SIST EN ISO 9614-2:1997
(Main)Acoustics - Determination of sound power levels of noise sources using sound intensity - Part 2: Measurement by scanning (ISO 9614-2:1996)
Acoustics - Determination of sound power levels of noise sources using sound intensity - Part 2: Measurement by scanning (ISO 9614-2:1996)
Specifies a method for measuring the component of sound intensity normal to a measurement surface which is chosen so as to enclose the noise source(s) of which the sound power level is to be determined.
Akustik - Bestimmung der Schalleistungspegel von Geräuschquellen aus Schallintensitätsmessung - Teil 2: Messung mit kontinuierlicher Abtastung (ISO 9614-2:1996)
Dieser Teil von ISO 9614 beschreibt ein Verfahren für die Messung der zu einer Meßfläche senkrechten Schallintensitätskomponente. Die Meßfläche wird so gewählt, daß sie die Geräuschquelle(n), deren Schalleistungspegel bestimmt werden soll, einschließt.
Acoustique - Détermination par intensimétrie des niveaux de puissance acoustique émis par les sources de bruit - Partie 2: Mesurage par balayage (ISO 9614-2:1996)
La présente partie prescrit une méthode de mesurage de la composante de l'intensité acoustique normale à une surface de mesurage entourant la (les) source(s) de bruit dont on souhaite déterminer le niveau de puissance acoustique. L'intégration sur la surface de mesurage de la composante de l'intensité normale à la surface est approchée en divisant la surface de mesurage en éléments contigus et en passant la sonde d'intensité sur chaque élément de surface le long d'une trajectoire continue qui couvre l'étendue de l'élément de surface. L'instrument de mesure détermine la composante de l'intensité normale moyenne et la pression acoustique quadratique moyenne sur la durée de chaque balayage. L'opération de balayage peut être effectuée soit manuellement, soit au moyen d'un système mécanique. À partir des valeurs mesurées, on calcule le niveau de puissance acoustique par bandes d'octave ou de tiers d'octave, ou le niveau pondéré sur une plage de fréquences limitée. La méthode est applicable à toute source pour laquelle on peut définir une surface de mesurage physiquement stationnaire et sur laquelle les signaux acoustiques émis par la source et par les sources parasites significatives, sont stables dans le temps (comme défini en 3.13). La source est définie par le choix de la surface de mesurage. La méthode peut être appliquée in situ ou dans des environnements d'essai particuliers. La présente partie prescrit certaines procédures complémentaires décrites dans l'annexe B, à appliquer lors de la détermination de la puissance acoustique. Les résultats obtenus indiquent la qualité de la détermination et donc la classe de précision de la méthode. Si la qualité de la détermination n'est pas conforme aux prescriptions de la présente partie de l'ISO 9614, la méthode d'essai doit être modifiée de la façon indiquée. La présente partie de l'ISO 9614 ne s'applique pas aux bandes de fréquences dans lesquelles la puissance acoustique de la source mesurée est négative.
