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1、BRITISH STANDARD BS 2011- 2.1Fda: 1973 Incorporating Amendment Nos. 1 and 2 Methods for Basic environmental testing procedures Part 2.1: Tests Test Fda. Random vibration wide band reproducibility high (This part should be read in conjunction with Part 1.1 General and it is recommended that reference
2、s 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 13:45:26 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 2011-2.1Fda:1973 ISBN 0 580 07517 6 Amendments issued since publication Amd. No.DateComments 2338September 1977 446
3、7June 1984Indicated by a sideline in the margin Licensed Copy: sheffieldun sheffieldun, na, Tue Nov 28 13:45:26 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 2011-2.1Fda:1973 BSI 06-1999i Contents Page Forewordii 1Object1 2Mounting and control1 2.1Mounting1 2.2Text deleted1 2.3Text deleted1 2.4Refer
4、ence and control points1 3Frequency response measurements and resonance searches1 3.1Sinusoidal amplitude1 3.2Frequency response measurement procedure1 3.3Resonance search procedure2 4Vibration motion requirements2 4.1Basic motion2 4.2Distribution2 4.3Acceleration spectral density spectrum and total
5、 r.m.s. acceleration requirements3 4.4Total r.m.s. acceleration values within the specified frequency range3 4.5Displacement limitations3 5Choice of confirmation method3 5.1Criteria for choice3 5.2Applicability of the recommended confirmation methods3 5.3Mixed confirmation methods4 6Initial measurem
6、ents4 7Excitation prior to conditioning4 8Conditioning4 9Final measurements5 Appendix A Confirmation method by swept filter technique11 Appendix B Confirmation method by fixed filter technique15 Appendix C Confirmation method by swept sinusoidal technique17 Figure 1 Determination of peak-notch ampli
7、tude ratio Ap/An8 Figure 2 Peak-notch pairs8 Figure 3 Tolerance band for distribution of instantaneous acceleration value9 Figure 4 Acceleration spectral density spectrum and tolerance limits10 Figure 5 Illustration of accumulation of errors13 Figure 6 Analyser error in notch region14 Figure 7 Analy
8、ser error in peak region14 Figure 8 Remaining ripple after equalization16 Table 1 Acceleration spectral density and related sinusoidal amplitude1 Table 2 Tolerance limits for true acceleration spectral density and true total r.m.s. acceleration3 Table 3a Total r.m.s. acceleration values6 Table 3b To
9、tal r.m.s. acceleration values7 Table 4 Tolerances on sum of variations and errors12 Table 5 Tolerances on sum of ripple, deviation and errors16 Table 6 Variation in acceleration spectral density plus instrumentation errors17 Licensed Copy: sheffieldun sheffieldun, na, Tue Nov 28 13:45:26 GMT+00:00
10、2006, Uncontrolled Copy, (c) BSI BS 2011-2.1Fda:1973 ii BSI 06-1999 Foreword This British Standard, incorporating Amendment No. 1 published in 1977 and Amendment No. 2 published in 1984, is technically equivalent to IEC Publication 68-2-35:1973 “Basic environmental testing procedures, Part 2: Tests
11、Test Fda : Random vibration wide band Reproducibility High”, published by 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 poss
12、ible degrees of Reproducibility have been specified called High, Medium and 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 h
13、igh. BS 2011-2.1, Test Fdb Random vibration: wide band, reproducibility medium. 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
14、test engineer is contained in Tests Fda, Fdb or Fdc, whichever is specified. 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 2011-2.1Fd and that part of BS
15、 2011 Test Fd containing the reproducibility required. It should be noted that 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
16、to the reader. Acceleration spectral density (hereinafter abbreviated to A.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
17、 not purport to include all the necessary provisions of a contract. Users of British Standards are responsible for their correct application. Compliance with a British Standard does not of itself confer immunity from legal obligations. Summary of pages This document comprises a front cover, an insid
18、e front cover, pages i and ii, pages 1 to 17 and a back cover. This standard has been updated (see copyright date) and may have had amendments incorporated. This will be indicated in the amendment table on the inside front cover. Licensed Copy: sheffieldun sheffieldun, na, Tue Nov 28 13:45:26 GMT+00
19、:00 2006, Uncontrolled Copy, (c) BSI BS 2011-2.1Fda:1973 BSI 06-19991 1 Object 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
20、in service be subjected to conditions involving 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 w
21、ith the requirements of that specification. During 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, th
22、is test requires particular care in its preparation 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 Text deleted 2.3 Text deleted 2.4 Reference and con
23、trol points. The test requirements are confirmed by measurements made at a reference point and control points related to the fixing points of the specimen. In the case of a large number of small specimens mounted on one fixture, the reference and/or the control points may be related to the fixture r
