US3774190A

US3774190A - Intrusion alarm with signal processing and channel identification

Info

Publication number: US3774190A
Application number: US00222745A
Authority: US
Inventors: W Kyle
Original assignee: Scan Systems Inc
Current assignee: GEOTRONIX Inc; Scan Systems Inc
Priority date: 1972-02-02
Filing date: 1972-02-02
Publication date: 1973-11-20
Anticipated expiration: 1990-11-20

Abstract

An intrusion detector employs a signal processor capable of not only recognizing the vibrational signature of a single intrusion event, but of recognizing a sequential pattern of the vibrations of a plurality of such events. A plurality of channels, each having sensor arrays at the inputs thereof, are connected to respective inputs of a common signal processor. An output is produced from the signal processor when the signal supplied thereto falls within prescribed limits. This output enables a respective channel to activate a tone code generator to produce an output having a group of frequencies corresponding to the particular channel. The modulated RF signal is then transmitted to a remote readout station. The signal processor recognizes the vibrations of each intrusion event and initiates a timer in response to the first of such events. Each subsequent event reinitiates the timing period of the timer until the full time period thereof has elapsed without the receipt of a subsequent pulse. A counter counts the number of such events, and if a predetermined count is achieved before an output is supplied by the timer, an alarm or similar indicator is actuated.

Description

Matted States Patent Kyle, Jr. Nov. 20, 1973 llNTRUSION ALARM WITH SIGNAL PROCESSING AND CHANNEL [57] ABSTRACT DENTIFICATION An intrusion detector employs a signal processor ca- 7 5 Inventor; William Kyle, Jr L Gatos, pable of not only recognizing the vibrational signature m of a single intrusion event, but of recognizing a sequential pattern of the vibrations of a plurality of such [73 Assrgnee: Scan Systems Incorporated, events. A plurality of channels, each having sensor ar- Campben- Cahfrays at the inputs thereof, are connected to respective [22] Filed; 2, 1972 inputs of a commonsignal processor. An output is produced from the signal processor when the signal PP 222,745 supplied thereto falls within prescribed limits. This output enables a respective channel to activate a tone 52 us. c1 340/258 R, 340/224, 340/261 code genartor to P Output f a group 51 1m. 01. G08b 13/00 of frequencles coffesponfimg P the P chan- [58] Field of Search 340/258 R, 258 D, The modulated B slgnal transmmed to a 340/2 27 224 225 147 C remote readout stat1on. The slgnal pI'0C8SS0l TC CQg nlzes the vlbrations of each lntruslon event and mm- [56] References Cited ates a timer in response to the first of such events. Each subsequent event reinitiates the timing period of UNITED STATES PATENTS the timer until the full time period thereof has elapsed 52 without the receipt of a subsequent pulse. A counter Sey counts the number of such events, and if a predeter- SBtlfrtrtleer; et al. 242326 mined count is achieved before an output is supplied 3:480:90 11/1969 Hirschberg:I:..................::::. 340/261 by the time, alarm or Similar indicamr is actuated 11 Claims, 12 Drawing Figures Primary Examiner-John W. Caldwell Assistant Examiner- -Glen R. Swann, III AttorneyLeslie M. Hansen AMPL. DETECTOR AND ENGODER i 3/ l TONE 2/ 23 27 29 GENERATOR l8 AMPL DETECTOR AND ENCODER N30 a? 24 TIMER SIGNAL L i l PROCESSOR m O 3 4 53 g DECODER 36 1 37 DISPLAY ALARM PAiiminuuvzoms SHEEI 1 OF 3 Illl' mokaimzww mzOP m whw Pmmsnmvz 3; 714, 190

sum 3 OF '3 F1610 H F169 FIG. 12

INTRUSION ALARM WITH SIGNAL PROCESSING AND CHANNEL IDENTIFICATION BACKGROUND OF THE INVENTION FIELD OF THE INVENTION This invention relates generally to intrusion detectors and more particularly to a system for detecting the presence of an intruder within a prescribed area by sensing the vibrations caused by such intrusion.

