BS-EN-60118-4-1998 IEC-60118-4-1981.pdf

BRITISH STANDARD BS EN 60118-4:1998 IEC 60118-4: 1981 (Including Amendment No. 1:1998) Hearing aids Part 4: Magnetic field strength in audio-frequency induction loops for hearing aid purposes The European Standard EN 60118-4:1998 including amendment A1:1998 has the status of a British Standard ICS 17.140.50 Licensed Copy: sheffieldun sheffieldun, na, Thu Nov 09 04:04:06 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS EN 60118-4:1998 This British Standard, having been prepared under the direction of the Electrotechnical Sector Committee, was published under the authority of the Standards Committee and comes into effect on 15 November 1998 © BSI 05-1999 ISBN 0 580 30681 X National foreword This British Standard is the English language version of EN 60118-4:1998 including amendment A1:1998. It is identical with IEC 60118-4:1981 including amendment 1:1998. It supersedes BS 6083-4:1981 which will be withdrawn on 2001-05-01. The CENELEC common modifications have been implemented at the appropriate places in the text and are indicated by a sideline in the margin. The UK participation in its preparation was entrusted to Technical Committee EPL/29, Electroacoustics, which has the responsibility to: aid enquirers to understand the text; present to the responsible international/European committee any enquiries on the interpretation, or proposals for change, and keep the UK interests informed; monitor related international and European developments and promulgate them in the UK. A list of organizations represented on this committee can be obtained on request to its secretary. From 1 January 1997, all IEC publications have the number 60000 added to the old number. For instance, IEC 27-1 has been renumbered as IEC 60027-1. For a period of time during the change over from one numbering system to the other, publications may contain identifiers from both systems. Cross-references Attention is drawn to the fact that CEN and CENELEC Standards normally include an annex which lists normative references to international publications with their corresponding European publications. The British Standards which implement these international or European publications may be found in the BSI Standards Catalogue under the section entitled “International Standards Correspondence Index”, or by using the “Find” facility of the BSI Standards Electronic Catalogue. A British Standard does not purport to include all the necessary provisions of a contract. Users of British Standards are responsible for their correct application. Compliance with a British Standard does not of itself confer immunity from legal obligations. Summary of pages This document comprises a front cover, an inside front cover, pages i and ii, the EN title page, pages 2 to 4 and a back cover. This standard has been updated (see copyright date) and may have had amendments incorporated. This will be indicated in the amendment table on the inside front cover. Amendments issued since publication Amd. No.DateComments Licensed Copy: sheffieldun sheffieldun, na, Thu Nov 09 04:04:06 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS EN 60118-4:1998 © BSI 05-1999i Contents Page National forewordInside front cover Foreword2 Text of EN 60118-43 Licensed Copy: sheffieldun sheffieldun, na, Thu Nov 09 04:04:06 GMT+00:00 2006, Uncontrolled Copy, (c) BSI ii blank Licensed Copy: sheffieldun sheffieldun, na, Thu Nov 09 04:04:06 GMT+00:00 2006, Uncontrolled Copy, (c) BSI EUROPEAN STANDARD NORME EUROPÉENNE EUROPÄISCHE NORM EN 60118-4 August 1998 + A1 August 1998 ICS 17.140.50Supersedes HD 450.4 S1:1984 Descriptors: Hearing aids, induction loop, audio frequency English version Hearing aids Part 4: Magnetic field strength in audio-frequency induction loops for hearing aid purposes (includes amendment A1:1998) (IEC 60118-4:1981 + A1:1998) Appareils de correction auditive Partie 4: Intensité du champ magnétique dans les boucles dinduction audiofréquences utilisées à des fins de correction auditive (inclut lamendement A1:1998) (CEI 60118-4:1981 + A1:1998) Hörgeräte Teil 4: Magnetische Feldstärke in Sprechfrequenz-Induktionsschleifen für Hörgeräte (enthält Änderung A1:1998) (IEC 60118-4:1981 + A1:1998) This European Standard was approved by CENELEC on 1998-08-01; amendment A1 was approved by CEN on 1998-08-01. CENELEC 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 Central Secretariat or to any CENELEC 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 CENELEC member into its own language and notified to the Central Secretariat has the same status as the official versions. CENELEC members are the national electrotechnical committees of Austria, Belgium, Czech Republic, Denmark, Finland, France, Germany, Greece, Iceland, Ireland, Italy, Luxembourg, Netherlands, Norway, Portugal, Spain, Sweden, Switzerland and United Kingdom. CENELEC