Basic version of this device consists of an infrared
source (a Infrared light bulb) with a focused beam and a receiver as separate units.
Infrared light in not visible to humans and hence an intruder can't know of the presence
of the Infrared light. Normally these units are mounted on opposite walls at the entrance
of the area to be protected. The units must be aligned correctly. The infrared light
source gives an invisible beam of light that falls directly on the receiver unit.
Interruption of the beam by an intruder triggers the alarm. Photoelectric/Infrared devices
provide protection indoors across staircases, corridors, doors, windows and any passage /
entry point. For outdoors the transmitter and receiver units in weather proof enclosures
are available for ease of installation across protected areas. Multiple beams can be used
for protecting a larger area.
Avoiding False Alarms With Infrared Sensors
Care should be taken to raise the beam height to allow
for pet animals to pass through without interrupting the beam. When using such beams on
boundary walls, it must be kept in mind that boundary walls may be used by birds to sit or
for cats and squirrels to wander around. Simple photoelectric devices are susceptible to
false alarms due to flashing lights (from passing vehicles), indirect sunlight, power
supply transients and radio frequency interference. So, it is important to test the
equipment and adjust sensitivity under various conditions.
Advanced Versions
The susceptibility to false alarm aspects in the basic
version of the device is overcome in the currently available devices where pulse
modulation of the beam and other features are used. In pulse modulation, a specific
pattern of Infrared light is emitted by the transmitter and the same pattern is expected
by the receiver. This makes the device immune to the causes of false alarm pointed out
above and also to problems like, vibrations, slight misalignment which may set in over a
period of time. |
