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Publication numberUS2093600 A
Publication typeGrant
Publication dateSep 21, 1937
Filing dateDec 8, 1933
Priority dateDec 8, 1933
Publication numberUS 2093600 A, US 2093600A, US-A-2093600, US2093600 A, US2093600A
InventorsDenzler Felix F
Original AssigneeDenzler Felix F
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Electric signaling system
US 2093600 A
Abstract  available in
Images(6)
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Claims  available in
Description  (OCR text may contain errors)

Sept. 21, 1937. F. F. DENZLER ELECTRIC SIGNALING SYSTEM 6 Sheets-Sheet 1 Filed Dec. 8, 1933 FEGORDEI? Sept. 21, 1937. F. F. DENZLER ELECTRIC SIGNALING SYSTEM Filed Dec. 8, 1953 6 Sheets-Sheet 2 WW M Sept. 21, 1937. F. F. DENZLER ELECTRIC SIGNALING SYSTEM Filed Dec. 8, 1933 6 Sheets-Sheet 5 I 4 y 5 T 4 a L H i u T H 3 a 4 En .n 1B f w l i I? lfillf A 0m r I x, w Mmm 0 M Mi g I. -|I%.MW---I|,

Mira/max Inventor Sept. 21, 1937. F. F. DENZLER ELECTRIC SIGNALING SYSTEM FiledDec. 8.

1933 6 Sheets-Sheet 4 It'll l lll llllllllll.

plllorneys Se t. 2]., 1937. F. F. DENZLER ELECTRIC SIGNALING SYSTEM 6 Sheets-Sheet 5 Filed Dec. 8, 1933 Inventor Sept. 21, 1937. F. F. DENZLER ELECTRIC SIGNALING SYSTEM 6 Sheets-Sheet 6 Filed Dec. 8, 1933 l/mrneys Patented Sept. 21, 1937 UNITED STATES PATENT OFFICE 47 Claims.

This invention relates broadly to electric signaling systems and has particular application to safety systems such as fire alarm and burglar alarm systems, although certain features of the invention may be used in other communication systems.

A broad object of the invention is to increase the reliability and usefulness of electric safety systems by making their operation less subject to interruption by line troubles, both those resulting from unavoidable causes and those maliciously caused.

Another object is to prevent any line fault that does not totally incapacitate the line for signaling purposes from transmitting a false alarm while at the same time giving an indication that there is trouble on the line, and connecting the line to an alarm circuit in a different manner so that the line is still effective to transmit a bona fide alarm should one be sent, while sending in an alarm in case the line is totally incapacitated.

Another object is to provide, in a burglar alarm system, means for restoring the local alarm circuit at a protected premises from a central station and to provide a signal at the premises to indicate to the occupant or a watchman that the circuit is in proper condition.

Another object is to provide a plurality of lines from an alarm system central station to fire or police headquarters with means for automatically supervising the lines from the central station to indicate the existence of trouble on any one of the lines to fire or police headquarters.

The attainment of the foregoing objects makes practicable a system employing existing line circuits of telephone and telegraph companies, which are more subject to trouble than specially made and protected,alarm circuits, and also makes practicable the automatic relaying of alarms directly to fire or police headquarters without the use of an intermediate operator to ascertain whether an alarm is false or bona fide.

This is a continuation in part of my application Serial No. 639,329, filed October 24th, 1932 on Electrical signaling systems. and now abandoned.

Various other objects and features of the invention will be apparent from the following detailed description which refers to the drawings.

In the drawings:

Fig. 1 is a schematic layout of an entire system in accordance with the invention;

Fig. 2 is a detail circuit diagram of that portion of a fire alarm system, in accordance with the invention, located at the protected premises P, and on the supervisory panel SP associated with that premises circuit but located at the central station;

Fig. 3 is a schematic circuit of the same portion of the system shown in Fig. 2, with certain switch contacts and auxiliary apparatus eliminated to 5 simplify the tracing of the main circuits;

Fig. 4 is a simplified schematic diagram of a modification of the premises circuit shown in Fig. 3;

Fig. 5 is a detail diagram of a subscribers premises and a subscribers supervisory panel circuit in a burglar alarm system in accordance with the invention;

Fig. 6 is a simplified schematic. circuit showing the most important features of the circuit in Fig. 15 5 with certain reset switches and auxiliary apparatus eliminated;

Fig. '7 is a detail schematic circuit showing a modification of the premises portion of the circuit shown in the schematic diagram of Fig. 6;

Fig. 8 is a schematic diagram of an automatic alarm code transmitter indicated at T in Figs. 1, 2, 3, 5 and 6; and

Fig. 9 is a detail diagram of a headquarters line supervisory panel circuit.

Referring to Fig. 1, a complete system in accordance with my invention, whether a fire alarm or burglar alarm system, comprises a plurality of sub stations at premises to be protected, the apparatus at each station comprising a group of apparatus indicated at P having connected thereto a protection loop L which may extend throughout the premises, and being connected to a central station CS by a line SL. The lines SL are indicated with a single line in Fig. 1 but actually each line comprises a pair of metallic conductors.

At the central station CS each line SL is connected through a subscribers supervisory panel SP to a code transmitter T, which when actuated connects itself through an associated line finder LF to any one of a plurality of lines HL extending to fire or police headquarters SD. At the headquarters SD each line HL connects to an individual alarm recorder AR. Each headquarters line HL also has associated therewith at its central station end a headquarters line supervisory panel HP, the function of which is to indicate to the line finders LF whether or not that particular headquarters line BL is in condition to transmit an alarm. 0

The operation of my system will now be explained in detail with reference to the detail drawings of the various units L, P, SL, SP, T, LF, HP, HL and AR, shown schematically in Fig. 1.

The code transmitter T, line finders LF, headquarters line supervisory panels HP, headquarters lines HL, and alarm recorders AR are the same in both the fire and burglar alarm systems. However, the subscribers loop circuits L, premises apparatus panels P, and subscribers supervisory panels SP at the central station are different in the fire and burglar alarm systems, respectively.

Fire alarm system Referring to Fig. 2, in my fire alarm system the equipment at the protected premises includes a loop L which comprises a pair of conductors H and I2, respectively, extending out of a control box P out over the premises and back into the control box P. A plurality of danger responsive devices l3 are bridged across the conductors II and I2 and are adapted to short circuit these conductors in case of a fire. Thus, some of the devices l3 may be thermostatic devices located in various rooms in a building and adapted to short circuit the conductors I! and I2 in response to a rise in temperature above a predetermined limit, and other of the devices l3 may be pull-boxes located at different points on the premises and adapted to be manually operated to short circuit the conductors II and I2.

The control box P includes relays l, 0 and 2, a resistor l4, a resistor l5, an alarm bell l6, and a manually operated restoring key Z. The key Z is shown as two separate units to simplify the circuit connections but it actually comprises a plurality of contact members operated by a single handle. Relay is a sensitive relay which is fast to release when its operating circuit is interrupted. Relay 0 is a marginal relay which normally carries current of a predetermined value but remains unoperated until the current therethrough is increased above normal value. The relay 0 is provided with a mechanical latch I! which looks it up when it has once been pulled and maintains it locked until manually released by an operator. The relay 2 is a slow-release relay.

The line SL connecting the control box P at the protected premises to the subscribers supervisory panel SP at the central station comprises two metallic conductors X and Y, respectively, as shown.

The subscriber's supervisory panel SP includes a pair of marginal relays 3 and 4, a sensitive fast release relay 8, a pair of slow release relays 6 and 1, a main battery l8, which may be common to all of the supervisory panels SP at the central ofiice, an auxiliary battery l9, a trouble alarm relay ID, a trouble alarm buzzer 20, a white signal lamp W, a red signal lamp R, a blue signal lamp B, current limiting resistors 2|, 22 and 23, and a key A. Key A is shown in two sections to simplify the circuit connections but it is to be understood that it really consists of a single key having a single control handle. The marginal relay 0 is adjusted to operate before the marginal relays 3 and 4 and the slow release relay 2 is 1 designed to release faster than the slow release relays 6 and 1.

Key A in the subscribers supervisory panel SP and key Z in the control box P at the subscribers premises are used only to restore the system to normal following the transmission of an alarm or the existence of trouble on the circuit. These keys can, therefore, be disregarded in following the normal operation of the circuit up to the reset operation. For this reason they have been eliminated in the schematic circuit of Fig. 3, to which reference is now made. Likewise, certain auxiliary circuits, including the alarm bell I 6 in the control box P, the trouble alarm relay l0, and the signal lamps W, R and B have been eliminated from the circuit of Fig. 3.

As shown in Fig. 3, all the relays in the circuit are in their normal position waiting for an alarm. Under these conditions a closed circuit is completed from battery at the central station out over the line conductor X, through the control box P and loop L and back over the line conductor Y to ground at the supervisory panel SP. This circuit is shown in heavy lines and may be traced as follows: From battery ill at the central station, through contacts T2 and F2 on relay 8, through contacts T2 and B2 on relay 4, through the winding of relay 4, through contacts TI and BI on relay 4, out over line X through contacts TI and Fl of relay 2 and the winding of relay 2, to the loop conductor ll, through the resistor 24 at the end of the loop, back over the loop conductor l2, through contacts F3 and T3 of relay 2, through the winding of relay 0, through the contacts T2 and B2 of relay 0, through contacts T3 and F3 on relay I and the winding of relay I, out over line Y, through the contacts B4 and T4 and the winding of relay 3, contacts T2 and B2 of relay 3, contacts F4 and T4 and the winding of relay 8, the winding of relay 1, and over the contacts F5 and T5 of relay 8 to ground. (It will be observed that in the reference numerals on the various contacts in the circuit the letter prefix indicates the nature of the contacts. Thus where the contact number is preceded by the letter T, it means that the contact is an armature contact or a transfer contact, Where the number is preceded by the letter F, it means that the contact is a front contact, and where the number is preceded by the letter B, it means that the contact is a back contact.)

