Communications: electrical – Systems – Call station
Patent
1975-12-08
1978-05-09
Swann, III, Glen R.
Communications: electrical
Systems
Call station
340261, G08B 1304
Patent
active
040889890
ABSTRACT:
In an active system a transmitter transducer and a receiver transducer are both secured to an object such as a glass panel the intrusion through which is to be monitored. The transmitter transducer establishes a relatively low frequency signal in the panel and a supervisory branch which couples from the receiver transducer monitors the presence of this supervisory signal. A second branch which also couples from the receiver transducer is for monitoring intrusion and comprises digital circuitry including a pair of monostable multivibrators and a counter which counts pulses from one of the monostable multivibrations during a time interval determined by the other monostable multivibrator to discriminate between panel breakage and panel rapping, for example. The tampering with voltage lines is also detected and a special holder is employed for fastening the transducers to the panel.
REFERENCES:
patent: 2987713 (1961-06-01), Bagno
patent: 3697989 (1972-10-01), Bailey et al.
patent: 3793617 (1974-02-01), Tolman
patent: 3889250 (1975-06-01), Solomon
patent: 3925773 (1975-12-01), Green
patent: 3946377 (1976-03-01), Zetting
Gulf & Western Manufacturing Company
Swann III Glen R.
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