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JB/T 4364—1999
former
Words|| tt||This standard is a revision of JB4364--86 "Performance Test Method for Mufflers Matched by Fans". This standard is compared with JB4364-86. The main technical content changes are as follows:
Added reference standards;
A pair of defined nouns, terminology and content provisions of test records and test reports have been increased or decreased; "Test items, test principles" have been deleted "; The test device, test equipment, test conditions, and test methods have been re-edited. This standard is recommended to replace JB4364--86 from the date of implementation. This standard is proposed and coordinated by the National Fan Standardization Technical Committee. The unit responsible for drafting this standard: Wuhan Ventilator and Muffler Research Institute. The main drafters of this standard are: Zhong Wei, Du Gaoyou 112
.
1 Scope
Machinery Industry Standard of the People's Republic of China
Fan matching muffler
Performance Test methods
Methods of performance test for auxiliary silencer of fanJB/T4364-1999
Replaces JB4364--86
This standard specifies the manufacturer's performance test for fan silencer on the test bench Methods and requirements for factory testing of acoustic and aerodynamic performance in air.
Determine the acoustic and aerodynamic performance parameters of the muffler through tests and calculations. Test quantities: insertion loss within the rated flow rate or operating flow rate range of the muffler, ILi; - pressure loss within the rated flow rate or operating flow rate range of the muffler, force; - force The resistance coefficient within the rated flow rate or operating flow rate range of the muffler; the airflow regeneration noise within the rated flow rate or operating flow rate range of the muffler, SL. This standard is applicable to mufflers that are mainly resistive, but does not apply to the performance of exhaust vent mufflers that control jet noise. test. Large loudspeakers are not suitable for factory testing and can be replaced by smaller models and prototypes. 2 Referenced standards
The provisions contained in the following standards constitute provisions of this standard by being quoted in this standard. At the time of publication, the editions indicated were valid. All standards are subject to revision and parties using this standard should explore the possibility of using the latest version of the standard listed below. GB/T3785--1983 Electroacoustic performance and test method of sound level meter GB/T1236-1985 Test method for aerodynamic performance of ventilator GB/T2888-1991 Fan and Roots blower operating sound measurement method 3 definition
3.1 Muffler insertion loss
The reduction in the sound power level of the nozzle radiated noise compared to before the muffler is installed compared to after the muffler is installed. Symbol: IL, unit: decibel (dB).
3.2 Replacement pipe
An empty pipe of the same length and channel cross-section as the muffler to be tested. 3.3 Empty pipe test
A test conducted when a replacement pipe is used to replace the muffler under test. 3.4 Muffler test
The test is carried out with the test system removed and the replacement pipe inserted into the muffler under test. 3.5 upstream pipe
The part of the muffler performance test pipe of the tested muffler near the sound source port, 3.6 Downstream pipe
The part of the muffler performance test pipe of the tested muffler far from the sound source port National Machinery Industry Bureau 1999-07 -12Approved for implementation on 2000-01-01
113
3.7 Measuring point
The location of the microphone when measuring noise. 3.8 Quiet airflow
JB/T 4364—1999
The noise contained in the airflow itself will not affect the airflow when the muffler airflow regenerates the noise measurement value. 3.9 Test system muffler
A muffler used to obtain quiet air flow when doing the muffler air flow regeneration noise test. 3.10 Background noise
All noise other than the object to be measured measured at the measuring point. 3.11 Resistance coefficient
The ratio of the pressure loss of the muffler to be measured to the average dynamic pressure in the channel. The drag coefficient is a dimensionless quantity. symbol:. 4 Test devices and equipment
4.1 The test device is divided into two categories: the air inlet muffler test system device and the air outlet muffler test system device. 4.1.1 Air inlet muffler test system device
The muffler performance test pipe is connected to the air inlet end of the fan, and the air outlet end is connected to the fan performance test outlet test device that complies with GB/T1236. see picture 1.
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6
7
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9
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Figure 1 Intake muffler test system device
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4.1.2 Outlet muffler test System device
JB/T 4364-- 1999
The muffler performance test pipe is connected to the fan outlet end, and the air inlet end is connected to the fan performance test air inlet test device that complies with GB/T1236. See Figure 2.
>9.75D2+L
>4. 5D2 1D2 >3D2
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10
Note: In Figure 1. In Figure 2: 1 - Fan; 2 - Aerodynamic performance test device: 3 - Hose: 4 - Fan reducing pipe 5 - Rectifier grid: 6 - Upstream pipe: 7 - Transition pipe; 8 - Replacement pipe: 9 - Downstream pipe; 10-Precision sound level meter and filter: 11-Pressure gauge 12-Test system muffler; 13--Add Figure 2 Outlet muffler test system device
4.1.3 For air inlet mufflers, the air inlet muffler test system is generally used Device test: For the outlet muffler, the device test of the outlet muffler test system is generally used.
It is allowed to use the air inlet muffler test system device to test the air inlet muffler; it is not allowed to use the air inlet muffler test system device to test the air outlet muffler.
4.2 Test equipment and instruments
4.2. T fan
Generally, the fan (including transmission group, drive motor, etc.) matching the muffler under test is selected. For fixed test benches The gas flow rate provided by the test system fan should be able to meet the specified requirements of the rated flow rate and operating flow rate range of the muffler under test, and the fan pressure should be greater than the total resistance of the test system at the corresponding flow rate.
4.2.2 Hose
is a flexible pipe sewn with rubber or multi-layer artificial leather to isolate solid sound transmission, with a length of 200~~400mm. One end is connected to the inlet (outlet) of the fan, and the other end is connected to the muffler performance test pipe. 4.2.3 Rectifier grid
A rectification device that regulates the air flow in the pipeline and is manufactured in accordance with the regulations of GB/T1236. 115
4.2.4 Main piping
JB/T4364-1999
Basic piping system for muffler testing, including pipes in the upstream and downstream directions of the muffler to be tested, transition pipes connected to the muffler and Replace pipe. The upstream and downstream pipelines have circular cross-sections, and their straight parts should be no shorter than 5 times the equivalent diameter of the pipeline, and within the test buccal ratio range should be no shorter than half the wavelength of the lowest center frequency sound wave. The main pipeline should be a straight, rigid pipeline with a smooth inner surface and vibration reduction and sound insulation measures on the outer wall. Main duct passages shall be circular in cross-section. The cross-sections of the upstream and downstream pipes should be the same as those of the inlet and outlet ends of the muffler to be tested respectively. If they are different, they should be connected to transition pipes so that the pipe cross-section changes smoothly with distance. The pipe wall of the transition pipe is straight, and its center line should coincide with the center line of the main pipe and the muffler to be tested. The expansion angle of the side wall of the transition pipe should not be greater than 30°, and the ratio of the cross-sectional areas at both ends should be controlled within the range of 0.7 to 2.0. 4.2.5 Instruments and meters
The acoustic quantity directly measured during measurement is mainly the octave band or 1/3 octave band sound pressure level. A sound level meter and matching filter or other measuring instruments with equivalent functions should be used for measurement. . The sound level meter used should comply with the regulations on type I sound level meters in GB/T3785, and the supporting filters should comply with the regulations of the relevant standards.
