US3271754A - Monitoring system - Google Patents

Description

I I I I I I I I I I I I I I I I I I I I I I I I I I INVENTOR ATTORNEYS SYSTEM I- I E I I Q: o t z o 2 I-.o '3 I I I I I z I EI- I 82 I {33 o I LA I I I I PAUL I CORBELL BYf Q WY M P. I. CORBELL MONITORING Filed July 9,

Sept. 6, 1966 United States Patent 3,271,754 MONITORING SYSTEM Paul I. Corbell, Rockville, Md., assignor to Johnson Service Company, Milwaukee, Wis., a corporation of Wisconsin.

Filed July 9, 1963, Ser. No. 293,649 5 Claims. (Cl. 340-258) The present invention relates to the field of automatic area security protection, and particularly to a monitoring system therefor.

In the protection of buildings, warehouses and other areas, it is customary to utilize automatic detection units strategically located throughout the area being protected, to maintain the entire area under constant surveillance agains intrusion. It is common to employ, for example, microwave radio detection units, ultrasonic detection units, or light photoelectric cell units for the purpose of detecting the intrusion of a person either by entry into, presence in, or movement within the area under surveillance by the particular unit.

In order to effectively police large areas by means of automatic detection units, it is necessary to employ a number of detection units, for example one in each room of a building; or in large open areas, it is frequently necessary to employ several such units with each surveying a portion of the area. It is desirable to integrate the several detection units utilized for surveying a given installation into a monitoring system, so that at one monitor station the condition of each detection unit can be observed to determine whether an unauthorized intrusion has occurred, and if one does occure, to initiate an alarm and indicate which unit detected the intrusion.

In order for such a monitoring system to be fully effective, it must of course be essentially tamper proof in order that the monitor cannot be deactivated or interrupted. The monitoring system must also be essentially fail-safe to be fully effective. These objectives are accomplished in accordance with the present invention by providing an electrical monitoring system for a plurality of intrusion detection units, wherein upon any momentary change in the line current of the system (either an increase or a decrease), as would result from tampering with any of the lines of the system, or the occurrence of a defect or malfunction of any element in the monitoring system, the intrusion alarm of the monitoring system will be initiated and will remain activated until the malfunction in the system is corrected and the alarm unit is manually reset.

It is accordingly one object of the present invention to provide a monitoring system for an automatic intrusion detection installation which is essentially tamper proof.

Another object of the present invention is to provide a monitoring system for an automatic intrusion detection installation which is failsafe.

Still another object of the present invention is to provide an electrical monitoring system for an automatic intrusion detection installation that is self-policing against attack and malfunction by activation of an alarm upon a change either up or down in the monitoring system line current, even where such change is only momentary.

Other objects and advantages of the present invention will become apparent to those skilled in the art from a consideration of the following detailed description of one specific example of the invention, had in conjunction with the accompanying drawing, which is in part a schematic circuit diagram and in part a functional block diagram of a system embodying the present invention,

Referring to the drawing, an intrusion detection unit A is schematically indicated as located in an area A. Detection unit A may be a conventional intrusion detection unit designed and intended to detect the presence or entry of an intruder in area A, as will be fully understood by those skilled in the art. The output of detection unit A comprises a relay 10 whose switch 11 is of the type that is biased open. So long as there is no intrusion detection, the unit A is designed to energize relay 10 and thus hold switch 11 closed. However, should an intrusion detection output be obtained, or should the power input (not shown) to detection unit A fail, or should its operation otherwise fail, an alarm condition is created by the resultant deenergization of relay 10, which permits switch 11 to respond to its bias and open. Preferably, the output circuit of the detection unit is designed with a holding circuit, so that once an alarm condition is obtained, it will continue until the unit is appropriately reset. However, since the detection unit per se is not part of the present invention, and since such units are known in the art, these details are not illustrated in the drawing.

Switch 11 is located in a line circuit 14 running to the remote monitor area, particularly to monitor unit A located in the monitor area or station. The line circuit 14 includes a resistor 12 and a shunt 13 thereacross. Switch 11 operates to place the shunt 13 in or out of the circuit. For the purpose of illustration, the normal condition for line 14 is with switch 11 closed and shunt 13 applied across resistor 12; while in the alarm condition, switch 11 is open cutting the shunt 13 out of the circuit 14, thereby increasing the resistance of the line circuit.

