This standard specifies the measurement method of the emitted sound pressure level at the working position and other designated positions near the machine equipment in the approximately free field above a reflecting surface. The working position is the position where the operator is located. It can be located in the open space in the room where the sound source is working, or in the operating room fixedly connected to the sound source, or in a closed space far away from the sound source. The designated position can be located near the working position or near the unattended machine. When some of the positions are occupied occasionally or at regular time intervals, these positions can be used as bystander positions. The emitted sound pressure level is measured with A weighting, and the C weighted peak sound pressure level and band sound pressure level can be measured if necessary. GB/T 17248.2-1999 Acoustics Noise emitted by machines and equipment Measurement of emitted sound pressure level at the working position and other designated positions Engineering method for approximately free field above a reflecting surface GB/T17248.2-1999 Standard download decompression password: www.bzxz.net
This standard specifies the measurement method of the emitted sound pressure level at the working position and other designated positions near the machine equipment in the approximately free field above a reflecting surface. The work position is the position where the operator is located. It can be located in an open space indoors where the sound source is working, in an operating room fixedly connected to the sound source, or in a closed space far away from the sound source. The designated position can be located near the work position, or near an unattended machine. When some of the positions are occupied occasionally or at regular time intervals, these positions can be used as bystander positions. The emission sound pressure level is measured with A weighting, and the C weighted peak sound pressure level and band sound pressure level can be measured if necessary.

GB/T17248.2-1999
This standard is equivalent to the international standard ISO11201:1995 "Measurement of sound pressure level of noise emitted by acoustic machines and equipment at work and other designated positions - Engineering method for approximate free field above a reflecting surface". This standard is the second standard in the GB/T17248.1~GB/T17248.5 series of standards, which include: GB/T17248.1 Guidelines for the use of basic standards for determining sound pressure level of noise emitted by acoustic machines and equipment at work and other designated positions
GB/T17248.2 Measurement of sound pressure level of noise emitted by acoustic machines and equipment at work and other designated positions - Engineering method for approximate free field above a reflecting surface GB/T17248.3
Measurement of sound pressure level of noise emitted by acoustic machines and equipment at work and other designated positions - On-site simplified method
GB/T 17248. 4
Acoustic Noise emitted by machines and equipment Determination of emission sound pressure level at working position and other designated positions by sound power level
Acoustic Noise emitted by machines and equipment Measurement of emission sound pressure level at working position and other designated positions GB/T17248.5
Environmental correction method
This series of standards specifies various methods for measuring the emission noise of machines and equipment or equipment parts. Appendix A, Appendix B and Appendix C of this standard are all suggestive appendices. This standard is proposed and coordinated by the National Technical Committee for Acoustic Standardization. The drafting units of this standard are: Institute of Acoustics, Chinese Academy of Sciences, Beijing Institute of Labor Protection. The main drafters of this standard are: Lv Yadong, Ren Wentang, Zhang Ruwei. 353
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ISO Foreword
The International Organization for Standardization (ISO) is a worldwide joint organization composed of national standardization committees (ISO member countries). The formulation of international standards is usually completed by ISO technical committees. Each member country has the right to participate in a technical committee when it is interested in a standard determined by a technical committee. International organizations, both governmental and non-governmental, that have ties to ISO may also participate in the work. The International Organization for Standardization (ISO) and the International Electrotechnical Commission (IEC) maintain close cooperation in all aspects of electrotechnical standardization. Draft international standards adopted by technical committees shall be distributed to member countries for voting. Draft international standards require at least 75% of the votes of member countries to be published as international standards. International standard ISO11201:1995 was drafted by ISO/TC43 Acoustics Technical Committee SC1 Noise Subcommittee. The first edition of ISO11201, as a technical revision, cancels and replaces ISO6081:1986. Appendices A, B and C of this standard are indicative and for reference only. 3.
