall apply during the foll
31、owing sinusoidal test phases. 3.1 Sinusoidal amplitude. Unless otherwise stated in the relevant specification, the sinusoidal amplitude to be used for resonance searches and frequency response measurements is determined by the specified A.S.D. level. (see Table 1). This amplitude shall be applied at
32、 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 Specified A.S.D. level Sinusoidal amplitude (peak values) (m/s2)2/Hz Equivale
33、nt g2/Hz m/s2 Equivalent g 19.2 0.2 9.8 14.7 19.6 1.0 1.5 2.0 Licensed Copy: sheffieldun sheffieldun, na, Tue Nov 28 13:45:28 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 2011-2.1 Fdb:1973 2 BSI 03-1999 3.2 Frequency response measurement procedure. The A.S.D. spectrum confirmation methods always re
34、quire a frequency response measurement in the intended direction at the reference point with the specimen mounted. The frequency range shall be swept with a sinusoidal signal from f1 to f2 and back, at a sweep rate not exceeding 1 octave/minute. During the sweep the sinusoidal amplitude at the refer
35、ence point shall be kept constant in accordance with 3.1 while the a.c. input voltage to the power amplifier shall be measured. The measured voltage as a function of frequency is an approximation of the inverse response. To take care of the displacement limitations of the vibrator, the sinusoidal ac
36、celeration amplitude may be reduced at the low frequency end, and this shall be taken into consideration when calculating the frequency response. The acceleration shall be measured at all control points. Transverse measurements should be made as stated in 4.3. Exciter equalizers (instrumentation use
37、d to correct for the general response of the unloaded vibrator), low pass filters (to reject above f2), high pass filters (to reject below f1) and other broad band types are allowed when measuring the frequency response. Narrow band equalizers, such as peak-notch filters, are not to be inserted duri
38、ng this measurement. The peak-notch frequency ratio Ap/An (see Figure 1) is determined as the ratio between the maximum and minimum values of the frequency response. This quantity can be measured without using an accurate frequency meter. The peak-notch frequency ratio (Bpn) (see Figure 2) is determ
39、ined from the equation below where fp is the frequency of the peak and fn the frequency of the notch. This measurement can only be done with an accurate frequency meter. In the A.S.D. confirmation method of Appendix A and Appendix B the “most severe peak-notch pairs” are mentioned. If the peak-notch
40、 frequency ratio is to be used, the quantities Ap/An and Bpn shall be measured for several pairs (four pairs in Figure 2) and the analysing errors and remaining ripple estimated for each pair in order to find the most severe one. 3.3 Resonance search procedure. If the relevant specification calls fo
41、r resonance searches, the initial resonance search can, to some extent, be done at the same time as the frequency response measurement. A complete sinusoidal sweep (up and down) of the frequency range shall be carried out. During the searches the specimen shall be examined in order to determine freq
42、uencies at which: 1. specimen malfunctioning and/or deterioration of performance are exhibited which are dependent on vibration; 2. mechanical resonances occur. The sweep may be interrupted in order to examine the effects more carefully and find the exact frequencies. During the initial resonance se
43、arch, all frequencies and amplitudes at which these effects occur shall be noted for comparison with those found in the final search. The relevant specification shall state what action should be taken if any change of resonance frequency occurs. The specimen shall be functioning during the resonance
44、 search, if appropriate. Where the mechanical vibrational characteristics cannot be assessed because the unit is functioning, an additional resonance search with the specimen not functioning shall be carried out. Any arrangement made to detect the effect upon internal parts shall not substantially c
45、hange the dynamic behaviour of the specimen as a whole. It may be necessary to provide a period of time after the conditioning in which 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 r
46、equirements 4.1 Basic motion. The basic motion of the fixing points of the specimen shall be rectilinear and of a stochastic nature with a normal (gaussian) distribution of instantaneous acceleration values. They shall also have substantially identical motions. 4.2 Distribution. The distribution of
47、instantaneous acceleration values at the reference point shall be normal within the tolerance band given in Figure 3. If a fictitious point is used, the distribution applies to a control point. NOTEFor most random vibration testing, the distribution falls within the tolerance band, therefore confirm
48、ation need only be done in exceptional circumstances. Nevertheless, where possible, it is recommended that the acceleration waveform be visually examined to ensure that peaks of at least 2“ times the r.m.s. value of the signal are present. Bpn fpfn fpfn - -= Licensed Copy: sheffieldun sheffieldun, n
49、a, Tue Nov 28 13:45:28 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 2011-2.1 Fdb:1973 BSI 03-19993 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. spectrum shall be as shown in Figure 4. These quantities together determine the nominal r.m.s. value of the acceleration. The value can be found in Table 3a and Table 3b. The tolerances on the true A.S.D. and total r.m.s. acceleration are given in Table 2. As seen from th