US 3559194 A
Description (OCR text may contain errors)
mam xaII-wm A. BISBERG FIRE ALARM SYSTEM 5 Sheets-Sheet 1 Filed Sept. 13, 1967 ALARM APPARATUS AMPLIFIER DEMODULATOR I I I I I I I l I I 1 I I I I I I I I I I I I 74w FREQUENCY STABIL IZING SIGNAL PRODUCING SYSTEM ELEMENT f 7 SENSITIVITY TEMPERATURE l2 ADJUSTMENT SENSING ELEMENT FEET-FT FTECETVET? UNTT EFT-E I I I I I I l I I L DETECTOR UNIT FIG. I
37 AMPLIFIER DEMODULATOR CIRCUIT FIG 3 ARTHUR BIQBERG A 7' TORNFYS" COOCH AND O/CONNELL A. BISBERG FIRE ALARM SYSTEM Filed Sept. 13, 1967 3 Sheets-Sheet 2 ROOM RooM n A} 56 5a 50 70 ROOM1 WW POWER f2 56 58 SOURCE 10 Rfibfiz w 59 DEMODULATOR I CIRCUIT I f l n 5a 4 IO ALARM APPARATUS FIG. 7
EEES RELAYS f A. AMPLIFIER fb AQ AND RELAY2 v62 DEMODULATOR I CIRCUITRY fn i A RELAYn 62 I POWER 0 SOURCE FIG. 8
- TRANSISTOR FIG 2A l/Vl/E/VTOR' ARTHUR BISHERG ATTORNEYS;
COOCH AND O'CONNELL Jan. 26, 1971 A. BISBERG FIRE ALARM SYSTEM 3 Sheets-Sheet 5 Filed Sept. 13, 1967 TUNNEL DIODE ARTHUR Etlahf F16;
COOCH AND O'CONNELL United States Patent-= 3,559,194 FIRE ALARM SYSTEM Arthur Bisberg, Lexington, Mass., assignor, by mesne assignments, to General Eastern Corporation, Boston, Mass., a corporation of Massachusetts Filed Sept. 13, 1967, Ser. No. 667,577 Int. Cl. G08b 17/12 US. Cl. 340-224 Claims ABSTRACT OF THE DISCLOSURE A fire alarm system which utilizes a plurality of low energy fire detection units, each operating solely from energy received from a fire and each being capable of producing and transmitting a stabilized radio frequency signal in response to an environmental temperature change resulting from a fire. A single remote alarm unit receives and demodulates the transmitted signal received from one or more detection units and produces an audible and/or visual alarm in response thereto. The sensitivity of the detection units is made adjustable and the radio frequency signal from each of such units may be appropriately modulated by an audio frequency signal. The frequency values of such radio frequency signals and/or audio frequency signals may be different for each detection unit and such signals may be suitably utilized .at the receiver alarm unit to identify the location of the This invention relates generally to systems for detecting the presence of fire and for providing a warning alarm to the occupants of abuilding or others and, more particularly, to a system for producing an oscillating signal having a stabilized frequency in the radio-frequency range, such signal being generated solely in response to energy obtained from the fire itself, and for transmitting said signal to a remote receiver alarm unit.
In fire alarm systems, particularly those which are adaptable for use in homes or-, ,business establishments, it has long been desired to obtain a system which is reliable and relatively inexpensive and which can be easily installed, tested and maintained by an untrained individual, such as a homeowner himself. Presently available fire alarm systems usually require relatively high manufacturing costs and-include elaborate wiring arrangements which in turn increase installation and maintenance costs so as to make the overall expense to the average home owner excessively high, if not generally prohibitive. Moreover, even relatively expensive presently known systems are not always reliable, especially those systems using wires which are subject to damage or destruction by the fire itself thereby causing the system to fail to operate at the very time when it is needed.
- Moreover, wireless fire alarm systems which have been proposed up to now utilize self-contained detection-alarm units having power requirements so high that the overall unit does not operate effectively or the detection portion thereof requires auxiliary external power, as from A-C power lines or batteries, in order to provide a sensing signal which has sutficient power to actuate an audible alarm loud enough to be heard in other parts of a building. A-C power failure or limited battery shelf life contribute to the danger of system failure. Such self-con tained wireless units as are now known are not capable of providing a remote alarm indication which is more desirable in most practical applications.
