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Mechanical Industry Standard of the People's Republic of China
JB/T5973-92
Determination of Sound Power Level of Dryer Noise
Simplified Method
Published on July 20, 1992
Implementation of the Ministry of Machinery and Electronics Industry of the People's Republic of China on January 1, 1993
People's Republic of China
Mechanical Industry Standard
Determination of Sound Power Level of Dryer Noise
Simplified Method
JB/T5973-92
Published by the Mechanical Standardization Research Institute of the Ministry of Machinery and Electronics Industry Printed by (P.O. Box 8144, Beijing, 100081)
Copyright reserved, no reproduction allowed
Format 880×1230
5/8 Sheet 5/8
Word count 12000
First edition October 1992 First printing October 1992 Print run 0.001500 Price 1.50 yuan
Mechanical Industry Standard of the People's Republic of China
Determination of sound power level of dryer noise
Simplified method
1 Subject content and scope of application
This standard specifies the determination method of sound power level of dryer noise. This standard applies to the noise measurement of dryer main engine with noise source. 2 Referenced standards
GB3241
GB3785
GB3947
JJG188
JJG217
Acoustic quantities and units
Electroacoustic functions and measurement methods of sound level meters with 1/1 or 1/3 octave filters for sound and vibration analysis Acoustic terminology
Trial verification procedure for sound level meter calibrators
Trial verification procedure for sound level meters
Verification procedure for standard sound sources
3 Terms, quantities and units
JB/T 5973---92
The names and symbols of the terms, quantities and units used in this standard shall be in accordance with the provisions of GB3947 and GB3102.7. 4
Measurement items and measurement errors
4.1 Measurement items
The main measurement item is the A-weighted sound power level. In the free sound field or semi-free sound field, the frequency band sound power level is selected as needed. 4.2 Measurement error
4.2.1 The standard deviation of the A-weighted sound power level shall not exceed 5dB(A). 4.2.2 When measuring the same type of sound sources in the same test environment, the standard deviation of the comparison results shall not exceed 3dB(A). 4.3 Acoustic measurement environment
Measurement environment
A free sound field laboratory with a reflecting surface; b.
A hard and flat outdoor place;
A room that meets the requirements of Appendix A and determines the environmental correction value K according to the method specified in Appendix A, where the value of K should not be greater than 7dB(A) c.
4.3.2 Background noise
The difference between the A-weighted or frequency band sound pressure level of the dryer radiated noise and the background noise sound pressure level measured at the same measuring point should be above 10dB(A). When the difference between the two is 3-10dB(A), the measured value shall be corrected according to Table 1. If the difference is less than 3dB, the measurement is invalid. Table 1
Difference between the sound pressure level of radiated noise of dryer and the sound pressure level of background noise Correction value of background noise
Approved by the Ministry of Machinery and Electronics Industry on July 20, 1992 3
Implemented on January 1, 1993
JB/T5973--92
4.3.3 Outdoor measurement
When measuring outdoors, a wind shield should be used. When the wind speed is greater than 6m/s (equivalent to a level 4 wind), the measurement should be stopped. 4.4 Measuring instruments
4.4.1 Selection and requirements
The measuring instrument should be a sound level meter of type ⅡI or above specified in GB3785, or other measuring instruments with equivalent accuracy. The sound level meter or other measuring instruments and the microphone should be connected by an extension cable or extension rod. When performing spectrum analysis, the 1/1 or 1/3 octave filter used should meet the requirements of GB3241. 4.4.2 Calibration
Before and after each measurement, the entire system (including cables) shall be calibrated at one or more frequencies using a sound level meter calibrator with an accuracy within the range of ±0.5dB(A). The sound level meter calibrator may use a piston generator and shall be calibrated regularly in accordance with JJG176. Sound level meters and other measuring instruments shall be calibrated regularly in accordance with JJG188.
