US2492432A - Electrical protective alarm system - Google Patents

Description

. 27, 1949 H. M. LAFORD ELECTRICAL PROTECTIVE ALARM SYSTEM 2 Shets-Sheet 1 Filed July 27, 1946 INVENTOR H. M. LAF'ORD ATTORNEYS @em 7, Y H. M. LAFORD 9 9 ELECTRICAL PROTECTIVE ALARM SYSTEM Filed July 27,1946 2 Sheets-Sheet 2 1 1 Pas a INVENTQJ; #34 M. LAF-mi m BY I: g

ATTORNEYS.

Patented Dec. 27, 1949 2,492,432 7 ELECTRICAL PROTECTIVE ALARM SYSTEM Herbert M. Laford, Allwood, N. J., assignor to Electro-Protective CorporatiomNewark, N. J., a corporation of New Jersey Application July 27, 1946, Serial No. 686,694

7 Claims. 1

This invention relates to electrical protective alarm systems, such as burglar alarms.

system which is foolproof, extremely simple to test, use and supervision, and is also compact and inexpensive. A single container or housing may be provided to house all the units of the apparatus, except for the protective wiring itself which obviously must be placed in or around the door, window or other location that might provide unauthorized entry.

The foregoing and other objects of the invention will be best understood from the following description of exemplifications thereof, reference being had to the accompanying drawings wherein Fig. 1 is a diagrammatic representation of an electrical protective alarm system according to the invention; and

Fig. 2 diagrammatically illustrates a modified apparatus of the invention.

In the apparatus of the invention, a self-contained battery is provided so as to avoid reliance on the public utilities as well as to make an external vulnerable power supply cable unnecessary. Two protection circuits are provided, one of which is permanently set to detect tampering, as,

for example, with show windows, unused doorways, the housing of the burglar alarm apparatus itself, etc. The other circuit is applied to doorways that are locked for the night, for example, and is only set for night use. This arrangement enables the detection of unauthorized tampering during the day when prior art devices are normally not functioning. This tampering may be unauthorized entry into window displays, showcases, safes or the like or may merely be attempted alteration in the operation of the alarm or its {controls to render them inoperative for night use.

Another feature of the invention is the provision of delaying'means to prevent the sounding of false alarms by transient vibrations which might momentarily open contacts.

Fig. 1 illustrates diagrammatically one form of protective alarm system of the invention. It has a control unit housing 35 containing a battery 20, a multi-blade key-operated setting switch 22, a buzzer 32 and associated wiring. An alarm bell 34 may be in a separate housing'placed high upon an outside wall so as not to be easily available although easily heard by passers-by or the patrolman or watchman on his rounds. Permanent protection wiring 24 and releasable protection or tamper wiring 2| are suitably disposed on windows as window foil lacing, on doors and in any other location that might afford unauthorized entry.

The key-controlled multi-blade setting switch 22 has two sets of contacts, three contact blades in each set and each set having a member connecting the movable endsof its blades. A cam 30 mounted on a shaft 28 is located between the sets of blades so that by rotation in one direction, the day'set of switch'contact blades DI, D2 and D3 is moved to the right (as seen in the figure) and by rotation in the other direction, the night set of switch contact blades NI, N2, and N3- is moved to the left. In a neutral intermediate position of thecam' 36, as illustrated, the contact blades ofswitch 22,are all biased centrally toward the cam.

The control unit also includes an alarm relay 23 and alocking relay 36. When switch .22 is in the neutral position ,shown, the battery is placed in circuit with the releasable protection "wiring 2I, contacts D2 of switch 22, the permanent protection wiring 24 and the windings of the alarm relay 23, all in series. This circuit also includes a milliammeter 25 and a variable resistance 26 enabling the current to be read and adjusted-to a suitable value suflicient to actuate the armature, of the alarm relay 23 and hold it away from its contact. When the switch 22 is in the intermediate or off position shown, a .c-apacitor 42 is placed in series with the protective circuit connected across the winding of the alarm relay-23 by means of the blade DI. When the switch 22 is placed in the night position- 5 by rotation of the shaft 28 so that the cam 30 moves the left-hand set of contact blades to the" left, the contacts of the respective switch blade pairs NI, N2 and N3 close. The NI contact pair connects one terminal (positive) of the battery with the LI contact blade of the locking relay 36, the N2 Contact pairsimultaneously connecting the same battery terminal with the L2 contact of locking relay 36. The N3 contact pair is connected in series with the L3 contact pair and both together establish a shunt circuit across resistor 21 connected in a circuit used for sounding an alarm at a distant central alarm station 41 located, for example, at police headquarters.