24、ather than to the fixing points of 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 at a point where the specimen is no
25、rmally 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 as close as possible to the fixing po
26、int and in any case shall be rigidly connected to the fixing point. If 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 defined in the relevant specification, these to be used as control points. NOTEFor
27、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 obtained to confirm the test requirements and is taken to represent the motion of the sp
28、ecimen. 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 reference signal is defined as the arithmetic mean, at each frequency, of the A.S.D. values of the signals from
29、 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 the point to be used or how it should be chosen. It is recommended that for large
30、 and/or complex specimens a fictitious point be used. 3 Frequency response measurements and resonance searches The tolerances given in the sinusoidal vibration test BS 2011-2F Vibration, shall apply during the following sinusoidal test phases. 3.1 Sinusoidal amplitude. Unless otherwise stated in the
31、 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 the reference point. Where a fictitious reference point is to be used during the rando
32、m vibration conditioning, this sinusoidal amplitude shall be applied at a control point. Table 1 A.S.D. and related sinusoidal amplitude 3.2 Frequency response measurement procedure. The A.S.D. spectrum confirmation methods always require a frequency response measurement in the intended direction at
33、 the reference point with the specimen mounted. Specified A.S.D. levelSinusoidal amplitude (peak values) (m/s2)2/HzEquivalent g2/Hzm/s2Equivalent g 19.2 0.219.62.0 Licensed Copy: sheffieldun sheffieldun, na, Tue Nov 28 13:45:26 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 2011-2.1Fda:1973 2 BSI 06-
34、1999 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 reference point shall be kept constant in accordance with 3.1, while the a.c. input voltage to the power amplifier
35、shall be measured. The measured voltage as a function of frequency is an approximation of the inverse of the frequency response. To take care of the displacement limitations of the vibrator, the sinusoidal acceleration amplitude may be reduced at the low frequency end, and this shall be taken into c
36、onsideration 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 used to correct for the general response of the unloaded vibrator), low pass filters (to reject
37、 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 during this measurement. The peak-notch amplitude ratio Ap/An (see Figure 1) is determined as th
38、e 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 determined from the equation below where fp is the frequency of the peak and fn the frequency of t
39、he notch. This measurement can only be done with an accurate frequency meter. In the A.S.D. confirmation methods ofAppendix A and Appendix B the “most severe peak-notch pairs” are mentioned. If the peak-notch frequency ratio is to be used, the quantities Ap/An and Bpn shall be measured for several p
40、airs (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 for resonance searches, the initial resonance search can, to some extent, be done at the same
41、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 frequencies at which: 1) specimen malfunctioning and/or deterioration of performance are exhibit
42、ed 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 search, all frequencies and amplitudes at which these effects occur shall be noted for compari
43、son 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 search, if appropriate. Where the mechanical vibrational characteristics cannot be assessed
44、 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 change the dynamic behaviour of the specimen as a whole. It may be necessary to provide a per
45、iod 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 requirements 4.1 Basic motion. The basic motion of the fixing points of the specimen shall be
46、 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 instantaneous acceleration values at the reference point shall be normal within the toleranc
47、e 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 confirmation need only be done in exceptional circumstances. Nevertheless, where possible, it is reco
48、mmended that the acceleration waveform be visually examined to ensure that peaks of at least 2 times the r.m.s. values of the signal are present. Bpn fpfn fpfn - -= Licensed Copy: sheffieldun sheffieldun, na, Tue Nov 28 13:45:26 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 2011-2.1Fda:1973 BSI 06-1
49、9993 4.3 A.S.D. spectrum and total r.m.s. acceleration requirements. The A.S.D. spectrum shall be as shown in Figure 4. The A.S.D. level and frequency range shall be stated in the relevant specification. These quantities together determine the nominal total r.m.s. value of the acceleration. This 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 this table the tolerances on the true total r.m.s. value are considerably tighter than
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