A definite need exists for an intrusion detector which can be employed in a variety of situations ranging, for example, from domestic use to use in a relatively large, remote, and isolated areas. When used domestically, an intrusion detector may be required to sense the presence of an intrusion upon the grounds surrounding the dwelling house or to sense the presence of an intrusion at isolated locations within the house. The detection of a single, isolated intrusion generally presents fewer problems than those encountered in the detection of an intrusion across a perimeter. As a result, intrusion detectors are generally not available which are suitable for different types of applications.

One of the most urgent needs for intrusion detectors at the present time is for the protection of remote, isolated areas, such as, for example, electrical power substations, and the like. Such areas require perimeter protection and some means for communicating an alarm corresponding to an intrusion to another station, since personnel are generally not present at all times thereon.

One of the major problems encountered in the prior attempts to design an intrusion ddtector, particularly one which is capable of both limited area protection and perimeter protection, is that of providing a sensor and signal processor which has sufficient sensitivity to sense an actual intrusion, yet has relatively low incidence of false alarms. This problem is particularly inherent in those intrusion detectors which sense vibrations caused by the intrusion. Prior attempts to overcome this difficulty have employed frequency discrimination techniques for differentiating between the frequency of the vibration caused, for example, by a footstep or similar intrusion event. Although such frequency discrimination techniques are useful in eliminating false alarms caused by certain types of events, a large number of vibration producing events which are not actual intrusions cannot be distinguished from the actual intrusion events. That is, certain non-intrusion events may produce vibrations which fall within the frequency range of, for example, the vibrations produced by footstep. For example, a loose shutter which occasionally is driven by the wind against the side ofa house will produce vibrations having a frequency which falls within a range encompassing the frequencies of vibrations caused by typical intrusion events.

In an attempt to overcome this difficulty, threshold detectors have been employed to eliminate the relatively low amplitude vibrations caused by some of the non-intruding vibration producing events. However, this feature does not eliminate the relatively high amplitude, non-intrusion events from being detected as an intrusion. Various techniques have been attempted to eliminate the relatively high amplitude vibration producing events of a non-intrusion nature. One such attempt employs a timer which is initiated with the first sensed event and a counter for sensing the number of events which occurred during the timing period of the timer. Although this technique is partially successful in reducing the incidences of false alarms caused by nonintrusion events, it fails to eliminate a large percentage of such false alarms which could be eliminated by attempting to distinguish between different patterns of vibration producing events.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide an intrusion detector having a relatively high sensitivity and a relatively low incidence of false alarms.

Another object of the present invention is to provide an intrusion detector which is capable of observing and recognizing the signature of the vibrations caused by certain intrusion events.

Still another object of the present invention is to provide an intrusion detector which is capable of not only observing and recognizing the signature of a single intrusion event, but the pattern of a series of vibrations caused by such events over a predetermined time period.

These and other objects features and advantages of the present invention will be more fully realized and understood from the following detailed description, when taken in conjunction with the accompanying drawings, wherein:

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram of an intrusion detector system constructed in accordance with the principles of the present invention;

FIG. 2 is a partial block and partial schematic diagram of an intrusion detector constructed in accordance with the principles of the present invention which employs the signal processor illustrated in FIG.

FIG. 3 is a schematic diagram of the timer illustrated in FIG. 2; and

FIGS. 4l2 are graphical representations of the waveforms of signals at different locations in the signal processor circuit illustrated in FIG. 2.

DESCRIPTION OF THE PREFERRED EMBODIMENT Like references numerals throughout the various views of the drawings are intended to designate the same or similar elements.

With reference to FIG. 1, there is shown an intrusion detector system constructed in accordance with the principles of the present invention for protecting a relatively large area. The system is formed of a plurality of channels, two of which are shown and generally designated with the

reference numerals

16 and 17. The input to each channel is a sensor array formed of a plurality of sensors 18 connected in series with one another. The sensors 18 are seismic transducers or geopho'nes which are responsive to vibrations passing through the material to which they are mounted. In a typical installation, the sensors 18 are mounted in direct contact with the earth to pick up vibrations transmitted therethrough.

Each sensor array is connected to the input of an amplifier, l9 and 21, respectively, in each channel. The amplified signal from each array is rectified by

detectors

22 and 23, respectively and supplied to respective inputs of a signal processor 24 and to one input of a respective one of

AND gates

26 and 27.