The system of this invention, on the other hand, provides an overall capability for detecting fire at many dilferent locations throughout a building or group of buildings and for further providing an alarm indication "ice at an appropriately located remote point such as at or near the bedroom of a home, for example, to Warn the occupants of the presence of fire. Moreover, the system can be manufactured so as to sell at a relatively low cost in comparison to presently available systems and, as will subsequently be shown, is capable of being installed with little effort by a homeowner or other untrained individual. Furthermore, the system is extremely reliable and requires little or no maintenance for continued reliable operation.
-In order to achieve the superior operation of the system of the invention, the invention utilizesone or more self-energized fire detection units, suitably located throughout a building, and a remotely located receiver unit. The fire detection units produce a frequency stabilized oscillating signal as a result of a rate of rise in environmental temperature. Such units require little energy for operation and, since they comprise elements which operate solely in response to energy produced by the fire itself, they do not require external sources of power. Moreover, such low energy units are extremely sensitive to small changes in environmental temperatures, thelevel of such sensitivity being capable of adjustment over a relatively wide range to provide an output oscillatiri'g signal in response to a rate of temperature rise as low "as 15 F. per minute.
...In one preferred embodiment of the invention, for example, such a unit includes means for providing a stabilized radio-frequency carrier signal which is suitably modulated by an audio frequency oscillating signal produced in response to the output of a thermoelectrie sensing element. Such modulated R-F signal is thereupon transmitted to a remote receiver warning alarm unit. ap-
P propriately placed in the building. The received modulated signal is then amplified and appropriately demodulated to provide an actuation signal for an alarm such'as a bell, gong, buzzer, or other suitable indicator which can alert the occupants of the building to the presence of the fire. Since no external power sources are required for the plurality of fire detection units located at the points where the fire is likely to occur, reliability of the overall system is considerably increased over presently known fire alarm systems.
In order to appreciate the advantages of the system of the invention, the operation thereof can be best' described in more detail with reference to the accompanying drawings in which:
FIG. 1 shows a block diagram of the overall system of the invention;
FIG. 2 shows a representative circuit used in the selfcontained fire detection unit of FIG. 1;
FIG. 2a shows an alternate embodiment of a portion of the circuit shown in FIG. 2;
FIG. 3 shows a representative circuit of a remote receiver alar-m unit of the invention;
FIG. 4 shows a pictorial representation of a typical fire detector unit of the invention;
FIG. 5 shows a pictorial representation of a typical remote receiver alarm unit of the invention;
FIG. 6 shows an alternative embodiment of the circuitry which can be used in the fire detection unit of FIG. 1; and
FIG. 7 shows an embodiment of the overall system of the invention for identifying the location of a fire as well as providing an alarm; and
FIG. 8 shows an alternative embodiment of the overall system of the invention. 7
As can be seen in the block diagram configuration shown in FIG. 1, the system comprises at least one, and preferably more thon one, fire detector unit 10 and a receiver unit 11. Fire detector unit 10 is a self-contained unit which responds to a rate of change in temperature of the environment in which it is placed and thereupon produces an output oscillating signal in the radio fre quency range which can be transmitted by an appropriate antenna 16. Receiver unit 11 receives the transmitted signal at an appropriate antenna 17 and suitably utilizes the incoming signal to trigger an alarm apparatus.
The receiver unit may be placed in an appropriate location, such as at or near the bedroom of a house, and one or more fire detector units can be placed at various other locations, remote from the receiver unit, throughout the house wherever the likelihood of fire may exist. A single receiver unit, thus, can be used to provide an alarm in response to many different detector units.
In general, each detector unit is provided with a temperature sensing element 12 for providing a D-C output voltage in response to a rate of rise of the environmental temperature and a signal producing circuit responsive to such voltage for producing a radio frequency oscillating signal. The frequency of the latter signal is appropriately stabilized by a frequency stabilization device 14 and the signal is applied to an antenna 16 for transmission. The sensitivity of the overall unit may be adjusted by a signal adjusting element 15 which is used to set the point at which oscillation of the signal producing circuit begins in response to the voltage output from element 12. Receiver unit 11 receives the transmitted oscillating signal by way of antenna 17 which signal is then applied to an appropriate amplifier-demodulator circuit 18 to produce a signal for actuating an appropriate alarm apparatus 19. The amplifier-demodulator circuit is energized via a suitable power source 20 which may be conventional 60-cycle A-C line power or a battery source. Thus, only the single receiver unit of the overall system requires an external power source and reliability of the system is extremely high.
