US3623049A

US3623049A - Direct wire burglar alarm system providing subscriber testing of motion detecting devices

Info

Publication number: US3623049A
Application number: US857450A
Authority: US
Inventors: Frederick G Hill
Original assignee: American District Telegraph Co
Current assignee: American District Telegraph Co
Priority date: 1969-09-12
Filing date: 1969-09-12
Publication date: 1971-11-23
Anticipated expiration: 1988-11-23

Abstract

The present invention comprises a direct wire central station burglar alarm system having means whereby the operation of certain motion detection devices forming a portion of the protection system may be tested by the subscriber to the protection service. Means are also provided for giving visual indication of the results of such testing, for retaining alarm signals until intentionally released, for operation with more than one motion detection device, for operation with motion detection devices of different types and for operation with reversed polarity power supply.

Description

United States Patent Inventor Frederick G. Hill Yonkers, N.Y.

Appl. No. 857,450

Filed Sept. l2, 1969 Patented Nov. 23,1971

Assignee American District Telegraph Company Jersey City, N.J.

DIRECT WIRE BURGLAR ALARM SYSTEM PROVIDING SUBSCRIBER TESTING OF MOTION DETECTING DEVICES [56] References Cited UNITED STATES PATENTS 3,022,496 2/l962 Bagno 340/4 l O 3,254,334 5/1966 Mitchell 340/276 Primary Examiner-John W. Caldwell Assistant Examiner-Michael Slobasky Attorney-James D. Bock ABSTRACT: The present invention comprises a direct wire central station burglar alarm system having means whereby 7 Claims,5Drawing Figs. the operaition of certain motion detection devies forhming a portion o the protection system may be teste by t e sub- U.S. Cl 340/214, scriber to the protection Service. Means are also provided for 340/2Z;%83b4l03/)l00 giving visual indication of the results of such testing, for Int. Cl Gogh 29//06 retaining alarm signals until intentionally released, for opera- 340 410 tion with more than one motion detection device, for opera- Fleld of Search 4/ 276, tion with motion detection devices of different types and for 21 operation with reversed polarity power supply.

r' u T u l PREM|sEs"`T L l Uil" l Ri (IK) fnscmcs) l V37 E i l I' E Lsa E COMPONENT l 7" BoRD CW) 7W" (zNTalasi) l i i l i I DEvicE CENTRAL. Di. D4 4g R4(s.ei l Il (LBK) l sTAlTc-)xoN T a ww I (arl-139|) RSHK) A i PATENTEDrmv 23 Ism SHEET- 3 F 3 I l IIL' I I I IJ W-'MI-lllll m QIIIIII@ l mmmzmmu OmFOmFOma DIRECT WIRE BURGLAR ALARM SYSTEM PROVIDING SUBSCRIBER TESTING OF MOTION DE'I'ECTING DEVICES BACKGROUND OF THE INVENTION Direct wire central station burglar alarm systems are in widespread use for the protection of banks, stores, private residences, industrial establishments and the like against burglary. In such systems, the protected premises are equipped with various devices designed to detect the presence of an intruder and transmit a warning signal thereof to the central station. The protected premises are connected to the central station by a transmission line which is conventionally a telephone line leased for the purpose and which may be as long as 20 miles and pass through several telephone exchanges. The central station is staffed at all hours by specially trained operators who, upon the receipt of a burglar alarm signal, will dispatch private guards or the police as the circumstances direct, notify the owner of the premises and the insurance company, etc.

The protection devices at the premises may be classified as being of either the entry detection type or the motion detection type. The former are designed to detect the entry of an intruder through a door, window or other building opening into the protected area. The latter devices are intended to detect the presence of an intruder inside the protected area who has succeeded in evading the entry detection devices or had been able to conceal himself within the area before the protection system was turned on. Such devices are usually actuated by the motion of the intruder within the protected area.

Many of the premises protected by central station alarm systems such as banks and stores are open for business during the daylight weekday hours and are closed at night and on weekends and holidays. While open, portions of such premises are protected by the presence of the employees and the alarm system is not needed. In fact, it would be a great nuisance if an alarm signal were created every time the front door of a busy store was opened during the day. On the other hand, there are remote portions of buildings such as skylights and basement openings where it is desirable that the protection be maintained at all times. Therefore the protection system at the premises is provided with a manually operated switch to disconnect a portion of the system dun'ng the normal business hours when the premises are open. Accordingly, when the premises are opened for business in the morning at a prescribed hour, the switch is thrown to the "o" position and likewise, when closing in the evening, the switch is thrown to the "on" position. The operation of the switch changes the load on the protection circuit producing variations in the current flowing therethrough and' resulting in signals at the central station which enable the operators to know whether` the protected premises are open or closed. A typical central station alarm system is described in U.S. Pat. No. 3,254,334 issued May 3 l l966, to I..:H. Mitchell.

