SIST EN 61672-3:2008
(Main)Electroacoustics - Sound level meters -- Part 3: Periodic tests
Electroacoustics - Sound level meters -- Part 3: Periodic tests
This part of IEC 61672 describes procedures for periodic testing of conventional, integrating-averaging, and integrating sound level meters conforming to the class 1 or class 2 requirements of IEC 61672-1:2002. The aim of the standard is to ensure that periodic testing is performed in a consistent manner by all testing laboratories. The purpose of periodic testing is to assure the user that the performance of a sound level meter conforms to the requirements of IEC 61672-1:2002 for a limited set of key tests and for the environmental conditions under which the tests were performed. The extent of the tests in this part of IEC 61672 is deliberately restricted to the minimum considered necessary for periodic tests. Periodic tests described in this part of IEC 61672 apply to sound level meters for which the model has been, or has not been, pattern approved by an independent testing organization responsible for pattern approvals and in accordance with the test procedures of IEC 61672-2:2003. Periodic tests described in this part of IEC 61672 also apply to sound level meters for which the manufacturer claims conformance to the requirements of IEC 61672-1. Because of the limited extent of the periodic tests, if evidence of pattern approval is not publicly available no general conclusion about conformance to the requirements of IEC 61672-1:2002 can be made, even if the results of the periodic tests conform to all applicable requirements of this part of IEC 61672.
Elektroakustik - Schallpegelmesser - Teil 3: Periodische Einzelprüfung
Electroacoustique - Sonomètres -- Partie 3: Essais périodiques
Décrit les procédures des essais périodiques des sonomètres conventionnels, des sonomètres intégrateurs-moyenneurs et des sonomètres intégrateurs conformes à la classe 1 ou à la classe 2 des exigences de la CEI 61672-1:2002. L'objet de la présente norme est d'assurer que les essais périodiques sont effectués de manière cohérente par tous les laboratoires. Le but des essais périodiques est d'assurer l'utilisateur que la performance d'un sonomètre est conforme aux exigences de la CEI 61672-1:2002 pour un nombre limité d'essais clé et pour les conditions d'environnement dans lesquelles ces essais ont été réalisés. Dans la présente partie de la CEI 61672, l'étendue des essais est volontairement restreint au minimum considéré comme nécessaire pour des essais périodiques. Les essais périodiques décrits dans la présente partie de la CEI 61672 s'appliquent aux sonomètres dont le modèle a été ou n'a pas été approuvé par un organisme d'essai indépendant, responsable des approbations de modèles, et conformément aux procédures d'essai de la CEI 61672-2:2003. Les essais périodiques décrits dans la présente partie de la CEI 61672 s'appliquent aussi aux sonomètres pour lesquels la conformité aux exigences de la CEI 61672-1 a été déclarée par le fabricant. Du fait de l'étendue limitée des essais périodiques, si la confirmation de l'approbation du modèle n'est pas disponible publiquement, il ne doit pas en être tiré de conclusion quant à la conformité aux exigences de la CEI 61672-1:2002, même si les résultats des essais périodiques répondent à toutes les exigences applicables de la présente partie de la CEI 61672.
Elektroakustika – Merilniki zvočne jakosti - 3. del: Redno preskušanje (IEC 61672-3:2006)
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Standards Content (Sample)
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.Electroacoustics - Sound level meters - Part 3: Periodic tests (IEC 61672-3:2006)Electroacoustique - Sonometres - Partie 3: Essais périodiques (IEC 61672-3:2006)Elektroakustik - Schallpegelmesser - Teil 3: Periodische Einzelprüfung (IEC 61672-3:2006)Ta slovenski standard je istoveten z:EN 61672-3:2006SIST EN 61672-3:2008en17.140.50ICS:SLOVENSKI
STANDARDSIST EN 61672-3:200801-februar-2008
EUROPEAN STANDARD EN 61672-3 NORME EUROPÉENNE
EUROPÄISCHE NORM December 2006
CENELEC European Committee for Electrotechnical Standardization Comité Européen de Normalisation Electrotechnique Europäisches Komitee für Elektrotechnische Normung
Central Secretariat: rue de Stassart 35, B - 1050 Brussels
© 2006 CENELEC -
All rights of exploitation in any form and by any means reserved worldwide for CENELEC members.
