Acoustics - Noise test code for compressors and vacuum pumps - Engineering method (Grade 2) (ISO 2151:2004)

This International Standard specifies methods for the measurement, determination and declaration of the noise emission from portable and stationary compressors and vacuum pumps. It prescribes the mounting, loading and working conditions under which measurements are to be made, and includes measurement or determination of the noise emission expressed as - the sound power level under specified load conditions, - the emission sound pressure level at the work station under specified load conditions.

Kompressoren und Vakuumpumpen - Bestimmung der Geräuschemission - Verfahren der Genauigkeitsklasse 2 (ISO 2151:2004)

Diese Internationale Norm enthält Festlegungen für Verfahren zur Messung, Bestimmung und Angabe der Geräuschemission von mobilen und stationären Kompressoren und Vakuumpumpen. Sie schreibt die Aufstellungs , Belastungs- und Betriebsbedingungen vor, unter denen die Messungen vorzunehmen sind, und enthält die Messung oder Bestimmung der Geräuschemission, die angegeben wird als
   Schallleistungspegel unter festgelegten Belastungsbedingungen,
   Emissions-Schalldruckpegel am Arbeitsplatz unter festgelegten Belastungsbedingungen.
Dieser Norm gilt für
   Kompressoren (Verdichter) für verschiedene Gase,
   Luftverdichter mit Ölschmierung,
   Luftverdichter mit Ölspülung,
   Luftverdichter mit Wassereinspritzung,
   ölfreie Luftverdichter,
   Kompressoren für gefährliche Gase (Gasverdichter),
   Kompressoren für Sauerstoff,
   Kompressoren für Acetylen,
   Hochdruckkompressoren (über 40 bar/4 MPa),
   Kompressoren für den Einsatz bei niedrigen Temperaturen auf der Ansaugseite, d. h. unter 0 °C,
   Großkompressoren (über 1 000 kW Eingangsleistung),
   mobile und in oder auf einem Transportgestell montierte Luftverdichter,
   Rotations- und Zentrifugalgebläse sowie Sauggebläse für Anwendungen bei  2 bar/0,2 MPa.
Dieser Norm gilt nicht für
   Kompressoren für andere Gase als Acetylen, deren höchster zulässiger Betriebsdruck unter 0,5 bar/ 0,05 MPa liegt,
   Kältekompressoren in Kühlanlagen sowie Wärmepumpen,
   handgehaltene Kompressoren.

Acoustique - Code d'essai acoustique pour les compresseurs et les pompes à vide - Méthode d'expertise (classe de précision 2) (ISO 2151:2004)

L'ISO 2151:2004 spécifie des méthodes pour la détermination et la déclaration de l'émission sonore des compresseurs mobiles et fixes et des pompes à vide. Elle fixe les conditions de montage, de mise en charge et de fonctionnement pendant la réalisation des mesurages et inclut des méthodes pour le mesurage ou la détermination de l'émission sonore exprimée en niveau de puissance acoustique dans des conditions de mise en charge spécifiées et en niveau de pression acoustique d'émission au poste de travail dans des conditions de mise en charge spécifiées.
L'ISO 2151:2004 est applicable aux types de compresseur suivants: compresseurs pour différents types de gaz, compresseurs d'air lubrifiés à l'huile, compresseurs d'air à injection d'huile, compresseurs d'air à injection d'eau, compresseurs d'air sans huile, compresseurs pour gaz dangereux (compresseurs de gaz), compresseurs d'oxygène, compresseurs d'acétylène, compresseurs haute pression (plus de 40 bar/4 MPa), compresseurs pour application à basses températures d'admission, c'est-à-dire au-dessous de 0 °C, gros compresseurs (puissance à l'arbre supérieure à 1 000 kW), compresseurs d'air mobiles ou montés sur châssis, soufflantes volumétriques rotatives, soufflantes centrifuges et aspirateurs dans les applications à 2 bar/0,2 MPa ou moins.
L'ISO 2151:2004 n'est pas applicable aux types de compresseur suivants: compresseurs pour des gaz autres que l'acétylène, ayant une pression de service maximale admissible inférieure à 0,5 bar/0,05 MPa, compresseurs de réfrigération utilisés dans les systèmes de réfrigération ou de pompes à chaleur, compresseurs mobiles tenus à la main.

