US 5283551 - Intrusion alarm system

Title:

Intrusion alarm system

Patent ID:

US5283551

Issue Date:

February 01, 1994

Abstract:

A passive intrusion alarm system having an array of infrared sensing elements arranged and sampled so as to provide a two dimensional thermographic image of an intruder.

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Translations

Spanish, Italian, Japanese, French, Chinese - Simplified, Chinese - Traditional, Korean,
Greek, German, Dutch, Arabic, Swedish, Portuguese, Russian

Inventor(s):

Guscott; John K. (Hickory, NC, US)

Email and Contact Information

Assignee:

Aritech Corporation; (Hickory, NC, US)

Agent:

Weingarten, Schurgin, Gagnebin & Hayes

Application No.:

815490

Filing Date:

December 31, 1991

Primary Class:

340/567

Other Classes:

250/332 250/334 250/342 250/349 250/DIG.1

Field of Search:

340/567,518,588,523,309.15,573 358/105,108,113 250/342,349,338.1

Primary Examiner:

Crosland; Donnie L.

Assistant Examiner:

Mullen, Jr.; Thomas J.

US Patent Document(s):

4246480	Clark	January 01, 1981
4249207	Harman et al.	February 01, 1981
4618854	Miyake et al.	October 01, 1986
4769545	Fraden	September 01, 1988
4814870	Crall	March 01, 1989
4906976	Guscott	March 01, 1990
4999610	Guscott	March 01, 1991
4999614	Veda et al.	March 01, 1991
5008522	Lundin	April 01, 1991
5012099	Paturel et al.	April 01, 1991
5021660	Tomita et al.	June 01, 1991
5023597	Salisbury	June 01, 1991
5091780	Pomerleau	February 01, 1992

Foreign Reference(s):

149196 JP June 01, 1989

Claim(s):

What is claimed is:

1. An intrusion alarm system comprising:

a stationary linear array of infrared sensors disposed in a first plate and producing output signals in response to detection of infrared emissions from an intruder, said detection occurring when said intruder travels in a direction of motionhaving a component in a predetermined direction with respect to said array;

said linear array of infrared sensors oriented substantially orthogonal with respect to said predetermined direction of said component, said predetermined direction of said component being in a second plane spaced from and parallel to said firstplane; and

a data processing system in communication with said array of infrared sensors;

said data processing system receiving data corresponding to said output signals from said linear array of infrared sensors, and generating pixel data to provide a two dimensional thermographic image of said intruder in response to said receiveddata.

2. The intrusion alarm system of claim 1 further comprising a trigger sensor in communication with said data processing system, said trigger sensor producing an output trigger signal in response to detection of infrared emissions from saidintruder and causing said data processing system to store data corresponding to said output signals from said linear array of infrared sensors.

3. The intrusion alarm system of claim 1 further comprising a commutator in communication with each said infrared sensor in said linear array of infrared sensors, said commutator sequentially sampling the output signal from each infrared sensorin response to an output trigger signal from a trigger sensor to produce a commutated output signal.

4. The intrusion alarm system of claim 3 further comprising an analog-to-digital converter in communication with said commutator, said analog-to-digital converter converter said commutated output signal from said commutator into data forstorage.

5. An intrusion alarm system comprising:

a stationary linear array of infrared sensors disposed in a first plane and producing output signals in response to detection of infrared emissions from an intruder, said detection occurring when said intruder travels in a direction of motionhaving a component in a predetermined direction with respect to said array;

a data processing system in communication with said array of infrared sensors and processing data corresponding to said output signals from said linear array of infrared sensors; and

a central processing facility in communication with said data processing system;

said central processing facility receiving said data corresponding to said output signals from said infrared sensors from said data processing system and generating pixel data to provide a two dimensional thermographic image of said intruder inresponse to said received data.

