User's Manual

Hardware and Wiring Installation Guide 9
3.2.1 Sensor Connection Length Limitations
The sensor wire runs can be up to 1000 feet in length from the Collector to the sensor. If the
environment is known to be electrically "noisy,” consider shorter line lengths for stronger signals and
immunity to interference.
3.2.2 Infrared (IR) Sensor Location Planning
3.2.2.1 IR Sensor "field-of-view"
If an IR sensor is placed in a room with obstacles and reflections eliminated, the field of view of the
sensor appears in the shape of six overlapping lobes forming a 15-foot radius.
Top view of sensors in a hallway
An IR sensor “sees” the environment under it in a largely predictable pattern. However, there are
factors that can affect this field of view. The sensor is like an eye, which is sensitive only to a narrow
spectrum of light, and the ID badge appears as a bright splash in an otherwise dark world to the sensor.
Even if the badge is blocked from the view of a sensor, it can often be detected. The infrared light from
a badge does not penetrate solid objects or bend around corners, but it does reflect off surfaces. This
can sometimes be mistaken for “seeing around corners”. The effect of reflection can be used to
advantage by the system designer, but can also pose problems for the unwary. Sensors have a given
field of view when obstacles are not present, but the field of view of an installed sensor will vary due
to room confi guratio ns.
A sensor may have a field of view that extends out of the designated area through a doorway or
passage. This can cause badges to be detected incorrectly and reported to be in the room when only
passing by. Place sensors near the middle of rooms, but offset from doors or entryways to prevent false
detection. The position of a sensor can limit its view by placing it in a location where existing
obstacles will block the unwanted sensor view.
Due to the line-of-sight nature of the infrared light created by the ID badges, it is also possible to apply
masking to the sensor to limit or control the field of view by opening the sensor case and placing
electrical tape over the receiver “eye” whose field of view needs to be blocked. However, proper
placement is always the preferred method for controlling, rather than eliminating, sensor field of view.
3.2.2.2 Effective coverage of rooms
A single sensor placed near the middle of the ceiling can us ually effectively cover a n office or meeting
room. Offices or rooms as large as 30 feet square are generally covered by a single sensor. The sensor
should be located so that it has the best possible view of the room. If the room is very large or has a
complex shape and no single sensor position will provide adequate coverage, multiple sensors will be
needed.