1、BRITISH STANDARD BS6955-1: 1994 ISO5347-1: 1993 Calibration of vibration and shock pick-ups Part1: Methods for primary vibration calibration by laser interferometry UDC 534.1:681.327.7:53.089.6BS6955-1:1994 This British Standard, having been prepared under the directionof the General Mechanical Engi
2、neering Standards Policy Committee, waspublished under theauthorityof the StandardsBoard and comes into effect on 15 March1994 BSI11-1999 The following BSI references relate to the work on this standard: Committee referenceGME/21 Draft for comment87/72304DC ISBN 0 580 23080 5 Committees responsible
3、for this British Standard The preparation of this British Standard was entrusted by the General Mechanical Engineering Standards Policy Committee (GME/-) to Technical CommitteeGME/21, upon which the following bodies were represented: Electricity Association Federation of Civil Engineering Contractor
4、s Imperial College of Science and Technology Institute of Sound and Vibration Research Institution of Mechanical Engineers Lloyds Register of Shipping Ministry of Defence Open University Power Generation Contractors Association PGCA (BEAMA Ltd.) Railway Industry Association of Great Britain Sira Tes
5、t and Certification Ltd. Society of British Aerospace Companies Limited The following bodies were also represented in the drafting of the standard, through subcommittees and panels: British Coal Corporation Health and Safety Executive Society of Environmental Engineers University of Cranfield Amendm
6、ents issued since publication Amd. No. Date CommentsBS6955-1:1994 BSI 11-1999 i Contents Page Committees responsible Inside front cover National foreword ii 1 Scope 1 2 Apparatus 1 3 Ambient conditions 2 4 Preferred amplitudes and frequencies 2 5 Method 1 2 6 Method 2 3 Annex A (normative) Calculati
7、on of uncertainty 6 Annex B (normative) Formulae for the calculation of acceleration 9 Figure 1 Measuring system for the fringe-counting method (Method1) 3 Figure 2 Measuring system for the minimum-point method (Method2) 5 Table 1 Displacement amplitudes for minimum points 4 Table B.1 Values for J n
8、for zero points of the Bessel function 10BS6955-1:1994 ii BSI 11-1999 National foreword This Part of BS6955 has been prepared under the direction of the General Mechanical Engineering Standards Policy Committee. It is identical with ISO5347-1:1993 Methods for the calibration of vibration and shock p
9、ick-ups Part1: Primary vibration calibration by laser interferometry published by the International Organization for Standardization (ISO). ISO5347-1 was prepared by Technical Committee ISO/TC108, Mechanical vibration and shock, in which the UK played an active part. BS6955 consists of the following
10、 Parts, which are identical with the corresponding Parts of ISO5347: Part0: Guide to basic principles; Part1: Methods for primary vibration calibration by laser interferometry; Part2: Method for primary shock calibration by light cutting; Part3: Method for secondary vibration calibration; Part4: Met
11、hod for secondary shock calibration; Part5: Method for calibration by Earths gravitation; Part6: Method for primary vibration calibration at low frequencies; Part7: Methods for primary calibration by centrifuge; Part8: Method for primary calibration by dual centrifuge; Part9: Method for secondary vi
12、bration calibration by comparison of phase angles; Part10: Method for primary calibration by high impact shocks; Part11: Method of test for transverse vibration sensitivity; Part12: Method of test for transverse shock sensitivity; Part13: Method of test for base strain sensitivity; Part14: Method of
13、 test for resonance frequency of undamped accelerometers on a steel block; Part15: Method of test for acoustic sensitivity; Part16: Method of test for mounting torque sensitivity; Part17: Method of test for fixed temperature sensitivity; Part18: Method of test for transient temperature sensitivity;
14、Part19: Method of test for magnetic field sensitivity. Part20 of ISO5347 is in preparation. It is envisaged that when it is published it will be implemented as Part20 of BS6955. A British Standard does not purport to include all the necessary provisions of a contract. Users of British Standards are
15、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, pagesi andii, pages1 to10 and a back cover. This standard has been updated (see copy
16、right date) and may have had amendments incorporated. This will be indicated in the amendment table on the inside front cover.BS6955-1:1994 BSI 11-1999 1 1 Scope ISO5347 comprises a series of documents dealing with methods for the calibration of vibration and shock pick-ups. This part of ISO5347 lay
17、s down detailed specifications for the instrumentation and procedure to be used for primary calibration of rectilinear accelerometers using laser interferometry for dynamic displacement measurements. It is applicable for a frequency range from20Hz to5000Hz and a dynamic range from10m/s 2to1000m/s 2(
18、frequency-dependent). The limits of uncertainty applicable are as follows: 0,5% of reading at reference frequency(160Hz or80Hz) and reference amplitude(100m/s 2or10m/s 2 ) and reference amplifier gain setting; 1% of reading for frequenciesu 1000Hz; 2% of reading for frequencies1000Hz. 2 Apparatus 2.