An essential feature of a burglar alarm system is the provision of means to test the circuit to make certain that no accidental or malicious damage has occurred that would interfere with the normal functioning of the system. It is customary for such tests to be made from the central station when the premises are closed at the end of the business day and periodically during the hours the premises remain closed.

Testing of a protection system is relatively simple when there are no motion detectiondevices in the circuit since it is essentially simply a matter of determining the continuity ofthe circuit. However, when motion detectors are present, the problem is more complex because then means must be provided to simulate the results of the motion of an intruder within the protected area in order to be certain the detection devices will function as intended. i

Usually tests are initiated by the operators at the central station as generally described in the aforementioned patent to Mitchell. However, in large central stations serving many subscribers to the protection service and especially so when there are large numbers of motion detection devices involved, such testing becomes a heavy burden on the operators.

ln U.S. Pat. No. 3,562,730 issued Feb. 9, l97l to Hill et al., on an application filed Apr. 29, 1968, there is disclosed a system wherein the central station operator performs the entire testing procedure including the actuation of motion simulating means for testing of motion detecting devices located in the protected premises. In said Hill et al. patent the central station operator must go through a sequence of operations and if such operations show that the motion detecting devices are in operative condition an indication of that fact is made both at the central station and at the protected premises. The system disclosed in said Hill et al., patent thus places an additional burden upon the central station operator insofar as it requires a greater amount of his time than would be required if he did not have to include the motion detecting test in his duties incident to the closing of a protected premises equipped with that system. lt therefore is desirable that a portion of the testing, namely that of the motion detection devices, be performed by the individual subscribers. Accordingly, the principal object of the present invention has been the provision of simple, inexpensive means that can be readily added to existing protection circuits to enable the subscriber to test the motion detection devices at his premises without sending alarm signals to the central station.

A feature of the invention has been the provision of means to lock-in alarm signals which are sent to the central station so that they will not be lost when the detecting device restores to the nonnal condition.

Another feature of the invention has been the provision of visual indication means to inform the subscriber that a test has been successfully performed.

Other and further objects, features and advantages of the invention will be apparent from the following description of the invention.

BRIEF DESCRIPTION OF THE INVENTION the results of tests applied to motion detection devices. Means are provided for locking in any alarm signals sensed by the electronic switching means when it is desired to send an alarm signal to the central station, while alarm signals caused by testing need not be sent but merely shown by the milliammeter for observation by the person making the test.

In addition, provision has also been made for test and actual operation with a transmission line voltage of opposite polarity, operation with more than one detection device and operation with detection devices having a transistor circuit for the output element as well as those devices which employ an electromechanical relay for that purpose.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will now be described in greater detail with reference to the appended drawings in which:

FIG. l is a schematic diagram showing the inclusion of the present invention in a direct wire central station burglar alarm system;

FIG. 2 is a portion of FIG. 1 showing the circuit changes necessary to accommodate anothertype of motion detection device;

FIG. 3 is similar to FIG. 2 but illustrating the means of connecting several motion detection devices to the system;

FIG. 3A is another portion of FIG. l illustrating a switch arrangement for testing a number of motion detection devices; and

FIG. 4 is a schematic diagram showing the changes needed to operate the system on potential of opposite polarity.

DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION Referring now to FIG. l, a central station l is shown connected to a protected premises 1l by a telephone line or similar direct wire connection 12. The return may be by ground connections 31-15 as shown or by a separate wire connection. Typical values for the resistors and capacitors are shown on the drawings in ohms and microfarads respectively as well as the identification of the various standard solid state components except the diodes which may all be of the IN2070 type. This information as well as the operating voltages mentioned in the following description are for illustrative purposes only and are not to be interpreted as limitations of the invention.

One end of line l2 is coupled at the central station to the negative terminal of a source of potential 13 (which typically might be a 52 volt battery) through a series circuit comprising back contact 14 of a manually operable switch SW1 and the windings G and B ofthe ground and break relays respectively. As is well known in the art, the ground and break relays respond respectively to increases and decreases in the supervisory current flowing through the system and operate various visual and audible signal annunciation devices (not shown) to call the operators attention to changes in the condition of the circuit. The positive terminal of the normal operation battery 13 is connected to ground at 15.