Ref. No. EN 61672-3:2006 E
ICS 17.140.50
English version
Electroacoustics -
Sound level meters
Part 3: Periodic tests (IEC 61672-3:2006)
Electroacoustique -
Sonomètres
Partie 3: Essais périodiques (CEI 61672-3:2006)
Elektroakustik -
Schallpegelmesser
Teil 3: Periodische Einzelprüfung (IEC 61672-3:2006)
This European Standard was approved by CENELEC on 2006-11-01. CENELEC members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European Standard the status of a national standard without any alteration.
Up-to-date lists and bibliographical references concerning such national standards may be obtained on application to the Central Secretariat or to any CENELEC member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by translation under the responsibility of a CENELEC member into its own language and notified to the Central Secretariat has the same status as the official versions.
CENELEC members are the national electrotechnical committees of Austria, Belgium, Cyprus, the Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, the Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland and the United Kingdom.
EN 61672-3:2006 - 2 -
Foreword The text of document 29/607/FDIS, future edition 1 of IEC 61672-3, prepared by IEC TC 29, Electroacoustics, in cooperation with the International Organization of Legal Metrology (OIML), was submitted to the IEC-CENELEC parallel vote and was approved by CENELEC as EN 61672-3 on 2006-11-01. The following dates were fixed: – latest date by which the EN has to be implemented
at national level by publication of an identical
national standard or by endorsement
(dop)
2007-08-01 – latest date by which the national standards conflicting
with the EN have to be withdrawn
(dow)
2009-11-01 Annex ZA has been added by CENELEC. __________ Endorsement notice The text of the International Standard IEC 61672-3:2006 was approved by CENELEC as a European Standard without any modification. __________
- 3 - EN 61672-3:2006
Annex ZA
Normative references to international publications with their corresponding European publications
The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
NOTE
When an international publication has been modified by common modifications, indicated by (mod), the relevant EN/HD applies.
Publication Year Title EN/HD Year
IEC 60942 -1) Electroacoustics - Sound calibrators EN 60942 20032)
IEC 61094-6 -1) Measurement microphones
Part 6: Electrostatic actuators for determination of frequency response EN 61094-6 20052)
IEC 61672-1 2002 Electroacoustics - Sound level meters
Part 1: Specifications EN 61672-1 2003
IEC 61672-2 2003 Electroacoustics - Sound level meters
Part 2: Pattern evaluation tests EN 61672-2 2003
BIPM, IEC, IFCC, ISO, IUPAC, IUPAP and OIML 1995 Guide to the expression of uncertainty in measurement (GUM) - -
BIPM, IEC, IFCC, ISO, IUPAC, IUPAP and OIML 1993 International vocabulary of basic and general terms in metrology (VIM) - -
1) Undated reference. 2) Valid edition at date of issue.
NORME INTERNATIONALECEIIEC INTERNATIONAL STANDARD 61672-3Première éditionFirst edition2006-10 Électroacoustique –
Sonomètres – Partie 3: Essais périodiques
Electroacoustics –
Sound level meters – Part 3: Periodic tests Pour prix, voir catalogue en vigueur For price, see current catalogue© IEC 2006
Droits de reproduction réservés
⎯
Copyright - all rights reserved Aucune partie de cette publication ne peut être reproduite ni utilisée sous quelque forme que ce soit et par aucun procédé, électronique ou mécanique, y compris la photocopie et les microfilms, sans l'accord écrit de l'éditeur. 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 Electrotechnical Commission,
3, rue de Varembé, PO Box 131, CH-1211 Geneva 20, SwitzerlandTelephone: +41 22 919 02 11 Telefax: +41 22 919 03 00 E-mail: inmail@iec.ch
Web: www.iec.ch CODE PRIX PRICE CODE Q Commission Electrotechnique InternationaleInternational Electrotechnical Commission
61672-3 © IEC:2006 – 3 –
CONTENTS
FOREWORD.5
1 Scope.9 2 Normative references.9 3 Submission for testing.11 4 Conformance.13 5 Preliminary inspection.13 6 Power supply.15 7 Environmental conditions.15 8 General test requirements.15 9 Indication at the calibration check frequency.15 10 Self-generated noise.17 11 Acoustical signal tests of a frequency weighting.19 12 Electrical signal tests of frequency weightings.23 13 Frequency and time weightings at 1 kHz.25 14 Level linearity on the reference level range.25 15 Level linearity including the level range control.27 16 Toneburst response.27 17 Peak C sound level.29 18 Overload indication.31 19 Documentation.31
61672-3 © IEC:2006 – 5 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION ___________
ELECTROACOUSTICS – SOUND LEVEL METERS –
Part 3: Periodic tests
FOREWORD 1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising all national electrotechnical committees (IEC National Committees). The object of IEC is to promote international co-operation on all questions concerning standardization in the electrical and electronic fields. To this end and in addition to other activities, IEC publishes International Standards, Technical Specifications, Technical Reports, Publicly Available Specifications (PAS) and Guides (hereafter referred to as “IEC Publication(s)”). Their preparation is entrusted to technical committees; any IEC National Committee interested in the subject dealt with may participate in this preparatory work. International, governmental and non-governmental organizations liaising with the IEC also participate in this preparation. IEC collaborates closely with the International Organization for Standardization (ISO) in accordance with conditions determined by agreement between the two organizations. 2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international consensus of opinion on the relevant subjects since each technical committee has representation from all interested IEC National Committees.
