US2094211A - Alarm circuit - Google Patents

Description

Sept. 28, 1937. H. c. GRANT, JR 2,094,211`

ALARM CIRCUIT Original Filed Nov. 21, 1929 3 Sheets-Sheet 1 DCIEIDI'JDDD DDUDDDDDD UDDDUDDUD UDDD DDU DDDUDDDEEDDDDDDDUDDDDUDUDDDCIDDUDDUUUDDDD IN VENTOR www@ w ATTORNEYS ALARM CIRCUIT Original Filed Nov. 2l, 1929 3 Sheets-Sheet 2 To F ra H

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H15 ATTORNEYS Sept. 28, 1937. H. c. GRANT, JR

ALARM CIRCUIT 3 Sheets-Sheet 3 Original Filed Nov. 21, 1929 9W [115 ATTORNEYS Patented Sept. 28, 1937 ALARM CIRCUIT Harry Campbell Grant, Jr., New York, N. Y., as-

signor to Walter Kidde & Company, Inc., New York, N. Y., a corporation o! New York Griginal application November 21, 1929, Serial No. 408,740. Patent No. 2,003,358.' Divided and this application November 10, 1931, Serial No. 574,092. Renewed December 3, 1936 4 claims. (ci. r11- 355) E The present application is aA division of applicant's copending application Ser. No. 408,740 for System for indicating the presence and location of fire, iiled November 21, 1929, now Letters- 5 Patent No. 2,003,358 dated June 4, 1935, and relates to that portion of the system shown and described in the above copending application which includes the alarm circuits for actuating an alarm mechanism upon the existence of a l disorder in the alarm system or the actuation of an alarm initiating-mechanism.

More particularly, the invention embodies an improved alarm system wherein supervising alarm mechanism is utilized in connection with l a general alarm mechanism, means being provided to disconnect the supervising alarm and prevent its actuation upon the actuation of the general alarm mechanism. In this fashion, the functions of the supervising or trouble alarm mechanism and the general alarm mechanism are isolated and a correct indication given as to the nature of a disturbance in the alarm system.

An object of the invention, accordingly, is to provide an alarm system wherein a general alarm,

as well as a 'trouble alarm are utilized, means being provided to isolate the function and opera- `tion'of these two alarms whereby each will properly respond only to the particular conditions which it is desired that the respective alarm mechanisms shall actuate.

A further object of the invention is to provide an improved alarm mechanism of the above character wherein a supervising relay is provided for controlling the actuation of trouble alarm 3 mechanism, such relay being adapted to be short circuited upon the existence of a condition which actuates the general alarm, further means being provided to open the circuit of the trouble alarm mechanism upon the short circuiting of the said relay to prevent operation of the trouble alarm mechanism upon such condition.

Further objects, not specifically enumerated above, will be apparent as the invention is described. in greater detail in connection with the accompanying drawings, wherein:

Figure 1is a wiring diagram showing schematically a fire detecting system constructed in accordance with the present invention.

AFigures 2 and 3 `are diagrammatic views showing the system of Figure 1 enlarged.

At the outset, the general detecting and signalling system in connection with which the present alarm system is used will be described in order that the present invention may be more fully understood and its scope appreciated.

Referring to the above drawings, a battery' is indicated at BAT. having its positive terminal connected to a positive bus wire I which includes ra battery supervising relay 2, a switch Su having switch points3 and 4, connections 5 and 6, switch 5 Sm having switch points 1 and 8, and positive bus wire 9. A plurality of externalr circuits, in which thermostats or other suitable heat operated devices are connected, is used in connection with the system shown and described herein, but for 10 the purposes of description and in the interest of clarity, only two such circuits have been shown. These circuits have 'been marked as A and B and one side of each of these circuits is connected to the positive bus wire 9. Since the 15 circuits A and B are identical and are connected to similar relays and associated elements, only the connection for circuit B will be described herein, it being understood that the corresponding elements of circuit A, as well as other circuits, 20 not specifically shown, function in the same man-x ner as the elements of circuit B. The other side of each external circuit is connected to the negative terminal oi the battery and the elements for so connecting these circuits include, in the case 25 of circuit B, a Wire I6, a contact I1, a trouble `alarm relay Ti, a fire alarm relay M1, wire I8,

wire I9, and negative bus wire 20, such negative bus wire being connected to the negative terminal of the battery.v 30