In parallel with the battery 13 and the coils G and B of the ground and break relays is a circuit comprising a source of potential 16 (which typically might be a hundred and thirty volt battery) in series with the primary winding 17 of a transformer TR and contact 18 of switch SW1. The negative terminal of battery 16 is connected to ground at l5 so that battery 16 is of opposite polarity to battery 13. The secondary winding 19 of transformer TR is connected to a neon lamp 20. Battery 16 and associated components are employed in the testing of the entry detection portion of the protection system as will be explained in detail hereinafter.

At the protected premises 11, line 12 is connected to a local circuit which includes both entry detection and motion detection devices. The entry detection portion of the circuit is shown in a highly simplified form and may be traced from line 12, through a current adjusting resistor RXl, a foil circuit 21, terminal A, a Zener diode Z, terminal B, another foil circuit 22, armature 23 and back Contact 24 of a door protection switch 2S, another current adjusting resistor RX2, the armature 26 of a bell interrupter contact 36, foil circuit 27, terminal C, back contact 28 of a protection control switch SW2, foil circuit 30, diode D8 and to ground at 31. Since central station battery 13 is positively grounded, current tlow at the protected premises will be from ground 31 and diode D8 shunts the winding BL of a bell coil.

The

foil circuits

21, 22, 27, 30 may consist of conventional lead foil strip adhered to the glass panels of windows (or doors) and carry the normal supervisory current of the system. If an intruder breaks a glass panel in an effort to enter the premises, the current carrying foil will be severed and result in the production of a break signal at the central station. Typically such a break signal might be represented by a decrease in current in line 12 from a normal value of l5 to 9 milliamperes or less. A similar form of protection for walls, floors and ceilings is sometimes provided by means of foil or ne wire ap plied to the surfaces thereof in such manner that it will be mptured if the surface is breached.

Items

21, 22, 27, 30 of FIG. l are intended to represent this form of protection regardless of whether installed on glass panels or other building structure elements.

lf the door protected by the switch 25 is opened, the armature 23 will transfer from the back contact 24 to the front contact 32 and result in the production of a brief break signal (while the annature 23 is in motion) followed by a ground signal at central station because the resistor RX2 is now shunted out of the circuit and allows the current flow to increase. Typically, a ground signal might be represented by an increase in current in line 12 from the normal value of l5 to 2l milliamperes.

The motion detection devices are included in a branch circuit connected between terminals A and B. With a positively grounded central station battery, the current flow will be from tenninal B, via resistor R6. terminal D, armature 33 and contact 34 of the alarm relay 35 forming a part of a motion detection device (shown diagrammatically) and then via resistor R8, diodes D6, D7 and resistor R7 to terminal A. The motion detection device may operate in response to any of a variety of disturbances, usually but not always caused by movement of an intruder, e.g., it may be actuated by the passage of the intruder through a light beam, the acoustic detection of noises made by the intruder, the disturbance of an ultrasonic sound pattern or the changes in a capacitance field surrounding an object approached by the intruder. All that is necessary for the immediate description is that the motion detector have an alarm relay whose contact is normally closed when the detector is in the operable condition and which opens under alarm conditions. Circuit connections for motion detection devices which employ a transistor circuit instead of an alarm relay and for more than one detector will be described hereinafter.

As previously stated, the present invention is concerned with the circuitry means provided for interconnecting the motion detection devices with the entry device protection system in such manner that the operation ofthe motion detectors may be tested by the subscriber at the protected premises without causing a signal at the central station provided that the switch SW2 is in the OFF (premises open for business) position. Also the alarm signal produced by such motion detecting devices when the protection system is in the 0N position (premises closed for business), is converted into a locked-in signal at the central station.

In the installation of central station burglar alarm systems it is customary to provide a control unit mounted on a wall at the protected premises which comprises a relatively small box containing the resistors RXl and RX2 which are used to adjust the current flowing through the system, a manually operable switch SW2 employed to switch the system from the business hours condition to the after hours condition, a bell coil BL and bell interrupter contact 36 which are used in the testing of the system and a terminal strip.

ln accordance with one embodiment of the present invention there are provided an indicating unit 37 and an electronic component board 38. The indicating unit 37 consists of a manually operable switch SW3 and a milliammeter MA in a separate box which is wall mounted adjacent to the control unit. The electronic component board 38 which supports various resistors, capacitors and solid state devices is designed to be mounted on brackets within the control unit and is connected to the protection circuit by means of four terminals.