3) IEC Publications have the form of recommendations for international use and are accepted by IEC National Committees in that sense. While all reasonable efforts are made to ensure that the technical content of IEC Publications is accurate, IEC cannot be held responsible for the way in which they are used or for any misinterpretation by any end user. 4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications transparently to the maximum extent possible in their national and regional publications. Any divergence between any IEC Publication and the corresponding national or regional publication shall be clearly indicated in the latter. 5) IEC provides no marking procedure to indicate its approval and cannot be rendered responsible for any equipment declared to be in conformity with an IEC Publication. 6) All users should ensure that they have the latest edition of this publication. 7) No liability shall attach to IEC or its directors, employees, servants or agents including individual experts and members of its technical committees and IEC National Committees for any personal injury, property damage or other damage of any nature whatsoever, whether direct or indirect, or for costs (including legal fees) and expenses arising out of the publication, use of, or reliance upon, this IEC Publication or any other IEC Publications.
8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is indispensable for the correct application of this publication. 9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of patent rights. IEC shall not be held responsible for identifying any or all such patent rights. International Standard IEC 61672-3 has been prepared by IEC technical committee 29: Electroacoustics, in cooperation with the International Organization of Legal Metrology (OIML).
The text of this part of IEC 61672 is based on the following documents: FDIS Rapport de vote 29/607/FDIS 29/614/RVD Full information on the voting for the approval of this part of IEC 61672 can be found in the report on voting indicated in the above table. This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.
61672-3 © IEC:2006 – 7 –
At the time of publication of this standard, the IEC 61672 series was scheduled to consist at least of the following parts under the general title Electroacoustics – Sound level meters:
Part 1: Specifications Part 2: Pattern evaluation tests,
Part 3: Periodic tests. The committee has decided that the contents of this publication will remain unchanged until the maintenance result date indicated on the IEC web site under "http://webstore.iec.ch" in the data related to the specific publication. At this date, the publication will be
• reconfirmed; • withdrawn; • replaced by a revised edition, or • amended.
61672-3 © IEC:2006 – 9 –
ELECTROACOUSTICS – SOUND LEVEL METERS –
Part 3: Periodic tests
1 Scope 1.1 This part of IEC 61672 describes procedures for periodic testing of conventional, integrating-averaging, and integrating sound level meters conforming to the class 1 or class 2 requirements of IEC 61672-1:2002. The aim of the standard is to ensure that periodic testing is performed in a consistent manner by all testing laboratories.
1.2 The purpose of periodic testing is to assure the user that the performance of a sound level meter conforms to the requirements of IEC 61672-1:2002 for a limited set of key tests and for the environmental conditions under which the tests were performed.
1.3 The extent of the tests in this part of IEC 61672 is deliberately restricted to the minimum considered necessary for periodic tests.
