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Ultrasonic anti-theft alarm


Introduction


Using ultrasonic sensor as transmitter and receiver, transmitter emission amplitude ultrasound to area being detected, the receiver receives the reflected ultrasound. When there is no moving object is detected to enter the area, the reflected ultrasound is amplitude. When there are active objects into the detection area, the magnitude of the reflected ultrasonic ranging, and changing. Receiver circuit detect changes in the signal control circuit and then alarm.




The principle of Ultrasonic anti-theft alarm


According to the Installed methods and its structure, we may divide into two types: One is to install two ultrasonic transducers in the same case, that is the sending and receiving co-set type, and its working principle is based on the acoustic Doppler effect, also known as the Doppler-type. When there is no moving object is detected to enter the area, the reflected ultrasound is amplitude. When there are active objects into the detection area, the magnitude of the reflected ultrasonic ranging, and changing. The emission of ultrasonic energy field distribution has a certain direction, usually oval-shaped area for the direction to field distribution. Another is the two transducers were placed in different locations, namely the sending and receiving sub-set type, known as the acoustic detector, its transmitter and receiver to use more non-directional type (ie, omnidirectional) sensors or half the sensor. Non-directional sensors have hemispherical energy field distribution pattern, and a half to the type of field distribution patterns can produce tapered.




The example of continuous wave transmitting circuit


The example of continuous wave transmitting circuit



Applications field of Ultrasonic anti-theft alarm


Because it can detect moving objects, ultrasonic detectors have a wide range of applications. For example: automatic door detection, controller; elevator automatic starter; burglar alarm detectors. The detector characteristics can be detected to determine whether the activities of people within the region or other moving objects, animals, control around a large, high reliability.

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