BS ISO 6798-1:2020 pdf download.Reciprocating internal combustion engines — Measurement of sound power level using sound pressure.
5 Instrumentation
5.1 General
The instrumentation system, including the microphones, cables and windscreen, II used, shall meet the requirements of IEC 61672-1, class 1, and the filters shall meet the requirements of IEC 61260-1, class 1.
5.2 Calibration
Before and after each series of measurements, a sound calibrator meeting the requirements of IEC 60942. class 1 shall be applied to each microphone to verify the calibration of the entire measuring system at one or more frequencies within the frequency range of interest. Without any adjustment, the difference between the readings made before and after each series of measurements shall be less than or equal to 0,5 dB. If this value is exceeded, the results of the series of measurements shall be discarded.
The sound calibrator, filter and the instrumentation system which meet the requirements, and the reference sound source (RSS) that meets the requirements of ISO 6926, shall be verified at intervals in a laboratory making calibrations traceable to appropriate standards.
Unless otherwise specified, the sound calibrator should be calibrated at intervals not exceeding 1 year, the instrumentation system, filter and the reference sound source should he calibrated at intervals not exceeding 2 years.
5.3 Application
To minimize the influence of observers on the noise measurements, the microphones shall be preferably mounted on a rigid frame or stand which is not connected to the vibrating surface, the microphone shall always be oriented in such a way that the angle of incidence of the sound waves is that for which the microphone is calibrated and always be oriented to the centre of the tested object (the measurement unit(s) related to the microphone position).
The sound pressure level shall he measured using an integrating sound level meter. If the sound level meter is used to measure time-weighting sound pressure level, the time-weighting characteristic “Sw shall be used for the noise source under test operated in steady condition and the time-weighting characteristic FN shall be used for the noise source under test operated in non-steady condition (e.g. engine operated in the accelerated or decelerated condition). The measured average value can be expressed as the sound pressure level.
The period of stationary measurement for the sound pressure level shall be at least 4 s, 8 s or above is better.
6 Installation and operation conditions
6.1 General
The way the engine under test is installed and operated has a significant influence on the sound power radiated by a noise source. This clause specifies conditions that are intended to minimize variations in the sound power level due to the installation and operating conditions of the noise source under test.
The engine is a multiple noise source, including the following noise sources:
— air-borne noise (this document);
— exhaust gas noise;
— intake-air noise;
— structure-borne noise.BS ISO 6798-1 pdf download.