Acoustics-Determination of sound power levels of noise sources using vibration velocity-Measurement for seal machinery
Some standard content:
GB/T16539—1996
This standard is compiled on the basis of the corresponding work in my country and with reference to ISO/TR7849-1987 "Determination of Air Noise Radiated by Machines by Vibration Measurement".
Before the first draft of the international standard was proposed in 1979, my country had already conducted research on this technology. After more than ten years of research and application, it has been shown that my country has made great progress in application technology and standardization. Industrial production also urgently needs this technology to be promoted and applied in the form of standards as soon as possible. Therefore, it is necessary to formulate this national standard in a timely manner to meet the needs of my country's economic and technological development and industrial production. There are four main factors that affect the standardization of this technology. First, as a standard, the scope of application of this method needs to be further clarified. Second, in actual applications, the problem of standardization of radiation index curves of similar machines; third, the complexity of testing with general instruments; and fourth, the understanding of the accuracy of the test method. my country has solved these problems well. After a large number of tests and calculations, the standardized curves of radiation index of some machines (such as motors, electrical appliances, refrigerators, etc.) have been obtained. At the same time, my country has also developed a vibration noise detector with these standardized curve weighting networks and A weighting, making the vibration measurement method more convenient and practical. On this basis, after a large number of experimental verifications, the engineering accuracy of this method has been proved; at the same time, this method is limited to the test of closed machines. This has promoted the formulation of this standard. These aspects also reflect the improvement of this standard to ISO/TR7849-87. Appendix A, Appendix B, Appendix C, Appendix D, Appendix E, and Appendix F of this standard are all appendices of the standard. This standard is proposed and managed by the National Acoustic Standardization Technical Committee. The drafting units of this standard are: Shanghai Electric Science Research Institute of the Ministry of Machinery and Shanghai Aviation Measurement and Control Technology Research Institute of China Aviation Industry Corporation. The main drafters of this standard are: Chen Yeshao and Mu Jingkun. 278
1 Scope
National Standard of the People's Republic of China
Acoustics-Determination of sound power levels ofnoise sources using vibration velocity--Measurement for seal machineryGB/T16539—1996
This standard specifies the measurement method for determining the airborne sound power radiated by the surface vibration of the machine by measuring the surface vibration. This method is particularly suitable for those occasions where it is impossible to directly and correctly measure the airborne noise according to the basic standards or professional standards such as GB3767, GB3768, GB6881, GB6882, GB10069 that use the sound pressure method to measure machine noise due to high background noise or other large environmental influences. This standard is only applicable to the case of noise radiated by the surface vibration of closed solid structures, and is not applicable to the case of noise generated by aerodynamic forces. The method specified in this standard is mainly applicable to steady-state sound sources. The guidelines for calculating the radiation coefficient are given in Appendix D. The selection of recommended frequency bands is given in Appendix E. The procedure specified in this standard can determine the sound power radiated by the vibration of the entire machine structure by measuring the vibration of each part of the surface. The accuracy of the A-weighted sound power level determined by this standard is level 2, and the uncertainty of its measurement method is no more than 2dB. When the sound radiation index is unknown and the theoretical value is used for measurement, the accuracy of the measurement result should be at least level 3, otherwise the method of this standard should not be used.
