Installation Manual

Versus Technology, Inc.
DT10000-A0001 11 Revision 8 December 1998
3.8 Special Problems with Sensor Coverage
The placement of sensors is usually a simple matter, but there are some special things to remember when
planning a system installation. The system planner should consider that a sensor may have a field of view
which extends out of the designated area through a doorway or passage, and that tagged persons might be
detected incorrectly and reported to be in the room when only passing by. Consider placing sensors away from
doors or entryways to prevent this. Sensors can be positioned so as to limit their view by placing them in
locations where existing obstacles serve to block the unwanted sensor view.
Due to the line-of-sight nature of the infrared light created by the ID tags, it is also possible to apply masking to
the sensor to limit or control the field of view. This masking of the sensor has been done with great success, but
may require some experimentation to refine for each application. However, proper placement is always the
preferred method for controlling, rather than eliminating, sensor field of view.
If the room has windows that allow a large amount of sunlight to enter the room, the sensor is best placed in a
position such that the sunlight is not reflected directly into it by the floor or furniture. Extremes of daylight 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.
Of course, the sensor should be located such that it is afforded the best possible view of the room and the
persons in it. If the room is of complex shape and no single sensor position will provide adequate coverage,
multiple sensors should be considered.
3.9 Overlapping Sensors
Sensor overlap occurs when two (or more) sensors are placed such that their fields of view are coincident
(overlap) in some area. Allowing the field of view of one sensor to overlap that of another will, as one would
expect, cause some indecision in the system if both sensors observe an ID tag at the same time. The software
will not change the location of a tag when it is in an overlap area unless the software is told to ignore overlaps.
If overlaps are ignored a tag may appear to bounce back and forth as long as it is in an overlap condition.
3.10 High Frequency Light Interference
NOTE: Certain types of energy efficient lighting and associated electronic ballast’s may interfere
with the operation of a sensor that is within in the range of the light fixture.
In addition, the light emitted by fluorescent fixtures adds a high degree of noise to the sensor environment. The
sensor should be mounted such that light from florescent fixtures is not in direct sensor view. Excessive noisy
fluorescent energy can cause intermittent sensor reception and reduced range. "Warm White" and other tubes
designed to emit more red color energy are more of a problem than conventional "cool white" tubes.
• The use of High Frequency sensors will avoid most light interference problems.
The most common offenders are classified as T8 lights and have electronic ballast in the 40 kHz
range.