GB/T17248.21999
This standard specifies the method for measuring the emitted sound pressure level at working positions and other specified positions near machinery and equipment in an approximately free field above a reflecting surface. Generally speaking, this sound pressure level is less than or equal to the sound pressure level of the machine when it is operating in a normal environment. This is because this sound pressure level is measured without considering the influence of other reflected sounds besides the background sudden sound and the reflected sound of the reflective surface where the measured machine is located. This standard is one of the standards in the GB/T17248.1~GB/T17248.5 series, which specifies various methods for measuring the noise emission of machines or equipment parts. GB/T17248.1 provides guiding principles for how to choose the specific method for measuring the emitted sound pressure level of machines and equipment, and provides standard details of various methods for measuring sound power levels. 355
National Standard of the People's Republic of China
Acoustics ---Noise emitted by machinery and equipment-Measurement of emission sound pressure levels at a work stationand at other specified positions--Engineering methodin an essentially free field over a reflecting plane1 Scope
1.1 Overview
GB/T 17248.2—1999
eqv ISO 11201:1995
This standard specifies the method for measuring the emission sound pressure levels at work stations and at other specified positions near machinery and equipment in an essentially free field over a reflecting plane. The work station is the position where the operator is located. It can be located in an open space indoors where the sound source is working, in an operating room fixedly connected to the sound source, or in an enclosed space far away from the sound source. The designated positions may be located near the working position or near unattended machinery. When some of the positions are occupied occasionally or at regular intervals, these positions may be used as bystander positions. The emission sound pressure level is measured with A-weighting, and the C-weighted peak sound pressure level and band sound pressure level may be measured if necessary. Note 1: The contents of this standard and related standards are summarized in Table 1 of GB/T17248.1. This standard specifies the requirements for the test environment and instrument accuracy (engineering level). Corrections are made for background noise rather than the acoustic environment. This standard also gives specific instructions for the installation and operation of the machine under test, as well as the selection of microphone effect positions at the working position and other designated positions. The purpose of the measurement is to compare the performance of a given series and different machine equipment units under specified environmental conditions and uniform installation and operating conditions. The data obtained can also be used for the emission sound pressure level noise label marking and verification as specified in GB/T 14574. NOTE 2: At any given location and given installation and operating conditions associated with a particular machine, the emission sound pressure level measured according to the method of this standard is generally lower than the sound pressure level of the same machine measured directly in a typical workplace, due to the effects of reverberation and other machines. For the calculation method of the sound pressure level near a group of machines operating alone in a workplace, see ISO/TR 11690-3. Generally, the difference between the two is 1~5 dB, and in some cases the difference is greater.
1.2 Types of noise and noise sources
The method specified in this standard is applicable to all types of machines, including mobile and fixed, indoor or outdoor machines. This method is applicable to machines of all sizes and all types of noise defined in GB/T14259 and ISO12001. 1.3 Test environment
The type of test environment affects the measurement accuracy of the emission sound pressure level. This standard requires that the test environment is an approximately free field above a reflecting plane (indoor or outdoor).
1.4 Specified positions
This standard applies to working positions and other specified positions where the emission sound pressure level needs to be measured. Some examples of positions where measurements can be made are as follows: Approved by the State Administration of Quality and Technical Supervision on March 8, 1999 356
Implementation on September 1, 1999
GB/T 17248.2—1999
a) A working position near the machine being measured, which is the case for many industrial machines and household appliances; b) A working position in an operating room, which is an integral part of the machine being measured, which is the case for many trucks and earth-moving machinery;
c) A working position in a partially or fully enclosed space (or behind a barrier), which is an integral part of the machine equipment provided by the manufacturer;
d) A working position that is partially or fully enclosed by the machine being measured, which is the case for some large industrial machines; e) A bystander position who is not responsible for operating the machine; f) Other designated positions, not necessarily working positions or bystander positions; working positions may also be located along a designated path for the operator to move. 1.5 Measurement uncertainty
It is impossible to give a widely applicable value for the standard deviation of the reproducibility of the emission sound pressure level at the working position. Guidance is given in Chapter 4 of this standard.
2 Referenced standards
The provisions contained in the following standards constitute the provisions of this standard through reference in this standard. When this standard was published, the versions shown were valid. All standards will be revised, and parties using this standard should explore the possibility of using the latest version of the following standards. GB/T3102.7—1993 Acoustic quantities and units GB/T 3222--1994 Methods of measurement of environmental noise GB/T 3241—1998 Octave and fractional octave filters (egvIEC1260:1995) GB/T 3767—1996 Acoustics—Determination of the sound power level of a noise source by the sound pressure method—Engineering method for approximating the free field above a reflecting surface (eqvISO 3744:1994) GB/T 3768-1996 Acoustics—Determination of the sound power level of a noise source by the sound pressure method—Simplified method using an envelope measuring surface above a reflecting surface (eqvISO 3746:1995) GB/T 3785—1983 GB/T 3947-—1996 GB/T 6882--1986
Electrical and acoustic properties and test methods of sound level meters. Acoustic terminology
Determination of sound power level of noise sources - Precision method for anechoic and semi-anechoic chambers (neqISO3745: Acoustics
GB/T14259--1993 Acoustics - Guide to standards for the measurement of airborne noise and the assessment of its effects on people (neqISO2204:1979)
GB/T 14574--1993J
Acoustics - Noise labels for machines and equipment (neqISO4871:1984) GB/T 15173--1994J
Sound calibrator (eqvIEC1014:1989)
GB/T 17181—1997
Integrating average sound level meter (idtIEC804:1985) GB/T17248.11) Acoustic machines and equipment Determination of noise emitted by work and other designated positions Emission sound pressure level Guide for the use of basic standards eqvISO11200:1995) GB/T17248.3-1999 Acoustic machines and equipment Noise emitted by work and other designated positions Emission sound pressure level measurement field simplified method (eqvISO11202:1995) GB/T17248.4-1998 Acoustic machines and equipment Noise emitted by work and other designated positions determined by sound power level GB/T 17248.5—1999
Emission sound pressure level of working position and other specified position (eqvISO11203:1995) 9 Noise emitted by machines and equipment Measurement of emission sound pressure level at working position and other specified position - Environmental correction method (eqvISO11204:1995) ISO4871:1996 Acoustics
1) This standard will be published.
