6
AFILS TEST AND COMISSIONING PROCEDURE
This procedure is intended to be used in conjunction with an Ampetronic
Certificate of Conformity for AFILS according to IEC60118-4
1
Volume of use (3 dimensions not sound level)
PURPOSE - define and record the three dimensional
useful magnetic field
volume
for the loop system and determine a series of reference
measurement points.
•
Define the area of use and all required listening positions. Determine the
height of use, i.e. the normal height of the hearing aid - typically 1.2m for
seated persons, with a possible range of 1.0m to 1.4m.
For standing adults a typical height of 1.7m, with a possible range of up
to 2.0m and down to 1.0m for children or wheelchair users.
•
Confirm the expected orientation of users hearing aid telecoils.
This is usually vertical, but in some environments where the user may be
laying down the horizontal field strength may also need to be considered.
All subsequent measurements using the FSM must take this into
account.
The coil position inside the case, and orientation are indicated on the
FSM by an inductor symbol as shown below:
•
Sketch the
floor plan
and
useful magnetic field volume
on the
Certificate of Conformity. Include any areas where overspill needs to be
examined.
•
Select 4 to 6 measurement points (e.g. A to F on the Certificate of
Conformity) inside the loop where the system will be used.
These should be points that are representative of the whole volume of
use. Experience will suggest where best to choose in order to get a good
sample of the range of magnetic field strengths.
•
Consideration should be given to the use of the room and furniture
layout. Some venues may have multiple room set-ups – e.g. movable
seating / tables.
y
z
y
x
The coil picks up signals parallel
to the axis (y) of the symbol
Signals on other axes
(x and z) are not measured