US2942245A - Combined fire alarm and intercommunication system - Google Patents

Description

June 21, 1960 s. D. WOOTEN, JR

COMBINED FIRE ALARM AND INTERCOMMUNICATION SYSTEM Filed Feb. 13, 1956 2 Sheets-Sheet 1 INVENTOR SPENCER D. WOOTEN JR.

June 21, 1960 s. D. WOOTEN, JR

COMBINED FIRE. ALARM AND INTERCOMMUNICATION SYSTEM Filed Feb. 15, 1956 2 Sheets-Sheet 2 I N VENTOR i WH N3 wen owm 1% J 0% I: 0 3n n 3N g m E. Q N Q m mg a H mum n 8m m IL w SPENCER D. WOOTEN JR United tesatfint O COMBINED FIRE ALARM AND INTERCOM- MUNICATION SYSTEM Spencer D. Wooten, Jr., 646 Madison Ave., Memphis, Tenn.

I Filed Feb. 13, 1956, Ser. No. 565,072 I 3 Claims. Cl. 340-213 system including. a master unit having a speaker station, a

and a plurality of speaker stations located remotelyv from the master unit, in which any speaker station can'call all other stations in the system using only a single ampli': fierat the master unit. This intercommunicati'on system also includes an override arrangement which automaticallyj causes all speaker stations whose control switches are in'Ofi position, and thus are disconnected from the out: put of, the. amplifier for non-intercom reception, to be connected to the output of the amplifier when the control switch of any speaker station is in Intercom position.

It is an object of this invention to provide in combination with an intercommunication system of the type disclosed in my prior application an automatic fire-alarm system which causes the amplifier of the system to emit an alarm sound upon the occurrence of a fire in any loca: tion having a fire-detection device.

It is another object of this invention to provide a fire alarm system in which the alarm sound is produced by a conventional vacuum tube amplifier without the use of any special alarm signaling devices.

It is still another object of this invention to provide in combination with an intercommunication system of :the type disclosed in my prior application an automatic fire alarm system which cooperates with the override circuit of my prior application to sound an alarm even at speaker stations which are in Off position.

In achievement of these objectives, there is provided in accordance with this invention a fire alarm system in which the actuation of a fire sensing element, such as. a thermal responsive element, causes the output and input ends of a vacuum tube amplifier to be connected to each other in feed-back relation to thereby cause the amplifier to emit an alarm sound which indicates to the occupants of the premises that there is a fire.

- A further feature of the invention is the combination of a fire alarm device of the type just described with an iritercommunication system of the type described in my prior application Serial No. 493,137, filed March 9, 1955,

and-issued at Patent No. 2,896,022, dated luly 21, 1959;

in such manner that actuation of any fire sensitive element automatically connects all speakers in- Off position to the output of the amplifier through an override circuit so that these speakers are connected to the amplifier to indicate the presence of a fire.

Further objects and advantages of the invention will become apparent-from the following description taken in conjunction with the accompanying drawings in which: Fig 1a is an electrical circuit diagram ofithe portion tern including the amplifier; and

of the combined fire alarm and'intercommunicationsys Patented June 21, 1960 2 Fig. 1b is a continuation of the circuit diagram of Fig. la showing the switching and distribution arrangement of the speaker stations and also including the circuit connections of the fire-detection devices. Referring now to the drawings, and more particularly to Fig. 1a, the combined fire alarm and intercommunication system of the invention includes a superheterodyne radio receiver of conventional design generally indicated at 10. Receiver 10 includes a radio frequency section generally indicated at 12 including an antenna 14 which is coupled to the input grid of the oscillator-converter tube 16. The output of oscillator-converter tube 16is coupled through an I.F. transformer 18 to theinput of tube 20 of the intermediate frequency section 22.. The output of intermediate frequency section 22 is coupled to tube 24 of the combined second detector and first-audio stage 26. The audio output of stage 26 is coupled to amplifier tube 28 which constitutes the second amplifier stage. The primary winding 32 of an audio frequency output transformer generally indicated at is connected in the output or plate circuit of amplifier tube 28.

Output transformer 30 includes a secondary winding 34 having output conductors 36 and 38, respectively. Output conductor 36 is connected to ground at line 40.