Board 38 has a conductor 39 which is connected to terminal A and a conductor 40 connected to terminal B. A Zener diode Z is connected between

conductors

39 and 40 so that the current flow from terminal B to terminal A from the positively grounded central battery 13 when the switch SW2 is in the ON position (premises closed for business) will produce an` operating voltage in the form of the potential drop across diode Z (which might conveniently be 6.8 volts) for the other components on board 38. When switch SW2 is in the OFF position (premises open for business), the current will flow via a terminal F, conductor 43 and a diode D3 to the Zener diode Z, thus an operating voltage is provided regardless of the position of the protection control switch SW2.

Connected in parallel with diode Z between

conductors

39 and 40 is a series circuit comprising a resistor R7, diodes D7 and D6, resistor R8, tenninal E, contact 34 and armature 33 of a motion detector alarm relay 35, terminal D and resistor R6. The terminals D and E thus provide the means of interconnection with the motion detectors and while but one alarm relay type of detector is indicated in FIG. 1, other forms of connection will be disclosed hereinafter.

A transistor T2 in series with a resistor R5 is also connected between

conductors

39 and 40 with the emitter thereof connected to conductor 39 and the collector to conductor 40 via the resistor R5. The base of transistor T2 is connected to the junction of resistor R7 and diode D7 while a conductor 4l having one end connected between the base of transistor T2 and the junction of resistor R7 and diode D7 joins a capacitor C2 and diodes D2, D1 to the gate of a silicon controlled rectifier SCR. A capacitor Cl and a resistor Rl are joined in parallel between conductors 39 and 41 to form a radio frequency filter to eliminate any circuit disturbances which might be caused by pickup of radio frequencies.

The cathode of the silicon controlled rectifier SCR is connected to conductor 39 at the junction with resistor R1 and the anode thereof is joined to terminal C by conductor 47. The emitter of a transistor T1 is joined to conductor 41 at the junction of capacitor C2 and diode D2 while the collector thereof joins a resistor R3, the milliammeter MA of the indicating unit 37 and a resistor R2 in series connection with terminal F by means of conductor 43. The base of transistor T1 is connected to a conductor 42 at the junction of the series connection of a resistor R4 and diodes D4 and D5 contained therein. The cathode of diode D5 is connected to conductor 39 and the other end of conductor 42 joins resistor R4 to the junction of resistor R2 and terminal F., which point is also connected to conductor 40 by means of diode D3.

OPERATION OF THE EMBODIMENT SHOWN lN F lG. l.

During the hours the premises are open for business, the protection control switch SW2 will be in the OFF position and contact 34 of the alarm relay 35 will be open since the power supply (not shown) for the motion detection device is switched o'. Current therefore flows from the central station battery 13 via ground connections l5 and 3l, diode D8, foil circuit 30, switch SW2, terminal F,

conductors

43 and 42, diode D3, diode Z, terminal A, foil circuit 21, resistor RX1, line l2, switch SW1, ground relay G and break relay B to battery 13,

When the subscriber wishes to close the premises for the day, he shuts all of the protected doors and windows and turns on the power, supplied by the local power lines or batteries (not shown) to the motion detection device. Contact 34 of alarm relay 35 is now closed and current flows from the cathode of diode D3 through resistor R6, tenninal D, armature 33. contact 34, terminal E, resistor R8, and diodes D6, D7 to provide base current for transistor T2 thereby causing it to become conductive. Current also flows via conductor 42 and resistor R4 to the base of transistor T1 causing it to be conductive also, the base voltage being maintained by diodes D4 and D5.-Another current path therefore exists through resistor R2, milliammeter MA, resistor R3 and the collectoremitter circuits of transistors T1 and T2 in series to conductor 39. The milliammeter MA will read about 3.0 milliamperes thereby indicating that the motion detection device circuits are complete.

To test the operation of the motion detector, the subscriber momentarily closes switch SW3 which might conveniently be of the spring loaded type. This switch actuates a motion simulating device (locally powered) which will simulate the disturbance that would be caused by the presence of an actual intruder. The nature of the simulated disturbance must, of course, be compatible with the principle of operation of the motion detection device. Thus, in the case of a projected beam photoelectric device, the intensity of the light source could be reduced by dropping the voltage to the lamp thereby simulating the blocking of the light beam by an intruders body. ln the case of an ultrasonic sound system, a small fan could be turned on to produce a disturbance that is detectable by the protection apparatus. ln like manner, a hom might be sounded for detection by an acoustic type of detecting device or the capacitance may be varied in the circuit of a capacitance type of detecting device to simulate the effects of the presence of an actual intruder.