Before and after each test, the sound level meter should be calibrated with a sound level calibrator with an accuracy better than ±0.5dB. The difference between the first and last calibrations should not be greater than 1dB.
The measured aerodynamic quantities are mainly airflow velocity, static pressure, dry and wet bulb temperature and atmospheric pressure. The instruments and meters used are in accordance with GB/T1236.
Instruments and meters are calibrated in accordance with relevant regulations to ensure the accuracy of the testing instruments. 5 Test conditions
5.1 Test conditions
The unit under test and its ancillary equipment equipped with a muffler during the test should be in normal working conditions or rated conditions, and the working conditions of the muffler test and the empty pipe test should be Must remain the same. The sound field environment at the measuring point should comply with the requirements for measurement environment in GB/T2888. The acoustic environment around the measuring point should be relatively stable without artificial changes.
For the inlet muffler test system, the measuring point is located on the axis of the nozzle; for the outlet muffler test system, the measuring point is located at 45° to the axis of the nozzle. When D≤1m, take the distance r=1m between the measuring point and the center of the downstream pipe. When D>1 m, take =D. And the measuring point and the axis of the downstream pipeline are on the same horizontal plane, and the height from the ground should be greater than or equal to 1m. 5.2 Meteorological conditions
During the empty pipe test and muffler test, the meteorological conditions should remain basically unchanged, the temperature difference should be less than or equal to ±5C, and the relative humidity difference should be less than or equal to ±5%.
6 Test Methods
6.1 Background Noise
Before the empty pipe test and muffler test, background noise testing should be done for each working condition. That is, remove the hose and make sound insulation plugs at the open ends of the upstream and downstream pipes, turn on the fan, measure the corresponding working condition points at measuring points C (C') and A (A'), and compare the measured octave frequency bands Or the difference between the sound pressure levels Lci and LAi in the 1/3 octave band, and calculate the correction value K according to Table 1. Table 1 Background noise correction value K of frequency band sound pressure level difference
Correction value K
3
3
4~5
2
Experimental data with a sound pressure level difference of 3dB can be recorded, but is for reference only. The background noise level of each frequency band is determined by formula (1): 116
6~9
1
>10
0
dB||tt ||JB/T4364--1999
LpAi = Lc — Kci
Where: LpAi - background noise sound pressure level in each frequency band.dB; Lci\——C(C') point measurement Obtained sound pressure level, dB; Kc-——Background noise correction value of each frequency band, dB. 6.2 Muffler insertion loss
(1)
6.2.1 The muffler insertion loss test consists of an empty pipe test and a muffler test. When the test conditions are met, the values ??measured in the two tests The obtained sound pressure level difference is equal to the sound power level difference, which is the insertion loss of the muffler. 6.2.2 When measuring the insertion loss of the muffler, an empty tube test should be done before installing the muffler, and each working condition should be measured at a given measuring point A. The sound pressure level Lri1 of each octave band or 1/3 octave band of the noise radiated downstream, and the difference Lpci between Im and the design value of the muffler insertion loss must be higher than the background noise LPA: 3 dB or more. If this condition is not met, it will not be possible. Obtain the accurate insertion loss value. 6.2.3 After meeting the above conditions, replace the replacement pipe with a muffler, keep the working conditions and measuring points the same as during the empty pipe test, and measure the sound in each octave band or 1/3 octave band. The voltage level Lp2, and the difference between Lri!, Lpiz and the background noise level LrAi is used to calculate the correction values ??K,, K2 according to Table 1. The insertion loss of each frequency band is determined by formula (2): IL; = Lpi - Lpiz + K2 - K,
where: IL; insertion loss of each frequency band of the muffler, dB; Ipl—the sound pressure level at point A (A') measured during the empty tube test, dB; Lr—muffler test The measured sound pressure level at point A (A\), dB; K, - the background noise correction value during the empty pipe test, dB; K - the background noise correction value during the muffler test, dB. 6.3 Muffler pressure loss ||tt. ||(2)
6.3.1 The pressure loss of the muffler is the end face pressure difference of the muffler. Since the cross-sectional area of ??the pipes at both ends of the muffler is the same, the pressure loss is equal to the difference in static pressure at both ends
6.3. 2. When measuring the static pressure in the pipeline, the static pressure pipe can be separated from the Pitot tube, or a small hole can be opened in the pipe wall to connect it. 6.3.3 Adjust the working conditions of the fan and measure the pressure loss value of the muffler at different flow rates. , to obtain the relationship curve between the muffler pressure loss or resistance coefficient and the average flow rate.
6.3.4 The fan flow rate is tested and calculated according to the regulations of GB/T1236. 6.3.5 The average flow rate in the muffler is calculated by formula (3): Q. || tt | 6.3.6 The pressure loss of the muffler is calculated by equation (4): Ap = ps - pst2
where: A—pressure loss, Pa;
ps! Upstream static pressure, Pa;|| tt||ps2——Downstream end static pressure, Pa.
6.4 Muffler resistance coefficient is calculated by formula (5): = 2Ap/pu2
Wuzhong: 0-
(3 )
(4)
·(5)
Air density, for the device shown in Figure 1, take β = β (atmospheric density); for the device shown in Figure 2, take = p (Air density at the air outlet); pa2 is measured and calculated according to the regulations of GB/T1236. 6.5 Muffler air flow regeneration noise
Connect the test system muffler between the fan reducer and the hose as shown in Figure 1 and Figure 2. Carry out empty pipe test and muffler test respectively. 117
JB/T 4364- 1999
Measure the quiet airflow sound pressure level SL under each working condition; and the muffler airflow regeneration noise sound pressure level SLpi2. When SLpi2—SLrii≥3dB, the difference After correcting SL according to Table 1, we get SIpi. If SIri-SLri<3dB, it is considered that the muffler airflow regeneration noise cannot be measured. The muffler air flow regeneration noise is calculated by formula (6): SL = SLp + 10lg2 yuan r2
where: SLui - muffler air flow regeneration noise sound power level, dB; SLri - muffler air flow regeneration noise sound pressure level, dB ;The distance from a measuring point to the center of the pipe mouth, m.