The input power to the radio circuit is obtained through i a rectifier tube 43 which is connected to a sourceof AC. power through switch 45. v The radio receiver thus far described is a conventional five-tube-superheterodyne receiver. This receiver, together with a speaker station generally indicated; at 100, and

a control switch generally indicated at 164, is positioned in the master unit ,of the intercommunication system: Any number of substations, such as those generally '.-indicated at 200 and 300, respectively, are connected to the master unit. The substations are located remotely from the master unit as, for example, in various rooms of the house or ofiice or oifice building. s

In the embodiment shown in the drawings, two sub stations 200 and 300, each with their respective control switches 204 and 304 are shown in addition-to thespeaker station 100 located at the master unit. However, any number of speaker stations may be connected in the system consistent with the power rating of the master unit; v In order to interrupt the radio signal input to-the amplifier stages 26 and 28 when it is desired touse the apparatus for intercommunication purposes, means-are station to interrupt the circuit of cathode 44 of tube 20 in the intermediate frequency stage 22. For this purpose, a' conductor 42 conected to cathode 44 extends between each of the stations 100, 200 and 390 in series with ape propriate contacts at the respective stations in such man ner that movement of the control switch at any station to Intercom position causes opening of the circuit of cathode 44, thereby interrupting the radio signalinput to the amplifier stages. The circuit of cathode 44 is completed to the ground line 40 at' the last station 300. l i

In order'to couple the audio frequency input of the various speaker stations 100, 200 and 300 to the audio" frequency stages 26 and 28 when the apparatus is being.

used for intercommunication purposes, an audio fre quency transformer generally indicated at 46 is provided and includes an input or primary winding 48 and an out put or secondary winding 50. Conductors 52 and 54 are connected to opposite ends of input winding 48, conductors 52 and 54 being connected to speaker stations 100, 200 and 300 as will be hereinafter described.

I One end of secondary winding 50 of audio frequency transformer 46 is connected to ground line 40. The op= positeend of winding 50 is connected'by means of conductor 56, junction 58 and conductor 60 to control grid 3 62 of tube 24 in the first amplifier stage 26. A volume control potentiometer generally indicated at 64, includ ing movable contactor 66 and resistance 68 in the output circuit of intermediate section 22 is also connected to control grid 62 of tube 24 in accordance with the conventional method of obtaining manual volume control. However, the conventional circuit has been modified at this point by the introduction of a resistor 70, which may have a magnitude of approximately 220,000 ohms, for example, between movable contact 66 of potentiometer 64 and junction 58 where conductor 56 of transformer winding 50 joins conductor 60 leading to grid 62 of tube 24. The purpose of introducing resistor 70 is to prevent short circuiting of secondary winding 50 when movable contact 66 of the potentiometer is turned to Oh or to a low-volume position.

Each of the respective speaker stations 100, 200 and 300 is provided with a terminal strip to which the conductors 33, 40, 52, 54 and 42 are connected. In addition, a pair of conductors 72 and 74 extend between the ter* minal strips of the respective speaker stations as part 'of an override circuit to be hereinafter described. In practice, conductors 38, 40, 52, 54, 42,- 72 and 74 may be included in a single seven-conductor cable. ductors 38 and 40 from output winding 34 are preferably twisted on themselves in the cable, and similarly conductors 52 and 54 to input winding 48 are preferably twisted on themselves. By twisting the respective pairs fixed contacts 108, 110 and 112, respectively; movable contact 114 is selectively movable into engagement with Conof conductors 38'40 and 5254 as just described, feedback between the output and input circuits is substantially eliminated.

At each speaker station 100, 200, and 300 a four-pole three- position switch 104, 204 or 304 is provided, the switch being movable from an Ofi position at the left with respect to the view shown in Fig. 1b, to a Listen position (the intermediate position) to an Intercom or' Speak position at the right. The control switch is preferably so constructed that it must be moved against a spring bias when moved into Intercom or Speak position, the

switch moving out of Intercom position when manual pressure is released. This insures that the switch is not placed in Intercom position unless the operator intenti'onally moves the switch to this position. Suitable latch ing' means may be provided to hold the switch in Intercom position when desired. The contacts and internal connections of switch 104 or speaker station 100 will be described. The contacts and connections of switches 204 and 304 at speaker stations 200 and 300 are similar to those of switch 104, corresponding parts of switches 204 and 304 being identified by corresponding numbers in the 200 and 300 series, respectively. 7 Switch 104 includes movable contacts 106, 114, 122 and 138 which move in tandem to corresponding positions with respect to the three fixed contacts associated with each movable contact. 114 are connected to opposite ends of speaker coil 103 of speaker 102. The function of contacts 106 and 114 is to selectively connect speaker coil 103 to output transformer winding 34 when the switch is in the intermediate or Listen position, to input transformer winding 48 when the switch is in Intercom position, and in Off position to set up the override circuit through conductors 72 and 74 so that speaker 102 may receive intercom signals even when switch 104 is in Off position.

