ISO 10494:2018
(Main)Turbines and turbine sets - Measurement of emitted airborne noise - Engineering/survey method
Turbines and turbine sets - Measurement of emitted airborne noise - Engineering/survey method
ISO 10494:2018 specifies methods for measuring the noise emission of a turbine or turbine set under steady-state operating conditions. It specifies methods for measuring the sound pressure levels on a measurement surface enveloping a source, and for calculating the sound power level produced by the source. It gives requirements for the test environment and instrumentation, as well as techniques for obtaining the surface sound pressure level from which the A-weighted sound power level of the source and octave or one-third-octave band sound power levels are calculated. These methods can be used to conduct performance tests even if the purpose of the test is simply to determine the sound pressure level around the machine.
ISO 10494:2018 is applicable to turbines and turbine sets:
- for power plant and industrial applications (e.g. stationary);
- for installation on board ships, or offshore installations, road and railway vehicles.
ISO 10494:2018 does not apply to gas turbines in aircraft applications.
ISO 10494:2018 is applicable to only the part of the turbine set (turbine, driven equipment and attached components) located above the floor and inside a continuous enveloping measurement surface bounded by this floor.
ISO 10494:2018 is applicable to steady-state operation and excludes transients such as start-up and shut-down, when the noise emission can be higher for short times. Under these conditions, this document does not apply.
Turbines et groupes de turbines - Mesurage du bruit aérien émis - Méthode d'expertise/de contrôle
ISO 10494:2018 spécifie les méthodes de mesure du bruit émis par une turbine ou un groupe de turbines en régime stabilisé. Il spécifié les méthodes de mesure des niveaux de pression acoustique sur une surface de mesure enveloppant une source, et les méthodes de calcul du niveau de puissance acoustique produit par la source. Il établit les exigences applicables à l'environnement et à l'appareillage d'essai, ainsi que les techniques permettant d'obtenir le niveau de pression acoustique surfacique à partir duquel sont calculés le niveau de puissance acoustique pondéré A de la source ou les niveaux de puissance acoustique par bande d'octave ou de tiers d'octave. Ces méthodes peuvent être utilisées pour réaliser des essais de réception, même si l'essai n'a que pour but de déterminer le niveau de pression acoustique autour de la machine.
ISO 10494:2018 s'applique aux turbines et aux groupes de turbines:
- utilisés dans les centrales de production d'énergie et dans les applications industrielles (par exemple, stationnaires);
- installés à bord des navires, des installations de forage en mer, des véhicules routiers ou des véhicules de chemins de fer.
ISO 10494:2018 ne s'applique pas aux turbines à gaz destinées aux applications aéronautiques.
ISO 10494:2018 s'applique uniquement à la partie du groupe de turbines (turbine, équipement entraîné et accessoires) située au-dessus du sol et à l'intérieur d'une surface de mesure enveloppante continue délimitée par ce sol.
ISO 10494:2018 s'applique à un fonctionnement en régime stabilisé et exclut les transitoires (par exemple, démarrage et arrêt), au cours desquels les émissions de bruit peuvent être ponctuellement plus élevées. Le présent document ne s'applique pas dans ces conditions.