Nominalization and verification of noise emission values ​​for machines and equipment 357
ISO 7779:1988 Acoustics
GB/T 17248.2---1999
Measurement of airborne sound emitted by computers and business equipment ISO/TR11690-3:1997 Acoustics — Recommended practices for the design of low-noise workplaces containing machines — Part 3: Sound propagation and noise prediction in workplaces
ISO12001:1996 Acoustics
3 Definitions
Noise emitted by machines and equipment —
—Drafting of noise test procedures and criteria for their presentation This standard adopts the following definitions. Other acoustic terms, quantities and units shall be in accordance with the provisions of GB/T3947 and GB/T3102.7. 3.1 Emission
Airborne sound radiated by a determined sound source (the machine under test). Note 3: The noise emission characterization quantity can be included in the product label or product manual. The basic noise emission characterization quantity is the sound power level of the sound source and the emission sound pressure level at the working position near the sound source and other specified positions (if any). 3.2 Emission sound pressure (p) emission sound pressure The sound pressure at a specified position near the sound source working under the specified installation and operating conditions on a reflecting plane. It does not include the background noise and the influence of other sound reflections outside the reflecting surface allowed by this test method, unit Pa. 3.3 Emission sound pressure level (L,) emission sound pressure level The logarithm of the ratio of the square of the emission sound pressure force 2(t) to the square of the reference sound pressure multiplied by 10. It is measured using the time weighting and frequency weighting specified in GB 3785, unit dB. The reference sound pressure is 20 μPa. p2(t) represents the change of the square of the effective value of the sound pressure over time. Note 4: For example: F time-weighted maximum A-weighted emission sound pressure level LpAFmx, C-weighted peak emission sound pressure level LsC,peak. The emission sound pressure level shall be measured at the specified position, which shall comply with the test procedures of the machine series; if there is no corresponding test procedure, the method used shall comply with the provisions of the GB/T17248 series of standards. 3.3.1 Time-averaged emission sound pressure level (Lpeq) time-averaged emission's sound pressure level Within the measurement time T, the mean square sound pressure of a noise signal that varies with time is equal to the square of the sound pressure of the continuous steady-state sound within the same time, then the sound pressure level of the continuous steady-state sound is the time-averaged emission sound pressure level, unit dB. Expressed by formula (1): dt
Lrar = 10lg Ning]. %
A weighted time-averaged emission sound pressure level is expressed as LpAegT, which can be abbreviated as LpA. Its measuring instrument shall comply with the requirements of GB/T 17181. Note 5: In general, since the time-averaged emission sound pressure level must be measured within a certain measurement time, the subscripts eq and T can be omitted. Note 6: Formula (1) is similar to the expression of "equivalent (continuous) sound pressure level" for the environmental noise characterization quantity defined in GB/T 3222. However, the emission quantity defined in this standard is used to characterize the noise emission of the machine under test, and is measured using standard measurement and operating conditions and a limited acoustic environment. 3.3.2 Peak emission sound pressure level (Lppeak) Peak emission sound pressure level The maximum transient value of the emission sound pressure level measured within an operating cycle, in dB. 3.3.3 Single-event emission sound pressure level (Lp,) Single-event emission sound pressure level The time-integrated emission sound pressure level of a single isolated acoustic event within the specified measurement time T (normalized to T as T.-1 s), in dB. Expressed by formula (2):
rp(t)dt
Lp=10lg.
=Lrar+10lg .
