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Motion and presence sensors

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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.