GB/T 21231-2007Acoustics -- Measurement of airborne noise emitted and structure-borne vibration induced by small air-moving devices -- Part 1: Airborne noise measurement (English PDF)

3.1 General definition

3.1.1

Ventilation unit air-movingdevice (AMD) Fan fan A device that drives the impeller to rotate by electronically or mechanically controlling the motor to flow air.

Note 1. A ventilator has at least one air inlet and one air outlet. The air inlet and outlet may have connections to the piping system or other airflow paths.

Note 2. Testing may be performed in a specific frame, motor, rotor, and different accessories (eg, guard) configurations. For this part, each such configuration is called A ventilation device.

Note 3. The term "fan" in this section is used to mean "ventilation device" and can be in various forms such as axial flow, centrifugal or mixed flow. Need to distinguish type at the time, an attribute (such as axial flow, centrifugal or mixed flow, etc.) is added.

3.1.2

Micro fan fan

The ventilation device with a maximum volume flow rate less than or equal to 0.015 m3/s.

Note 1. The micro-fan is a refinement of the fan when tested in this section.

Note 2. Table 4 of 22.4.2 of ISO 5801:2007 is only applicable to the range of Reynolds number not less than 12000. The lower limit of this Reynolds number and volume flow 0.01m3/s approximates. Since many cooling applications pursue lower displacement fans, the method in Appendix A of JBMS-72.2003 is used.

Measure the pq curve of the microfan.

3.2 Acoustic definition

3.2.1

Sound power level LW the base 10 logarithm of the ratio of the sound power P to the reference sound power P0 is expressed by the equation (1) and the unit is decibel (dB).

LW = 10lg

In the formula.

P0---reference sound power, in watts (W), P0 = 1pW.

Note. If the frequency band weighted and/or specified in IEC 61672-1 [6] is used, it is recommended to indicate it with the corresponding subscript. For example, LW A indicates A weighting Sound power level.

3.2.2

Test frequency range frequencyrangeofinterest from 1/3 octave frequency range from 100Hz to 10kHz.

Note 1. ISO 266 [1] gives the center frequency of 1/3 octave.

Note 2. For the measurement of small, low-noise fans (ie micro-fans), the radius of the test hemisphere may be less than 1 m depending on the size of the test box used, but should not Less than 0.5m. However, a radius of less than 1 m limits the frequency range of the test. For details, please refer to B.1 in ISO 7779:2010.

3.2.3

Test box insertion loss insertionlossoftestplenum deltaL the sound power level difference measured when the sound source is installed inside and outside the test box is defined as equation (2).

deltaL=LW, out-LW,in (2) in the formula.

LW, out---the sound power level when the sound source is installed outside the test box;

LW,in --- The sound power level when the sound source is installed in the test box.

Note. The insertion loss of the test box is expressed in dB.

3.3 Aerodynamic definition

3.3.1

Test box testplenum

A structural member on which the ventilating device to be tested is mounted for measuring noise radiation.

Note. The test box creates ventilation resistance to the ventilation unit, but allows the noise of the ventilation unit to enter the test chamber with little additional attenuation. Can be tested the sound power radiated by the ventilation device outside the box is measured.

3.3.2

Ventilation performance curve air-movingdeviceaerodynamicperformancecurve "pq curve" A plot of the static pressure of a fan as a function of volumetric flow under standard air conditions and a constant operating voltage and frequency.

Note 1. For the purposes of this section, the modifier "pneumatic" is inserted before the "performance curve" to distinguish the noise radiation characteristics from the volumetric flow.

Note 2. The representation of this curve is taken from ISO 5801 or Appendix A, which are complementary to each other. The method specified in Appendix A applies to volume flow not Small air mobile devices over 0.015m3/s.

Note 3. For convenience, this section uses the term "pq curve".

3.3.3

Point of operation

The point on the aerodynamic performance curve of the ventilation device that corresponds to a specific volume flow.

Note. When testing, the operating point is controlled by adjusting the slider of the test box outlet part.

3.3.4

Full static efficiency of ventilation unit overalstaticefficiencyofair-movingdevice etao,s the product of the fan static pressure and volume flow divided by the input electrical power.

Note 1. The full static efficiency of the ventilation device is expressed as a percentage, as in equation (3).

etao, s=

Ps, fqV

Pinput

×100 (3)

In the formula.

Ps, f---fan static pressure, the unit is Pascal (Pa);

qV --- volume flow in cubic meters per second (m 3/s);

Pinput---The motor input power provided at the motor terminals in watts (W), (effective power, reactive power without resistance component).

Note 2. The definition of the ventilation device includes the motor, the impeller and the frame. Therefore, full static efficiency includes both motor efficiency and aerodynamic efficiency of the impeller and frame.

3.3.5

Standard atmospheric density standardairdensity Air density at standard atmospheric conditions.

Note. The air density under standard atmospheric conditions is 1.20kg/m3.

3.3.6

Standard atmospheric conditions (for aerodynamic performance measurements) standardairconditions(foraerodynamicperformancemeasurement) Specific atmospheric conditions.

Note. The standard atmospheric conditions are. temperature 20 ° C, relative humidity 50%, atmospheric pressure 1.013 × 105 Pa.

5.1 Overview

The design is intended to meet the limits of the specified maximum volume flow and maximum fan static pressure. This design provides adjustable ventilation Flow resistance, while ensuring sound.

Note 1. Please refer to 5.5 for the requirements for confirming the sound transmission rate according to this section.