1.4 Periodic tests described in this part of IEC 61672 apply to sound level meters for which the model has been, or has not been, pattern approved by an independent testing organization responsible for pattern approvals and in accordance with the test procedures of IEC 61672-2:2003. Periodic tests described in this part of IEC 61672 also apply to sound level meters for which the manufacturer claims conformance to the requirements of IEC 61672-1. Because of the limited extent of the periodic tests, if evidence of pattern approval is not publicly available no general conclusion about conformance to the requirements of IEC 61672-1:2002 can be made, even if the results of the periodic tests conform to all applicable requirements of this part of IEC 61672. 2 Normative references The following referenced documents are indispensable for application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
IEC 60942, Electroacoustics – Sound calibrators IEC 61094-6, Measurement microphones – Part 6: Electrostatic actuators for determination of frequency response IEC 61672-1:2002, Electroacoustics – Sound level meters – Part 1: Specifications IEC 61672-2:2003, Electroacoustics – Sound level meters – Part 2: Pattern evaluation tests BIPM, IEC, IFCC, ISO, IUPAC, IUPAP and OIML:1995, Guide to the expression of uncertainty in measurement (GUM) BIPM, IEC, IFCC, ISO, IUPAC, IUPAP and OIML:1993, International vocabulary of basic and general terms in metrology. ISBN 92-67-01075-1
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3 Submission for testing 3.1 An instruction manual applicable to the model and version of the sound level meter shall be available in order to perform periodic tests for a sound level meter. If an applicable instruction manual is not submitted along with the sound level meter, nor available at the testing laboratory nor publicly accessible from the Internet web site of the manufacturer or supplier of the sound level meter, then no periodic tests shall be performed. 3.2 The source for the instruction manual shall be described in the documentation for the periodic tests.
3.3 All items or accessories with which the sound level meter is required to be tested shall accompany the sound level meter that is submitted for testing. A device specified in the instruction manual for inserting electrical signals equivalent to signals from the microphone shall also be submitted if requested by the testing laboratory. 3.4 Periodic tests as described in this part of IEC 61672 shall not be performed unless the markings on the sound level meter are as required by IEC 61672-1:2002 or there is evidence that the sound level meter was originally so marked. At least the model designation and serial number shall be visible on the sound level meter. 3.5 Data required to perform the periodic tests shall be available and the source of the data shall be recorded by the laboratory. The data shall include all relevant information required by Clause 9 of IEC 61672-1:2002. 3.6 A sound calibrator shall be available. The sound calibrator shall be supplied with the sound level meter, if required by the user or if requested by the testing laboratory, or shall be supplied by the testing laboratory itself. If a sound calibrator is supplied by the user, it shall be used by the testing laboratory to establish the acoustical sensitivity of the sound level meter.
3.7 The sound calibrator shall either be a model specified in the instruction manual for use with the sound level meter, or a sound calibrator producing the same nominal sound pressure level and frequency as a model specified in the instruction manual. In this latter case, any adjustments to be applied when that model of calibrator is coupled to the model of microphone supplied on the sound level meter shall be known and agreed by the manufacturer of the sound level meter. 3.8 An instruction manual for the sound calibrator also shall be available. If an appropriate sound calibrator and its instruction manual are not available, no periodic tests shall be performed. 3.9 For periodic testing of a class 1 sound level meter, the sound calibrator shall be shown by calibration to conform to the requirements of IEC 60942 within class 1 tolerance limits. For periodic testing of a class 2 sound level meter, the sound calibrator shall be shown by calibration to conform to the requirements of IEC 60942 within class 1 or class 2 tolerance limits. Conformance shall be demonstrated for sound pressure level, frequency, and total distortion using the methods given in IEC 60942 for periodic testing.
NOTE Evidence that the sound calibrator conforms to the applicable requirements of IEC 60942 may be provided by documentation from a periodic test performed in accordance with the procedures given in IEC 60942. If such evidence is not available, the testing laboratory may offer to perform a calibration for the sound calibrator. The uncertainty of measurement associated with use of the sound calibrator may increase with the time that has elapsed since the last calibration of the sound calibrator.
61672-3 © IEC:2006 – 13 –
3.10 Calibration of the sound calibrator shall be performed using equipment with calibrations for the appropriate quantities traceable to national standards. The calibration of the sound calibrator shall use the model of microphone supplied with the sound level meter, or an equivalent model of microphone, or a suitable microphone and correction data appropriate to the model of microphone supplied with the sound level meter. Where correction data are used, the source of the data shall be the manufacturer of the sound calibrator, microphone, or sound level meter, and shall be stated. A calibration certificate for the sound calibrator showing the results of the calibration shall be supplied.
