US2821699A - Burglar alarm - Google Patents

Description

Jan., 28, 1958 M. w. MUEHTER BURGLAR ALARM Filed Dec. 30, 1955 I I I I IN l ZOTrdFW I ,QEPZMU .N MN tm WN rI I l l I l I I I I.

INN QN MIIIIIL United States PatentY BURGLAR ALARM Manfred W. Muehter, Nutley, N. J., assignor to American District Telegraph Company, Jersey City, N. J., a corporation of New Jersey Application December 30, 1955, Serial No. 556,633

4 Claims. (Cl. 340-276) The present invention relates to supervisory systems and more particularly such systems which include a protection circuit for signaling the entering of a protected area by an intruder.

Protection circuits have been provided which include one or more components which when actuated by an intruder seeking to enter a protected area results in the actuation of an annunciator or the like located at a central or supervisory station. The protection circuit components may include, among other things, contacts actuated by the opening of a door or window or conductive foil which is broken, as when a window to which the foil is applied is broken. The local protection circuit is usually in circuit with a supervisory circuit which may include the power supply, generally a battery, and various signaling devices such as relay actuated annunciators which respond to a change in the current flow through the local protection circuit. Decrease in current flow may represent a break impulse while an increase in current ow may represent a ground impulse. Relays provided at the central station respond to these impulses and initiate operation of signaling devices.

Hitherto, considerable effort had been expended to insure dependable transmission of break and ground impulses to the central station and to provide apparatus at the central station which consistently responded to such impulses. Nevertheless, such systems leave much to be desired. For example, a transient, short duration, decrease in current liow often results in the initiation of a signal as though a true break impulse had been received. Again, a break impulse may be of such short duration as to require the presence of a sensitive or fast acting break impulse relay in order to secure initiation of a signal at the central station which, in turn, renders the system objectionably sensitive to spurious impulses.

It is, therefore, a principal object of this invention to provide a supervisory system including a protection circuit which substantially reduces or minimizes the occurrence of spurious signals due to transient effects.

Another object is to provide a protection circuit in which transient effects of relatively short duration such as may be caused by vibration, momentary shock or the like, are ineffective to initiate an alarm signal, thereby substantially reducing the occurrence of spurious signals while at the same time insuring positive response to relatively short duration signal impulses.

In accordance with my invention I introduce a delay period following actuation of a protection device so that immediately following such actuation and for the duration of the delay period, the condition of the circuit as sensed by the supervisory station along the connection line remains unchanged. I preferably utilize a slow-release type relay characterized by a delay period which is long enough to permit operation of the signaling device at the central station. The central station signaling device is selected so that its time characteristic is long compared to the relatively short time duration of spurious impulses which may occur during service, while the delay period provided after actuation of a protection device insures sufficient time for the central station device to react thereto.

Further objects as well as advantages of this invention will be apparent from the following description and the accompanying drawing in which Figure 1 is a schematic diagram showing the normal condition of a protection circuit in accordance with this invention;

Figure 2 is a schematic diagram illustrating an intermediate step in the actuationof the circuit; and

Figure 3 is a schematic diagram of the circuit in the condition in which an alarm signal is initiated.

Referring now to the drawings in detail protection devices which may be used about an area to be protected in connection with doors or windows include switches indicated at 10 and 11 having movable switch members 12 and 13, respectively. Switch device 10 has a protection on contact 14 normally engaged by switch member 12 and a grounded contact 15. Switch device 1l has a protection on contact 16 and a grounded Contact 17. A fixed resistance is indicated at 1S representing a conductive foil, such as may be utilized to signal the breaking of a glass through which entrance may be made into the protected area. It will be understood that the number and type of protection devices utilized may be varied as desired. However, for illustrative purposes, devices 10 and 11 are of the type that remain as shown in Figure l in the absence of a disturbance and are actuated upon opening of a door or window to the position as shown in Figure 2 and 3 in connection with device 1i) where switch member 12 is shown in engagement with grounded contact 15'.

A slow-release type relay R has a coil one side of which is grounded as indicated while the other side is connected through connection 19 to front contact 20 associated with contact arm 2l and back Contact 22 while connection 23 serves to connect said other side of relay coil R to back contact 24 associated with a front contact 25 and contact arm 26. Contact arms 21 and 26 are governed by relay R which with its coil energized main` tains the contact arms in engagement with their respective front contacts 2t) and 25. As indicated in the drawing, slow-release relay R may include a slug of a suitable material such as copper for delaying movement of the relay armature when the circuit to the relay winding is opened. Other types of slow-release relays may be used such as one provided with an auxiliary coil.