Note 7: The above formula is the same as the expression of the similar environmental noise description quantity "exposure level". However, the emission quantity defined in this standard is used to characterize the characteristics of the noise source and assumes that a limited acoustic environment is used for measurement. 3.4 Impulsive noise index (impulsiveness) This index is used to characterize the impulse characteristics of the noise emitted by the sound source (see Appendix A), unit: dB. 3.5 Free field over a reflecting plane The sound field in an isotropic homogeneous medium in the half space above the infinite, hard plane where the machine under test is located. 358
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3.6 Work station, operator's position The position near the machine under test, designated for the operator. 3.7 Operator operatorwwW.bzxz.Net
A person engaged in work tasks related to the machine near the machine under test. 3.8 Specified position specified position The position related to the machine, including but not limited to the operator's position. The position can be a single fixed point, or a number of points on a path, or a number of points on a surface at a specified distance from the machine. If there is a relevant test procedure, it shall be stated in it. Note 8: A specified position near the working position or near an unattended machine can be regarded as a "bystander position". 3.9 Operational period The time interval for the tested machine to complete a specified process (such as: the time required for a dishwasher to complete washing or rinsing or drying). 3.10 Operational cycle The time required for the tested machine to complete a working cycle, in which the various operating periods appear in a specified sequence, and each operating period is associated with a specific process, which may appear only once in an operating cycle, or it may be repeated multiple times (such as: the process of a dishwasher from washing to rinsing to drying).
3.11 measurement time interval part or multiple of an operating period or operating cycle. During this period, the emission sound pressure level is measured or the maximum emission sound pressure level is obtained. 3.12 time history
a continuous record of the emission sound pressure level as a function of time is obtained in one or more operating periods of the operating cycle. 3.13 background noise background noise all sound sources other than the measured machine. Note 9: Background noise should include air noise, structure-borne noise and instrument electrical noise. 3.14 background noise level background noise level the sound pressure level measured when the measured machine is not working, in dB. 3.15 background noise correction (K,) background noise correction This correction value is used to indicate the influence of background noise on the emission sound pressure level at a specified position of the measured machine, K, is related to the frequency, in dB. The correction term K1A in the A-weighted case is obtained from the A-weighted measurement value. 3.16 Environmental correction value (K,) environmental indicator This correction value is used to indicate the influence of sound reflection or sound absorption on the surface sound pressure level. K is related to frequency and is expressed in dB. In the case of A weighting, it is expressed as K2A (see GB/T3767, GB/T3768). 4 Measurement uncertainty
The single value of the emission sound pressure level of the noise source measured by the method specified in this standard may be different from the true value of the corresponding quantity at a fixed position within the measurement uncertainty range. The measurement uncertainty of the emission sound pressure level is caused by several factors that affect its results, one part of which is related to the test environment conditions and the other part is related to the test technology. The measurement uncertainty depends on the standard deviation of reproducibility and the expected confidence. In order to determine the standard deviation of the reproducibility of the emission sound pressure level at each position, a large amount of measurement data must be obtained, and for many different types of machines and equipment to which this standard applies, the range of standard deviation may be large, so it is impossible to provide widely applicable data. Here, only the relevant data of individual types of noise sources are provided as a reference for noise test procedures.
Since the measurement is carried out under limited environmental conditions, the engineering method level described in this standard is higher than the simplified method level introduced in GB/T17248.3.
For this standard engineering method, it is expected that the reproducibility standard deviation of the A-weighted emission sound pressure level of the noise source with a relatively flat noise spectrum in the frequency range of 10010000Hz is less than or equal to 2.5dB (here, the influence of changes in operating and installation conditions is not included).
GB/T 17248.2—1999
The reproducibility standard deviation given above is the maximum value, but for a certain machine series, this value is smaller. For example: for a series of woodworking machine tools, the reproducibility standard deviation is equal to 1.0dB. Note 10: If the measured machine has strong directivity or its noise spectrum contains pure tone components, the measurement uncertainty will be larger. The possibility of this situation can be reduced by making the environmental correction value (see 6.2) less than 0.5dB. 5 Measuring instruments
The instrument system including microphone and cable shall meet the requirements of type 1 sound level meter specified in GB/T3785; when using an integrating average sound level meter, it shall meet the requirements of type 1 integrating average sound level meter specified in GB/T17181. For octave and 1/3 octave measurements, the filters used shall meet the requirements of GB/T3241. Before and after each measurement, the microphone shall be calibrated with an acoustic calibrator with an accuracy better than ±0.3dB (class 1 accuracy specified in GB/T15173) to calibrate the entire measurement system at one or more frequencies within the test frequency range. The acoustic calibrator shall be calibrated once a year in accordance with the requirements of GB/T15173. The instrument system shall be calibrated at least once every two years in accordance with the requirements of GB/T3785 (or GB/T17181 when using an integrating average system). The date of the last calibration in accordance with national standards shall be recorded. 6 Test environment
6.1 Specified location in free space near the machine under test The test environment suitable for the measurement of this standard is a flat outdoor area or indoor space that can provide a near free field condition above a reflecting plane.