The current flowing through the closed circuit traced from the battery 58 is normally limited to a predetermined value by proper adjustment of the resistance 2d at the end of the loop conductors H and I2. This current value is suilicient to maintain relays E and 8 the supervisory panel and relays l and in the premises control box P operated but is ins cient to actuate the marginal relay i! and the marginal relays 3 and 4. It will be observed that, as long as relay 1 is operated, it closes an actuating circuit through its contacts T and F for the relay 6, thereby maintaining the latter operated. Relay 6 in turn closes a circuit from the battery to the input leads 25 23 to the code transmitter T. The construction and operation of the code transmitter T will be described in detail later. It will suffice at this point to state that the code transmitter T is locked against operation as long as battery supplied to its input terminals 25 and 26.

Normal operation-Fire alarm system the circuit traced in heavy lines at the contacts T2 and B2 of relay 0, thereby causing an immediate release of relay I in the control box P and relay 8 on the supervisory panel SP. The circuits for relays 2 and I are also opened but those relays do not release immediately because of the fact that they are slow to release.

The release of relay 8 on the supervisory panel SP reconverts the circuit to connect the battery I8 directly through the winding of relay I toboth sides of the line X and Y, respectively. This circuit be traced as follows: From battery I8, over contacts T2 and B2 of relay 8, through the winding of relay through the contacts TI and BI of relay 8, to the contact T2 of relay 4, and through the contacts B3 and T3 of relay 8, to the contact B2 of relay 3. From contact T2 on relay 4 the circuit continues as originally traced to the line conductor X. From contact B2 on relay 3 the circuit also continues as originally traced to the line conductor Y.

The net result is that following release of relay 8 battery is applied through relay 1 to both line conductors X and Y in parallel. If there is any path to ground from either conductor X or Y in the control box P, current flow will be resumed from battery It through the winding of relay I before the latter had time to release. However, there can be no such flow of current from either line conductor X or Y to ground because the only path to ground in the control box over the contact TI of the relay ii and, with relay I) locked up in operated position, any ground path to either line conductor is open at contact BI on relay 8. Referring for the moment to Fig. 2, it will be observed that the operation of relay ll applies ground over contacts Tl and Fl to operate the alarm bell Ill in box P over a local circuit.

Since there is no path to ground over either line conductor X or Y, there can be no resumption of current flow from battery I8 through the winding of relay I and the latter finally releases its armature, opening the actuating circuit of relay 6. Relay 6 is also a slow release relay but it finally releases, thereby opening the ground connection to input terminal 25 of the transmitter T and releasing the transmitter to send in an alarm to the fire headquarters.

Operation of the premises station and. subscribers supervisory panel circuits in the fire alarm system in response to an open on the X line followed by a bona fide alarm Referring again to Fig. 3 with the circuit in normal condition as shown, assume that from any cause the X line goes open somewhere between the supervisory panel SP and the subscribers control box P. This stops the normal flow of current through the windings of relays 4, 2, D, I, 8, and l, and relays I and 8 thereupon immediately release.

The release of relay 8 connects the battery I8 in series with the winding of relay I from ground to both line conductors X and Y. No

current can flow out over the X conductor, however, for the reason that that conductor is open. Neither can any current flow out over the Y conductor immediately for the reason that the release of relay I opened contacts F3 and T3 on that relay. However, the release of relay I completed a path from ground over contacts TI and BI of relay 0 and contacts B3 and T3 of relay I through the contacts B2 and T2 and the win ing of relay Il to contact T3 on relay 2.

Following the release of relays I and 8, slowrelease relay 2 releases. This completes the path previously traced from ground up to contact T3 of relay 2 through contact B3 to conductor II of the loop circuit. At the same time conductor I I is disconnected from the X line by the opening of contacts TI and FI on relay 2. The release of relay 2 also closes contacts T2 and B2 on that relay connecting the other loop conductor I2 to the line conductor Y. The final result is that the loop conductors II and I2, including the resistor 24, are left connected in series with the marginal relay 8 between ground at the premises station and the Y line conductor. Current flow is therefore resumed from battery at the supervisory panel SP through the relay I and through the winding of relay 3 out over the Y line conductor and, because of the fact that the slow release relay 2 is designed to release more quickly than the slow release relay I, the latter is reenergized before it has opened its contacts F and T. It will be observed, therefore, that an open on the the line conductor X does not release the alarm code transmitter T.

With the circuit rearranged as described in response to an open on X line, the total resistance in the circuit is reduced as a result of the elimination of relays I, 2, 3 and 8, and line X. This might increase the current flow in the winding of the marginal relay ii sufllciently to operate that relay. To prevent such operation, resistances I4 and I5 (referring for the moment to Fig. 2) are provided in series with the contact BI on relay 0 and the contact B2 on relay 2, respectively, which relays are cut into the circuit in response to release of relays I and 2. The resistance I4 compensates for the resistance of relays I, 3, 3 and the X line, and the resistance I5 compensates for the resistance of relay 2.

Now assume that a bona fide alarm is turned in, thereby short circuiting the loop conductors II and I2 and shunting out the resistance 24. This increases the current flow through the marginal relay ll sufficiently to actuate that relay which locks up mechanically, as previously described. The operation of relay 0 breaks the contacts BI and TI on the latter relay, thereby opening the path to ground over which current previously flowed from the line conductor Y. The interruption of current flow over conductor Y permanently opens the circuit over which relay I was operated. thereby releasing that relay, which in turn releases relay 6 and opens the path from ground to the input terminal 25 of the transmitter T releasing the transmitter and sending in an alarm to the fire station.

Should line X, in addition to being opened, be grounded on the premises side of the break, it would not afiect the foregoing operation since the. release of relay 2 opens the premises end of X line at contacts TI and Fl on relay 2.

Should line X, in addition to being opened, be grounded on the central station side of the break, then there would have been an increase of current flow from battery I 8 through the winding of relay 4 to ground on the X line, which increased current flow would operate relay 4. When once operated, relay 4 looks up with the current supplied from battery over its contacts T3 and F3, through its winding and through its contacts TI and Fl to ground. The operation of relay 4 opens the circuit to the X line at contacts B2 and T2, thereby preventing further flow of current through relay I to the ground on the X line. Thereafter the only current flowing through winding of relay I is that which flows out over the Y line. When relay 4 operates, it completes a circuit from battery I8 through relay I over contacts T2 and F2 of relay 4 to contact T3 of relay 3, but under the conditions outlined relay 3 is not operated and therefore its contact T3 remains open.

Operation of the premises station and. subscribers supervisory panel circuits in the fire alarm system in response to open on Y Zine followed by a bona fide alarm With the circuit in the condition shown in Fig. 3, assume that the Y line goes open. This opens the circuit shown in heavy lines and stops the flow of current through relays 4, 2, 0, I, 3, 8 and I. Relays I and 8 release immediately, relay I opening the Y line at its contact F3 and grounding the loop conductor I2 through contacts F3 and T3 on relay 2, the winding of relay 0, contacts T2 and B2 of relay 0, contacts T3 and B3 of relay I and contacts BI and TI of relay 0; and relay 8 connecting battery I8 through its contacts T2 and B2, through the winding of relay I, and through contacts TI and BI of relay 8 to both line conductors X and Y through the relays 4 and 3, respectively. No current can flow out over the Y line because the latter is open. However, current can flow from battery I8 through the winding of relay I and the winding of relay 4 out over the X line, through contacts TI and Fl, and the winding of relay 2, to the loop conductor II and thence through the loop resistor 24 to the loop conductor I2 and thence to ground over the circuit previously traced. The resumption of current flow through relay I over the path traced prevents relay I from releasing so that the transmitter T is not released.

The circuit will now respond to a bona fide alarm in substantially the manner described in connection with an open on X line. Thus, a short on the loop conductors II and I2 shunts out the resistor 24, permitting an increase in the flow of current through the marginal relay 0 to actuate the latter, which breaks the path to grounds at contacts TI and BI on relay 0. This stops the flow of current from the battery I8 through the relay I and out over the X line, causing the relay I to release, which in turn releases relay 6 and breaks the path from ground to the terminal 25 of the transmitter, releasing the transmitter and sending in an alarm.

In case the Y line also becomes grounded on the premises side of the break, the circuit still functions exactly as described up to the time the loop conductors II and I2 are short circuited in response to a bona fide alarm. Thereafter the operation is slightly different. Thus, when the relay 0 pulls in response to short circuiting of the resistor 24, the current from X line through the relay 2 to ground is broken at contacts B2 and T2 and also at contacts TI and BI on relay 0, whereupon, after a slight delay, relay 2 releases. The release of relay 2 connects the loop conductor I2 through contacts T2 and B2 on relay 2 to the premises end of conductor Y which, if grounded as assumed, would supply an alternative path to ground independently of the normal path to ground through the contacts on relay 0. However, this makes no difference in the operation of the circuit in response to an alarm for the reason that the release of relay 2 also opens contacts TI and FI on the latter, thereby opening the X line at the premises end and preventing any flow of current through relay I. The latter therefore releases, as previously described, to actuate the transmitter T.