Akustika - Ugotavljanje ravni zvočnih moči virov hrupa z merjenjem jakosti zvoka - 2. del: Zvezno merjenje po ploskvi
General Information
Standards Content (Sample)
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.Akustik - Bestimmung der Schalleistungspegel von Geräuschquellen aus Schallintensitätsmessung - Teil 2: Messung mit kontinuierlicher Abtastung (ISO 9614-2:1996)Acoustique - Détermination par intensimétrie des niveaux de puissance acoustique émis par les sources de bruit - Partie 2: Mesurage par balayage (ISO 9614-2:1996)Acoustics - Determination of sound power levels of noise sources using sound intensity - Part 2: Measurement by scanning (ISO 9614-2:1996)17.140.01Acoustic measurements and noise abatement in generalICS:Ta slovenski standard je istoveten z:EN ISO 9614-2:1996SIST EN ISO 9614-2:1997en01-april-1997SIST EN ISO 9614-2:1997SLOVENSKI
STANDARD
SIST EN ISO 9614-2:1997
SIST EN ISO 9614-2:1997
SIST EN ISO 9614-2:1997
INTERNATIONAL STANDARD IS0 9614-2 First edition 1996-08-01 Acoustics - Determination of sound power levels of noise sources using sound intensity - Part 2: Measurement by scanning Acoustique - Dhermination par intensim&rie des niveaux de puissance acoustique hmis par /es sources de bruit - Partie 2: Mesurage par balayage Reference number IS0 96142:1996(E) SIST EN ISO 9614-2:1997
IS0 9614=2:1996(E) 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 which 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 matters of electrotechnical standardization. Draft International Standards adopted by the technical committees are circulated to the member bodies for voting. Publication as an lnternational Standard requires approval by at least 75 % of the member bodies casting a vote. International Standard IS0 9614-2 was prepared by Technical Committee ISO/TC 43, Acoustics, Subcommittee SC 1, Noise. IS0 9614 consists of the following parts, under the general title Acoustics - Determination of sound power levels of noise sources using sound intensity: - Part 1: Measurement at discrete points Part 2: Measurement bY scanning - Part 3: Precision method for measurement by scanning Annexes A and B form an integral part of this part of IS0 9614. Annexes C, D, E and F are for information only. 0 IS0 1996 All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from the publisher. International Organization for Standardization Case Postale 56 l CH-1211 Geneve 20 l Switzerland Printed in Switzerland ii SIST EN ISO 9614-2:1997
0 IS0 IS0 9614=2:1996(E) Introduction 0.1 The sound power radiated by a source is equal in value to the inte- gral of the scalar product of the sound intensity vector and the associated elemental area vector over any surface totally enclosing the source. Pre- vious International Standards which describe methods of determination of sound power levels of noise sources, principally IS0 3740 to IS0 3747, without exception specify sound pressure level as the primary acoustic quantity to be measured. The relationship between sound intensity level and sound pressure level at any point depends on the characteristics of the source, the characteristics of the measurement environment, and the disposition of the measurement positions with respect to the source. Therefore IS0 3740 to IS0 3747 necessarily specify the source charac- teristics, the test environment characteristics and qualification procedures, together with measurement methods which are expected to restrict the uncertainty of the sound power level determination to within acceptable limits. The procedures specified IS0 3740 to IS0 3747 are not always appropri- ate, for the following reasons. a) Costly facilities are necessary if high precision is required. It is fre- quently not possible to install and operate large pieces of equipment in such facilities. b) They cannot be used in the presence of high levels of extraneous noise generated by sources other than that under investigation. 0.2 This part of IS0 9614 specifies methods of determining the sound power levels of sources, within specific ranges of uncertainty, under test conditions which are less restricted than those required by IS0 3740 to IS0 3747. The sound power level is the in situ sound power level as de- termined by the procedure of this part of IS0 9614; it is physically a function of the environment, and may in some cases differ from the sound power level of the same source determined under other conditions. It is recommended that personnel performing sound intensity meas- urements according to this part of IS0 9614 are appropriately trained and experienced. 0.3 This part of IS0 9614 complements IS0 9614-1 and the series IS0 3740 to IS0 3747 which specify various methods for the determi- nation of sound power levels of machines and equipment. It differs from the IS0 3740 to IS0 3747 series principally in three aspects: SIST EN ISO 9614-2:1997