European Committee for Electrotechnical Standardization Comité Européen de Normalisation Electrotechnique Europäisches Komitee für Elektrotechnische Normung Central Secretariat: rue de Stassart 35, B-1050 Brussels © 1998 CENELEC All rights of exploitation in any form and by any means reserved worldwide for CENELEC members. Ref. No. EN 60118-4:1998 + A1:1998 E Licensed Copy: sheffieldun sheffieldun, na, Thu Nov 09 04:04:06 GMT+00:00 2006, Uncontrolled Copy, (c) BSI EN 60118-4:1998 © BSI 05-1999 2 Foreword The text of the International Standard IEC 60118-4:1981, prepared by IEC TC 29, Electroacoustics, was approved by CENELEC as HD 450.4 S1 on 1984-09-11. This Harmonization Document was submitted to the formal vote for conversion into a European Standard and was approved by CENELEC as EN 60118-4 on 1998-08-01. The following date was fixed: Foreword to EN 60118-4:1998/A1:1998 The text of document 29/401/FDIS, future amendment 1 to IEC 60118-4:1981, prepared by IEC TC 29, Electroacoustics, was submitted to the IEC-CENELEC parallel vote and was approved by CENELEC as amendment A1 to EN 60118-4:1998 on 1998-08-01. The following dates were fixed: Contents Page Foreword2 Introduction3 1Scope3 2Object3 3Explanation of terms3 4Recommended magnetic field strength4 5Interference4 latest date by which the EN has to be implemented at national level by publication of an identical national standard or by endorsement(dop) 1999-05-01 latest date by which the amendment has to be implemented at national level by publication of an identical national standard or by endorsement(dop) 1999-05-01 latest date by which the national standards conflicting with the amendment have to be withdrawn(dow) 2001-05-01 Licensed Copy: sheffieldun sheffieldun, na, Thu Nov 09 04:04:06 GMT+00:00 2006, Uncontrolled Copy, (c) BSI EN 60118-4:1998 © BSI 05-19993 Introduction Induction loop systems generate an alternating magnetic field which may be detected, over a definable area, by receivers equipped with induction pick-up coils. Induction loop systems are used for various applications, e.g. in public address, paging and simultaneous interpretation systems, and as an aid for the hearing-impaired. Audio-frequency induction loop systems, in particular, are often employed in schools for hearing-impaired children, as attachments to domestic radio and television receivers and in churches, theatres and cinemas, for the benefit of hearing-impaired people. The pick-up device for an audio-frequency induction loop system will usually be a personal hearing aid, of a type fitted with a pick-up coil; however, special induction loop receivers may be used in certain applications. Transmission of an audio-frequency signal via an induction loop system can often establish an acceptable signal-to-noise ratio in conditions where a purely acoustical transmission would be degraded by reverberation and background noise. The use of personal hearing aids as loop system receivers enables the wearers of these aids to take advantage of induction loop signal transmission wherever such loops are provided. For this advantage to be most effective it is necessary for a standard value of magnetic field strength to be adopted, thus allowing a corresponding adjustment of the sensitivity of the pick-up coil in the hearing aid. The magnetic field strength must be chosen so that: a) it is high enough to produce an acceptable signal-to-noise ratio over ambient electro-magnetic noise from power installations, etc.; b) it is not so high as to cause overloading of the hearing aid. The value of magnetic field strength recommended in this standard has been chosen so that these requirements are met. The lower limit of magnetic field strength is governed by the expected level of ambient electro-magnetic noise, measurements of which have been made in a number of homes, churches, schools, theatres, etc., in order to determine typical values. Measurements have also been made on hearing aids currently in use, to determine an acceptable range of input levels and on which the higher limit is based. An induction loop system will typically incorporate a driving amplifier which is not specified in this standard. However, a recommendation of the frequency dependence of the magnetic field strength is included. The recommended value for magnetic field strength may also be applicable to transmitting coils intended for very short range (i.e. close contact) inductive coupling of other devices, such as radio and television receivers, to hearing aids. In the case of large areas or magnetic disturbances from mains or lighting regulation systems, it may be necessary to deviate from this standard or refrain from using an induction loop system. 