73000S
The Sentry™ uses the principle of forward scattering. The optical
system is designed such that the infrared light projected from the
transmitter (TX) intersects the field of view of the receiver (RX)
with a forward angle of 42º. The area of intersection is known as
the sample volume. The 42º forward angle ensures performance
over a wide range of particle sizes in the sample volume including
smoke, dust, haze, fog, rain and snow.
When the air is clear, very little light is scattered since there are
few particles in the sample volume resulting in a small signal
received by the sensor. As the number of particles in the sample
volume increases, the amount of light detected by the receiver
also increases. In other words, the received signal strength is
inversely proportional to the visibility.