In case the Y conductor should be grounded on the central station side of the break, there would be an increased current flow through relay 3 immediately following the release of relay 8, to operate relay 3, which locks up over a local circuit the same as does relay 4, and open the Y line at the central station end at contact B4 on relay 3. At the same time flow of current from battery I8 through relay I and relay 3 is stopped by the opening of contacts T2 and B2 on relay 3.

Operation of the premises station and subscribers supervisory panel circuits in the fire alarm system in response to an open on the protection loop followed by a bona fide alarm With the circuit in the condition shown in Fig. 3, assume that either one of the loop conductors II or I2 is. broken. This interrupts the normal flow of current over the circuit shown in heavy lines, immediately releasing relays I and 8, as previously described. The release of relay 8 applies current from the battery I8 through the winding of relay I out over both line conductors X and Y. No current can flow over the Y conductor, however, for the reason that it is opened at the premises end at contact F3 of relay I upon the release of that relay. Relay I in releasing, however, completes the circuit from ground over contacts TI and BI of relay 0, contacts B3 and T3 of relay I, through the contacts B2 and T2 and the winding of relay 0 over contacts T3 and F3 of relay 2 to the loop conductor I2. At the same time the release of relay I boxes the loop. In other words, both ends of the loop conductor I2 are connected together over contacts B2 and T2 of relay I and both ends of the loop conductor I I are connected together over the contacts BI and TI of relay I. Therefore, a circuit is established from the X line through the contacts TI and FI and the winding of relay 2 to the loop conductor II and a circuit is completed to the resistor 24, regardless of an open on conductor II, through the boxing conductor and contacts BI and TI of relay I. Likewise the circuit is continued from resistor 24 to the ground connection previously described, regardless of an open circuit condition on loop conductor I2, through the boxing conductor and contacts BI and TI of relay I. If the loop conductors II and I2 are now short circuited by one of the danger responsive devices I3, the resistor 24 is short circuited and the current through the marginal relay 0 increased to operate that relay as previously described, and the operation of relay 0 breaks the path to ground at the premises station, thereby stopping the flow of current through relay I, releasing the latter, which in turn releases relay 6 and actuates the transmitter T.

Operation of the premises station and subscribers supervisory panel circuits in the fire alarm system in response to a short on the line conductors followed by a bona fide alarm With the circuit in the condition shown in Fig. 3, a short across the line conductors X and Y shunts out the relays I and 2 and relay I immediately releases to connect the alarm loop and winding of relay 0 in series between the line conductor X and ground in the manner previously described.

At the same time the short circuit on line conductors X and Y permits an increased current to flow through the relays 3 and 4 connected in series with the X and Y lines, respectively. Relay 3 is adjusted to operate before relay 4 and under most conditions will be the only one of the two relays to operate in response to a short on the line conductors X and Y. The operation of relay 3 immediately opens the Y line at contact B4 on relay 3 and also breaks the heavy-line circuit including relay 8 at contact B2 on relay 3. Relay 8 thereupon immediately releases and in doing so connects the relay I in series with the battery I8 through relay 4 to the X line over the circuit previously traced. Current thereafter flows from battery I8 through relay I and relay 4 out over the X line through the relay 2, the loop and the marginal relay 8 to ground over the contacts T3 and B3 of relay I. The fact that X and Y lines are short circuited produces no efiiect for the reason that the Y line is now open at each end.

The occurrence of a bona fide alarm shunting out the resistor 24 increases the current flow through relay 8 to operate the latter and break the ground connection at the premises station, as previously described. This stops the flow of current out over the X line and releases relays I and 6 to actuate the transmitter T.

Should for any reason both relays 4 and 3 operate in response to a short on the line conductors X and Y, the circuit still functions as described except for the following difference: The operation of relay 4 opens the X line at contact BI on relay 4 and also opens the path from battery through relay I at contact B2 on relay 4. However, when relay 4 operates a circuit is completed over contacts T2 and F2 on relay 4 to contact T3 on relay 3, and operation of relay 3 completes this circuit from contact T3 over contact F3 back to the X line so that a circuit is restored from the winding of relay I to X line. A bona fide alarm thereafter causes the release of relay I exactly as outlined above.

Operation of the premises station and subscribers supervisory panel circuits in the fire alarm system in response to a ground on the Y line followed by a bona fide alarm With the circuit in normal condition, as shown in Fig. 3, a ground on the Y line shunts out relay 8 causing the latter to release. As relay 8 releases, the normal circuit from battery I8 out through relay 4 and over the X line is momentarily interrupted at contacts T2 and F2 on relay 8, causing the release of relay I at the premises station. Following this momentary break, however, the relay 8 reestablishes a circuit from battery I8 through relay I to both the X and Y lines, as previously explained. The release of relay I at the premises station establishes a circuit from X line through the loop and resistor 24 and thence through the relay 8 to ground, as previously explained. At the same time the release of relay I disconnected the Y line from the premises circuit at contact F3 on relay I.

The establishing of a circuit from battery I8 through relay 1 and relay 3 to the Y line permits a heavy flow of current through relay 3 to the Y line and thence to ground. This operates relay 3 and the latter in operating opens the Y line at the central station end at contact B4 on relay 3 and also breaks connection from relay 3 to relay I at contact B2 on relay 3. Thereafter normal current flow continues from battery I8 through relay I and relay 4 out over X line through relay 2, the loop circuit, and the marginal relay 0 to ground, and if the resistance 24 is shunted out in response to a bona fide fire alarm the current through relay 8 is increased to operate the latter relay and break the ground connection, as previously described, thereby releasing relay I and actuating the transmitter T.

Operation of the premises station and subscribers supervisory panel circuits in the fire alarm system in response to a ground on the X line followed by a bona fide alarm With the circuit in the condition shown in Fig. 3, a ground on the X line shunts out relays 2, I, 8 and I, causing relays I and 8 to immediately release. Relay 8 in releasing reestablishes the circuit from battery I8 through relay I, through both relays 3 and 4 to the line conductors X and Y. The release of relay I opens the Y line at contact F3 on relay I and establishes a ground connection through contacts TI and BI of relay 8. contacts T3 and B3 of relay I, contacts B2 and T2 and the winding of relay 8, to contact T3 of relay 2. Relay 2 thereafter releases, completing the circuit from its contact T3 over contact B3 to the loop conductor II, at the same time completing a circuit from loop conductor I2 over contacts T2 and B2 of relay 2 to line conductor Y.

Following release of relay 8, excessive current flowed from battery I8 through relay I and relay 4 to line X and thence to the ground on that line. This operated relay 4 which looked up in the manner previously described and opened the X line at contact BI, and opened the circuit from relay I at contact B2.

The net result of the foregoing operations in response to a ground on X line is that normal battery feed is reestablished through relay I and relay 3 out over Y line, thence over contacts B2 and T2 on relay 2 to loop conductor I2, thence through resistor 24 and loop conductor II through contacts B3 and T3 on relay 2, through the winding of relay 0 to ground. Thereafter shunting out of the resistor 24 in response to an alarm operates the relay 0 to break the ground connection and interrupt the current flow through relay I to release the transmitter T.

Operation of the premises station and subscribers supervisory panel circuits in the fire alarm system in response to ground on the loop conductor 11 followed by a bona fide alarm With the circuit in normal condition as shown in Fig. 3, assume that the outside loop conductor II becomes grounded. This shunts out the relays I, 8 and I, immediately releasing relays l and 8. The release of relay 8 reestablishes the circuit from battery I8 through relay I and through relays 4 and 3 to line conductors X and Y. No current flow can occur over the Y conductor, however, because the latter is opened at contact F3 on relay I at the premises end. However, the ground on the outside loop conductor II permits an abnormal current flow through relay 4, causing that relay to operate and lock up in the manner previously described. In operating, relay 4 opens the X line at contact BI on relay 4 and also completes a circuit from relay I over contacts T2 and F2 on relay 4 to contact T3 on relay 3.

Following the interruption of current flow over the X line by relay 4, relay 2 releases, disconnecting the outside loop conductor II from the X line and connecting it through contacts B3 and T3 on relay 2 through the winding and contacts T2 and B2 of relay 0, through contacts T3 and B3 on relay I and contacts BI and Tl on relay 0 to ground. The release of relay 2 also connects the loop conductor l2 through back contacts T2 and B2 of relay 2 to the Y line conductor.

This establishes a circuit for normal current flow from battery l8 through relay 1 and relay 3 out over the Y line conductor to loop conductor l2, thence through the resistor 24 to the loop conductor ll and thence to ground over the trouble ground on loop conductor II. There is also a path to ground, previously traced, from loop conductor I I through the relay 0 but unless the trouble ground is of considerable resistance, little or no current will flow through relay ii in response to shunting of the resistor 24.

shunting of the resistor 24 in response to a bona fide alarm permits an increased current flow through relay 3 out over line conductor Y, to loop conductor l2, thence to loop conductor ll and to ground. This increased current flow actuates relay 3, which locks up in the manner previously described and breaks the Y conductor at contact B4 of relay 3 and breaks the circuit from relay 1 to relay 3 at contact B2 on relay 3. This stops flow of current through relay 1, releasing the latter to actuate the transmitter T.

It will be observed that there is another path for current from the battery l8 through relay 1 over the contacts T2 and F2 of relay 4, and the contacts T3 and F3 of relay 3 to the line conductor X. However, there can be no current flow to hold up relay I out over this path for the reason that the line conductor X has been opened at the central station end at contact Bl on relay 4 and at the premises end on contact Tl of relay 2.