7 Reading methods and corrections
*(6)
7.1 When measuring the sound pressure level with a sound level meter or other instruments, the "slow\ gear" should be used. When the measurement value fluctuates less than 3dB , take the arithmetic average as the measured value. And for each working condition, two readings should be taken. If the difference between the two readings is greater than 3dB, two more readings should be added, and the final result should be taken as the average of each reading and rounded up to an integer. .
7.2 For pressure measurement, if there is a large fluctuation in the reading, the median value of the fluctuation range should be taken as the measurement value. 7.3 When obvious discrete frequency noise pulse noise occurs, it should be noted in the test report. and test report
8.1 Test data record
The test data record should list the following items: a) Test location;
b) Test H period and time;
c ) tester;
d) test device parameters;
e) model and parameters of the muffler to be tested;
f) fan parameters;
g) various working conditions 8.2 Test report
The test report shall include the following contents:
a) Test data record table;
b) Test data calculation and Correction results;
c) Octave insertion loss spectrum curve within rated flow or specified flow rate range d) Relationship curve between pressure loss or resistance coefficient and average flow rate within rated flow or specified flow rate range; e) Test System layout diagram;
f) Brief record of problems during the test; g) Test result analysis and conclusion
118
Use a 5dB sound level calibrator to calibrate the sound level meter. The difference between the first and last calibrations should not be greater than 1dB.
The measured aerodynamic quantities are mainly airflow velocity, static pressure, dry and wet bulb temperature and atmospheric pressure. The instruments and meters used are in accordance with GB/T1236.
Instruments and meters are calibrated in accordance with relevant regulations to ensure the accuracy of the testing instruments. 5 Test conditions
5.1 Test conditions
The unit under test and its ancillary equipment equipped with a muffler during the test should be in normal working conditions or rated conditions, and the working conditions of the muffler test and the empty pipe test should be Must remain the same. The sound field environment at the measuring point should comply with the requirements for measurement environment in GB/T2888. The acoustic environment around the measuring point should be relatively stable without artificial changes.
For the inlet muffler test system, the measuring point is located on the axis of the nozzle; for the outlet muffler test system, the measuring point is located at 45° to the axis of the nozzle. When D≤1m, take the distance r=1m between the measuring point and the center of the downstream pipe. When D>1 m, take =D. And the measuring point and the axis of the downstream pipeline are on the same horizontal plane, and the height from the ground should be greater than or equal to 1m. 5.2 Meteorological conditions
During the empty pipe test and muffler test, the meteorological conditions should remain basically unchanged, the temperature difference should be less than or equal to ±5C, and the relative humidity difference should be less than or equal to ±5%.
6 Test Methods
6.1 Background Noise
Before the empty pipe test and muffler test, background noise testing should be done for each working condition. That is, remove the hose and make sound insulation plugs at the open ends of the upstream and downstream pipes, turn on the fan, measure the corresponding working condition points at measuring points C (C') and A (A'), and compare the measured octave frequency bands Or the difference between the sound pressure levels Lci and LAi in the 1/3 octave band, and calculate the correction value K according to Table 1. Table 1 Background noise correction value K of frequency band sound pressure level difference
Correction value K
3
3
4~5
2
Experimental data with a sound pressure level difference of 3dB can be recorded, but is for reference only. The background noise level of each frequency band is determined by formula (1): 116
6~9
1
>10
0
dB||tt ||JB/T4364--1999
LpAi = Lc — Kci
Where: LpAi - background noise sound pressure level in each frequency band.dB; Lci\——C(C') point measurement Obtained sound pressure level, dB; Kc-——Background noise correction value of each frequency band, dB. 6.2 Muffler insertion loss
(1)
6.2.1 The muffler insertion loss test consists of an empty pipe test and a muffler test. When the test conditions are met, the values ??measured in the two tests The obtained sound pressure level difference is equal to the sound power level difference, which is the insertion loss of the muffler. 6.2.2 When measuring the insertion loss of the muffler, an empty tube test should be done before installing the muffler, and each working condition should be measured at a given measuring point A. The sound pressure level Lri1 of each octave band or 1/3 octave band of the noise radiated downstream, and the difference Lpci between Im and the design value of the muffler insertion loss must be higher than the background noise LPA: 3 dB or more. If this condition is not met, it will not be possible. Obtain the accurate insertion loss value. 6.2.3 After meeting the above conditions, replace the replacement pipe with a muffler, keep the working conditions and measuring points the same as during the empty pipe test, and measure the sound in each octave band or 1/3 octave band. The voltage level Lp2, and the difference between Lri!, Lpiz and the background noise level LrAi is used to calculate the correction values ??K,, K2 according to Table 1. The insertion loss of each frequency band is determined by formula (2): IL; = Lpi - Lpiz + K2 - K,
where: IL; insertion loss of each frequency band of the muffler, dB; Ipl—the sound pressure level at point A (A') measured during the empty tube test, dB; Lr—muffler test The measured sound pressure level at point A (A\), dB; K, - the background noise correction value during the empty pipe test, dB; K - the background noise correction value during the muffler test, dB. 6.3 Muffler pressure loss ||tt. ||(2)
6.3.1 The pressure loss of the muffler is the end face pressure difference of the muffler. Since the cross-sectional area of ??the pipes at both ends of the muffler is the same, the pressure loss is equal to the difference in static pressure at both ends
6.3. 2. When measuring the static pressure in the pipeline, the static pressure pipe can be separated from the Pitot tube, or a small hole can be opened in the pipe wall to connect it. 6.3.3 Adjust the working conditions of the fan and measure the pressure loss value of the muffler at different flow rates. , to obtain the relationship curve between the muffler pressure loss or resistance coefficient and the average flow rate.
6.3.4 The fan flow rate is tested and calculated according to the regulations of GB/T1236. 6.3.5 The average flow rate in the muffler is calculated by formula (3): Q. || tt | 6.3.6 The pressure loss of the muffler is calculated by equation (4): Ap = ps - pst2
where: A—pressure loss, Pa;
ps! Upstream static pressure, Pa;|| tt | )
(4)
·(5)
Air density, for the device shown in Figure 1, take β = β (atmospheric density); for the device shown in Figure 2, take = p (Air density at the air outlet); pa2 is measured and calculated according to the regulations of GB/T1236. 6.5 Muffler air flow regeneration noise
Connect the test system muffler between the fan reducer and the hose as shown in Figure 1 and Figure 2. Carry out empty pipe test and muffler test respectively. 117
JB/T 4364- 1999
Measure the quiet airflow sound pressure level SL under each working condition; and the muffler airflow regeneration noise sound pressure level SLpi2. When SLpi2—SLrii≥3dB, the difference will be After correcting SL according to Table 1, we get SIpi. If SIri-SLri<3dB, it is considered that the muffler airflow regeneration noise cannot be measured. The muffler air flow regeneration noise is calculated by formula (6): SL = SLp + 10lg2 yuan r2
where: SLui - muffler air flow regeneration noise sound power level, dB; SLri - muffler air flow regeneration noise sound pressure level, dB ;The distance from a measuring point to the center of the pipe mouth, m.
