Importance

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Abstract

An intruder detection system is provided with circuitry for reducing the risk of false alarms from spurious sources. Such circuitry comprises a pulse generator for producing current pulses of predetermined pulsewidth and amplitude each time the output of an intrusion detecting element exceeds or falls belows a preset threshold level, an integrating circuit for integrating the output of the pulse generator, threshold sensing means for activating an alarm when the integrator output exceeds a preset level, and a timing circuit for establishing a predetermined time interval and for discharging the integrating circuit in the event the integrator output fails to exceed such preset level within such predetermined time interval. According to a preferred embodiment, means are provided for resetting the time interval each time the detector output exceeds or falls below the selected threshold level. By selecting a relatively short time interval and by resetting such time interval every time a potential target is detected, certain types of spurious sources are prevented from producing false alarms.

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First Claim