General Information
Standards Content (Sample)
INTERNATIONAL ISO
STANDARD 10494
Second edition
2018-04
Turbines and turbine sets —
Measurement of emitted airborne
noise — Engineering/survey method
Turbines et groupes de turbines — Mesurage du bruit aérien émis —
Méthode d'expertise/de contrôle
Reference number
ISO 10494:2018(E)
©
ISO 2018
---------------------- Page: 1 ----------------------
ISO 10494:2018(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2018
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting
on the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address
below or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: +41 22 749 01 11
Fax: +41 22 749 09 47
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii © ISO 2018 – All rights reserved
---------------------- Page: 2 ----------------------
ISO 10494:2018(E)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Acoustic environment . 5
4.1 Criteria of adequacy of the test environment . 5
4.2 Criteria for background noise . 6
4.3 Wind . 6
4.4 Special measurement methods . 6
5 Instrumentation . 6
6 Installation and operation of turbine set. 6
6.1 General . 6
6.2 Mounting of turbine set . 7
6.3 Operation of turbine set during test . 7
6.4 Auxiliary equipment and coupled machines . 7
7 Sound pressure levels on the measurement surface . 7
7.1 Reference surface and measurement surface. 7
7.2 Location and number of microphone positions . 9
7.2.1 General. 9
7.2.2 Additional microphone positions on measurement surface .10
7.2.3 Surface noise .11
7.3 Conditions of measurement .11
7.3.1 General.11
7.3.2 Calibration .11
7.3.3 Measurement of the A-weighted sound pressure level .11
7.3.4 Measurement of sound pressure spectrum .11
8 Calculation of surface sound pressure level and sound power level .12
8.1 Corrections for background noise .12
8.2 Calculation of sound pressure level averaged over the measurement surface .13
8.3 Calculation of surface time-averaged sound pressure levels .13
8.4 Calculation of sound power level .13
8.5 Calculation of directivity index and directivity factor .14
9 Information to be recorded .14
9.1 General .14
9.2 Noise source under test .14
9.3 Acoustic environment .14
9.4 Instrumentation .14
9.5 Acoustical data .15
9.6 Date and location .15
10 Test report .15
Annex A (normative) Qualification procedures for the acoustic environment .16
Annex B (normative) Gas turbines .20
Annex C (normative) Steam turbines .31
Annex D (informative) Calculation of directivity index and directivity factor using a
hemispherical microphone array .36
Bibliography .37
© ISO 2018 – All rights reserved iii
---------------------- Page: 3 ----------------------
ISO 10494:2018(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www .iso .org/directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www .iso .org/patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation on the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to the
World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT) see the following
URL: www .iso .org/iso/foreword .html.
This document was prepared by Technical Committee ISO/TC 192, Gas Turbines, in collaboration with
Technical Committee IEC/TC 5, Steam Turbines.
This second edition cancels and replaces the first edition (ISO 10494:1993), which has been technically
revised.
The main changes compared to the previous edition are as follows:
— the measurement of airborne noise from steam turbines and steam turbine sets has been added;
— the content has been aligned with ISO 3744:2010 and ISO 3746:2010;
— the title has been updated.
iv © ISO 2018 – All rights reserved
---------------------- Page: 4 ----------------------
ISO 10494:2018(E)
Introduction
0.1 Background
Control of noise from machines or equipment requires effective exchange of acoustical information
among the several parties concerned. These include the manufacturer, specifier, installer and user of
the machine or equipment. This acoustical information is obtained from measurements.
These measurements are useful only if they are carried out under specified conditions to obtain defined
acoustical quantities using standardized instruments.
The sound power level data determined according to this document is essentially independent of the
environment in which the data are obtained. This is one of the reasons for using sound power level to
characterize the sound emitted by various types of machine equipment.
Sound power level data are useful for the following:
a) calculating the approximate sound pressure level at a given distance from a machine operating in a
specified environment;
b) comparing the noise radiated by machines of the same type and size;
c) comparing the noise radiated by machines of different types and sizes;
d) determining whether a machine complies with a specified upper limit of noise emission;
e) planning in order to determine the amount of transmission loss or noise control required under
certain circumstances;
f) engineering work to assist in developing quiet machinery and equipment.
This document gives requirements for the measurement of the noise emission of turbines and turbine
sets. It has been prepared in accordance with ISO 3740:2000 on the basis of ISO 3744:2010. Due to the
special conditions concerning turbines and turbine sets, it is necessary to define different noise sources
and to use measurement surfaces differing from those specified in ISO 3744:2010.
For some environmental conditions, it can be necessary to use the survey methods based on
ISO 3746:2010 resulting in a lower grade of accuracy. Frequency information is still recorded and
reported.
0.2 Aims
The methods defined in this document apply to the measurement of the noise emission of a turbine
or turbine set under steady-state operating conditions. The results are expressed as sound pressure
levels, and sound power levels in A-weighted and in octave bands.
The aim of this document 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 4 dB but is less than 7 dB, then a grade 3 (survey) result is obtained (see Table 2).
Measurements made in conformity with this document should result in standard deviations which
are equal to or less than those given in Table 3. The uncertainties in Table 3 depend not only on the
accuracies with which sound pressure levels and measurement surface areas are determined, but also
on the “near-field error” which increases for smaller measurement distances and lower frequencies
(i.e. those below 250 Hz). The near-field error always leads to measured sound power levels which are
higher than the real sound power levels.