IS0 9614-2:1996(E) 0 IS0 a) measu pressu remen re; ts are made of sound intensity as well as of sound b) the uncertainty of the sound power level determined by the method specified in this part of IS0 9614 is classified according to the results of specified ancillary tests and calculations performed in association with the test measurements; c) current limitations of intensity measurement equipment which con- forms to IEC 1043 restricts measurements to the one-third-octave range 50 Hz to 6,3 kHz; band-limited A-weighted values are deter- mined from the constituent one-octave or one-third-octave band values and not by direct A-weighted measurement. 0.4 The integral over any surface totally enclosing the source of the scalar product of the sound intensity vector and the associated elemental area vector provides a measure of the sound power radiated directly into the air by all sources located within the enclosing surface and excludes sound radiated by sources located outside this surface. In practice, this exclusion is effective only if the source under test and other sources of extraneous intensity on the measurement surface are stationary in time. In the presence of sound sources operating outside the measurement surface, any system lying within the surface may absorb a proportion of energy incident upon it. The total sound power absorbed within the measurement surface will appear as a negative contribution to source power, and may produce an error in the sound power determination. In order to minimize the associated error, it is therefore necessary to remove any sound-absorbing material lying within the measurement surface which is not normally present during the operation of the source under test. This method is based on sampling of the intensity field normal to the measurement surface by moving an intensity probe continuously along one or more specified paths. The resulting sampling error is a function of the spatial variation of the normal intensity component over the meas- urement surface, which depends upon the directivity of the source, the chosen sampling surface, the pattern and speed of the probe scan- ning, and the proximity of extraneous sources outside the measurement surface. The accuracy of measurement of the normal component of sound inten- sity at a position is sensitive to the difference between the local sound pressure level and the local normal sound intensity level. A large difference may occur when the intensity vector at a measurement position is directed at a large angle (approaching 90’) to the local normal to the measurement surface. Alternatively, the local sound pressure level may contain strong contributions from sources outside the measurement surface, but may be associated with little net sound energy flow, as in a reverberant field in an enclosure; or the field may be strongly reactive because of the pres- ence of the near field and/or standing waves. The accuracy of determination of sound power level is adversely affected by a flow of sound energy into the volume enclosed by the measurement surface through a portion of that surface, even though it is, in principle, compensated by increased flow out of the volume through the remaining portion of the surface. This condition is caused by the presence of a strong extraneous source close to, but outside, the measurement surface. iv SIST EN ISO 9614-2:1997
INTERNATIONAL STANDARD 0 ISO IS0 9614=2:1996(E) Acoustics - Determination of sound power levels of noise sources using sound intensity - Part 2: Measurement by scanning 1 Scope 1.1 This part of IS0 9614 specifies a method for measuring the component of sound intensity normal to a measurement surface which is chosen so as to enclose the noise source(s) of which the sound power level is to be determined. Surface integration of the intensity component normal to the measurement surface is approximated by sub- dividing the measurement surface into contiguous segments, and scanning the intensity probe over each segment along a continuous path which covers the extent of the segment. The measurement instrument determines the average normal intensity component and averaged squared sound pressure over the dur- ation of each scan. The scanning operation may be performed either manually or by means of a mechan- ical system. Band-limited weighted sound power level is calcu- lated from the measured octave or one-third-octave band values. The method is applicable to any source for which a physically stationary measurement sur- face can be defined, and on which the noises gener- ated by the source under test and by other significant extraneous sources are stationary in time, as defined in 3.13. The source is defined by the choice of meas- urement surface. The method is applicable in situ, or in special-purpose test environments. This part of IS0 9614 specifies certain ancillary pro- cedures described in annex B, to be followed in conjunction with the sound power determination. The results are used to indicate the quality of the deter- mination, and hence the grade of accuracy. If the in- dicated quality of the determination does not meet the requirements of this part of IS0 9614, the test procedure is to be modified in the manner indicated. This part of IS0 9614 does not apply in any frequency band in which the sound power of the source is found to be negative on measurement. 