3.1 OPTICAL SYSTEM
The MR601TEx detects visible particles produced in fires
by using the light scattering properties of the particles. The
detector uses the optical arrangement shown
diagrammatically in Fig. 1.
The optical system consists of an infra-red emitter and
receiver, with a lens in front of each, so arranged that their
optical axes cross in the sampling volume. The emitter,
with its lens, produces a narrow beam of light which is
prevented from reaching the receiver by the baffles. When
smoke is present in the sampling volume a proportion of the
light is scattered, some of which reaches the receiver. For a
given type of smoke, the light reaching the photodetector is
proportional to the smoke density. The amplified output
from the sensor can be used to activate an alarm circuit at a
predetermined threshold.
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