User's Manual

Hardware and Wiring Installation Guide 11
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 configurations.
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.
3.3.2.2 Effective coverage of rooms
A single sensor placed near the middle of the ceiling can usually effectively cover an 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.
3.3.2.3 Overlapping Sensors
Sensor overlap occurs when two (or more) sensors are placed so that their fields of view overlap. This
will cause some indecision in the system if both sensors see a badge at the same time. The software
will not change the location of a badge when it is in an overlap area unless the option to send duplicate
hits is selected in the Badge Server software. If the option is selected, a badge may appear to bounce
back and forth as long as it is in an overlap condition. This increases the traffic on the system and it is
not recommended that the option be selected.
3.3.2.4 Sunlight interference
If the room has windows that allow a large amount of sunlight to enter the room, place the sensor in a
position where the sunlight does not reflect directly into it from objects in the room. Sunlight can
decrease sensor range and field of view if allowed to enter the sensor. Window tint films that block
infrared (heat) energy greatly reduce this effect.
3.3.2.5 IR Sensor interference from nearby lighting or other electrical fixtures that
may emit EMI noise
System performance can be adversely affected by;
1. Light that is aimed directly into the sensor.
2. EMI noise emitted by nearby electrical fixtures.
Symptoms of sensor interference are:
1. A voltage drop below 15.5 volts.
2. Badges that are not picked up by the sensor or only picked up intermittently.