A semi-anechoic chamber (see GB/T6882) or a flat outdoor area paved with asphalt or concrete that meets the requirements of 6.4 and 6.5 meets the measurement purpose and requirements of this standard. In addition, other test environments that meet the requirements of 6.2, 6.4 and 6.5 can also be used without environmental correction. 6.2 Criteria for test environment applicability
The ideal test environment should have no reflective objects other than a reflecting surface. In this way, the noise from the machine can be radiated into the free field above a reflecting plane. Appendix A of GB/T3767-1996 gives a method for determining the environmental correction value K2, K, which is used to characterize the degree to which the test environment deviates from the ideal condition. For this standard, the environmental correction value K2A of the measurement surface surrounding the measurement position should not exceed 2dB. Note 11: If the measurement must be carried out in a space where K2A exceeds 2 dB, GB/T17248.3 or GB/T17248.5 standards may be used. 6.3 Enclosed working position
When the operator is located in a closed operating room or an enclosed space away from the machine under test, since the operating room or enclosed space is an integral part of the machine under test. Therefore, the sound reflection in the operating room or enclosed space is considered to have an impact on the emission sound pressure level, and environmental correction is not allowed.
In the noise emission measurement, the doors and windows of the operating room or enclosed space should be opened or closed in accordance with the relevant provisions of the noise test procedures for the machine equipment.
If the machine's working position or bystander position is in the operating room or workshop (for maintenance), the noise test procedures should specify an additional "customary" working position or bystander position outside the operating room or workshop of the machine under test. 6.4 Background noise correction criteria
At the microphone position, the background noise measured as the weighted sound pressure level or in each measurement frequency band (including wind noise at the microphone) should be at least 6 dB lower than the machine level or frequency band level under test (preferably lower than 15 dB). The background noise correction value is given by formula (3): K, = - 10lg(1 - 10-0.14)
where: △L is the difference in sound pressure level measured at a specified position when the machine under test is turned on and off. For this standard, if AL>15dB, K,=0 is specified. If △L<6dB (i.e. KiA>1.3dB), the measurement is invalid according to this standard.
KI should be determined for each microphone position. 360
6.5 Environmental conditions during measurement
GB/T17248.2—1999
Environmental conditions may have an adverse effect on the microphone used for measurement. The microphone and its position should be properly selected to avoid the influence of strong electric and magnetic fields, strong winds, high and low temperatures, exhaust shock of the machine under test, etc. 7 Test quantities
The basic test quantities at each specified position during the specified operating period or operating cycle of the machine under test are: - A-weighted sound pressure level L'pA (withdrawal indicates measured value) C-weighted peak sound pressure level Ixneak
Note 12 According to the design requirements of low-noise machines, other frequency weightings or octave or 1/3 octave sound pressure levels may also be measured, as well as other expectations related to the time history of noise emission (such as impulse and sound pressure level as a function of time). NOTE 13 For some applications, it is not necessary to measure the C-weighted beep sound pressure level (see ISO 4871:1996, Chapter 5, Note 19). 8 To be determined
In order to obtain the emission sound pressure level at a specified location, the background noise correction value K is only applicable to the measured sound pressure level, not to the peak sound pressure level Lpc,peak. No correction is allowed for the peak sound pressure level. The correction term K considered here is related to the frequency weighting or frequency band of the sound pressure level measurement. For the frequency band and A weighting respectively: L = L' K
LpA = L pA -- KiA
Where: the apostrophe indicates the measured value, and the absence of the apostrophe indicates the emission value. NOTE 14: If the machine under test produces isolated single-event noise, the single-event emission sound pressure level L.1 at the specified location can be determined (see 3.3.3). 9 Installation and operation of the machine under test
9.1 General
(4)
The installation and operation of the machine under test have a significant impact on the emission sound pressure level at the specified location. This chapter specifies the relevant installation and operating conditions to ensure that the changes in emission noise caused by the installation and operation of the machine under test are minimized. For the machine equipment series to which the machine under test belongs, if there is a noise test procedure, its relevant provisions should be followed. The same installation and operating conditions should be used to determine the emission sound pressure level and sound power level. The noise test procedure for the relevant machine should give detailed information on its installation, placement and operating conditions. NOTE 15: For equipment used on tabletops, the noise test procedure may require that the same installation, placement and operating conditions are not met. When determining the sound power level, the equipment can be placed on the floor.
