| 摘要 |
An ultrasonic intrusion alarm system has a central control unit and a plurality of remote processors connected to the control unit by means of a single cable having two conductors which need not be shielded. All signals necessary for the proper operation of the system flow along the cable. The control unit provides a modulated ultrasonic signal and DC power to the remote processors along the cable, and each remote processor sends back an alarm along the cable when an intrusion is detected. The signal from each receiving transducer is applied to circuitry in an associated remote processor which detects the presence of doppler shifted signals representative of a moving object in the protected premises. The control unit includes processing circuitry for detecting signals on the cable which indicate that a remote processor has detected a moving object. The control unit further includes circuitry for applying the modulated signal to the cable in a manner which enhances the reliability and performance of the intrusion alarm system, including a novel switching modulator which is very efficient and wastes little energy.
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