BS EN 60118-13:2011 pdf download
BS EN 60118-13:2011 pdf download.Electroacoustics —Hearing aids Part13: Electromagnetic compatibility (EMC).
A.1 General
In 1994, the European hearing instrument manufacturers association (EHIMA) undertook a series of measurements to establish a basis for measuring the effects of interference on hearing aids, and for quantifying a practical limit of Immunity. In Australia similar work was undertaken at around the same time. This work concentrated on providing the basis for measuring and specifying what is now known as the bystander compatibility. At that time, the issue of user compatibility and the need to deal with it was limited by the lack of knowledge on the subject and the low use of digital wireless devices in most countries.
However, the rapid growth in the use of digital wireless devices produced an urgent need to address the issue of the hearing aid wearer who wanted to use a digital wireless device. Work on this problem commenced in the USA in 1997 and led to proposals for methods of measurement for both hearing aids and mobile phones. This work led to the ANSI C83.19 [4] standard, which provided the impetus for further work in Europe to evaluate the proposals
A.2 Test methods
The EHIMA GSU project was set up to establish a test environment enabling the GSM Interference problems to be addressed. The project’s final report [2] presents the results of the development phase. It also includes results from other investigations. The relevant parts of the project are summarised below.
Five hearing aid types were selected for a laboratory investigation, representing different electroacoustic characteristics, interference levels and interference spectra. The overall input related interference level (OIRIL), expessed as SPL. in decibels, was chosen to characterise the interference performance of the hearing aids.
First, the aids were tested acoustically according to IEC 60118-0. To enable the metallic ear simulator to be removed from the RF-field. coupling between the hearing aid and ear simulator was modified by using 500 mm long tubing Relatively large variations in the acoustical effect of this modification were seen This means that the hearing aid gain should be measured for the individual hearing aid under test in the determination of OIRIL.
The hearing aids were then exposed to a simulated GSM RF-field in an RF anechoic room. placed in a position corresponding to normal use. A test signal having a peak field strength of 10 VIm was used. This corresponds to a digital wireless device having a power of 8 W at a distance of 2 m, or a 2 W device at a distance of 1 m. The frequency spectrum of the interference signal at the orientation causing maximum interference was determined. The input related spectrum was then calculated by subtracting the hearing aid gain, and finally the OIRIL was determined.
The input related spectra appeared almost identical for all the hearing aids tested, the level of the harmonics decreasing with increasing frequency. This means that Only the low frequency part of the spectrum is needed to determine OlRlL with sufficient accuracy for the purpose of measuring immunity.
It was seen that rotation of the hearing aid in the horizontal plane affected the interference performance to some degree and that maximum interference occurs at different angles for different hearing aids. In practically all cases,vertical E-polarisation of the RF-field, as usedin the GSM system, gave rise to the highest interference levels.
Relatively large differences in OIRIL between different hearing aid types were seen,and alsoin a small number of cases between samples of the same type.
A ratio of 1:2 between field strength and interference level, expressed in dB,was seen for afield strength range where the interference signal is above the noise floor of the (linear)hearing aid and does not saturate it (Figure A.1).