At the monitor station, line circuit 14 includes a sensitive electrical meter 15, as for example a microammeter or galvanometer. Meter 15 is of a type having a moving element Whose position is controlled by the amount of current flowing in circuit 14. A mirror or reflective surface 17 is mounted upon or formed as a part of the moving element of meter 15. A light source 18 is located to illuminate the mirror 17, and the reflections therefrom are caused to illuminate the photoconductor 19 when the mirror 17 is porperly oriented. To set the system in operation initially, potentiometer 16 is varied to adjust the current flowing in circuit 14 so that the position or angle of mirror 17 causes full or maximum illumination of photoconductor 19. Thereafter, any change in the current flow through circuit 14 (increase or decrease) causes a change in the position of mirror 17, hence a decrease in the illumination of the photoconductor 19, thus detecting any change in condition of circuit 14 by a decrease in the resistance of photoconductor 19. For example, should the monitor lines 14 be attacked and cut, or should an alarm condition prevail at detection unit A, the resultant change in current flow through circuit 14 could cause a decrease in illumination of resistor 19, and a corresponding change in its resistance. As 'will be apparent, the photoconductor 19 will thus detect by an increase in resistance either an increase or decrease in current through circuit 14, and the degree of sensitivity desired for the detection can be selected simply by appropriate design of the optical illumination system and selection of meter 15.

Changes in resistance of photoconductor 19 are detected by the trigger circuit including transistors 20 and 21, photoconductor 19 being connected to the base biasing network of transistor 20. When the line current for circuit 14 is normal (photoconductor 19 fully illuminated), the trigger circuit is designed to provide transistor 20 with a heavy forward bias causing it to conduct at saturation. Accordingly, the collector voltage of transistor 20 is low and establishes a reverse cut-off bias on the base of transistor 21. The emitter electrodes of transisters 20 and 21 are clamped by diode 23. When the illumination of photoconductor 19 decreases to a point where the bias on the base of transistor 20 falls below its emitter potential, this transistor is below cut-off, causing the base of transistor 21 to become forwardly biased and this transistor to conduct to saturation.

The function of this trigger circuit is to control relay 24 and its switch 25. Under normal conditions for line 14, transistor 21 is cut off, providing an appropriate voltage at the collector of this transistor to energize the relay 24 to a degree sufiicient to hold its switch 25 closed to the normal contact 26 against its bias. However, when transistor 21 becomes conductive, the voltage at its collector electrode drops to a point where relay 24 becomes relatively deenergized, and switch 25 responds to its bias and closes to its alarm contact 27. This action opens the supply circuit to the collector of transistor 21 and to the relay 24, and thus provides a holding circuit whereby the alarm condition cannot be changed until both the cause for the alarm trigger is removed and manual reset switch 31 (shunting relay switch 25) is closed.

The alarm circuit comprises an alarm light 28 and an audible alarm device 38. When switch 25 is closed to normal contact 26, alarm light 28 is partially illumi nated, say to about one quarter brilliance, through resistor 39. Diode 30 isolates this current from the audible alarm 38. When switch 25 is closed to its alarm contact 27, alarm light 28 is illuminated to full brilliance and audible alarm 38 is activated. In this instance, diode 29 functions to isolate transistor 21 and relay 24 from the alarm current so that the relay cannot by this means become reset.

In addition to the above described detection unit A, the system can include any number of detection units and corresponding monitor units. This is schematically illustrated by indicating a second surveillance area B, policed by detection unit B, transmitting over line 14b to monitor unit B identical to monitor unit A. The alarm circuits of each of the monitor units may conveniently be connected to the same audible alarm 38. In this event, to isolate an alarm signal originating in one monitor unit from the alarm light of each of the other monitor units, each unit is provided with a blocking diode 37, 37b, etc.

A further feature of the present circuit is embodied in ganged switches 32 and 35. Upon the occurrence of .an alarm, the audible signal can be shut ofi by moving switch 32 from contact 34 to contact 33. At the same time switch 35 is closed to energize light 36 as a reminder that the audible alarm has been silenced. Further to insure that the audible alarm -is not left disconnected from the system, the circuit associated with contact 33 will activate the audible alarm when the relay 24 is reset and the switch 25 is returned to normal position, until the switch 35 is opened and the switch 32 is re- .turned to its normal position closed to contact 34.

Considering the operation of the circuit, it will be assumed that the circuits are all as shown in the drawing-in normal or nonalarm condition, and in each monitor unit the photoconductor (19 in monitor unit A, e.g.) are fully illuminated by light reflected from the optically coupled meter (15 in monitor unit A, e.g.). Upon the occurrence of either: an alarm condition at a detection unit, a power failure or other malfunction in a detection unit (if the detection units are of a failsafe design), an attack upon the monitor system which causes even a momentary increase or decrease in the current of the monitor circuit lines 14, 14b, etc., a deterior-ation of a monitor unit photopcondctor, a failure or deterioration of a light illuminating such photoconductor, a power failure in the monitoring system, or any other failure -or malfunction inthemonitoring system,

the alarm switch (25 in monitor unit A, e.g.) is actuated to its alarm condition to create an audible alarm and a visible indication of the particular monitor unit and detection unit causing the alarm. Effective reset of the system to nonalarm condition can be effected only after removal or correction of the condition that caused the alarm.

Accordingly, there has been presented a specific embodiment of the present invention, illustrating a monitoring system for an automatic area security protection installation, which is essentially tamper-proof and fail-safe. It is understood that this specific embodiment is presented merely for purposes of illustration to enable a complete understanding of the present invention, and that numerous modifications, changes, and variations will be apparent to those skilled in the art. For example, it is obvious that instead of a current meter 15, one might design the line circuit 14 to detect a change in its electrical parameters by means of a voltmeter. modification, changes, and variations as are embraced by the spirit and scope of the appended claims are contemplated as within the purview of the present invention.

