JB/T 7665-1995 Field determination of sound power level of general machinery noise - Sound intensity method
Some standard content:
Mechanical Industry Standard of the People's Republic of China
JB/T 7665-95
On-site determination of sound power level of noise for general machinery--Sound intensity method
Published on June 16, 1995
Ministry of Machinery Industry of the People's Republic of China
Implemented on July 1, 1996bzxZ.net
Mechanical Industry Standard of the People's Republic of China
On-site determination of sound power level of noise for general machinery--Sound intensity method
1 Subject content and scope of application
This standard specifies the method for determining the sound power level of noise by sound intensity measurement on site. Its accuracy is engineering grade. JB/T 766595
This standard applies to the on-site noise sound power level measurement of various types of general machinery (hereinafter referred to as units) such as compressors, refrigerators, separation machinery, reciprocating pumps, HVAC, etc. with prime movers, especially for large units that do not meet the environmental conditions required by the general sound power level measurement method.
2 Reference standards
GB3102.7 Acoustic disks and units
GB3947
Acoustic terms and terms
3 Quantities to be measured and measurement errors
3.1 Quantities to be measured
A sound power level and the six times the sound power level of the central frequency between 125~4000Hz. 3.2 Measurement error
The standard deviation of the A sound power level shall not exceed 1.5dB. The standard deviation of the six times the sound power level shall not exceed the value specified in Table 1. Table 1
Octave band center frequency H2
Standard deviation dB
250~500
1000~4000
Note: The measurement error refers to the cumulative standard deviation caused by various factors, but does not include the deviation of the instrument itself and the change of the unit's own sound power caused by the change of the unit installation and operating status in each measurement. 4 Measurement environment
The ground is required to be a reflecting plane composed of hard materials (such as concrete, asphalt and steel plates) with a sound absorption coefficient less than 0.06, and meet the following requirements:
When there are other sound sources outside the unit under test, the sound source should be Steady state; a.
During measurement, the air flow velocity near the sound intensity probe should not be greater than 2m/s. When measuring outdoors or there is air flow near the probe, the probe should use a wind shield:
Avoid using the probe in places with large temperature differences (such as the exhaust pipe of a compressor). The distance between the probe and objects with significant temperature differences should be no less than 20mm:
When there is a sound source outside the unit being measured, there should be no sound-absorbing material on the measuring base surface; the operator should not stand on or near the axis of the probe. 5 Test instruments
Approved by the Ministry of Machinery Industry on June 16, 1995
Implementation on July 1, 1996
JB/T 766595
The sound intensity measuring instrument and probe used should meet the requirements of relevant standards. 5.2 Calibration
The measuring instruments and probes shall be sent to the metrology department for calibration regularly every year, and before each measurement, the entire test instrument system shall be calibrated according to the following provisions:
Use a sound level calibrator or a special sound intensity head calibrator with an accuracy better than 0.5dB to check the sound intensity probe. The sound pressure intensity probe of each microphone is located on the measuring surface with its axis perpendicular to the measuring surface. Measure the normal sound intensity at that location, and then turn the sound intensity probe in the b.
direction so that the two probes exchange positions. Measure the sound intensity again. The sound intensity level values of the highest frequency band of the two measurements must have opposite signs, and the difference should be less than 1.5dB, otherwise the measurement will be invalid.
6 Installation and operation of the unit
6.1 Installation of the unit
6.1.1 The unit should be installed in accordance with the provisions of the relevant technical documents. If there is no clear provision, it should be installed according to normal use. Otherwise, it should be stated in the test report.
6.1.2 All components should be installed completely. However, no additional sound insulation and sound absorption components should be added. 6.2 Operation of the unit
6.2.1 Generally, noise measurement should be carried out after stable operation under rated conditions. If measured under other conditions, it should be noted in the test report. 6.2.2 The medium for unit operation should comply with relevant regulations. If it needs to be changed, it should be noted in the test report. 7 Measurement
7.1 Selection of measurement surface
7.1.1 When the unit under test is installed on a reflective plane, the measurement surface of the shape shown in Figure 1 (excluding the reflective surface) is preferred. Or a regular shape is selected according to the typical shape of the unit. This measurement surface surrounds the unit under test and is located on the reflective plane. 7.1.2 When the unit under test is installed at a high place instead of on a reflective plane, a reflective surface with a sound absorption coefficient less than 0.06 should be set at this position, and then the measurement surface surrounding the unit under test is preferentially selected according to Figure 1 (excluding the reflective surface). The preferred measurement base surface in Figure 1
7.1.3 The average distance between the measurement surface and the surface of the unit under test should be not less than 0.5m. 7.2 Initial test
The measurement of normal sound intensity component and sound pressure level should be carried out on the selected measurement surface. 7.2.1 Selection of measuring points
7.2.1.1 When there is no large noise source outside the unit under test, that is, the background noise is more than 10dB lower than the A-weighted sound pressure level of the unit under test), at least 10 measuring points shall be evenly arranged on the measuring surface, and at least one measuring point shall be arranged per square meter. If the measuring surface area is greater than 50m, 50 measuring points shall be evenly arranged.