ln all cases, provided that the motion detecting device is in proper order, the apparatus will respond by detecting the disturbance and alarm relay 35 will open contact 34. Transistor T2 is thereby deprived of base current and becomes nonconductive after a brief` delay of about milliseconds provided by capacitor C2 to eliminate the eects of contact bounce in the alarm relay 35. With transistor T2 nonconductive, transistor Tl also becomes nonconductive since the emitter circuit thereof is in effect open and the reading on milliammeter MA drops to zero thereby indicating that the motion detection device has been tested successfully. During this test operation by the subscriber no alarm signal is transmitted to the control station 10 and the silicon controlled rectifier SCR does not lock into conductive state because no potential is supplied to the anode thereof through line 47.

The subscriber then moves the protection control switch SW2 to the ON position as shown in FIG. l thereby removing potential from terminal F, milliammeter MA, transistor Tl and the circuits associated therewith by means of conductor 43. Current now flows from contact 28 of switch SW2, terminal C, the elements of the entry detection circuit that had been shunted during the business hours, terminal B, diode Z, the circuit containing the contact of alarm relay 35 and the circuit containing transistor T2 to terminal A, the remainder of the entry detection circuit and line 12 to the central station. Also current-now flows from contact C through line 47 to the anode of the silicon controlled rectifier SCR. Therefore, if the subscriber were now to perform the test, described above, of the motion detecting device the silicon controlled rectifier SCR would become conductive and a signal would be transmitted to the central station 10.

When armature 29 of switch SW2 is transferred from contact 44 to contact 28, the circuit is momentarily opened causing operation of the break relay at the central station. The operator at the central station will recognize the signal as a closing signal since it will occur at a prearranged time of day and proceed to test the entry detection portion of the protection system by transferring armature 45 of switch SW1 to contact 18. Reverse polarity current now flows from the high voltage test battery 16 through primary winding 17 of transformer TR at the central station via line 12 and thence through terminals A, B, C and bell coil BD to ground 31 at the protected premises provided that the protection circuit is complete. The bell coil becomes energized sounding the bell at the protected premises and opening the bell interrupter contact 36 causing the coil BL to become deenergized. Contact 36 then closes again to reenergize coil BL and this action is repeated to cause a continuous sounding of the bell to indicate to the subscriber that the protection circuit is in proper order. Meanwhile, at the central station, the flow of current through primary winding 17 of transformer TR energizes the secondary winding 19 causing the lamp 20 to be illuminated. The pulsing ofthe bell interrupter contact 36 causes lamp 20 to flash in synchronization so that the operator is informed of the success of the test of the system. Switch SW1 is then returned to the normal battery position and the full protection circuit is established.

Should an intruder subsequently manage to evade the entry detection devices, but actuate a motion detector, the alarm relay 35 will open contact 34 and transistor T2 becomes nonconductive since the base current has been interrupted. With transistor T2 conductive, current flows from conductor 40 via resistor R5 and diodes D2, D1 (which provide a back-bias voltage to keep transistor Tl nonconductive when the system is in the closed for business condition) to the gate of the silicon controlled rectifier SCR which becomes conductive, and once thus triggered, will remain conductive until the circuit is opened. Since the silicon controlled rectifier SCR is conductive, terminal A is connected directly via

conductors

39 and 47 to terminal C causing resistor RX2 to be shunted out of the circuit and the resulting increase in current flow will cause the operation of the ground relay G at the central station. The operator will treat this signal as an alarm in the prescribed manner and then release the silicon controlled rectifier SCR by momentarily moving switch SW1 to a central position provided that the alarm relay 35 has returned to the normal closed contact condition.

An additional benefit is derived from the present invention in that should an intruder endeavor to disable the system by tampering with switch SW3 when the system is in the closed for business condition, he will cause a test of the motion detection device which will result in an alarm signal at the central station. Such alarm signal would become locked in the same manner as would a signal initiated by an intruder caused disturbance of the motion detecting device.

MODIFIED EMBODIMENTS OF THE INVENTION The motion detection device described in conjunction with FIG. l gave indication of an alarm condition by opening the circuit through the alarm relay contact. Other types of motion detection devices respond by closing a circuit and FIG. 2 illustrates how such a device may be connected to the protection circuit when a transistor is employed instead of an electromechanical alarm relay.

