1、BRITISH STANDARD BS6955-8: 1994 ISO5347-8: 1993 Calibration of vibration and shock pick-ups Part 8: Method for primary calibration by dual centrifuge UDC 534.1:681.327.7:53.089.6BS6955-8:1994 This British Standard, having been prepared under the directionof the General Mechanical Engineering Standar
2、ds Policy Committee, waspublished under the authorityof the Standards Boardand comes into effect on 15March1994 BSI 11-1999 The following BSI references relate to the work on this standard: Committee reference GME/21 Draft for comment87/72304DC ISBN 0 580 23098 8 Committees responsible for this Brit
3、ish Standard The preparation of this British Standard was entrusted by the General Mechanical Engineering Standards Policy Committee (GME/-) to Technical Committee GME/21, upon which the following bodies were represented: Electricity Association Federation of Civil Engineering Contractors Imperial C
4、ollege 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 Test and Certif
5、ication 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 Amendments issued
6、since publication Amd. No. Date CommentsBS6955-8:1994 BSI 11-1999 i Contents Page Committees responsible Inside front cover National foreword ii 1 Scope 1 2 Apparatus 1 3 Preferred amplitudes and frequencies 1 4 Method 1 Annex A (normative) Calculation of uncertainty 2BS6955-8:1994 ii BSI 11-1999 Na
7、tional foreword This Part of BS6955 has been prepared under the direction of the General Mechanical Engineering Standards Policy Committee. It is identical with ISO5347-8:1993 Methods for the calibration of vibration and shock pick-ups Part8: Primary calibration by dual centrifuge published by the I
8、nternational Organization for Standardization (ISO). ISO5347-8 was prepared by Technical Committee ISO/TC108, Mechanical vibration and shock, in which the UK played an active part. BS6955 consists of the following Parts, which are identical with the corresponding Parts of ISO5347: Part 0: Guide to b
9、asic principles; Part 1: Methods for primary vibration calibration by laser interferometry; Part 2: Method for primary shock calibration by light cutting; Part 3: Method for secondary vibration calibration; Part 4: Method for secondary shock calibration; Part 5: Method for calibration by Earths grav
10、itation; Part 6: Method for primary vibration calibration at low frequencies; Part 7: Methods for primary calibration by centrifuge; Part 8: Method for primary calibration by dual centrifuge; Part 9: Method for secondary vibration calibration by comparison of phase angles; Part 10: Method for primar
11、y calibration by high impact shocks; Part 11: Method of test for transverse vibration sensitivity; Part 12: Method of test for transverse shock sensitivity; Part 13: Method of test for base strain sensitivity; Part 14: Method of test for resonance frequency of undamped accelerometers on a steel bloc
12、k; Part 15: Method of test for acoustic sensitivity; Part 16: Method of test for mounting torque sensitivity; Part 17: Method of test for fixed temperature sensitivity; Part 18: Method of test for transient temperature sensitivity; Part 19: Method of test for magnetic field sensitivity. Part20 of IS
13、O5347 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 responsible for their correct application. Compliance with a Britis
14、h 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 to3 and a back cover. This standard has been updated (see copyright date) and may have had amendments incorporated. This will be i
15、ndicated in the amendment table on the inside front cover.BS6955-8:1994 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 lays down detailed specifications for the instrumentation and procedure
16、 to be used for primary calibration of accelerometers using centrifuge calibration. It applies to all types of rectilinear accelerometers, primary standards and working pick-ups. This part of ISO5347 is applicable for a frequency range from0,7Hz to10Hz and a dynamic range from10m/s 2to100m/s 2 . The
17、 limits of uncertainty applicable are 2% of reading. 2 Apparatus 2.1 Equipment capable of maintaining room temperature at23 C 3 C. 2.2 Balanced table, rotating about a vertical axis with uniform angular speed. A smaller table rotating with independent and uniform angular speed in the reverse directi
18、on shall be mounted eccentrically and perpendicularly on the table. The tables shall be levelled within 0,5 . The angular speed of the larger table shall be uniform within 0,1%. The angular speed of the smaller table shall be uniform within1%. The distance between the centres of rotation of the two
19、tables shall be measured with an uncertainty of less than 0,1%. The centre of the pick-up mass element shall be located at the centre of rotation of the smaller table with an uncertainty of less than 0,1% of the distance between the axes of rotation of the two tables. 2.3 Instrumentation for measuri
20、ng rotational frequency, with an uncertainty of maximum 0,1% of reading. 2.4 Voltage instrumentation for measuring true r.m.s. accelerometer output, with an uncertainty of maximum 0,1% of reading. The r.m.s. value shall be multiplied by a factor of to obtain (single) amplitude used in the formulae.