When a signal is supplied to the signal processor 24 which falls within prescribed limits, an output will be provided therefrom and supplied to the other input of the

AND gates

26 and 27. Assuming, for example, that one or more of the sensors 18 in the channel 16 produces a signal which will provide an output from the signal processor 24, the AND gate 26 will produce an output. The outputs of

AND gates

26 and 27 are connected to inputs of

preset encoders

28 and 29, respectively. Each encoder, when energized, supplies at its output a digital code corresponding to its respective channel. Outputs of the

encoders

28 and 29 are supplied to a tone generator 31 which generates a keyed group of tones in accordance with the digital code supplied thereto, which group of tones modulates an RF. signal. That is, each discrete level of the digital code generates a signal having a particular frequency which, in coded combination, modulate an R.F. signal. Outputs of the

AND gates

26 and 27 are also connected to a timer 30 which maintains the

encoders

28 and 29 energized for a predetermined time period.

The tone coded signal supplied at an output of the tone generator 31 is connected to one end ofa communication link 32, such as a transmitter. The other end of the communication link 33, which is a receiver, supplies the signal to a decoder 34. The output of the decoder 34 is a digital code corresponding to the particular one of the

channels

16 and 17 which senses the vibrations resulting from the intrusion event. The digital output is supplied to a display 36 wherein the particular channel in which the intrusion producing vibrations were sensed are displayed visually. The output of the decoder 34 is also connected to an alarm 37 to indicate that an intrusion has occurred.

A better understanding of the signal processor 24 will be had from the following description of FIG. 2. FIG. 2 is a partial schematic and partial block diagram of an intrusion detector which employs the signal processor 24 illustrated in FIG. 1. The signal processor circuit illustrated in FIG. 2 is supplied with inputs directly from a plurality of transducers and its output is employed directly to drive an alarm or similar device.

Input transducers

41 and 42 are shown as geophones, but may be any vibration sensing element. Outputs of the

transducers

41 and 42 are supplied to inputs of the signal processor 24, the first stage of which is a preamplifiermixer 43 which has a predetermined frequency response to eliminate certain frequencies caused by nonintrusion events. The waveform of a typical output of the amplifier of 43 in response to one of the

transducers

41, 42 sensing a footstep in immediate proximity thereto is shown in FIG. 4. The output of amplifier 43 is further amplified and frequency limited by amplifier 44. The resultant amplified signal is rectified by a diode 46, integrated by circuit 47 and supplied to the input of a high impedance amplifier, generally designated with reference numeral 48. The waveform of the rectitied and integrated signal is illustrated to FIG. 5.

The high impedance amplifier 48 is formed ofa field effect transistor 49 connected in series with a potentiometer 51 and a constant current source 52 between a source of positive voltage and a source of negative voltage. This circuit provides DC restoration to the signal supplied thereto and produces a signal at the output thereof which has a waveform as illustrated in FIG. 6.

The output of the amplifier 48 is supplied to a threshold detector 53 which is essentially a differential comparator. The operating parameters of the detector 53 are selected so that there is an output therefrom only when the input signal pulse (see FIG. 6) is of sufficient amplitude to cross a predetermined threshold level in a positive-going direction, at which time a sharp rise time pulse will appear at its output. If three successive pulses, such as the one shown in FIG. 6, are supplied to the input of the detector 53, the resultant output signal will have a waveform as shown in FIG. 7 of the drawings. The waveforms shown in FIGS. 8-12 are based on the conditions shown by the waveform in FIG. 7.

The output of the detector 53 is supplied through an inverter 54 to one input ofa timer circuit 56. The first pulse supplied to this input of the timer 56, when an enable signal is supplied to its other input, initiates a predetermined timing period which is reinitiated with each subsequent pulse supplied thereto before the timing period lapses. That is, each subsequent pulse supplied to the input of the timer 56 extends its timing period by an equal amount before an output is supplied there from.

