BS-5944-5-1985.pdf

BRITISH STANDARD BS 5944-5: 1985 Measurement of airborne noise from hydraulic fluid power systems and components Part 5: Simplified method of determining sound power levels from pumps using an anechoic chamber UDC 62 822:534.61 + 621.65:534.62 Licensed Copy: sheffieldun sheffieldun, na, Fri Dec 01 14:21:26 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 5944-5:1985 This British Standard, having been prepared under the direction of the Machinery and Components Standards Committee, was published under the authority of the Board of BSI and comes into effect on 31 July 1985 © BSI 10-1999 The following BSI references relate to the work on this standard: Committee reference MCE/18 Draft for comment 84/76091 DC ISBN 0 580 14515 8 Committees responsible for this British Standard The preparation of this British Standard was entrusted by the Machinery and Components Standards Committee (MCE/-) to Technical Committee MCE/18, upon which the following bodies were represented: Association of British Mining Equipment Companies Association of Hydraulic Equipment Manufacturers British Compressed Air Society British Hydromechanics Research Association British Steel Corporation British Telecommunications Department of Trade and Industry (National Engineering Laboratory) Electricity Supply Industry in England and Wales Federation of Manufacturers of Construction Equipment and Cranes Health and Safety Executive Institution of Mechanical Engineers Machine Tool Industry Research Association Ministry of Defence National Coal Board The following bodies were also represented in the drafting of the standard, through subcommittees and panels: Bath University Institution of Production Engineers Amendments issued since publication Amd. No.Date of issueComments Licensed Copy: sheffieldun sheffieldun, na, Fri Dec 01 14:21:26 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 5944-5:1985 © BSI 10-1999i Contents Page Committees responsibleInside front cover Forewordii 0Introduction1 1Scope1 2Definitions1 3Measurement uncertainty2 4Test environment2 5Instrumentation2 6Installation conditions for pump2 7Operating conditions3 8Location and number of sound measuring points3 9Test procedure3 10Calculation of pump mean sound pressure levels and sound power levels4 11Calculation of mean sound pressure level at a reference distance4 12Information to be recorded4 13Test report5 Appendix A Errors and classes of measurement6 Appendix B Reference dimensions, axes and location of sound measuring points6 Appendix C Corrections for pump sound power level7 Appendix D Calculation of mean sound pressure level at a reference distance8 Figure 1 Key reference axes and dimensions7 Table 1 Standard deviation of sound power level determination2 Table 2 Allowable variations in test conditions3 Table 3 Permissible systematic errors of measuring instruments as determined during calibration6 Table 4 Coordinates of microphone locations6 Publications referred toInside back cover Licensed Copy: sheffieldun sheffieldun, na, Fri Dec 01 14:21:26 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 5944-5:1985 ii © BSI 10-1999 Foreword This Part of BS 5944 has been prepared under the direction of the Machinery and Components Standards Committee and is one of a group of British Standards related to the measurement of noise emanating from hydraulic fluid power systems and components. It is intended that this standard will unify testing methods and enable the performance of different pumps to be compared on a common basis. The standard comprises the following Parts. Part 1: Method of test for pumps; Part 2: Method of test for motors; Part 3: Guide to the application of Part 1 and Part 2; Part 4: Method of determining sound power levels from valves controlling flow and pressure. Further Parts are planned. 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 British Standard does not of itself confer immunity from legal obligations. Summary of pages This document comprises a front cover, an inside front cover, pages i and ii, pages 1 to 8, an inside back cover 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, Fri Dec 01 14:21:26 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 5944-5:1985 © BSI 10-19991 0 Introduction In hydraulic fluid power systems, power is transmitted and controlled through a liquid under pressure in a closed circuit. Pumps are components which convert rotary mechanical power into fluid power. During the process of converting mechanical power into hydraulic fluid power, airborne noise, fluid-borne vibrations and structure-borne vibrations are radiated from the pump. The airborne noise level of a hydraulic fluid power pump is an important consideration in component selection. The noise measurement technique should, therefore, be such as to yield accurate appraisals of these airborne noise levels. The determination of noise levels is