7 Reading methods and corrections
*(6)
7.1 When measuring the sound pressure level with a sound level meter or other instruments, the "slow\" gear should be used. When the measurement value fluctuates less than 3dB , take the arithmetic average as the measured value. And for each working condition, two readings should be taken. If the difference between the two readings is greater than 3dB, two more readings should be added, and the final result should be taken as the average of each reading and rounded up to an integer. .
7.2 For pressure measurement, if there is a large fluctuation in the reading, the median value of the fluctuation range should be taken as the measurement value. 7.3 When obvious discrete frequency noise pulse noise occurs, it should be noted in the test report. and test report
8.1 Test data record
The test data record should list the following items: a) Test location;
b) Test H period and time;
c ) tester;
d) test device parameters;
e) model and parameters of the muffler to be tested;
f) fan parameters;
g) various working conditions 8.2 Test report
The test report shall include the following contents:
a) Test data record table;
b) Test data calculation and Correction results;
c) Octave insertion loss spectrum curve within rated flow or specified flow rate range d) Relationship curve between pressure loss or resistance coefficient and average flow rate within rated flow or specified flow rate range; e) Test System layout diagram;
f) Brief record of problems during the test; g) Test result analysis and conclusion
118
Use a 5dB sound level calibrator to calibrate the sound level meter. The difference between the first and last calibrations should not be greater than 1dB.
The measured aerodynamic quantities are mainly airflow velocity, static pressure, dry and wet bulb temperature and atmospheric pressure. The instruments and meters used are in accordance with GB/T1236.
Instruments and meters are calibrated in accordance with relevant regulations to ensure the accuracy of the testing instruments. 5 Test conditions
5.1 Test conditions
The unit under test and its ancillary equipment equipped with a muffler during the test should be in normal working conditions or rated conditions, and the working conditions of the muffler test and the empty pipe test should be Must remain the same. The sound field environment at the measuring point should comply with the requirements for measurement environment in GB/T2888. The acoustic environment around the measuring point should be relatively stable and free of artificial changes.
For the inlet muffler test system, the measuring point is located on the axis of the nozzle; for the outlet muffler test system, the measuring point is located at 45° to the axis of the nozzle. When D≤1m, take the distance r=1m between the measuring point and the center of the downstream pipe. When D>1 m, take =D. And the measuring point and the axis of the downstream pipeline are on the same horizontal plane, and the height from the ground should be greater than or equal to 1m. 5.2 Meteorological conditions
During the empty pipe test and muffler test, the meteorological conditions should remain basically unchanged, the temperature difference should be less than or equal to ±5C, and the relative humidity difference should be less than or equal to ±5%.
6 Test Methods
6.1 Background Noise
Before the empty pipe test and muffler test, background noise testing should be done for each working condition. That is, remove the hose and make sound insulation plugs at the open ends of the upstream and downstream pipes, turn on the fan, measure the corresponding working condition points at measuring points C (C') and A (A'), and compare the measured octave frequency bands Or the difference between the sound pressure levels Lci and LAi in the 1/3 octave band, and calculate the correction value K according to Table 1. Table 1 Background noise correction value K of frequency band sound pressure level difference
Correction value K
3
3
4~5
2
Experimental data with a sound pressure level difference of 3dB can be recorded, but is for reference only. The background noise level of each frequency band is determined by equation (1): 116
6~9
1
>10
0
dB||tt ||JB/T4364--1999
LpAi = Lc — Kci
Where: LpAi - background noise sound pressure level in each frequency band.dB; Lci\——C(C') point measurement Obtained sound pressure level, dB; Kc-——Background noise correction value of each frequency band, dB. 6.2 Muffler insertion loss
(1)
6.2.1 The muffler insertion loss test consists of an empty pipe test and a muffler test. When the test conditions are met, the values ??measured in the two tests The obtained sound pressure level difference is equal to the sound power level difference, which is the insertion loss of the muffler. 6.2.2 When measuring the insertion loss of the muffler, an empty tube test should be done before installing the muffler, and each working condition should be measured at a given measuring point A. The sound pressure level Lri1 of each octave band or 1/3 octave band of the noise radiated downstream, and the difference Lpci between Im and the design value of the muffler insertion loss must be higher than the background noise LPA: 3 dB or more. If this condition is not met, it will not be possible. Obtain the accurate insertion loss value. 6.2.3 After meeting the above conditions, replace the replacement pipe with a muffler, keep the working conditions and measuring points the same as during the empty pipe test, and measure the sound in each octave band or 1/3 octave band. The voltage level Lp2, and the difference between Lri!, Lpiz and the background noise level LrAi is used to calculate the correction values ??K,, K2 according to Table 1. The insertion loss of each frequency band is determined by formula (2): IL; = Lpi - Lpiz + K2 - K,
where: IL; insertion loss in each frequency band of the muffler, dB; Ipl—the sound pressure level at point A (A') measured during the empty tube test, dB; Lr—muffler test The measured sound pressure level at point A (A\), dB; K, - the background noise correction value during the empty pipe test, dB; K - the background noise correction value during the muffler test, dB. 6.3 Muffler pressure loss ||tt. ||(2)
6.3.1 The pressure loss of the muffler is the end face pressure difference of the muffler. Since the cross-sectional area of ??the pipes at both ends of the muffler is the same, the pressure loss is equal to the difference in static pressure at both ends
6.3. 2. When measuring the static pressure in the pipeline, the static pressure pipe can be separated from the Pitot tube, or a small hole can be opened in the pipe wall to connect it. 6.3.3 Adjust the working conditions of the fan and measure the pressure loss value of the muffler at different flow rates. , to obtain the relationship curve between the muffler pressure loss or resistance coefficient and the average flow rate.
6.3.4 The fan flow rate is tested and calculated according to the regulations of GB/T1236. 6.3.5 The average flow rate in the muffler is calculated by formula (3): Q. || tt | 6.3.6 The pressure loss of the muffler is calculated by formula (4): Ap = ps - pst2
where: A—pressure loss, Pa;
ps! Upstream end static pressure, Pa;|| tt||ps2——Downstream end static pressure, Pa.
