(57) A measuring head, e.g. for a smoke detector, includes a tubular holder (1) intended
for being disposed in a ventilation duct for being passed through by the air which
is to be monitored. The portion of the holder to be introduced in the ventilation
duct is ended by an optical reflector (6) defining one end of a measuring path while
the opposite defining surface of the measuring path includes a beam transmitting means
and a detector means. The peripheral surface of the holder around the measuring path
has a number, preferably six, of rows of holes (2) with at least six holes in each
row. The holes in a row are staggered relative the holes in adjacent rows, the staggering
amounting to between 1/4 and 1/3 of the hole width. At least 1/4 of the peripheral
surface of the holder introduced in the ventilation duct and surrounding the measuring
path is covered by the holes.
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