complicated by the interactions which occur during noise measurement. The fluid-borne and structure-borne vibrations from the pump can be transmitted to the circuit and ultimately give rise to background airborne noise levels which could affect the determination of the pump airborne noise levels. The procedures described in this Part of BS 5944 are intended to measure only the airborne noise radiated directly from the pump under test. This standard closely follows the methods described in BS 5944-1 and BS 5944-2 but allows the use of alternative pump mounting and drive configurations which are simpler and cheaper to implement in an anechoic chamber. Much of the guidance given in BS 5944-3 is equally applicable to this standard. The data obtained has been shown to be sufficiently accurate in industrial terms for frequency A weighted, octave and 1/3 octave noise measurements. 1 Scope This Part of BS 5944 describes procedures for the determination of the sound power levels of a hydraulic fluid power pump, under controlled conditions of installation and operation, suitable for providing a basis for comparing the noise levels of pumps in terms of: a) A-weighted sound power level; b) octave band sound power levels. From these sound power levels, sound pressure levels may be calculated for reporting purposes (see clause 11). For general purposes, the frequency range of interest includes the octave bands with centre frequencies between 125 Hz and 8 000 Hz. This method is applicable to all types of hydraulic fluid power pumps operating under steady-state conditions, irrespective of size, except for any limitations imposed by the size of the test environment (see clause 4). NOTEThe titles of the publications referred to in this standard are listed on the inside back cover. 2 Definitions For the purposes of this Part of BS 5944, the definitions given in BS 661 apply together with the following. 2.1 free sound field a sound field produced in a homogeneous, isotropic medium free of boundaries NOTEIn practice, it is a field in which the effects of the boundaries are negligible over the frequency range of interest. 2.2 free-field over a reflecting plane a field produced by a source in the presence of one reflecting plane on which the source is located 2.3 free-field over two reflecting planes a field produced by a source in the presence of two mutually perpendicular reflecting planes 2.4 anechoic room a test room having boundaries which absorb essentially all of the incident sound energy over the frequency range of interest, thereby affording free-field conditions over the measurement surface 2.5 mean-square sound pressure the sound pressure averaged in space and time on a mean-square basis NOTEIn practice, this is estimated by space and time averaging over a finite path length or over a number of fixed microphone positions. 2.6 mean sound pressure level (Lp) ten times the logarithm to the base 10 of the ratio of the mean-square sound pressure to the square of the reference sound pressure in decibels (dB) NOTEThe weighting network or the width of the frequency band used should always be indicated; for example, A-weighted sound pressure level, octave band sound pressure level. The reference sound pressure is 20 4Pa. 2.7 sound power level (Lw) ten times the logarithm to the base 10 of the ratio of a given sound power to the reference sound power in decibels (dB) Licensed Copy: sheffieldun sheffieldun, na, Fri Dec 01 14:21:26 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 5944-5:1985 2 © BSI 10-1999 NOTEThe weighting network or the width of the frequency band used should always be indicated. The reference sound power is 1 pW. 2.8 volume of source under test the volume of the envelope of the whole pump under test 3 Measurement uncertainty With the exception of the measurement environment specified in 4.1, use methods of measurement which tend to result in standard deviations which are equal to or less than those given in Table 1. To meet this requirement the engineering methods given in clause 4 and Appendix A of BS 4196-4:1981 shall be used. 4 Test environment 4.1 Conduct the tests in an environment generally in accordance with that described in BS 4196-4 and which provides “free-field” conditions over two mutually perpendicular reflecting planes, at least one of which extends beyond the projected area of the microphone measuring array. NOTEThe other reflecting surface, which will usually be formed by an acoustic enclosure over the pump mounting, may be smaller if required. Table 1 Standard deviation of sound power level determination 4.2 Calibrate the acoustic test environment thus formed by the substitution technique. NOTEA reference sound source meeting the requirements of BS 4196-001) may be used for calibration purposes. Ascertain the environmental corrections for each frequency band of interest (see 10.4). 