For large machines, the noise test procedure is particularly important, which lists in detail the parts, components, auxiliary equipment, power sources, etc. of the machine under test.
9.2 Location of sound sources
The machine under test should be installed in one or more locations on the reflecting surface under normal use. The machine under test should be away from any wall, ceiling or other reflective surface.
Note 16: For some machines, typical installation conditions include: two or more reflective surfaces (such as: wall-mounted equipment) or free space (such as: elevator) or an opening in a reflective surface (sound radiation appears on both sides of the vertical plane). The detailed installation conditions should be based on this standard and the relevant noise test procedures.
9.3 Sound source installation
In many cases, the noise emission of the specified location of the machine under test is related to the supporting installation conditions of the machine. When the machine has typical installation conditions, such conditions should be used and simulated as much as possible. If typical installation conditions are not available or these conditions cannot be used for testing, care should be taken to avoid changes in the machine radiated noise caused by the installation system used for testing, and measures should be taken to try to reduce the radiated noise of the equipment installation structure. Many small machines, although they radiate little low-frequency sound themselves, due to installation reasons, their vibration energy is transferred to a large surface that is sufficient to effectively radiate energy, thereby radiating more low-frequency sound. If possible, elastic supports should be added between the machine under test and its base surface to minimize the transmission of vibrations to the base and the response of the sound source. In this case, the mounting base should have a sufficiently high force impedance to prevent additional sound radiation due to large amplitude vibrations. However, when the typical installation environment of the machine under test can only be elastic, elastic mounting should be used.
Note 17: Coupling conditions (such as between the prime mover and the driven machine) may also have a significant impact on the sound radiation of the sound source under test. 9.3.1 Hand-held mechanical equipment
This mechanical equipment should be hand-held and suspended in the air so that the structure-borne sound is not transmitted through any accessories that are not part of the machine under test. If a support is required for the operation of the machine under test, the structure of the support should be small enough to be considered as part of the machine under test and described in the noise test procedures (if any).
9.3.2 Foundation-supported and wall-mounted machinery Such machinery should be placed on a reflective surface (acoustically hard surface, such as a floor or wall). For machinery with a foundation mounted in front of a wall, the machinery should be mounted on an acoustically hard surface in front of an acoustically hard wall. Table-type machinery should be placed on a table or stand in accordance with the operating requirements of the noise test procedure for the machine under test. The distance from the table or stand to any sound-absorbing surface in the test room should be at least 1.5 m. Such machinery should be placed in the center of a standard test table. For the design of the test table, see Appendix B. 9.4 Auxiliary equipment
Any cable ducts, air ducts, etc. connected to the machine under test should not radiate significant sound energy into the test environment. All auxiliary equipment that is not part of the machine under test but is necessary for the operation of the machine under test should be placed outside the test environment as far as possible; if this is not possible, the auxiliary equipment should be included in the test equipment and the operating conditions should be described in the test report. 9.5 Operation of the machine during the test
During the noise measurement, if there is a noise test procedure for the machine equipment series to which the machine under test belongs, the operating conditions specified in the test procedure shall be used. If there is no test procedure, the machine under test shall be operated in normal use as far as possible. In this case, one or more of the following operating conditions shall be selected:
a) under specified load and operating conditions,
b) under full load conditions;
c) under no load (no load) conditions,
d) under working conditions corresponding to the maximum noise output during normal use;
e) under simulated load conditions of the specified operating conditions,
f) under conditions with a characteristic operating cycle. The emission sound pressure level at the specified location shall be determined under any expected operating conditions (such as temperature, humidity, device speed, etc.). These test conditions shall be selected in advance and remain unchanged during the test. Before any noise measurement is made, the machine under test shall be in the expected set of operating conditions. If the noise emission also depends on other operating parameters (e.g. type of material being processed or type of tool), then appropriate parameters should be selected as far as possible to minimize the change in the sound radiation and to obtain typical sound radiation conditions. For some special tests, one or more conditions can be set appropriately to ensure a high reproducibility of the noise emission of the same series of machines and equipment and the operating conditions are the most common and typical for the machine series. These operating conditions should be specified in the professional noise test procedures.
If simulated operating conditions are used, those conditions should be selected that give a sound pressure level representative of the emission at the specified position of the machine under normal use.
In special cases, the results of several operating conditions can be combined by the energy averaging method to obtain the results under the main operating conditions (see 10.1).