Operation of the premises station and subscribers supervisory panel circuits in the fire alarm system in response to a ground on the loop conductor 12 followed by a bona fide alarm With the circuit in normal condition as shown in Fig. 3, assume that a ground occurs on the inside loop conductor i2. This shunts out the relays l, 3, I, and 8 and relays l and 8 immediately release. The release of relay 8 reestablishes connection from battery l8 through relay 1 and through the relays 3 and 4 in parallel to the line conductors X and Y. No current flow can occur over the Y conductor for the reason that the line is opened at contact F3 on relay l at the premises end. Normal current flow, however, is restored through the relay 4, line conductor X, through the contacts Tl and F! and Winding of relay 2 to the loop conductor ll, through the resistor 24 to the loop conductor l2 and thence to ground over the trouble ground thereon. This condition obtains until resistance 24 is shunted out in response to a bona fide alarm. Shunting out of the resistor 24 increases the current flow through marginal relay 4 sufiiciently to actuate the latter relay, which looks up as previously described and opens the line conductor X at contact Bl on relay 4. This stops the flow of current over line X, causing relay 2 to release. The release of relay 2 establishes a connection from 1ine Y over contacts B2 and T2 of relay 2 directly to the loop conductor l2 which is grounded. This immediately produces a heavy current flow through relay 3, operating the latter and looking it up. The operation of relay 3 breaks the flow of current through relay 1 to the Y line at contact B2 on relay 3, causing relay 1 to release and actuate the transmitter T.

There is also a path for current through relay I over contacts T2 and F2 of relay 4, thence over contacts T3 and F3 of relay 3 to the line conductor X but no current flow can occur over this path for the reason that the X line is opened at the central station end at contact Bl on relay 4 and is opened at the premises end at contact TI on relay 2.

Alternative premises circuit for fire alarm system A modification of the premises circuit shown in Fig. 3 is. disclosed in Fig. 4, in which elements corresponding to those in Fig. 3 bear the same reference numerals with the suffix a.

It will be observed that the circuit of Fig. 4 is substantially the same as. that of the premises circuit in Fig. 3 except for the arrangement and connections of the contacts on relays la and 2a, respectively. Thus in Fig. 4, while the contacts for boxing the loop conductor l2ai are on the relay la, as in Fig. 3, the contacts for boxing the loop conductor I la are on relay 2a. This alteration in the boxing circuits permits the connection of the coil of marginal relay 0a directly to the loop conductor l2a instead of connection through the contacts T3 and F3 of relay 2, as shown in Fig. 3.

The circuit shown in Fig. 4 gives the same final result under each of the conditions of operation outlined hereinbefore, except in response to a ground on the loop conductor II, as the premises circuit shown in Fig. 3. Thus relay la immediately releases in response to interruption of current therethrough to connect the relay 0a in series between ground and the loop conductor l2a and to open the connection between the Y conductor and the winding of relay la. Relay 0a functions in response to an increase in current flow therethrough above normal value to break the path to ground and open the connection from the loop conductor lZa, through the winding of relay 0a, to the contact T3 of relay la. Relay 2a functions in response to prolonged interruption of current therethrough to open the line conductor X at the premises end, connect the line conductor Y to the loop conductor Ho and box the loop conductor lla.

Thus with the line conductors X and Y in normal condition, the shorting of one of the thermostatic elements l3 causes relay 0a to pull and lock up, thereby breaking all connection to ground at the premises end of the line regardless of the positions of relays la. and 2a, and permanently stopping flow of current through relay 1 to release the latter, which in turn releases relay 6 and opens the ground connection to the transmitter T causing the latter to transmit an alarm.

In response to an open on the Y line, relays la and 8 release as previously described, connecting the battery l8 through relay 1 out over the X line through the contacts TI and Fl and winding of relay 2a to the loop conductor lla, through the resistance 24a, through the winding and contacts T2 and B2 of relay 0a, through the contacts T3 and B3 of relay la and contacts BI and Tl of relay 0a to ground. Thereafter shorting of one of the thermostatic elements l3a causes relay 0a to pull and lock up, permanently breaking the path to ground at contact Bl on relay 0a and causing the release of relays 'l and 6 and the actuation of transmitter T, as previously described.

In response to an open on the X line, relays l and 8 release and thereafter relay 2 releases exactly as described in connection with Figure 3,

the circuit being reconverted to connect battery I8 through relay I out over the Y line and through the contacts B2 and T2 on relay 2a to loop conductor Ila, the other loop conductors l2a being connected to ground through the winding and contacts of relay 8a and the contacts T3 and B3 of relay la. shorting of one of the elements l3a thereafter actuates the relay a to break the connection to ground and actuate the transmitter T at the central station in the manner previously described.

In response to an open on the loop conductor I2a, relays la and 8 release. Relay la in releasing boxes the loop conductor l2a. over its contacts B2 and T2 and completes a circuit from ground through contacts TI and BI of relay 8a, contacts B3 and T3 of relay la, contacts T2 and B2 of relay 8a and the winding of relay Ila to the loop conductor l2a. At the same time the release of relay 8 has applied battery through relay 'I out over the X line through the contacts TI and FI and the winding of relay 2a to the loop conductor Ila. The system is therefore restored for transmission of an alarm. Shorting the circuit of the loop conductors Ila. and l2a in response to actuation of one of the alarm responsive devices l3a thereafter causes relay 0a to pull and lock up in the manner previously described to break all connections to ground and cause the release of relays l and 6 and the actuation of the transmitter T.

In response to an open on the loop conductor Ila, the circuit of Fig. 4 functions as follows: Relays l and 8 immediately release, as previously described, the release of relay la completing the path to ground through relay 0a to the loop conductor l2a. However, since the loop conductor Ila is open, current feed from the X line to relay 2a is cut off and the latter relay releases, thereby opening the X conductor at contact TI on relay 2a, boxing the conductor loop Ila over the contacts T3 and B3 on relay 2a and also connecting the boxed loop conductor Ila through contacts T2 and B2 on relay 2a to the Y line conductor. Thereafter current is supplied from the battery l8 on the central station through relay 1 out over the Y line to loop conductor Ila and thence through the resistance 24a, through the loop conductor l2a and the relay Ila to ground. Short circuiting of the loop conductors Ila and l2a in response to an alarm thereafter causes relay 8a to pull and lock up, permanently opening the path to ground and causing the release of relays l and 6 and the actuation of the transmitter T at the central station.

In response to a short on the line conductors X and Y, the operation of the circuit of Fig. 4a is substantially the same as that of the circuit of Fig. 3. Relay la first releases, connecting the loop conductor I2a through the Winding or relay lla to ground. Thereafter relay 3 at the central station operates, opening the Y line conductor and causing the release of relay 8, which upon releasing applies battery through relay I and relay 4 out over line conductor X through the contacts TI and FI and the winding of relay 2a to the loop conductor II a. Thereafter shorting of the loop conductors in response to an alarm pulls and locks up the relay Ila to break the path to ground and cause the release of relays I and 6 and the actuation of transmitter T at the central station.

The operation of the circuit of Fig. 4 in response to a ground on Y line is also substantially the same as in the case of Fig. 3. Relay 8 releases, connecting the battery I8 directly through relay I and through relays 3 and 4 to both the X and Y line conductors. At the same time the momentary opening of the normal circuit by relay 8 before the application by that relay of current to both line conductors X and Y releases the relay la. Thereafter heavy flow of current through the relay 3 to the ground on the Y conductor pulls relay 3, opening the Y line. This leaves the circuit with current flowing from battery l8 through relay I out over the X line, through the contacts TI and Fl and the winding of relay 2a, through the loop conductors and resistance 24a and the winding of relay 8a to ground. Thereafter short circuiting of the loop resistance 24a in response to an alarm causes relay 8a to pull and open the path to ground, releasing relays I and B and actuating the transmitter T at the central station.

In response to a ground on the X line, the circuit of Fig. 4 also functions substantially the same as that of Fig. 3. Thus, relay I a and relay 4 pull, opening the X line at the central station end and releasing relay 8. After a short interval relay 2a releases. Thereafter current fiows from battery l8 through relay I out through relay 3 over the Y conductor, through the contacts B2 and T2 of relay 2a to the loop conductor Ila, thence through the resistance 24a to a loop conductor l2a and through the relay 0a to ground. Short circuiting of the loop resistor 24a in response to an alarm thereafter causes the relay 8a to operate and open the path to ground, which in turn causes the release of the relays l and 6 and the actuation of the transmitter T at the central station.

In response to a ground on the loop conductor l2a, the circuit of Fig. 4 functions as follows: Relays la and 8 release, completing a circuit for current from battery l8 through relay I, relay 4, line conductor X, the contacts TI and FI and winding of relay 2a to the loop conductor Ila and thence through the resistor 24a to the ground on the loop conductor l2a. Thereafter short circuiting of the resistor 24a in response to an alarm increases the current through relay 4, causing the latter to pull and open the X line at the central station end. Since the Y line conductor was previously opened at contact F3 on relay la, no current can flow at this time out over the Y conductor from the central station. However, following the opening of the X conductor by the relay 4, relay 2a releases which connects the Y conductor to the loop conductor Ila, through contacts T2 and B2 on relay 2a. This permits a heavy flow of current through relay 3, causing the latter to pull and open the Y conductor at the central station end. With relays 3 and 4 both pulled, a circuit is completed from the battery l8 throug'h relay I, the contacts T2 and F2 of relay 4, and the contacts T3 and F3 of relay 3 to the X line conductor. However, there can be no flow of current out over the X line at this time because the latter is opened at the premises end at contact TI on relay 2a. Therefore, all paths to ground from relay I are broken and the latter releases, causing the release of relay 6 and the actuation of the transmitter T.