NOTE 1 If the methods specified in this document 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 Table 3, provided that the measurements are
performed in the same environment with the same shape of measurement surface.
© ISO 2018 – All rights reserved v
---------------------- Page: 5 ----------------------
ISO 10494:2018(E)
NOTE 2 The standard deviations given in Table 3 reflect the cumulative effects of all causes of measurement
uncertainty, excluding variations in the sound power levels from test to test which can be caused, for example, by
changes in the mounting or operating conditions of the source. The reproducibility and repeatability of the test
result can be considerably better (i.e. smaller standard deviations) than the uncertainties given in Table 3 would
indicate.
Table 1 — International Standards specifying various methods for determining the sound
power levels of machines and equipment
Character of Sound power
International Classification Test Volume of
noise levels
Standard of method environment source
obtainable
Normative
No restrictions; A-weighted and
Grade 2 Outdoors or in limited only by in octave bands
ISO 3744 Any
(engineering) large rooms available test or one-third
environment octave bands
No restrictions;
Grade 3 No special test limited only by
ISO 3746 Any A-weighted
(survey) environment available test
environment
Informative
Steady, non-
steady, fluctu-
Reverberation A-weighted and
ating, isolated
Grade 1 room meeting Less than 2 % of in octave bands
ISO 3741 bursts of sound
(precision) specified re- test room volume or one-third
energy, broad-
quirements octave bands
band, discrete
frequency
Steady, non-
Less than 2,5 % steady, fluctu-
Grade 2 Hard-walled test A-weighted and
ISO 3743-1 of test room ating, isolated
(engineering) room in octave bands
volume bursts of sound
energy
Steady, non-
steady, fluctu-
Preferably less
Grade 2 Special reverber- ating, broad- A-weighted and
ISO 3743-2 than 1 % of test
(engineering) ation test room band, narrow- in octave bands
room volume
band, discrete
frequency
Anechoic- or Preferably less A-weighted and
Grade 1 (preci-
ISO 3745 hemi-anechoic than 0,5 % of test Any in one-third
sion)
room room volume octave bands
No special test Steady, non-
environment, No restrictions; steady, fluctu-
Grade 2 and 3
but sufficiently limited only by ating, isolated A-weighted and
ISO 3747 (engineering
reverberant; available test bursts of sound in octave bands
and survey)
source under test environment energy, primari-
non-movable ly broad-band
Grade 1, 2 and A-weighted and
3 (precision, No special test Any, but station- in octave bands
b
ISO 9614-1 No restrictions
engineering environment ary in time or one-third
and survey) octave
a
Method to determine the sound power of airborne noise caused by machinery surface vibration specifically.
b
For measurements in anechoic or hemi-anechoic rooms limited by the size of the test room.
vi © ISO 2018 – All rights reserved
---------------------- Page: 6 ----------------------
ISO 10494:2018(E)
Table 1 (continued)
Character of Sound power
International Classification Test Volume of
noise levels
Standard of method environment source
obtainable
A-weighted and
Grade 2 and 3
No special test Any, but station- in octave bands
b
ISO 9614-2 (engineering No restrictions
environment ary in time or one-third
and survey)
octave bands
A-weighted and
Grade 1 No special test Any, but station- in octave bands
b
ISO 9614-3 No restrictions
(precision) environment ary in time or one-third
octave bands
Grade 3 No special test
a
ISO/TS 7849-1 No restrictions Any A-weighted
(survey) environment
A-weighted and
Grade 2 No special test in octave bands
a
ISO/TS 7849-2 No restrictions Any
(engineering) environment or one-third
octave bands
a
Method to determine the sound power of airborne noise caused by machinery surface vibration specifically.
b
For measurements in anechoic or hemi-anechoic rooms limited by the size of the test room.
Table 2 — Limits for correction
Grade of accuracy Background noise Environment
correction correction
dB dB
Grade 2 ≤1,3 ≤4
Grade 3 ≤3 ≤7
a
Special case >3 >7
a
For higher values of background noise and/or environmental corrections, the real
sound power level cannot be determined with acceptable uncertainty, but the results
can be useful to estimate an upper limit of the noise emission of the turbine or the
turbine set to be tested.