Akustika - Postopek merjenja hrupa kompresorjev in vakuumskih črpalk - Inženirska metoda (2. stopnja) (ISO 2151:2004)

General Information

Status
Published
Publication Date
11-Sep-2008
Technical Committee
Current Stage
6060 - National Implementation/Publication (Adopted Project)
Start Date
26-Aug-2008
Due Date
31-Oct-2008
Completion Date
12-Sep-2008

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SLOVENSKI STANDARD
SIST EN ISO 2151:2008
01-november-2008
1DGRPHãþD
SIST EN ISO 2151:2004
SIST EN ISO 2151:2004/AC:2006
$NXVWLND3RVWRSHNPHUMHQMDKUXSDNRPSUHVRUMHYLQYDNXXPVNLKþUSDON
,QåHQLUVNDPHWRGD VWRSQMD  ,62

Acoustics - Noise test code for compressors and vacuum pumps - Engineering method

(Grade 2) (ISO 2151:2004)
Kompressoren und Vakuumpumpen - Bestimmung der Geräuschemission - Verfahren
der Genauigkeitsklasse 2 (ISO 2151:2004)

Acoustique - Code d'essai acoustique pour les compresseurs et les pompes à vide -

Méthode d'expertise (classe de précision 2) (ISO 2151:2004)
Ta slovenski standard je istoveten z: EN ISO 2151:2008
ICS:
17.140.20 Emisija hrupa naprav in Noise emitted by machines
opreme and equipment
23.140 .RPSUHVRUMLLQSQHYPDWLþQL Compressors and pneumatic
VWURML machines
23.160 Vakumska tehnologija Vacuum technology
SIST EN ISO 2151:2008 en

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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SIST EN ISO 2151:2008
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SIST EN ISO 2151:2008
EUROPEAN STANDARD
EN ISO 2151
NORME EUROPÉENNE
EUROPÄISCHE NORM
August 2008
ICS 17.140.20; 23.140 Supersedes EN ISO 2151:2004
English Version
Acoustics - Noise test code for compressors and vacuum pumps
- Engineering method (Grade 2) (ISO 2151:2004)

Acoustique - Code d'essai acoustique pour les Kompressoren und Vakuumpumpen - Bestimmung der

compresseurs et les pompes à vide - Méthode d'expertise Geräuschemission - Verfahren der Genauigkeitsklasse 2

(classe de précision 2) (ISO 2151:2004) (ISO 2151:2004)
This European Standard was approved by CEN on 18 July 2008.

CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European

Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references concerning such national

standards may be obtained on application to the CEN Management Centre or to any CEN member.

This European Standard exists in three official versions (English, French, German). A version in any other language made by translation

under the responsibility of a CEN member into its own language and notified to the CEN Management Centre has the same status as the

official versions.

CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Cyprus, Czech Republic, Denmark, Estonia, Finland,

France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal,

Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland and United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
Management Centre: rue de Stassart, 36 B-1050 Brussels

© 2008 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 2151:2008: E

worldwide for CEN national Members.
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SIST EN ISO 2151:2008
EN ISO 2151:2008 (E)
Contents Page

Foreword..............................................................................................................................................................3

Annex ZA (informative) Relationship between this European Standard and the Essential

Requirements of EU Directive 98/37 EEC............................................................................................4

Annex ZB (informative) Relationship between this European Standard and the Essential

Requirements of EU Directive 2006/42/EC .........................................................................................5

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SIST EN ISO 2151:2008
EN ISO 2151:2008 (E)
Foreword

The text of ISO 2151:2004 has been prepared by Technical Committee ISO/TC 118 “Compressors, pneumatic

tools and pneumatic machines” of the International Organization for Standardization (ISO) and has been taken

over as EN ISO 2151:2008 by Technical Committee CEN/TC 232 “Compressors - Safety” the secretariat of

which is held by SIS.

This European Standard shall be given the status of a national standard, either by publication of an identical

text or by endorsement, at the latest by February 2009, and conflicting national standards shall be withdrawn

at the latest by December 2009.

Attention is drawn to the possibility that some of the elements of this document may be the subject of patent

rights. CEN [and/or CENELEC] shall not be held responsible for identifying any or all such patent rights.

This document supersedes EN ISO 2151:2004.

This document has been prepared under a mandate given to CEN by the European Commission and the

European Free Trade Association, and supports essential requirements of EC Directive(s).