2 Referenced standards
The provisions contained in the following standards constitute the provisions of this standard through reference in this standard. When this standard is published, the versions shown are valid. All standards will be revised, and parties using this standard should explore the possibility of using the latest version of this standard. GB3238-82 Levels of acoustic quantities and their reference values GB3240-82 Frequencies commonly used in acoustic measurements (negISO266:1975) GB3241-82 1/1 and 1/3 octave filters for sound and vibration analysis (neqIEC225:1966) GB3767-1996 Acoustics - Determination of sound power level of noise source by sound pressure method - Engineering method for approximate free field above reflecting surface (eqvISO3744--1994)
GB3768-1996 Acoustics - Determination of sound power level of noise source by sound pressure method - Simple method using envelope measuring surface above reflecting surface (eqvISO3746--1995)
GB3785-83 Electroacoustic properties and test methods of sound level meter GB6881-86 Determination of sound power level of acoustic noise source - Precision method and engineering method in reverberation chamber (neqISO3741:1975, neq ISO 3742:1975,neq ISO 3743:1976) Acoustic noise sources - Determination of sound power levels - Anechoic and semi-anechoic chamber precision method (neg ISO 3745:1977) GB 6882—86
GB10069.1—88 Method for determination of noise of rotating electrical machines and limit value Method for engineering determination of noise Approved by the State Administration of Technical Supervision on September 13, 1996 and implemented on March 1, 1997
3 General Principles
GB/T16539-1996
This standard is suitable for determining the airborne noise radiated by the vibration of the machine surface in the following cases: when the background noise (such as the noise of other machines or the reflected sound from the surfaces of the room) is higher than the noise directly radiated by the machine under test;
when it is necessary to separate the structure-borne noise from the aerodynamic noise (that is, in those occasions where the new sound intensity test technology is not convenient to apply);
when it is necessary to determine whether the structure-borne noise of the entire sound source comes from the structure-borne noise of the machine or from another part of the unit; when it is necessary to determine the noise of the machine under load and exclude the influence of the dragged load and other noise. The test procedures proposed in this standard are particularly suitable for sound sources with relatively simple external shapes of machines. It is easier to deal with some simple sound sources (zero-order vibration sources or point vibration sources) with good correlation. They can be treated with corresponding theories according to idealized structures (such as spheres, plates, cylinders). For most machines, the distribution of their vibration velocity depends on factors such as the vibration mode of the corresponding frequency, the structural characteristics of the machine and the excitation force, and their radiation factor is not only related to the above factors but also to the size of the radiation surface and the wavelength of the relevant frequency sound wave in the air. Therefore, experimental methods are usually used to obtain the radiation factor of the same type of machine, and this standard also gives relevant experimental procedures. Usually, for cases where the radiation factor is greater than one, it is roughly assumed that the radiation coefficient is one. 4 Definitions
This standard adopts the following definitions.
4.1 Structure-borne sound is vibration in the audible sound frequency range transmitted through the solid structure of the machine. It can be characterized by the vibration velocity or vibration acceleration of the surface of the solid structure.
4.2 Sealed machine
refers to the type of machine equipment in which the mechanical structure vibration noise is mainly radiated through the outer surface of the machine. 4.3 Vibration velocity is the vector of the time rate of change of displacement. The root mean square value (rms) of the vibration velocity is represented by the symbol V, and the unit is meter per second, m/s. Note: Vibration displacement is the integral of vibration velocity over time. When the frequency is, the effective value (rms) of sinusoidal vibration displacement D is calculated by the following formula: D= 2 yuan
Vibration acceleration is the differential of vibration velocity over time. When the frequency is, the effective value (rms) of sinusoidal vibration acceleration A is calculated by the following formula: A=2 yuan/V
4.4 Vibration velocity level is the logarithm of the ratio of velocity to reference velocity with the base 10 multiplied by 20, in bels, B. But usually dB is used as the unit. The speed level in decibel (dB) is expressed by formula (1): Iw = 10 gv
Where: V—effective value of vibration speed within the effective frequency band; V, reference speed, generally equal to 10-°m/s (=1 nm/s). Note
1 The properties of the reference speed V. of air sound and structure sound are the same as those of the sound intensity level, sound pressure level and vibration speed level of plane waves in air, and their values are almost equal. Therefore, this standard usually adopts V. =5×10*m/s. 2 The V. value listed in the above formula is the reference value of GB3238; it should be noted that different reference values will result in different speed levels during use. Therefore, the reference speed must be specified in practical applications.
4.5 Radiation factor αradiation factor, o280
GB/T16539—1996
The factor that indicates the sound radiation efficiency is calculated by formula (2): a
Where: p.1—Sound power radiated by the vibrating surface of the machine, W; S. ——Area of the vibrating surface (see 3.8), m\, p
pc—Air acoustic impedance (p: average air density, c: air sound velocity), Pa·s/m, vz——S, square mean of the effective value of the vibration velocity on the surface, mm/s. a, p,,2 are three quantities in the same period. 4.6 Radiation index
is expressed in 10 igg.