19、1 Equipment capable of maintaining the ambient conditions, within the requirements specified in clause3. 2.2 Frequency generator and indicator, having the following characteristics: uncertainty, for frequency: maximum 0,01% of reading; frequency stability: better than 0,01% of reading over the measu
20、rement period; amplitude stability: better than 0,01% of reading over the measurement period. 2.3 Power amplifier/vibrator combination, having the following characteristics: total distortion:2% maximum; transverse, bending and rocking acceleration: kept to a minimum, maximum10% of the acceleration i
21、n the intended direction at frequencies used; above1000Hz, a maximum of20% is permitted; hum and noise:70dBmin. below full output; acceleration amplitude stability: better than0,05% of reading over the measurement period. The attachment surface shall not introduce base strain to the accelerometer. 2
22、.4 Seismic block for vibrator and laser interferometer (the same block), with a mass at least2000 times the mass of moving elements of vibrator, fixture and transducer. The seismic block shall be suspended by low damped springs. If floor vibrations influence, the suspension resonance frequency verti
23、cally and horizontally shall be2Hz. 2.5 Laser, of helium-neon type; in laboratory conditions of air pressure100kPa, temperature23 C and relative humidity50% the wavelength is0,632 84m, which value is used in this part of ISO5347. If the laser has manual or automatic atmospheric compensation, this sh
24、all be set to zero or switched off. 2.6 Interferometer, of Michelson type, with light detector for sensing the interferometer bands and having a frequency response from d.c. to15MHz. 2.7 Counting instrumentation, (for Method1, frequency range from20Hz to800Hz), having the following characteristics:
25、frequency range:10Hz to20MHz; uncertainty, maximum: 0,01% of reading. The counter can be substituted by a ratio counter having the same uncertainty. 2.8 Tunable band-pass filter or spectrum analyser, (for Method2, frequency range from1000Hz to5000Hz), having the following characteristics: frequency
26、range:100Hz to10000Hz; bandwidth:12% of centre frequency; filter slopes: better than24dB/octave; signal-to-noise ratio: better than70dB below maximum signal; dynamic range: better than60dB. 2.9 Instrumentation for zero detection, (for Method2 not needed with spectrum analyser), with a frequency rang
27、e from30Hz to5000Hz. The range shall be sufficient for detection of output noise from the bandpass filter. 2.10 Voltage instrumentation, measuring true r.m.s. accelerometer output, having the following characteristics: frequency range:20Hz to5000Hz; uncertainty, maximum 0,01% of reading; below40Hz:0
28、,1%. The r.m.s. value shall be multiplied by a factor of to obtain the (single) amplitude used in the formulae. 2.11 Distortion-measuring instrumentation, capable of measuring total distortion of0 to5% and having the following characteristics: frequency range:5Hz to10kHz; uncertainty, maximum: 10% o
29、f reading. 2BS6955-1:1994 2 BSI 11-1999 2.12 Oscilloscope (optional), for checking the waveform of the accelerometer signal, with a frequency range from5Hz to5000Hz. 2.13 Other apparatus requirements In order to achieve the required0,5% accuracy, the accelerometer and accelerometer amplifier shall b
30、e considered as one unit and calibrated together. The accelerometer shall be structurally rigid. The base strain sensitivity shall be0,2 10 8 m/s 2at a base strain of2,5 10 4 m/s 2 , the transverse sensitivity shall be1% and the stability of the accelerometer/amplifier combination shall be better th
31、an0,2% of the reading per year. 3 Ambient conditions Calibration shall be carried out in the following ambient conditions: room temperature:(23 3) C; air pressure:(100 5)kPa; relative humidity:(50 25)%. 4 Preferred amplitudes and frequencies Six amplitudes and six frequencies equally covering the ac
32、celerometer range shall be chosen from the following series: a) Acceleration (Method1 only), in metres per square second: 10,20,50,100,500; reference acceleration100m/s 2(secondchoice:10m/s 2 ). b) Frequency, in hertz: 20,40,80,160,315,630,1250,2500,5000; reference frequency160Hz (secondchoice:80Hz)
33、. 5 Method1, for frequency range from20Hz to800Hz 5.1 Test procedure After optimizing the interferometer(2.6) settings, determine the reference calibration factor at preferably160Hz (second choice:80Hz),100m/s 2(second choice:10m/s 2 ) and the standard position of amplifier range switch by measuring
34、 either the fringe frequency with the counter(2.7) the fringe-counting method in accordance with Figure 1 shall be used or the ratio between the vibration frequency and the fringe frequency with a ratio counter(2.7). Then determine the calibration factor at the other selected standard acceleration l
