G - Physics – 08 – B
Patent
G - Physics
08
B
340/124.3
G08B 13/24 (2006.01)
Patent
CA 1100208
ABSTRACT OF THE DISCLOSURE An improved intrusion warning or alarm system of the type wherein the presence of an intruder within a given area is detected by determining the change, caused by the motion of an intruder, of a quasi-stationary electrical field produced within the given area. The electric field is produced by means of an oscillator whose output signal has a frequency in the range of from about 1-40 KHz and is fed to a field wire which is positioned within the area to be protected and the electric field is de- tected by an antenna whose output is connected to an amplifier. An AM detector is connected to the output of the amplifier and the output of the AM detector is connected via a lowpass filter to a high gain amplifying means including a bandpass filter arrangement so that at the output of this high gain amplifier only signals within the relatively low frequency range of from 0.2 to 2Hz associated with movement of an intruder are present. The output signal from the high gain amplifier is fed to a threshold circuit which produces an output signal whenever the input signal thereto exceeds a predetermined threshold value, and this output signal is fed to an alarm producing circuit. The frequency of the electric field is preferably approximately midway between two successive harmonics of the frequency of any a.c. power existing in the vicinity of the area to be protected in order to decrease the possibility of false alarms. Other techniques for reducing the possibility of false alarms and for extending the utility of such a system are disclosed. - 1 -
285767
Geiszler Theodore D.
Mongeon Ronald W.
Moffat & Co.
Stellar Systems Inc.
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