Detail of GB/T 34877.4-2024

Introduction of GB/T 34877.4-2024

GB/T 34877.4-2024 Industrial fans - Determination of fan sound power levels under standardized laboratory conditions - Part 4 : Sound intensity method 1 Scope This document applies to industrial fans as defined in ISO 5801 and ISO 13349 (all parts). It is limited to the determination of airborne sound emission for the specified set-ups. Vibration is not measured, nor is the sensitivity of airborne sound emission to vibration effects determined. This document applies to the sizes of the fan, but does not apply to the limit of the practical aspects of the test installations. This document determines sound power by using sound intensity measurements on a measurement surface which encloses the sound source. It provides guidelines on the acoustical environment, ambient noise, measurement surface, and number of measurements. The design of the test set-ups and the physical orientation of a fan installed shall be in accordance with ISO 5801 and ISO 13347-2. 2 Normative references The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. ISO 5136 Acoustics - Determination of sound power radiated into a duct by fans and other air-moving devices- In-duct method Note: GB/T 17697- 2014 Acoustics - Determination of sound power radiated into a duct by fans and other air-moving devices - In-duct method (ISO 5136 : 2003, IDT) ISO 5801 Fans - Performance testing using standardized airways Note: GB/T1236-2017 Industrial fan - Performance testing using standardized airways (ISO 5801 : 2007, IDT) ISO 9614-1 Acoustics - Determination of sound power levels of noise source using sound intensity - Part 1 : Measurement at discrete points Note: GB/T 16404-1996 Acoustics-Determination of sound power levels of noise sources using sound intensity - Part 1: Measurement at discrete points (ISO 9614-1:1993, EQV) ISO 9614-2 Acoustics - Determination of sound power levels of noise sources using sound intensity - Part 2 : Measurement by scanning ISO 13347-1 : 2004 Industrial fans - Determination of fan sound power levels under standardized laboratory conditions - Part 1 : General overview Note: GB/T 34877.1-2023 Industrial fans - Determination of fan sound power levels under standardized laboratory conditions - Part 1 : General overview (ISO 13347-1 :2004,IDT) ISO 13347-2 Industrial fans - Determination of fan sound power levels under standardized laboratory conditions - Part 2 : Reverberant room method Note: GB/T 34877.2-2023 Industrial fans - Determination of fan sound power levels under standardized laboratory conditions - Part 2 : Reverberant room method (ISO 13347-2 :2004,IDT) ISO 13349 (all parts) Industrial fans - Vocabulary and definitions of categories Note: GB/T 19075-2003 Industrial fans - Vocabulary and definitions of categories (ISO 13349:1999, IDT) IEC 61094-2 Electroacoustics - Measurement microphones - Part 2 : Primary method for pressure calibration of laboratory standard microphones by the reciprocity technique Note : GB/T 20441.2-2018 Electroacoustics - Measurement microphones - Part 2:Primary method for pressure calibration of laboratory standard microphones by the reciprocity technique (IEC 61094-2 :2009 ,IDT) 3 Terms and definitions No terms and definitions are defined in this document. 4 Instruments and methods of test 4.1 General Full details of the instrumentation and its requirements are given in ISO 13347-1. Particular requirements are given in the following subclauses. 4.2 Reference sound source (RSS) The RSS shall be used to qualify the performance of the sound intensity measurement system and personnel, and to determine a sound power level adjustment for the specific site conditions. To be used for these purposes, the RSS shall be of an appropriate type, be calibrated accurately and be properly maintained. AII requirements for the RSS are specified in ISO 13347-1. Note: For sound intensity measurements, the use of two or more different configurations of the intensity probe, or different probes, maybe required to cover the entire frequency range in conformance with Table 1. The useful frequency range for accurate sound intensity measurements is dependent upon the character of the sound field. Care should be taken to verify that sound intensity measurements are accurate in the actual measurement environment. 4.3 Transducer and instrumentation system calibration checks Before and after each sound power determination, the following calibration checks shall be performed. A calibration cheek of the entire measuring system at one or more frequencies within the frequency range of interest shall be made for each microphone. An acoustical calibrator conforming to IEC 61094-2 and having an accuracy of ±0.5 dB shall be used for this purpose. In conformance with IEC 61094-2, the calibrator shall be checked at least once every year to verify that its output has not changed. In addition, an electrical calibration of the instrumentation system over the entire frequency range of interest shall be performed periodically, at intervals of not more than one year. In addition to the calibration check, the field check procedure for sound intensity measurement specified by the manufacturer shall be performed. If no field check procedure is specified, the following procedure shall be performed The intensity probe shall be placed on the measurement surface, oriented normal to the surface, at a position where the noise is characteristic for the fan equipment under test. The sound intensity shall be measured. The intensity probe shall be rotated through 180° and placed with its acoustical centre in the same position as the initial measurement. The sound intensity shall be measured again. The intensity probe should be mounted on a stand or other mechanical device so that its acoustical centre retains the same position when the probe is rotated. For the octave band with the highest level, the absolute difference between the two levels shall be less than the value in Table 2 for the measuring equipment to be acceptable. The two sound intensities shall be of opposite sign. 4.4 Performance verification Periodically, the performance of the instrumentation system shall be verified by determining the sound power of a reference sound source using the procedures specified in ISO 13347-1. The sound power level determined for the reference source shall differ from its calibrated value over the frequency range of interest by no more than the tolerances given in Table 3. 4.5 Test method The basis of the test method originated in ISO 9614-1. The test method covers a wider frequency range and contains requirements somewhat more specific and restrictive than those of ISO 9614-1, and also provides for sound power level adjustments as described below. With the exception of the adjustments, however, measurements made in conformance with this test method will be in conformance with ISO 9614-1 over their common frequency range. The basic requirement is the measurement of the sound intensity distribution around the fan. A measurement surface is defined which encloses the entire fan, fan inlet, or fan outlet, depending upon the objective of the test. A set of sound intensity measurements is made about this surface. The results of these measurements are compared with a set containing half the number of measurements, to ensure the adequacy of the number of measurements and the accuracy of the data. The sound power level is calculated using the surface area and the measured sound intensity data. Adjustments shall be made for duct-end corrections, if required, and based on measurements of a calibrated RSS. Prior to sound intensity measurements on the source of interest, the sound intensity measurement instrumentation and personnel are to be qualified by conducting measurements about an RSS.

Contents of GB/T 34877.4-2024