' Movable contact 122 is connected to conductor 38 as part of the override circuit and serves to connect conductor 38 to override conductor 72 when switch 104 is in Intercom position. The function of movable contact 138 is to open or close the circuit of cathode 44 of tube 20 to interrupt the connection of the radio signal to the amplifier stages 26 and 28 when the controlswitch is in Intercom position. i

. In the Of Listen and-Intercom positions, movable contact 106 is selectively movable into engagement with Movable contacts 106 and fixed contacts 116, 118 and 120, respectively; movable contact 122 is movable into engagement with fixed contacts 124, 126 and 128, respectively; and movable contact 138 is movable into engagement with fixed contacts 140, 142 and 144, respectively.

The connection from speaker station to theoutput of the amplifier is obtained through fixed contacts and 118 which are respectively connected to condoctors 38 and 40 and thus to the output transformer winding 34 of the amplifier stage. 'Fixed resistance 150 is interposed between fixed contact 118 and conductor 40 to limit the volume of speaker 102; Adjustable resistances 250 and 350 are used in thejcorresponding circuit positions at speaker stations 200 and 300.

The connection of station 100 to the input of the am plificr is accomplished through fixed contacts 112 and which are respectively connected to conductors 52 and 54 and thus to winding 48 of input transformer 46.

The set up connection of speaker station 100 to the override circuit which permits the speaker to receive intercom signals when its control switch is in Off position is obtained through fixed contacts 108 and 116 which are respectively connected to conductors 146 and 148 and thus to conductors 72 and 74 of the override circuit. Similarly, fixed contacts 208 and 216 of speaker station 200 are connected by conductors 246 and 248 to conductors 72 and 74 of the override circuit. Also, fixed contacts 308 and 316 of speaker station 300 are connected through conductors 346 and 348 to conductors 72 and 74 of the override circuit. I

The override circuit set up by the engagement of movable contacts 106 and 114 with fixed contacts 108 and 116 of the speaker in Off position is completed through the engagement of movable contact 322 with fixed contact 328 of speaker station 300 which is in Intercom position, or bythe engagement of movable contact 122 with fixed contact 128 or of movable contact 22 with fixed contact 228. Movable contact 322 is connected by conductor 352 to conductor 38 and thus to one side of output transformer winding 34. Thus, when movable contact 322 engages fixed contact 328, override conductor 72 is connected through conductor 38 to one side of output transformer winding 34. The other override conductor 74 is already permanently connected to conductor 40 and thus to other side of output transformer winding 34. Hence, the movement of any one of the movable contacts '122, 222, 322 into Intercom position connects any speaker whose control switch is in Oif position to output winding 34.

Conductor 42 in the cathode circuit of tube 20 is connected to fixed contact 140, contacts and 142 being connected together. Similar contacts are provided at the other stations. Movable contacts 138, 238 and 338 are connected in series with conductor 42and with fixed contacts 140 -442, 240--242, 340342 to close the cathode circuit of tube 20. Conductor 42 is connected to conductor 40 at junction 76 in speaker station 300 when movable contact 338 at station 300 is in engagement with either fixed contact 340.0r 342. of the movable contacts 138, 238 and 338 to open circuit position at contacts 144, 244, 344 opens the circuit of cathode 44 and thus disconnects the radio input signal to the amplifier.

Fire Alarm Circuit In accordance with this invention, a fire alarm device, such as that generally indicated at at station 100 is associated with one or more of the speaker stations. In the illustrated embodiment shown in Fig. 1b, it is assumed that a single fire alarm device is associated with each speaker station, the alarm devices at stations 200 and 300 being indicated at 260 and 360, respectively. However, it is to be understood'that any number of fire alarm Movement of any one devices may be used and need not be located in the same room a's'a speaker station.

