Intruder detection system

Claim 2

A security system comprising: a transmitter for emitting a continuous series of signal pulses of short duration along a predetermined line of sight, a receiver spaced from the transmitter along the line of sight and including detector means responsive to the signal pulses to produce corresponding receiver pulses, first signal responsive means connected to receive the receiver pulses for producing an output signal which varies in amplitude according to the time varying amplitude quality of the receiver pulses whereby receiver pulses of a relatively highly time varying amplitude produce a first output signal level and receiver pulses of relatively slow time varying amplitude produce a second output signal level, second signal responsive means connected to receive the outputs of the first signal responsive means and including means for producing a signal quantity which varies in amplitude progressively from a reference value according to time, means for resetting the signal quantity to the reference value only upon occurrence of an output of at least a predetermined level, and alarm means for producing an alarm signal when the signal quantity varies beyond a predetermined amplitude due to the inordinate time delay in the receipt of an output of at least said predetermined level.

Claim 3

A security system as defined in claim 1 wherein the first signal responsive means is an amplifier having an input and an output and having a variable gain characteristic which is related to the time varying amplitude quality of signals applied to the input.

Claim 4

A security system as defined in claim 2 including tuned feedback means connected between the output and the input of the amplifier to produce a high amplifier gain only for input signals of high time varying amplitude quality.

Claim 5

A security system as defined in claim 2 including means for maintaining the alarm signal for a predetermined time interval.

Claim 6

A security system as defined in claim 1 wherein the means for producing the signal quantity includes a voltage source, a capacitor connected to be charged by the source and a transistor connected to discharge the capacitor in response to receipt of outputs from the first signal responsive means.

Claim 7

A security system as defined in claim 6 including latch means responsive to energIzation of the alarm means to maintain the transistor nonconductive irrespective of the receipt of pulses from the detector means.

Claim 8

A security system as defined in claim 1 wherein the signal pulses are of infrared radiant energy, and the detector means comprises a semiconductor diode responsive to the infrared radiant energy to produce a variable electrical resistivity, a power supply, and circuit means for connecting the diode to the power supply for producing the receiver pulses.

Claim 9

A security system as defined in claim 5 wherein the second signal responsive means includes a transistor having an input electrode connected to the capacitor whereby the charge in the capacitor controls the conductivity of the transistor.

Claim 10

A security system as defined in claim 8 including means for adjusting the sensitivity of the detector means to signals of various amplitudes.

Claim 11

A security system comprising: a transmitter for emitting a continuous series of signal pulses of short duration at a predetermined rate, a receiver spaced from the transmitter for receiving the radiant energy pulses and including detector means arranged to intercept the signal pulses and to produce receiver signals in response thereto, means for varying the sensitivity of the detector means to variations in pulse signal amplitude, amplifier means connected to the detector means for producing an amplified output only in response to the short duration receiver signals, trigger means connected to the amplifier means output and responsive to signals at a first rate to assume a first output condition and responsive to the absence of signals for a predetermined period to assume a second output condition, and alarm means operatively connected to the trigger means for producing an alarm signal when the trigger means assumes the second output condition.

Claim 12

A security system comprising: a transmitter for emitting a continuous series of signal pulses of short duration at a predetermined rate, a receiver spaced from the transmitter for receiving the radiant energy pulses and including detector means arranged to intercept the signal pulses and to produce receiver signals in response thereto, means for varying the sensitivity of the detector means to variations in pulse signal amplitude, amplifier means connected to the detector means for producing an amplified output only in response to the short duration receiver signals, trigger means connected to the amplifier means output and responsive to signals at a first rate to assume a first output condition and responsive to the absence of signals for a predetermined period to assume a second output condition, and alarm means operatively connected to the trigger means for producing an alarm signal when the trigger means assumes the second output condition.

Claim 13

A security system as defined in claim 10 wherein the amplifier means includes at least one operational amplifier having a negative feedback circuit for producing a unity gain in response to relatively steady state signals and a high gain in response to relatively short duration signals.

Claim 14

A security system as defined in claim 10 wherein the trigger means includes output means for establishing the first and second output conditions, first means for producing a control signal having an amplitude related to the rate of occurrence of the amplified detector signal, and means connected to the output means for establishing the second output condition when the control signal amplitude reaches a predetermined level.

