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Anubis
Systems Technologies
MOTION
DETECTORS/BEAM DETECTORS:
Unauthorized
access or intrusions into a protected premise are best detected
by movement (or motion) sensors. These types of units utilize
a variety of methods to sense motion of an individual.
These methods are:
Infrared
(PIRO ELEMENT) Detectors
Commonly
referred to as PIR's
(short for Passive
Infrared Detector).
The most common type of detector utilized today, and the most
cost-effective. All are referred to as "dual element" detectors
which, simply put, allows them to discriminate between commonly
encountered background "noise" and the physical presence of an
intruder. These detectors sense infrared light energy emitted
by or reflected from an object. Infrared light is simply
heat. All objects in a room emit some form of heat energy,
some more than others. Humans and household pets (dogs &
cats) emit a lot of infrared light in the form of body heat.
We are surrounded by a "halo" of infrared energy. We can't
see it ourselves, but these detectors are designed specifically
to sense it. Some areas of a room can also emit a
lot of infrared light or heat. A fireplace or a patch of
floor illuminated by the sun for long periods of time produce
a "bloom" of infrared light that is brighter than any living target.
The way PIR's work is actually quite ingenious. The actual
detection element is mounted behind a faceted lens usually made
of an opaque plastic. This plastic is essentially a light
filter. It allows free passage of infrared light, but restricts
other bands of light (the middle oranges, yellows, greens, and
blues (or ultraviolet). White light is composed of all the
bands put together (including red and infrared) which is why the
lens is often referred to as a "white light" filter. A moving
target or object passes in front of the lens. It moves from
one facet to another. Circuitry onboard the detector "times"
the movement from facet to facet. When it falls into a preprogrammed
set of variables (most often associated with a moving target),
the "alarm thresh hold" is reached and the sensor is triggered.
Unfortunately it is often difficult for the sensor to distinguish
between an "animal" target and a human one (such as an intruder).
Larger animals will often trigger "false alarms". Your security
consultant should ask about pets and may even suggest restricting
their movements (closing off the areas protected by motion sensors
to the pet) to avoid the possibility of false alarms. New technology
has advanced the capability of the PIR sensor, and "pet proof"
detectors are now widely available. Pet immune or pet proof
detectors are more expensive than standard motion sensors, but
this is an option you may well wish to consider.
These
are pictures of some of the more popular infrared sensors:
Ultra-sonic
Detectors
are motion sensors that are rarely utilized today because of the
advances made in the PIR detector. These types of detectors
utilize high frequency sound (a frequency well beyond human hearing)
emitted by the detector. The "Doppler Shift" effect caused
by a target or individual moving towards the sensor activates
detection circuitry and causes the sensor to "alarm". Unfortunately
over time, the high frequency sound emitted by the sensor can
become modulated to a lower frequency and begin to disturb pets
in the home. Cats & dogs that refuse to enter certain
rooms in the house or act differently when in the same room as
one of these detectors are sure signs that the sensor may require
adjustment or replacement (usually the latter). The major
drawback with these types of sensors is the ease with which they
are "cheated". An intruder that recognizes the distinctive
shape of the sensor has only to walk through the room PARALLEL
to the sensor. As long as he/she doesn't approach the sensor,
the "Doppler Shift" essential to the units activation will not
occur.
Microwave
Detectors
are very similar to the ultra-sonic detector with one major exception.
Instead of sound energy, this type of sensor utilizes radar energy
to sense the "Doppler Shift" caused by a moving target.
Because it utilizes radar (microwave) energy it can also sense
"side" Doppler (that is movement parallel to the sensors line
of sight), so the drawback encountered with the ultra-sonic detector
is eliminated. Unfortunately and because it utilizes this
technology, it can also virtually see through most walls or barriers.
It will also sense the movement of liquids in household water
and drain pipes. It's ability to be focussed very tightly
and it's uncommon range (some units can "see" three hundred feet
or one hundred & eighty metres or more) makes it an excellent
fence line protector. In the home or workplace, however,
it is usually coupled to a PIR element and built into the same
case. In this instance both detectors have to be in alarm
before a signal is transmitted to the alarm control unit.
Beam
Detectors
are not motion detectors in the strictest sense. Most often
they utilize infra-red light energy, but instead of being "passive"
(that is strictly an infra-red sensor), a beam system requires
two separate elements to complete the "circuit", namely an emitter
and a receiver. Both these units are mounted facing each
other. The emitter shines a beam of infra-red light at the
receiver. When the beam is broken, the receiver trips the
alarm. A less expensive "cousin" to this type of unit is
usually seen in a lot of retail stores. When a customer
enters the store, he usually "breaks the beam" and a chime or
buzzer is sounded to alert the shopkeeper to the presence of the
patron. In a security system, beam detectors can literally
become invisible "walls" or "curtains" of protection, and since
the detectors housings can be easily disguised or hidden, an intruder
usually won't know where or when he breaks the beam.
For
more information you can email us or telephone (778) 863-7147.
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