4 Conformance 4.1 Conformance to the requirements of this part of IEC 61672 is demonstrated when the measured deviations from the corresponding design goals given in IEC 61672-1:2002, extended by the actual expanded uncertainties of measurement of the testing laboratory, do not exceed the applicable tolerance limits given in IEC 61672-1:2002.
4.2 The testing laboratory shall use instruments that have been calibrated for the appropriate quantities at appropriate intervals. As required, the calibrations shall be traceable to national standards.
4.3 Laboratories performing periodic tests shall calculate the uncertainties associated with all measurements in accordance with the Guide to the expression of uncertainty in measurement. Metrological terms shall be as defined in the International vocabulary of basic and general terms in metrology. Actual expanded uncertainties shall be calculated for a level of confidence of 95 %, using the necessary coverage factor.
NOTE 1 When a testing laboratory is only required to make only a single measurement, it is necessary for the laboratory to make an estimate of the contribution of random effects to the total uncertainty. The estimate should be determined from an evaluation of several measurement results previously obtained for a similar sound level meter. NOTE 2 Generally, a coverage factor of 2 approximates to a level of confidence of 95 %, unless the contributions are such that it is necessary to use a different coverage factor to maintain the 95 % level of confidence. NOTE 3 Calculation of the expanded uncertainty of measurement for a particular test should consider at least five components, as applicable. The first component is the uncertainty attributed to calibration of the individual instruments and equipment used to perform the test, including the sound calibrator noted in 3.6 and any free-field facility used. The second component is any contribution resulting from environmental effects or adjustments. The third component is any contribution resulting from small errors that may be present in the applied signals. The fourth component is any contribution to the uncertainty attributed to effects associated with the repeatability of the results of the measurements. The fifth component is an uncertainty contribution for reading the indication from the display device of the sound level meter under test. For digital display devices that indicate signal levels with a resolution of 0,1 dB, the uncertainty component should be taken as a rectangular distribution with semi-range of 0,05 dB. 4.4 For any test, the actual expanded uncertainty of measurement of the laboratory shall not exceed the corresponding maximum expanded uncertainty given in Annex A of IEC 61672-1:2002. If an actual expanded uncertainty of measurement for a test performed by the testing laboratory exceeds the corresponding maximum expanded uncertainty, the result of the test shall not be used to determine conformance to this part of IEC 61672 for periodic testing.
5 Preliminary inspection Prior to any measurements, the sound level meter and all accessories shall be visually inspected, paying particular attention to damage to, or accumulation of foreign material on, the protection grid or diaphragm of the microphone. All relevant controls shall be operated to ensure that they are in working order. If the controls, display, and other essential elements are not in proper working order, no periodic tests shall be performed.
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6 Power supply For all tests, the sound level meter shall be powered from its preferred supply or a suitable alternative if requested by the user. Before and after conducting the set of tests with acoustical signals and before and after conducting the set of tests with electrical signals, the voltage delivered by the power supply for the sound level meter shall be checked by the method stated in the instruction manual to ensure that it is within the specified operating limits. If the voltage is not within the operating limits and the reason cannot be attributed to partially discharged batteries or an incorrect selection of the voltage of the public power supply, then no periodic tests shall be performed as a malfunction is indicated.
7 Environmental conditions 7.1 Periodic tests shall be performed within the following ranges of environmental conditions: 80 kPa to 105 kPa for static air pressure, 20 °C to 26 °C for air temperature and 25 % to 70 % for relative humidity.
7.2 As a minimum, the static air pressure, air temperature and relative humidity shall be measured and recorded at the start and end of the testing.
8 General test requirements 8.1 Periodic tests described in subsequent clauses apply only for those design features that are required by IEC 61672-1:2002 and that are available in the sound level meter submitted for test. All such features shall be tested. 8.2 Electrical signals shall be inserted into the sound level meter through the input device or by the means specified in the instruction manual. The frequency of the input signals shall not exceed ±0,25 % of the specified frequency. 8.3 For a sound level meter that has an electrical output that is to be used for the periodic tests, the indications obtained from the electrical output and the corresponding indications on the display device of the sound level meter shall be confirmed to be identical within the tolerance limits given in 5.16.3 of IEC 61672-1:2002. Where multiple outputs are present, if an output is specified in the instruction manual for testing, this output shall be used for periodic testing.
