Communications: electrical – Systems – Call station
Patent
1974-06-21
1976-03-23
Wilbur, Maynard R.
Communications: electrical
Systems
Call station
340261, 73 675R, 73 677, G08B 1308
Patent
active
039463770
ABSTRACT:
To detect breakage of glass panes, panels of display cases, or movement in a room, ultrasonic waves, preferably in the order of from 120 kHz to 180 kHz, are transmitted to the sonically conductive medium (glass panes, plastic sheets, or into the air of the room), and the waves are received in a receiver. The time shift of the received waves at the receiver location, with respect to the transmitted waves is determined, and if this time shift changes beyond a predetermined limit, an alarm signal is generated. Preferably, the ultrasonic signals are frequency modulated, for example by shifting the generated waves by a predetermined frequency shift, and determining the temporal change, or delay of the frequency shift, as received, with respect to the time of frequency shift at the transmitter. To prevent the effect of drift, the rate of change of received with respect to transmitted frequency shift can be used to generate the alarm.
REFERENCES:
patent: 2987713 (1961-06-01), Bagno
patent: 3050989 (1962-08-01), Henry
patent: 3111657 (1963-11-01), Bagno
patent: 3712119 (1973-01-01), Cross et al.
patent: 3801977 (1974-04-01), Cotter
patent: 3889250 (1975-06-01), Solomon
Blum T. M.
Cerberus AG
Wilbur Maynard R.
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