Back contact 22 and front contact 25 through connection 27 are connected to line 28 which includes variable line resistor 29 for adjusting current ilow as well as signaling devices represented by coils 30, 31 located at the central station for operating annunciators or other devices. Line 28 is connected to one side of power supply 32, indicated as a battery, the other side of which is grounded and connected to common ground connection 33. As indicated, common ground connection 33 is provided for power supply 32, grounded contacts 15, 17 and relay R to facilitate, among other things, maintenance of the proper current under normal conditions although local ground connections may also be utilized. Coil 30 represents a signaling device which is actuated when the current ow in line 28 drops below a predetermined value and signals the occurrence of a break or open condition. Coil 31 represents a signaling device which is actuated when the current in line 28 exceeds a predetermined value and signals the occurrence of a short circuit or a groundv condition. Line resistor 29 is normally adjusted so that the steady current ilow along line 28 falls about midway. between the low requird to de-energize coil 36 and the high required to energize coil 31.

A manually operated day-night switch 3S may be prov' vided asshown so that the system may be placed in prol tection-on or protection-off service at will. Movement of the contact Earm of switch 35 to close its left-hand contact opens the circuit of relay R which on shifting contact arm 21 serves to complete the connection of line 23 to ground line 33.

With the various devices in their protection-ony condition, as shown in Figure l, the current path may be traced from current source 32 through central station coils 30, 31, along line 28 through line resistor 29, connection 27, contact 25, contact arm 26in its forward position, contact 14 and switch arm 12 ot' device 19, contact 16 and switch arm 13 of device 11, foil 1S, switch 35 in its righ-hand position, contact arm 21 also in its forward position, contact 20, connection 19, relay coil R and then through ground connection 33 back to source 32, thereby completing the circuit.

As was indicated, relay E is of the'slow-release type and its armature which governs contact arms 21, 26 does not immediately drop out when current ow through its coil is interrupted. The relay is selected such that the delay period provided between interruption of current through its coil and actuation of contact arms 21, 26 is somewhat greater than the time required for signaling device 30 to respond to decrease in current below a predetermined value. In the case of relay 30 this would be the time required to permit its armature to complete its excursion. The coil of relay R also has such resistance that when it is cut out of the circuit the current in line 28 increases above the value necessary to energize coil 31 to pick up its armature. With relay R in the circuit sutlicient` current flows to prevent dropping out of the armature of coil 3i).

Assuming that protection device is associated with a door which is now opened, switch member 12 is actuated to disengage its contact 14 and then to engage its contact 15. Current to relay R is interrupted when switch member 12 leaves contact 14 but since the relay is slow acting, the condition shown in Figure 2 continues through the delay period, characteristic of the relay. Thus, a break or open circuit condition is presented to line 28 which is sustained for a sufliciently long time to insure de-energization of coil 30 for a time long enough for its armature to drop out, thereby actuating the alarm device associated therewith.

At the expiration of the delay period the armature of relay R moves to disengage contact arms 21, 26 from their front contacts 20, 25 and to engage them with their respective back contacts. This presents a ground condition to line 28 through resistor 29, contact 22, switch 35, protective device 18, switch member 13 in engagement with contact 16, switch member 12 now in engagement with grounded contact 15. The increased current flow through line 2S and coil 31 results in energization of coil 31 and actuation of its `alarm device.

The .delay period provided by relay R not only insures proper operation of device 30 at the central station .butV

also makes it possible to utilize a slower Vacting device than hitherto. Consequently device 30 even though slower acting than heretofore, nevertheless responds to short duration break impulses due to the presence of -relay R and at the same time remains insensitive to short duration transient efr'ects, which may occur along the connection between the central station and the protected area. Another cause of spurious break impulses is shock or vibration at the protected area. In the absence of a slow device 30 the break condition would be represented at once even though members 12 and 13 do not reach their contacts 15, 17 but return almost immediately to their contacts 14, 16, thereby preventing any discrimination between such a condition and a true break impulse.

It will be understood that the system. is restored by returning switch member 12 or 13 to its "respectiveprotection-on contact and unnecessary signaling is avoided when relay R is re-energized and shifts its contact 'arms 4 back to their normal position by utilizing contacts of the make-before break type.

It will be apparent that as in the case of the protection devices, operation of day-night switch 35 also results in the transmission of a break impulse. Consistent detection and response to this break impulse is also important and even though switch 35 may be operated rapidly relay R insures transmission of an etective impulse.

The terms and expressions which have been employed herein are used as terms of description and not of limitation, and there is no intention in the use of such terms and expressions of excluding any equivalent of the features shown and described or portions thereof, but it is recognized that various modications are possible within the scope of the invention claimed.