4.7 Airborne sound power level Lwairborne sound power level, Lw(2)
The ratio of the sound power given to the reference sound power is taken as 10 times the logarithm with base 10. Sometimes it is expressed in a specified frequency width, such as octave sound power level, 1/3 octave sound power level, etc. The airborne sound power level is expressed in decibels (reference sound power: 1pW). The airborne sound power level Lw. for a specified portion of the machine surface is given by formula (3): Lws = 10 lg
where: p. Sound power radiated by the relevant machine surface, W, p. —reference sound power (10-12W1 PW), W. 4.8 Vibration measurement surface The surface or part of the surface assumed for the distribution of measurement positions. Its area is represented by the symbol S. 4.9 Extraneous structure-borne velocity level.....(3)
The vibration velocity level measured when the machine is not working or otherwise affected by irrelevant vibration sources. Additional structure-borne sound is generated by other structures outside the machine being measured, such as by a coupled assembly. 4.10 Spherical source of zero order Spherical vibration of the same phase and amplitude on the entire outer surface. 5 Test instruments
5.1 Overview
This standard specifies the test instruments and the sensors used. In most cases, lightweight accelerometers are suitable. Of course, other types of instruments and test techniques are also needed in special cases. (For example, non-contact sensors, laser Doppler test methods, etc.). 5.2 Vibration sensors
Vibration sensors should be able to be mounted on the vibrating surface. For vibration measurement over a wide frequency range, piezoelectric accelerometers are preferred. When selecting sensors for special occasions, the parameters of the sensors should be selected according to the requirements of environmental conditions.
When using an accelerometer, the flat part of its frequency response should be consistent with the measurement frequency range. The upper frequency limit of the accelerometer should be set at 1/3 of the resonant frequency of the accelerometer.
As long as the sensitivity is sufficient, the accelerometer should be as light as possible, so that the dynamic mass of the sensor is much smaller than the dynamic mass of the attachment point structure [for a flat plate, it should be 0.2ch2/f, see formula B2]. 5.3 Measuring amplifier
The signal generated by the sensor should be passed through a charge amplifier, an integrator, an amplifier, a filter and indicate the effective value: The instrument used for measuring structure-borne noise should also use a vibration meter that meets the standard requirements and has an A-weighting and radiation index weighting network. The instrument should have a decibel value indication, and its accuracy should meet the accuracy requirements of type 0 or type 1 sound level meters specified in GB3785. 5.4 Filter
GB/T16539—1996
The filter used for structure-borne noise measurement vibration meter, in addition to the high and low pass filters required by general vibration meters, should also be equipped with the following filters: - a band pass filter that meets the requirements of GB3241 standard; - an A-weighting network that meets the accuracy requirements of type 1 of GB3785 standard; - if possible, it is best to have a weighting network filter that meets the radiation index 10lga curve of the machine being measured. These radiation index curves should be set as standardized curves in the relevant test method standards of the corresponding machines. 5.5 Calibration
Vibration meters equipped with general bandpass filters should be inspected annually by the metrology department. Vibration and noise detectors equipped with radiation index weighting networks should be inspected once a year by designated professional metrology and testing departments. 6 Installation and operating conditions
6.1 In most cases, the radiation of sound power depends on two factors: installation and operating conditions, which are usually considered in accordance with Articles 6.2 and 6.3. However, for machines with corresponding airborne sound measurement procedures, they should be carried out in accordance with the provisions of their regulations. 6.2 Description of the machine
If the parts or auxiliary equipment of the machine have sound radiation, the operating status of the auxiliary equipment during the test should be specified. Additional structural sound sources should be described.
Note: If the procedures specified in this standard cannot directly measure additional structure-borne noise, the vibration spectrum of the connection system can be compared or related measurements can be performed if necessary.
6.3 Installation
The machine should be installed as close to the actual final use as possible. If the structural surface of the machine is covered with non-structural materials (such as sound insulation), the sensor should be installed on the surface of the non-structural material (see Appendix B). 6.4 Operating conditions
The machine should be operated under conditions that represent normal use. One or more of the following operating conditions are appropriate (see 6.1): a) The machine is under rated load or rated operating conditions; b) If it is different from a), the machine is under full load; c) The machine is unloaded (idling);
d) The machine is operated under normal use conditions with maximum sound radiation; e) The machine is operated under specified conditions with simulated load. 7 Determination of vibration velocity on the vibration measurement surface
7.1 The provisions of clauses 7.2 to 7.8 are general regulations. For professional test procedures for corresponding machines, some special provisions may be adopted.