6.4 Muffler resistance coefficient is calculated by formula (5): = 2Ap/pu2
Wuzhong: 0-
(3 )
(4)
·(5)
Air density, for the device shown in Figure 1, take β = β (atmospheric density); for the device shown in Figure 2, take = p (Air density at the air outlet); pa2 is measured and calculated according to the regulations of GB/T1236. 6.5 Muffler air flow regeneration noise
Connect the test system muffler between the fan reducer and the hose as shown in Figure 1 and Figure 2. Carry out empty pipe test and muffler test respectively. 117
JB/T 4364- 1999
Measure the quiet airflow sound pressure level SL under each working condition; and the muffler airflow regeneration noise sound pressure level SLpi2. When SLpi2—SLrii≥3dB, the difference After correcting SL according to Table 1, we get SIpi. If SIri-SLri<3dB, it is considered that the muffler airflow regeneration noise cannot be measured. The muffler air flow regeneration noise is calculated by formula (6): SL = SLp + 10lg2 yuan r2
where: SLui - muffler air flow regeneration noise sound power level, dB; SLri - muffler air flow regeneration noise sound pressure level, dB ;The distance from a measuring point to the center of the pipe mouth, m.
7 Reading methods and corrections
*(6)
7.1 When measuring the sound pressure level with a sound level meter or other instruments, the "slow\ gear" should be used. When the measurement value fluctuates less than 3dB , take the arithmetic average as the measured value. And for each working condition, two readings should be taken. If the difference between the two readings is greater than 3dB, two more readings should be added, and the final result should be taken as the average of each reading and rounded up to an integer. .
7.2 For pressure measurement, if there is a large fluctuation in the reading, the median value of the fluctuation range should be taken as the measurement value. 7.3 When obvious discrete frequency noise pulse noise occurs, it should be noted in the test report. and test report
8.1 Test data record
The test data record should list the following items: a) Test location;
b) Test H period and time;
c ) tester;
d) test device parameters;
e) model and parameters of the muffler to be tested;
f) fan parameters;
g) various working conditions 8.2 Test report
The test report shall include the following contents:
a) Test data record table;
b) Test data calculation and Correction results;
c) Octave insertion loss spectrum curve within rated flow or specified flow rate range d) Relationship curve between pressure loss or resistance coefficient and average flow rate within rated flow or specified flow rate range; e) Test System layout diagram;
f) Brief record of problems during the test; g) Test result analysis and conclusion
118
1 Test conditions
During the test, the unit under test equipped with a muffler and its ancillary equipment should be in normal working conditions or rated operating conditions, and the working conditions of the muffler test and the empty pipe test must remain the same. The sound field environment at the measuring point should comply with the requirements for measurement environment in GB/T2888. The acoustic environment around the measuring point should be relatively stable and free of artificial changes.
For the inlet muffler test system, the measuring point is located on the axis of the nozzle; for the outlet muffler test system, the measuring point is located at 45° to the axis of the nozzle. When D≤1m, take the distance r=1m between the measuring point and the center of the downstream pipe. When D>1 m, take =D. And the measuring point and the axis of the downstream pipeline are on the same horizontal plane, and the height from the ground should be greater than or equal to 1m. 5.2 Meteorological conditions
During the empty pipe test and muffler test, the meteorological conditions should remain basically unchanged, the temperature difference should be less than or equal to ±5C, and the relative humidity difference should be less than or equal to ±5%.
6 Test Methods
6.1 Background Noise
Before the empty pipe test and muffler test, background noise testing should be done for each working condition. That is, remove the hose and make sound insulation plugs at the open ends of the upstream and downstream pipes, turn on the fan, measure the corresponding working condition points at measuring points C (C') and A (A'), and compare the measured octave frequency bands Or the difference between the sound pressure levels Lci and LAi in the 1/3 octave band, and calculate the correction value K according to Table 1. Table 1 Background noise correction value K of frequency band sound pressure level difference
Correction value K
3
3
4~5
2
Experimental data with a sound pressure level difference of 3dB can be recorded, but is for reference only. The background noise level of each frequency band is determined by formula (1): 116
6~9
1
>10
0
dB||tt ||JB/T4364--1999
LpAi = Lc — Kci
Where: LpAi - background noise sound pressure level in each frequency band.dB; Lci\——C(C') point measurement Obtained sound pressure level, dB; Kc-——Background noise correction value of each frequency band, dB. 6.2 Muffler insertion loss
(1)
6.2.1 The muffler insertion loss test consists of an empty pipe test and a muffler test. When the test conditions are met, the values ??measured in the two tests The obtained sound pressure level difference is equal to the sound power level difference, which is the insertion loss of the muffler. 6.2.2 When measuring the insertion loss of the muffler, an empty tube test should be done before installing the muffler, and each working condition should be measured at a given measuring point A. The sound pressure level Lri1 of each octave band or 1/3 octave band of the noise radiated downstream, and the difference Lpci between Im and the design value of the muffler insertion loss must be higher than the background noise LPA: 3 dB or more. If this condition is not met, it will not be possible. Obtain the accurate insertion loss value. 6.2.3 After meeting the above conditions, replace the replacement pipe with a muffler, keep the working conditions and measuring points the same as during the empty pipe test, and measure the sound in each octave band or 1/3 octave band. The voltage level Lp2, and the difference between Lri!, Lpiz and the background noise level LrAi is used to calculate the correction values ??K,, K2 according to Table 1. The insertion loss of each frequency band is determined by formula (2): IL; = Lpi - Lpiz + K2 - K,
where: IL; insertion loss of each frequency band of the muffler, dB; Ipl—the sound pressure level at point A (A') measured during the empty tube test, dB; Lr—muffler test The measured sound pressure level at point A (A\), dB; K, - the background noise correction value during the empty pipe test, dB; K - the background noise correction value during the muffler test, dB. 6.3 Muffler pressure loss ||tt. ||(2)
6.3.1 The pressure loss of the muffler is the end face pressure difference of the muffler. Since the cross-sectional area of ??the pipes at both ends of the muffler is the same, the pressure loss is equal to the difference in static pressure at both ends
6.3. 2. When measuring the static pressure in the pipeline, the static pressure pipe can be separated from the Pitot tube, or a small hole can be opened in the pipe wall to connect it. 6.3.3 Adjust the working conditions of the fan and measure the pressure loss value of the muffler at different flow rates. , to obtain the relationship curve between the muffler pressure loss or resistance coefficient and the average flow rate.
6.3.4 The fan flow rate is tested and calculated according to the regulations of GB/T1236. 6.3.5 The average flow rate in the muffler is calculated by formula (3): Q. || tt | 6.3.6 The pressure loss of the muffler is calculated by formula (4): Ap = ps - pst2
where: A—pressure loss, Pa;
ps! Upstream end static pressure, Pa;|| tt||ps2——Downstream end static pressure, Pa.