5 Instrumentation 5.1 Use instrumentation to measure fluid flow, fluid pressure, pump speed and fluid temperature in accordance with the recommendations for “industrial class” accuracy of testing, i.e. class C given in Appendix A. 5.2 Use type 2 instruments for acoustical measurements in accordance with BS 5969. This instrumentation shall be in accordance with BS 4196-4 for both performance and calibration. 6 Installation conditions for pump 6.1 Pump location Locate the pump with its mounting flange flush with one reflecting plane. Arrange the second reflecting plane to intersect the first at right angles as close to the pump as practicable. 6.2 Pump mounting 6.2.1 Use a method of mounting the pump that will minimize the noise radiated as a result of pump vibrations. 6.2.2 Construct the mounting bracket of high damping material, or with sound damping and sound insulating material applied to the bracket as required. 6.2.3 If necessary, employ vibration isolation techniques, even if the pump is securely mounted. 6.3 Pump drive Locate the drive motor outside the test space and drive the pump through flexible couplings and an intermediate shaft or isolate the motor in an acoustic enclosure. 6.4 Hydraulic circuit 6.4.1 Include in the circuit all oil filters, oil coolers, reservoirs and restrictor valves as required to meet the pump hydraulic operation conditions (see clause 7). 6.4.2 Use test fluid and filtration in accordance with the manufacturers recommendations. 6.4.3 Install inlet and discharge lines having bores in accordance with the manufacturers recommended practice. Exercise extra care when assembling inlet lines to prevent air leaking into the circuit. 6.4.4 Mount the inlet pressure gauge at the same height as the inlet fitting or calibrate for any height difference. Octave band centred on frequency of Standard deviation Hz 125 250 500 1 000 to 4 000 8 000 dB 5.0 3.0 2.0 2.0 3.0 NOTE 1The standard deviations include the effects of allowable variations in the positioning of the measurement points and in the selection of any prescribed measurement surface, but exclude variations in the sound power output of the source from test to test. NOTE 2The A-weighted sound power level will, in most practical cases, be determined with a standard deviation of approximately 2 dB. 1) In preparation. In the meantime ISO/DIS 3748, prepared by the International Organization for Standardization, may be used. Licensed Copy: sheffieldun sheffieldun, na, Fri Dec 01 14:21:26 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 5944-5:1985 © BSI 10-19993 6.4.5 Select the lengths of pipe between the pump and the load valve which minimize setting up standing waves in the discharge line which can increase the sound radiated from the pump. NOTEIt has been found that a long length of hydraulic hose can minimize standing wave effects. 6.4.6 Use a stable load valve. NOTEUnstable load valves in the discharge line can generate and transmit noise through the fluid and piping which can emerge as airborne sound at the pump. 6.4.7 Position the load valve as far as possible from the pump, preferably outside the test room, to minimize interaction. Locate the load valve close to the pump only when adequate control of its acoustic performance can be provided. 6.4.8 Enclose all fluid lines and load valves in the test space within acoustic ducts and enclosures, as required, to meet the specified background noise suppression (see 9.1). Use enclosures having a sound transmission loss of at least 10 dB at 125 Hz and greater loss at higher frequencies. 7 Operating conditions 7.1 Determine the sound power levels of the pump for any desired set of operation conditions (see 10.4). 7.2 Maintain these test conditions during the test within the limits given in Table 2. 7.3 Test the pump in the “as delivered” condition together with any integral ancillary pumps and valves operating normally during the test, so as to include their noise contributions to the airborne noise level of the pump. Table 2 Allowable variations in test conditions 8 Location and number of sound measuring points Provide and locate measuring microphones in a quadrispherical array in accordance with Appendix B. Centre the quadrispherical array at the intersection of the two reflecting planes, on the projected centre line of the pump. 9 Test procedure 9.1 Background noise measurements 9.1.1 Measure the background noise over the frequency range of interest that is present during the pump noise test which does not emanate from the pump itself. NOTEOver the frequency range of interest, the band sound pressure levels of this background noise should be at least 6 dB below the pump band sound pressure levels at each measurement point. 9.1.2 Correct for this background noise, if evidenced by measurement, by applying the corrections for this purpose given in BS 4196-4. 9.1.3 When measuring band levels of background noise is no