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ISO 10494

1st Edition, January 1, 1993

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Gas Turbines and Gas Turbine Sets - Measurement of Emitted Airborne Noise - Engineering/Survey Method

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Description / Abstract:

This International Standard specifies methods for measuring the Sound pressure levels on a measurement surface enveloping a Source, and for calculating the Sound power Ievel produced by the Source. lt gives requirements for the test environment and instrumentation, as well as techniques for obtaining the surface Sound pressure Ievel from which the A-weighted Sound power level of the Source and octave or one-third-octave band Sound power Ievels are calculated. This method may be used to perform acceptance tests.

The aim of this International Standard is a grade 2 (engineering) result (see table 1). When the correction for background noise exceeds the limit of 1,3 dB but is less than 3 dB, and/or the correction for environment exceeds the limits of 2 dB but is less than 7 dB, then a grade 3 (Survey) result is obtained.

This International Standard applies to gas turbines and gas turbine sets - for industrial applications (e.g. stationary), - for installation on board ships, or offshore installations, road and railway vehicles. lt does not apply to gas turbines in aircraft applications.

The methods defined in this International Standard apply to the measurement of the noise emission of a gas turbine or gas turbine set under steady-state operating conditions. The results are expressed as Sound pressure Ievels, and Sound power levels in Aweighted and in octave bands.

Measurements made in conformity with this International Standard should result in Standard deviations which are equal to or less than those given in table3. The uncertainties in table 3 depend not only on the accuracies with which Sound pressure Ievels and measurement surface areas are determined, but also on the "near-fieId error" which increases for smaller measurement distances and lower frequencies (i.e. those below 250 Hz). The near-field error always leads to Sound power Ievels which are higher than the real Sound power levels.


1 If the methods specified in this International Standard are used to compare the Sound power levels of similar machines that are omnidirectional and radiate broad-band noise, the uncertainty in this comparison tends to result in Standard deviations which are less than those given in table3, provided that the measurements are performed in the same environment with the same shape of measurement surface.

2 The Standard deviations given in table3 reflect the cumulative effects of all Causes of measurement uncertainty, excluding variations in the Sound power levels from test to test which may be caused, for example, by changes in the mounting or operating conditions of the Source. The reproducibility and repeatability of the test result may be considerably better (i.e. smaller Standard deviations) than the uncertainties given in table3 would indicate.
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