1.2 This part of IS0 9614 is applicable to sources situated in any environment which is neither so vari- able in time as to reduce the accuracy of the meas- urement of sound intensity to an unacceptable degree, nor subjects the intensity measurement probe to gas flows of unacceptable speed or un- steadiness (see 5.22, 5.3 and 5.4). In some cases it will be found that the test conditions are too adverse to allow the requirements of this part of IS0 9614 to be met. Extraneous noise levels may exceed the dynamic capability of the measuring in- strument or may vary to an excessive degree during the test. In such cases the method given in this part of IS0 9614 is not suitable for the determination of the sound power level of the source. NOTE 1 Other methods (e.g. determination of sound power levels from surface vibration levels as described in ISO/TR 7849) may be more suitable. 2 Normative references The following standards contain provisions which, through reference in this text, constitute provisions of this part of IS0 9614. At the time of publication, the editions indicated were valid. All standards are subject to revision, and parties to agreements based on this 1 SIST EN ISO 9614-2:1997
IS0 9614=2:1996(E) 0 IS0 part of IS0 9614 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. T = lim 1 I T-+ T--+00 T 0 I(t) dt where T is the integration period. . . . (2) Also I EC 942: 1988, Sound calibrators. is the signed magnitude of i; the sign is an indication of directional sense, and is dictated by the choice of positive direction of energy flow; I EC 1043: 1993, Electroacoustics - Instruments for the measurement of sound intensity - Meas- urements with pairs of pressure sensing micro- phones. is the unsigned magnitude 0f i. 3 Definitions 3.4 normal sound intensity, 1”: Component of the sound intensity in the direction normal to a meas- urement surface defined by the unit normal vector n’: For the purposes of this part of IS0 9614, the follow- ing definitions apply. 31 . Sound pressure levels In = Li . . . (3) 3.1.1 sound pressure level, &: Ten times the log- arithm to the base 10 of the ratio of the mean-square sound pressure to the square of the reference sound pressure. The reference sound pressure is 20 PPa. where z is the unit normal vector directed out of the volume enclosed by the measurement surface. 3.5 normal sound intensity level, L,: Logarithmic measure of the unsigned value of the normal sound intensity, 11” I, given by: LI = 10 kIcI~“I/1,1 dB . . . n (4) Sound pressure level is expressed in decibels. 3.1.2 segment-average sound pressure level, Lpi: Ten times the logarithm to the base 10 of the ratio of the spatial-average mean-square pressure on seg- ment i to the square of the reference sound pressure. where IO is the reference sound (= IO-‘* Wm-*). intensity It is expressed in decibels. It is expressed in decibels. 3.2 instantaneous sound intensity, 16): Instan- taneous rate of flow of sound energy per unit of sur- face area in the direction of the local instantaneous acoustic particle velocity. When In is negative, the level is expressed as (-1 XX dB, except when used in the evaluation of 6, (see 3.1 I). This is a vectorial quantity which is equal to the prod- uct of the instantaneous sound pressure at a point and the associated particle velocity: 3.6 Sound powers 3.6.1 partial sound power, PiI Time-averaged rate of flow of sound energy through an element (seg- ment) of a measurement surface, given by: Pi = (Ini)Si . . . (5) . . . (1) PC4 is the instantaneous sound pressure at a point; where (I > ni is the signed magnitude of the segment- average normal sound intensity measured on the segment i of the measurement surface; 4 is the associated instantaneous particle velocity at the same point; t is the time. si is the area of the segment i. 3.3 sound intensity, i: Time-average value of 16) in a temporally stationary sound field: AISO I PiI is the magnitude of Pi- 2 SIST EN ISO 9614-2:1997