1 claim:

l. In an electrical protection system, the combination of a pair of signaling devices at a central station connectedin series relation with one responsive to increase in current therethrough above a predetermined upper value and the other responsive to decrease in current therethrough below a predetermined lower value, a slowrelease relay and contact means governed by said relay, at least one protection device in a protected area and a single pole double throw switch means governed thereby and normally completing through one of its contacts a series circuit between said signaling devices and said relay through said contact means, a power supply connected in said circuit with the current ow normally ranging between said predetermined values, said switch means in its actuated position providing a connection to ground through its other contact, actaution of said protection device and the switch means governed thereby serving to open the circuit between said power supply and said relay thereby reducing the current ow through said signaling devices substantially below said lower value, said relay being adapted after a predetermined delay period to actuate said contact means, and said contact means with said relay de-energized shunting said signaling devices around said relay to ground through the connection thereto provided by said switch means.

2. In an electrical protection system, the combination of a pair of signaling devices in series relation at a central station with one of said signaling devices responsive to decrease in current therethrough below a predetermined lower value and the other responsive to increase in current therethrough above a predetermined upper value, at least one protection device at a protected area having single pole double throw switch means governed thereby, means for normally maintaining the flow of current through said signaling devices at a value ranging between said lower and upper values and including a slow-release relay and contacts governed thereby, said slow-release relay being normally connected on one side thereof through one ofthe contacts of said switch means and said contact means in a series circuit with said signaling devices, said contact means being operable by said slow-release relay upon deenergization thereof only after a predetermined delay period, said switch means upon actuation thereof by said protection device opening the circuit at said one contact between said signaling devices and said slow-release relay thereby increasing the impedance of said circuit presented toward said signaling devices and decreasing the flow of current through said signaling devices below said lower value for actuating said one signaling device, said switch means in its actuated position through its other contact providing a connection to the other side of said relay, said contact means being adapted to connect said signaling devices to saidother contact and thereby bypass said signaling devices around said relay after said delay period for decreasing the impedance presented to and increasing the'ilow of current through said signaling devices above said upper value and actuating said `other signaling device.v

3. in an' electrical protection system, the combination.

of a pair of signaling devices in series relation at a central station with one of said signaling devices responsive to decrease in current therethrough below a predetermined lower value and the other responsive to increase in current therethrough above a predetermined upper value, at least one protection device at a protected area having single pole double throw switch means governed thereby, double throw contact means on opposite sides of said switch means, a slow-release relay governing said contact means and having one side connected to ground and the other Side thereof normally connected in a series circuit with said signaling devices through said contact means and one of the contacts of said switch means for maintaining the ow of current through said signaling devices at a value between said lower and upper values, said switch means upon actuation thereof by said protection device opening said series circuit at said one contact thereby reducing the tlow of current through said signaling devices below said lower value to actuate said one signaling device, said slow-release relay maintaining said contact means unactuated `for a predetermined delay period following actuation of said switch means, said switch means in its actuated position through its other contact providing a connection to said grounded side of said relay, and said slow-release relay after said delay period actuating said contact means to connect said signaling devices to said other contact and thereby bypass said slow-release relay for increasing the flow of current through said signaling devi-ces above said upper value and actuating said other signaling device.

4. In an electrical protection system, the combination of a pair of signaling devices in series relation at a central station with one of said signaling devices responsive to decrease in current therethrough below a predetermined lower value and the other responsive to increase in current therethrough above a predetermined upper value, at least one protection device at a protected area having single pole double throw switch means governed thereby, means for normally maintaining the ow of current through said signaling devices at a value ranging between said lower and upper values and upon actuation of said switch means by said protection device for reducing the How of current through said signaling devices below said lower value for a predetermined interval and thereafter increasing the How of current above said upper value, said means including a slow-release relay, a pair of contact means governed by said relay aud on opposite sides of said switch means with said relay normally energized and in a series circuit with said signaling devices through one of the contacts of said switch means and said contact means, ground connection means connected to the other contact of said switch means engaged upon actuation of said protection device, and means for shunting said signaling devices to ground around said relay comprising said contact means and said other contact of said switch means, and means for retarding actuation of said contact means by said relay yfor said predetermined interval.

References Cited in the le of this patent UNITED STATES PATENTS 1,840,637 Reid Jan. 12, 1932 2,093,600 Danzlar Sept. 21, 1937 2,492,432 Laford Dec. 27,1949 FOREIGN PATENTS 563,590 Germany Nov. 7, 1932

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