For relationship with EC Directives, see informative Annex ZA and ZB, which are integral part of this

document.

According to the CEN/CENELEC Internal Regulations, the national standards organizations of the following

countries are bound to implement this European Standard: Austria, Belgium, Bulgaria, Cyprus, Czech

Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia,

Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain,

Sweden, Switzerland and the United Kingdom.
Endorsement notice

The text of ISO 2151:2004 has been approved by CEN as a EN ISO 2151:2008 without any modification.

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SIST EN ISO 2151:2008
EN ISO 2151:2008 (E)
Annex ZA
(informative)
Relationship between this European Standard and the Essential
Requirements of EU Directive 98/37 EEC

This European Standard has been prepared under a mandate given to CEN by the European Commission and

the European Free Trade Association to provide a means of conforming to Essential Requirement ESR

1.7.4.f) of the New Approach Directive 98/37 EEC.

Once this standard is cited in the Official Journal of the European Communities under that Directive and has

been implemented as a national standard in at least one Member State, compliance with the normative

clauses of this standard given in Table ZA.1 confers, within the limits of the scope of this standard, a

presumption of conformity with the corresponding Essential Requirements of that Directive and associated

EFTA regulations.

WARNING: Other requirements and other EU Directives may be applicable to the product(s) falling within the

scope of this standard.
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SIST EN ISO 2151:2008
EN ISO 2151:2008 (E)
Annex ZB
(informative)
Relationship between this European Standard and the Essential
Requirements of EU Directive 2006/42/EC

This European Standard has been prepared under a mandate given to CEN by the European Commission

and the European Free Trade Association to provide a means of conforming to Essential Requirement ESR

1.7.4.2 u) and of the New Approach Directive 2006/42/EC on machinery.

Once this standard is cited in the Official Journal of the European Communities under that Directive and has

been implemented as a national standard in at least one Member State, compliance with the normative

clauses of this standard confers, within the limits of the scope of this standard, a presumption of conformity

with the relevant Essential Requirements of that Directive and associated EFTA regulations.

WARNING — Other requirements and other EU Directives may be applicable to the product(s) falling within

the scope of this standard.
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SIST EN ISO 2151:2008
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SIST EN ISO 2151:2008
INTERNATIONAL ISO
STANDARD 2151
Second edition
2004-02-01
Acoustics — Noise test code for
compressors and vacuum pumps —
Engineering method (Grade 2)
Acoustique — Code d'essai acoustique pour les compresseurs et les
pompes à vide — Méthode d'expertise (classe de précision 2)
Reference number
ISO 2151:2004(E)
ISO 2004
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SIST EN ISO 2151:2008
ISO 2151:2004(E)
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© ISO 2004

All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by any means,

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ii © ISO 2004 – All rights reserved
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SIST EN ISO 2151:2008
ISO 2151:2004(E)
Contents Page

Foreword............................................................................................................................................................ iv

Introduction ........................................................................................................................................................ v

1 Scope...................................................................................................................................................... 1

2 Normative references........................................................................................................................... 2

3 Terms and definitions........................................................................................................................... 2

4 Sound power level determination ....................................................................................................... 5

4.1 General................................................................................................................................................... 5

4.2 Uncertainty............................................................................................................................................. 6

4.3 Test arrangement.................................................................................................................................. 6

5 Emission sound pressure level determination at the work station ................................................. 7

5.1 Work station.......................................................................................................................................... 7

5.2 Determination of L from L ...................................................................................................... 8

pWSA WA

5.3 Method for determination of L when L is not to be determined ........................................ 9

pWSA WA
6 Mounting, loading and operating conditions of compressor or vacuum pump during

noise tests.............................................................................................................................................. 9

6.1 General................................................................................................................................................... 9

6.2 Mounting................................................................................................................................................ 9

6.3 Loading and operating conditions ...................................................................................................... 9

7 Test report............................................................................................................................................ 10

8 Declaration and verification of noise emission values ................................................................... 10

Annex A (informative) Example test reports.................................................................................................. 11

Annex B (informative) Model form for declared noise emission values..................................................... 17

Annex C (normative) Parallelepiped measurement surface ........................................................................ 18

Annex D (normative) Hemispherical measurement surface ........................................................................ 20

Annex E (informative) Examples of reference box for different machines................................................. 22

Bibliography ..................................................................................................................................................... 25

© ISO 2004 – All rights reserved iii
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SIST EN ISO 2151:2008
ISO 2151:2004(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.