The LI contact leads to the other (negative) terminal of the battery through the windings of the locking relay 36. The L2 contact blade leads to one terminal of the outer alarm bell 34, the other terminal of which is connected to the negative terminal of the battery. The L3 contact pair is used to close the circuit of the buzzer 32 in addition to its shunting function described above.

Conventional tamper contacts 31 are inserted in the various circuits in the housing of the outer alarm bell 34, the housing of the control unit 35, as well as in the protection or tamper circuits themselves and are sensitive contacts which open upon roughv handling. The tampencircuit may be afiixed to a door=-50,a-as shown. A::pair.of detachable contacts are provided on a parting surface, one portion of each contact being fixed to the door frame and the other portion of the contact 5! fixed to the doorin sucha.manner that closing of the door. establishes a circuit through the detachable contactsiz5l. .The upper portion of the door 50 may be glazed, a metallic foil being applied to the glazed portion. The lower panel of the door may also have a foil attached. A small gauge wire screen .-.may..be

substituted for the metallic foil on'the lower panel of .the .door. A .key operated switch 52 ;-.parallels. the pair-.01. contactsil. andifunctions to keep the protection circuit inthe door closed even though. thedoor .istopen. Other parts of" the ,protection.circuitamay be similarly disposed in connection with sliding, swinging on immovable windows, transoms, ventilator openings and-even drawers ofsafes, desks. or other furniture.

.Any tamperingwith a, portion of the protection circuit -such-as, for. example," the breaking of "a foil-containing ,glass, panel. will open "the tamper circuit eithenbre'aking' the foil or the small gauge --.wire.s.creen, opening .theeasily opened tamper contacts .or. evenseverance of the wiring at other points. ,-An. openjtamper circuitdea'ctivates the ..windings.of.jthe galarm relay23 permitting the alarm relay armature to closethe circuit through the. windingsof. locking relay 36. Allthree armaituressoflthellocking r"e1ayf"36 are Zthus'caused .to close .their. individualgcircuits. The' Ll contact pair. lthe windings of jthe. locking relay a:

energized. .and. -.operated .even though' the open .tampencircuit ishlosdagainor the alarm relay contacts are opened. :The'LZ contact pair estabdishes. the circuittdthej'alarm bell 3,4, and.the.L3 contact pairssetsun operation'lthe buzzer 3.2 and .also shunts .the. resistor 2], thereby. setting in .-.,-operation theldistantlalarm' .bell" 40.

- ';The keyoperationbfi'the setting switch 22 may beladjustedsolthat'the.key cannot be withdrawn .unless the .switcnisset .in eitherlits.dayor ffnightf position,.to insure'the setting of the alarm ibyanyone taking the key away.

.The wires in cableitil connectithebatteryxin .'.the control unit iwiththei'windings 'of' the distant.alarmrelaytdandthe windings of the ldistant .yvarning relay 39 in' series through the .resistcnzl' andits accompanying shunt. With the resistor shunt-:circuitopened, the resistor 21 his so chosen oradjusted; as to-permit passage of sufilcient current throughthe' distant relay 1 windings 38, 39 to-actuate only the armature of the warning relay-39 and not enough to actuate -the*armature of' the *distant alarm-relay '38. Warning -relay' 39-is selected 'or' adjusted to raise its armature when a relativ'ely-small: amount of current "is" passed through its windings and to "keep its-contacts open as longasa current at least -as high as this n'iin-imumpasses through its windings. "Thedistantalarm relay 38, howeveryis-selected or-adjusted so-as 'to be less sensitive and-'toraise itsarmature-only when a larger --current passes through its wind-ings. The' raising-of the armature of the distant'alar-m relay will cause'sounding of the distant alarm bell 40,

whereas' the dropping of the armatureot the 4 warning relay 39 will cause sounding of the warning buzzer 4|.