9 Indication at the calibration check frequency 9.1 The indication of the sound level meter at the calibration check frequency shall be checked by application of the calibrated sound calibrator noted in 3.6 and adjusted, if necessary, to indicate the required sound pressure level for the environmental conditions under which the tests are performed. For multi-channel sound level meter systems, the indication shall be checked for as many of the channels as are required to be tested. The indications of the sound level meter before and after adjustment shall be recorded. The adjustment shall use the procedure given in the instruction manual for the sound level meter to account for the effect of a windscreen or other accessory submitted for test with the sound level meter.
NOTE When the sound calibrator is supplied with the sound level meter, but is not to be calibrated by the laboratory performing the test of the sound level meter, an additional independent measurement is recommended using a suitable sound calibrator provided by the testing laboratory. The latter sound calibrator should be applied to the sound level meter following any adjustment from 9.1 and the indication noted, without any further adjustment. This indication provides a consistency check of the indication obtained in 9.1, and is important to ensure that the sound pressure level generated by the sound calibrator has not changed significantly since its latest calibration. When the indications appear to be inconsistent, the testing laboratory should perform further investigations to determine the reasons for the inconsistency. Unless the reasons for the inconsistency can be satisfactorily resolved, no further measurements should be performed.
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9.2 The effect of the prevailing environmental conditions on the sound pressure level produced in the coupler of the sound calibrator, relative to the sound pressure level produced under the reference environmental conditions of IEC 61672-1:2002, shall be accounted for in accordance with the procedure from the instruction manual for the sound calibrator and data from its calibration. 10 Self-generated noise 10.1 Microphone installed 10.1.1 Self-generated noise shall be measured with the microphone installed on the sound level meter. The sound level meter shall be in the configuration submitted for periodic testing, but with any supplied windscreen installed as appropriate, and with the most-sensitive level range and frequency weighting A selected. The results of the measurements of self-generated noise shall be recorded.
10.1.2 The level of the A-weighted ambient sound at the microphone of the sound level meter shall not exceed the highest anticipated level of the A-weighted self-generated noise stated in the instruction manual for the configuration of the sound level meter submitted for periodic testing.
NOTE If the level of ambient sounds in the laboratory is not sufficiently low, a tightly sealed enclosure, lined with sound-absorbing material, may be constructed, into which the sound level meter is placed, with suitable leads for a.c. power, if required. The enclosure should have an appropriate device by which the display device can be observed. For sound level meters that have a detachable microphone and pre-amplifier, only the microphone and pre-amplifier need to be placed in the enclosure and connected to the sound level meter by an extension cable. 10.1.3 The indication of time-average A-weighted sound level averaged over 30 s, or longer if so required by the instruction manual for measurements of the level of self-generated noise, shall be recorded. Time-average sound level may be measured directly or calculated from an indication of sound exposure level and integration time. If time-average sound level cannot be determined, the time-weighted sound level from the average of 10 observations taken at random over a 60 s interval shall be recorded. If the time-weighted sound level is recorded, the S time weighting shall be used if available; otherwise the F time weighting shall be used. 10.1.4 If the measured level of the A-weighted self-generated noise does not exceed the highest anticipated level of A-weighted self-generated noise, this by itself verifies that the level of ambient sound was sufficiently low. If the measured level of the A-weighted self-generated noise exceeds the highest anticipated level of A-weighted self-generated noise stated in the instruction manual for the tested configuration of the sound level meter, the testing laboratory shall determine and record evidence that the ambient sound did not influence the measurement of self-generated noise by more than 3 dB.
NOTE 1 The influence of low-frequency sounds on indications of the level of A-weighted self-generated noise should not be underestimated. NOTE 2 Measurements of the A-weighted level of the ambient sound may require use of a separate microphone and associated equipment designed to measure low sound levels. 10.2 Microphone replaced by the electrical input signal device With the microphone replaced by the electrical input signal device (or the specified means of inserting electrical signals), and terminated in the manner specified in the i
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