US3696359A

US3696359A - Intrusion alarm system

Info

Publication number: US3696359A
Application number: US109866A
Authority: US
Inventors: Gerald F Ross; Hugh C Maguire
Original assignee: Sperry Rand Corp
Current assignee: Sperry Corp
Priority date: 1971-01-26
Filing date: 1971-01-26
Publication date: 1972-10-03
Anticipated expiration: 1989-10-03

Abstract

A wireless point of entry intrusion alarm system having a central monitor and alarm cooperates with magnetically actuable entry detectors placed at potential entry locations. Each sensor is automatically reset by the same magnetic means upon reclosure of the guarded entry.

Description

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Oct. 3, 1972 [56] References Cited [54] INTRUSION ALARM SYSTEM XXX 44 2 2 C 2 2 O0 //5 002 44 33% m mm T 6 mm A P w s wn EMn T e AMDm T S 60 we? W999 111 m 2 2 .l 111 7 7 6 0O 9 5 403 494 5 3 3 3 C .ns m x HM n m O n m m .mm a a m L m r s 0 m w c 0 1 m FmR d V. mm," a m. @MS S e m m m .e v I A l 2 3 7 7 [22] Filed: Jan. 26, 1971 Primary Examiner-David L. Trafton Attorney-Samuel C. Yeaton [21] Appl.No.: 109,866

52 US. Cl. ..................340/224, 325/105, 325/169, ABSTRACT A wireless point of entry intrusion alarm system hav- 340/274 .G08b 13/08 ing a central monitor and alarm cooperates with mag- .340/224, 274', 325/105, 115, netically actuable entry detectors placed at potential 325 1 9 1 5 entry locations. Each sensor is automatically reset by the same magnetic means upon reclosure of the guarded entry.

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8 Claims, 3 Drawing Figures mm @[pi MULTI VI BRATOR OSClLLATOR ALARM POWER SOURCE PATENTEU OCT 3 I972 II. I

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RECEIVER Q INVENTORS GER/1L0 F. R055 HUGH MAGU/RE ATTORNEY MULTI VI BRATOR ALARM POWER SOURCE 41% OSCILLATOR FIG.2.

BACKGROUND OF THE INVENTION 1. Field of the Invention The invention pertains to means for providing protection of buildings or other elements of property from forced entry or unauthorized treatment and more specifically relates to magnetically actuable radio signal transmission devices for detecting the unauthorized entry of buildings or for detecting unauthorized access to or movement of guarded property.

2. Description of the Prior Art Prior art intrusion devices of many types have served advantageously in the protection of lives and property from intruders, but. generally have been complex, expensive, and difficult to install and maintain. There has been an unfulfilled need for inexpensive and easily installed and easily operated intrusion sensing apparatus which has the reliability of such prior devices, but which offers greater economy of ownership and flexibility of use. Many prior devices require relatively large batteries and charging installations for their successful operation. Others use permanent wiring which is complex to install even in a building while under construction. Sensing systems that depend on the physical breaking of electrical contacts have not afforded great reliability, as well as being difficult to install and to conceal. For example, the kind of alarm sensor using conductive tapes fastened to the glass of windows is expensive and difficult to install and maintain. Further, it is particularly sensitive to development of high false alarm rates as the condition of the building degrades and causes misalignment of electrical contacts. False alarm rates are high where sensors are used that notice disturbances in sonic or electromagnetic standing wave fields.

SUMMARY OF THE INVENTION The present invention relates to a wireless alarm system for providing protection of buildings or of other property from unauthorized entry or removal. The intrusion system utilizes a centrally located radio receiver and alarm system cooperating with magnetically actuable radio transmitters placed at points of possible entry. Each transmitter is furnished with a magnetically actuated condenser charging circuit having a very low cur rent drain demand on an associated miniature battery. Further, each transmitter is magnetically actuated upon the event of an intrusion to transmit a short, low energy level signal to the centrally located receiver for actuating an alarm. No further transmission is made by the affected transmitter until it is magnetically reset, for instance, by the manual closing of the associated entry.

BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1A and 1B are respective elevation views of two situations showing a representative installation of the novel intrusion sensor.

