1、DEUTSCHE NORM Julv 1999 Mechanical vibration and shock Mechanical mounting of accelerometers (IS0 5348 : 1998) DIN IS0 5348 ICs 17.160 Mechanische Schwingungen und Ste - Mechanische Ankopplung von Beschleunigungsaufnehmern (IS0 5348 : 1998) This standard incorporates International Standard IS0 5348
2、Mechanical vibration and shock - Mechanical mounting of accelerometers. A comma is used as the decimal marker. National foreword This standard has been prepared by ISO/TC 108. The responsible German body involved in its preparation was the Normenausschu Akustik, Larmminde- rung und Schwingungstechni
3、k (Acoustics, Noise Control and Vibration Engineering Standards Committee). DIN 45666 is the standard corresponding to International Standard IS0 2954 referred to in clause 2 of the IS0 Standard. IS0 Standard comprises 13 pages. No pari of this standard may be reproduced without the prior permission
4、 of Ref. No. DIN IS0 5348 : 1999-0 - Y Deutsches Institut fur Normung e VI Berlin wth Verlag GmbH, D-10772 Berlin, has the exclusive right of sale for German Standards (DIN-Normen) English price group IO . Sales No Page 1 IS0 5348 : 1998 Mechanical vibration and shock Mechanical mounting of accelero
5、meters Foreword IS0 (the International Organization for Standardization) is a worldwide federation of national standards bodies (IS0 member bodies). The work of preparing International Standards is normally carried out through IS0 technical committees. Each member body interested in a subject for wh
6、ich a technical committee has been established has the right to be represented on that committee. International organizations, governmental and non-governmental, in liaison with ISO, also take part in the work. IS0 collaborates closely with the International Electrotechnical Commission (IEC) on all
7、matters of electrotechnical standardization. Draft International Standards adopted by the technical committees are circulated to the member bodies for voting. Publication as an International Standard requires approval by at least 75 % of the member bodies casting a vote. International Standard IS0 5
8、348 was prepared by Technical Committee ISOTTC 108, Mechanical vibration and shock, Subcommittee SC 3, Use and calibration of vibration and shock measuring instruments. This second edition cancels and replaces the first edition (IS0 5348:1987), which has been technically revised. In trod uction The
9、method most commonly used for determining the vibratory motion, vs, of a structure or body S is that using an electromechanical transducer T. Vibration-monitoring transducers fall into two broad classes: contacting and non-contacting transducers. Non- contacting structural response transducers are p
10、laced in close proximity to the structure and include such generic types as eddy-current probes and optical proximity probes. Contacting transducers are placed in mechanical contact with the structural system and inelude such generic types as piezoelectric and piezoresistive accelerometers and seism
11、ic velocity transducers. This International Standard is concerned with the contacting type of accelerometers which currently are in wide use. The concern with using such transducers is that the mechanical coupling between the accelerometer and the test structure may significantly alter the response
12、of the accelerometer, the structure, or both. This International Standard attempts to isolate parameters of concern in the selection of a method to mount the accelerometer onto the structure. This International Standard deals with accelerometers which are connected to the surface of the structure in
13、 motion by means of a mechanical mounting F (see figure 1). The information supplied by such a transducer is the electric signal, u, generated by the action of its own motion, F, The information desired is the vibratory motion, vs, at a specified location on the structure S. The electric signal, u,
14、generated by the transducer deviates from what it would have been, if that particular accelerometer effectively measured the vibratory motion, vs, of the structure, owing to non-ideal transfer of motion from S to the sensitive elements of the accelerometer T. Deviations may also occur owing to misal
15、ignment of the sensitive axis of the transducer, base bending, temperature transients, mounting torque and cable whip. The mechanical mounting will change the useful frequency range for a given accuracy with regard to amplitude as well as phase response (see 5.4.5). Page 2 IS0 5348 : 1998 1 Scope Th
16、is International Standard describes the mounting characteristics of accelerometers to be specified by the manufacturer and makes recommendations to the user for mounting accelerometers. Application of this International Standard is limited to the mounting of accelerometers which are mounted on the s
17、urface of the structure in motion, as illustrated in the simplified diagram shown in figure 1. It is not applicable to other types of transducers, such as relative motion pick-ups. Key S is the structure; F is a means of mounting; T is an accelerometer; vs is vibratory motion of the structure; VT is
18、 vibratory motion of the accelerometer. Figure 1 - Accelerometer mounting 2 Normative references The following standards contain provisions which, through reference in this text, constitute provisions of this international Standard. At the time of publication, the editions indicated were valid. All
19、standards are subject to revision, and parties to agreements based on this International Standard are encouraged to investigate the possibility of applying the most recent editions of the standards indicated below. Members of IEC and IS0 maintain registers of currently valid International Standards.