When the control unit is set in its night" position and the locking relay 36 actuated as 3 by a break in the protection circuit upon unauthorized entry into the protected premises, the .distantalarmbell will sound and will continue to sounduntil the key-pperated switchi22 is moved from the night position. Failure of the power supply in the control unit, or open circuiting of wiring in the cable 60, or its associated wiring, -:.willzdeaactiizatefthemvindings of the warning relay 39 and permit its armature to close the circuit .toi.the warning. buzzer 4| from the distant power ..supply.68. Forlfthe provision of the local protective current through the protection circuits and operationof= :the-:alarm 34 and buzzer 32 only about-4V or 6 volts supplied by local battery 20 are necessary. The distant alarm, however, sometimes requires higher voltage for operation through long-"cables" inwhich case 'a" separate local battery-supply may='-be ';-p1'ovided,-' operating *through a separate *p'a-ir of'contacts-"i-n the 'locking 'relay- 36.

'The --lines ----in the cable -61! =are-=usually -leased lincssimilar- 'tothose provided by the telephone "company and these lines are-sometimes open circuited without notice.

-='Itis understood that where-"the relay-=arma- =-tures are biaseddownwardly by the action of gravity and moved --upwardly under-the action ofthe activated windingsy -these= armatures may be operated in any othenmannenas-bybeing held "upward-1y by "springs-and pulled downward-ly by the windings -when= activated. Similarly a dig-ht -'--may-""beused-insteai iof a vvar-ning buzzer- 4 lto indicate when investigation of the control unit and/or cable'circuits is necessary. Furthermore, althou'ghthe power supply is shown :by plus and minus signs to be D. C., A.--"C. supply may-be used-'w-it-h equal faciiity andthe same resul-ts with relays that respond to-A-FC.

'Thecapacitor i Z on series with the protective -circuit connected to' the-'-windin'gs-;of alarm relay 23 servesas -an electrical delaying means and ---.p-revents the sounding of f alse alarms ca-used --'by =intern' .ittent. open circuits, such as-may be wpno'duce'd by the vibration or doors, windows,- etc. by-windsi thunden -heavy traffic :or thelike. This actions-results from the ability of the capacitor to-' store:-electric charges.

With the protective :current i flowing through the protectiorr-circuits as adjusted=by=the resistor 26;'avoltage appearslacross the terminals of the 1. .nd ings of thealarm relay 23 uwhich windings shave-an appreciable resistance. f with the switch 2 2 in the 'i night: position, :the capacitor 42 is also charged vwdthQthessamenpotential' .and a momentary openinginLthepr-Qtection circuits will (30: cause zthe capacitor to idischarge through. the viwindings. 0f the relayi 23eso that itwontinues t to -.holdi its armature=raway from-.titszcontact for ,1 a may shortzztime. :Theccurrent may be'aboutfive milliamperesifatheacurrent drain. on. the battery :2 Bristol be minimized. :With suchsmall currents the nseiulLlif-erof the standardlargesize: dry cells uwillzbe almost :asalongtas thetshelf; life.

,rsetting. ecf; ithe.- -.switche22 totthe '"f day posizition,;.vvith ibladesiDl .-D2o;D3 ,;thr.own; to: the right,

- opens-ithe capacitor circuit, the* D2. contact pair opening the-:rernovable: protection .-wiring:;circuit an'd ljthe DI i-conta'cts, substituting -for the caqoaciton fl' aresistor 44 chosenor -adj-uste'd to have a a "resistanceapproxim'ately equal to r the resistance of the:removablei protectionz'wiri-ng circuit so as to maintain the current approximately constant regardless of the setting of the switch 22.