FIG. 2 is a circuit diagram illustrating the electrical connection of components of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1A illustrates one manner of use of the novel intrusion sensor 1 with its associated antenna 3 when affixed to a stationary part or frame 5 of a window 4, that window 4 to be monitored against unauthorized entry. Closely associated with intrusion sensor of detector 1, when the movable part of window or barrier 4 is in its normal closed position, is a small bar magnet or other source of magnetic field 2 affixed to window 4 by an adhesive or other conventional fastening means. The intrusion sensor 1 and magnet 2 may be installed permanently or temporarily by untrained personnel and may readily be shifted from one location to another since no electrical wiring is required. In such a manner, sensors may be installed to detect the opening of a window, door, sky light, or roof hatch or to detect an unauthorized act causing relative movement between a magnet placed on an expensive object of art relative to a sensor affixed to the wall from which the object is supported.

Opening of an entry such as the window 4 of FIG. 1A is illustrated in FIG. 1B. It is seen that by raising the frame of window 4, magnet 2 is removed from the proximity of sensor 1, and sensor 1 is no longer affected by the magnetic field of magnet 2. Sensor 1 is thereby caused to transmit a short duration alarm signal via antenna 3 to a central receiver 51 yet to be described in connection with FIG. 2.

The general disposition of sensor 1 and magnet 2 in FIGS. 1A and 1B is intended to be illustrative of one of many ways of using the apparatus. If desired, elements 1, 2, and 3 may be mounted in a completely concealed manner. Various other alternative configurations will be apparent to those skilled in the art, all permitting sensor 1 to sense a characteristic of an element in a normal position (open or closed) and to sense a change of the element from its normal position induced by the removal of the normal magnetic field from proximity to sensor 1.

Referring now to FIG. 2, details of the intrusion sensor 1 of FIGS. 1A and 1B will be described; it will be understood that the intrusion sensor 1 is normally placed adjacent an avenue of possible entry so that its element 10 sensitive to the position of magnet 2 is close to magnet 2 when the window, door, or other entry barrier is in a normal position, such as a closed position. Sensitive element 10 is a conventional single pole, double throw, dry reed switch, though other reed switches or other switches capable of changing state according to the presence or absence of a magnetic field of predetermined level may alternatively be employed. In a preferred embodiment, reed switch 10 has contactbearing leads 1] and 12 supported in generally parallel relation at one end 13 of a hermetic envelope 14. At the opposite end 15 of switch 10 is a lead 16 similarly sealed within envelope 14 and supporting a contactbearing switch blade spring 17. Lead 16 is coupled through low internal leakage condenser 20 to ground.

Lead 1 l is connected through charging resistor 21 to the positive terminal of battery or other electrical source 22. The second terminal of battery 22 is grounded. On the other hand, lead 12 of switch 10 is coupled through resistor 23 to ground and also to the gate electrode of field effect transistor 24. The source electrode of transistor 24 is grounded, while its drain electrode is connected through solenoid 31, in which a second switch 30 is immersed, to the positive terminal of battery 22.

Switch 30 may be generally similar to switch in that it may be a conventional dry reed switch, but having a single pole, single throw characteristic whose conductivity state is determined by the presence or absence of a magnetic field generated by the surrounding solenoid or coil 31. For example, switch 30 may comprise a hermetic envelope 32 with

leads

33 and 34 projecting through its ends to support the respective internal contact-bearing

switch blade springs

35 and 36. Switch 30 is connected at its lead 33 to a positive pole of battery 22 and at lead 34 to a transmitter device yet to be explained that comprises, in series relation, multivibrator 40, oscillator 41, and antenna 3.

In one form of the apparatus, the sensor 1 employed a 9 volt battery 22, the charging resistor 21 was 1 megohm, resistor 23 was 82,000 ohms, and condenser 20 was 10 microfarads; subminiature elements are used throughout.

The output of switch 30 on lead 34 is the input to a conventional multivibrator circuit 40. Multivibrator 40 is a free running circuit, when supplied with the input signal, whose output serves as a modulation signal, as will be seen. Multivibrator 40 is preferably of the simple conventional type producing a semi-square low audio frequency wave output with a comparatively slow rise time, the wave having a frequency, for example, of 1 KHz. On the other hand, either amplitude, frequency or pulsed modulation may be employed.

Multivibrator 40 serves as a modulator for oscillator 41, in effect turning it on and off. Oscillator 41 may be an inexpensive crystal-controlled oscillator operating, for example, at a 100 milliwatt level at a suitable carrier radio frequency, such as 27.255 MHZ. Modulator 40 produces 100 per cent modulation of the carrier radio frequency within oscillator 41, and its limited rise time characteristic satisfactorily limits the harmonic content of the output radio frequency signal. The output of oscillator 41 is radiated into space by antenna 3, which may comprise a simple conventional un-tuned wire antenna. The duration of the output or pulse burst is minimized for the purpose of preserving the life of battery 22. However, it is also desired to prevent false alarms, such as may be triggered by electrical storms. Thus, an optimum duration when using amplitude modulation may be on the order of 1 second.

