1、BRITISH STANDARD BS 6955-7: 1994 ISO 5347-7: 1993 Calibration of vibration and shock pick-ups Part 7: Methods for primary calibration by centrifuge UDC 534.1:681.327:53.089.6BS6955-7:1994 This British Standard, having been prepared under the directionof the General Mechanical Engineering Standards P
2、olicy Committee, waspublished under the authorityof the Standards Boardand comes into effect on 15March1994 BSI 10-1999 The following BSI references relate to the work on this standard: Committee reference GME/21 Draft for comment87/72304 DC ISBN 0 580 23097 X Committees responsible for this British
3、 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 Coll
4、ege 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 Certifica
5、tion 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 sin
6、ce publication Amd. No. Date CommentsBS6955-7:1994 BSI 10-1999 i Contents Page Committees responsible Inside front cover National foreword ii 1 Scope 1 2 Apparatus 1 3 Preferred values 1 4 Method1 1 5 Method2 2 Annex A (normative) Calculation of uncertainty 3 List of references Inside back coverBS69
7、55-7:1994 ii BSI 10-1999 National foreword This Part of BS6955 has been prepared under the direction of the General Mechanical Engineering Standards Policy Committee. It is identical with ISO5347-7:1993 Methods for the calibration of vibration and shock pick-ups Part7: Primary calibration by centrif
8、uge published by the International Organization for Standardization (ISO). ISO5347-7 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 ISO53
9、47: 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: Method for secondary shock calibration; Part5: Method for calibratio
10、n 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 vibration calibration by comparison of phase angles; Part10: Method
11、 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 test for resonance frequency of undamped accelerometers on a ste
12、el 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; Part19: Method of test for magnetic field sensitivity. Part20 of
13、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 responsible for their correct application. Compliance with a Brit
14、ish 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 to6, an inside back cover and a back cover. This standard has been updated (see copyright date) and may have had amendments inco
15、rporated. This will be indicated in the amendment table on the inside front cover.BS6955-7:1994 BSI 10-1999 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 instr
16、umentation and procedure to be used for primary calibration of accelerometers using centrifuge calibration. This part of ISO5347 applies to rectilinear accelerometers with zero-frequency response, mainly of the strain gauge or piezoresistive type, and to primary standard and working pick-ups. It is
17、applicable for a calibration range from10m/s 2to1000m/s 2(higher accelerations possible) at0Hz. The limits of uncertainty applicable are 1% of reading. 2 Apparatus 2.1 Equipment capable of maintaining room temperature at23 C 3 C. 2.2 Balanced table or arm, rotating about a vertical axis with uniform
18、 angular speed. For the calibration range from10m/s 2to100m/s 2the table/arm shall be level within 0,5 of horizontal. For ranges higher than100m/s 2 , levelling is allowed to within 2 . The rotational frequency shall be uniform within 0,05% of the nominal value. The pick-up axis of sensitivity shall
19、 be aligned within 0,5 . The radius of rotation to the centre of the pick-up mass element shall be measured with an uncertainty less than 0,1%. If the accelerometer is substituted by impedances not sensitive to acceleration, the hum and noise when the centrifuge is rotating at the calibration speeds
20、 shall be at least60dB below reading. 2.3 Instrumentation for measuring rotational frequency, With an uncertainty of maximum 0,05% of reading. 2.4 Voltage instrumentation for measuring accelerometer d.c. output, with an uncertainty of maximum 0,01% of reading. 3 Preferred values Six acceleration val
21、ues, in metres per second squared, equally covering the accelerometer range, shall be chosen from the following series: 10;20;50;100;200;500 or their multiples of ten. The reference acceleration shall be100m/s 2(secondchoice:50m/s 2 ). 4 Method1 (with measurement of the radius of rotation) 4.1 Test
22、procedure Rotate the table or arm at different frequencies determined by calculation from the standard levels using the following formula: a=4 2 n 2 r Measure the pick-up output for every level. Determine the reference calibration factor at the reference acceleration. Then determine the sensitivity
23、for the other calibration amplitudes. The results shall be given as a percentage deviation from the reference calibration factor. 4.2 Expression of results The calibration factor, S, in volts per (metre per second squared) V/(m/s 2 ), is given by the following formula: When the calibration results a
24、re 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 be used. where n is the rotational frequency, in hertz; r is the radius of rotation to the centre of the acceler
25、ometer mass element, in metres. where V is the accelerometer output, in volts; n is the rotational frequency, in hertz; r is the radius of rotation to the centre of the accelerometer mass element, in metres. S V 4 2 n 2 r - =BS6955-7:1994 2 BSI 10-1999 5 Method2 (without measurement of the radius of
26、 rotation) 5.1 Test procedure If the rotational radius cannot be measured with the specified accuracy, the pick-up can be rotated in two different positions, the radial distance between these to be measured with uncertainty maximum of 0,5%. Measure the two rotational frequencies giving the same pick