20、 IS0 2041 :1990, Vibration and shock - Vocabulary. IS0 2954: 1 975, Mechanical vibration of rotating and reciprocating machinery - Requirements for instruments for measuring vibration seventy. Page 3 IS0 5348 : 1998 IS0 5347-14:1993, Methods for the calibration of vibration and shock Pick-ups - Part
21、 74: Resonance frequency testing of undamped accelerometers on a steel block. IS0 5347-22:1997, Methods for the calibration of vibration and shock Pick-ups - Part 22: Accelerometer resonance testing - General methods. IS0 8042:1988, Shock and vibration measurements - Characteristics to be specified
22、for seismic Pick-ups. 3 Definitions For the purposes of this International Standard, the terms and definitions given in IS0 2041 apply. 4 Characteristics to be specified by manufacturers of accelerometers The manufacturer shall specify the following characteristics: a) mounting-surface characteristi
23、cs pertinent to the mounting device(s) furnished with the accelerometer, e.g. surface finish roughness, surface flatness, hole perpendicularity and tap class; b) the geometrical dimensions of the accelerometer including - the position of the centre of gravity of the accelerometer as a whole, - the p
24、osition of the centre of gravity of the seismic mass of the accelerometer; the mounting technique used during calibration; the recommended and maximum (.e. for less than 2 % change in the useful frequency range) mounting torque; c) d) e) temperature limitations of the accelerometer and fastening dev
25、ice; f) pertinent mechanical characteristics, .e. - total mass, - material of base, - the lowest unmounted resonance frequency of the accelerometer, - the frequency response characteristic under well-defined mounting conditions, describing the object on which the transducer is mounted in terms of ma
26、ss, material and dimensions, - the maximum transverse sensitivity, and the frequency at which it was determined; a description of the various fastening devices provided for the accelerometer, .e. - diameter, g) - thread, - material; h) the frequency response curves of the accelerometer with the type
27、 of mechanical mounting recommended by the manufacturer and the effect of special mounting devices supplied with the accelerometer, in particular - axial stiffness, with account taken of the state of the surface of the structure in contact with the accelerometer and the tightening torque of the acce
28、lerometer, - transverse deflection stiffness, on the same basis. For other characteristics to be specified by the manufacturer, refer to IS0 8042. Page 4 IS0 5348 : 1998 5 Consideration in the selection of a mounting method 5.1 General considerations 5.1.1 Procedures An accelerometer will achieve op
29、timal performance only if the following general procedures are followed: a) the accelerometer shall perform as nearly as possible the same motion as the structure under test at the accelerometer attachment; b) the motion of the structure shall be changed as little as possible by the addition of the
30、accelerometer; c) the ratio of the signal from the accelerometer to the motion of the accelerometer shall not be distorted by operating too near to its mounted fundamental resonance frequency. 5.1.2 Conditions In order to achieve these ideal conditions, it is necessary to ensure that: a) the acceler
31、ometer and its mounting are as rigid and firm as possible (the mounting surfaces shall be as clean and flat as possible); b) the mounting introduces minimum distorting motions of its own (for example, simple symmetrical mountings are best); c) the mass of the accelerometer and mounting are small in
32、comparison with that of the dynamic mass structure under test (see IS0 2954). of the 5.2 Specific considerations 5.2.1 Frequency range of operation The accelerometer shall be used well below its fundamental resonance frequency. If it is possible to use the manufacturers recommended mounting, then op
33、eration at frequencies not greater than 20 % of their quoted mounted resonance should, in the case of undamped accelerometers (resonance magnification factor Q greater than 30 dB), ensure in most cases that errors of only a few percent on the amplitude response occur. If an estimate of the approxima
34、te error is required, it may be made on the basis of an equivalent linear spring-mass system with a given value of damping. NOTE - For single shock measurements, one may expect errors of only a few percent if the mounted fundamental resonance frequency is ten times greater than the inverse of the pu
35、lse duration. 5.2.2 Mounting torque When screw thread mounting is used, the mounting torque shall be as recommended by the manufacturer. 5.2.3 Cables Stiff cables can cause case strain when used with accelerometers with axial connectors. Careful clamping of the cables is required to avoid such probl