FIG. 2 illustrates the situation arbitrarily defined as normal for purposes of explanation, when window 4 is closed, so that magnet 2 is at its closest proximity to sensor 1; Le, window 4 is in the position shown in FIG. 1A. In this condition, switch blade spring 17, being constituted of magnetic material, is held by the magnetic field of magnet 2 against the contact-bearing lead 11 of switch 10, as illustrated in FIG. 2. In this same normal situation, switch 30 is non-conducting, their spring characteristics holding switch blade springs 35 and 36 apart. In this state, condenser 20 has normally been charged from battery 22 through a path including charging resistor 21, lead 11, switch blade spring 17, lead 16, and ground. Charging of condenser 20 is slow, since the time constant of the R-C circuit comprising resistor 21 and condenser 20 is quite large. Thus, the

maximum current drain to which battery 22 is subjected is very low, and battery 22 has a life substantially equal to its normal shelf life.

Should magnet 2 be moved so that its magnetic field no longer influences reed switch 10, the spring nature of switch blade spring 17 forces it to break the circuit between resistor 21 and condenser 20. Instead, a circuit between condenser 20 and lead 12 is established; thus, a voltage is developed across resistor 23. Such an event causes field efiect transistor 24 to conduct and current from battery 22 is allowed to flow through coil 31 and transistor 24 to ground. The magnetic field generated by coil 31 consequently causes switch blade springs 35 and 36 of reed switch 30 to come into contact with one another. The modulating multivibrator 40 is then caused to supply its semi-square wave output wave to high frequency oscillator 41. Pulsed radio frequency carrier energy is thereby transmitted by antenna 3.

Transmission from antenna 3 continues for a short time, for example, about one second and is ended when the charge stored on condenser 20 is dissipated. Thus, the voltage across resistor 23 fails to maintain field effect transistor 24 in its conducting state, reed switch 30 is opened, and the supply of an excitation signal to multivibrator 40 ends, ending operation of oscillator 41. Thus, if window 4 remains open, no further drain is imposed on battery 22. However, sensor 1 is automatically in condition to be recycled by shutting window 4 and thus reestablishing a charging circuit for condenser 20 from battery 22 through charging resistor 21 and reed switch 10. The sensor thereafter operates each time its associated window or other entry barrier is opened, radiating one short train of radio frequency energy pulses once for each such opening event, and being reset for the next opening event by each successive closure of the entry barrier.

It will be understood that a plurality of sensors 1 may be used in a dwelling or business building or other location, one at each door, window, or other potential entry. Each may be provided with an identifying radiation characteristic merely by adjustment of the relative modulating frequency of the corresponding free running multivibrator. In a simple form of the system, all modulation frequencies may be substantially the same. The radiated carrier train, when received by an antenna 50 of a central monitor receiver 51, may be demodulated therein for the purpose of supplying the audio signal to an alternating current sensitive relay within receiver 51. Operation of the relay may supply power to a device 52 for producing a sustained visual or audible alarm within the building or outside of it. Receiver 51 and alarm 52 may be supplied from a common power source if desired. Operation of receiver 51 may alternatively or additionally supply an alarm signal via telephone lines to a conventional alarm device at a central police station or detective agency. Where discrete modulation frequencies characterize the several sensors used in a building, the several differentfrequency signals provided by sensors with adjustable frequency multivibrators may be demodulated by receiver 51 and supplied through corresponding audio frequency filters to activate relays which light tell-tale lamps (not shown). Such relays would preferably latch in the activated position so that a display indicating the location of the disturbed entry is readily afforded. Unauthorized movement of a safe, a display case, valuable painting, or the like may be similarly signalled locally or at a police headquarters. Where the system supplies alarm signals to a remote headquarters, the owner has the option of disabling receiver 51 when present in the protected building by operating switch 54 and observing the state of indicator lamp 55. He may similarly disable the connection to alarm 52 in his presence so that police headquarters will not be subjected to false alarms when the building entries are permissibly used. Receiver 51 may be adapted to handle inputs from other conventional sensor devices, such as smoke or fire detectors. i

While the invention has been described in its preferred embodiment, it is to be understood that the words which have been used are words of description rather than of limitation and that changes within the purview of the appended claims may be made without departure from the true scope and spirit of the invention in its broader aspects.