The output pulses from the inverter 54 are also supplied to the input of a counter 57 to provide at its output a signal in parallel format corresponding to the total number of pulses received in a particular counting cycle. The counting cycle is determined by the amount of time which elapses from the receipt of a first pulse to the occurrence of an output from the timer 56. An output is provided from the timer 56 at the end of the timing period thereof following the receipt of the last pulse supplied at its input. This output is supplied through an inverter 58 to one input ofa bistable multivibrator 59 having its other input connected to an output of the detector 53. The waveform of the signal at the output of inverter 58 is shown in FIG. 9. The bistable multivibrator 59 has two states, one of which is achieved by supplying a negative going pulse to one of its inputs from the output of the detector 53 (FIG. 7) and the other of which is achieved by supplying a negative going pulse to its other input from the inverter 58 (FIG. 9). In one of its states, the bistable multivibrator 59 enables the timer 56 and in the transition from that state to its other state, it resets the counter 57. The waveform of the output signal supplied from the multivibrator 59 to the timer 56 and to the reset input of the counter 57 is shown in FIG. 8. The state of the bistable multivibrator 59 beginning at t which enables the timer 56 is achieved in response to a negative going pulse from the output of the detector 53.

The output of the counter 57 is decoded by a matrix circuit 61 to provide an output, the waveform of which is shown in FIG. 10, through an inverter 62 to one input of a bistable multivibrator 63 when a predetermined count is established in the counter 56. The output of the bistable mulvibrator 63 is disposed for energizing an alarm or other indication device, and the waveform of such output is shown in FIG. 11.

When the signal processor 24 is employed in a system, such as that illustrated in FIG. 1, the outputs of the

detectors

22 and 23 are connected to respective inputs of the mixer 43 and the output of the multivibrator 63 is connected to respective inputs of the AND

gates

26 and 27. Furthermore, in the system illustrated in FIG. I, the output of the signal processor may be employed to energize a local alarm or to operate other devices, such as flood lights and the like.

FIG. 3 is a schematic diagram of the timer 56 illustrated in FIG. 2. As shown therein, the circuit is provided with a pair of

input terminals

66 and 67 which are connected through

respective resistors

68 and 69 to the base of a transistor 71. As previously described, one input is supplied from an output of the inverter 54 and another input is supplied from one output of the bistable multivibrator 59. Accordingly, the waveform of one of the input signals will be the inverse of the waveform illustrated in FIG. 7 and the waveform of the other input signal corresponds to that shown in FIG. 8. When both of these signals are low, the normally conducting transistor 71 will be rendered non-conductive, thereby permitting a charge to develop on a capacitor 72 connected in parallel with the collector and emitter of the transistor 71. The charge on the capacitor 72 is developed by current flow from a source of positive voltage through a resistor 73. Each subsequent positive going pulse applied to the terminal 66 from the inverter 54 will render the transistor 71 conductive, thereby discharging the voltage developed on the capacitor 72. However, if the voltage on capacitor 72 attains a predeterm ined level before the transistor 71 is rendered conductive, a unijunction transistor 74 will fire, thereby providing an output on a line 76 which constitutes the output of the timer 56. The waveform of the voltage charge capacitor 72 is shown in FIG. 12.

The invention claimed is:

1. An intrusion detector comprising:

a. a plurality of channels each including at least one sensor,

b. means in common with each of said sensors for processing signals from each of said sensors and providing a detection output when said signals are within prescribed limits, and

c. output means responsive to outputs of each of said sensors and also to the output of said processing means for providing an indication of the particular one of said channels generating the signal which is within said prescribed limits.

2. An intrusion detector as defined in claim 1, wherein said output means includes a plurality of encoders, one for each of said channels and responsive to the output of respective sensors and said processing means for generating a distinct output, and a display responsive to the outputs of each of said encoders for providing a visual indication of the particular one of said channels generating the signal which is within said prescribed limits.

3. An intrusion detector as defined in claim 2, wherein said output means further includes a tone burst generator connected to the outputs of said encoders and having a distinct frequency output for each distinct output supplied thereto from said encoders, means for transmitting the output of said generator to a remote location, means at the remote location for receiving the transmitted output of said generator, and a decoder connected between said receiving means and said visual indication means.