Note: The accuracy of the test results depends to a large extent on the distribution and number of measuring points and the distribution of vibration velocities on the vibration measurement surface; the uncertainty of the method may increase when individual bandwidths have strong monotonous components. 7.2 Vibration test surface
7.2.1 A suitable measurement surface should be selected according to the criteria specified in 7.2.2 to 7.2.4. Note: When selecting the test surface, the results of any preliminary tests (7.2.4) and the composition of the radiating area (e.g. the presence of reinforcement members) should be considered. 7.2.2 Machines of the same structure
If the machines have the same structure and are geometrically symmetrical, and the excitation forces are uniform and symmetrical, then the results of preliminary tests have proved that the corresponding average velocity levels of all unit structures in any frequency band are equivalent, so that the tests can be carried out on a single structure. 7.2.3 Uniform distribution of measuring points
The vibration measurement surface is divided into N parts with an area equal to S./N, and the measuring points are arranged at the center of each part. 7.2.4 Uneven distribution of measuring points
If it is known from the initial results that some parts of the vibration test surface vibrate more strongly than other parts, the measuring points should be arranged more densely on the stronger part.
GB/T16539—1996
In this case, each measuring point i represents the area Ssi of that part. 7.3 Number of measuring points
The initial number of measuring points on the vibration measurement surface should be selected according to Table 1. Table 1 Initial number of measuring points
Area of vibration measurement surface S., m2
110 Spherical source of zero order Spherical vibration with the same phase and amplitude on the entire outer surface. 5 Test instrument
5.1 Overview
This standard specifies the test instrument and the sensor used. In most cases, it is suitable to use a lightweight accelerometer. Of course, other types of instruments and test techniques are also needed in special cases. (For example, non-contact sensors, laser Doppler test methods, etc.). 5.2 Vibration sensor
The vibration sensor should be able to be installed on the vibrating surface. As a vibration measurement with a wide frequency range, piezoelectric accelerometers are preferred. When selecting sensors for special occasions, the parameters of the sensor should be selected according to the requirements of environmental conditions.
When using an accelerometer, the flat part of its frequency response should be consistent with the measurement frequency range. The upper frequency limit of the accelerometer should be set at 1/3 of the resonant frequency of the accelerometer.
As long as the sensitivity is sufficient, the accelerometer should be as light as possible so that the dynamic mass of the sensor is much smaller than the dynamic mass of the structure at the attachment point [for a flat plate, it should be 0.2ch2/f, see formula B2]. 5.3 Measuring amplifierbzxZ.net
The signal generated by the sensor should be passed through a charge amplifier, an integrator, an amplifier, a filter and an effective value should be indicated: The instrument used for measuring structure-borne noise should also use a vibration meter that meets the standard requirements and has an A-weighting and radiation index weighting network. The instrument should have a decibel value indication, and its accuracy should meet the accuracy requirements of type 0 or type 1 sound level meters specified in GB3785. 5.4 Filters
GB/T16539—1996
Filters used in vibration meters for structure-borne noise measurement, in addition to the high-pass and low-pass filters required for general vibration meters, should also be equipped with the following filters: - a bandpass filter that meets the requirements of GB3241 standard; - an A-weighting network that meets the accuracy requirements of GB3785 standard type 1; - if possible, it is best to have a weighting network filter that meets the 10lga curve of the radiation index of the machine being measured. These radiation index curves should be set as standardized curves in the relevant test method standards for the corresponding machines. 5.5 Calibration
Vibration meters equipped with general bandpass filters should be inspected annually by the metrology department. Vibration noise detectors equipped with radiation index weighting networks should be inspected once a year by designated professional metrology and testing departments. 6 Installation and operating conditions
6.1 In most cases, the radiation of sound power depends on two factors: installation and operating conditions, which are usually considered in accordance with Articles 6.2 and 6.3. However, for machines with corresponding airborne sound measurement procedures, the measurement should be carried out in accordance with the provisions of the regulations. 6.2 Description of the machine
If the parts or auxiliary equipment of the machine have sound radiation, the operating status of the auxiliary equipment during the test should be specified. Additional structural sound sources should be described.