We claim: 1. An intrusion alarm system for detecting relative motion between first and second parts comprising:

magnetic field generating means affixed to one of said parts, first switch means having first and second states with respect to first and second magnitudes of said magnetic field, respectively, charging circuit means operative in series circuit relation only when said first switch means is in said first state, comprising: electrical current source means, first resistor means, and capacitor storage means, alarm actuator circuit means operative in series circuit relation only when said first switch means is in said second state comprising: said capacitor storage means, voltage sensing means for providing an output signal when the voltage stored on said capacitor storage means exceeds a predetermined value, and said electrical current source means, second switch means responsive to said output signal by changing from a non-conducting to a conducting state, and alarm circuit means operative in series relation with said second switch means only when in said conducting state comprising:

said electrical current source means,

multivibrator means, and

oscillator means for transmitting an alarm signal. 5 2. Apparatus as described in claim 1 wherein said oscillator means is responsive to said multivibrator means for producing a train of pulsed radio frequency signals for space transmission.

3. Apparatus as described in claim 2 wherein said multivibrato means is adapted to produce an audio frequency semi-square wave output with rise times suf ficiently slow for substantially limiting the harmonic content of the output of said radio frequency oscillator means.

4. Apparatus as described in claim 1 wherein said first switch means compris gs single pole, double throw reed switch means having irst, second, and third electrical terminal means,

said first terminal means supports said double throw reed, and

said reed supports contact means for contacting said first or second terminal means with respect to the magnitude of said magnetic field.

5. Apparatus as described in claim 4 wherein:

said first terminal means is connected to said capacitor storage means,

said second terminal means is connected to said first resistor means, and

said third terminal means is connected to said second resistor means.

6. Apparatus as described in claim 4 wherein said second switch means comprises:

magnetically actuatable single pole, single throw reed switch means connected to said electrical source means, and

solenoid magnetic field generating means connected to said electrical source means for actuating said magnetically actuatable single pole, single throw reed switch means.

7. Apparatus as described in claim 6 wherein said voltage sensing means comprises transistor switch means for controlling current flow through said solenoid magnetic field generating means when said voltage drop across said second resistor exceeds a predetermined value.

8. Apparatus as described in claim 1 including remotely located receiver means indicating reception of said pulsed radio frequency space transmitted signals for alarm purposes.

Claims

1. An intrusion alarm system for detecting relative motion between first and second parts comprising: magnetic field generating means affixed to one of said parts, first switch means having first and second states with respect to first and second magnitudes of said magnetic field, respectively, charging circuit means operative in series circuit relation only when said first switch means is in said first state comprising: electrical current source means, first resistor means, and capacitor storage means, alarm actuator circuit means operative in series circuit relation only when said first switch means is in said second state comprising: said capacitor storage means, voltage sensing means for providing an output signal when the voltage stored on said capacitor storage means exceeds a predetermined value, and said electrical current source means, second switch means responsive to saId output signal by changing from a non-conducting to a conducting state, and alarm circuit means operative in series relation with said second switch means only when in said conducting state comprising: said electrical current source means, multivibrator means, and oscillator means for transmitting an alarm signal.

2. Apparatus as described in claim 1 wherein said oscillator means is responsive to said multivibrator means for producing a train of pulsed radio frequency signals for space transmission.

3. Apparatus as described in claim 2 wherein said multivibrato means is adapted to produce an audio frequency semi-square wave output with rise times sufficiently slow for substantially limiting the harmonic content of the output of said radio frequency oscillator means.

4. Apparatus as described in claim 1 wherein said first switch means comprises single pole, double throw reed switch means having first, second, and third electrical terminal means, said first terminal means supports said double throw reed, and said reed supports contact means for contacting said first or second terminal means with respect to the magnitude of said magnetic field.

5. Apparatus as described in claim 4 wherein: said first terminal means is connected to said capacitor storage means, said second terminal means is connected to said first resistor means, and said third terminal means is connected to said second resistor means.

6. Apparatus as described in claim 4 wherein said second switch means comprises: magnetically actuatable single pole, single throw reed switch means connected to said electrical source means, and solenoid magnetic field generating means connected to said electrical source means for actuating said magnetically actuatable single pole, single throw reed switch means.