The fire alarm device 160 includes two movable thermal responsive bimetal contacts 162 and 164 which both engage with a fixed contact 166 when suflicient heat, such as that caused by fire, actuates the respective bimetal elements. Bimetal contacts 162'and 164 close substantially simultaneously. Bimetal contact 162 is connected by a conductor 168 to override conductor 72. Fixed contact 166 which is engaged by movable bimetal contact 162 is connected by conductor 170 to conductor 38 which is connected to one side of output transformer winding 34. Thus, movement of bimetal contact 162 into engagement with fixed contact 166 completes a circuit from override conductor 72 to conductor 38 and thus to one side of output transformer winding 34. The closure of bimetal contact 162 thus performs the same electrical function as the movement of movable contact 122, 222, or, 322 into engagement with fixed contacts 128, 228 or 328 to complete the connection of override conductor 72 to one side of the outputtransformer winding. Since the other override conductor 74 is permanently connected to the other conductor 40 leading to the output transformer .winding 34, movement of bimetal contact 162 into engagement with fixed contact 166 connects output transformer winding 34 across override conductors 72 and 74.

Bimetal contact 1 64 is connected in series with resistance 172 and conductor 174 to conductor 52 which leads to one side of input transformer winding 48. Bimetal contact 164 is movable under the influence of heat into engagement with fixed contact 166 to complete aconnection from conductor 52 leading to input transformer winding 48 to conductor '38 leading to output transformer winding 34; Conductor 54 which leads to the other side of input transformer winding 48 is permanently connected at junction 176 '(Fig; 1a) to conductor 36 and thus to the other side of transformer winding 34; Thus,

the movement of bimetal element 164 into engagement with fixed contact 166, with the resultant connection of conductor 52 to conductor 38, completes the connection of output transformer winding 34 in parallel with input transformer winding 48. The connection of the output Winding 34 to input'winding 48 upon the occurrence of a fire causes an alarm signal to be transmitted to all of the speaker stations, producing a sound at the speaker stations having a predetermined tone such as 1,000 cycles per second, for example. This sound passing through the speakers serves as an alarm to the occupants of the premises. The pitch of the alarm sound is controlled by adjustment of resistance 172 in series with bimetal contact 164.

In case of fire, with consequent actuation of bimetal contacts 162 and 164, all of the speaker stations receive the fire alarm sound regardless of the positions of the respective control switches. Any speaker whose control switch is in Listen position receives the fire alarmsignal since it is directly connected to the output transformer 34. Also, any speaker whose control switch is in Intercom or Speak position receives the fire alarm signal since the input transformer winding 48 is connected in parallel with output transformer winding 34. Furthermore, any speaker station whose control switch is in Off position receives the fire alarm signal since the speaker stations whose switches are in Off position are automatically connected to the output transformer 34 through the connection of bimetal contact 162, or a bimetal contact having a corresponding member, to the override circuit and thus to the output transformer winding.

Summary of operation in engagement with fixed contacts 312 and 320, respectively, coil 303 of'speaker 302 is directly connected across conductors 52 and 54 and thus to input transformer 46; Speaker 302 when spoken into will develop a signal volt age which is applied through secondary winding 50 to input grid 62 of amplifier stage 26 and thence to amplifier tube 28. The audio output of tube 28 passes through primary winding 32 of output transformer 30 and from secondary winding 34 to conductors 38 and 40.

With switch 304 in Intercom position, movable contact 338 engages blank fixed contact 344 and thus opens the circuit of cathode 44 of tube 20. Hence, no radio signal is applied to the amplifier stages.

Speaker 202 is connected directly across conductors 38 and 40 by the engagement of movable contacts 206 and 214 with fixed contacts 210-and 218, respectively. Speaker 202 is thereby directly connected to winding 34 of output transformer 30 and thus receives the audio output signal from the amplifier in accordancewith the audio intercom signal developed at speaker 302. With switch 304 of station 300 inIntercom position. as shown, an override circuit is also completed through contacts 322 and 328 which connects override conductor 72 to conductor 38 and, since override conductor 74is already connected to conductor 40, both ovem'de conductors are connected to output transformer winding 34. Thus, the intercom signal developed in speaker 302'is heard at speaker 102 in spite of the fact that the control switch of speaker 102 is in Off position. I I It will thus be seen that the control switch which is in Off position sets up an override circuit to the output of the amplifier, the override circuit being completed through the switch which is turned to Intercom position.- Thus,'any speaker station whose control switch is in Off position receives intercom signals.