In response to a ground on the loop conductor II a, the circuit of Fig. 4 transmits a fire alarm instead of reconverting the circuit into operative condition to receive a bona fide alarm. Thus in response to a ground on the loop conductor II a relays I and 8 release, completing a circuit for current from battery l8 through relay 1, relay 4, the X line conductors, contacts TI and F I and the winding of relay 2a to ground on the loop conductor Ila. This causes a heavy flow of current through relay 4 which operates to open the X line. Thereafter relay 2a releases, connecting the grounded loop conductor Ila over contacts B2 and T2 on relay 2a to the Y line conductor. This results in a heavy flow of current through relay 3 at the central station, causing the latter to operate and open the Y line conductor but at the same time completes another circuit from battery I8 through relay I, contacts Tl and BI of relay 8, contacts T2 and F2 of relay 4, contacts T3 and F3 of relay 3, to the X line conductor. However, the X line conductor is now open at the premises end at contact TI on relay 2a. Therefore, all paths to ground are opened and the relays I and 6 release, causing the actuation of the transmitter T.

It will be observed from the foregoing description that the circuit of Fig. 3 is superior to that shown in Fig. 4 in that it will respond to a ground on the outside loop conductor II to reconvert the circuit for reception of a bona fide alarm without actually sending in an alarm at the time the ground occurs.

E fleet on the fire alarm system of an open on both line conductors or a ground on both Zine conductors If both line conductors X and Y (Fig. 3) are opened or grounded, the line is totally incapacitated for any signaling between the premises and central stations.

An open on both line conductors sends in a fire alarm since it first causes the release of relay 8 and thereafter the release of relays I and 6. It will be observed that relay 1 must release because when the circuit has been converted by the release of relay 8 there can be no path for current from battery I8, through relay I without a ground somewhere on the system. This ground can be provided only at the premises station and with both line conductors X and Y open there is no connection to the premises station.

A ground on both line conductors X and Y does not automatically send in a fire alarm. Thus, in response to a ground on both line conductors X and Y, relay 4 pulls causing the release of relay 8. Thereafter relay 3 pulls. With both relays 3 and 4 operated, a path is completed from battery I8 through relay I over contacts TI and BI of relay 8, contacts T2 and F2 of relay 4, contacts T3 and F3 of relay 3 to the X line and thence to ground, and current flow over this circuit maintains relay I operated. It is to be understood that in an actual system an operator is always on duty at the central station who will immediately be acquainted, in a manner to be described, of trouble conditions on the line so that following the grounding of both line conductors X and Y this operator would immediately take steps to insure the protection of the premises associated with the grounded line until the line has been repaired.

Circuit for indicating the existence of line faults in the fire alarm system It will have been observed from the foregoing description of the operation of the fire alarm system shown schematically in Fig. 3 that either a short on the line conductors X and Y, an open on either or both line conductors X or Y, a ground on either or both line conductors X or Y,

an open on either or both loop conductors II or I2, or a ground on either or both loop conductors II or I2, caused the release of relay 8 at the central station. It is apparent, therefore, that relay 8 releases in response to any of the line or loop faults enumerated and that this relay may therefore be employed to give an indication at the central oflice of the existence of any of the enumerated faults.

Referring now to Fig. 2, it will be observed that relay 8 is provided with an extra armature contact T6 and cooperating front contact F6 (these contacts not being shown in the schematic circuit of Fig. 3). It will be observed that when relay 8 is operated, which condition obtains only when the entire circuit is in normal condition, a circuit is completed from ground over contacts F6 and T5 of relay 8, through the winding of the trouble alarm relay I8 and thence back to battery I8. Therefore, when the system is in normal condition relay I0 is actuated and maintains its associated contacts in open condition. However, when relay 8 releases in response either to any line trouble or to a fire alarm, relay I8 is released by the opening of contacts F6 and T6 on relay 8. 'I'hereupon relay I0 releases, completing a circuit from ground over its contacts T2 and B2, through a buzzer cutout key 21, and a buzzer 20 to the battery I9 and completes another circuit from ground over contacts TI and BI on relay I8 through the blue lamp B to battery I9. Therefore, as soon as any trouble arises in the system or a bona fide fire alarm is sent in, the buzzer 28 sounds and the blue lamp B lights. The buzzer 20 may be silenced by manually opening the buzzer cutout key 21 but the blue lamp B continues lighted until relay 8 is restored to normal position.

To enable the attendant at the central station to ascertain whether the blue lamp B has been lighted in response to line faults or a bona fide alarm, the red lamp R is provided. This lamp is connectible between the battery I9 and ground through the back contact B and armature T of relay 6. It will have been observed from the description of operation in response to a fire alarm that the trasmitter T is never released to transmit an alarm until relay 6 releases. Therefore, the red lamp R is never lighted unless the transmitter T has been released to transmit an alarm. Accordingly, if lamp B only is lighted, the attendant knows that a trouble condition has arisen on the line or loop circuit whereas if both lamps B and R are lighted the attendant knows that an alarm has been sent in.

Restoration of the premises station and subscribers supervisory panel circuits to normal condition following an alarm or trouble condition Following the existence of line trouble and/or the transmission of a bona fide alarm, some or all of relays I, and 2 at the premises station and relays 6, I, 8 and II) on the subscribers supervisory panel SP are released and some or all of relays 0 at the premises station and relays 3 and 4 on the subscribers supervisory panel may be locked up. It is to restore these relays to normal condition (the condition shown in Fig. 2) that key A on the subscribers supervisory panel and key Z at the premises are provided. The resetting or restoring operation is performed as follows:

The handle Al on key A on the subscribers supervisory panel is first moved to the right.

to contact Bl on relay 8.

This disconnects the battery A from the feed circuit to transfer contact T2 on relay 8 at contacts B2 and T2 on key A and connects the battery feed through contacts T2 and F2 on key A Contacts T3 and F3 on key A connect the white lamp W in series between the battery l9 and ground, causing this lamp to light and remain lighted as long as the handle Al on key A is actuated to the right.

1 Key A is preferably designed to remain locked in the right position until released and the white lamp W serves as a constant indicator to the operator that this key is out of its normal position. Contacts B4 and T4 on key A are in series with the contact TI on relay 8 and serve to break the connection between the X line and relay 'l which was closed at the time relay 8 released in response to a trouble or alarm condition in the circuit. Contacts B1 and TI on key A are con- 0 nected in series between the contact T3 on relay 8 and the contact B2 on relay 3, over which connection was made in response to release of relay 8 between the Y line and relay 1. Contacts T1 and F1 on key A are bridged across contacts F4 and T4 on relay 8 and serve to reestablish connection between the winding of relay 8 and the Y line. Contacts T8 and F8 on key A are bridged across contacts F5 and T5 on relay 8 and serve to reestablish normal connection between the winding of relay 1 and ground. Contacts T9 and F9 on key A serve to apply ground to the winding of relay 6 to restore that relay.

it will be observed from the foregoing that movement of handle Al on key A to the right directly restores relay 6; reconnects the battery ill to contact T2 on relay 4 (and through contact B2, the winding of contacts TI and Bl of relay 4 if the latter is released to the X line conductor) reconnects the relay 8 and the relay 1 in series between ground and the contact B2 on relay 3 (and thence through contact Tl, the winding of contacts T4 and B4 of relay 3 and contacts T5 and B5 and key A to the Y line if relay 3 is not operated) and lights the signal lamp W.

In the meantime an attendant has been sent to the premises station and following the movement of key A and. the subscribers supervisory circuit at the central station to the right as described, this attendant actuates the key Z at the premises station and releases the latch H on the relay 0 if the latter has been operated. Actuation of key Z closes contacts Fl and TI on that key, which bridge the contacts Fl and TI on relay 2, thereby reestablishing connection between the X line to the loop conductor l I through the winding of relay 2. At the same time actuation of key Z closes contacts T2 and B2 thereon to bridge the contacts F3 and T3 on relay l and reconnect the Y line through the winding of relay ;.l and the contacts B2 and T2 and the winding of relay 0 to contact T3 on relay 2. Actuation of key Z also opens the normally closed path from contact B3 on relay l to ground over contacts T3 and B3 of key Z. It will be observed,

"therefore, that actuation of key Z completes a circuit from line conductor X through the winding of relay 2 to loop conductor ll, thence through the loop resistor 24 to the loop conductor l2, and thence through contacts T2 and B2 on relay 2, and the resistor l5 to the Y line conductor. Now if relays 3 and 4 at the central station were not operated, the movement of key A to the right connected line conductor X to battery and line conductor Y to ground at the central station. However, to restore relays 3 and 4 to normal unoperated condition in case one or both of them happens to be operated, the central station attendant next moves the handle A2 on key A momentarily to the left. This opens the battery feed through resistance 22 to the locking contacts of relays 3 and 4 at contacts Tl and BI on key A to release those relays.

With relays 3 and 4 released, current from the battery l3 flows out over X line, through the contacts TI and Fl on key Z, through the winding of relay 2, through the loop conductor ll, loop resistor 24, loop conductor l2, contacts T2 and 332 of relay 2, through resistor IE, to line conductor Y and thence to ground at the central station. This energizes relay 2, which when it pulls up completes a circuit from line conductor X, contacts Ti and Fl and winding of relay 2, loop conductor ll, loop resistor 24, loop conducior l2, contacts F3 and T3 on relay 2, the winding of contacts T2 and B2 of relay 0, contacts B2 and T2 of key Z, the winding of relay I, back to the Y line conductor, causing relay l to pull and complete its holding circuit through its own contacts F3 and T3.