Table 3 — Uncertainty in determining sound power levels and sound pressure levels, expressed
as the standard deviation
Grade of Octave band centre frequency A-weighted
accuracy
dB dB
31,5 Hz to 125 Hz 250 Hz to 1 000 Hz to 8 000 Hz
63 Hz 500 Hz 4 000 Hz
Grade 2 5 3 2 1,5 2,5 2
Grade 3 3
NOTE 1 Grade 3 uncertainty is related to stable conditions.
NOTE 2 The value of the standard deviation for air intake and gas exhaust outlet of gas turbines can be higher.
© ISO 2018 – All rights reserved vii
---------------------- Page: 7 ----------------------
INTERNATIONAL STANDARD ISO 10494:2018(E)
Turbines and turbine sets — Measurement of emitted
airborne noise — Engineering/survey method
1 Scope
This document specifies methods for measuring the noise emission of a turbine or turbine set under
steady-state operating conditions. It specifies methods for measuring the sound pressure levels on a
measurement surface enveloping a source, and for calculating the sound power level produced by the
source. It gives requirements for the test environment and instrumentation, as well as techniques for
obtaining the surface sound pressure level from which the A-weighted sound power level of the source
and octave or one-third-octave band sound power levels are calculated. These methods can be used to
conduct performance tests even if the purpose of the test is simply to determine the sound pressure
level around the machine.
This document is applicable to turbines and turbine sets:
— for power plant and industrial applications (e.g. stationary);
— for installation on board ships, or offshore installations, road and railway vehicles.
It does not apply to gas turbines in aircraft applications.
This document is applicable to only the part of the turbine set (turbine, driven equipment and attached
components) located above the floor and inside a continuous enveloping measurement surface bounded
by this floor.
It is applicable to steady-state operation and excludes transients such as start-up and shut-down, when
the noise emission can be higher for short times. Under these conditions, this document does not apply.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements 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.
IEC 60942, Electroacoustics — Sound calibrators
IEC 61260-1, Electroacoustics — Octave-band and fractional-octave-band filters — Part 1: Specifications
IEC 61672-1, Electroacoustics — Sound level meters — Part 1: Specifications
ISO 3744:2010, Acoustics — Determination of sound power levels and sound energy levels of noise sources
using sound pressure — Engineering methods for an essentially free field over a reflecting plane
ISO 3746:2010, Acoustics — Determination of sound power levels and sound energy levels of noise sources
using sound pressure — Survey method using an enveloping measurement surface over a reflecting plane
ISO 6926, Acoustics — Requirements for the performance and calibration of reference sound sources used
for the determination of sound power levels
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
© ISO 2018 – All rights reserved 1
---------------------- Page: 8 ----------------------
ISO 10494:2018(E)
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https: //www .iso .org/obp
— IEC Electropedia: available at http: //www .electropedia .org/
3.1
sound pressure
p
difference between instantaneous pressure and static pressure
Note 1 to entry: Adapted from ISO 80000-8:2007, 8-9.2.
Note 2 to entry: Sound pressure is expressed in pascals.
[SOURCE: ISO 3744:2010, 3.1]
3.2
sound pressure level
L
p
ten times the logarithm to the base 10 of the ratio of the square of the sound pressure (3.1), p, to the
square of a reference value, p , expressed in decibels
0
2
p
L =10lg dB
p
2
p
0
where the reference value, p , is 20 μPa
0
Note 1 to entry: If specific frequency and time weightings as specified in IEC 61672-1 and/or specific frequency
bands are applied, this is indicated by appropriate subscripts; e.g. L denotes the A-weighted sound pressure level.
pA
Note 2 to entry: This definition is technically in accordance with ISO 80000-8:2007, 8-22.
[SOURCE: ISO 3744:2010, 3.2]
3.3
time averaged sound pressure level
L
p,T
ten times the logarithm to the base 10 of the ratio of the time average of the square of the sound pressure
(3.1), p, during a stated time interval of duration, T (starting at t and ending at t ), to the square of a
1 2
reference value, p , expressed in decibels
0
t
2
1
2
pt()dt
∫
T
t
1
L =10lg dB
pT,
2
p
0
where the reference value, p , is 20 μPa
0
Note 1 to entry: In general, the subscript “T” is omitted since time-averaged sound pressure levels are necessarily
determined over a certain measurement time interval.
Note 2 to entry: Time-averaged sound pressure levels are often A-weighted, in which case they are denoted by
L , , which is usually abbreviated to L .
pA T pA
Note 3 to entry: Adapted from ISO/TR 25417:2007, 2.3.