Claim 15

A security system as defined in claim 12 wherein the trigger means includes means for maintaining the output means in the second output condition for a predetermined time.

Claim 16

A security system as defined in claim 12 wherein the alarm means includes a voltage source, a relay coil connected to be energized by the output means when in the first output condition, an alarm signal producing device, and a relay switch having a normally closed condition but being opened by energization of the coil, said source, switch and device being connected in series such that the coil is deenergized when the output means assumes the second output condition.

Claim 17

A security system as defined in claim 12 including selectively operable latching means for maintaining the alarm means in an activated condition after the detector means once assumes the second output condition.

Claim 18

In a security system, receiver means responsive to radiant energy signal pulses and including detector means for producing voltage pulses in response to the receipt of the signal pulses, amplifier means having an input connected to the detector means and an output, feedback means connected between the input and output for varying the gain of the amplifier means in accordance with the time varying amplitude quality of the voltage pulses applied to the input for maximizing the gain for pulses of relatively short duration and minimizing the gain for pulses of relatively long duration, means connected to the output for producing a control voltage which varies substantially inversely according only to the repetition rate of pulses producing the maximum amplifier gain, trigger means responsive to the control voltage to produce an ouTput signal when the control voltage reaches a predetermined value, and alarm means energized by the output signal.

Claim 19

In a security system, receiver means responsive to radiant energy signal pulses and including detector means for producing voltage pulses in response to the receipt of the signal pulses, amplifier means having an input connected to the detector means and an output, feedback means connected between the input and output for varying the gain of the amplifier means in accordance with the time varying amplitude quality of the voltage pulses applied to the input for maximizing the gain for pulses of relatively short duration and minimizing the gain for pulses of relatively long duration, means connected to the output for producing a control voltage which varies substantially inversely according only to the repetition rate of pulses producing the maximum amplifier gain, trigger means responsive to the control voltage to produce an ouTput signal when the control voltage reaches a predetermined value, and alarm means energized by the output signal.

Claim 20

Receiver means as defined in claim 16 wherein the feedback means includes a resonant circuit defining the frequency response of the amplifier means related to the width of the signal pulses.

Claim 21

In a security system, receiver means responsive to signal pulses including detector means for producing voltage pulses corresponding to signal pulses received thereby, amplifier means having an input connected to the detector means and an output, the amplifier means being responsive to rapidly varying voltage pulses for producing an amplified signal on the output thereof, a power supply, a capacitor, a charging circuit connected to the power supply for producing a control voltage across the capacitor, a discharging circuit connected between the output and the capacitor for discharging the capacitor in response to the amplified signals whereby the average value of the control signal is related to the repetition rate of the amplified signals, trigger means including a first transistor having an input electrode connected to receive the control voltage, an output electrode connected to the power supply and a common electrode, bias means connected between the power supply and the common electrode for varying the bias thereon in proportion to variations in the power supply voltage whereby the transistor is rendered conductive by a control signal corresponding to a fixed portion of the power supply voltage, and alarm means controlled by the transistor to be energized when the transistor is rendered conductive.

Claim 22

In a security system, receiver means responsive to signal pulses including detector means for producing voltage pulses corresponding to signal pulses received thereby, amplifier means having an input connected to the detector means and an output, the amplifier means being responsive to rapidly varying voltage pulses for producing an amplified signal on the output thereof, a power supply, a capacitor, a charging circuit connected to the power supply for producing a control voltage across the capacitor, a discharging circuit connected between the output and the capacitor for discharging the capacitor in response to the amplified signals whereby the average value of the control signal is related to the repetition rate of the amplified signals, trigger means including a first transistor having an input electrode connected to receive the control voltage, an output electrode connected to the power supply and a common electrode, bias means connected between the power supply and the common electrode for varying the bias thereon in proportion to variations in the power supply voltage whereby the transistor is rendered conductive by a control signal corresponding to a fixed portion of the power supply voltage, and alarm means controlled by the transistor to be energized when the transistor is rendered conductive.

Claim 23

Receiver means as defined in claim 18 including an output transistor connected to the first transistor to be controlled thereby, and relay means connected between the output transistor and the alarm means for maintaining the alarm means deenergized until the first transistor conducts.

Claim 24

Receiver means as defined in claim 19 including means connected between the output and first transistors for maintaining the first transistor conductive for a predetermined time following energization of the alarm means.