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.
An intruder detection system comprising: (a) sensing means for sensing the presence of an intruder in a region under surveillance, said sensing means being adapted to produce a first output signal which changes in level in response to the presence of an intruder in such region; (b) pulse generating means for producing pulses of current each time said first output signal exceeds or falls below a preset threshold level; (c) integrating means, operatively coupled to said pulse generating means, for integrating said current pulses and for providing a second output signal representative of the integrated value of such pulses; (d) threshold sensing means for producing an alarm signal in the event said second output signal exceeds a predetermined level; and (e) timing circuit means for discharging said integrating means in the event said second output signal fails to exceed said predetermined level within a preselected time interval, said time interval being reset (i.e. re-established) each time said first output signal exceeds or falls below said preset threshold level.
Claim 2
Dependent Claim
168 words
An intruder detection system comprising: (a) sensing means for sensing the presence of an intruder in a region under surveillance, said sensing means being adapted to produce a first output signal which changes in level in response to the presence of an intruder in such region; (b) pulse generating means for producing pulses of current each time said first output signal exceeds or falls below a preset threshold level; (c) integrating means, operatively coupled to said pulse generating means, for integrating said current pulses and for providing a second output signal representative of the integrated value of such pulses; (d) threshold sensing means for producing an alarm signal in the event said second output signal exceeds a predetermined level; and (e) timing circuit means for discharging said integrating means in the event said second output signal fails to exceed said predetermined level within a preselected time interval, said time interval being reset (i.e. re-established) each time said first output signal exceeds or falls below said preset threshold level.
Claim 3
Dependent Claim
49 words
The invention as defined in claim 1 wherein said pulses of current have a predetermined amplitude and pulsewidth, and wherein the amplitude and/or the pulsewidth of said current pulses is adjustable to control the number of current pulses required for said second output signal to exceed said predetermined level.
Claim 4
Dependent Claim
18 words
The invention as defined by claim 1 wherein said time interval is adjustable to control the system sensitivity.
Claim 5
Dependent Claim
23 words
The invention as defined by claim 1 wherein said predetermined level of said threshold sensing means is adjustable to vary the system sensitivity.