It' will thus be seen that a supervisory current lflows through the external circuit, the trouble alarm relay T1 and the re alarm relay M1. I! a break should occur in the wire so 'that current through the trouble alarm relay T1 is interrupted, 5 this relay will be deenergized and will close contacts 2| and 22, causing a trouble alarm lamp L1 to be lighted. Current flows through the trouble alarm lamp L1 from the positive bus wire 9 through the' lamp, contact 2l, to connection 23, contact 24, and connection 25 to the negative bus wire 20. 'I'his light indicates trouble in the external circuit B. At the same time, the general trouble alarm bell T. B. is sounded since it is connected to the positive bus wire through wire I0, point 26, point 21, point 2,8, point'29, through the bell T. B., point 30, wire 32, points 33, 35, and 31, contact 22, contacts 38 and 39 of switch Si, point 23 through contact 24 and point 25, 5o to negative wire 20. In order to clear the gen'- eral trouble alarm bell so that it may be free to indicate trouble in other circuits, the switch S1 is thrown to the left to make contact at point 40, thus opening the circuit through the general 55 trouble alarm bell and clearing the bell for the indication oi' trouble in the other circuits. The trouble alarm lamp L1 remainslighted until the trouble has been repaired whereupon the trouble alarm relay T1 picks up its armature thus opening the contacts 2| and 22. The trouble alarm lamp L1' remains lighted, however, by reason of its connection from the positive wire 9 to the successive points 40, 39, 23, 24, and 25, the latter of which is on the negative wire 20. In order to clear the trouble alarm lamp L1, the switch S1 is thrown to its normal position at the right, as viewed in the gure, to make contact atv point 39, thus opening the circuit through the trouble alarm lamp L1 just described.

The battery supervising relay 2 is in series with the circuit supplying current to the external cir- Vcults and if the current from the battery should fail, the battery supervising relay 2 will be deenergized and close contacts 4I and 42, thus causing the battery supervising trouble alarm lamp la to be lighted and the general trouble alarm bell T. B. to be sounded. Current iows through the trouble alarm lamp La from the positive bus wire 9 through wire I0, points 26, 21, 12 and 30|, through the lamp La, contact 4I, and point 302 lto the negative line at point 303; while the path of current through the general trouble alarm bell T. B. is from the positive bus wire 9 through wire I0, points 26, 21, 28 and 29, through the general trouble alarm bell T. B., points and 304, contact 42, switch S1, and point 302 to the negative line atpoint 303. The switch S1 is provided to clear the general trouble alarm bell in the same manner as that described in connection with the trouble alarm relay T1.

Two lire alarm bells are provided, one supervised and one unsupervised. The supervised iire alarm bell is indicated at S. A. while the unsupervised bell is indicated at U. A. The supervised bell is in series with a relay 43 which is of such resistance as to prevent the ringing of the supervised nre alarm bell, at the same time permitting a supervisory current to ow. The supervisory connection is from the positive wire 9 to the successive points 26, 21, and 28, through the supervised re alarm bell to the point 44, through the winding of the relay 43 and connection 45 to the point 48 on the negative bus wire 20. It the supervised alarm bell should become inoperative, the supervising current will fail and the relay 43 will become deenergized, thus permitting the closing of its contacts at 41 and 48, thus lighting the supervised-flre-alarm-bell-trouble alarm lamp L: and sounding the general trouble alarm bell. Current flows through the trouble alarm lamp La from the positive busl wire 9 through wire I0, points 26, 21 and 12, through the lamp Le, contact 41, point 13, wire 14 and contact 89 to the negative line; while the path oi' current through the general trouble alarm bell T. B. is from the positive bus wire 9 through wire I0, points 28, 21, 28 and 29, through the general trouble alarm bell T. B., contact 48, switch Se, point 13, wire 14 and contact 69 to the negative line. The switch Se is provided for clearing the general trouble alarm bell in the same manner as that described in connection with th trouble alarm relay T1.

A iuse 22| will be found in one lead to the supervised nre alarm bell. The reason for installing this fuse is that the resistance of the -winding oi' the supervised nre alarm bell is ordinarily only a fraction of one percent of l,the resistance ofthe winding of the ilre alarm 'bell supervising relay 43. Ita short circuit of the supervised fire alarm bell leads should occur, no trouble signal would be given because the short circuit oi the winding or the supervised re alarm bell would allow a -slightly greater supervising current to ow through the supervising relay, this increase in current not being, however, great enough to blow Ithe fuse I22|. If a ilre signal should be given, at which time the high resistance of the supervised nre alarm bell supervising relay is cut out of the circuit, the short circuit of the rlre alarm bell connecting wires would constitute a direct short circuit across the source of current and, therefore, the fuse 22| is placed in one lead to the supervised rire alarm bell to relieve, immediately, this short circuit condition which otherwise would seriously aiect the operation of the other circuits of the system. The blowing out of thisiuse places the system in a condition to ren'der a delayed trouble signal in a manner to be described hereinafter.