The operating conditions of the machine under test during the noise measurement should be fully described in the test report. 10 Measurement
10.1 Measurement time
10.1.1 Overview
GB/T 17248. 2-1999
The principle of selecting the measurement time is to be able to determine the time characteristics of the emission sound pressure level and noise emission at the specified location under the specified operating conditions (if required by the regulations).
For a given sound source under test, the measurement time consists of a series of sub-measurement times T, each of which corresponds to a specified operating period of the sound source. In this case, it can usually be described by a single emission sound pressure level, which can be averaged according to formula (5) for the A-weighted emission sound pressure level of each sub-measurement time:
LpA = 10lg[
where: T is the total measurement time, s;
T, is the sub-measurement time, s;
N is the total number of sub-measurement times or operating periods; X100.1LpA.ro
is the A-weighted emission sound pressure level in the sub-measurement time T, dB. (5)
For machines and equipment with a specified operating cycle, it is usually necessary to extend the measurement time to an integer multiple of the continuous operating cycle. The measurement time is only related to the operating period for which the emission sound pressure level and the time characteristics of the sound emission (if required) are expected. The value of the measurement time, the possible sub-measurement time and the number of operating cycles included in the measurement time should comply with the noise test procedures for the machine under test (if any). In any case, these values ​​are the same as those specified for determining the sound power level of the machine under test. 10.1.2 Steady-state noise
If the noise emission at the specified location is steady-state noise under the specified operating conditions (see GB/T14259 and ISO12001), the measurement time shall be at least 15 s.
10.1.3 Non-steady-state noise
If the noise emission at the specified location is non-steady-state noise under the specified operating conditions, the measurement time and the operating period of the machine under test shall be specified in detail in the test results and reported. If there is a noise test procedure, the measurement time and the operating period of the machine under test are usually specified in the test procedure.
10.1.4 Frequency band measurement
If octave or 1/3 octave band measurements are performed, the minimum measurement observation time should be 30s for frequency bands with a center frequency of 160Hz and below, and the minimum measurement observation time should be 15s for frequency bands with a center frequency of 200Hz and above. 10.2 Measurement process
10.2.1 Overview
The emission sound pressure level should be measured over a typical operating period of the machine under test (see 10.1) and the emission sound pressure level reading should be obtained at the specified position.
Usually, the emission sound pressure level is measured using an integrating average sound level meter that meets the requirements of GB/T17181 (see Chapter 5). If it is known that the sound pressure level fluctuation measured using the time-weighted characteristic \S\ is less than ±1dB,A conventional sound level meter that complies with the provisions of GB/T3785 can be used. In this case, the sound pressure level can be taken as the average of the maximum and minimum sound levels measured according to the time-weighted characteristic "S" during the measurement observation period. 10.2.2 Repeatability of measurement
In order to reduce the uncertainty in determining the emission sound pressure level at a specified location, it is necessary to repeat multiple measurements of the machine equipment in accordance with the provisions of the noise test procedure for the machine under test. If there is a noise test procedure, the measurement value (i.e., the average or maximum value) adopted after repeated measurements should be taken in accordance with the provisions of the test procedure. Repeated measurements include the following processes: a) If feasible, turn off and turn on the machine under test again; b) move the microphone away and place it again at the specified location; c) measure again under the same environmental conditions, under the same installation and operating conditions, using the same measuring instrument, and at the same measurement time.
10.2.3 Measurement process of impulse noise
GB/T17248.2—1999
If the sound emission is an impulse sound (as described in Appendix A), the instrument should have a sufficiently large dynamic range when measuring the emission sound pressure level, and the sound level meter should be equipped with an overload indicator.
To measure the time characteristics of impulse sound emission (i.e. many peaks), in addition to the repeated measurement process described in 10.2.2 above, the measurement time should include at least 10 pulses. If the noise test procedure has other provisions, the test procedure shall be followed. The measurement value is usually the average value. When measuring the peak value, the maximum value of each peak value is retained. If the noise test procedure specifies a more precise measurement process, this measurement process shall be used. If the machine under test generates isolated single-event noise, the single-event emission sound pressure level Lp1 at the working position shall be measured (see 3.3.3).
To determine whether the sound emission contains an impulse component, a measurement method given in Appendix A may be used. 11 Microphone Position
11.1 General
The specific measurement position can be selected from the various positions described in 11.2, 11.3, 11.4 or 11.5. The microphone should be oriented so that the sound incident direction is consistent with the direction of the microphone reference axis specified by the manufacturer (meeting the requirements of GB/T3785 or GB/T17181 respectively). If possible, no one should be present near the machine when measuring the emission sound pressure level, and the microphone should be pointed at the main sound source.
