Intruder detection system utilizing artificial ambient light

Claim 2

An intruder system responsive to artificial ambient light derived at least in part from a 60 cycle alternating power supply, the system comprising a photosensor disposed so as to provide an electric signal having a value representative of the amount of ambient light impinging thereon which signal contains a fluctuating component in accordance with the frequency of said power supply, means controlled only by a sufficient change in value of the fluctuating component of said electric signal to provide an output signal, a reference lamp energized from said power supply, a second photosensor disposed so as to receive light only from said reference lamp to provide an electric signal having a value representative of the amount of reference light impinging thereon, said photosensors being connected in series with a junction therebetween, and said controlled means being connected to said junction, whereby the system is sensitive to a change in ambient light derived only from said alternating current power supply when caused by an intruder and is insensitive to changes in ambient light derived from sources other than said power supply.

Claim 3

An intruder detection system comprising a photocell, a capacitor having one side connected to said photocell so as to forward an electric signal containing an alternating component variable in accordance with the frequency of artificial light derived from an alternating current power source and to block any signal derived from generally steady-state ambient light, an operational amplifier having a pair of input terminals and a feedback potentiometer to vary the gain of said amplifier, one of which terminals inverts the signal applied thereto, the output side of said capacitor being connected to said inverting terminal, an isolation transformer having its primary winding connected to the output terminal of said operational amplifier and having a secondary winding, a rectifier bridge connected to said secondary winding, a differentiating network connected to said rectifier bridge for passing a signal when the output from said rectifying bridge is changing, a second operational amplifier having a pair of input terminals, one of which is a non-inverting terminal, said non-inverting terminal being connected to said differentiating network, a resistor connected to the output terminal of said second operational amplifier, a threshold device connected to said resistor for providing an output signal when the signal obtained from said resistor is of sufficient magnitude as determined by the feedback potentiometer associated with said first amplifier, and an alarm connected to said threshold device which is energized when said threshold device is triggered into operation.

Claim 4

An intruder detection system comprising a photocell, a capacitor having one side connected to said photocell so as to forward an electric signal containing an alternating component variable in accordance with the frequency of artificial light derived from an alternating current power source and to block any signal derived from generally steady-state ambient light, an operational amplifier having a pair of input terminals and a feedback potentiometer to vary the gain of said amplifier, one of which terminals inverts the signal applied thereto, the output side of said capacitor being connected to said inverting terminal, an isolation transformer having its primary winding connected to the output terminal of said operational amplifier and having a secondary winding, a rectifier bridge connected to said secondary winding, a differentiating network connected to said rectifier bridge for passing a signal when the output from said rectifying bridge is changing, a second operational amplifier having a pair of input terminals, one of which is a non-inverting terminal, said non-inverting terminal being connected to said differentiating network, a resistor connected to the output terminal of said second operational amplifier, a threshold device connected to said resistor for providing an output signal when the signal obtained from said resistor is of sufficient magnitude as determined by the feedback potentiometer associated with said first amplifier, and an alarm connected to said threshold device which is energized when said threshold device is triggered into operation.

Claim 5

A system in accordance with claim 2 including a second photocell connected in series with said first photocell to provide a junction therebetween, and an auxiliary lamp connected to said alternating power source for supplying reference light to said second photocell, said capacitor being connected to said junction, whereby spurious voltages from said power source are nullified at said junction and are not transmitted through said capacitor.

Claim 6

A system in accordance with claim 3 in which said auxiliary lamp also functions as an indicating lamp.

Claim 7

A system in accordance with claim 3 including a parabolic reflector, said first photocell being located at the focal point of said reflector and said reflector having an opening via which ambient light enters to strike said first photocell.

Claim 8

An intruder system responsive to artificial ambient light at least partially provided by a lamp connected to an alternating power supply, the system comprising a first photosensor disposed so as to provide an electric signal having a value representative of the amount of ambient light impinging thereon which signal contains a fluctuating component in accordance with the frequency of said power supply, a second photosensor disposed so as to provide an electric signal having a value representative of the amount of reference light impinging thereon, said photosensors being connected in series with a junction therebetween, an auxiliary lamp disposed relative to said second photosensor to provide said reference light, said auxiliary lamp also being connected to said alternating current supply, and means connected to said junction controlled only by sufficient change in value of the fluctuating component of the electric signal provided by said first photosensor to provide an output signal, whereby the system is sensitive to a change in ambient light derived from said alternating current power supply when caused by an intruder and is insensitive to changes in ambient light derived from sources other than said power supply.

Claim 9

An intruder system responsive to artificial ambient light at least partially provided by a lamp connected to an alternating power supply, the system comprising a first photosensor disposed so as to provide an electric signal having a value representative of the amount of ambient light impinging thereon which signal contains a fluctuating component in accordance with the frequency of said power supply, a second photosensor disposed so as to provide an electric signal having a value representative of the amount of reference light impinging thereon, said photosensors being connected in series with a junction therebetween, an auxiliary lamp disposed relative to said second photosensor to provide said reference light, said auxiliary lamp also being connected to said alternating current supply, and means connected to said junction controlled only by sufficient change in value of the fluctuating component of the electric signal provided by said first photosensor to provide an output signal, whereby the system is sensitive to a change in ambient light derived from said alternating current power supply when caused by an intruder and is insensitive to changes in ambient light derived from sources other than said power supply.

Claim 10

A system in accordance with claim 6 including a casing, said auxiliary lamp being contained in said casing.

Claim 11

A system in accordance with claim 7 in which a portion of the light from said auxiliary lamp passes through a lens in said casing so as to indicate when the system is operational.

Claim 12

An intruder system responsive to artifical ambient light derived at least in part from a conventional alternating power supply having a 60 hertz frequency, the system comprising a photosensor for receiving at least a portion of said ambient light, means in circuit with said photosensor for passing only a 120 hertz signal derived from said 60 hertz power supply which varies in magnitude depending upon the magnitude of said ambient light portion received by said photosensor, an alarm, means connected to said passing means for activating said alarm when said 120 hertz signal is below a given magnitude, an auxiliary lamp for connection to said power supply so as to furnish a reference level of light intensity, and a second photosensor responsive to only said reference level of light, said passing means being connected to both of said photosensors so that voltage changes in said power supply concomitantly influence both of said photosensors so as not to affect the magnitude of said 120 Hertz signal by reason of any such voltage changes.

Claim 13

An intruder system responsive to artifical ambient light derived at least in part from a conventional alternating power supply having a 60 hertz frequency, the system comprising a photosensor for receiving at least a portion of said ambient light, means in circuit with said photosensor for passing only a 120 hertz signal derived from said 60 hertz power supply which varies in magnitude depending upon the magnitude of said ambient light portion received by said photosensor, an alarm, means connected to said passing means for activating said alarm when said 120 hertz signal is below a given magnitude, an auxiliary lamp for connection to said power supply so as to furnish a reference level of light intensity, and a second photosensor responsive to only said reference level of light, said passing means being connected to both of said photosensors so that voltage changes in said power supply concomitantly influence both of said photosensors so as not to affect the magnitude of said 120 Hertz signal by reason of any such voltage changes.