초록 ▼

A capacitance intrusion detection system for use with a metal object or objects insulated from ground comprises a circuit for cyclically charging and discharging the object at a relatively low frequency, for example, less than 500 Hz, and simultaneously integrating the charge on the object to develo

A capacitance intrusion detection system for use with a metal object or objects insulated from ground comprises a circuit for cyclically charging and discharging the object at a relatively low frequency, for example, less than 500 Hz, and simultaneously integrating the charge on the object to develop a DC voltage proportional to the capacitance of the object. The integrating network is AC coupled to a bandpass filter which passes signals having frequencies corresponding to changes in capacitance of the object caused by an intruder and these signals are applied to a threshold circuit for activating an alarm when an intrusion occurs. Tamper alarm circuits are provided to detect unauthorized disconnection of any portion of the protected object (decrease capacitance) or the addition of capacitance in an attempt to defeat the system.

대표청구항 ▼

An intrusion detection system for an object having a capacitance comprising a charge pump having an input and an output, a voltage source connected to said input, said object being connected to said output of the charge pump, means to cyclically switch said charge pump between first and second state

An intrusion detection system for an object having a capacitance comprising a charge pump having an input and an output, a voltage source connected to said input, said object being connected to said output of the charge pump, means to cyclically switch said charge pump between first and second states whereby alternately to connect and disconnect said voltage source and said object for successively charging the latter, storage means connected to said charge pump for producing a DC voltage proportional to the charge on said object, bandpass filter means having a low cutoff frequency f1 and a high cutoff frequency f2, capacitor means interconnecting said storage means and said filter means whereby changes in the capacitance of said object at a rate between f1 and f2 produce an output from said filter means, and means responsive to the output of said filter means for producing an alarm.