If the operator is present, the operator should not wear clothing with abnormal sound absorption characteristics or any hat or scarf (other than a protective helmet required for safety reasons, or a wind shield or bracket for fixing the microphone), which will affect the noise measurement. If the operator is present, the microphone should be located on the operator's head, 0.20m ± 0.02m to one side of the center plane of the line between the two eyes, with its axis parallel to the operator's line of sight and on the side with the higher measured A-weighted sound pressure level LA. NOTE 18: If the measured sound pressure level is highly dependent on position, it is recommended to use the spatial average of the position within a small volume centered at the specified position.
Unless otherwise specified in the noise test procedure, the operator position shall be as specified in 11.2 to 11.5. 11.2 Microphone Position for Seated Operator If the operator is not present and the seat is connected to the machine under test, the microphone shall be located 0.8 m ± 0.05 m above the center of the seat plane unless the noise test procedure specifically states otherwise. If the operator is not present and the seat is not connected to the machine under test, if there is a noise test procedure, the microphone position shall be determined in accordance with the test procedure. If there is no test procedure, it shall be noted in the test report. If the operator is present, the seat shall be adjusted so that the operator can comfortably control the controls. The distance from the seat plane to the top of the operator's head is set at 0.91 m ± 0.05 m.
11.3 Microphone positions for standing, fixed-position operators If the operator is present during the measurement, 11.1 of this standard applies. If the operator or bystander is not present and the noise test procedure does not specify another position for the standing operator, the microphone position can be defined as the reference point on the ground where the operator usually stands. The reference point is the vertical projection of the center of the operator's head on the ground. The microphone position should be located at a height range of 1.55m ± 0.075m above the reference point. The noise test procedure (if any) generally specifies the height. 11.4 Microphone positions when the operator moves along a specified path When the operator moves along a specified path near the machine under test, there should be a sufficient number of microphone positions or movable microphones to determine the sound pressure level along the specified path. The sound pressure level along the specified path can be determined by continuous integration along the length of the path, or by making a sufficient number of measurements at discrete positions or at specified time intervals, and then applying equation (5) to determine the sound pressure level. The reference line is defined as a line on the ground directly below the center of the operator's head along a typical specified path. If the noise test procedure does not specify a different height for a moving operator, the microphone should be located directly above the reference line within the range of 1.55m ± 0.075m.
The microphone position should be defined for all fixed operator positions and, if there is a noise test procedure, should be located along the specified path given in the procedure.1 applies. If the operator or bystander is not present and the noise test procedure does not specify other positions for standing operators, the microphone position can be defined as a reference point on the ground where the operator usually stands. The reference point is the vertical projection of the center of the operator's head on the ground. The microphone position should be located at a height range of 1.55m ± 0.075m above the reference point. The noise test procedure (if any) generally specifies the height. 11.4 Microphone positions when the operator moves along a specified path When the operator moves along a specified path near the machine equipment under test, there should be a sufficient number of microphone positions or movable microphones to determine the sound pressure level along the specified path. The sound pressure level along the specified path can be determined by continuous integration along the length of the path, or by making a sufficient number of measurements at discrete positions or at specified time intervals, and then applying equation (5). The reference line is defined as a line segment on the ground directly below the center of the operator's head along a typical specified path. If the noise test procedure does not specify a different height for a moving operator, the microphone should be located within the range of 1.55 m ± 0.075 m above the reference line.
The microphone position should be defined for all fixed operator positions and, if there is a noise test procedure, should be specified along the specified route given in the procedure.1 applies. If the operator or bystander is not present and the noise test procedure does not specify other positions for standing operators, the microphone position can be defined as a reference point on the ground where the operator usually stands. The reference point is the vertical projection of the center of the operator's head on the ground. The microphone position should be located at a height range of 1.55m ± 0.075m above the reference point. The noise test procedure (if any) generally specifies the height. 11.4 Microphone positions when the operator moves along a specified path When the operator moves along a specified path near the machine equipment under test, there should be a sufficient number of microphone positions or movable microphones to determine the sound pressure level along the specified path. The sound pressure level along the specified path can be determined by continuous integration along the length of the path, or by making a sufficient number of measurements at discrete positions or at specified time intervals, and then applying equation (5). The reference line is defined as a line segment on the ground directly below the center of the operator's head along a typical specified path. If the noise test procedure does not specify a different height for a moving operator, the microphone should be located within the range of 1.55 m ± 0.075 m above the reference line.
The microphone position should be defined for all fixed operator positions and, if there is a noise test procedure, should be specified along the specified route given in the procedure.
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