0 IS0 IS0 9614=2:1996(E) 3.6.2 sound power, P: Total sound power gener- ated by a source, as determined using the method given in this part of IS0 9614, given by: N P= Pi c i=l and IPI = N c pi i=l where N is the total number of segments of the . . . (6) . . . (7) measurement surface. 3.6.3 partial sound power level, &i: Logarithmic measure of the sound power passing through seg- ment i of the measurement surface, given by: L Wi= lo ~~~lpiI/pOl dB . . . (8) where PO is the reference sound power (= 10ql* W). 3.10 probe: That part of the intensity measurement system which incorporates the sensors. 3.11 pressure-residual intensity index, $ : The difference between the indicated Lp and indicated LI when the intensity probe is placed and oriented in a sound field such that the sound intensity is zero. It is expressed in decibels. Details for determining dPl, are given in IEC 1043. 6 PI0 = (Lp - 4 . . . (10) 3.12 dynamic capability index, Ld: Given by: Ld = bpr, - K . . . (1 I> It is expressed in decibels. The value of K is selected according to the grade of accuracy required (see table I). Table 1 - Bias error factor, K It is expressed in decibels. Grade of accuracyl) When Pi is negative, it is expressed as (-) XX dB. I Engineering (grade 2) I 10 1 3.6.4 sound power level, &,: Logarithmic measure of the sound power generated by a source, as deter- mined using the method given in this part of IS0 9614, given by: L,= 10 kt-lfwo1 dB . . . (9) It is expressed in decibels. When P is negative, the level is expressed as (-1 XX dB for record purposes only. 3.7 measurement surface: Hypothetical surface on which intensity measurements are made, and which either completely encloses the noise source under test or, in conjunction with an acoustically rigid, con- tinuous surface, encloses the noise source under test. In cases where the hypothetical surface is penetrated by bodies possessing solid surfaces, the meas- urement surface terminates at the lines of inter- section between the bodies and the surface. 3.8 segment: One of a set of smaller surfaces into which a measurement surface is divided. 3.9 extraneous intensity: Contribution to the sound intensity which arises from the operation of sources external to the measurement surface (source mech- anisms operating outside the volume enclosed by the measurement surface). Survey (grade 3) 7 I 1) Defined in IS0 12001. 3.13 stationary signal: A signal of which the time- averaged properties during a measurement on one segment of the measurement surface are equal to those obtained on the same segment when the aver- aging period is extended over the total time taken to measure on all segments. NOTE 2 Cyclic signals are, by this definition, stationary, if on each segment the measurement period extends over at least ten cycles. 3.14 field indicators FpI and F+,-: See annex A. 3.15 scan: A continuous movement of an intensity probe along a specified path on a segment of a measurement surface. 3.16 scan-line density: Inverse of the average sep- aration of adjacent scan lines. 4 General requirements 4.1 Size of noise source The size of the noise source is unrestricted. The ex- tent of the source is defined by the choice of the measurement surface. 3 SIST EN ISO 9614-2:1997
IS0 9614=2:1996(E) 0 IS0 4.2 Character of noise radiated by the source The signal shall be stationary in time, as defined in 3.13. If a source operates according to a duty cycle, within which there are distinct continuous periods of steady operation, for the purposes of application of this part of IS0 9614, an individual sound power level is determined and reported for each distinct period. Action should be taken to avoid measurement during times of operation of non-stationary extraneous noise sources of which the occurrences are predictable (see table B.l in annex B). 43 . Measurement uncertainty The value of the sound power of a noise source de- termined by a single application of the procedures of this part of IS0 9614 is likely to differ from the true value. The actual difference cannot be evaluated, but the confidence that the value determined lies within a certain range about the true value can be stated, on the reasonable assumption that the values deter- mined by numerous applications of the procedure are normally distributed about the true value. Where re- peated applications are made to a source located at a given test site under nominally identical test con- ditions, using the same test procedures and instru- mentation, the values so determined constitute the data set which statistically describes the repeatability of the determination. Where the values are deter- mined from tests conforming to this part of IS0 9614 made on the given source at different test sites using physically different instruments, the data set so ob- tained statistically describes the reproducibility of the determination. Reproducibility is affected by variations of environmental conditions at the test sites and of experimental technique. The standard deviations do not account for variations of sound power output caused by changes in operating conditions of a source (e.g. rotational speed, line voltage) or mounting con- ditions. For the procedures specified in this part of IS0 9614, the highest standard deviations of reproducibility are stated in table 2. NOTES 3 If certain operatives use similar facilities and instrumen- tation, the results of sound power determinations on a given source at a given site are likely to exhibit smaller standard deviations than those indicated in table 2. 