The D3 contact pair is'in parallel with the NI tion but the outer alarm bell 34 and the distant alarm will not. Such arrangement gives all the desired daytime protection and additionally permits the testing of the entire system or any portion without the embarrassment and inconvenience of the sounding of the external alarms. A manually operable switch 45 mounted inside the control unit is provided in the capacitor circuit so as to permit opening of this circuit for test purposes by authorized individuals with the switch 22 in either night or off position. The day operationv since it is without the capacitor 42 will cause the sounding of the alarm upon such intermittent open circuits in the protection circuits as are caused by transient vibrations, as indicated above, and is useful for determining when the transient vibrations become serious enough to cause false alarms at night.

Upon the authorized opening of the protected premises in the morning, the key-operated switch 22 is set to its off position to interrupt the sounding of the alarm. This method of authorized entry is satisfactory when the distant alarm is not installed, but to prevent any alarm sounding upon entry, an additional key-operated switch 52 may be operated before entry tomaintain the door protection circuit closed when the door is opened. The control unit mayalso be mounted so that the key-operated switch 22 is externally available and the switch 52 may then be dispensed with.

The above described apparatus is foolproof, simple to operateand simple to test having very few component members. The construction may be made more foolproof and simple, however, by incorporating the alarm bell 34 in the control unit thus removing. some of the wiring from its vulnerable, exposed, location. Further simplification may be effected byproviding the alarm relay 23 with another set of contacts which open the tamper circuit upon the de-activation of its winding. This causes the alarm relay to lock itself and makes it unnecessary to use a separate locking relay. The apparatus of Fig. 1 may be made more foolproof by providing additional relay means to detect short circuits, such as may sometimes be produced by the cutting of a pair of wires leading to the tamper circuits. These tamper circuits have inherent resistances or can be adjusted to have. resistances of the order of several hundred ohms, and the short circuit deteeting relay may be adjusted so as only to be actuated when more current flows through tive alarm system of Fig. 1, modified in the manner described above. It comprises a control housing I 35 in which are housed a local battery I2Il, an open-circuit detector relay I23, a buzzer I32,

and a setting switch I22 interconnected through operating circuits including. rheostats I44 and I26 to the releasable protection or tampe r W11.-

ing I2I and to thehpermanen't protection" or.

.its windings than can flow through the relatively high resistance of the protection circuits. Additional simplification may be effected by tamper wiring I24 for operation in the manner described in connection with the corresponding elements 20, 23, 32. 22, 44, 26, 2| and 24 of Fig. 1. A capacitor I42 is arranged to be connected between the protective circuit and the winding of the alarm relay I23 by a switch I45 for operation in the manner described in connection with the capacitor 42 and switch 45 of the system of Fig. 1. The alarm device or bell I34 is shown mounted within the housing I35 instead of outside thereof. The milliammeter 25 is arranged to operate in the same manner as in the system of Fig. 1.

By way of example, a protective system of the type shown in Fig. 2, may be designed to give effective protection with conventional protective relays and alarm devices if the current through the two alarm detector relays I23 and I53 is adjusted to about five or six millimeters so as to be suificient to hold in closed position the mainswitch contact blades of the open circuit alarm relay I23, but insufiicient to close the main switch contact blades of the short circuit alarm relay I53, the latter being actuated to the closed position in which it sets off the alarm, if any part of the protective circuit, including tamper circuits I2I, I24, is short-circuited.

The protective system of Fig. 2 is also shown.

provided with the additional alarm relay I53 provided with two sets of switch contacts which are connected in the protective circuit to complete an alarm circuit and set ofi the operation of the alarm bell I34 whenever any part of the protective circuit including the protective circuit portions I2I, I24 is short-circuited. In other words, in the same way a's'the open circuit alarm relay I23 is arranged to be actuated to the operative position for setting ofi the alarm when any portion of the protective wiring circuit is opened, the short-circuit detecting alarm relay I53 is actuated to the operative position if portions of the protective circuit including the protection or tamper circuit portions I2I, I24 are short-circuited. An additional capacitor I56 is arranged to be comiected in between the protective circuit and the actuating windings of the short-circuit detecting alarm relay I53 by the switch I45 in order to perform for the shor -circuit alarm relay I53 the functions which the capacitor I42 performs for the open-circuit alarm relay I23. The protective circuit of Fig. 2 is also arranged to be interconnected through a wire cable'ltii to a distant central alarm station I4'I for setting off a distant alarm device I46 in a manner analogous to that described with the corresponding elements 50, 41 nd 46' of Fig. l.

