US 4,377,808 A · Infrared intrusion alarm system

Abstract

An improved dual-sensor infrared intrusion alarm system includes a motion discriminator that renders the system responsive to only radiation-emanating objects that are moving through the system's scope of surveillance. A positive or negative sensor signal is developed depending on the relative amounts of radiation impinging on the sensors. A switching amplifier selectively discharges one of two capacitors depending on the polarity of the sensor signal. The voltages across the capacitors are coupled to the inputs of a voltage comparator and the capacitor recharge time constants are selected so that an alarm is indicated only when the length of the time interval between the occurrence of a sensor signal of a given polarity and the subsequent occurrence of a sensor signal of the opposite polarity is within prescribed limits, for example, two seconds.

Claims10

Dependent claims

An intrusion alarm system comprising:

at least first and second sensors responsive to radiation emanating from spatially distinct locations;
means for subtractively combining the output signals of said sensors to produce an output signal having a first or second signal level respectively on opposite sides of a quiescent operating level, depending on the radiation impinging on said sensors;
and,
motion discriminating means for receiving said output signal from said combining means and determining the time delay between the occurrence of an output signal of one signal level and the subsequent occurrence of an output signal of the opposite signal level, said motion discriminating means activating an alarm device only when said determined time delay is within a predetermined limit indicating movement of a radiation emanating object between spatially distinct locations.

1 more element

An intrusion alarm system comprising:

first and second sensors responsive to radiation emanating from spatially distinct locations;
a differential amplifier means having inputs respectively coupled to the outputs of said first and second sensors, said amplifier means developing at its output a sensor signal that may assume either of two signal levels on opposite sides of a quiescent signal level, as determined by the radiation incident on the sensors,
a motion discriminator having an input coupled to receive the output of said differential amplifier means and an output adapted to be coupled to an alarm, said motion discriminator operating so as to activate the alarm only when the time delay between the occurrence of a sensor signal of one level at the output of the differential amplifier means and the subsequent occurrence of a sensor signal of an opposite level at the output of the differential amplifier means is within a prescribed time limit.

Dependencies are inferred from the claim text.

Infrared intrusion alarm system

Life of this patent

Infrared intrusion alarm system

Life of this patent

Abstract

Claims10