【法规名称】
【法规编号】 79202 什么是编号？
【正 文】
第2页 CAP 400C NOISE CONTROL (AIR COMPRESSORS) REGULATIONS
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[接上页] Po is the effective reference sound pressure, equal to 20x10-6 Pa. The value LpA of the A-weighted sound pressure level, expressed in dB(A), is obtained by applying the weighting A to the measuring system. 3.2 Measuring surface The measuring surface of area S (see paragraph 8.3) is a hypothetical surface surrounding the sound source and on which the measuring points are arranged (see paragraph 6.3). 3.3 Surface sound pressure level LpAm The surface sound pressure level LpAm is the root mean square of the sound pressures recorded on the measuring surface, calculated in accordance with the method set out in paragraph 8.4. 3.4 Sound power level LWA The sound power level LWA is obtained by applying the weighting A to the sound power level LW. The sound power level LW, expressed in dB, of a sound source is defined by- LW = 10 log10W/Wo Where- W is the total sound power generated by the sound source, expressed in watts; Wo is the reference sound power, equal to 10-12W. The value LWA of the A-weighted sound power level, expressed in dB, is obtained by applying the weighting A to the measuring system. 3.5 Extraneous noise Extraneous noise means the noise resulting from background noise and parasitic noise. 3.5.1 Background noise Background noise means any noise recorded at the measuring points which is not generated by the appliance. 3.5.2 Parasitic noise Parasitic noise means any noise at the measuring points which is generated by the appliance but not directly radiated by it. 4. CRITERION TO BE USED FOR EXPRESSING RESULTS 4.1 Acoustic criterion for the environment The acoustic criterion for the environment of the appliances is their sound power level. 5. MEASURING INSTRUMENTS 5.1 General The instruments shall be designed to measure the A-weighted level of the root mean square of the sound pressure. The level of the root mean square value in time for a measurement point is obtained either by direct reading of the instrument, or by calculation in accordance with paragraph 11. 5.2 Measuring instruments The following instruments may be used- (a) a sound level meter meeting the requirements of International Electrotechnical Commission (IEC) publication 651:1979 (type 1). The meter shall be set at "slow" response; (b) an integrating sound level meter effecting analog or digital integration of the squared signal over a given time interval meeting the requirements of IEC 804:1985 (type 1). The meter shall be set at "fast" response. 5.3 Microphone with cable Use shall be made of a microphone with cable complying with IEC publication 651:1979, and calibrated for free field measurement. 5.4 Weighting network Use shall be made of an A-weighting network meeting the requirements of IEC publication 651:1979. 5.5 Inspection of the measuring apparatus Before the tests, the acoustic properties of the entire apparatus (measuring instruments including microphone and cable) shall be checked by means of a calibrated sound source with an accuracy of at least 0.5 dB (e.g. a pistonphone); the apparatus shall be checked again immediately after each series of measurements. 6. TEST CONDITIONS 6.1 Operation of the appliance during measurements The appliance shall be brought to its steady-state temperature within the range specified by the manufacturer. It shall be operated at its nominal speed and its nominal pressure. The nominal speed and pressure are those recommended by the manufacturer. 6.2 Measuring site The measuring site must be flat and horizontal. 6.3 Measurement surface, measuring distance, location and number of measuring points 6.3.1 Measuring surface and measuring distance The measuring surface to be used for the test shall be a hemisphere. The radius shall be- -4 m, where the greatest dimension of the appliance to be tested is not more than 1.5 m; -10 m, where the greatest dimension of the appliance to be tested is more than 1.5 m but not more than 4 m; -16 m, where the greatest dimension of the appliance to be tested is more than 4 m. 6.3.2 Location and number of measuring points For the measurements there shall be 6 measuring points on a hemisphere of radius r, i.e. points 1, 2, 3, 4, 5 and 6 arranged as illustrated in figures 1 and 2, with variations in the value of z of points as shown in Table 1. For testing of the appliance, the geometric centre of the appliance shall be positioned vertically above the centre of the hemisphere. The x-axis of the set of coordinates, in relation to which the positions of the measuring points are fixed, shall be parallel to the main axis of the appliance. The 6 measuring points shall have the following coordinates (Table 1) as measured from the centre of the hemisphere- TABLE 1 X Y Z 1 r 0.0 1.50 m 2 0.0 r 1.50 m 3 -r 0.0 1.50 m 4 0.0 -r 1.50 m 5 -0.27 r 0.65 r 0.71 r + 1.5 m 6 0.27 r -0.65 r 0.71 r + 1.5 m r = radius of hemisphere 7. MEASUREMENTS 7.1 Measurement of extraneous noise Only the background noise shall be taken into account for the purpose of corrections. Background noise shall be recorded at the measuring points (see paragraph 6.3.2) with the appliance switched off, i.e. no sound emission (see paragraph 7.2). |
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