This part of ISO 1680 defines a measurement method for rotating electrical machines operating under steady noise con-ditions, the result of which can be expressed in sound power levels so that all machines tested using this code can be directly compared.
This part of ISO 1680 applies to the measurement of airborne noise from rotating electrical machines, such as motors and generators (d.c. and a.c. machines) of all sizes, when fitted with all auxiliaries which are necessary to achieve the agreed operating conditions (see clause 6).
This part of ISO 1680 requires the sound pressure levels to be measured on a rectangular parallelepiped surface enveloping the machines from which the A-weighted sound power level produced by the machine is calculated. It outlines the pro-cedures which shall be used to evaluate the test environment and specifies the characteristics of suitable measuring instruments.
This part of ISO 1680 applies to measurements carried out in environmental conditions that meet the criteria given in clause 4 and annex A (environmental correction K < 7 dB, correction for background noise < 3 dB).
1.2 Measurement uncertainty
Measurements carried out in conformity with this part of ISO 1680 usually result in standard deviations which are equal to or less than those given in table 1.
Table 1 — Uncertainty in determining A-weighted sound power level by the survey method
Standard Application deviation
dB
For a source which produces sounds that ,.
contain prominent discrete tones
For a source which produces broad-band .
sounds without prominent discrete tones
NOTES
1 The standard deviations in table 1 include the effects of allowable variations in the positioning of the measurement positions and in the selection of the stipulated measurement surface.
2 The standard deviations given in table 1 reflect the cumulative effects of all causes of measurement uncertainty, excluding variations in the sound power level 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 results may be considcrably better (that is, smaller standard deviations) than the uncertainties given in table 1 would indicate.
3 If the method specified in this part of ISO 1680 is used to compare the A-weighted sound power levels of similar machines which radiate noise acoustically omnidirectional and broad-band in its character, the uncertainty in comparison tends to result in a standard deviation which is equal to or less than 3 dB, provided that the measurements are carried out in the same environment.
4 The standard deviations given in table 1 may be higher when the environmental correction, K, established in accordance with the pro cedure given in annex A, exceeds 7 dB.