Photoelectric detection systems use a light-sensitive cell and a directed light source
which points directly at the cell. Photoelectric security systems can be
classified as motion detection systems since an object or person must move across
the photoelectric connection to break the light transmission to the sensor.
The
source transmits invisible light beams to the adjacent cell or sensor.
Often an infrared filter covers the light source to make it non-visible
to intruders. If an intruder crosses the light beam, it breaks the beam's continuous
contact with the photoelectric cell and trips the alarm. Mirrors can be installed
with photoelectric security systems in order to allow one light beam to
be projected across a large area, thus allowing a criss-crossing of the light
beam across a room. This makes it much more difficult for an intruder to crawl
under, or step over the light beam.
Photoelectric may seem an old technology,
however it is still in use in many home security systems. |
