Movement and presence detectors
Motion and presence detectors are devices that have entered our lives
for good. They can be found primarily wherever objects do not need to be
illuminated continuously, i.e. in corridors, staircases, driveways,
toilets, etc. Thanks to this, users do not have to look for switches of
individual devices, because their entrance or presence in given room
gives an impulse to start devices. Motion and presence sensors operate
on several principles.
The first group are passive PIR sensors, based on the detection of rapid
temperature changes indoors or outdoors. Detection occurs when a
temperature change occurs in the monitored area, which the device
interprets as motion. Due to the fact that PIR sensors are passive
sensors, they do not send any signals, but only receive those coming
from the environment. In order for them to function properly, the
temperature difference between the surroundings and the detected object
is necessary. Therefore, IR sensors work well in low temperatures, while
in high summer temperatures they can be blind - the temperature
difference in this case is too small to trigger such a sensor.
The next group of sensors, this time active, are microwave sensors. They
work like radar because they send out radio waves which, when reflected
from objects, return to the sensor. If motion is detected in the
detection field, the reflected wave is disturbed, and thus the sensor is
activated, which, for example, will turn on the lighting. These are
sensitive detectors because they can react to the movement of even small
objects, such as the passage of insects or stronger vibrations of
devices used in interior furnishings, which can often lead to false
alarms. For this reason, they are usually not used outside buildings -
their operation is even caused by raining or blowing wind. The
disadvantages of the above types of sensors can be effectively limited
by using dual sensors, in which the operation takes place only after
movement is confirmed by both types of detectors. Thanks to this, the
number of false start-ups, caused e.g. by the movement of objects at the
ambient temperature, is reduced. Due to the two types of sensors used,
dual devices are more expensive than models with only one type of
sensor.
Ultrasonic sensors base their operation on ultrasound and investigate
the magnitude of the disturbance reflected by various objects of the
wave.
Cameras are another group of detectors. In their case, the detection of
objects is based on rapid image analysis, performed by artificial
intelligence, which can be programmed to detect objects with specific
parameters, such as detecting human silhouettes while ignoring animal
silhouettes, distinguishing between trucks and cars, etc.
How to choose motion sensors?
Motion sensors perfectly replace all kinds of standard switches. They
can be used both indoors and outdoors. In both of these cases, attention
must be paid to the degree of protection against moisture, dust or dirt.
While in residential premises these safeguards are not so important,
they will be very important outdoors and in wet rooms, such as toilets,
especially in service premises or in dusty communication routes in
production plants. An important selection criterion is the operating
range of the device and the "surface coverage" - in the case of
lighting the driveways, for example, detection outside the driveway
itself is unnecessary.
What to look for when choosing presence detectors?
Presence detectors are very sensitive motion detectors in the detection
field. A properly calibrated device will detect even a small movement in
the monitored rooms. A good type of sensor used to detect presence is an
ultrasonic sensor, which is sensitive enough to detect minimal movement
even in hard-to-reach places, such as a hand movement on a keyboard. For
this reason, it is used in offices or toilets, where the equipment
cannot be turned off after a certain time, but only after people have
left the room.