6. An intrusion alarm system comprising: a stationary linear array of infrared sensors disposed in a first plane, each of said infrared sensors producing an output signal in response to detection of infrared emissions from an intruder, said detection occurring when said intruder travels in a direction of motion having a component in a predetermined direction with respect to said array; said linear array of infrared sensors oriented substantially orthogonal to said predetermined direction of said component, said predetermined direction of said component being in a second plane spaced from and parallel to said first plane; a commutator in communication with each of said infrared sensors of said linear array of infrared sensors, said commutator sequentially selecting each of said infrared sensors of said linear array of infrared sensors and receiving said output signal from said selected infrared sensor to produce a commutated output signal in response to said received output signal; an amplifier in communication with said commutator, said amplifier amplifying said commutated output signal from said commutator to produce an amplified output signal in response to said commutated output signal; a sample and hold circuit in communication with said amplifier, said sample and hold circuit sampling and holding said amplified output signal from said amplifier to produce a sampled output signal in response to said amplified output signal; an analog to digital converter in communication with said sample and hold circuit, said analog to digital converter converting said sampled output signal from said sample and hold circuit to a digital representation of said sampled output signal and producing a digitized output signal in response to said sampled output signal; a microprocessor in communication with said analog to digital converter, said microprocessor receiving said digitized output signal from said analog to digital converter, processing said digitized output signal and producing pixel data in response to said digitized output signal; a memory in communication with said microprocessor, said memory storing said pixel data produced by said microprocessor; a display for generating a two dimensional thermographic image of said intruder from said stored pixel data; an output driver in communication with said memory, said output driver communicating said stored pixel data from said memory to said display; and a trigger sensor in communication with said microprocessor, said trigger sensor producing an output trigger signal in response to detection of infrared emissions from said intruder, said output trigger signal triggering said microprocessor to produce said pixel data.

Description:

FIELD OF THE INVENTION

The invention relates to the field of intrusion alarm systems and more particularly to the field of passive infrared intrusion alarms.

BACKGROUND OF THE INVENTION

Passive infrared intrusion alarm systems are susceptible to false alarms caused by the detection of infrared emissions from animals or other heat sources which are not human and which do not pose a security threat. Typically, the reception of analarm signal at a security station results in security personnel being dispatched to determine the cause of the threat. This use of security personnel to determine if an alarm indicates a real threat is expensive, especially when the monitoring stationand security personnel are located at a distance from the area under surveillance.

Alternatively, the area to be monitored may be under surveillance by a more expensive video camera and occurrence of an alarm causes the security monitor to use the video camera to view the area. This technological approach, which requiresspecial communications lines and equipment, is also expensive, especially when the area under surveillance is located a distance from the monitoring station.

The present invention provides the verification capability similar to that of a video camera but at a much reduced cost.

SUMMARY OF THE INVENTION

The invention relates to a passive infrared intrusion alarm system having an array of infrared sensors arranged and sampled so as to produce a two dimensional thermographic image of an intruder of sufficient resolution to enable securitypersonnel to determine if a security threat exists. In one embodiment the intrusion alarm system includes a linear array of infrared sensors oriented orthogonally to the direction of anticipated intruder motion. When the presence of an intruder isdetected by the intruder's infrared emissions, the intrusion alarm system is activated. Each sensor of the array is then repeatedly and sequentially accessed and the signals from each sensor are sampled and digitized. The sampled data is transmitted toa central monitoring station which generates a two dimensional thermographic image of the intruder. In a second embodiment, a microprocessor processes the digitized signals from all the sensors and generates a two dimensional thermographicrepresentation of the intruder locally.

Using the linear array, only a few sensors are required to produce a low resolution representation of the intruder which is suitable to determine whether the intruder is human and hence whether further action need be taken. Another embodimentutilizes a two dimensional array of infrared sensors which is capable of producing a two dimensional thermographic image of a stationary intruder. Yet another embodiment mechanically sweeps a linear array of sensors across the area to be viewed.