35、evels and frequencies. The results shall be given as a percentage deviation from the reference calibration factor. For every frequency and acceleration combination, the distortion, the transverse, bending and rocking accelerations, hum and noise shall be measured and the values shall be within the l
36、imits specified in2.3. 5.2 Expression of results (see alsoB.1, Annex B) Calculate the acceleration amplitude, a, of the accelerometer, expressed in metres per second squared, from the fringe frequency readings using the following formula: a =3,122 8 10 6 f f f and calculate the calibration factor, S
37、, from the following formula: If a ratio counter is used, calculate the acceleration amplitude, a, expressed in metres per second squared, using the following formula: a =3,122 8 10 6 f 2 R f and calculate the calibration factor, S, from the following formula: where R fis the ratio between the vibra
38、tion frequency and the fringe frequency, f f , over at least100vibration periods. When the calibration results are reported, the total uncertainty of the calibration and the corresponding confidence level, calculated in accordance with Annex A, shall also be reported. A confidence level of99% shall
39、be used (secondchoice:95% confidence level). where V is the accelerometer output, in volts (single) amplitude; f is the frequency of the vibrator, in hertz; f f is the number of fringe signal periods over a time period which is long compared with the vibration period the number of periods is divided
40、 by the time in order to obtain the fringe frequency in hertz; S 0,320 210 6 = V ff f - S 0,320 210 6 = V f 2 R f - BS6955-1:1994 BSI 11-1999 3 6 Method 2, for frequency range from800Hz to5000Hz 6.1 Test procedure Filter the signal from the light detector(2.6) through a bandpass filter(2.8) with the
41、 centre frequency equal to the accelerometer frequency. This filtered signal has a number of minimum points at accelerometer displacements in accordance with Table 1. After setting the frequency, adjust the vibrator amplitude from zero to the value at which the filtered light detector signal, after
42、reaching maximum value, returns to a minimum value. This minimum value is minimum point No.1, at which the amplitude is0,193 04m. The amplitude for the other minimum points in order can be taken from Table 1. The measuring system for the minimum point method is shown in Figure 2. Figure 1 Measuring
43、system for the fringe-counting method (Method1)BS6955-1:1994 4 BSI 11-1999 Table 1 Displacement amplitudes for minimum points 6.2 Expression of results (seealsoB.2, Annex B) Calculate the acceleration, a, expressed in metres per second squared, from the following formula: a =39,478 10 6 d f 2 and ca
44、lculate the calibration factor, S, from the following formula: The different calibration factors determined are used to calculate the deviations relative to the160Hz(80Hz)/100m/s 2 (10 m/s 2 ) value obtained in accordance with Method1 (seeclause5). When the calibration results are reported, the tota
45、l uncertainty of the calibration and the corresponding confidence level, calculated in accordance with Annex A, shall also be reported. A confidence level of99% (second choice:95% confidence level) shall be used. Minimum point No. Displacement amplitude, d 4m 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
46、 17 18 19 20 21 22 23 24 25 26 27 28 29 30 0 0,193 0 0,353 3 0,512 3 0,670 9 0,829 4 0,987 8 1,146 1 1,304 4 1,462 7 1,621 0 1,779 2 1,937 5 2,095 7 2,253 9 2,412 2 2,570 4 2,728 6 2,886 8 3,045 0 3,203 3 3,361 5 3,519 7 3,677 9 3,836 1 3,994 3 4,152 5 4,310 7 4,468 9 4,627 1 4,785 3 where V is the
47、accelerometer output, in volts (single) amplitude; d is the displacement amplitude, in micrometres, for the different minimum points in accordance with Table 1; f is the frequency of the vibrator, in hertz. S 0,253 3110 5 = V df 2 - BS6955-1:1994 BSI 11-1999 5 Figure 2 Measuring system for the minim
48、um-point method (Method2)BS6955-1:1994 6 BSI 11-1999 Annex A (normative) Calculation of uncertainty A.1 Calculation of total uncertainty The total uncertainty of the calibration for a specified confidence level CL (for the purposes of this part of ISO5347, CL=99% or95%), X CL , shall be calculated f
49、rom the following formula: The random uncertainty for a specified confidence level, X r(CL) , is calculated from the following formula: The systematic errors shall, first of all, be eliminated or corrected. The remaining uncertainty, X s(CL) , shall be taken into account by using the following formula: A.2 Calculation of the absolute uncertainty for the calibration factor,