Note: If the procedures specified in this standard cannot directly measure additional structure-borne noise, the vibration spectrum of the connection system can be compared or relevant measurements can be made if necessary.
6.3 Installation
The machine should be installed as much as possible according to the actual final use conditions. If the structural surface of the machine is covered with non-structural materials (such as sound insulation materials), the sensor should be installed on the surface of the non-structural material (see Appendix B). 6.4 Operating status
The machine should be operated under conditions that represent normal use. One or more of the following operating conditions is suitable (see 6.1): a) the machine is under rated load or rated operating conditions; b) if different from a), the machine is under full load; c) the machine is unloaded (idling);
d) the machine is operated in normal use conditions with maximum sound radiation; e) the machine is operated under specified conditions with simulated load. 7 Determination of vibration velocity on vibration measurement surface
7.1 The provisions of 7.2 to 7.8 are general procedures. For special test procedures for corresponding machines, some special provisions may be adopted.
Note: The accuracy of the test results depends to a large extent on the distribution and number of measurement points and the distribution of vibration velocities on the vibration measurement surface; when individual bandwidths have strong monotonous components, the uncertainty of the method may increase. 7.2 Vibration test surface
7.2.1 The appropriate measurement surface should be selected according to the criteria specified in 7.2.2 to 7.2.4. NOTE When selecting the test surface, the results of any preliminary tests (7.2.4) and the composition of the radiating area (e.g. the presence of reinforcements) should be considered. 7.2.2 Machines of the same construction
If the machines have the same construction and are geometrically symmetrical, and the excitation forces are uniform and symmetrical, then the results of preliminary tests have shown that the corresponding average velocity levels of all unit structures in any frequency band are equivalent, so that the tests can be carried out on a single structure. 7.2.3 Uniform distribution of measuring points
The vibration test surface is divided into N parts with an area equal to S./N, and the measuring points are arranged at the center of each part. 7.2.4 Uneven distribution of measuring points
If it is known from preliminary results that some parts of the vibration test surface vibrate more strongly than other parts, the measuring points should be arranged more densely on the stronger part.
GB/T16539—1996
In this case, each measuring point i represents the area of the part Ssi. 7.3 Number of measuring points
The initial number of measuring points on the vibration measuring surface should be selected according to Table 1. Table 1 Initial number of measuring points
Area of vibration measuring surface S., m2
110 Spherical source of zero order Spherical vibration with the same phase and amplitude on the entire outer surface. 5 Test instrument
5.1 Overview
This standard specifies the test instrument and the sensor used. In most cases, it is suitable to use a lightweight accelerometer. Of course, other types of instruments and test techniques are also needed in special cases. (For example, non-contact sensors, laser Doppler test methods, etc.). 5.2 Vibration sensor
The vibration sensor should be able to be installed on the vibrating surface. As a vibration measurement with a wide frequency range, piezoelectric accelerometers are preferred. When selecting sensors for special occasions, the parameters of the sensor should be selected according to the requirements of environmental conditions.
When using an accelerometer, the flat part of its frequency response should be consistent with the measurement frequency range. The upper frequency limit of the accelerometer should be set at 1/3 of the resonant frequency of the accelerometer.
As long as the sensitivity is sufficient, the accelerometer should be as light as possible so that the dynamic mass of the sensor is much smaller than the dynamic mass of the structure at the attachment point [for a flat plate, it should be 0.2ch2/f, see formula B2]. 5.3 Measuring amplifier
The signal generated by the sensor should be passed through a charge amplifier, an integrator, an amplifier, a filter and an effective value should be indicated: The instrument used for measuring structure-borne noise should also use a vibration meter that meets the standard requirements and has an A-weighting and radiation index weighting network. The instrument should have a decibel value indication, and its accuracy should meet the accuracy requirements of type 0 or type 1 sound level meters specified in GB3785. 5.4 Filters
GB/T16539—1996
Filters used in vibration meters for structure-borne noise measurement, in addition to the high-pass and low-pass filters required for general vibration meters, should also be equipped with the following filters: - a bandpass filter that meets the requirements of GB3241 standard; - an A-weighting network that meets the accuracy requirements of GB3785 standard type 1; - if possible, it is best to have a weighting network filter that meets the 10lga curve of the radiation index of the machine being measured. These radiation index curves should be set as standardized curves in the relevant test method standards for the corresponding machines. 5.5 Calibration
Vibration meters equipped with general bandpass filters should be inspected annually by the metrology department. Vibration noise detectors equipped with radiation index weighting networks should be inspected once a year by designated professional metrology and testing departments. 6 Installation and operating conditions
6.1 In most cases, the radiation of sound power depends on two factors: installation and operating conditions, which are usually considered in accordance with Articles 6.2 and 6.3. However, for machines with corresponding airborne sound measurement procedures, the measurement should be carried out in accordance with the provisions of the regulations. 6.2 Description of the machine
If the parts or auxiliary equipment of the machine have sound radiation, the operating status of the auxiliary equipment during the test should be specified. Additional structural sound sources should be described.