Referring now to FIG. 2, terminals D and E are joined by means of a strap 46 and connected to the collector of a transistor T. Transistor T is in the output circuit of a motion detection device the rest of which is not shown. The emitter of transistor T is connected to conductor 39 between the junction of terminal A and diode Z. Transistor T is normally in the nonconductve state and becomes conductive when an alarm condition occurs, thereby shunting resistor R8, diodes D6, D7 and resistor R7 and removing base voltage from transistor T2. The result is the same as occurred when the alarm relay of FIG. l opened contact 34 and the rest of the circuit performs as previously described. In the event that transistor T should not become fully conductive, diodes D6 and D7 have been provided to absorb any voltage inv that branch of the circuit which might otherwise appear at the base of transistor T2 and prevent it from turning off. Those skilled in the art will recognize that transistor T in the motion detection device could readily be replaced by a normally open relay contact arranged to close under alarm conditions.

At times it may be desirable to provide more than one motion detection device. if the additional devices are also of the type having a normally closed electromechanical relay described in connection with FIG. l, the contacts thereof are arranged in series with contact 34 between terminals D and E. If additional devices having transistor outputs of the type shown in FIG. 2 are to be provided, the output transistors thereof are placed in parallel with transistor T.

Should, however, it be desired to employ motion detection devices of both types, the circuit arrangement of FIG. 3 should be used. Here a second alarm relay 35 is shown in series with alarm relay 35 between terminals D and E and a second transistor output T; is shown in parallel with transistor T with both connected between conductor 39 and the junction of terminal D and resistor R6. Operation of either relay 35 or 35' will open the circuit and deprive transistor T2 of base voltage. Similarly, if either transistor T or T becomes conductive, the base voltage for transistor T2 will be shunted. In either case, transistor T2 becomes nonconductve and the system operates as previously explained.

Testing of the individual devices may be accomplished with switch SW2 in the OFF position without transmitting alarm signals to the central station l by providing sufficient extra contacts (not shown) on switch SW3 one for each device) so that closure thereof will operate the testing means at each device and all devices are tested simultaneously. However, if the test should fail, there would be no immediate means for determining which device was faulty. Therefore the arrangement of FIG. 3A is preferred. Here is shown an indicating unit 37' having three additional switches SW4, SWS and SW6 each independently associated with a motion detection device. Each device may therefore be tested independently in succession thus eliminating the objection to the previous arrangement. During such successive tests the silicon controlled rectitier SCR remains nonconductive so long as switch SW2 remains in the OFF position.

It may also be desirable at times to operate the system with reversed polarity and FIG. 4 shows the changes necessary for such operation. The batteries at the central station I0 are reversed so that the negative terminal of the normal operation battery 13 and the positive terminal of the test battery 16 are connected to ground at l5. At the protected premises 1l, the electronic component board 38 and indicating unit 37 (with no internal changes) are connected to the opposite side of the circuit. Thus terminals A. F, B which were formerly on the high side between foil circuits 2l, 22 are now on the low side between

foil circuits

27, 30 and terminal C which was formerly at the ground side of foil circuit 27 is now at the battery side of foil circuit 22. Normal current flows from battery 13 via the line l2 to the protected premises and returns via the ground connections 3l to l5 while the test current flows from battery 16 via the ground connections 15 to 3l and returns via the line l2. Under alarm conditions, the silicon controlled rectifier SCR connects terminal C to terminal A via

conductors

47 and 39 to shunt resistor RX2 thereby increasing the current to operate the ground relay at the central station.

While the invention has been described in conjunction with specic embodiments thereof and in specific uses, various modifications thereof will occur to those skilled in the art without departing from the spirit and scope of the invention as set forth in the claims.

What is claimed is:

1. In an electrical protection system in which a protected place is connected to a station by a conductive line,

said station having a source of direct current potential coupled to said line and having current-sensitive means coupled to said line to detect changes in current flowing through said line,

said protected place having:

at least one protective device of a disturbance-detecting type having alarm switch means the conductive state of which is changed from a normal to an alarm state in response to a disturbance of a particular type likely to be produced by an intruder in said protected place;

manually controlled switch means operative in one mode to prevent a change in the conductive state of said alarm switch means to the alarm state from altering the current flow in said line;

and said manually controlled switch means being operative in another mode to permit a change in the cond uctive state of said alarm switch means to the alarm state to alter the current flow in said line;

the improvement which comprises means for testing at least said one protective device comprising:

a disturbance simulating means operable at will within said protected place to produce a disturbance of a type to which said disturbance detecting device is designed to respond;

means for deriving an operating potential for use in sensing the state of conductivity of said alarm switch means from said source of direct current in said station when said manually controlled switch means is in either said one or said another mode;

electronic switching means including means utilizing operating potential derived from said means for deriving potential to sense the state of conductivity of said alarm switch means;

indicating means in said protected place for giving a recognizable indication of the state of conductivity of said alann switch means;

and said electronic switching means including means for connecting said indicating means with said alarm switch means and said means for deriving potential only when said manually controlled switch means is in said one mode, whereby only when said manually controlled switch means is in said one mode the change of conductivity of said alarm switch means to the alarm state in response to said disturbance simulating device is effective to produce said recognizable indication by said indicating device. 2. An electrical protection system in accordance with claim l in which said alarm switch means comprises contact points movable to open or to closed position by an armature of an electrical relay actuated by said one protective device in response to a disturbance of said particular type.