6.4 Muffler resistance coefficient is calculated by formula (5): = 2Ap/pu2
Wuzhong: 0-
(3 )
(4)
·(5)
Air density, for the device shown in Figure 1, take β = β (atmospheric density); for the device shown in Figure 2, take = p (Air density at the air outlet); pa2 is measured and calculated according to the regulations of GB/T1236. 6.5 Muffler air flow regeneration noise
Connect the test system muffler between the fan reducer and the hose as shown in Figure 1 and Figure 2. Carry out empty pipe test and muffler test respectively. 117
JB/T 4364- 1999
Measure the quiet airflow sound pressure level SL under each working condition; and the muffler airflow regeneration noise sound pressure level SLpi2. When SLpi2—SLrii≥3dB, the difference After correcting SL according to Table 1, we get SIpi. If SIri-SLri<3dB, it is considered that the muffler airflow regeneration noise cannot be measured. The muffler air flow regeneration noise is calculated by formula (6): SL = SLp + 10lg2 yuan r2
where: SLui - muffler air flow regeneration noise sound power level, dB; SLri - muffler air flow regeneration noise sound pressure level, dB ;The distance from a measuring point to the center of the pipe mouth, m.
7 Reading methods and corrections
*(6)
7.1 When measuring the sound pressure level with a sound level meter or other instruments, the "slow\ gear" should be used. When the measurement value fluctuates less than 3dB , take the arithmetic average as the measured value. And for each working condition, two readings should be taken. If the difference between the two readings is greater than 3dB, two more readings should be added, and the final result should be taken as the average of each reading and rounded up to an integer. .
7.2 For pressure measurement, if there is a large fluctuation in the reading, the median value of the fluctuation range should be taken as the measurement value. 7.3 When obvious discrete frequency noise pulse noise occurs, it should be noted in the test report. and test report
8.1 Test data record
The test data record should list the following items: a) Test location;
b) Test H period and time;
c ) tester;
d) test device parameters;
e) model and parameters of the muffler to be tested;
f) fan parameters;
g) various working conditions 8.2 Test report
The test report shall include the following contents:
a) Test data record table;
b) Test data calculation and Correction results;
c) Octave insertion loss spectrum curve within rated flow or specified flow rate range d) Relationship curve between pressure loss or resistance coefficient and average flow rate within rated flow or specified flow rate range; e) Test System layout diagram;
f) Brief record of problems during the test; g) Test result analysis and conclusion
118
1 Test conditions
During the test, the unit under test equipped with a muffler and its ancillary equipment should be in normal working conditions or rated operating conditions, and the working conditions of the muffler test and the empty pipe test must remain the same. The sound field environment at the measuring point should comply with the requirements for measurement environment in GB/T2888. The acoustic environment around the measuring point should be relatively stable and free of artificial changes.
For the inlet muffler test system, the measuring point is located on the axis of the nozzle; for the outlet muffler test system, the measuring point is located at 45° to the axis of the nozzle. When D≤1m, take the distance r=1m between the measuring point and the center of the downstream pipe. When D>1 m, take =D. And the measuring point and the axis of the downstream pipeline are on the same horizontal plane, and the height from the ground should be greater than or equal to 1m. 5.2 Meteorological conditions
During the empty pipe test and muffler test, the meteorological conditions should remain basically unchanged, the temperature difference should be less than or equal to ±5C, and the relative humidity difference should be less than or equal to ±5%.
6 Test Methods
6.1 Background Noise
Before the empty pipe test and muffler test, background noise testing should be done for each working condition. That is, remove the hose and make sound insulation plugs at the open ends of the upstream and downstream pipes, turn on the fan, measure the corresponding working condition points at measuring points C (C') and A (A'), and compare the measured octave frequency bands Or the difference between the sound pressure levels Lci and LAi in the 1/3 octave band, and calculate the correction value K according to Table 1. Table 1 Background noise correction value K of frequency band sound pressure level difference
Correction value K
3
3
4~5
2
Experimental data with a sound pressure level difference of 3dB can be recorded, but is for reference only. The background noise level of each frequency band is determined by equation (1): 116
6~9
1
>10
0
dB||tt ||JB/T4364--1999
LpAi = Lc — Kci
Where: LpAi - background noise sound pressure level in each frequency band.dB; Lci\——C(C') point measurement Obtained sound pressure level, dB; Kc-——Background noise correction value of each frequency band, dB. 6.2 Muffler insertion loss
(1)
6.2.1 The muffler insertion loss test consists of an empty pipe test and a muffler test. When the test conditions are met, the values ??measured in the two tests The obtained sound pressure level difference is equal to the sound power level difference, which is the insertion loss of the muffler. 6.2.2 When measuring the insertion loss of the muffler, an empty tube test should be done before installing the muffler, and each working condition should be measured at a given measuring point A. The sound pressure level Lri1 of each octave band or 1/3 octave band of the noise radiated downstream, and the difference Lpci between Im and the design value of the muffler insertion loss must be higher than the background noise LPA: 3 dB or more. If this condition is not met, it will not be possible. Obtain the accurate insertion loss value. 6.2.3 After meeting the above conditions, replace the replacement pipe with a muffler, keep the working conditions and measuring points the same as during the empty pipe test, and measure the sound in each octave band or 1/3 octave band. The voltage level Lp2, and the difference between Lri!, Lpiz and the background noise level LrAi is used to calculate the correction values ??K,, K2 according to Table 1. The insertion loss of each frequency band is determined by formula (2): IL; = Lpi - Lpiz + K2 - K,
where: IL; insertion loss of each frequency band of the muffler, dB; Ipl—the sound pressure level at point A (A') measured during the empty tube test, dB; Lr—muffler test The measured sound pressure level at point A (A\), dB; K, - the background noise correction value during the empty pipe test, dB; K - the background noise correction value during the muffler test, dB. 6.3 Muffler pressure loss ||tt. ||(2)
6.3.1 The pressure loss of the muffler is the end face pressure difference of the muffler. Since the cross-sectional area of ??the pipes at both ends of the muffler is the same, the pressure loss is equal to the difference in static pressure at both ends
6.3. 2. When measuring the static pressure in the pipeline, the static pressure pipe can be separated from the Pitot tube, or a small hole can be opened in the pipe wall to connect it. 6.3.3 Adjust the working conditions of the fan and measure the pressure loss value of the muffler at different flow rates. , to obtain the relationship curve between the muffler pressure loss or resistance coefficient and the average flow rate.
6.3.4 The fan flow rate is tested and calculated according to the regulations of GB/T1236. 6.3.5 The average flow rate in the muffler is calculated by formula (3): Q. || tt | 6.3.6 The pressure loss of the muffler is calculated by formula (4): Ap = ps - pst2
where: A—pressure loss, Pa;
ps! Upstream end static pressure, Pa;|| tt||ps2——Downstream end static pressure, Pa.
