Communications – electrical: acoustic wave systems and devices – Echo systems – Presence or movement only detection
Patent
1978-09-29
1982-03-09
Caldwell, Sr., John W.
Communications, electrical: acoustic wave systems and devices
Echo systems
Presence or movement only detection
340554, 343 5PD, 367136, G01S 1304, G01S 1504, G08B 1316
Patent
active
043193498
ABSTRACT:
Apparatus and method of processing in an ultrasonic alarm system to detect the doppler-shifted components which indicate the presence of an intruder. A master control applies to each of the transmitter transducers a signal which alternates between two frequencies at a modulation frequency. The output signal from the receiving transducer is synchronously detected and low pass filtered. The filtered signal is applied to electronics which respond to the presence of modulation frequency components in the filter output signal. A first embodiment utilizes a high-Q bandpass filter having a resonance frequency equal to the modulation frequency. In a second embodiment, the modulation frequency is used to effectively perform a correlation between the received signal and the modulation frequency.
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Caldwell Sr. John W.
Nowicki Joseph E.
Pfund Charles E.
Pittway Corporation
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