Using the ultrasonic sensor as the transmitter and receiver, the transmitter emits an equal amplitude ultrasonic wave to the detected area and the receiver receives the reflected ultrasonic wave, when there is no moving object into the detected area, the reflected ultrasonic wave is of equal amplitude. When there is a moving object into the detection area, the reflected ultrasonic wave amplitude varies and changes constantly, and the receiving circuit detects the changing signal to control the circuit to react, that is, to drive the alarm.
Ultrasonic burglar alarm
█ Working principle of ultrasonic anti-theft alarm
According to its structure and installation methods are divided into two types: one is the installation of two ultrasonic transducers in the same housing, that is, the transceiver and transmitter combined type, its working principle is based on the Doppler effect of sound waves, also known as Doppler type. When no moving object enters the detected area, the reflected ultrasonic waves are of equal amplitude. When a moving object enters the detected area, the reflected ultrasound is of unequal amplitude and constantly changes. The energy field distribution of the emitted ultrasound has a certain directionality, generally for the direction-facing area in an elliptical energy field distribution.
The other is the two transducers are placed in different positions, that is, receiving and transmitting split type, known as the sound field detector, its transmitter and receiver are mostly non-directional (i.e. omnidirectional) transducer or half-way type transducer. The non-directional transducer produces a hemispherical energy field distribution pattern and the semi-directional type produces a conical energy field distribution pattern.
Doppler type working principle
█ Example of an ultrasonic continuous wave signal transmission circuit.
Example of an ultrasonic continuous wave signal transmission circuit
█ Areas of use for anti-theft alarms.
Ultrasonic detectors that can detect moving objects have a wide range of applications, for example, automatic door opening and closing detection and control; automatic lift starters; anti-theft alarm detector, etc. The characteristic of this detector is that it can judge whether there are active human animals or other moving objects in the detected area. It has a large control circumference and high reliability.
Post time: Dec-19-2022