FIG. 2 shows a representative circuit for fire detector unit in which a thermoelectric generator 22 produces an output voltage in response to an environmental temperature change. The operation of thermoelectric generator 22 depends on the well-known Seebeck effect in which a D-C output voltage results from a difference in temperature between two dissimilar metals having a common junction. In a suitable thermoelectric generator for use in the invention, the dissimilar metals may be a bismuth-telluride combination in which a plurality of hot junctions 23 are in contact with a suitable'cold junction 24 to produce a D-C voltage at line 21. Cold junction 24 may be appropriately attached to a heat sink, such as the wall of the room, while hot junctions 23 extend into the interior of the room where they are appropriately exposed to the temperature therein. D-C output voltage 21 is thereupon applied in the embodiment shown to a tunnel diode element which produces an output oscillating signal, the frequency of which can be controlled by the use of an output tuned circuit 29 comprising a parallel connected inductance 30 and capacitance 31.
In the particular embodiment shown, circuit 29 may be tuned so as to produce a signal in the audio frequency range which can then be used to modulate a fixed carrier frequency signal in the radio frequency range which carrier signal is generated by the operation of parallel circuit 25 which includes a quartz crystal 28 and a tuned circuit combination of inductance 26 and capacitance 27. Carrier frequency generator circuit 25 produces a signal in the radio frequency range which, when amplitude modulated by the audio signal from the output of tuned circuit 29, can be transmitted by antenna'16 to a remote location. The sensitivity of the overall unit may be appropriately varied by adjusting the value of a variable resistor 33. The use of a bismuth-telluride thermoelectric generator enhances the sensitivity of the unit since it can produce a voltage sufficient to cause oscillatory operation of tunnel diode 32 in response to a rate of rise of environmental temperature as low as F. per minute. Variable resistor ,33 allows. such sensitivity to be modulator circuit 37, which, for example, may be in the form of a multi-stage transistor receiver circuit. Such circuit produces an audio output signal for operating a relay 39 which, when its contacts are closed, actuates alarm apparatus 40 as shown. Appropriate power is supplied to amplifier-demodulator 37, for example, from an A-C power source 43, such as the conventional A-C line power source found in the home. The A-C power from power source 43 is appropriately converted to D-C voltage by a suitable power supply rectifier 42 and an appropriate panel light 41 can be used to indicate that the unit is in operation.
FIG. 4 shows a pictorial representation of one particular embodiment of a typical fire detector unit 10 of the invention. -In such figure the unit is shown as comprising a mounting section 44 having a rear mounting plate 46 on which thermoelectric generator 22 is mounted with its hot junctions 23 exposed to the environmental temperatnre via openings 45 in an appropriate cover 38 which in apreferred embodiment is fabricated from a suitable plastic material. Cold junction material 24 is mounted on a rear mounting plate 46 which operates as a heat sink which can be bonded to the wall of a room, for example. Appropriate inductance, resistance and capacitance elements are also mounted on rear mounting plate 46 along with tunnel diode 32. An externally available screwdriver adjustment 60 for varying the position of the movable arm of variable resistor 33, for example, is provided for adjusting the sensitivity of the operation of unit 10, that is, for controlling the voltage level at which oscillation occurs. An antenna 16 radiates R-F energy via an aperture 47 in side wall 48 of mounting structure 44. The overall structure is very light in weight and can be bonded to the wall of a room by screws or by an appropriate adhesive placed on its rear surface. Thus, detector unit 10 can be installed in any desired location by an untrained individual, such as the homeowner or any member of the household.
A pictorial representation of receiver unit 11 is shown in FIG. 5 wherein an appropriate A-C plug 49 is mounted at the rear wall 50 of the overall alarm unit case. A screwdriver adjustment 51 for varying the gain of the amplifier-demodulator circuit and, hence, the loudness of an audio alarm, for example, is placed on a side wall thereof. Thus, the receiver unit can be easily installed by a homeowner merely by plugging it in at the rear of the unit to a conventional A-C outlet.
