P R O D U C T S
Occupancy Sensors for lighting
in public access areas
Increasing awareness for energy
efficiency and the need to meet the
requirements set for the green mark
design had fuelled need for “OnDemand” lighting control solutions
based on human presence. In order
to realise this objective, sensors are
required to detect and determine the
presence of humans. Occupancy
sensors are commonly used for this
purpose. These sensors have been
implemented in facilities such as
schools or office buildings, such as in
meeting rooms, toilets, staircases and
other office areas.
The “On-Demand” lighting control
solution is also applicable for public
or semi-public areas including
basements, multi-storey car parks,
staircases, covered-walkways,
pedestrian underpasses or overhead
bridges and public bus stops.
Energy savings can be substantial
as human activities in these areas
tend to be low during off peak hours.
There are many kinds of Occupancy
Sensors available. To determine
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ELECTRONICS REVIEW
the best sensors to be used, various
environmental factors have to be
considered for an effective “OnDemand” lighting systems. The
factors are:
•
Ambient temperature
•
Ambience noises
•
Possibility of vandalism
•
Fault reporting
•
Safety and security
Choosing the right sensors
The three most common occupancy
sensors or motion detectors
technologies are Passive Infrared
(PIR), Ultrasonic and High Frequency
(HF).
PIR is by far the most common
occupancy sensor technology for
indoor applications, used especially
for meeting rooms and small offices
where there is a line-of-sight between
the sensor and human. Ultrasonic
and HF are used mainly in toilets,
warehouses or offices which may have
high cubicles where despite the lineof-sight being limited, sensing human
movement is still possible as sound
or radio waves are able to bounce
between walls.
For outdoor or semi-outdoor and
public access areas, considerations
for occupancy sensors would be
different from those for indoor use.
PIR Motion Detector
PIR is a passive sensor with low
power consumption. Its operating
principle is detecting human body
surface temperature (33 degrees
Celsius) compared to the ambient
temperature. Sensitivity of PIR
sensors is proportional to the delta
temperature between the human body
and the ambient temperature.
In Singapore, ambient temperatures
at night vary from 23 to 33 degrees
Celsius. The sensitivity of PIR
sensor deteriorates when ambient
temperatures rise. Theoretically,
PIR is ‘blind’ and is unable to detect
human presence at 33 degrees
Celsius ambient temperature.
Lighting system designers must take
this factor into consideration when
using PIR sensors in outdoor or non
air-conditioned areas for lighting
control.
Like many other optical instruments,
the performance of PIR sensors will
be impaired if the Fresnel lens of
the sensor is covered with dust or
oil. Regular cleaning is therefore
necessary for the PIR sensors to
operate effectively in a dusty or oily
environment. Fresnel lenses are
probably the weakest link of the PIR
sensor where vandalism is a concern
in the area of installation.
Ultrasonic Motion Detector
Ultrasonic sensors emit inaudible
sound waves and ‘listen’ for the
Doppler shifts of the echoes bouncing
back from moving objects. Unlike PIR
sensors that detect body heat, the
ultrasonic sensors detect all moving
objects, living and non-living. Such
sensors cover a relatively large area
and are therefore effective in areas
where line-of-sight is limited, such as
in toilets and offices with high cubicles
or warehouses with high ceiling.
Ultrasonic sensors however, do not
work well in noisy environments
and where there is likelihood of high
pitched sounds such as the jamming
of car brakes and blaring of car horns,
and in heavy winds. These sounds
may ’confuse’ the sensors. Another
shortcoming of ultrasonic sensors
is the inherent poor environmental
protection for enclosures where air
outlets are needed for sound wave
propagation. Additional protection
is required if the sensor is operating
in a harsh environment or prone to
vandalism.
HF Motion Detector
The operation principle of the
HF Motion Detector is similar to
Ultrasonic sensors, except that the HF
transmits high frequency radio waves
instead of sound. It can also detect
all moving objects, living and nonliving. As such, swinging plants, stray
dogs and vibrations may trigger false
alarms.
Because of its shorter wavelength,
the HF sensor is able to detect the
slightest movement; and is less
sensitive to ambient temperature and
noises. Another advantage of the HF
sensor is its ability to ‘see through’
a fully sealed enclosure without
affecting its performance. HF sensors
are therefore a suitable choice for
operating in dusty environments or
in areas prone to vandalism offering
an added advantage of requiring very
little maintenance.
control in public access areas, such
as basements, multi-storey car
parks, staircases, common corridors,
walkways, void decks, pedestrian
overhead bridges and underpasses.
These sensors are designed with
robust enclosures, anti-mask/block
and fail-safe features, achieving
energy saving without comprising
pedestrian safety and security.
For more information, please contact
Bentley Chen at (65) 6521 7545 or email:
chen.jinrong@stee.stengg.com
Safety and Security
Motion detectors are commonly used
for security intruder alarms. The
operating principle is similar to that of
occupancy sensors in lighting control.
The main difference between these
two applications lies with their ‘on-off’
algorithm.
To detect intruders, decision
algorithms require more steps to
confirm valid human movements
for alarm activation, as false alarms
are unacceptable. For occupancy
sensors, a light has to be turned on
immediately once a person steps into
the detection zone. In public areas,
lighting has to be maintained at all
times for safety and security reasons.
It is therefore critical for occupancy
sensors to have fail-safe features so
as to avoid black-outs in certain areas
due to faulty sensor or vandalism.
Products
ST Electronics (Satcom & Sensor
Systems) designs and manufactures
both PIR and HF occupancy sensors
that are specially designed for lighting
MAY 2014
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