What is claimed is:

1. A system for monitoring the condition of a remote station, comprising a monitoring unit, a line circuit connecting said unit with said station, said unit comprising an electrical meter connected to said line circuit and having a movable member responsive to the current-voltage parameter of said line circuit, a light reflective element associated with said member and movable in response to said member, a light source illuminating said element, photoresponsive means optically coupled to said element, means for adjusting the optical coupling between said element and said photoresponsive means to a desired condition, a bistable circuit electrically coupled to said photoresponsive means, means biasing said bistable circuit to a first state when a given optical coupling is obtained between said photoresponsive means and said element and biasing said bistable circuit to a second state when a lesser optical coupling is obtained, a relay controlled by said bistable circuit to be relatively energized when said bistable circuit is in said first state and relatively deenergized when said bistable circuit is in said second state, a switch biased to a first position and controlled by said relay to be moved to a second position against its bias when said relay is relatively energized, a holding circuit associated with said switch for controlling the application of current to said relay to maintain said relay deenergized once said switch is moved to said first position, reset means for bypassing said holding circuit to permit the application of current to said relay and the resetting of said switch thereby, and indicator means controlled by said switch and activated when said switch is in said first position.

2. A system as set forth in claim 1, including a plurality of stations and a monitoring unit for each station.

3. A system as set forth in claim 2, wherein each station includes an intrusion detection unit adapted to change the current-voltage parameter of the respective line circuit on detection of an intrusion.

Accordingly, such 1 4. A system as set forth in claim 3, wherein said photoresponsive means is a photoconductor means.

5. A system as set forth in claim 4, wherein said photoconductor means is included in the input to said histable circuit.

References Cited by the Examiner UNITED STATES PATENTS Clarke 340-266 Coleman.

Haagn 340266 Hammond 250231 X Mitchell.

Young.

NEIL C. READ, Primary Examiner.

R. M. GOLDMAN, Assistant Examiner.

Claims (1)

1. A SYSTEM FOR MONITORING THE CONDITION OF A REMOTE STATION, COMPRISING A MONITORING UNIT, A LINE CIRCUIT CONNECTING SAID UNIT WITH SAID STATION, SAID UNIT COMPRISING AN ELECTRICAL METER CONNECTED TO SAID LINE CIRCUIT AND HAVING A MOVABLE MEMBER RESPONSIVE TO THE CURRENT-VOLTAGE PARAMETER OF SAID LINE CIRCUIT, A LIGHT REFLECTIVE ELEMENT ASSOCIATED WITH SAID MEMBER AND MOVABLE IN RESPONSE TO SAID MEMBER, A LIGHT SOURCE ILLUMINATING SAID ELEMENT, PHOTORESPONSIVE MEANS OPTICALLY COUPLED TO SAID ELEMENT, MEANS FOR ADJUSTING THE OPTICAL COUPLING BETWEEN SAID ELEMENT AND SAID PHOTORESPONSIVE MEANS TO A DESIRED CONDITION, A BISTABLE CIRCUIT ELECTRICALLY COUPLED TO SAID PHOTORESPONSIVE MEANS, MEANS BIASING SAID BISTABLE CIRCUIT TO A FIRST STATE WHEN A GIVEN OPTICAL COUPLING IS OBTAINED BETWEEN SAID PHOTORESPONSIVE MEANS AND SAID ELEMENT AND BIASING SAID BISTABLE CIRCUIT TO A SECOND STATE WHEN A LESSER OPTICAL COUPLING IS OBTAINED, A RELAY CONTROLLED BY SAID BISTABLE CIRCUIT TO BE RELATIVELY ENERGIZED WHEN SAID BISTABLE CIRCUIT IS IN SAID FIRST STATE AND RELATIVELY DEENERGIZED WHEN SAID BISTABLE CIRCUIT IS IN SAID SECOND STATE, A SWITCH BIASED TO A FIRST POSITION AND CONTROLLED BY SAID RELAY TO BE MOVED TO A SECOND POSITION AGAINST ITS BIAS WHEN SAID RELAY IS RELATIVELY ENERGIZED, A HOLDING CIRCUIT ASSOCIATED WITH SAID SWITCH FOR CONTROLLING THE APPLICATION OF CURRENT TO SAID RELAY TO MAINTAIN SAID RELAY DEENERGIZED ONCE SAID SWITCH IS MOVED TO SAID FIRST POSITION, A RESET MEANS FOR BYPASSING SAID HOLDING CIRCUIT TO PERMIT THE APPLICATION OF CURRENT TO SAID RELAY AND THE RESETTING OF SAID SWITCH THEREBY, AND INDICATOR MEANS CONTROLLED BY SAID SWITCH AND ACTIVATED WHEN SAID SWITCH IS IN SAID FIRST POSITION.

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