Spis treści:
They detect people, animals and objects in a specific area. They are widely used in many areas of life. In combination with other sensors and devices such as cameras and alarms, they allow to create a comprehensive security system or home automation.
Motion sensor - what is it?
Sensor, or sensor. Motion sensors originate from industrial automation. There they can be found in the greatest number of variants. Motion detectors retrofit manufacturing plants and factories, where they are used to operate machinery and increase overall workplace safety. In the medical field, sensors are used to track patient movement, detect falls or track the patient’s activity level. Motion sensors are used in such routine activities as turning lights on and off, as well as in complex devices responsible for transportation, industry and entertainment.
How the motion sensor works
Detailed construction motion sensor depends on its type, but in most cases we can distinguish certain elements.
- The element responsible for detecting motion, or the sensing element.
This is the core of any sensor and can be made of materials such as silicon or ceramic. - A lens used to focus the sensor’s field of view on the sensing element.
The shape and design vary depending on the application of the sensor. - An electronic circuit responsible for processing signals from a sensor element and triggering an appropriate response, such as turning on a light or setting off an alarm.
- Housing to protect components.
Every motion sensor generates or detects some kind of wave. This can be an electromagnetic wave or a sound wave.
Solid elements in the environment reflect these waves, or, in the case of infrared radiation (PIR) waves, emit them at a certain frequency. When a moving object appears in the sensor’s field of view, the frequency of the waves reaching the sensor will change, and this in turn causes the system to react – for example, to sound an alarm.
Types of motion sensors
Each motion sensor is designed to detect changes in the environment. The change is supposed to trigger a specific response from the system to which the sensor is connected. Depending on the technology used in the sensor, this change is measured in different ways.
Passive infrared sensor
(PIR, for passive infrared). Passive infrared sensors measure infrared radiation emitted by objects in their field of view.
The thin pyroelectric material contained in the device changes temperature due to absorption of IR radiation, leading to the generation and transmission of an electrical charge. These sensors are ideal for burglar or fire alarm systems.
The alarm is activated when there is an influx of electricity, which is usually triggered – in the case of an anti-burglary system – by the appearance of a stationary warm being, such as a human being, or actually any object that emits infrared radiation.
The downside of such a solution is that a PIR sensor can catch detection… a cat, for example.
However, these sensors are cheap, energy-efficient and long-lasting. When choosing an infrared sensor, it is worth remembering that they have a limited field of view and that it can be obscured by objects, atmospheric phenomena, dust or smoke. For this reason, installing PIRs near garden plants or in industrial yards is a bad idea.
Ultrasonic sensors
Passive ultrasonic sensors are calibrated to a selected sound, such as the sound of breaking glass. These sensors are highly accurate and sensitive, which can lead to false alarms, although for different reasons than their predecessors.
Active ultrasonic sensors emit high-frequency waves that bounce off objects in their field of view. When a person or object moves within this field, this causes a change in the reflection pattern and leads to activation of the sensor.
For ultrasonic sensors, the field of view is not as important a factor, and their area of operation can even cover the entire space in which they are located – hence the argument that they work better in offices, corridors, stairwells and where kinks are encountered. The high-frequency sounds produced by the sensor can be unpleasant for pets – from here it’s not far to another class of devices that should not be confused with sensors, namely ultrasonic repellents.
Microwave sensors
Principle of operation microwave sensors is similar to ultrasonic sensors with the difference that instead of sound waves, the sensor generates microwave waves. When the microwaves bounce off a moving person or object, a change in the frequency of the waves returning to the sensor is recorded. Microwave sensors are very sensitive, but they consume a large amount of energy during operation. In addition, the microwave frequency does not penetrate metallic objects and therefore the range of microwave sensors is simply limited by metallic obstacles.
Tomographic sensors
Tomographic sensors use radio waves to create a three-dimensional map of the monitored area. When a person or object moves through the area monitored by the tomographic sensors, it then triggers changes in the frequency pattern of the waves leading to the triggering of an action trigger. Radio waves are able to penetrate walls and other solid objects, so that the field of view of tomographic sensors cannot be obscured in any way. These sensors are definitely more expensive and are used in large warehouses, logistics centers and any place that requires a high level of security.
Where are motion sensors used?
We have already talked about alarms and access control systems. They can be found “inside” certain devices we are all familiar with, or as integrated into them – these are all doors, gates, navigation systems and sensors mounted in key locations.
Popular home automation (smart home) and IoT systems use motion sensors in lighting control, which allows not only automation, but also savings. There is also no shortage of them in DIY projects when planning an alarm, automatic start-up, irrigation, monitoring or security system for bicycles and vehicles.