International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.

The main task of technical committees is to prepare International Standards. Draft International Standards

adopted by the technical committees are circulated to the member bodies for voting. Publication as an

International Standard requires approval by at least 75 % of the member bodies casting a vote.

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.

ISO 2151 was prepared by Technical Committee ISO/TC 118, Compressors, pneumatic tools and pneumatic

machines, Subcommittee SC 6, Air compressors.

This second edition cancels and replaces the first edition (ISO 2151:1972), which has been technically revised.

iv © ISO 2004 – All rights reserved
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SIST EN ISO 2151:2008
ISO 2151:2004(E)
Introduction

The noise test code presented by this International Standard describes methods for determining and

presenting the acoustical characteristics of compressors and vacuum pumps, i.e. the total noise level from the

compressor or vacuum pump expressed as sound power level, or the emission sound pressure level at the

work station or other specified positions.

Based on current industry practice, this noise test code requires the compressor or vacuum pump under test

to be run under conditions representing the noisiest operation in typical usage — full-load for compressors

and off-load for vacuum pumps.

It needs to be noted that operators' exposure to noise depends upon the characteristics of individual

applications and environmental factors beyond the control of the manufacturers of compressors and vacuum

pumps.

This International Standard does not give requirements for octave band analysis, however, where there is an

interest this can be undertaken.
© ISO 2004 – All rights reserved v
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SIST EN ISO 2151:2008
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SIST EN ISO 2151:2008
INTERNATIONAL STANDARD ISO 2151:2004(E)
Acoustics — Noise test code for compressors and vacuum
pumps — Engineering method (Grade 2)
1 Scope

This International Standard specifies methods for the measurement, determination and declaration of the

noise emission from portable and stationary compressors and vacuum pumps. It prescribes the mounting,

loading and working conditions under which measurements are to be made, and includes measurement or

determination of the noise emission expressed as
 the sound power level under specified load conditions,

 the emission sound pressure level at the work station under specified load conditions.

It is applicable to
 compressors for various types of gases,
 oil-lubricated air compressors,
 oil-flooded air compressors,
 water injected air compressors,
 oil-free air compressors,
 compressors for handling hazardous gases (gas compressors),
 compressors for handling oxygen,
 compressors for handling acetylene,
 high-pressure compressors [over 4 Mpa (40 bar)],
 compressors for application at low inlet temperatures, i.e. below 0 °C,
 large compressors (over 1 000 kW input power),
 portable and skid-mounted air compressors, and

 rotary positive displacement blowers and centrifugal blowers and exhausters in applications u 0,2 MPa

(u 2 bar).
It is not applicable to

 compressors for gases other than acetylene having a maximum allowable working pressure of less than

0,5 bar/0,05 MPa,
 refrigerant compressors used in refrigerating systems or heat pumps,
 hand-held portable compressors.
© ISO 2004 – All rights reserved 1
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SIST EN ISO 2151:2008
ISO 2151:2004(E)
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 3744:1994, Acoustics — Determination of sound power levels of noise sources using sound pressure —

Engineering method in an essentially free field over a reflecting plane

ISO 4871:1996, Acoustics — Declaration and verification of noise emission values of machinery and

equipment

ISO 9614-1:1993, Acoustics — Determination of sound power levels of noise sources using sound intensity —

Part 1: Measurement at discrete points

ISO 9614-2:1996, Acoustics — Determination of sound power levels of noise sources using sound intensity —

Part 2: Measurement by scanning

ISO 11201:1995, Acoustics — Noise emitted by machinery and equipment — Measurement of emission

sound pressure levels at a work station and at other specified positions — Engineering method in an

essentially free field over a reflecting plane

ISO 11202:1995, Acoustics — Noise emitted by machinery and equipment — Measurement of emission

sound pressure levels at a work station and at other specified positions — Survey method in situ

ISO 11203:1995, Acoustics — Noise emitted by machinery and equipment — Determination of emission

sound pressure levels at a work station and at other specified positions from the sound power level

IEC 61672-1:2002, Electroacoustics — Sound level meters — Specifications
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
compressor

machine which compresses air, gases or vapours to a pressure higher than the inlet pressure

NOTE A compressor comprises the bare compressor itself, the prime mover and any component or device supplied

with the compressor.
3.2
vacuum pump
device for creating, improving and/or maintaining vacuum

NOTE A vacuum pump comprises the bare pump, the prime mover and any component or device supplied with the

vacuum pump.
3.3
emission

airborne sound radiated by a well-defined noise source (e.g. the machine under test) under specified

operating and mounting conditions
NOTE 1 Adapted from ISO 11203:1995.