- The distant alarm equipment I 41 is shown provided with two relays I68, I69, which control the operation of the distant alarm device I46, the operation of the two relays I68, I69 being controlled by the operation of additional switch contacts I25, I of the open-circuit alarm relay I23 and the short-circuit alarm relay I53. In the system of Fig. 2, the energy source, namely the battery I25 of the local alarm system is utilized to control the operation of the distant alarm equipment I41. The additional blade contacts I25, I55 of the twoalarm relays I23, I53, respectively, are arranged to connect a local resistor I in parallel with a resistor I66 connected across the leads through which the wires of cable i611 are connected at the distant alarm equipment I41 to its two operating relays I68 and IE9, the. windings of which are connected I in series with the circuit, leading by way of the ?7 wires- ,4 6 hand: the. operatingzelementspof; the-rlocal equipment i 1352130 .the local energy: source [20. .In". thegdistant; alarm equipment M1,; relay 568 is;.ar,rangednto operate aspzan vopenecircuitdetects n relay,: and the relay. 1 Skis arranged to. oper- .ate-as a shortrcirouit-detecti g relay; for; setting .{Ofia thev distantsalarmnbelh I 40'-wheneve1-,;an opencircuit conditionomshort-circuit condition .occurs 3011'; the protective Wiring --circui.t,; including ..protec,tive :wiring circuit cportions I 2 l 1.24,, inwa :rnanner. analogous: to 3 thegoperationchof i the .corresponding local alarmdetecting relays I23, I53.

The current through the serially connected :ivindings -.of the; remote open-circuit ..-detecting relay itegandshortecircuit .detectingvrelay 4.69 ,;is so ;=,adiuste.d that "when w the two resistances 165, Hi6 remain intercon=nected .With 3 .the cable circuit 168 of thecdistantwalarm relays, the cur- :rent through the. winding oi the'remote open-circuit alarm relay; 1 88 will be -su-fiicient to maintain {-1165 is open, thereby e-decreasing the current in .theyremote open c-ircuit -relay- [Bea-and increasing .the current :in. theshortwircuit.alarrn relayit 9, thereby-actuating their respective contacts to the .olosed p sition inawhich'thev complete anenergizing circuit for ,the remote 1.alarm' device M0 l and setting it. oii to sound. the alarm.

-With sucharrangemenn an open circuit on the protective or tamper. circuits !2 i,:.l 24-.will-.act uate the local open-circuit ;detector:"relayv I23 .to the alarm -position,:therehy causing the setting off 10f the-local alarm,device I34. and.the;remote alarm device MB. =In-. a" similar; manner,. hort- .circuiting of any parts .,0f =.the localgprotective .wiring. circuits 12],. 124. will actuate the shortcircuit detecting relay. .l23utothe-alarm position, thereby setting into-soperation. the-local alarm device l34-and the; remote alarm. device I43. .if desired, thezremote-alarrn station=l47 may-be provided with 1 an 5 additional-energysupply. source .connected across leads l 18.

When using a-short circuitdetecting apparatus, as inF-iggEh together .withan externally operated shunting switch-.52 care must be taken that the shunting line operated by the switch-.52 yincludes a resistance approximating-.that, oi the wiring in the door 55.

The construction off .the setting :sw-itch. 22 of .;Fig.. land the corresponding-switch1220f Fig.2 should be. such that when moved-to the day --setting; thevDil contact pair does not '=make con- ..tactuntil aiterthe DI contact blade closesthe .protective circuit through the. resistor=44- .to pre- .vent the actuation of the locking relay 36 before the protective circuit. is 1 set.

The. contact blades ofthe. setting.,switch,2'2 .of. the system shown in. Fig. 2. should..also,be -so designed that the, extreme right-hand .blade .does not open its left-hand. contact circuit until the protective circuit through .the resistor .144 is Closed.