Note: If the procedures specified in this standard cannot directly measure additional structure-borne noise, the vibration spectrum of the connection system can be compared or relevant measurements can be made if necessary.
6.3 Installation
The machine should be installed as much as possible according to the actual final use conditions. If the structural surface of the machine is covered with non-structural materials (such as sound insulation materials), the sensor should be installed on the surface of the non-structural material (see Appendix B). 6.4 Operating status
The machine should be operated under conditions that represent normal use. One or more of the following operating conditions is suitable (see 6.1): a) the machine is under rated load or rated operating conditions; b) if different from a), the machine is under full load; c) the machine is unloaded (idling);
d) the machine is operated in normal use conditions with maximum sound radiation; e) the machine is operated under specified conditions with simulated load. 7 Determination of vibration velocity on vibration measurement surface
7.1 The provisions of 7.2 to 7.8 are general procedures. For special test procedures for corresponding machines, some special provisions may be adopted.
Note: The accuracy of the test results depends to a large extent on the distribution and number of measurement points and the distribution of vibration velocities on the vibration measurement surface; when individual bandwidths have strong monotonous components, the uncertainty of the method may increase. 7.2 Vibration test surface
7.2.1 The appropriate measurement surface should be selected according to the criteria specified in 7.2.2 to 7.2.4. NOTE When selecting the test surface, the results of any preliminary tests (7.2.4) and the composition of the radiating area (e.g. the presence of reinforcements) should be considered. 7.2.2 Machines of the same construction
If the machines have the same construction and are geometrically symmetrical, and the excitation forces are uniform and symmetrical, then the results of preliminary tests have shown that the corresponding average velocity levels of all unit structures in any frequency band are equivalent, so that the tests can be carried out on a single structure. 7.2.3 Uniform distribution of measuring points
The vibration test surface is divided into N parts with an area equal to S./N, and the measuring points are arranged at the center of each part. 7.2.4 Uneven distribution of measuring points
If it is known from preliminary results that some parts of the vibration test surface vibrate more strongly than other parts, the measuring points should be arranged more densely on the stronger part.
GB/T16539—1996
In this case, each measuring point i represents the area of the part Ssi. 7.3 Number of measuring points
The initial number of measuring points on the vibration measuring surface should be selected according to Table 1. Table 1 Initial number of measuring points
Area of vibration measuring surface S., m2
11): a) the machine is under rated load or rated operating conditions; b) if different from a), the machine is under full load; c) the machine is unloaded (idling);
d) the machine is operating under normal use conditions with maximum sound radiation; e) the machine is operating under specified conditions with simulated load. 7 Determination of vibration velocity on the vibration measurement surface
7.1 The provisions of clauses 7.2 to 7.8 are general procedures. For special test procedures for corresponding machines, some special provisions may be adopted.