[SOURCE: ISO 3744:2010, 3.3]
2 © ISO 2018 – All rights reserved
---------------------- Page: 9 ----------------------
ISO 10494:2018(E)
3.4
acoustic free field
sound field in a homogeneous, isotropic medium free of boundaries
Note 1 to entry: In practice, an acoustic free field is a field in which the influence of reflections at the boundaries
or other disturbing objects is negligible over the frequency range of interest.
[SOURCE: ISO 3744:2010, 3.6]
3.5
acoustic free field over a reflecting plane
acoustic free field (3.4) in the half-space above an infinite reflecting plane in the absence of any other
obstacles
[SOURCE: ISO 3744:2010, 3.7]
3.6
reflecting plane
sound-reflecting planar surface on which the noise source under test is located
[SOURCE: ISO 3744:2010, 3.6]
3.7
frequency range of interest
for general purposes, the frequency range of octave bands with nominal mid-band frequencies from
31,5 Hz to 8 000 Hz (including one-third octave bands with mid-band frequencies from 25 Hz to
10 000 Hz)
Note 1 to entry: Any band may be excluded in which the level is more than 50 dB below the highest band
pressure level.
Note 2 to entry: For special purposes, the frequency range can be extended or reduced, provided that the test
environment and instrument specifications are satisfactory for use over the modified frequency range. For
sources which radiate predominantly high (or low) frequency sound, the frequency range of interest may be
limited in order to optimize the test facility and procedures. Changes to the frequency range of interest are
included in the test report.
Note 3 to entry: Adapted from ISO 3744:2010, 3.9.
3.8
reference box
hypothetical right parallelepiped terminating on the reflecting plane(s) (3.6) on which the noise
source under test is located, that just encloses the source including all the significant sound radiating
components and any test table on which the source is mounted
Note 1 to entry: If required, the smallest possible test table can be used for compatibility with emission sound
pressure measurements at bystander positions in accordance with, for example, ISO 11201:2010.
[SOURCE: ISO 3744:2010, 3.10]
3.9
measurement distance
d
distance from the reference box (3.8) to a parallelepiped measurement surface (3.10)
Note 1 to entry: Measurement distances are expressed in metres.
[SOURCE: ISO 3744:2010, 3.12]
© ISO 2018 – All rights reserved 3
---------------------- Page: 10 ----------------------
ISO 10494:2018(E)
3.10
measurement surface
hypothetical surface of area, S, on which the microphone positions are located at which the sound
pressure levels (3.2) are measured, enveloping the noise source under test and terminating on the
reflecting plane(s) (3.6) on which the source is located
[SOURCE: ISO 3744:2010, 3.14]
3.11
background noise
noise from all sources other than the noise source under test
Note 1 to entry: Background noise includes contribution from airborne sound, noise from structure-borne
vibration, and electrical noise in instrumentation.
[SOURCE: ISO 3744:2010, 3.15]
3.12
background noise correction
K
1
correction applied to the mean (energy average) of the time-averaged sound pressure levels (3.3) over all
the microphone positions on the measurement surface (3.10), to account for the influence of background
noise (3.11)
Note 1 to entry: Background noise correction is expressed in decibels.
Note 2 to entry: The background noise correction is frequency dependent; the correction in the case of a frequency
band is denoted K , where f denotes the relevant mid-band frequency, and that in the case of A-weighting is
1f
denoted K .
1A
[SOURCE: ISO 3744:2010, 3.16]
3.13
environmental correction
K
2
correction applied to the mean (energy average) of the time-averaged sound pressure levels (3.3) over all
the microphone positions on the measurement surface (3.10), to account for the influence of reflected or
absorbed sound
Note 1 to entry: Environmental correction is expressed in decibels.
Note 2 to entry: The environmental correction is frequency dependent; the correction in the case of a frequency
band is denoted K , where f denotes the relevant mid-band frequency, and that in the case of A-weighting is
2f
denoted K .
2A
Note 3 to entry: In general, the environmental correction depends on the area of the measurement surface and
usually K increases with S.
2
[SOURCE: ISO 3744:2010, 3.17]
3.14
surface time-averaged sound pressure level
L
...
Questions, Comments and Discussion
Ask us and Technical Secretary will try to provide an answer. You can facilitate discussion about the standard in here.