BM-SCAN -
Magnetic field strenght meter
Page 16
English
Standard EN 60118-4 of March 2007
This standard defines 4 very precise parameters.
The following procedure is recommended:
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The peak magnetic field must reach 400mA/m (integration time 0.125ms).
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Frequency responses should not vary more than 3dB between 100Hz and 5000Hz.
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The signal-to-noise ratio must be 47 dB (A-weighting).
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The magnetic field must be uniform throughout the listening area.
The type-approval procedure
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Recommendation
Thanks to the law of February 2005, establishments receiving the public (ERP) are gradually equip-
ping themselves with magnetic induction loops in order to facilitate listening for people with hearing
difficulties. To be effective these systems must be carefully calibrated to verify that the installation
has been made in compliance with standard EN60118-4. We recommend the delivery of a certifi-
cate of conformity to this standard, according to the model enclosed, signed by the installer.
To allow a good listening it is necessary to check all these conditions.
The respect of the magnetic field intensity guarantees that the sound intensity is sufficient, the
responses frequency control ensure that the entire sound spectrum is perceived in the same way
and the signal-to-noise ratio measures the impact of interference magnetic disturbances on intelligi-
bility. Despite the installation of adequate equipment, many factors can disturb these parameters:
the presence of metallic structures causes the magnetic field to drop, transformers or current at
50Hz in the proximity cause magnetic noises. The size and the form of the room can make it difficult
to meet the recommended values at all points.
Procedure for receiving
magnetic loops
Room managers must ensure that, when installing any magnetic induction loop, the installer delivers
this certificate of conformity. Even if the room manager does not have the competence to judge the
result of the measurements, this "installation report" should be able to be consulted at any time for a
possible control by a team of auditors.
About the room, determine the points where the measurements will be taken ( center, extremities,
points near metal structures or noise sources).
Measurements by the installer, after the adjustment of the installed equipment, of the various
parameters set by the standard.
Delivery of this document signed by the installer to the room manager.