In order that `this condition be assured, it is essential that the fuse 22| be of a lower rating than the main battery and main power supply fuses, so that the fuse 22| will blow first, as otherwise the system would be rendered inoperative. In fact, the normal current passing through each of the main fuses must be allowed for, so that the short-circuit current added to kthe normal current is not suflicient to blow a main fuse before the fuse 22|.

A resistance 49 is connected in the external circuit B at the extreme end thereof and the resistance is of such value as to limit the current which iows through the trouble alarm relay T1 and the lire alarm relay M1 to a value below that necessary to cause the re alarm relay M1 to pick up. If, however, by reason of a re in one of the spaces protected on the circuit B, a thermostat should function and thus short circuit the resistance 49, sufficient current will iiow through the circuit already described and cause the ilre alarm relay M1 to pick up its armature and close contacts at points 50, 5|, 52, and 53, at the same time breaking the contacts at Athe `points I1 and 24. The :tire alarm relay M1 is so constructed that the contact 5I will make before the contact I1 breaks. The purpose of contact I1 is to connect the resistanceof the external circuit across one portion of a Wheatstone bridge as described hereinaiter.l

The opening of the contact I1 would result in the deenergization of the fire alarm relay M1 were it not for the closing of contact 5| before the opening of contact I1. By reason of the closing of the contact 5|, a connection is made through the winding oi.' the iire alarm relay M1 from the positive bus wire 9 through conductor |4| to the successive points 54, 55, 56, 51, wire 58, connection 59, wire 60, connection 6| through contact 5|, the winding of iire alarm relay M1, wires I8 and I9, to the negative bus wire 20. 'I'he nre alarm relay M1, therefore, remains energized until the circuit through its winding is manually opened in the manner described hereinafter.

Upon the closing oi contact 52, a relay 62 is energized by reason of its connection to the posii contacts 41 cessive points 26, 21, 28, and

`connection 98, contact 99,

|8| connections |82 connection from the positive wire to the ' successive points 28, 21, and 28 through awire 18 to the point 44, through a wire 1 I, through contact 68, to the` point 45, and thence to the point 46 on the negative line. By reasonV of the short circulting ofl the supervised fire alarm bell supervising relay 43, the relay 43 is deenergized and the and 48 are closed. This would cause trouble alarm lamp La to light and the general trouble alarm bell to sound if it were not for the fact that the contact 69 of .the relay 62 opens the connection from the trouble alarm lamp and from the general trouble alarm bell to the negative line. It will be seen that the trouble alarm lamp circuit is from the positive wire 9 to the successive points 26, 21, 12 through the trouble alarm lamp and contact 41 to a point 13 (where the line from the general trouble alarm bell joins a common return 14) through such common return to the contact '69 and the negative line wire.

The unsupervised fire alarm bell U. A. is caused to ring at the same time as the supervised re alarm bell,v the circuit for accomplishing such ringing being closed through the contact 61. Current flows from the positive wire 9 to the suc- 29, through the unsupervised re alarm bell U. A. and through contact 61 to the negative line. Closing of the contact 66 produces an operation which will be described more fully hereinafter.

External circuit fire alarm lamps A', B', C', D', E', F', G', H', I', J', K', etc. corresponding to the external circuits A, B, etc. are connected in series with a supervising relay 15. The supervising current flows through a circuit from positive wire 9 through a wire I to a connection 16, through a wire |26 to a connection 11, through contact point 18 to connections 19, 88, wire 8|, connections 82 and 83, contact `point 84, connections 85 and 86, wire 81, connection 88, contact 89, connection 98 and wire 9|, connections 92 and 93, contact 94, connections 95 and 96, wire 91, connection |88, wire and |83, wire |04, relay 15, connection |85 and wire |86 to negative wire 28. Since the external circuit re alarm lamps are in series, if any of the lamps become defective, the supervising current will cease and the relay 15 will be deenergized, closing its contacts |89 and H8. Closing contact |89 establishes a connection from the positive wire 9 through wire I I to point 16, through the trouble alarm lamp L4, through the contact |89, point ||2, through wire I|3 and contact ||4 to wire ||5 and the negative wire 28. At' the same time, connectionis established from the positive wire 9 to the successive points 26, 21, 28, and 29 through the general trouble alarm bell to the point 38 through the wire 32 and point 33, wire I I6 to contact ||8 and point ||1, through switch S10 to point ||2 and negative wire as described above, thus causing the sounding of the general trouble alarm bell. The switch S10 is provided for clearing the general trouble alarm bell in the manner already described in connection with the trouble alarm relay T1.