Although the circuitry shown in FIG. 2 for fire detector unit 10 represents one preferred embodiment thereof, other alternative embodiments such as the one shown in FIG. 6, for example, may be used. In such figure, thermoelectric generator 22 produces an output voltage which can be applied to tunnel diode 32, the output of which is tuned so as to produce an oscillating signal having a frequency in the radio frequency range by means of a tuned circuit 52 comprising inductance 53, capacitance 54 and a frequency stabilizing quartz crystal 55. Such a system thereby provides an unmodulated R-F frequency signal at antenna 16, the frequency of which is determined by the values of the elements of tuned circuit 52 and is stabilized specifically by means of quartz crystal 55. In such an embodiment, the receiver system can merely be tuned to the particular radio frequency involved and then appropriately amplified and detected to produce an alarm actuation signal.-
As can be seen from the figures, -fire detector unit is made up of elements which are relatively small and, therefore, its overall size is such as to provide an extremely lightweight unit occupying little space. Such a unit can be inconspicuously placed in a room where it is not easily seen or it can be made in a decorative fashion so as not to detract fromthe overall decor of the room. Its size permits easy handling and, as mentioned above, the unit can be made with an appropriate adhesive backing so as to be easily placed in any appropriate location and just as easily removed therefrom. An important advantage of the system is that it can be readily tested at any time 'by a homeowner. Because of its high sensitivity, the remote alarm unit can be actuated by arelatively small rate of rise in environmental temperature. Hence, a simple non-destructive method of checking the operation of the system can be readily made merely by placing the fingers on the detection unit or by breathing thereon. Such action causes a sufficient temperature rise to produce an appropriate audible alarm at the remote receiver unit. Such a unit provides a unique advantage over presently known systems which require relatively high temperatures in order to test the alarm system.
The receiver unit 11 can be easily adapted to provide for an alarm which is essentially self-locking in that once it is actuated it remains actuated until turned off. Thus, even if the temperature environment should be temporarily reduced for some reason, the alarm remains in an actuated condition to continue to warn the occupants.
Although in order to provide an extremely sensitive system, the preferred embodiment of fire detector unit 10 is shown as utilizing a tunnel diode element responsive to a relatively low excitation voltage such element may be replaced, for example, by a transistor oscillator circuit, such as shown in FIG. 2a wherein transistor 63' is connected to line 21 and thence to tuned circuit 29. -In either event, appropriate frequency stabilization can be obtained by utilizing a quartz crystal, or other suitable stabilizing means. Different tuned circuit and crystal combinations can provide for different carrier frequencies in separate fire detector units. 'In this way the overall system can be made frequency selective so that, if the remote receiver is arranged to employ a plurality ofseparate input tuned circuits, it can be used not only to indicate the presence of a fire, but also to produce an appropriate signal to identify the location of the fire in accordance with the frequency of the incoming signal. In addition, in those embodiments of fire detector unit 10 which utilize an audio frequency modulation signal, the tunnel diode circuit, for example, can be tuned to produce signals having different audio frequencies for different fire detector units. Thus, by utilizing different radio frequencies as well as different audio modulation frequencies, a wide variety of selection and identification means can be obtained.
One such embodiment is shown in FIG. 7 wherein a plurality of fire detection units 10 are placed in a plurality of different rooms designated as Room 1, Room 2 Room n as shown. Each of said detection units is tuned to produce an output R-F signal tuned to a different frequency designated by f f i A receiver unit 11 has an antenna for receiving said signals and for feeding one or more of them to a plurality of tuned circuits 56, each of said circuits tuned to a difierent frequency corresponding to the frequencies f f f,,. If a signal is present at the output of any one of tuned circuits 56 such signal is thereupon fed to an a-mplifier58 and thence to a demodulator circuit 59, supplied with power from power source 60, to actuate alarm apparatus 19. The output signals from each of amplifiers 58 are separately connected to suitable indicators 57, such as appropriate panel lamps, one or more of which is thereupon actuated by the presence of a signal at the output of' one or more of said amplifiers to identify the location of the fire.
