In the modern world, a person seeks to automate any processes, including his daily actions. That is why a motion sensor is increasingly being installed in everyday life to turn on the light. How it works and what you need to know to choose a specific model, we will consider in this article.
Device and principle of operation
Structurally, the motion sensor contains several constituent elements, which will differ depending on the type.
For example, consider an infrared sensor device, which consists of:
- PIR pyroelectric element that responds to changes in the physical parameters of the environment;
- field-effect transistor T1, acting as an electronic switch;
- shunt resistor R1 connected in parallel to the pyroelectric element.
The principle of operation lies in the ability of the pyro material to change its own characteristics depending on the degree of thermal radiation falling on it. The luminous flux reduces the resistance of the PIR pyroelectric element and through it a signal comes to open the field-effect transistor. In this state, the current will flow through the load, which can be a relay coil or other logic element. In the event that a person or other object appears in the area of the sensor, the luminous flux is interrupted and will cease to affect the pyroelectric element, the automatics will work, giving a corresponding signal about the occurrence movement.
Varieties
The division of motion sensors for turning on the light into types is carried out according to several criteria. According to the principle of action, they can be divided into:
- Infrared - based on measuring the temperature of objects falling into the coverage area of the motion sensor. The main disadvantage is a false reaction to heating elements or incandescent lamps located in the immediate vicinity.
- Ultrasonic - operate on the basis of the Doppler effect. The emitted sound wave in the frequency range from 20 to 60 kHz is not audible to the human ear in accordance with clause 2.1.1.3 of GOST R 50030.5.2-99. When faced with an obstacle, the ultrasound is reflected and returned to the receiver, about which a signal is transmitted to an electronic key or relay.
- Microwave - use a special antenna that sends a high frequency signal to the surrounding area. When the signal collides with a moving object, a return signal is generated and returned to the sensor. Today these are the most sensitive, but also the most expensive models for turning on the light.
- Laser - consist, as a rule, of an LED and a photodiode, mounted in the controlled area. The LED emits a signal that propagates to the surrounding area. As soon as an object appears in the area of action, blocking the light flux, it is reflected and perceived by the photodiode. From which the signal is fed to the actuator of the motion sensor.
- Tomographic - use radio waves to diagnose space. Unlike other models, they are able to penetrate walls, structural elements and other obstacles. Used to turn on lighting in large areas, shopping centers, etc.
Depending on the method of interaction with moving objects, motion sensors can be active, passive or combined. Active ones independently emit measured signals, and then perceive them. Passive ones are focused on their own radiation of the human body or are repelled by their interaction with the environment. The combined ones consist of an active emitter installed on one side and a passive receiver located on the other side.
Depending on the place of installation, motion sensors are divided into devices for outdoor and indoor use.. The former are intended for outdoor use. The latter are used for placement indoors, sometimes under awnings, on verandas, covered terraces and patios.