At the same time that a re alarm relay, for example, M1 is energized with consequent energization of the relay 62, a relay ||8 is energized by reason of its connection from the positive Wire through the wire III- to the points 16 and 11, through the winding of the relay ||8 to a point ||9 and through a wire |28 to the point 63 which is connected to the negative line through wirev 64, contact 52 and point 25. Upon energization of the relay ||8, the contacts at 1a, s4, as, 9|, as and H4 are broken, while contacts are closed at I2I, |22," |23, |24, and |25.

'The external circuit re alarm lamp B', corresponding to the external circuit B, is then lighted by reason of its connection from the positive wire 9 through the wire 'to .the point 16, through wire |26 to point 11, throughcontact |2| to point 88, through wire 8| to point 62, through contact |22 to point |21, through contact |23 to point |28, through contact |24v to point |29, through contact |25 to point |82, through wire |8| and fire alarm lamp B to` point |88, through wire |3| to contact 53, and to connection 25 on the negative line. The reason that the deenergization of the relay 15 does not result in lighting the trouble alarm lamp L4 and ringing the general trouble alarm bell upon the breaking of the contacts at 18, 84, 89, 94, 99, and ||4 is that the contact ||4 is in the line which connects the trouble alarm lamp L4 and the general trouble alarm bell to the negative line. When the contact I4 is opened, the trouble alarm lamp L4 and the general trouble alarm bell cannot function.

The foregoing description has dealt chiefly with the Yvarious means for indicating trouble and with the means for indicating the particular circuit from which a fire signal has been given. It will be seen that the foregoing construction will function equally well regardless of the number of external circuits and the corresponding fire alarm lamps which are connected therewith. The following description is concerned principally with the means for detecting the. exact thergalvanometer and to one terminal of the variable known resistance |31. It will be seen that point |32 is connected through a resistance |38 to points |39, |48, wire |4I, contact 248, contact 24| to the negative Wire 28.

Point |35, on the other hand, is connected to the positive line through wire |44, resistance |45, movable contact |46, point |41, wire |48, resistance |49, and point |58 to a movable contact |5| and point |52 through wire |53 which isconnected to the positive line through point |54 and wire |55 to point 54 and positive wire 9. One side of the external circuit B is connected to the positive line and the other side of the circuit B, upon energization of the fire alarm relay M1, is connected to the point |36 through wire I6, contact 58, point |56, Wire |51, point |58, wire |59 and point 36.

Upon the occurrence of lre in any space, the fire alarm relay, corresponding to the circuit by which such space is protected, isgenergized. A iire alarm lamp indicating the circuit is lighted and the fire alarm bells are sounded. The resistance of that portion of the external circuit lying between the positive line and the particular thermostat which has functioned, is brought into proper relation with the Wheatstone bridge arrangement for;` permitting the automatic balancing of the resistance of the external circuit `and .the consequent determination of the particular' thermostat which has functioned. The variable resistance |31 consists of a rotary switch such as is now employed in automatic telephone work, resistances being connected be tween each of the adjacent points of the rotary switch.

With reference to the external ci/rcuit B, it will be seen that the path of the'supervisory circuit from the positive wire 6 is through a compensating resistance |60, a resistance U1, 'the terminal of a thermostat TTi, a resistance U2, through the terminal of a thermostat T'In, etc., 'there being similar resistances before each thermostat. With reference to the variable resistance arrangement I 31, the resistance |46 is of the same value as the resistance U1; and the resistances R2, Ra, R4, etc., are of the same Values as the corresponding resistances U2, Us, U4, etc., all of the resistances being of the same value. If, therefore, the contact |46 is moved from the ilrst point of the rotary switch to any other point,

there can be cut into the Wheatstone bridge ar-v rangement, enough resistance to balance the resistance from the external circuit which is thrown in as another leg of the Wheatstone bridge arrangement.

