Communications: radio wave antennas – Antennas – Balanced doublet - centerfed
Patent
1976-12-27
1978-05-02
Tubbesing, T.H.
Communications: radio wave antennas
Antennas
Balanced doublet - centerfed
340258B, 343 6R, G08B 1318
Patent
active
040878147
ABSTRACT:
Intruder alarm apparatus includes two detector systems each responsive to the presence of an intruder within a portion at least of a protected area and alarm means responsive to the actuation of the detectors in a predetermined logic or time sequence for signalling the presence of an intruder. One embodiment includes two microwave Doppler detectors each responding to the presence of an intruder by opening alarm contacts. The two alarm contacts are connected in parallel in the loop circuit of a closed-loop alarm system so that an alarm is given only if both detector contacts are opened simultaneously. Preferably the duration of contact opening is arranged to extend beyond the period of actual intruder response. In another embodiment, two intruder detectors spaced along a passageway each respond to the presence of an intruder by actuating an alarm contact, that detector past which an intruder must first pass in gaining access to a protected area closing its contact for a relatively long period, while the detector which will be passed later closes its contact for a short period. Thus the passage of authorized persons in the direction away from the protected area will not initiate an alarm while a person moving towards the protected area will initiate an alarm.
REFERENCES:
patent: 2649538 (1953-08-01), Marlowe et al.
patent: 3691558 (1972-09-01), Hoard et al.
patent: 3725888 (1973-04-01), Solomon
patent: 3727216 (1973-04-01), Antonio
patent: 3815131 (1974-06-01), Dautel et al.
patent: 3946376 (1976-03-01), Galvin
Laubscher Lawrence E.
Tubbesing T.H.
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