Note: The accuracy of the test results depends to a large extent on the distribution and number of measurement points and the distribution of vibration velocities on the vibration measurement surface; when individual bandwidths have strong monotonous components, the uncertainty of the method may increase. 7.2 Vibration test surface
7.2.1 A suitable measurement surface should be selected according to the criteria specified in clauses 7.2.2 to 7.2.4. Note: When selecting the test surface, the results of any preliminary tests (7.2.4) and the composition of the radiating area (such as reinforcement members) should be taken into account. 7.2.2 Machines of the same structure
If the machines have the same structure and are geometrically symmetrical, and their excitation forces are uniform and symmetrical, then the results of the initial tests have proved that the corresponding average speed levels of all unit structures in any frequency band are equivalent, so that the test can be carried out on a single structure. 7.2.3 Uniform distribution of measuring points
The vibration measurement surface is divided into N parts with an area equal to S./N, and the measuring points are arranged at the center of each part of the surface. 7.2.4 Uneven distribution of measuring points
If it is known from the initial results that some parts of the vibration test surface vibrate more strongly than other parts, the measuring points should be arranged more densely on the stronger part.
GB/T16539—1996
In this case, each measuring point i represents the area of the part Ssi. 7.3 Number of measuring points
The initial number of measuring points on the vibration measurement surface should be selected according to Table 1. Table 1 Number of initial measuring points
Area of vibration measuring surface S.,m2
11): a) the machine is under rated load or rated operating conditions; b) if different from a), the machine is under full load; c) the machine is unloaded (idling);
d) the machine is operating under normal use conditions with maximum sound radiation; e) the machine is operating under specified conditions with simulated load. 7 Determination of vibration velocity on the vibration measurement surface
7.1 The provisions of clauses 7.2 to 7.8 are general procedures. For special test procedures for corresponding machines, some special provisions may be adopted.
Note: The accuracy of the test results depends to a large extent on the distribution and number of measurement points and the distribution of vibration velocities on the vibration measurement surface; when individual bandwidths have strong monotonous components, the uncertainty of the method may increase. 7.2 Vibration test surface
7.2.1 A suitable measurement surface should be selected according to the criteria specified in clauses 7.2.2 to 7.2.4. Note: When selecting the test surface, the results of any preliminary tests (7.2.4) and the composition of the radiating area (such as reinforcement members) should be taken into account. 7.2.2 Machines of the same structure
If the machines have the same structure and are geometrically symmetrical, and their excitation forces are uniform and symmetrical, then the results of the initial tests have proved that the corresponding average speed levels of all unit structures in any frequency band are equivalent, so that the test can be carried out on a single structure. 7.2.3 Uniform distribution of measuring points
The vibration measurement surface is divided into N parts with an area equal to S./N, and the measuring points are arranged at the center of each part of the surface. 7.2.4 Uneven distribution of measuring points
If it is known from the initial results that some parts of the vibration test surface vibrate more strongly than other parts, the measuring points should be arranged more densely on the stronger part.
GB/T16539—1996
In this case, each measuring point i represents the area of the part Ssi. 7.3 Number of measuring points
The initial number of measuring points on the vibration measurement surface should be selected according to Table 1. Table 1 Number of initial measuring points
Area of vibration measuring surface S.,m2
1
100.1(Lwj+c,)
Where: Lw,-
1st octave or 1/3 octave band power level, dB:
jmx and C; are determined by the data given in Articles C2 and C3 according to octave or 1/3 octave respectively. Calculated by octave, the C1 value of jmx7 is given by Table C1: C2
C, value corresponding to octave number
Octave center frequency, Hz
C3 Calculated by 1/3 octave, the C1 value of jmx-21 is given by Table C2: 4
Table C2 C, value corresponding to 1/3 octave number
1/3 octave center frequency, Hz
1/3 octave center frequency, Hz
1/3 octave center frequency, Hz
Appendix D
(Standard Appendix)
—10, 9
Method for determining radiation index 10Igo
(Ci))
The radiation index 10Ig should be measured under the installation and operating conditions specified in 6.3 and 6.4. Specifically, the vibration required by the corresponding operating state (6.4) should be generated by passband or wideband excitation. The measurement of the frequency band sound power level should be carried out in a reverberation room or free field according to the methods specified in GB3767, GB6881, GB6882, GB10069.1, or ISO9614. The vibration velocity level Z is measured in accordance with Articles 7 and 8.2. Substituting the values of Lws, L and 10lgSs/S. (see 8.3) into formula (7), the 10Iga curve relative to frequency can be obtained. It is recommended to use a 1/3 standard bandpass filter to measure the radiation index curve. For a group of related machines, if there is experimental or theoretical proof, it can be put forward as the basis for the standard curve (as shown in Figure 4), then 289
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