'I'he automatic balancing of the resistance of the external circuit is accomplished through the medium of the Wheatstone bridge arrangement in combination with a. galvanometer relay, the relay being so connected to the circuit that its contact remains closed asvlong as the balancing resistance |31 is less than the resistance of the external circuit. It will be seen that the variable resistance |31 has been shown with the movable contact |46 on the first point of the rotary switch. This is the normal position of rest at which time only the resistance |46 is in the balancing resistance circuit so that theV resistance is always less than the resistance thrown in from the external circuit (except for the rst resist'- ance, which will be discussed later on). If, therefore, any thermostat beyond the rst one functions, a resistance greater than the balancing resistance will be thrown across the proper leg of the Wheatstone bridge, and the galvanometer relay contact |6| will be closed.

As soon therefore, as a ilre alarm relay, such as M1 is energized, a relay I 62 is energized by reason of its connection from the positive wire 9 through the connection 54, line |55, connection |54, wire |53, connection |63, wire |64, contact |65, wire |66, through relay |62, galvanometer contact |6|, wire |4|, contact 246, contact 24| to the negative wire 20. When the relay I 62 is energized, the contact I1 is closed. This results in energizing relays indicated as Mot. and Mot. 2, by reason of their connecton with the positive wire |53 throughthe motor relay windings, the

' parallel relay contacts 243 and 244, respectively,

wires 245 and 245" and connection 245, wire 246, connection 241, contact I1I, connection |05 and. wire |06 to the negative line wire 26. Upon the closing of the contact I'II of the relay |62, connection is established from the positive line to the negative line. The slow acting relay 231 is thus energized and contact |65 opened, thus deenergizing relay |62 so that contact III is opened and slow acting relay 231 deenergized. This cycle of operation is repeated as long as the galvanometer contact I6 I is closed. At the same time that the slow acting relay is deenergized by the opening of the contact I'II or the relay |62, the motor relays Mots. I and 2 are deenergized and simultaneously with the deenergizatlon of the motor relays, the movable arm |46 moves one step from the flrst to the second point of the rotary switch. 'I'he same cycle is repeated until the amount of the balancing resistance |31 which has beenv cutin, is equal to, or greater than, or

even somewhat less than, the cut-in portion of the resistance of the external circuit. Asv soon as this condition is reached, the current flow through the galvanometer Vwinding either weakens sufficiently, ceases, or reverses, so that the galvanometer contact |6| is broken, as well as the circuit through the relay |62. The rotary switch has therefore come to a position of rest and can be'made to indicate the exact thermostat which has functioned. This will be described in greater detail hereinafter. While ina theoretically perfect circuit the balancing resistance can be considered as exactly balancing the resistance of the external circuit, the resistance of the external circuit might be somewhat less than the proper balancing resistance due to slight negative errors in winding the resistance units U1, U2, etc., while it might be somewhat more than the proper balancing resistance due to more wiring being used in the external circuit than the theoretically correct amount. 'I'he galvanometer relay is therefore adjusted to,operate over a range such that the correct balancing resistance will be cut in not only when the resistance of the external circuit equals the proper balancing fresistance, but also when it is within predetermined negative .l and positive variations from the proper balancing resistance.

On the assumption that the flrst thermostat has functioned, the lamp O of the tens column and the lamp I of the units colum will be lighted in the following manner. The positive line wire 9 is connected to all of the lamps of each column and current flows through the proper lamp, in the hypothetical instance the lamp O, of the tens column to point |14, througha movable contact |15, connection |16, wire |11, and wire |43 to the connection |I6, wire |26 and connection 63 to wire 64, and contact 52 to connection 25 on the negative line. At the same time, current ows from the positive wire 9 through the units lamp I, wire |13, movable contact |66, and through the Aconnection |16 and path just traced. The connection of the points in the ilfth row is such that a. single set of lamps will serve for the unit indications, while the connection in the fourth row is such that one lamp is required for each of the tens of the series of thermostats and balancing resistances.

Relay 231 is a very slow acting relay to permit motors I and 2`to complete, with certainty, a cycle of operation before a new cycle is instituted. As before described, when galvanometer contact |6| is closed, connection is established from the positive line at |63, through contact |65, wire |66, relay |62 and galvanometer contact |6| to the negative line. Relay |62 is thus energized and contact I1I closed so that connection is established from the positive line at 228, through the winding of the relay 231, through contact |1I and to the negative line. The relay 231 is thus energized and contact |65 opened thus deenergizing relay |62 so that contact I1| is opened and relay 231 deenergized. 'Ihis cycle of operation is repeated as 'long as the galvanometer contact 6| is closed. Each time that contact |1I is closed, connection is established from the positive vto points 254 and line through the windings of the motor relays I and 2 through parallel contacts 243 and 244,.

wire 240, to the point,241 and which results 'in the deenergization of the motor relays and 2 and of the slow acting relay 231.

