Impedance sensitive power line intrusion alarm system

Details Impedance sensitive power line intrusion alarm system Impedance sensitive power line intrusion alarm system

1975-02-14

1977-01-25

Caldwell, John W.

Communications: electrical

Systems

Selsyn type

340216, 340416, H04M 1104

Patent

active

040053997

ABSTRACT:
An alarm intrusion system using existing power lines. A sweeping oscillator controlled by a second oscillator having a lower frequency is connected to the power line through a transient clipper and a power line isolator. Connected to the sweeping oscillator and transient clipper is a bandpass filter and automatic gain control circuit, the output of which is evelope detected and fed to a bandpass filter and then to a slope amplifier or differentiator. Positive and negative level detectors responsive to changes of envelope slope are fed to a latching flip-flop via an OR gate. Also fed to the latching flip-flop is a reset pulse derived from shaping the output of the second oscillator. This pulse is also fed to an up/down counter, the direction of the count being determined by the latching flip-flop output. The count is decoded and fed to alarm circuits. The power line is connected to an inductor-capacitor circuit having a predetermined resonant frequency that is altered upon the closing of an intrusion switch.

REFERENCES:
patent: 2206702 (1940-07-01), La Pierre
patent: 2587213 (1952-02-01), Polin
patent: 2630367 (1953-03-01), Rahmel
patent: 3115622 (1963-12-01), Jaffe
patent: 3268867 (1966-08-01), Pickett et al.
patent: 3456192 (1969-07-01), Mixsell

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