Occupancy Sensors
Introduction
Occupancy sensors are motion detectors that have an integrated timing device. They are most
commonly used to control indoor lighting. Traditional occupancy sensors turn lights on when an area
becomes occupied and turn lights off after the area becomes unoccupied. This technical review paper
briefly discusses the commercial applications, underlying technology, and implementation of occupancy
sensors.
Commercial Applications of Occupancy Sensor Technology
Current occupancy sensors on the market use passive infrared (PIR), ultrasonic technology (US),
or both technologies (DT) to detect motion [1].
Passive Infrared Sensors
PIR sensors are good at detecting major motion, such as a person walking, and work best in small
enclosed spaces with few obstacles [2]. These sensors can only detect movement that is in their line of
sight and are more sensitive to lateral movement. PIR sensors are most commonly used in small rooms
and store or warehouse aisles [3].
Ultrasonic Technology Sensors
US sensors are good at detecting minor motion, such as typing or reading, and do not require an
unobstructed line of sight in order to detect motion. These sensors are most sensitive to movement to and
from the sensor. US sensors are most commonly used in large open spaces such as offices.
Dual-technology Sensors
DT sensors use both PIR and US sensors in order to increase reliability. They are most commonly
used in classrooms, conference rooms, and areas where a high degree of detection is desirable [3].
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Technology of Occupancy Sensors
Passive Infrared Sensors
PIR technology detects motion by sensing the differences in the heat emitted by humans in
motion from that of the background space. The sensors use a segmented lens which divides the coverage
area into zones. Movement between these zones is interpreted as occupancy. Because they are passive, no
energy is consumed by PIR sensors. The range of a typical PIR sensor is about 15 feet [3]. The latest PIR
sensors from Lutron Electronics, a leader in the field of occupancy sensors, can detect minor motion up to
12 feet away and major motion up to 22 feet away [4].
Ultrasonic Technology Sensors
Ultrasonic technology senses occupancy by bouncing ultrasonic sound waves (32kHz – 45kHz)
off objects in a space and detecting a frequency shift between the emitted and reflected sound waves [3].
Movement by a person or object within the space causes a shift in the wave frequency, which is
interpreted as occupancy. Because US sensors emit ultrasonic waves, they do require a small amount of
power, unlike PIR sensors. The latest US sensors from Lutron Electronics can detect minor motion up to
23 feet away and major motion up to 32 feet away [4].
Implementation of Occupancy Sensors
Both hardware and software are required to implement occupancy sensors. A low power
embedded processor typically provides a timer and interprets signals from the sensor. Most occupancy
sensors also have some sort of automatic adjustment controlled by software in order to prevent false
positives.
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[1]
E. Fournier, “Specify the Optimal Occupancy Sensor,” Consulting-Specifying Engineer, vol. 43,
no. 6, p. 67-69, June 2008. [Abstract]. Available: EBSCO, http://www.ebscohost.com/. [Accessed
Jan. 24, 2010].
[2]
Occupancy Sensor Product Guide, Lutron Electronics Co., 2006. [Online]. Available:
http://www.lutron.com/products/pdf/367-1126.pdf. [Accessed Jan. 25, 2010]
[3]
C. DiLouie, “Occupancy Sensors 101,” Electrical Construction & Maintenance (EC&M), April
1, 2007. [Online]. Available: http://ecmweb.com/lighting/electric_occupancy_sensors/.
[Accessed: Jan. 25, 2010].
[4]
Lutron Electronics Co., “Dual Technology Ceiling Mount Sensor,” LOS-CDT Series datasheet,
Sept. 4, 2008. [Online]. Available: http://www.lutron.com/products/pdf/LOS-CDT%20Series.pdf.
[Accessed Jan. 25, 2010]
[5]
D. Nelson, “Electric Lighting Controls,” Whole Building Design Guide, Nov. 23, 2009. [Online].
Available: http://www.wbdg.org/resources/electriclighting.php. [Accessed: Jan. 26, 2010].
[6]
“Passive Infrared-motion Sensors,” Machine Design, vol. 80, no. 13, p. 48, July 10, 2008.
[Abstract]. Available: EBSCO, http://www.ebscohost.com/. [Accessed Jan. 26, 2010].
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