3. An electrical protection system in accordance with claim l in which said alarm switch means comprises a first transistor (T) changeable to conductive or to nonconductive state by said one protective device in response to a disturbance of said particular type.

4. An electrical protection system in accordance with claim 3 in which there is provided a second transistor (T2) and a first circuit branch connected across said means for deriving an operating potential said first circuit branch including diode means (D6 and D7) polarized to conduct current from one side of said means for deriving an operating potential to the base of said second transistor (T2) and a bias resistor (R7) connecting said base to the other side of said means for deriving an operating potential, the potential thus developed across said resistor (R7) being sufficiently high in value as to maintain said second transistor (T2) in conductive state, and in which said first transistor (T) is connected in series with a second circiit branch shunted across said first circuit branch and effective when said first transistor (T) is in the conductive state to so reduce the value of said bias developed across said bias resistor (R7) as to render said second transistor (T2) nonconductive, said diode means (D6 and D7) being effective to prevent the development across said bias resistor (R7) of a potential sufficiently high to maintain said second transistor (T2) in the conductive state even though in its conductive state said first transistor (T) is substantially less than fully conductive.

5. An electrical protection system in accordance with claim 4 in which said protected place has at least one additional protective device of the disturbance-detecting type including an alann relay switch having contact points movable to open position in response to a disturbance detected by said addi tional protective device, the contact points of said alarm relay switch being connected in series with said first circuit branch, whereby when said contact points are open no potential will be developed across said bias resistor (R7) and said second transistor (T2) is thus rendered nonconductive.

6. An electrical protection system in accordance with claim l in which said indicating means is a milliammeter, and in which said means for connecting said indicating means with said alarm switch means and with said means for deriving potential is a transistor (Tl) which is made conductive by the application to the base thereof of a potential directed thereto by the placing of said manually controlled switch means in said another mode, and in which said electronic switching means is e`ective to cause a flow of current through said transistor (Tl) and said milliammeter which gives a visual indication of said current flow so long as said alarm switch means is not in an alarm state, and in which said electronic switching means is effective to render said transistor (Tl) nonconductive when said alarm switch means is in an alarm state thus terminating said ow of current through said milliammeter which gives visual indication of such termination.

7. ln an electrical protection system in accordance with claim l the further improvement which comprises a silicon controlled rectifier (SCR) in said protected place for locking in an alami signal caused by a possibly momentary change in the conductivity of said alarm switch means when said manually controlled switch means is in said another mode, said silicon controlled rectifier (SCR) having an anode and a cathode connected in series with and polarized in the direction of current flow in a parallel branch of said line only when said manually controlled switch means is in said another mode, said silicon controlled rectifier (SCR) havinga ate connected with said electronic switching means, and said e ectronic switching means being effective only when the state of conductivity of said alarm switch means is changed to the alarm state to supply to said gate a potential sufficiently high in value to render said silicon controlled rectifier (SCR) continuously conductive in the direction of polarization thereof thereby causing an increase in current flow in said line which will be detected by said current-sensitive means in said station and which will persist until said current flow in interrupted to restore said silicon controlled rectifier (SCR) to a nonconductive state.

il t t il UNITED STATES PATENT OFFICE CERTIFICATE 0F CORRECTION Patent No. Dated November 23,

Frederick G. Hill Inventor(s) It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 6, line 43, "BD" should read BL line 62, "conductive" should read non-conductive Signed and sealed this 25th day of April 1972.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents :ORM P01050(1059) uscoMM-Dc soave-peo UTS GOVERNMENT PRINTING OFFICE 10|' O-SSSI