21、3 Preferred amplitudes and frequencies The following amplitudes, in metres per second squared, shall be used: 10;20;50;100. The following frequencies, in hertz, shall be used: 0,7;1;2;5;10. The reference acceleration shall be100m/s 2(secondchoice:50m/s 2 ) and the frequency shall be5Hz (second choic
22、e:1Hz). 4 Method 4.1 Test procedure Rotate the larger table at different frequencies determined by calculation of the calibration acceleration, a, in metres per second squared, from the standard levels using the following formula: a=4; 2n 2r + k Set the smaller table to the calibration frequency. De
23、termine the calibration factor at the reference frequency and reference acceleration. Then determine the sensitivity at the other frequencies and accelerations. The results shall be given as a percentage deviation from the calibration factor. 4.2 Expression of results The sensitivity, S, in volts pe
24、r (metre per second squared) V/(m/s 2 ), related to the (single) amplitude for every frequency is given by the following formula: where At the lowest acceleration level and the highest frequencies or when the tolerance between the centre of rotation of the smaller table and the centre of the pick-up
25、 mass element cannot be kept within the limits given above, the correction factor k shall be used. The value of k is given by the following formula: k=4; 2e d(n n x ) 2 where When the calibration results are reported, the total uncertainty of the calibration and the corresponding confidence level, c
26、alculated in accordance with Annex A, shall also be reported. A confidence level of95% shall be used. 2 n is the rotational frequency of the larger table, in hertz; r is the radius of rotation, in metres; k is a correction factor given by the formula below. n is the rotational frequency of the large
27、r table, in hertz; e d is the positional error between the centre of the pick-up mass element and the centre of rotation of the smaller table, in metres; n x is the calibration rotational frequency, which is equal to the rotational frequency of the smaller table, in hertz. S V 4; 2 n 2 rk + - =BS695
28、5-8:1994 2 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 (for the purposes of this part of ISO5347, CL=95%), X 95 , shall be calculated from the following formula: where The ra
29、ndom uncertainty for the specified confidence level, X r(95) , is calculated from the following formula: where The systematic errors shall, first of all, be eliminated or corrected. The remaining uncertainty, X s(95) , shall be taken into account by using the following formula: where A.2 Calculation
30、 of the absolute uncertainty for the calibration factor, e s , at calibrated levels and frequencies The absolute uncertainty for the calibration factor, e s , expressed in volts per (metre per second squared), at calibrated levels and frequencies is calculated by the law of the combination of errors
31、 from the following formula: where X r is the random uncertainty; X s is the systematic uncertainty. e r1 , e r2 , etc. are the deviations from the arithmetic mean of single measurements in the series; n is the number of measurements; t is the value from Students distribution for the specified confi
32、dence level and the number of measurements. K equals2,0 for the95% confidence level; e s is the absolute uncertainty for the calibration factor, at calibrated levels and frequencies, expressed in volts per (metre per second squared) (seeA.2). S is the calibration factor, in volts per (metre per seco
33、nd squared) (see4.2); V is the accelerometer output, in volts; e v is the absolute uncertainty for the accelerometer output, in volts; ! is the table levelling error, in degrees; a is the calibration acceleration, in metres per second squared (see4.1); n is the rotational frequency of the larger tab
34、le, in hertz;BS6955-8:1994 BSI 11-1999 3 A.3 Calculation of the total absolute uncertainty for the calibration factor, , over the complete frequency and amplitude range The absolute uncertainty for the calibration factor, e s , calculated in accordance withA.2, is only valid for the calibrated level
35、s and frequencies. The total absolute uncertainty for the calibration factor, e s , in volts per (metre per second squared), over the complete frequency and amplitude range is calculated from the following formula: where e n is the absolute uncertainty for the rotational frequency of the larger tabl
36、e, in hertz; e %n is the absolute uncertainty for the rotational frequency constancy of the larger table, in hertz; n x is the calibration rotational frequency, which is equal to the rotational frequency of the smaller table, in hertz; is the absolute uncertainty for the rotational frequency of the
37、smaller table, in hertz; is the absolute uncertainty for the rotational frequency constancy of the smaller table, in hertz; r is the radius of rotation to the centre of the accelerometer mass element, in metres; e r is the uncertainty in the radius of rotation, in metres; a H is the acceleration amp
38、litude caused by hum and noise, in metres per second squared; k is the correction factor for the induced acceleration of the smaller table, calculated in accordance with4.2, in metres per second squared; P is the voltage supply to the accelerometer; e P is the uncertainty in voltage supply to the ac
39、celerometer. S is the calibration factor, in volts per (metre per second squared), e S is the absolute uncertainty for the calibration factor, in volts per (metre per second squared), at calibrated levels and frequencies (seeA.2); L fA is the frequency linearity deviation, expressed as a percentage
40、of the reference calibration factor for the amplifier; L fP is the frequency linearity deviation, expressed as a percentage of the reference calibration factor for the accelerometer; L aA is the amplitude linearity deviation, expressed as a percentage of the reference calibration factor for the ampl
41、ifier; L aP is the amplitude linearity deviation, expressed as a percentage of the reference calibration factor for the accelerometer; I A is the instability uncertainty for the amplifier gain, expressed as a percentage of the reference calibration factor; I P is the instability uncertainty for the
42、accelerometer, expressed as a percentage of the reference calibration factor; R is the tracking uncertainty for the amplifier range (errors in gain for different amplification settings), expressed as a percentage of the reference calibration factor; E A is the error caused by environmental effects o
43、n the amplifier, expressed as a percentage of the reference calibration factor; E P is the error caused by environmental effects on the accelerometer, expressed as a percentage of the reference calibration factor. e n x e %n x e s 1BS6955-8: 1994 ISO5347-8: 1993 BSI 389 Chiswick High Road London W4
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