4 For a particular family of sound sources of similar size with similar sound power spectra operating in similar envi- ronmental conditions, and measured according to a specific test code, the standard deviations of reproducibility are likely to be less than those indicated in table2. Statistical methods for the characterization of batches of machines are described in IS0 7574-4. 5 The procedures of this part of IS0 9614 and the stan- dard deviations stated in table 2 are applicable to meas- urements on a given source. Characterization of the sound power levels of a batch of sources of the same family or type involves the use of random sampling techniques in which confidence intervals are specified, and the results are expressed in terms of statistical upper limits. In applying these techniques, the total standard deviation is either known or estimated, including the standard deviation of production, which is a measure of the variation in sound power output between individual machines within the batch, as defined in IS0 7574-l. For the purposes of application of this part of IS0 9614, two grades of accuracy are defined in table2. The stated uncertainties allow for random er- rors associated with the measurement procedure, to- gether with the maximum measurement bias error which is limited by the selection of the bias error fac- tor K appropriate to the required grade of accuracy (see table 1). They do not account for tolerances in nominal instrument performance which are specified in IEC 1043. Nor do they account for the effects of variation in source installation, mounting and operat- ing conditions. NOTE 6 Below 50 Hz there are insufficient data on which to base uncertainty values. For the purposes of this part of IS0 9614, the normal range for A-weighted data is covered by octave bands from 63 Hz to 4 kHz, and one-third-octave bands from 50 Hz to 6,3 kHz. The A-weighted value which is computed from octave band levels in the range 63 Hz to 4 kHz, and one-third-octave band levels in the range 50 Hz to 6,3 kHz, is correct if there are no significantly high levels in the bands for 31 Hz to 40 Hz and 8 kHz to 10 kHz. For the purpose of this assessment, significant levels are band levels which after A-weighting are no more than 6 dB below the A-weighted value computed. If A-weighted meas- urements and associated sound power level determinations are made in a more restricted frequency range, this range shall be stated in accordance with 10.6 b). The uncertainty of determination of the sound power level of a noise source is related to the nature of the sound field of the source, to the nature of the ex- traneous sound field, to the absorption of the source under test, and to the form of the intensity field sampling and measurement procedure employed. For this reason this part of IS0 9614 specifies initial pro- cedures for the evaluation of indicators of the nature of the sound field which exists in the region of the proposed measurement surface (see annex A). The results of this initial test are used to select an appro- priate course of action according to table B.l . 4 SIST EN ISO 9614-2:1997
0 IS0 IS0 9614=2:1996(E) Table 2 - Uncertainty in the determination of sound power levels Octave band centre One-third-octave band Standard deviations, s frequencies centre frequencies Engineering (grade 2) Survey (grade 3) Hz Hz dB dB 63 to 125 50 to 160 3 250 200 to 315 2 500 to 4 000 400 to 5 000 I,5 6 300 2,5 A-weighted 1) I ,52) 4 NOTE - The stated uncertainty of the A-weighted estimate does not apply if the total A-weighted power in the one-third- octave bands outside the range 400 Hz to 5 000 Hz exceeds the total within this range; individual band uncertainties then apply * 1) 63 Hz to 4 kHz or 50 Hz to 6,3 kHz. 2) The true value of the A-weighted sound power level is expected with a certainty of 95 % to be in the range of + 3dB - about the measured value. If only an A-weighted determination is required, any single A-weighted band level of 10 dB or more below the highest A-weighted band level may be neglected. If more than one band levels appear insignificant, they may be neglected if the level of the sum of the A- weighted sound powers in these bands is 10 dB or more below the highest A-weighted band level. If only an A-weighted overall sound power level is required, the uncertainty of determination of the sound power level in any band in which it is 10 dB or more below the overall weighted level, is irrelevant. 