It will be observed that following the foregoing operations all the relays in the system have been restored to normal condition. The operator at the central station thereafter restores the key A to normal position by moving the handle Al to the left, which reestablishes the subscribers supervisory panel circuit to the normal condition shown in Fig. 3. Thereafter the attendant at the premises station restores key Z to normal position, leaving the premises circuit in the normal condition shown in the schematic circuit of Fig. 3. Restoration of key A at the central station extinguishes the white lamp W. If the line and loop circuits are in normal condition, the relays 6, 1 and 8 will remain operated and the red and blue lamps R and B, respectively, will likewise be extinguished. These three signal lamps W, R and B, therefore, inform the operator that the entire circuit is in normal condition awaiting an alarm.

The apparatus at subscribers premises and on the subscribers supervisory panel in the butglar alarm system As previously mentioned, my burglar alarm system differs from my fire alarm system only in the apparatus at the subscribers premises and on the subscribers supervisory panel SP at the central ofilce, the transmitters T (referring for the moment to Fig. 1), line finders LF, headquarters lines supervisory panels HP, headquarters line HL and alarm recorders AR being identical in both fire and burglar alarm systems. The burglar alarm circuit for the apparatus at the subscribers premises P and on the subscribers supervisory panel SP is shown in detail in Fig. 5 and schematically in Figs. 6 and 7.

Referring first to Fig. 6, circuit elements in the burglar alarm system corresponding in function to those in the fire alarm system are indicated by the same reference numerals with the prime mark added. Thus it will be observed that relays l and 2' in Fig. 6 correspond to relays l and 2 at the premises station in Fig. 3 but that there is no relay at the premises station in the burglar alarm system corresponding to relay 0 in the fire alarm system. Relays 3', 4', 6, 'l' and B on the subscribers supervisory panel in the burglar alarm system correspond in function to relays 3, l, 6, 7 and 8 in the fire alarm system. However, the subscribers supervisory panel equipment in the burglar alarm system includes an add tional relay not present in the fire alarm 5 system.

The protection loop at the premises station in the burglar alarm system (Fig. 6) includes a pair of loop conductors II and i2, respectively, interconnected by a resistor 2 but the alarm 9 responsive devices I3 in the burglar alarm sys term are adapted to open the loop circuit in response to danger instead of shorting the loop circuit as was the case in the fire alarm system. It will be observed that whereas in the fire alarm 5 system the loop circuit was indirectly opened by the relay 0 in response to a short on the loop caused by a danger condition, the loop in the burglar alarm system is directly opened in response to danger without the use of a relay.

A full operation of the burglar alarm system disclosed in Figs. 6 and 7 will now be explained with reference to various line faults and alarm conditions that may arise. It will be shown that the system illustrated in Figs. 6 and 7 will respond to release the transmitter T and transmit -an alarm to police headquarters in response to any one of the following conditions:

(1) An open in any part of the loop circuit; (2) A ground on the loop conductor ll; (3) A short across the loop conductors II and (4) An open on both line conductors X and Y;

(5) A ground on both line conductors X and Y;

and that the system will give a trouble indication and restore the line and loop circuits into condition to transmit a bona fide alarm followmg:

(1) A short circuit on the line conductors X and Y;

(2) An open on either line conductor X or Y; (3) A ground on either line conductor X or Y; and that it will respond to a resistance bridge 45 maliciously placed across line conductors X and Y followed by an open circuit in the protection loop.

Normal operation of the premises station and subscribers supervisory panel circuits in the burglar alarm system in response to a bona fide alarm Referring to the schematic diagram of Fig. 6, which shows the premises and subscribers super- 55 Visory panel circuits in normal condition awaiting an alarm, assume that a burglar attempts to break into the premises and thereby actuates one of the danger-responsive devices I3 to open the loop circuit. This opening of the loop circuit 60 stops the flow of current from the central station over the circuit shown in heavy lines. Thus this circuit may be traced from grounded battery I8 through the wind ng of relay 5, over contacts T2 and FE of relay 8, the contacts B2 and T2,

65 the wind ng, and contacts BI and TI of relay 4,

out over the line conductor X through the winding, and contacts Fl and T! of relay 2 through the loop conductor ii, the loop resistor 24, the

70 loop conductor 2, contacts F3 and T3, winding of relay l, back over the line conductor Y, through contacts Bi and T4, the winding, and contacts T2 and B2 of relay 3 through the contacts F4 and T l, to the winding of relay 8,

75 through the winding of relay I and thence through contacts F5 and T5 on relay 8' back to ground. As in the fire alarm system described in connection with Fig. 3, the loop resistor 24 is of such value, relative to the potential of battery I8 and the characteristics of the various relays in the heavy line circuit that under normal conditions relays I, 2, I and 8 are operated (the condition shown in Fig. 6). This normal current flow, however, is insufficient to operate relays 3', 4 and 5. So long as the relay 7 is operated, it completes a circuit from ground over contacts T and F of relay I through the winding of relay 6, thence through the contacts B and T of relay 5 to battery I8, thereby maintaining relay 6 operated, and as long as relay 6 is operated, it connects ground to the input terminal 25 of the transmitter T. The other input terminal 26' of transmitter T is permanently connected to the battery, as shown. As was previously stated in connection with the fire alarm system, the

transmitter T remains locked up as long as the input terminal 25 is connected to ground and is released to transmit an alarm responsive to opening of the contacts F and T on relay 6.

With the loop circuit open, in response to an attempted burglary, as previously stated, the heavy line circuit is opened causing the immediate release of relays I and 8. The release of relay I disconnects the loop conductor I2 from the line conductor Y over contacts T3 and F3 on relay I and at the same time reconnects loop conductor I2 to ground over contacts T3 and B3 of relay I through a reactance element 32 (this reactance element has a low resistance for direct current but a high impedance for alternating current for a purpose to be described later).

The release of relay 8 reconverts the circuit on the supervisory panel to applybattery directly through relay 1 to both line conductors X and Y in substantially the same manner as was described in connection with the fire alarm circuit of Fig. 3. Thus following the release of relay 8 the circuit may be traced over battery I8 through the winding of relay 5 over contacts T2 and B2 of relay 8 through the Winding of relay I, thence through contacts TI to contact BI on relay 8. From contact BI a circuit is completed as previously traced over contacts T2 and B2, the winding, and contacts BI and TI of relay 4 to the line conductor X. At the same time a circuit is completed from contact BI on relay 8 to the line conductor Y which may be traced from contact BI over contacts B3 and T3 on relay 8, thence over contacts B2 and T2, the winding, and contacts B4 and T4 of relay 3.

The application of battery to line conductor Y produces no immediate flow of current therethrough because the latter is open at the premises end at contact F3 on relay l and contact B2 on relay 2'. However, an appreciable interval after the opening of the loop circuit in response to an attempted entry of the premises, the slow-release relay 2' releases. This opens the line conductor X at contact Fl on relay 2 to connect the loop conductor II through contacts Ta and B2 on relay 2 to the line conductor Y. Despite this circuit conversion at the premises station, no current flow can occur over either line conductor because of the fact that the loop circuit is open. Therefore, after an additional interval of time following the release of relay 2, relay I releases, causing the release after a further interval of time, of the slow-release relay 6 which releases the transmitter T to send in the alarm.

Operation of the premises station and subscribers supervisory panel circuit in the burglar alarm system in response to a ground on the loop conductor 11 The system will also respond to transmit an alarm in response to a ground on the loop conductor II, which ground might readily result from an attempt on the part of an intruder to tamper with the alarm circuit. The system responds to a ground on the loop conductor II as follows:

The ground on the loop conductor H shunts out both relays I and 8, causing their immediate release. The relay I in releasing transfers the loop conductor I2 from connection to the Y line conductor to ground, the release of relay 8 reapplies battery through relay 7' to both line conductors through relays 3 and 4. The ground on the loop conductor II causes a current in excess of normal value to flow out over the line conductor X, which current pulls relay 4 (this relay locking up over its contacts F3 and T3 and TI and FI exactly as described in connection with the fire alarm system of Fig. 1). The operation of relay 4 opens the line conductor X at contacts BI on relay 4 thereby stopping flow of current through relay 2 at the premises station, which releases after an interval. The release of relay 2 disconnects the loop conductor I I from the line conductor X and connects loop conductor II to line conductor Y. Thereafter a heavy current flows out through the Y line to the ground on the loop conductor II pulling relay 3 which looks up in exactly the manner described in connection with the fire alarm system. With both relays 3 and 4 pulled, the line conductor Y is permanently opened at contacts B4 on relay 3. However the circuit from battery I8 through the winding of relay 5, the various back contacts on relay 8, and the winding of relay 1 is recompleted to line. conductor X through contacts T2 and F2 on relay 4, contacts T3 and F3 on relay 3. No current, however, can flow out over the line conductor X because the latter is open at the premises end at contact FI on relay 2. Therefore all current flow through relay 1' is stopped and relays 'l and 6 release after an interval of time to release the transmitter T.