In order to reset the system, the push button switch |94 is operated to make contact with the point |92. Breaking the contact at 55 causes the deenergization of the fire alarm relay M1 with the consequent return to normal conditions of the apparatus controlled thereby. Connection is thus established from the positive lline at 54 to the point |92, through wire 250 to connection 25|, through the windings of relays 252 and 253, 255, to the interconnected points of the two rotary switches through wires 254' and 255. From these respective interconnected points, the circuit is completed to the negative line through points 235 and 236.y The relays 252 and 253 are therefore energized, causing the respective contacts at 24| and 243 for the relay 252, and 240 and 244 for the relay 253 to be broken and contacts 266 and 251, to be closed for the relay 253-, while the corresponding contacts are closed for the relay 252. With the closing .of the contacts 256 and 251, connection is established from the positive line |53 through points |52 and 232, through contact 251 and line 250, to the point 25|, through the windings of the relays 252 and 253 to the points 254 and 255 to the interconnected points of the rotary switches and thus to the negative line. Even though the pushv button -switch |94 is returned to its normal position in contact with point 55, the relays 252 and .253 remain energized until such time as movable contacts |9| and |98 rest upon the rst points'of the respective rotary switches. Through the closing of the contact 266 of the relay 253, connection is established from the positive line through the motor relay 2, through the contact 266, contact |69, to the interconnected points of the rotary switch and thus to the negative line. Corresponding action occurs for relay 252 and results in energization of the motor relay I. At the same time, contact |69 is opened and the motor relay 2 is deenergized,.causing the advance of lthe rotary `switch one step. After sueh advance, the contact |69 is again closed and the motor relay is again energized. Such operation continues until vthe movable contact |9| rests upon the first point of the rotary switch. Ii, for any reason, motor 2 should get out of. step with motor motor 2 will not continue to operate vits rotary switch but will come to rest because it is no longer energized after the movable contact |9| rests upon the rst point of the rotary switch. Motor is therefore free to return the other rotary switch to its initial position without being affected by the action of motor 2.

The switch 208 is a push button switch similar to the push button switch |94 and interconnected with the switch |94 in a series parallel arrangement, and is controlled!" by the opening of the door of4 the cabinet in which all of the apparatus s is arranged. Upon the occurrence of fire, the fire alarm bells sound and the system automatically balances itself. The fire watch attendant then runs to the central station and opens the door lof the cabinet, thus causing the switch 209 to momentarily close the circuit from the point 56 to the point |93, causing a'resetting action to occur in the same manner as caused by the push button switch |94. As soon, however. as the movable contacts reach the rst switch points, the fire indication is repeated and the fire watch attendant can determine from the lamps which are lighted the space which is aiire. He can then push down the manual reset push button |94 and reset the system, and when the movable contacts again reach the rst switch points the fire indication will be again given as a check upon the initial reading. This resetting operation can be made as many times as the fire watch attendant desires in order to be sure that the apparatus hasfunctioned properly and that the proper space hasbeen indicated.

After the fire has been extinguished and the thermostat has been renewed, the door of thev inserted at predetermined intervals in the exterl nal circuits while compensating resistance |45 may be inserted before the movable contact |46 to correspond with the resistance |60, while compensating resistance 2|0 may be inserted between the fourteenth and fifteenth contacts in the second row of contacts to correspond with the resistance 209.

A door switch C. D. S. is provided in the circuit of theflre alarm bell ringing relay 62, so that upon the opening of the cabinet door the fire alarm bells will stop sounding. If, however, the cabinet door is closed before the short circuited thermostat has been restored with a new, open circuited thermostat, the bell will again ring and indicate the failure to restore the thermostat. Attempting to reset the apparatus without restoring the thermostat will merely result in the repetition of the fire signal.