The reference design of the test box is given in 5.2~5.6, as shown in Figure 1~8. These sub-clauses and other provisions of this section also indicate the design can be different from this design, mainly in reducing the linear size of the frame and the selection of certain dimensions of other components, while at the same time the geometric ratio remains the same within the 1/4 scale. Such reduction reduces the maximum allowable volume flow of the tested ventilation unit and the test chamber the decrease in the product is proportional to the cube, which is reduced by the cubic of the linear scale [see equation (4)].

Note 2. These changes may be more suitable for smaller or quieter fans, as well as for test chambers that are too narrow for a full-scale test chamber.

The standard deviation of reproducibility resulting from the above allowable changes is within the scope of Table 1. Other changes to the reference design for the sound power of the ventilation unit the extent of the uncertainty in the measurement uncertainty is not clear.

5.2 Test Box. Main Components

5.2.1 General. As shown in Figure 1, the test box shall consist of a sealed cavity covered with a layer of sound-permeable but airtight polyester film on its frame.

A mounting plate and an adjustable outlet end unit.

The test box shall meet the requirements specified in 5.2.2~5.2.7.

5.2.2 Box size. Figure 1 shows the dimensions of the full-scale test box.

5.2.3 Cover layer. An isotropic polyester film with a nominal thickness of 25 µm to 50 µm. The overlay can be protected with a bead (see Figure 1 and figure 2).

5.2.4 Frame. A suitable material with a nominal size of 50 mm x 50 mm is used to ensure the structural integrity of the test box. The gusset is recommended Wooden structures sometimes require other materials (see Figure 3). The linear dimension of the frame including the thickness of the frame member should be larger than the test box Small proportion.

5.2.5 Frame material. Experience has shown that both hardwood (such as birch) and aluminum pipe have sufficient strength, rigidity and durability, and Acoustic performance requirements listed in 5.5.

5.2.6 Vibration isolation. For any size test box, the box legs or supports shall provide vibration isolation between the test box and the floor (platform). Purpose of vibration isolation it is to block the vibration transmission path between the test box and the floor. Regardless of the method chosen, the total height of the full test leg should be kept at 0.1m.

(See Figures 1 and 3). The height of the 0.1m box leg should be proportional to the box size.

5.2.7 Fan static pressure hole measurement. The pressure ring should be directly fixed behind the mounting plate, and the size of the ring matches the circumference of the mounting plate (see Figure 4).

The circumference of the pressure ring should match the size of the test box. The pressure ring diameter and the static pressure hole are not necessarily proportional, but need to remain unchanged.

5.3 Mounting plate components

The mounting plate components shall consist of a type of adapter plate that is packaged onto a reinforced rubber plate that is then packaged for testing by aluminum beading.

On the box frame (Figure 1, Figure 4 and Figure 5). Secure the fan to the rubber plate with the adapter plate. Can be adapted as shown in Figure 5.

In the form of installation of the axial flow fan, other installation forms more suitable for the particular ventilation device to be tested may also be used. The adapter plate should not handle airflow Interference is generated and does not produce any additional acoustic radiation other than the noise of the ventilation device itself.

The mounting plate components (including the adapter plate and the flexible plate) can be replaced by a single damper plate with an opening similar to the adapter plate (but without the adapter) Plate), damper material requirements have no significant effect on airborne sound measurements.

The technical requirement for the damping plate is to freely suspend the plate with a size of 1 m2 without fan mounting holes through two corners and measure at its center.

The mechanical admittance level in the frequency range of 25Hz~5000Hz does not exceed -45dB (reference value. 1m/Ns), and the mechanical admittance level measurement should be ANSI/ASAS2.32.

The tolerance of the admittance stage is ±8dB from 2Hz to 100Hz, ±4dB from 100Hz to.200Hz, and ±2dB from.200Hz to 5000Hz.

These tolerance limits ensure that the damper plate has sufficient damping to prevent frame excitation. These replacement plates are sometimes used in connection with fan vibration in measurement (see GB/T 21231.2). Using the same mounting plate for acoustic and vibration measurements will increase the efficiency of joint testing. If replaced for the design of the mounting plate, the mechanical admittance of the replacement version should be described in the test report according to the impedance test of the plate.

The opening of the adapter plate shall be the same as recommended by the manufacturer of the ventilation device. The opening of the pressure plate frame and the rubber plate shall be larger than the opening of the adapter plate.

Minimize disturbances to the airflow. The length, width, thickness of the aluminum bead and the length and width of the reinforced rubber mounting plate should be proportional to the size of the test box.

Other sizes, including the thickness of the board, may be disproportionate.

5.4 Adjustable air outlet parts

The adjustable air outlet part shall consist of a plate with fixed openings and a slider (slidable plate) for the exit of the full-scale test box the area is continuously adjustable from 0m2 to 0.2m2 (see Figure 6 to Figure 8). The maximum area of the outlet should be proportional to the square of the linear ratio of the test box.

Note. The operating point of the ventilation unit is controlled during the test by adjusting the position of the outlet part slide.

5.5 Test box insertion loss

For this part, the validity of the test box is evaluated by the insertion loss of the test box (3.2.3).

According to the following steps a) ~ c), the 1/3 octave band insertion loss of the test box should not exceed -2dB~3dB, it is recommended not to exceed ±1.5dB.

a) The sound source (such as the speaker) sound power level should be measured twice. once the sound source is in the test box, and the other time the sound source is outside the test box, but the measurement should be in the same location in the test chamber. Hemispherical sound transmission if the insertion loss is measured in a free field above the reflecting surface the array should be centered on the sound source.

b) if the position of the speaker source is moved relative to the reflective surface (ground and mounting panel) in two sound power measurements, then Measurement uncertainty may occur. To do this, mount the sound source on the ground, remove the mounting panel and flip the test box 90° so that the face normally covered by the mounting panel is parallel to the ground and the exit is on the top surface. This allows the test box to be mo...