BRIEF DESCRIPTION OF THE DRAWING

These and further benefits of the invention may be better understood with reference to the specification and the accompanying drawings in which:

FIG. 1 is a block diagram of an embodiment of the system of the invention;

FIG. 2 is a structural representation of the infrared sensor of the embodiment of the system of FIG. 1;

FIG. 2A is a schematic diagram the infrared sensor and buffer amplifiers of the embodiment of the invention shown in FIG. 1;

FIG. 3 is a graphical representation of the voltage signals from each element of the sensor array of FIG. 2, plotted against time, generated when a human passes by the sensor array;

FIG. 3A is a low resolution thermographic image constructed from the signals generated in FIG. 3;

FIG. 4 is a graphical representation of the voltage signals from each element of the sensor array of FIG. 2, plotted against time, generated when a dog passes by the sensor array;

FIG. 4A is a low resolution thermographic image constructed from the signals generated in FIG. 4; and

FIG. 5 is a perspective diagram of an embodiment of a sweeping linear array .

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIG. 1, in brief overview, an infrared intrusion alarm system 10 includes an infrared sensor array 12 including, in this embodiment, a linear array of sensors 14 and a triggering sensor 16. The triggering sensor 16 is incommunication with a microprocessor 20, through an analog to digital converter (A/D) 21. Alternatively, the trigger sensor 16 may be connected to the microprocessor 20 through a one-shot flip-flop which produces a digital pulse which is detectable bythe microprocessor 20.

The linear array of sensors 14 are connected through a commutator 30 to an amplifier 32. When activated by the microprocessor 20 in response to the signal from the trigger sensor 16, the commutator 30, as sequenced by a signal from clock 44,sequentially connects each sensor of the linear array of sensors 14 one at a time to the amplifier 32. In this manner, a single amplifier 32 may be used to amplify the signals from all the sensors of the linear array of sensors 14.

The output signal from the amplifier 32 is sampled by a sample and hold circuit 40 according to the clock signal supplied by clock 44. The use of the same clock signal to sequence the commutator 30 and to control the timing of the sample andhold circuit 40 permits the signal from the amplifier 32 to be sampled at a rate such that as each sensor of the linear array of sensors 12 is connected to the amplifier 32, the signal from that sensor is sampled only once. This sampled analog signal isconverted to a digital signal by an analog to digital converter (A/D) 46, under the control of the microprocessor 20. The microprocessor 20 stores the digital signal output from the A/D 46 in random access memory (RAM) 50. The contents of the RAMmemory 50 may then be accessed by an output driver 52 for transmission to another facility for processing and display. In an alternative embodiment, the microprocessor 20 may convert the digital signal from the A/D 46 into a pixel representation of thedigital signal and the output driver 52 may access the pixel data stored in RAM 50 for display locally.

Referring to FIG. 2, an embodiment of the infrared sensor array 12 constructed on a single substrate 60 is shown. In the embodiment shown, a linear array of sensors 14, having eight individual sensors 14(a)-14(h) (only two of which are labeledfor clarity) and a common electrode 62 are deposited on one surface of the substrate 60. On the opposing surface of the substrate 60 are deposited a second electrode 63 (shown in phantom) and a trigger sensor 16 (also shown in phantom). The secondelectrode 63 is positioned so as to be opposite to and extend beyond the boundaries of the linear array of sensors 14.

The sensors of the infrared array may be fabricated using any of the current technologies. Alternatively, the array may utilize thermopile or bolometric sensors rather than the ceramic, polyvinylidene fluoride or lithium tantalate pyroelectricsensors used in the embodiment disclosed. The number of sensors 14 is one factor in determining the resolution of the final thermographic image. However, only a few sensors need be used to provide a thermographic image of sufficient resolution to beused in verifying the nature of the intruder. Depending on the optics used in conjunction with the sensors, as few as four sensors 14 may produce a usable image.