7.2.1.2 When there is a large noise source outside the unit under test, at least 10 measuring points shall be evenly arranged on the measuring surface, and at least one measuring point shall be arranged per square meter. If the measuring surface area is greater than 50m, the total number of measuring points shall be greater than 50, and one measuring point shall be allowed for every 2m*. 7.2.1.3 For the surface with relatively large local noise, the surface can be divided into several parts. The measuring points of the part with large noise shall be evenly increased, and the calculation shall be carried out in parts.
7.2.2 Measurement of normal sound intensity component and sound pressure level Measure the normal sound intensity component and sound pressure level at each selected measuring point. 7.2.3 Check whether the accuracy of this method is achieved
7.2.3.1 Calculate the sound field index F,, F, and F, of each multiple band according to Appendix A. 7.2.3.2 Substitute the calculated value into the criterion of Appendix B for inspection. It should meet the requirements. Calculate the sound power level of the unit under test according to Chapter 8. Otherwise, re-measure according to Article 7.3.
7.3 Repeat the test
Take measures according to Appendix B and re-measure the normal sound intensity component and sound pressure level of each measuring point. Repeat the steps of 7.2.3 until it meets the requirements. Otherwise, the measurement is invalid.
8 Calculation of sound power level
8.1 Calculation of A-weighted and octave band sound power on each surface The A-weighted and octave band sound power W is calculated by formula (1): W,
Where: W,—-the A-weighted and octave band sound power of the jth surface, W; I—the normal sound intensity component measured at the jth surface measuring point 1, W/m; S,—the area corresponding to the jth measuring point on the jth surface, m\; N
the number of measuring points on the jth surface.
8.2 Calculation of A-weighted and octave band sound power level of the measured unit The A-weighted and octave band sound power level L is calculated by formula (2): Lw=10lgl
Where: L
the A-weighted and octave band sound power level of the measured unit.dB; reference sound power, 10-1W;
the number of measuring surfaces.
If Zw,/W. is a negative number, this standard cannot be used. -(1)
A1 Overview
JB/T7665-95
Appendix A
Calculation of sound field index
Supplement)
For the measurement surface and measurement point arrangement adopted, the sound field index of the octave band is calculated according to the formula given in Chapter A2. A2 Calculation of sound field index
A2.1 Surface sound pressure-sound intensity index
Surface sound pressure-sound intensity index F, calculated by formula (A1): F, =L-La
Wherein, F-
Surface sound pressure-sound intensity index, dB:
-Average sound pressure level of the measuring surface, dB, calculated by formula (A2): L
Ll-Unsigned average sound intensity level in the normal direction of the measuring surface, dB, calculated by formula (A3): L,10lg[
Wherein: Lp-Sound pressure level of the measuring point, dBN-
-Number of measuring points.
100:Lg
Lmm10lgL
Wherein: II.|-Unsigned normal sound intensity at measuring point 1, W/m\;I. —reference sound intensity, taken as 10-1W/m. A2.2 Negative local power index
Negative local power index F, calculated by formula (A4): (/)
F,-ZL
Where; F, —negative local power index. dBLa—signed normal average sound intensity level of the surface, dB. Calculated by formula (A5): L=10lgl
Where; I. —signed amplitude of the normal sound intensity component measured at point i on the measurement surface.W/m\If (I./I) is negative, the measurement position cannot meet the requirements of this standard. A2.3 Sound field non-uniformity index
The sound field non-uniformity index F is calculated by formula (A6): F,
Where: F,--sound field non-uniformity index, W/m; 7.
The average sound intensity normal to the surface, W/m\, is calculated by formula (A7): L.
·(A4)
Inspection requirements
JB/T7665-95
Appendix B
Inspection for the accuracy of this standard
(Supplement)
In order to ensure that the sound power level measurement reaches the engineering level accuracy, the suitability of the measurement surface, measurement distance and measurement point arrangement shall be inspected. Test for suitability of selection and arrangement of measuring points B2
When the total number of measuring points N meets the following criteria under the required multiple bands, the accuracy of this method is achieved. Criteria N>CF
C is the factor given in Table B1.
Center frequency of multiple bands Hz
Factor C
Measures to meet accuracy requirements
250~500
If the test according to the criteria in Chapter B2 is not suitable, measures should be taken according to Table B2 to meet the measurement accuracy. Table B2
Criteria not met and
F:-F,>3 dB
1 dB
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