Operation of the premises station and subscribers supervisory panel circuit in the burglar alarm system in response to a short on the loop conductors The system shown in Fig. 6 responds to a short circuit across the loop conductors II and I2 (which may be occasioned by tampering with the circuit), to transmit an alarm as follows:

Assuming the circuit in the condition shown in Fig. 6, a short across the loop conductors II and I2 shunts out the loop resistor 24, thereby causing an increase in the flow of current over the heavy line circuit sufficient to actuate relays 3 and 4. As in the fire alarm system, however, relay 3 is adjusted to pull before relay 4 and ordinarily will be the only one to pull immediately in response to the shunting of the loop resistor 24. The operation of relay 3 opens the line conductor Y at contact B4 on relay 3, immediately releasing relays I and 8. Relay I immediately transfers the loop conductor I2 from connection to the line conductor Y to connection to ground through the reactance element 32. The release of relay 8 immediately reestablishes current flow from battery I8 through the winding of relays 5, l and 4 out over the line conductor X through relays 2 to loop conductor II, thence through the short across the loop conductors to ground. This causes relay 4 to pull which opens the circuit from relay 5 to the line conductor X over the contacts BI and TI of relay 4 but reestablishes a circuit to the line conductor X over contacts T2 and F2 of relay 4, and contacts T3 and F3 of relay 3. Therefore, a current in excess of normal value continues to flow through the windings of relays 5 and I. Relay 5 is a marginal relay adapted to pull on this excessive current flow when pulled it opens its contacts T and B to break the current supply for the winding of relay 6 wit the result that after a short interval of time the relay 5 releases to release the transmitter T and transmit an alarm.

Operation of the premises station and. subscribers supervisory panel circuits in the burglar alarm system in response to an open or ground on both line conductors An open circuit condition of both line conductors X and Y completely incapacitates the line for indication or signaling purposes, and the system is therefore arranged to transmit an alarm to police headquarters in response to such a condition. The system functions in this respect as follows:

Opening of the line conductors X and Y immediately releases relay 8. The latter, in releasing, re-establishes a circuit from battery through relays 5 and l to both line conductors. However, the latter bein open, no current flow can occur and after an interval of time the slowrelease relays 'i and 6 release, thereby releasing the transmitter T to transmit an alarm code to the police headquarters.

Since a ground on both line conductors X and Y also totally incapacitates the line for signaling purposes, the system is adapted to transmit an alarm code to police headquarters in response to occurrence of such a condition.

With the circuit in the normal condition as shown in Fig. 6, the ground on either of the line conductors X or Y shunts out the relay 8 causing the latter to release and ire-establish connection from battery is through the windings of relays 5 and l to both line conductors. Thereafter the excessive current flow to both line conductors through relays 3 and 4' causes both of those relays to pull. As has been previously explained, with both relays 3 and 4 operated a circuit is completed through contacts T2 and F2 on relay 4 and contacts T3 and F3 on relay 3 to the line conductor X. Thereafter following the operation of relays 3 and 4 a heavy flow of current still persists through relays 5 and l to the ground on the line conductor X. This excessive current flow actuates the marginal relay 5 to open the operating circuit of relay 5 thereby releasing that relay which in turn releases the transmitter T.

Operation of the premises station subscribers supervisory panel circuits in the burglar alarm system response to a short on the line conductors X and Y followed by an abnormal condition the loop circuit A short on the line conductors X and Y does not incapacitate the line for signaling purposes. The system is, therefore, designed to convert this line to maintain the system in condition to respond to a bona fide alarm without actually sending in an alarm at the time trouble occurs.

With the system in the normal condition as shown in Fig. 6, a short across the line conductors X and Y immediately causes an increased current flow from battery I8 through relays and l to the line conductor X, thence through the short and through line conductor Y back through the relays 3, 8 and I to ground. Relay 3 immediately pulls, opening the line conductor Y and momentarily opening the energizing circuit for relay 8 causing the latter to release. The release of relay 8 reconnects the battery I8 through relays 5, l and 4 to the line conductor X. The short across the line conductors X and Y also shunted out the relays I and 2 at the premises station end and relay I immediately released to transfer the loop conductor I2 from connection to the line conductor Y to connection to ground. However, before the slow-release relay 2 had time to release, potential was restored to the line conductor X by the disconnection of the line conductor Y at the central station end, at contact B4 of relay 3. The momentary increase of current fiow to relay 5 might also have pulled that relay (although relay 5 is adjusted to operate on a heavier flow of current than relay 3') to open the operating circuit of relay 6'; however, relay 5 was again released in response to the opening of the line conductor Y by relay 3 before relay 6 had time to release.

As a result of the foregoing operations, the system is restored to alarm-responsive condition by completion of a circuit for normal current flow from battery I8 through relay 5, relay I, relay 4 through line conductor X, the relay 2, loop conductor II, loop resistor 24 and loop conductor I2 to ground. If the loop circuit is now opened in response to a bona fide alarm by actuation of one of the elements I3, the normal flow of current is interrupted, causing the release of relay I, which in turn releases relay 6 which in turn releases the transmitter T to send an alarm. Relay 2 also releases in response to the open loop condition but this does not prevent the release of relay 1 because, regardless of whether the line conductor X or Y is connected to the loop conductor II, there can be no current flow as the path to ground from the loop conductors I I has been opened.

The system (as converted after a short on the line conductors X and Y) will also respond to a short on loop conductors I2 and I3, shorting out the resistor 24. This causes relay 4 to pull but the only effect is to reestablish the connection from. relay I to the line conductor X over contacts F2 and T2 of relay 4 and contacts T3 and F3 of relay 3 instead of through contacts T2 and B2, the Winding and contacts BI and TI of relay 4. The increased current flow, therefore, continues and actuates the marginal relay 5 for a sufficient length of time to cause the release of relay Ii and the release of the transmitter T.

The system wil1 also respond to a ground on the loop conductor II to transmit an alarm. It will be unnecessary to trace the whole sequence of operations under these conditions, as they are identical with the sequence of operations in response to a short on the loop conductors which was outlined in the preceding paragraph.

Operation of the premises station and subscribers supervisory panel circuits in the burglar alarm system in response to an open on the line conductor X followed by an abnormal condition in the loop circuit With the circuit in normal condition, as shown in Fig. 6, an open on the line conductor X interrupts the normal flow of current over the path shown in heavy lines, immediately releasing relays I and 8. The release of relay I transfers the loop conductor I2 from connection to the line conductor Y to connection to ground and the release of relay 8 reconnects the battery I8 in series with the relays 5 and l to both line conductors. No current can flow out over the line conductor X, however, because the latter is open. Likewise at the moment no current can flow out over the line conductor Y because the latter is open at the premises end at contact F3 on relay I and contact B2 on relay 2. However, since the open circuit condition on line conductor X also interrupted the flow of current through relay 2 the latter releases after a short interval and in releasing disconnects loop conductor II from the line conductor X and connects it to the line conductor Y through contacts T2 and B2 of relay 2. Thereafter normal current flows from battery I8 through relays 5 and I and 3 out over the line conductor Y through contacts T2 and B2 of relay 2 to the loop conductor II and thence through the loop resistor 24 and loop conductor l2 to ground.

With the circuit in the condition last described an open in the loop conductor releases the relay I by cutting off the path to ground therefrom, causing the release of relay 6 and the release of transmitter T.

The system will also respond to a short on the loop or a ground on the loop conductor II (following an open on the line conductor X) to transmit an alarm as follows:

Either a short on the loop conductors II or I2 or a ground on the loop conductor II shunts out the resistor 24, thereby permitting an increased current flow through relay 3 causing the latter to pull thereby opening connection between relay I and line conductor Y at contact B2 on relay 3 causing relays I and 6 to release and release the transmitter T to transmit an alarm.

Operation of the premises station and subscribers supervisory panel circuits in the burglar alarm system in response to an open on the line conductor Y followed by an abnormal condition in the loop circuit With the circuit in normal condition as shown in Fig. 6, an open on the line conductor Y immediately releases relays I and 8 as described in connection with an open on the line conductor X, the relay I transferring the loop conductor I2 from connection to the line conductor Y to ground and the relay 8 applying battery through relays 5 and I and through relays 3' and 4 to both line conductors. The line conductor Y being open, no current flow can occur thereover. However, normal current flow is reestablished through relay 4 and line conductor X, the winding, and contacts FI and TI of relay 2 through the loop conductors and loop resistor to ground.

Thereafter an open on the loop circuit breaks the path to ground stopping the flow of current through relay I and causing the latter to release and release relay 6 which in turn releases the transmitter T. The system also functions to transmit an alarm in response to a short on the loop conductor or a ground on the loop conductor II since either condition shunts out the resistor 24 thereby increasing the current flow through relay 4 and causing the latter to operate. The operation of relay 4 breaks the current flow from relay I to the line conductor X causing the relay I to release and release relay 6 which in turn releases the transmitter T.

Operation of the premises station and subscribers supervisory panel circuits in the burglar alarm system in response to a ground on the line conductor X followed by an abnormal condition in the loop circuit With the circuit in normal condition as shown in Fig. 6, a ground on the line conductor X immediately shunts out relays I and 8 causing them to release. Relay I transfers the loop conductors I2 from connection to the line conductor Y to ground. Release of relay- 8 reconnects the relays 5 and l in series between the battery I8 and both line conductors X and Y through relays 4 and 3, respectively. Thereafter heavy flow of current occurs through relay 4 to ground on line conductor X opening the latter at contact B on relay 4. After a slight interval slow-release relay 2 also releases, transferring loop conductor II from connection with the line conductor X to connection with the line conductor Y. This reestablishes a circuit for normal current flow from battery I8 through relays 5, I and 3, thence out over the line conductor Y and through contacts B2 and T2 on relay 2 to the loop conductor II and thence through the loop resistor 24 and the loop conductor I2 to ground. With the circuit in the condition last described, an open in the loop circuit stops the flow of current through the relay l causing the release of the latter and the release of relay 6 to release the transmitter T.