6.4 Muffler resistance coefficient is calculated by formula (5): = 2Ap/pu2
Wuzhong: 0-
(3 )
(4)
·(5)
Air density, for the device shown in Figure 1, take β = β (atmospheric density); for the device shown in Figure 2, take = p (Air density at the air outlet); pa2 is measured and calculated according to the regulations of GB/T1236. 6.5 Muffler air flow regeneration noise
Connect the test system muffler between the fan reducer and the hose as shown in Figure 1 and Figure 2. Carry out empty pipe test and muffler test respectively. 117
JB/T 4364- 1999
Measure the quiet airflow sound pressure level SL under each working condition; and the muffler airflow regeneration noise sound pressure level SLpi2. When SLpi2—SLrii≥3dB, the difference After correcting SL according to Table 1, we get SIpi. If SIri-SLri<3dB, it is considered that the muffler airflow regeneration noise cannot be measured. The muffler air flow regeneration noise is calculated by formula (6): SL = SLp + 10lg2 yuan r2
where: SLui - muffler air flow regeneration noise sound power level, dB; SLri - muffler air flow regeneration noise sound pressure level, dB ;The distance from a measuring point to the center of the pipe mouth, m.
7 Reading methods and corrections
*(6)
7.1 When measuring the sound pressure level with a sound level meter or other instruments, the "slow\ gear" should be used. When the measurement value fluctuates less than 3dB , take the arithmetic average as the measured value. And for each working condition, two readings should be taken. If the difference between the two readings is greater than 3dB, two more readings should be added, and the final result should be taken as the average of each reading and rounded up to an integer. .
7.2 For pressure measurement, if there is a large fluctuation in the reading, the median value of the fluctuation range should be taken as the measurement value. 7.3 When obvious discrete frequency noise pulse noise occurs, it should be noted in the test report. and test report
8.1 Test data record
The test data record should list the following items: a) Test location;
b) Test H period and time;
c ) tester;
d) test device parameters;
e) model and parameters of the muffler to be tested;
f) fan parameters;
g) various working conditions 8.2 Test report
The test report shall include the following contents:
a) Test data record table;
b) Test data calculation and Correction results;
c) Octave insertion loss spectrum curve within rated flow or specified flow rate range d) Relationship curve between pressure loss or resistance coefficient and average flow rate within rated flow or specified flow rate range; e) Test System layout diagram;
f) Brief record of problems during the test; g) Test result analysis and conclusion
118
1 Background noise
Before the empty pipe test and muffler test, background noise testing should be conducted under each working condition. That is, remove the hose and make sound insulation plugs at the open ends of the upstream and downstream pipes, turn on the fan, measure the corresponding working condition points at measuring points C (C') and A (A'), and compare the measured octave frequency bands Or the difference between the sound pressure levels Lci and LAi in the 1/3 octave band, and calculate the correction value K according to Table 1. Table 1 Background noise correction value K of frequency band sound pressure level difference
Correction value K
3
3
4~5
2
Experimental data with a sound pressure level difference of 3dB can be recorded, but is for reference only. The background noise level of each frequency band is determined by equation (1): 116
6~9
1
>10
0
dB||tt ||JB/T4364--1999
LpAi = Lc — Kci
Where: LpAi - background noise sound pressure level in each frequency band.dB; Lci\——C(C') point measurement Obtained sound pressure level, dB; Kc-——Background noise correction value of each frequency band, dB. 6.2 Muffler insertion loss
(1)
6.2.1 The muffler insertion loss test consists of an empty pipe test and a muffler test. When the test conditions are met, the values ??measured in the two tests The obtained sound pressure level difference is equal to the sound power level difference, which is the insertion loss of the muffler. 6.2.2 When measuring the insertion loss of the muffler, an empty tube test should be done before installing the muffler, and each working condition should be measured at a given measuring point A. The sound pressure level Lri1 of each octave band or 1/3 octave band of the noise radiated downstream, and the difference Lpci between Im and the design value of the muffler insertion loss must be higher than the background noise LPA: 3 dB or more. If this condition is not met, it will not be possible. Obtain the accurate insertion loss value. 6.2.3 After meeting the above conditions, replace the replacement pipe with a muffler, keep the working conditions and measuring points the same as during the empty pipe test, and measure the sound in each octave band or 1/3 octave band. The voltage level Lp2, and the difference between Lri!, Lpiz and the background noise level LrAi is used to calculate the correction values ??K,, K2 according to Table 1. The insertion loss of each frequency band is determined by formula (2): IL; = Lpi - Lpiz + K2 - K,
where: IL; insertion loss of each frequency band of the muffler, dB; Ipl—the sound pressure level at point A (A') measured during the empty tube test, dB; Lr—muffler test The measured sound pressure level at point A (A\), dB; K, - the background noise correction value during the empty pipe test, dB; K - the background noise correction value during the muffler test, dB. 6.3 Muffler pressure loss ||tt. ||(2)
6.3.1 The pressure loss of the muffler is the end face pressure difference of the muffler. Since the cross-sectional area of ??the pipes at both ends of the muffler is the same, the pressure loss is equal to the difference in static pressure at both ends
6.3. 2. When measuring the static pressure in the pipeline, the static pressure pipe can be separated from the Pitot tube, or a small hole can be opened in the pipe wall to connect it. 6.3.3 Adjust the working conditions of the fan and measure the pressure loss value of the muffler at different flow rates. , to obtain the relationship curve between the muffler pressure loss or resistance coefficient and the average flow rate.
6.3.4 The fan flow rate is tested and calculated according to the regulations of GB/T1236. 6.3.5 The average flow rate in the muffler is calculated by formula (3): Q. || tt | 6.3.6 The pressure loss of the muffler is calculated by formula (4): Ap = ps - pst2
where: A—pressure loss, Pa;
ps! Upstream end static pressure, Pa;|| tt||ps2——Downstream end static pressure, Pa.
6.4 Muffler resistance coefficient is calculated by formula (5): = 2Ap/pu2
Wuzhong: 0-
(3 )
(4)
·(5)
Air density, for the device shown in Figure 1, take β = β (atmospheric density); for the device shown in Figure 2, take = p (Air density at the air outlet); pa2 is measured and calculated according to the regulations of GB/T1236. 6.5 Muffler air flow regeneration noise
Connect the test system muffler between the fan reducer and the hose as shown in Figure 1 and Figure 2. Carry out empty pipe test and muffler test respectively. 117
JB/T 4364- 1999
Measure the quiet airflow sound pressure level SL under each working condition; and the muffler airflow regeneration noise sound pressure level SLpi2. When SLpi2—SLrii≥3dB, the difference will be After correcting SL according to Table 1, we get SIpi. If SIri-SLri<3dB, it is considered that the muffler airflow regeneration noise cannot be measured. The muffler air flow regeneration noise is calculated by formula (6): SL = SLp + 10lg2 yuan r2
where: SLui - muffler air flow regeneration noise sound power level, dB; SLri - muffler air flow regeneration noise sound pressure level, dB ;The distance from a measuring point to the center of the pipe mouth, m.