4.5 Installation and working conditions of dryers
4.5.1 Requirements for installation of dryers
The installation of dryers shall comply with the requirements of relevant technical conditions, otherwise it shall be stated in the test report. 4.5.2 The dryer shall operate continuously under no-load conditions. When a stable state is reached, noise measurements shall be carried out, or measurements shall be made under other working conditions agreed by both parties, but detailed records shall be made in the test report. 5 Measurement method
5.1 Reference body and measurement surface
5.1.1 Reference body
A minimum rectangular hexahedron that envelops the dryer to be measured and terminates on the reflection plane is used as the reference body. The measurement surface and measurement points are arranged based on the reference body. When determining the size of the reference body, the protruding parts of the dryer can be ignored as long as they are not the main radiators of sound energy (such as handles, pull rods and connecting pipes, etc.).
5.1.2 Measurement surface and measurement point position
5.1.2.1 A rectangular hexahedron with each face parallel to the reference body is used as the measurement surface. The area of the measurement surface is calculated using formula (1): S=4(ab+bc+ca)...
Where: a=(L/2)+d
b=(L/2)+d
L, L, Ls are the length, width and height of the reference body respectively, d is the measurement distance, d=1m. (1)
5.1.2.2 Measurement point locations
All measurement points are located on the measurement surface determined in accordance with 5.1.2.1. The measurement points are divided into basic measurement points and additional measurement points. The measurement point locations on the rectangular hexahedron are shown in Figure 1, and the measurement point coordinates on the rectangular hexahedron measurement surface are shown in Table 2. 5.1.2.3 Basic measurement points
There are 5 basic measurement points, namely:
a. 4 points located in the middle of each measurement surface, at a height of hc/2 from the reflective surface; b. The point at the center of the top surface.
5.1.2.4 Additional measuring points
If the difference between the highest and lowest sound pressure levels of the five basic measuring points exceeds 5dB, the following measuring points need to be added: measuring points at the four corners of this height;
b. For machines with a horizontal scale exceeding 5.0m, an additional intermediate measuring point with a height of h should be added on the measuring surface exceeding 5.0m; for machines with a height exceeding 2.5m, it is necessary to add measuring points at the four top corners of the measuring surface and the point with the highest sound level A along the horizontal path at this height.
JB/T5973-92
5.2 Measurement
During measurement, the microphone should face the direction of the sound source to be measured. When the dryer radiates steady-state noise, the "slow" time-weighted feature of the sound level meter can be used to measure point by point. When the fluctuation amplitude of the sound level meter reading is within the range of ±3dB during the observation period, the sound pressure level reading can be averaged (the occasional excessive or too small value will not be considered). If necessary, the relevant frequency band can be measured. 5.2.2 Observation time
For the frequency band with A-weighted sound pressure level and center frequency above 200Hz, the observation reading time shall be at least 10s. For the frequency band with center frequency below 160Hz, the observation reading time shall be at least 308. 5.2.3 The tester should stay away from the sound field and keep at least 0.5m away from the microphone. Before or after the test, the background noise should be measured according to the above provisions. 5.2.4
6 Calculation
Measurement surface A-weighted average sound pressure level or band average sound pressure level Calculate according to formula (2): 3
JB/T597392
2100.1(LK）
LPA=10Lg[-
Wherein: LpA - the A-weighted average sound pressure level of the measuring point surface, or the band average sound pressure level, dB(A) (the reference value is 20μPa); the A-weighted sound pressure level or the band sound pressure level measured at the ith point dB(A) (the reference value is 20μPa); Lpas
K - the background noise correction value measured at the ith point, dB(A); N - the total number of measuring points.
When the change of Lpai-K value does not exceed 5dB(A), the arithmetic mean method can be used to calculate Lpa. The difference between the calculation method and formula (2) should not be greater than 0.7dB(A).