4. An intrusion detector as defined in claim 3, wherein each of said encoders produces a distinct digitally coded output, and further comprising means for activitating said encoders to repeat the coded output a predetermined number of times after initiation thereof.

5. An intrusion detector as defined in claim 1, wherein said signal is in the form ofa series of damped oscillations with all but the first thereof being spaced from a preceding one by no more than a predetermined timing period, and wherein said signal processing means includes a timer responsive to each of said oscillations for producing an output at the end of said timing period following receipt thereof in the absence of the receipt of a subsequent oscillation, means responsive to said signal for counting the oscillations which occur before an output is produced by said timer, and means responsive to a predetermined count in said counting means for producing said detection output.

6. An intrusion detector as defined in claim 5, wherein said output means includes a plurality of encoders, one for each of said channels and responsive to the output of respective sensors and said processing means for generating a distinct output, and a display responsive to the output of each of said encoders for providing a visual indication of the particular one of said channels generating the signal which is within said presecirbed limits.

7. An intrusion detector as defined in claim 6,' wherein said output means further includes a tone burst generator connected to the outputs of said encoders and having a distinct frequency output for each distinct output supplied thereto from said encoders, means for transmitting the output of said generator to a remote location, means at the remote location for receiving the transmitted output of said generator, and a decoder connected between said receiving means and said visual indication means.

8. A signal processor for an intrusion detector which is adapted for connection between one or more sensors and an indication device and wherein the signals from the sensors are in the form of a series of damped oscillations with all but the first thereof being spaced from a preceding one by no more than a predetermined timing period, comprising a. a timer responsive to each of said oscillations for producing an output at the end of said timing period following receipt thereof in the absence of the receipt of a subsequent oscillation.

b. means responsive to said signal for counting the oscillations which occur before an'output is produced by said timer, and 0. means responsive to a predetermined count in said counting means for producing an output to the incomprising an integrator connected to an output of the sensors, and a level detector connected between an output of said integrator and an input of said timer.

' *8 i I t

Claims

1. An intrusion detector comprising: a. a plurality of channels each including at least one sensor, b. means in common with each of said sensors for processing signals from each of said sensors and providing a detection output when said signals are within prescribed limits, and c. output means responsive to outputs of each of said sensors and also to the output of said processing means for providing an indication of the particular one of said channels generating the signal which is within said prescribed limits.

5. An intrusion detector as defined in claim 1, wherein said signal is in the form of a series of damped oscillations with all but the first thereof being spaced from a preceding one by no more than a predetermined timing period, and wherein said signal processing means includes a timer responsive to each of said oscillations for producing an output at the end of said timing period following receipt thereof in the absence of the receipt of a subsequent oscillation, means responsive to said signal for counting the oscillations which occur before an output is produced by said timer, and means responsive to a predetermined count in said counting means for producing said detection output.

7. An intrusion detector as defined in claim 6, wherein said output means further includes a tone burst generator connected to the outputs of said encoders and having a distinct frequency output for each distinct output supplied thereto from said encoders, means fOr transmitting the output of said generator to a remote location, means at the remote location for receiving the transmitted output of said generator, and a decoder connected between said receiving means and said visual indication means.

8. A signal processor for an intrusion detector which is adapted for connection between one or more sensors and an indication device and wherein the signals from the sensors are in the form of a series of damped oscillations with all but the first thereof being spaced from a preceding one by no more than a predetermined timing period, comprising a. a timer responsive to each of said oscillations for producing an output at the end of said timing period following receipt thereof in the absence of the receipt of a subsequent oscillation. b. means responsive to said signal for counting the oscillations which occur before an output is produced by said timer, and c. means responsive to a predetermined count in said counting means for producing an output to the indication device.

9. A signal processor as defined in claim 8, further comprising means connected between the sensors and said timer for passing signals having a frequency within a predetermined range which encompasses the frequency of the vibrations caused by a footstep.

10. A signal processor as defined in claim 9, further comprising an integrator connected to an output of the sensors, and a level detector connected between an output of said integrator and an input of said timer.

11. A signal processor as defined in claim 8, further comprising an integrator connected to an output of the sensors, and a level detector connected between an output of said integrator and an input of said timer.