36、ems (see figure 2). Loose cables may introduce tribo-electric effects for piezo-electric type transducers. Page 5 IS0 5348 : 1998 5.3 Determination of the mounted fundamental resonance frequency It is very useful, though at times difficult in practice, to determine accurately the mounted fundamental
37、 resonance frequency of the accelerometer mounted on the structure under test. The following method may be of use in finding the approximate resonance, thus ensuring that an adequate margin exists between it and the test frequency. 5.3.1 Vibration excitation method A suitable steel reference block w
38、ith well-defined shape and surface finish is recommended, e.g. a stainless steel block of mass 180 g. The motion of the reference block is monitored close to the mounting surface of the accelerometer being tested using an accelerometer with a resonance frequency higher than that of the first bending
39、 mode of the steel block itself. The excitation force can be generated electrodynamically. The influence of the quality of mounting surfaces and materials may be investigated by introducing typical samples between the steel surface and the accelerometer being tested (see figure 3). For common mounti
40、ngs and representative mounted frequency curves, see figures 5 to 1 O. For the method of determining the fundamental (resonance) frequency, see IS0 5347-14 and IC0 5347-22. NOTE - The frequency response curves given in the figures are typical; they are strongly influenced by the parameters that are
41、indicated in the figures. 5.3.2 Shock excitation methods The ballistic pendulum, the drop test and a simple hammer blow are three ways of using shock excitation. In the first, the accelerometer is attached to an anvil mass suspended as a pendulum while a second hammer mass, similarly suspended, is u
42、sed to provide the blow. In the drop test, the accelerometer is attached to a hammer which is guided in its vertical fall onto a stationary anvil to provide the shock. The attachment of the accelerometer to the mass shall be similar to the actual test body attachment. While it may be impossible to r
43、epresent the test body by the mass of the anvil or hammer, it shall be made of the same material and of sufficient size to be a reasonable representation of the test body with regard to the stiffness. The hammer blow applied near the mounted accelerometer on the actual structure may provide the nece
44、ssary information, if structural resonance in the measuring object can be disregarded. The accelerometer output produced by the shock under suitable conditions will have the resonance frequency superimposed (see figure 4). Some experimentation is required with the energy of shock (.e. the height fro
45、m which the mass is released) and the stiffness of the impact surface (for example, steel or lead lined) to obtain a suitable period of impact to display the resonance effect. Care shall also be taken to see that the lowest resonance is excited during the shock. The use of suitable single-event reco
46、rder storage device or photographing technique enables the frequency of the resonance ripple to be determined. These methods are particularly suited for high frequencies. Repeated well-defined shocks may give additional information in the stability of the mounting. 5.4 Recommendations for particular
47、 types of mountings 5.4.1 General The mounting surface shall be carefully examined for contamination and smoothness and, if necessary, it shall be machined flat. Any lack of alignment between the sensitive axis of the accelerometer and the direction of measurement shall be minimized, as otherwise th
48、is will lead to errors similar to those introduced by transverse sensitivity. These errors will be particularly large if the transverse motion is much greater than the axial motion. The condition of the mounting surface and method of mounting should be stated in any report. The recommended mounting
49、methods for the transducer should be followed in order to make the manufacturers data applicable. An overview of the criteria that affect selection of mounting methods, based on best practices, is given in table 1. Page 6 IS0 5348 : 1998 Table 1 - Criteria that affect selection of mounting methods (based on best practices) acrylate Beeswax Il Double-sided tape Quick mount Vacuum rnountec *) Depends entirely on distance between hand and measured surface Key: 0 high average 0 poor 5.4.2 Stud mounting 5.4.2.1 Surfaces shall be clean, flat and machined smooth to manufacturer?s toleranc
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