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Infrared Sensors

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.

Like any other sensors, these also need to be connected to Control Unit to activate the alarm.

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.

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