Motion sensors are compact devices which are irreplaceable in operation of security alarm systems. Also the sensors reacting to movements are used in lighting systems for the purpose of economy of the electric power.
The motion sensor is a device which is capable to find movement of any objects: people, animals, vehicles, etc. Such sensors are most often used in security alarm systems and the systems of automatic control of lighting. Infrared sensors happen two types: active and passive. Also there are ultrasonic active sensors.
Principle of operation of the passive infrared motion sensor
Passive sensors have the receiver of infrared radiation, and the transmitter of radiation is absent. Such sensors are equipped with a pyroelectric element which reacts to temperature change in a zone of sensitivity of the device. Therefore passive sensors are capable to find in an area of coverage only people and animals.
Passive sensors are absolutely safe for human health and animals as they are not emitters. However because they react to heat, false operations are possible. For example, the wave of warm air about streets or the switched-on heating device can become the reason of false operation.
Principle of operation of the active infrared motion sensor
Active infrared motion sensors differ from passive in the principle of work and existence of the transmitter of radiation. Such sensors in a zone of the action find any mobile objects, including cars. When the radiated signal is reflected from objects, the sensor catches movements in an emitter area of coverage. Active sensors are most often used in the security alarm system as they fix any moving objects, and false operations on warm air by it are not peculiar.
Principle of operation of the ultrasonic motion sensor
Ultrasonic sensors have the receiver and the transmitter of radiation. They radiate sound waves in frequency range from 20 to 60 kHz. The sound in this frequency range is not heard to the person, however some animals can hear it what causes in them discomfort. It is better not to install such sensors in premises. Ultrasound is radiated in a sensor area of coverage, it is reflected from surrounding objects then BONDS signals comes back to the receiver. When in a zone of operation the BONDS sensor there is a moving object, the frequency of the signal reflected from an object (Dopler's effect) changes. Ultrasonic motion sensors are used in the systems of the automatic parking (in parctronics) and also alarm systems and lighting systems to non-residential premises.