If on the other hand, the cabinet door is left open, ,as it should b until the thermostat hasA been restored and if the thermostat is removed from the line (the thermostats are not bridged across two continuous wires, but the external circuit wires are run in sections between the thermostats, and the thermostats are designed so that when removed, they break both sides of the externalV circuit and thus initiate a trouble signal) the trouble signal will not be given because the iire alarm relay has remained energized and the trouble circuit has been disconnected, but the wire break left by the removal of the thermostat constitutes an infinite resistance thrown across one leg of the Wheatstone bridge, and the arm of the rotary switch advances to the last point of the balancing arrangement when an infinite resistance is then thrown in to balance the infinite resistance of the open external circuit. When the thermostat has been restored, the arm of the rotary switch still rests on the last point because the current limiting resistance in the external circuit is great enough to require the infinite resistance to balance it, no other balancing resistanceV being available. All during this time the external circuit re alarm lamp has remained lighted. If now the cabinet door is closed, the reset button operated by the closingv action of the door will cause 'the fire alarm relay to be deenergized and the system to be restored to its normal condition, the rotary switch arm advancing to the ilrst point. Ii' on the other hand. someone should close the cabinet door between the time the short circuited thermostat was removed and a new thermostat installed, the nre alarm signals will be cleared immediately, and th'e trouble signal will be given. If, still further, a thermostat should be removed from an external circuit, the condition of the system being initially normal (for example, no nre signal has been previously given), the trouble signal will be immediately given, indicating a wire break,

Reference has been made hereinbefore to the use of a fuse 22| in the supervising circuit of the supervised fire alarmbell for the purpose of preventing the failure of the system due to a short circuit of the supervised ilre alarm bell. As previously described, the fuse 22| is designed to blow out at the time that a fire signal is given. As soon as the cabinet door is opened to stop the sounding oi' the ilre alarm bells, the bell ringing relay 82 is deenergized and the circuit through the trouble signal is closed so that the delayed trouble signal hereinbefore referred to is thus given, together with the fire signal.

In the explanation given at the beginning of this description, the battery was pointed out as the source of energy for furnishing the supervising current. This reference was made for simpliilcation of the description. In reality the battery is under trickle charge, the actual current normally supplying the supervising current to they positive line 9 being obtained directly from the power supply terminals indicated to the right of the battery terminal. The normal path of the supervising current is from the positive terminal 2|2 of the power supply to the point 2|2 through the contact 2|! through the successive points 2|5, 2|6, and 2|1, through the wire 2|8, through the contact 2|8, through the successive points 6, 6, l, and l and then through the external circuitsback to the negative line in the manner alrea described. It will be noted that the contact 2|9 short circuits the resistance 220.

'I'he path of the battery charging current is from the positive terminal 2|2 of the power supply to and through the successive points 2|3, 2| l, 2li, 2|6, and 2|,|, through the contact 2|9, to and through the successive points 5, 4, and 3through the winding of the relay 2, to the positive terminal I of the battery, and then to the negative line.

It so happens that when the flre alarm bells are sounding, a much greater current is required from the power supply, and the tendency would be for the voltage across the system to decrease below the battery voltage. In order to prevent such decrease, a portion of the resistance in the power supply circuit is cut out. 'Ihis resistance is shown at 222 and is short circuited by the closing of the contact 66 of the bell ringing relay 82.

On the other hand, if the battery should for any reason go oi! the line, a smaller current would be drawn from the power supply, and the tendency would be for the voltage across the system to increase. In order to prevent such increase, additional resistance must be added to the power supply line. This resistance is shown at 22|l, and is added by the removal of the short circuit at the contact 2|! of the battery supervising relay 2, which is deenergized upon the failure of the battery. with the result that the contact 2|! is opened.

The power supply is supervised by the relay 224 to be closed, at the same time opening contact 2 Il in order to prevent the discharge of the battery back through the circuits which may also be connected across the power supply. 'I'he closing of the contact 225 results in the lighting of the trouble alarm lamp L; and the-closing oi' the contact 228 results in the sounding of the general trouble alarm bell. Ihe switch Sa is provided to clear the general trouble alarm bell, in the manner already described in connection with the trouble relay T1.

From the foregoing description, it will be apparent that a ilre detecting system is provided embodying a minimum of wiring, the system being completely supervised against wire breaks, power supply trouble, battery trouble, external circuit alarm trouble, and external circuit flre alarm lamp trouble. A single general trouble alarm bell may be employed which may be readily cleared at all times for the indication of trouble mother circuits. 'I'he trouble alarm lamps will remain lighted until the trouble has been repaired and until the trouble alarm lamp switches have been returned to their normal positions, and the system is capable of indicating exactly the location of a fire, either through manual balancing means, or automatic balancing means. The system provides for checking the results rendered either manually or automatically, and permits the checking of the restoration of the thermostat that hasfunctioned since the system cannot be returned to its normal condition unless the therthe sounding of the fire alarm bells can be stopped by the opening of the cabinet door and so that the ilre must be attended to and the thermostat replaced before the cabinet door can be closed again without the repetition of the nre signal. In the event that the system is not properly reset, -the closing of the cabinet door can be made to operate a resetting switch.

While the invention has been described with speclnc reference to the accompanying drawings, it is not to be limited, save as defined in the appended claims.