7 Reading methods and corrections
*(6)bzxz.net
7.1 When measuring the sound pressure level with a sound level meter or other instruments, the "slow\" gear should be used. When the measurement value fluctuates less than 3dB , take the arithmetic average as the measured value. And for each working condition, two readings should be taken. If the difference between the two readings is greater than 3dB, two more readings should be added, and the final result should be taken as the average of each reading and rounded up to an integer. .
7.2 For pressure measurement, if there is a large fluctuation in the reading, the median value of the fluctuation range should be taken as the measurement value. 7.3 When obvious discrete frequency noise pulse noise occurs, it should be noted in the test report. and test report
8.1 Test data record
The test data record should list the following items: a) Test location;
b) Test H period and time;
c ) tester;
d) test device parameters;
e) model and parameters of the muffler to be tested;
f) fan parameters;
g) various working conditions 8.2 Test report
The test report shall include the following contents:
a) Test data record table;
b) Test data calculation and Correction results;
c) Octave insertion loss spectrum curve within rated flow or specified flow rate range d) Relationship curve between pressure loss or resistance coefficient and average flow rate within rated flow or specified flow rate range; e) Test System layout diagram;
f) Brief record of problems during the test; g) Test result analysis and conclusion
118
1 Background noise
Before the empty pipe test and muffler test, background noise testing should be conducted under each working condition. That is, remove the hose and make sound insulation plugs at the open ends of the upstream and downstream pipes, turn on the fan, measure the corresponding working condition points at measuring points C (C') and A (A'), and compare the measured octave frequency bands Or the difference between the sound pressure levels Lci and LAi in the 1/3 octave band, and calculate the correction value K according to Table 1. Table 1 Background noise correction value K of frequency band sound pressure level difference
Correction value K
3
3
4~5
2
Experimental data with a sound pressure level difference of 3dB can be recorded, but is for reference only. The background noise level of each frequency band is determined by formula (1): 116
6~9
1
>10
0
dB||tt ||JB/T4364--1999
LpAi = Lc — Kci
Where: LpAi - background noise sound pressure level in each frequency band.dB; Lci\——C(C') point measurement Obtained sound pressure level, dB; Kc-——Background noise correction value of each frequency band, dB. 6.2 Muffler insertion loss
(1)
6.2.1 The muffler insertion loss test consists of an empty pipe test and a muffler test. When the test conditions are met, the values ??measured in the two tests The obtained sound pressure level difference is equal to the sound power level difference, which is the insertion loss of the muffler. 6.2.2 When measuring the insertion loss of the muffler, an empty tube test should be done before installing the muffler, and each working condition should be measured at a given measuring point A. The sound pressure level Lri1 of each octave band or 1/3 octave band of the noise radiated downstream, and the difference Lpci between Im and the design value of the muffler insertion loss must be higher than the background noise LPA: 3 dB or more. If this condition is not met, it will not be possible. Obtain the accurate insertion loss value. 6.2.3 After meeting the above conditions, replace the replacement pipe with a muffler, keep the working conditions and measuring points the same as during the empty pipe test, and measure the sound in each octave band or 1/3 octave band. The voltage level Lp2, and the difference between Lri!, Lpiz and the background noise level LrAi is used to calculate the correction values ??K,, K2 according to Table 1. The insertion loss of each frequency band is determined by formula (2): IL; = Lpi - Lpiz + K2 - K,
where: IL; insertion loss of each frequency band of the muffler, dB; Ipl—the sound pressure level at point A (A') measured during the empty tube test, dB; Lr—muffler test The measured sound pressure level at point A (A\), dB; K, - the background noise correction value during the empty pipe test, dB; K - the background noise correction value during the muffler test, dB. 6.3 Muffler pressure loss ||tt. ||(2)
6.3.1 The pressure loss of the muffler is the end face pressure difference of the muffler. Since the cross-sectional area of ??the pipes at both ends of the muffler is the same, the pressure loss is equal to the difference in static pressure at both ends
6.3. 2. When measuring the static pressure in the pipeline, the static pressure pipe can be separated from the Pitot tube, or a small hole can be opened in the pipe wall to connect it. 6.3.3 Adjust the working conditions of the fan and measure the pressure loss value of the muffler at different flow rates. , to obtain the relationship curve between the muffler pressure loss or resistance coefficient and the average flow rate.
6.3.4 The fan flow rate is tested and calculated according to the regulations of GB/T1236. 6.3.5 The average flow rate in the muffler is calculated by formula (3): Q. || tt | 6.3.6 The pressure loss of the muffler is calculated by formula (4): Ap = ps - pst2
where: A—pressure loss, Pa;
ps! Upstream end static pressure, Pa;|| tt||ps2——Downstream end static pressure, Pa.
6.4 Muffler resistance coefficient is calculated by formula (5): = 2Ap/pu2
Wuzhong: 0-
(3 )
(4)
·(5)
Air density, for the device shown in Figure 1, take β = β (atmospheric density); for the device shown in Figure 2, take = p (Air density at the air outlet); pa2 is measured and calculated according to the regulations of GB/T1236. 6.5 Muffler air flow regeneration noise
Connect the test system muffler between the fan reducer and the hose as shown in Figure 1 and Figure 2. Carry out empty pipe test and muffler test respectively. 117
JB/T 4364- 1999
Measure the quiet airflow sound pressure level SL under each working condition; and the muffler airflow regeneration noise sound pressure level SLpi2. When SLpi2—SLrii≥3dB, the difference After correcting SL according to Table 1, we get SIpi. If SIri-SLri<3dB, it is considered that the muffler airflow regeneration noise cannot be measured. The muffler air flow regeneration noise is calculated by formula (6): SL = SLp + 10lg2 yuan r2
where: SLui - muffler air flow regeneration noise sound power level, dB; SLri - muffler air flow regeneration noise sound pressure level, dB ;The distance from a measuring point to the center of the pipe mouth, m.
7 Reading methods and corrections
*(6)
7.1 When measuring the sound pressure level with a sound level meter or other instruments, the "slow\ gear" should be used. When the measurement value fluctuates less than 3dB , take the arithmetic average as the measured value. And for each working condition, two readings should be taken. If the difference between the two readings is greater than 3dB, two more readings should be added, and the final result should be taken as the average of each reading and rounded up to an integer. .
7.2 For pressure measurement, if there is a large fluctuation in the reading, the median value of the fluctuation range should be taken as the measurement value. 7.3 When obvious discrete frequency noise pulse noise occurs, it should be noted in the test report. and test report
8.1 Test data record
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