FIG. 2A, depicts a buffer amplifier array 70 used to match the extremely high impedance of the infrared sensor array 12 to the commutator 30. Each sensor 14(a)-14(h) of the linear array of sensors 14 and the trigger sensor 16 is connected to thegate of a respective one of the FET transistors 70(a)-70(i) (only two FETs being labeled for clarity) of the buffer amplifier array 70. The emitter of each FET transistor 70 is connected to a power supply (not shown), while the collector of each FET72(a)-72(i) (only one being labeled for clarity) is in communication with the commutator 30. The voltage appearing at the collector 72 of a FET 70 is determined by the voltage on its gate, and hence, the strength of the signal detected by the sensor 14or 16. The second electrode 63 of the infrared sensor array 12 is connected to ground. A respective bias resistor 26 (only one shown for clarity) is connected between ground and the gate of each FET 70.

Referring to FIG. 3, in operation, as an intruder passes by the infrared sensors 12, the infrared radiation emitted by the intruder is detected by the trigger sensor 16. Once the trigger sensor 16 detects the intruder, and notifies themicroprocessor 20, the sensors in the linear array of sensors 14 are sampled by the commutator 30 and the digital representation of the time variation in the voltage level of the output signal from the amplifier 32 is stored in RAM 50. This data mayeither be transmitted to a central monitoring station or facility for conversion to a thermographic representation. Alternatively, the data from the amplifier 32 may be processed by the microprocessor 20 into pixel form prior to storing in RAM 50. Thedata from memory may be displayed locally as a thermographic image.

It should be noted that the system described could still function without the use of the trigger sensor 16. In this other embodiment the triggering of the system can be accomplished by requiring that a predetermined number of sensors of thelinear array 14 simultaneously detect the intruder for an alarm to be generated. In yet another embodiment the system may operate without a trigger by continuously storing in memory 50 data from the sensors. It is possible to accomplish this with afinite amount of memory 50 by storing a predetermined number of samples from each sensor and then permitting the next received datum from the sensor to overwrite first received datum from the sensor. That is, assuming fifty samples from sensor one havebeen stored, the next sample received from sensor one overwrites sample one and the next subsequent sample overwrites sample two and so on. In order to generate a thermographic image of sufficient resolution to be useful in intruder verification, thesensors 14 must be sampled at sufficient frequency. For an intruder moving at between 0.5 and ten feet per second, each sensor should be sampled between ten and twenty times per second to generate a thermographic image of sufficient resolution. The actof an intruder passing by the linear array of sensors 14 is approximately equivalent to sweeping the linear array of sensors 14 across a stationary intruder since the motion of the intruder is in a direction perpendicular to the orientation of the array14. Thus by setting the voltage intensity of the signal at a predetermined time equal to a given pixel value, a two dimensional thermographic representation of the intruder may be generated from the time variation of the voltage.

An example of the results of a human passing by the linear array of sensors 14 produces a variation in voltage over time is shown in FIG. 3 and the generated thermographic image is shown in FIG. 3A. Similarly, a dog passing before the sensors 14produces a variation in voltage over time as shown in FIG. 4 and produces a thermographic image as shown in FIG. 4A. Such images are of sufficient resolution to distinguish whether the intruder is human or animal.

Yet another embodiment of the invention makes use of a two dimensional array of sensors 14. Because with a two dimensional array it is not necessary to allow the intruder to pass across the array in order to generate an image, the rate ofsampling by the commutator 30 may be much lower than the rate of sampling of the sensor signals form a linear array. Such a system has the benefit of being able to image a stationary intruder.

Still yet another embodiment of the invention which is capable of imaging a stationary intruder uses a linear array of sensors as described previously. However, in this embodiment the linear array of sensors 12 is mechanically moved so as tosweep the sensors across the area under surveillance (FIG. 5). Although the motion of the array 12 is shown as a rotation in the FIGURE (arrow R), a linear sweep is also possible. Such a mechanical sweep is substantially equivalent to the viewing of amoving intruder by a stationary linear array of sensors.

These and other examples of the concept of the invention illustrated above are intended by way of example and the actual scope of the invention is to be determined solely from the following claims.

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US Patent:

5283551