NOTE 2 Noise emission values can be incorporated in a product label and/or published in a product specification. The

basic noise emission descriptors are the sound power level of the product itself and the emission sound pressure levels at

the work station and at other specified positions in the vicinity of the product (if any).

2 © ISO 2004 – All rights reserved
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SIST EN ISO 2151:2008
ISO 2151:2004(E)
3.4
emission sound pressure

sound pressure, expressed in pascals, at a specified position near a noise source, when the source is in

operation under specified operating and mounting conditions on a reflecting plane surface, corrected for

background noise and reflections from room surfaces other than the plane over which the machine under test

is placed
NOTE Adapted from ISO 11203:1995.
3.5
emission sound pressure level

ten times the logarithm to the base 10 of the ratio of the square of the emission sound pressure to the square

of the reference sound pressure, expressed in decibels, and measured with a particular time weighting and a

particular frequency weighting selected from those defined in IEC 61672-1:2002
EXAMPLE A-weighted emission sound pressure level, L .
NOTE 1 The reference sound pressure is 20 µPa.

NOTE 2 L levels are established as L time-averaged sound pressure levels measured with an integrating-

pA pAeqT

averaging sound level meter meeting the requirements of IEC 61672-1:2002. L is usually abbreviated to L . For

pAeqT pA
further details of L see ISO 3744:1994, 3.2.1.
pAeqT
NOTE 3 Adapted from ISO 11203:1995.
3.6
sound power

rate per unit time, expressed in watts, at which airborne sound energy is radiated by a source

[ISO 3744:1994]
3.7
sound power level

ten times the logarithm to the base 10 of the ratio of the sound power radiated by the source under test to the

reference sound power, expressed in decibels

NOTE 1 The frequency weighting or the width of the frequency band must be indicated. For example, A-weighted

sound power level L .
−12
NOTE 2 The reference sound power is 1 pW (1 pW = 10 W).
NOTE 3 Adapted from ISO 3744:1994.
3.8
sound intensity
product of the sound pressure at a point and the associated particle velocity
NOTE 1 It is a vectorial quantity.
NOTE 2 See ISO 9614-1 and ISO 9614-2 for further guidance on sound intensity.
© ISO 2004 – All rights reserved 3
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SIST EN ISO 2151:2008
ISO 2151:2004(E)
3.9
partial sound power

time-averaged rate of flow of sound energy through an element (segment) of a measurement surface, given

G G
P=×IS=I ×S
ii i ni i
where

I is the signed magnitude of the normal sound intensity component measured at position i on the

measurement surface;
S is the area of the segment of surface associated with point i.
3.10
background noise correction

correction term to account for the influence of background noise on the surface sound pressure level,

expressed in decibels
NOTE 1 K is frequency dependent.
NOTE 2 The correction in the case of A-weighting is denoted K .
NOTE 3 Adapted from ISO 3744:1994.
3.11
environmental correction

correction term to account for the influence of reflected or absorbed sound on the surface sound pressure

level, expressed in decibels
NOTE 1 K is frequency dependent.
NOTE 2 The correction in the case of A-weighting is denoted K .
NOTE 3 Adapted from ISO 3744:1994.
3.12
reference box

hypothetical surface which is the smallest rectangular parallelepiped that just encloses the source and

terminates on the reflecting plane
[ISO 3744:1994]
3.13
measurement surface

hypothetical surface of area S, enveloping the source, on which the measurements are made

NOTE The measurement surface terminates on the reflecting plane.
3.14
measurement distance

distance, d, from the reference box to the parallelepiped measurement surface, or radius, r, of the

hemispherical measurement surface
NOTE Adapted from ISO 3744:1994.
4 © ISO 2004 – All rights reserved
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SIST EN ISO 2151:2008
ISO 2151:2004(E)
3.15
noise emission declaration

information on the noise emitted by the machine given by the manufacturer or supplier in technical documents

or other literature concerning noise emission values
3.16
uncertainty

value of the total uncertainty associated with a measured noise emission value and the production, expressed

in decibels
[ISO 4871:1996]
NOTE See also 4.2.
3.17
declared dual-number noise emission value
L, K

noise emission value, L, and its associated uncertainty, K, given in the noise emission declaration