1 Scope This standard applies to audio-frequency induction loop systems producing an alternating magnetic field and intended to provide an input signal for hearing aids operating with an induction pick-up coil. 2 Object The object of this standard is to specify a standard value of magnetic field strength in audio-frequency induction loops for hearing aid purposes, such as will give an adequate signal-to-noise ratio without overloading the hearing aid. 3 Explanation of terms 3.1 Recommended average value for magnetic field strength The magnetic field strength obtainable within a specified area, corresponding to the long-time average of the speech signal applied to the system. 3.2 Maximum magnetic field strength The magnetic field strength obtainable within a specified area, corresponding to the maximum short-time average of the speech signal (approximately 0.125 s, referring to the integration time used during the averaging process) applied to the system. 3.3 Specified magnetic field area The area within which the hearing aid induction coil will be located under normal use of the hearing aid and within which the magnetic field strength is required to meet the recommended specifications. NOTEThe specified magnetic field area is not necessarily the geometrical area of the plane of the induction loop. 3.4 Specified vector component of the magnetic field strength 3.4.1 For many purposes, such as in spaces where the users of hearing aids are standing or sitting in upright positions, the vertical component of the magnetic field will be the significant one. In such cases the specified vector component relates to the vertical component. If other field components may be of importance, these should be reported and the direction stated. Licensed Copy: sheffieldun sheffieldun, na, Thu Nov 09 04:04:06 GMT+00:00 2006, Uncontrolled Copy, (c) BSI EN 60118-4:1998 4 © BSI 05-1999 3.4.2 For other cases, such as small transmitting coils used for close contact coupling, orientation of the coil for maximum sensitivity may be possible. Therefore the specified vector component relates to the field strength at the location and in the direction for maximum sensitivity of the users induction pick-up coil. 3.5 Specified frequency response of the magnetic field The variation with frequency of the magnetic field strength in relation to that at 1 000 Hz for a constant input level to the system. 4 Recommended magnetic field strength 4.1 Recommended average value for magnetic field strength in the specified magnetic field area The recommended value for magnetic field strength is: ( 20 ± 3) dB re 1 A/m created by a 1 000 Hz sinusoidal input signal, of level equal to the long-time average level of the speech signal applied to the input of the system. NOTEThe maximum value of magnetic field strength, for a system set up to this recommended field strength, will be approximately: 8 dB re 1 A/m This maximum is derived on the basis that the difference of the maximum short-time average level between a speech signal (approximately 0.125 s) and the long-time average level is approximately 12 dB. 4.2 Recommended frequency response of the magnetic field For an electrical input signal to the system which has a constant value over a frequency range of 100 Hz to 5 000 Hz, the measured frequency response of the magnetic field over that range should not differ by more than ± 3 dB from the value at 1 000 Hz. NOTEAt schools for hearing-impaired children, it may be desirable to introduce a low-frequency boost to compensate for the falling low-frequency response characteristic of induction loop transmission. 5 Interference 5.1 Interference to other equipment Interference may occur to telecommunication equipment or wiring which is very close to the induction loop, particularly where the loop covers a large area. Special measures may be necessary to limit this interference to an acceptable level. 5.2 Environmental audio-frequency magnetic background fields The function of the installed induction loop system may not be satisfactory if there are undue environmental magnetic background fields. The maximum A-weighted environmental magnetic background noise level re 1 A/m, measured with the time weighting S (as defined in IEC 61672), should not exceed 40 dB anywhere in the operational area. Licensed Copy: sheffieldun sheffieldun, na, Thu Nov 09 04:04:06 GMT+00:00 2006, Uncontrolled Copy, (c) BSI blank Licensed Copy: sheffieldun sheffieldun, na, Thu Nov 09 04:04:06 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS EN 60118-4:1998 IEC 60118-4: 1981 BSI 389 Chiswick High Road London W4 4AL BSI British Standards Institution BSI is the independent national body responsible for preparing British Standards. It presents the UK view on standards in Europe and at the international level. It is incorporated by Royal Charter. Revisions British Standards are updated by amendment or revision. Users of British Standards should make sure that they possess the latest amendments or editions. It is the constant aim of BSI to impr