I claim as my invention:

1. In an electric alarm system of the type comprising a normally inactive alarm circuit, a source of electrical potential for energizing said circuit,

a fuse in at least one of the main supply leads ing actuated; the provision of means for enabling an alarm to be rendered despite short-circuiting of the alarm leads and consequent short-circuiting of the source of electrical potential, said last named means comprising a second alarm adapted to be controlled by a normally open contact of said alarm actuating relay, and a fuse in said series circuit through the ilrst named alarm of lesser rating than a main supply fuse, whereby said last named fuse is adapted to open said series circuit through the ilrst named alarm upon shortcircuiting of the leads thereof and ensuing actuation of said alarm circuit and to thereby remove the resulting short-circuit of the source of electrical potential without blowing a main supply fuse, thereby leaving the alarm system in condition to render an alarm through said second named alarm.

2. In an electric alarm system of the type comprising a normally inactive alarm circuit, a source of electrical potential for energizing said circuit, a fuse in at least one ofthe main supply leads from the source of electrical potential, an alarm having a pair of leads subject to shortcircuiting in use, a relay controlled by said alarm circuit, and a contact controlled by said relay and arranged to control an alarm operating current in a series circuit including said alarm, said leads and said source of electrical potential upon said alarm circuit being actuated; `the provision of means for enabling an alarm to be rendered despite short-circuiting of the alarm leads and consequent short-circuiting of the source of electrical potential, said last named means comprising a second alarm adapted to be controlled by a normally open contact of said relay, and a fuse in said series circuit through the rst named alarm of lesser rating than a main supply fuse, whereby said last named fuse is adapted to open said series circuit through the rst named alarm following short-circuiting of the leads thereof and to thereby remove the resulting short-circuit of the source of electrical potential without blowing a main supply fuse, thereby leaving the alarm system in condition to render an alarm through said second named alarm.

3. In an electric alarm system of the type comprising a normally inactive alarm circuit, a source of electrical potential for energizing said circuit, a main alarm, a main alarm supervising relay, connections to connect said main alarm, said main alarm supervising relay and said source of electrical potential in a series circuit, whereby a supervisory current of limited value flows through said series circuit, a trouble alarm, a normally open contact controlledA by said main alarm supervising relay, connections to connect said trouble alarm, said normally open contact and a source of electrical potential in a normally open series circuit, a main alarm actuating relay controlled by said alarm circuit, and a normally open contact controlled by said main alarm actuating relay and arranged to short-circuit said main alarm supervising relay upon closing of said last named contact upon said alarm circuit being actuated; the provision of means for preventing operation of the trouble alarm, due to short-circuiting of the main alarm supervising relay, concurrently with the operation of the main alarm, said last named means comprising a normally closed contact controlled by said main alarm actuating relay and arranged in the normally open series circuit through the trouble alarm, whereby operation of the main alarm actuating relay to actuate the main alarm opens said last named contact and thereby prevents closing of the normally open series circuit through the trouble alarm upon closing of the norm'ally open contact controlled by the main alarm supervising relay.

4. In an electric alarm system of the type comprising anormally inactive alarm circuit, a source of electrical potential for energizing said circuit, a fuse in at least one of the main supply leads from the source of electrical potential, a main alarm having a pair of leads subject to short-circuiting in use, a main alarm supervising relay, connections to connect said main alarm, said leads, said main alarm supervising relay and said source of electrical potential in a series circuit, whereby a supervisory current of limited value ilows through said series circuit, a trouble alarm, a normally open contact controlled by said main alarm supervising relay, connections to connect said trouble alarm, said normally open contact and a source of electrical potential in a normally open series circuit, a main alarm actuating relay controlled by said alarm circuit, and a normally open contact controlled v by said main alarm actuating relay and arranged to short-circuit said main alarm supervising relay upon closing of said last named contact upon said alarm circuit being actuated; means for enabling an alarm to be rendered despite shortcircuiting of the main alarm leads and consequent short-circuiting of the source of electrical potential, said last named means comprising a secondary alarm adapted to be controlled by a normally open contact of said main alarm actuating relay, and a fuse in said series circuit through said main alarm of lesser rating than a main supply fuse, and means for preventing operation of the trouble alarm, due to short-circuiting of the main alarm supervising relay, concurrently with the operation of the secondary alarm, said last named means comprising a normally closed contact controlled by said main alarm actuating relay and arranged in the normally open series circuit through the trouble alarm.

HARRY CAMPBEIL GRANT, J R.

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