NOTE 1 The symbols used are
 A-weighted sound power level, L , with uncertainty, K , and
WAd WAd
 A-weighted emission sound pressure level, L , with uncertainty, K .
pAd pAd
NOTE 2 Adapted from ISO 4871:1996.
3.18
work station

position in the vicinity of the compressor or vacuum pump under test, intended for the operator

NOTE 1 For the purposes of this International Standard, this is the surface enveloping the machine on test at a

distance of 1 m from the reference box (see 3.12).
NOTE 2 Adapted from ISO 11203:1995.
3.19
A-weighted emission sound pressure level at the work station
pWSA

energy average of the A-weighted emission sound pressure levels at the work station

4 Sound power level determination
4.1 General

The sound power level shall be determined according to either of the basic standards ISO 3744 or ISO 9614-1

or ISO 9614-2, yielding Grade 2 level of accuracy.

The sound power level shall be given as A-weighted sound power level in decibels referenced to 1 pW (dB re

1 pW).
NOTE 1 Octave band information may also be obtained.
Consider the following when choosing which International Standard to use.

ISO 3744 assumes a non-reverberant environment and low background noise. It specifies a method to

calculate sound power level from sound pressure levels measured on a surface enveloping the compressor or

vacuum pump.
© ISO 2004 – All rights reserved 5
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SIST EN ISO 2151:2008
ISO 2151:2004(E)

ISO 9614-1 or ISO 9614-2 can be used in most environments including semi-reverberant and/or when

extraneous noise sources exist. It specifies methods for determining the sound power level from sound

intensity levels measured on a surface enveloping the compressor or vacuum pump. Depending on the level

of reverberation and extraneous noise, it can provide A-weighted sound power level data with Grade 2 or 3

accuracy.
NOTE 2 Further information on sound power is given in ISO 3740.
4.2 Uncertainty

The uncertainty of the determination of the sound power level comprises the measurement uncertainty of

reproducibility (which includes repeatability) conditions and the uncertainty of production. For definitions of

these components of the uncertainty, see ISO 4871.

In the basic standards ISO 3744, ISO 9614-1 and ISO 9614-2, measurement uncertainty is expressed in

terms of the standard deviation of reproducibility. These standards provide a maximum value of the standard

deviation of reproducibility. A manufacturer can use this value if he has no evidence, from his own experience

with noise emission determination, that a different value applies to a particular machine or machine family.

Determination of production uncertainty is the responsibility of the product manufacturer. A method of

determination is specified in ISO 4871:1996. Production uncertainty is expressed in terms of a standard

deviation of production.

ISO 4871 indicates how the standard deviation of reproducibility and the standard deviation of production

combine to provide uncertainty K.

Experience with the manufacture of compressors and vacuum pumps shows that uncertainty K for these

machines and for A-weighted levels is typically + 3 dB for measurements according to engineering Grade 2. If

a manufacturer can prove that his uncertainty statistically differs from 3 dB, he may use his own value of K.

4.3 Test arrangement
4.3.1 General

Vacuum pumps are used in a wide range of applications covering the complete vacuum spectrum. Designs of

vacuum pumps are available for pumping any combination of gases and vapours. For many applications, two

or more pumps are combined together and are supplied as a unit. These pumping units shall be tested as a

single unit.
4.3.2 Measurement according to ISO 3744:1994

When ISO 3744:1994 is applied, the measurement surface shall be either a parallelepiped or a hemisphere.

The reference box and the measurement surfaces are shown in Annex C and Annex D. The reference box

should only include parts of the machine that are acoustically relevant; connecting pipes shall be excluded.

Annex C and Annex D show microphone positions for both surfaces and identify typical arrays of

9 microphones for a parallelepiped and 10 for a hemisphere. The actual number of microphone positions and

their location depends on the size of the machine under test and the nature of its sound field. Guidance on this

is given in ISO 3744:1994, 7.2 and 7.4 for the hemisphere an
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