27、-up output at the two positions. 5.2 Expression of results The calibration factor, S, in volts per (metre per second squared), is given by the following formula: When the calibration results are reported, the total uncertainty of the calibration and the corresponding confidence level, calculated in
28、accordance with Annex A, shall also be reported. A confidence level of95% shall be used. where V is the accelerometer output, in volts; n 1 is the rotational frequency at the first accelerometer position, in hertz; n 2 is the rotational frequency at the second accelerometer position, in hertz; %r is
29、 the distance between the two accelerometer positions, in metres.BS6955-7:1994 BSI 10-1999 3 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%
30、(Method2) or CL=99% (Method1), X CL , shall be calculated from 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)
31、 , shall be taken into account by using the following formula: A.2 Calculation of the absolute uncertainty for the calibration factor, e S , at calibrated levels A.2.1 Calculation of e Sfor Method1 The absolute uncertainty for the calibration factor, e S , expressed in volts per (metre per second co
32、mbination of errors from the following formula: where X r is the random uncertainty; X s is the systematic uncertainty. where 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 distributio
33、n for the specified confidence level and the number of measurements. where K equals2,0 for the95% confidence level (CL=95% for Method2) or K equals2,6 for the99% confidence level (CL=99% for Method1); e S is the absolute uncertainty for the calibration factor at calibrated levels, expressed in volts
34、 per (metre per second squared) (seeA.2). where S is the calibration factor, in volts per (metre per second squared) (see5.2); V is the accelerometer output, in volts; e V is the absolute uncertainty for the accelerometer output voltmeter, in volts; is the table/arm levelling error, in degrees; is t
35、he misalignment of the accelerometer axis of sensitivity, in degrees; a is the calibration acceleration, in metres per second squared; (see4.1); n is the rotational frequency, in hertz;BS6955-7:1994 4 BSI 10-1999 A.2.2 Calculation of e Sfor Method2 The absolute uncertainty for the calibration factor
36、, e S , expressed in volts per (metre per second squared), at calibrated levels is calculated by the law of the combination of errors from the following formula: e n is the absolute uncertainty for the rational frequency, in hertz; e %n is the absolute uncertainty for the rotational constancy, in he
37、rtz; 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 amplitude caused by hum and noise, in metres per second squared; P is the voltage supply to the accelerometer; e P is the
38、uncertainty in voltage supply to the accelerometer. where S is the calibration factor, in volts per (metre per second squared) (see5.2); V is the accelerometer output, in volts; e V is the absolute uncertainty for the accelerometer output voltmeter, in volts; is the table/arm levelling error, in deg
39、rees; is the misalignment of the accelerometer axis of sensitivity, in degrees; a is the calibration acceleration, in metres per second squared; %r is the distance between the two accelerometer positions, in metres; e %r is the absolute uncertainty for the distance between the two accelerometer posi
40、tions, in metres; n 1 is the rotational frequency at the first accelerometer position, in hertz; e n1 is the absolute uncertainty for the rotational frequency at the first accelerometer position, in hertz; n 2 is the rotational frequency at the second accelerometer position, in hertz; e n2 is the ab
41、solute uncertainty for the rotational frequency at the second accelerometer position, in hertz; a H is the acceleration amplitude caused by hum and noise, in metres per second squared; P is the voltage supply to the accelerometer; e P is the uncertainty in voltage supply to the accelerometer; e %n i
42、s the absolute uncertainty for the rotational constancy, in hertz.BS6955-7:1994 BSI 10-1999 5 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 error, e S , calculated in accord
43、ance withA.2.1 orA.2.2, is only valid for the calibrated levels. The total absolute uncertainty for the calibration factor, , in volts per (metre per second squared), over the complete frequency and amplitude range is calculated from the following formula: Where S is the calibration factor, in volts
44、 per (metre per second squared) (see5.2 or6.2); e S is the absolute uncertainty for the calibration factor, in volts per (metre per second squared), at calibrated levels, calculated in accordance withA.2.1 orA.2.2; L fA is the frequency linearity deviation, expressed as a percentage of the reference
45、 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 amplifier; L aP is t
46、he 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 accelerometer, e
47、xpressed 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 on the amplifier,
48、 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 S 1 e S 16 blankBS6955-7:1994 BSI 10-1999 List of references See national foreword.BS6955-7: 1994 IS
49、O5347-7: 1993 BSI 389 Chiswick High Road London W4 4AL BSIBritishStandardsInstitution BSI is the independent national body responsible for preparing BritishStandards. It presents the UK view on standards in Europe and at the international level. It is incorporated by Royal Charter. Revisions BritishStandards are updated by amendment or revision. Users of BritishStandards should make sure that they possess the latest amendments or editions. It is the constant aim of BSI to imp