Claims

1. In an electrical protection system in which a protected place is connected to a station by a conductive line, said station having a source of direct current potential coupled to said line and having current-sensitive means coupled to said line to detect changes in current flowing through said line, said protected place having: at least one protective device of a disturbance-detecting type having alarm switch means the conductive state of which is changed from a normal to an alarm state in response to a disturbance of a particular type likely to be produced by an intruder in said protected place; manually controlled switch means operative in one mode to prevent a change in the conductive state of said alarm switch means to the alarm state from altering the current flow in said line; and said manually controlled switch means being operative in another mode to permit a change in the conductive state of said alarm switch means to the alarm state to alter the current flow in said line; the improvement which comprises means for testing at least said one protective device comprising: a disturbance simulating means operable at will within said protected place to produce a disturbance of a type to which said disturbance detecting device is designed to respond; means for deriving an operating potential for use in sensing the state of conductivity of said alarm switch means from said source of direct current in said station when said manually controlled switch means is in either said one or said another mode; electronic switching means including means utilizing operating potential derived from said means for deriving potential to sense the state of conductivity of said alarm switch means; indicating means in said protected place for giving a recognizable indication of the state of conductivity of said alarm switch means; and said electronic switching means including means for connecting said indicating means with said alarm switch means and said means for deriving potential only when said manually controlled switch means is in said one mode, whereby only when said manually controlled switch means is in said one mode the change of conductivity of said alarm switch means to the alarm state in response to said disturbance simulating device is effective to produce said recognizable indication by said indicating device.

2. An electrical protection system in accordance with claim 1 in which said alarm switch means comprises contact points movable to open or to closed position by an armature of an electrical relay actuated by said one protective device in response to a disturbance of said particular type.

3. An electrical protection system in accordance with claim 1 in which said alarm switch means comprises a first transistor (T) changeable to conductive or to nonconductive state by said one protective device in response to a disturbance of said particular type.

4. An electrical protection system in accordance with claim 3 in which there is provided a second transistor (T2) and a first circuit branch connected across said means for deriving an operating potential said first circuit branch including diode means (D6 and D7) polarized to conduct current from one side of said means for deriving an operating potential to the base of said second transistor (T2) and a bias resistor (R7) connecting said base to the other side of said means for derivIng an operating potential, the potential thus developed across said resistor (R7) being sufficiently high in value as to maintain said second transistor (T2) in conductive state, and in which said first transistor (T) is connected in series with a second circuit branch shunted across said first circuit branch and effective when said first transistor (T) is in the conductive state to so reduce the value of said bias developed across said bias resistor (R7) as to render said second transistor (T2) nonconductive, said diode means (D6 and D7) being effective to prevent the development across said bias resistor (R7) of a potential sufficiently high to maintain said second transistor (T2) in the conductive state even though in its conductive state said first transistor (T) is substantially less than fully conductive.

5. An electrical protection system in accordance with claim 4 in which said protected place has at least one additional protective device of the disturbance-detecting type including an alarm relay switch having contact points movable to open position in response to a disturbance detected by said additional protective device, the contact points of said alarm relay switch being connected in series with said first circuit branch, whereby when said contact points are open no potential will be developed across said bias resistor (R7) and said second transistor (T2) is thus rendered nonconductive.

6. An electrical protection system in accordance with claim 1 in which said indicating means is a milliammeter, and in which said means for connecting said indicating means with said alarm switch means and with said means for deriving potential is a transistor (T1) which is made conductive by the application to the base thereof of a potential directed thereto by the placing of said manually controlled switch means in said another mode, and in which said electronic switching means is effective to cause a flow of current through said transistor (T1) and said milliammeter which gives a visual indication of said current flow so long as said alarm switch means is not in an alarm state, and in which said electronic switching means is effective to render said transistor (T1) nonconductive when said alarm switch means is in an alarm state thus terminating said flow of current through said milliammeter which gives visual indication of such termination.

7. In an electrical protection system in accordance with claim 1 the further improvement which comprises a silicon controlled rectifier (SCR) in said protected place for locking in an alarm signal caused by a possibly momentary change in the conductivity of said alarm switch means when said manually controlled switch means is in said another mode, said silicon controlled rectifier (SCR) having an anode and a cathode connected in series with and polarized in the direction of current flow in a parallel branch of said line only when said manually controlled switch means is in said another mode, said silicon controlled rectifier (SCR) having a gate connected with said electronic switching means, and said electronic switching means being effective only when the state of conductivity of said alarm switch means is changed to the alarm state to supply to said gate a potential sufficiently high in value to render said silicon controlled rectifier (SCR) continuously conductive in the direction of polarization thereof thereby causing an increase in current flow in said line which will be detected by said current-sensitive means in said station and which will persist until said current flow in interrupted to restore said silicon controlled rectifier (SCR) to a nonconductive state.