I Operation of fire alarm system When the bimetal contacts 162 andf164 are subjectedto heat, as in the case-of fire, these two'contacts move substantially simultaneously into engagement with fixed contact'166. The engagement of bimetal contact 162 with fixed contact 166 completes a circuit from override conductor 72 to conductor 38 leading to output transformer winding 34. The override conductor 74 is already permanently connected to conductor 40 and thus to the other side of output transformer winding 34. Hence, the movement of bimetal element 162 into engagement with fixed contact 166 connects output transformer'winding 34 across override conductors 72 and 74. This insures completion of the override circuit in the event none of the control switches are in Intercom position. The movement of the other bimetal contact 164 into engagement with fixed contact 166 completes the connection of output transformer winding 34 in parallel with input transformer winding 48, since one side of each of these windings is already permanently connected to one side of the other of the windings at junction 176 (Fig. 1a). The parallel connection of output transformer winding 34 to input transformer winding 48 produces a feedback effect which causes a fire alarm signal of a predetermined frequency, such as 1,000 cycles per second, to be propagated from the output of the amplifier to all of the speakers, producing an alarm sound at each speaker. The pitch of the alarm sound may be adjusted by adjusting resistance 172. This fire alarm signal is received by all speaker stations regardless of the position of their respective control switches, due to the completion of the override circuit by movement of bimetal contact 162 into engagement with fixed contact 166.

It can be seen from the foregoing that there is provided in accordance with this invention a fire alarm system combined with an intercommunication system which has great utility for installation in homes, ofiices and the like. The fire alarm system provided in accordance with the invention provides a simple but unique alarm system which does not require the use of a special signaling or alarm device but rather utilizes the amplifier already present in the intercommunication system as a source of the alarm signal. Furthermore, the circuit arrangement oi the invention insures that the fire alarm device closes an override circuit in such manner that all speakers are connected to the fire alarm device.

While there has been shown and described a particular embodiment of the invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention and, therefore, it is aimed to cover all such changes and modifications as fall within the true spirit and scope of the invention.

What I claim as my invention is: a

1. A combined intercommunication and alarm apparatus comprising a plurality of speakers, an electrical amplifier having an input trunk and an output trunk, a plurality of electrical switches corresponding in number to the number of speakers, there being a switch associated with each speaker, electrical circuit means connecting each speaker to its associated switch, each switch including an Off terminal and an Intercom terminal and being operable selectively to connect its associated speaker to either of said OK terminal or said Intercom terminal, electrical circuit means connecting each Intercom terminal to said amplifier input trunk whereby an Intercom message may go from a speaker to said amplifier, an override electrical circuit connected between each Off terminal and said amplifier output trunk, said override circuit including override switch means movable with movement of any speaker switch to Intercom position to connect any Ofi" speaker to said amplifier output trunk whereby any Off speaker may receive an Intercom message, an alarm device electrically connected between each speaker and said amplifier output trunk, said last named electrical connection including said override circuit and said alarm device being operable to connect its associated spake! to said amplifier output trunk in response to a predetermined condition, said alarm device also being electrically connected between said amplifier output trunk and said amplifier input trunk and being operable in response to said predetermined condition to connect said amplifier output trunk in electrically parallel relation with the amplifier input trunk whereby the amplifier output may feed back to the amplifier input, said feedback connection including means to establish a predetermined alarm signal output from said amplifier.

I 2. A combined intercommunication and alarm apparatus according toclaim 1, wherein each speaker switch also includes a Listen terminal, and means electrically connecting each Listen terminal to said amplifier output trunk whereby, when any speaker switch is connected to Listen position, the speaker associated therewith may receive'an Intercom message. I

3. A combinedintercommunication and alarm apparatus according to claim 2, including a radio receiver, said electrical amplifier being a part of said radio receiver, an electrical circuit connected between said radio receiver and said output trunk and operable when broken to stop radio signal input to said amplifier, said last named electrical circuit including radio receiver control switch means associated with each speaker and connected in series, each of said radio receiver control switch means being closed when its associated speaker switch is in Listen References Cited in the file of this patent UNITED STATES IATENTS 2,279,739 Lurie Apr. 14, 1942 2,460,789 Thompson Feb. 1, 1949 2,489,202 Selinger Nov. 22, 1949 2,632,155 Lamb Mar. 17, 1953 2,694,148 Hagen Nov. 9, 1954 2,744,194

Auerback May 1, 1956

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