5 Acoustic environment 5.1 Criteria for adequacy of the test environment The test environment shall be such that the principle upon which sound intensity is measured by the par- ticular instrument employed, as given in IEC 1043, is not invalidated. In addition, it shall satisfy the require- ments stated in 5.2 to 5.5. 5.2 Extraneous intensity 5.2.1 Level of extraneous intensity The level of extraneous intensity shall be minimized so that it does not unacceptably reduce measurement accuracy [see equation (B.2) of annex B]. Attempt to reduce the value of indicator FpI (A.2.1 of annex A) to less than 10 dB by an appropriate choice of meas- urement surface and control of extraneous intensity. NOTE 7 If substantial quantities of absorbing material are part of the source under test, high levels of extraneous in- tensity may lead to an under-estimate of the sound power. Annex D gives indications of how to evaluate the resulting error in the special case where the source under test can be switched off. 5.2.2 Variability of extraneous intensity The variability of the extraneous intensity during the measurement period shall be minimized by appropri- ate actions prior to the test (e.g. disabling automati- cally switched sources of extraneous noise which are not essential to source operation; making plant oper- ators aware of the problem) and the selection of ap- propriate periods of measurement. 5.3 Wind and gas flows Annex C describes the adverse effects of flow and turbulence on sound intensity measurement. A probe windscreen shall be used in cases where fluid flow is present on the measurement surface. Do not make measurements when wind or gas flow conditions in the vicinity of the intensity probe contravene the limits for satisfactory performance of the measurement system, as specified by the manu- facturer. Unless it can be demonstrated by meas- urement that the maximum time-average wind/flow speed at all locations on the measurement surface is less than 4 m/s, the following procedure shall be used to qualify the test environment prior to the com- mencement of the sound power determination. SIST EN ISO 9614-2:1997
IS0 9614=2:1996(E) 0 IS0 Select a measurement segment on which the un- steadiness of the wind or gas flow is considered to be maximum. Determine the segment-average nor- mal sound intensity level L! according to the selected scanning procedure (8.1) by means of two successive scans only. Verify that criterion 3 of B.1.3 is satisfied. Source sound power determination according to this part of IS0 9614 is not possible in those frequency bands in which criterion 3 is not satisfied. It is not permissible to continue repetition of the procedure until satisfaction of criterion 3 is achieved. 5.4 Temperature The probe shall not be placed closer than 20 mm to bodies having a temperature significantly different from that of the ambient air. NOTE 8 The exposure of the probe to temperature grad- ients along the probe axis can produce time-dependent, differential modifications to the responses of the two microphones which introduce bias errors into the intensity estimates. 5.5 Configuration of the surroundings The configuration of the test surroundings shall, as far as possible, remain unchanged during the perform- ance of a test; this is particularly important if the source emits sound of a tonal nature. Cases where variation in the test surroundings during a test is un- avoidable shall be reported. Ensure, as far as possible, that the operator does not stand in a position on, or close to, the axis of the probe during the period of measurement at any position. If practicable, any ex- traneous objects shall be removed from the vicinity of the source. 5.6 Atmospheric conditions Air pressure and temperature affect air density and speed of sound. The effects of these quantities on instrument calibration shall be ascertained and appro- priate corrections shall be made to indicated inten- sities (see IEC 1043). 6 Instrumentation 6.1 General A sound intensity measurement instrument and probe that meet the requirements of the IEC 1043 shall be used. Class 1 instruments shall be used for grade 2 determinations and either class 1 or 2 instruments shall be used for grade 3 determinations. Adjust the intensity measurement instrument to allow for ambi- ent air pressure and temperature in accordance with I EC 1043. Record the pressure-residual intensity index of the instrument used for measurements, as defined by IEC 1043, for each frequency band of measurement. 6.2 Calibration and field check The instrument, including the probe, shall comply with IEC 1043. Verify compliance with IEC 1043 either at least once a year in a laboratory making calibrations in accordance with appropriate standards, or at least every two years if an intensity calibrator is used be- fore each sound power determination. Report the re- sults in accordance with 10.5. To check the instrumentation for proper operation prior to eac
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