' The features and principles underlying the. in- "70 vention describedabove inconnection with specific exemplifica'tions, will suggest to those skilled in the art many othermodi'fications thereof. :For example, it appears obvious. that. the permanent protection circuit may be placed'in parallel with "its-contacts open,:-.andthereurrent tl lrough the .thel temporary tamper-circuit. The ,relays 28.119 .theniadjuste'd to. respond tqa "decrease in; current caused by. -opening-.one:of' the temper. circuits ,or adjusted for responding:toneither@aridecrease:or increaseof current to: also detect. the:shorting of one or both of the tamper circuits. Also a single condenser :.:s.hunted1 across the 1 series connected windings ofn-bothi'relays '52and'54 may'be sub- ;stituted; for. the two: condensers: of Fig. 2.

:1. 'Imanelectrical'protective:apparatuszhaving acsignal-;controlling;:protective wiringazcircuit .in- .cluding .alarmr-means, part'iof. the:.protective. wirajingscircuitobeing;:arranged;to:beset torindicate --day-;or;;night tampering and .part'zbeing tempo- -'rarilysettable to indicate night tampering; switch emeans. in the circuit for;activatingand-.,de-acti- .vating the. temporarily settable. circuit; detecting relay means .in'theicircuit responsive to opencir- :cuits in:the.pr.oteotive iwiring'forclosing an alarm circuit; actuating-said. alarm means; and rendertitse'lf .iinoperative: to. open .the1alarm circuit; -said: switch. means having a. setting that activates athezopencirouitzdetecting relay means to permit resetting .of the apparatus the apparatus having iaselfecontained'sourceroienergy and except for ;.the .protectivejwiring, .the: alarm means and cirecuit. connections between thealarmrzmeans and the remairideroi: the apparatuabeing contained iinas tamperrproof; container.

2. :In. an electrical, protective apparatus; having .;a;. signalqcontrolling protective wiring circuit in- :cluding alarm means, part of -the protective-wiruing circu'it .-being' arranged-to be set to indicate iday or, nightytampering and; part' being tem-po- =rarily .settable to .indicate night tamp ering: aswitche-means .inthe circuit; for :activating and de-activating the temporarily settable circuit; detecting r'elay xmeans; in:.the-:circuit: responsive "zto opencircuits in the, protectiveiwiringior closan alarm circuit; actuating saidzalarm ;means and rendering itself inoperative to open thealarm circuit; said sW-itch means having a .setting that activates .theopen circu'it detecting relay means to -permit resetting of the-apparatus; the apparatus having ass'elf-contained source. of energy and except for the protectivewiring, the alarm "means and circuit connections between the-alarm means and the rema-i-nder of the apparatus, being contained in a tamper-proof container;and delay -mea-ns in the-circuit thatprevents actuation of the relay means by intermittent; circuit changes such as those caused ivy-shakingof doors and 'windows' containing circuit elements from causes such as wind; thunder and "heavy ,trafiic.

'*3.-:In an electrical protective apparatus 1 havinga signal controlling protective Wiring, circuit including alarm means, part of the protective -wiringcircuit being arranged'to'be set to' indi- "oateday ornight tampering and part being tem- "poraii'ly. settable ,to indicate night-tampering: switchrneans' in' the circuit, for activating .and de activating the"temp0rari1y settable circuit; detecting IEIaY mGBIIS' iHIthQ circuit responsive *to'open' circuits in" the protective Wiring for closing an alarm circuit, .actuatingjsaid alarm means and'rendering itself ;'inoperative to open the alarm'circuit; relay means in the circuit responsive toshort circuitsv in the protective wiring for closing. an alarm. circuitand rendering its'elf inoperative to open the alarmcircuit; .said switch meanshaving a I setting. that dc-activates the short-circuit-responsive relay means and .ac- .tivates the.open circuit-responsive. relay .to per- '75 mit'resetting of the apparatus.