A short circuit on the loop conductors II' and I2 causes an increased current flow through relay 3 which thereupon pulls and reconnects the relay I to the line conductor X over contacts T2 and F2 on relay 4 and contacts T3 and F3 on relay 3. Since the line conductor X is grounded, an increased current thereafter flows through relays 5 and I causing relay 5 to pull and release the relay 6 which, in turn, releases the transmitter T to transmit an alarm.

Since a ground on the loop conductors I I has the same direct effect as a short across the loop conductors I2 and I3, it likewise actuates the circuit to release the transmitter T in the manner just described.

Operation of the premises station and subscribers supervisory panel circuits in the burglar alarm system, in response to a ground on the line conductor Y, followed by an abnormal condition in the loop circuit With the circuit in normal condition as shown in Fig. 6, a ground on the line conductor Y shunts out the relay 8 causing the latter to release and re-establish current supply through relays 5 and l to both line conductors X and Y. In releasing, relay 8 momentarily interrupts the current supplied to line X, causing the release of relay I at the premises station, which transfers the loop conductor I2 from connection to the line conductor Y to connection with ground. Following the release of the relay 8 an excessive current flow occurs through the relays 5 and I and 3 to the ground on line conductor Y, causing relay 3 to pull and open the Y line conductor at contact B4 on relay 3. Thereafter normal current flow continues from battery I8 through relays 5, I and 4 out over the line conductor X through the relay 2 and its contacts F! and TI, thence through the loop conductor II, loop resistor 24 and loop conductor I2 to ground.

With the circuit in the condition last described an open in the loop circuit causes actuation of one of the devices I3, opens the path to ground for the current flow through relays 5 and I, and causes the release of relay I, the release of relay 6, and the release of the transmitter T to transmit an alarm.

If, instead of an open circuit occurring in the loop, the loop conductors II and I2 become shorted, or the loop conductor II becomes grounded, the resistor 24 is shunted out increasing the current flow sufficient to pull the relay 4. This produces no change in the circuit, however, since relay 3 was previously operated. and with both relays 3 and 4 operated, the circuit is reestablished from relay I to the line conductor X. Therefore the excessive current flow continues and pulls the relay 5 to release the relay 6 and release the transmitter T to transmit an alarm.

system in response to a ground on the loop 0012- ductor 12, followed by another abnormal condition in the loop circuit The system shown in Fig. 6 will respond to a ground on the loop conductor I2 to release relay 8 at the central station and thereby give a trouble indication, but will not transmit an alarm. Thus a ground on the loop conductor I2 shunts out relays I and 8 and causes their immediate release. The release of relay I breaks connection between the loop conductor I2 and the line conductor Y and reinforces the ground on loop conductor I2. Following the release of relay 8 a circuit is re-established from battery I8 through relay 5 and relay I out over the line conductor X through the winding of relay 2 to loop conductor II, and thence through the resistor 24 to ground on the loop conductor I2. The resistor 24 still being in circuit, the current flow is insufiicient to actuate relay 4 and the circuit will remain in the condition outlined ready to respond to an open circuit on the loop should one occur in response to a bona fide alarm. Should an open on the loop circuit occur the transmitter T will be released to transmit an alarm substantially as described in connection with the normal operation of the system.

Operation of the premises station and subscribers supervisory panel circuits in the burglar alarm system, in response to a resistance bridge across the line conductors X and Y, followed by an abnormal condition in the loop circuit In most instances, the only trouble or fault conditions that can occur on the line conductors X and Y, are those previously enumerated, namely, a short on the line, or a ground, or an open on either or both lines. However, skilled criminals might attempt to disable the circuit shown in Fig. 6 by shunting a resistance across the line conductors X and Y of such value as to carry enough current to maintain relay 8 operated without increasing the current flow sufficiently to operate relays 3, 4 or 5. If this were done, the criminal could thereafter open the line circuit on the premises side of the bridge without sending in an alarm. To prevent the possibility of the system being disabled in this manner, the premises circuit of Fig. 6 may be modified. as shown in Fig. '7 by replacing the loop resistor 24' with a slow-release relay 28 having contacts T and B shunted across the winding and contact T3 of relay I. The winding of the relay 28 has the same resistance as the resistor 24' for which it is substituted so that it functions to limit the normal current flow in the system to a value insufficient to actuate the relays 3, 4, I and 5. This normal current fiow through the winding of relay 28, however, is sufficient to maintain it operated under which condition the contacts T and B thereon are open.

Relay 28 is designed to release (following interruption of current flow there-through) even more slowly than the slow-release relays 2, I and 6 so that it does not interfere with the normal operation of the system under the various conditions specified hereinbefore.

Now with the circuit of Fig. 6, modified as shown in Fig. 7, in normal condition, assume that a resistance bridge is shunted across the line conductors X and Y of sufficiently low resistance to maintain the relays l and 8 operated independently of flow of any current through the premises. circuit, but of not low enough resistance to increase the current flow to a value sufficient to operate the relays 3, 4 and 5. Assume next that the criminal enters the premises and in doing so actuates one of the danger--responsive devices l3 and opens the loop. This interrupts the flow of current through relays I and 2, relay l releasing instantly and relay 2 releasing after a short interval. Up to this point, however, nothing has happened in the supervisory panel circuit for the reason that relay 8 is still held up by normal current flow through the resistance bridge across the line conductors X and Y. The opening of the loop circuit, however, deenergizes the relay 28 and after a prolonged interval of time this relay releases to close its contacts T and B and connect the line conductor Y to the loop conductor l2 which has previously been connected to ground over the contacts T3 and B3 of relay 1 when the latter released. This applies ground to the line conductor Y and shunts the normal current fiow away from relay 8 causing the latter to release and reconnect the battery it! through relays 5 and 1 to both line conductors. Insuflicient current flow can occur through relay 4 to operate it for the reason that the only path to ground from the line conductor X is through the resistance bridge. However, a heavy flow of current occurs through the relays 5 and 3' to the line conductor Y, causing relays 5 and 3' to operate. The operation of relay 3 opens the line conductor Y at contact B4 on relay 3, thereby interrupting the heavy initial flow of current through relay 5. However, three is still a fiow of current through relays 5 and 'l to the line conductor X, thence through the resistance bridge across the line conductors to line conductor Y and thence through the contacts of relay 28 and the contacts T3 and B3 of relay l to ground. It was previously stated that this flow of current was insuflicient to operate relay 5. However. after relay 5 has once been pulled by the initial heavy flow of current through relay 3 to the line conductor Y, rela 5 will hold up on the current flowing to the line conductor X, thereby opening the contacts T and B on relay 5 for a prolonged interval of time to release relay 6 which in turn releases the transmitter T to transmit an alarm.

Line fault indicating equipment on the subscribers supervisory panel in the burglar alarm system The equipment and circuits for indicating the existence of trouble on the line or loop circuit in the burglar alarm system are substantially the same as in the fire alarm system. Thus in each system the relay 8 or 8 releases in response to a trouble condition, and auxiliary contacts T6 and F3 on this relay are opened in response to release of the relay 8 or 8 to release the trouble alarm relay H) or H! in the respective circuits. The release of the relay I in the burglar alarm system (Fig. closes circuits for the operation of the alarm buzzer 2B and the blue lamp B exactly the same as the corresponding elements were operated in the fire alarm system of Fig. 2.

Likewise the release of the relay 6 in the burglar alarm circuit of Fig. 5 to release the code transmitter T also completes a circuit to energize the red lamp R and visually indicate that an alarm has been transmitted.

Restoration of premises and subscribers panel apparatus in the burglar alarm system to normal condition following a trouble condition or the transmission of an alarm The burglar alarm system shown in detail in Fig. 5 includes on the subscribers supervisory panel SP a key A corresponding in function to the key A in the fire alarm system previously described. The circuit connections to this key need not be described in detail since they correspond to those in the fire alarm system.

The apparatus for restoring the relays at the premises station, however, is quite difierent from that in the fire alarm system since in the burglar alarm system I provide special means for resetting the premises relays from the central station by means of a key 30 and a key 33. The complete operation of resetting is as follows:

First handle A2 on key A is moved to the left to release relays 3 and 4 in case they were locked up. Then the handle Ai on key A is moved to the right and left in that position to operate relay 6 and relay 8. Next the handle 301 of key 30 is moved to the right to close contacts T5 and F5 thereon and place a shunt around the marginal relay 5 to prevent it from operating and releasing relay 6. (The remaining circuit operations performed by the manipulation of key 39 are of no interest in connection with the resetting operation but are useful for a different purpose to be described later). Thereafter the handle 302 on key 30 is moved to the right closing contacts T8 and F8 to shunt out relay 3 and prevent its operation and to close contacts T9 and F9, shunting relay 4 to prevent its operation; thereafter while handle 302 is held to the right the key 33 is actuated first to the right and then to the left or vice versa to successively apply alternating current from a source 3 to the two line conductors X and Y. Alternating current applied to the line conductor X flows out to the premises station, through the winding of relay 2, through a condenser 35 bridging the contacts TI and Fl

Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US2821699 *Dec 30, 1955Jan 28, 1958American District Telegraph CoBurglar alarm
US4945344 *Nov 23, 1987Jul 31, 1990Farrell Jonathon EFluid flow sensor having light reflective slider
Classifications
U.S. Classification340/287, 340/508, 340/292, 340/521, 340/305, 340/533
International ClassificationG08B29/00, G08B29/06
Cooperative ClassificationG08B29/06
European ClassificationG08B29/06