6.2 Calculation of sound power level
A-weighted sound power level or band sound power level is calculated by formula (3): Lwa=Lnx+10Lg%
Where: LwA-bzxZ.net
A-weighted sound power level or band sound power level, dB(A), (the reference value is 1pW); S-measurement surface area,m;
S. Reference area, S=1m;
K, environmental correction value, dB(A) (determined according to Appendix A). Measurement report
The content of the measurement report should include:
Model, name, specifications and installation and operation status of the tested dry coal machine; model and specifications of the noise measuring instrument used; description of the measurement environment and correction value;
location and schematic diagram of the measuring point;
data of the measuring point and calculated sound power level;
meteorological conditions, test unit, test personnel, time and location. ·（3）
A1 Overview
JB/T5973-92
Appendix A
Determination of environmental correction value K,
(Supplement)
This appendix stipulates the determination of environmental correction value K, by using the standard sound source method and the ratio of the sound absorption A of the measuring room to the area S of the measuring surface: the ratio A/S of the sound absorption A of the room to the area of the measuring surface in a given test room should be not less than 1, and the environmental correction value K determined by it should not be greater than 7dB(A).
A2 Determination of environmental correction value K,
A2.1 Determination of K value by standard sound source method
A2.1.1 The standard sound source qualified by JJG217 shall be placed in the test environment at the same location as the dryer to be tested, and the sound power level of the standard sound source shall be measured and calculated according to the methods in Chapters 5 and 6 (no environmental correction value is required). In the case of placing standard sound sources at multiple locations, the sound power level of the standard sound source should be averaged for each placement point. The environmental correction value K is obtained by formula (A1): K, = Lw-Lw
-the power level of the standard sound source measured on site, dB(A) (the reference value is 1pW); where: Lw—
-the sound power level calibrated by the standard sound source, dB(A) (the reference value is 1pW). (A 1)
A2.1.2 The placement of the standard sound source in the measurement environment is divided into two methods: substitution method and parallel method. The medium-sized dryer that can be moved away from the site adopts the substitution method. The standard sound source is placed on the reflecting plane at the same position as the sound source to be measured. Generally, it only needs to be placed in one position. For equipment with an aspect ratio greater than 2, the standard sound source should be placed in four positions. These four positions are: the midpoints of the four rectangular sides of the projection of the reference body on the reflecting plane. The parallel method is used for larger dryers that cannot be moved away from the measurement site or medium-sized dryers measured on site. Place the standard sound source at the midpoint of the four rectangular sides. If the equipment surface is attached with sound-absorbing materials, the parallel method is not applicable and the method of A2.2 can be used. A2.2 Determine the noise volume A of the test room and the measurement surface area S, and calculate the K value by formula (A2). K = 10Lg [1 +
K. The value can also be found from Figure A1.
dB (A)
Experimental determination of sound absorption
Determine the reverberation time of the test room using broadband noise or pulse Lu excitation, and use A-weighted characteristic reception. The sound absorption A is determined by formula (A3). 5
Where: V
-test room volume, m\;
T-.-test room reverberation time,.
A2.2.2 Estimation of sound absorption A
JB/T5973-92
A=0.16(V/T)
Use Table A1 to estimate the average surface sound absorption coefficient α of the test room, and calculate the sound absorption A by formula (A4). A=αs..
Where: α-average sound absorption coefficient (see Table A1); S, -total surface area of the test room (walls, ceiling, floor), m. Table A1
Average sound absorption coefficient
Additional notes:
Description of the room
Nearly empty rooms with hard concrete, bricks, plaster Partially empty rooms, rooms with bare walls
Rectangular machines with furniture, rectangular industrial rooms Irregular rooms with furniture, irregularly shaped machines or industrial rooms Rooms with machinery or rooms covered with a small amount of acoustic materials (such as partially sound-absorbing ceilings and ceilings)
Ceilings and walls covered with sound-absorbing materials
Ceilings and towers covered with a large amount of sound-absorbing materials
This standard was proposed and coordinated by the National Vacuum Technology Standardization Technical Committee. This standard was drafted by the Tieling Drying Technology Research Institute of Liaoning Province. The main drafters of this standard are Xu Luji and Zhao Jian. 6
..(A4)
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