4. In an electrical protective apparatus having a signal controlling protective wiring circuit including alarm means, part of the protective wiring circuit being arranged to be set to indicate day or night tampering and part being temporarily settable to indicate night tampering: switch means in the circuit for activating and de-activating the temporarily settable circuit; detecting relay means in the circuit responsive to open circuit in the protective wiring for closing an alarm circuit, actuating said alarm means and rendering itself inoperative to open the alarm circuit; relay means in the circuit responsive to short circuits in the protective wiring for closing an alarm circuit and rendering itself inoperative to open the alarm circuit; said switch means having a setting that de-activates the shortcircuit-responsive relay means and activates the open-circuit-responsive relay to permit resetting of the apparatus; and delay means in the circuit that prevents actuation of the relay means by intermittent circuit changes such as those caused by shaking of doors and windows containing circuit elements from causes such as wind, thunder and heavy trafiic.

5. In an electrical protective apparatus having a signal controlling protective wiring circuit including alarm means, part of the protective wiring circuit being arranged to be set to indicate day or night tampering and part being temporarily settable to indicate night tampering: switch means in the circuit for activating and de-activating the temporarily settable circuit; detecting relay means in the circuit responsive to open circuits in the protective wiring for closing an alarm circuit, actuating said alarm means and rendering itself inoperative to open the alarm circuit; relay means in the circuit responsive to short circuits in the protective wiring for closing an alarm circuit and rendering itself inoperative to open the alarm circuit; said switch means having a setting that de-activates the shortcircuit-responsive relay means and activates the open-circuit-responsive relay to permit resetting of the apparatus; said switch means being operable by key; the apparatus having a self-contained source of energy and except for the protective wiring, the alarm means and circuit connections between the alarm means and the remainder of the apparatus, being contained in a tamper-proof container.

6. In an electrical protective apparatus having a signal controlling protective wiring circuit including alarm means, part of the protective wiring circuit being arranged to be set to indicate day or night tampering and part being temporarily settable to indicate night tampering: switch means in the circuit for activating and de-activating the temporarily settable circuit; detecting relay means in the circuit responsive to open circuits in the protective wiring for closing an alarm circuit, actuating said alarm means and rendering itself inoperative to open the alarm circuit; said switch means having a setting that de-activates an alarm circuit so that the, apparatus may be checked without actuating the alarm means; said switch means being operable by key; said switch means having a setting that activates the open-circuit-responsive relay means to permit resetting of the apparatus; delay means in the circuit that prevents actuation of the relay means by intermittent circuit changes such as those caused by shaking of doors and windows containing circuit elements from causes such wind, thunder and heavy trafiic; the apparatus having a self-contained source of energy and except for the protective wiring, the alarm means and circuit connections between the alarm means and the remainder of the apparatus, being contained in a tamper-proof container.

7. In an electrical protective apparatus having a signal controlling protective wiring circuit including alarm means, part of the protective wiring circuit being arranged to be set to indicate day or night tampering and part being temporarily settable to indicate night tampering: switch means in the circuit for activating and de-activating the temporarily settable circuit; detecting relay means in the circuit responsive to open circuits in the protective wiring for closing an alarm circuit, actuating said alarm means and rendering itself inoperative to open the alarm circuit; relay means in the circuit responsive to short circuits in the protective wiring for closing an alarm circuit and rendering itself inoperative to open the alarm circuit; said switch means having a setting that de-activates an alarm circuit so that the apparatus may be checked without actuating the alarm means; said switch means being operable by key; said switch means having a setting that activates the open circuitresponsive relay means to permit resetting of the apparatus; said switch means having a setting that de-activates the short-circuit responsive relay and activates the open circuit detecting relay to permit resetting of the apparatus; delay means in the circuit that prevents actuation of the relay means by intermittent circuit changes such as those caused by shaking of doors and windows containing circuit elements from causes such as wind, thunder and heavy trafiic; the apparatus having a self-contained source of energy and except for the protective wiring, the alarm means and circuit connections between the alarm means and the remainder of the apparatus, being contained in a tamper-proof container.

HERBERT M. LAFORD.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 726,292 Holmes Apr. 28, 1903 1,840,637 Reid Jan. 12, 1932 1,881,832 Miranda Oct. 11, 1932 1,920,742 Chapman et al Aug. 1, 1933 2,224,548 McFerron Dec. 10, 1940 2,346,171 Laford Apr. 11, 1944 2,353,452 Fruh July 11, 1944

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