Alternatively, the system shown in FIG. 8 may be used wherein a plurality of fire detection units 10 are placed in a plurality of different rooms in the same manner as suggested above with reference to FIG. 7. In the case of the system shown in FIG. 8, each unit is tuned so as to produce the same R-F reference signal 1",, which is modulated by an appropriate audiosignal f f f as shown, A receiver unit 11 has an antenna for receiving said signals and for feeding them to appropriate amplifier-demodulator circuitry 61 capable of producing one or more audio frequency signals corresponding to the audio frequency signals from fire detection units 10. When an audio frequency signal is present, it actuates an appropriate resonant reed delay 62 which thereby produces an audible signal for indicating the presence of fire. The frequency of the audible tone can provide an indication of the location of the fire or, alternatively, the relay actuation signal may be appropriately used to actuate any other suitable display means for identifying the location of the fire.
Thus, the overall system of the invention can be made extremely flexible depending on the application for which it is used. A selection of the actual configuration depends primarily on the degreeof complexity which one is willing to utilize in the receiver unit and the fire detector circuit can be made to operate as an amplitude modulation, frequency modulation or pulse modulation system with suitable changes well known to those in the art.
Although the various embodiments of the system described in the figures are shown as utilizing antenna means which may be in the form of a suitable ferrite loop antenna, for example, the system can be made to operate without an antenna at all if the required range of transmission is relatively short. Moreover, in some applications the oscillating signal may preferably be transmitted to the receiver via absorption of a portion thereof by the power lines of the house.
The receiver unit can be either operated via line power or from a battery source or from both. In the latter case the battery may be appropriately connected to the power line source so as to remain on a trickle charge so that if the line power fails, the battery which is thereby suitably charged, can be automatically switched into the circuit for operating .the receiver. Concurrently, an auxiliary alarm may be actuated, if desired, to indicate that power failure has occurred. Thus, the chance of a system failure due to faulty receiver operation can be reduced considerably and overall system reliability is further increased.
To further improve the versatility of the system, the receiver unit can also be made to operate from a voltage produced by presently known smoke detection devices, such as those utilizing photocell systems which operate in response to a change in light impinging thereon, such as may be brought about by the presence of smoke accompanying a fire. A suitable photoelectric, or other, smoke detector device may be placed adjacent the receiver unit and its output signal can be applied thereto so that the overall system is capable of producing an alarm actuation signal in response to the presence of smoke as well as to the presence of fire.
What is claimed is: 1. A fire alarm system comprising: at least one fire detection means including temperature sensing means operating solely from energy received from a fire for producin a voltage in response to a rate of change of environmental temperature; I
tunnel diode circuit means for-producing a radio frequency oscillating signal in response to said voltage whenever said voltage has a value corresponding to a rate of change of environmental temperature of approximately 15 F. per minute or greater; 7
a quartz crystal means for'stabilizing the frequency of said oscillating signal;
means for transmitting said oscillating signal; and remote means including means for receiving said transmitted oscillating signal;
means for amplifying said received signal to produce an amplified alarm signal; and
alarm circuit means for producing an alarm in response to said amplified signal.
2. A fire alarm system in accordance with claim 1 wherein said tunnel diode circuit means includes variable adjusting means for controlling the voltage level at which said oscillating signal is produced.
3. A fire alarm system comprising i a plurality of fire detection units, each of said units comprising temperature sensing means operating solely from energy received from a fire for producing a voltage in response to an environmental temperature change due to said fire;
solid state circuit means for producing an oscillating signal in response to said voltage whenever said voltage has a value corresponding to a rate of change of environmental temperature of approximately 15 F. per minute or greater, the frequency of said oscillating signal being different in each of said fire detection units;
quartz crystal means for stabilizing the frequency of said oscillating signal; and
means for transmitting said oscillating signal;
remote receiving means for receiving said transmitted oscillating signals; said receiving means including a plurality of filter circuits for producing a plurality of separate signals, each of said filter circuits being responsive to one of said oscillating signals;
means for amplifying each of said separate signals to produce one or more separate output signals;
a plurality of separate indicator means each responsive to one of said separate output signals for producing an indication of the location of said fire; and
means for producing an alarm in response to any one of said separate output signals.
4. A fire alarm system in accordance with claim 3 wherein said solid state circuit means produces an audio frequency oscillating signal, the frequency thereof being different in each of said fire detection units and further includes;
means for producing a radio frequency oscillating signal; means for modulating said radio frequency oscillating signal with said audio frequency oscillating signal; and said transmitting means transmits said modulated signal; and wherein said remote receiving means includes means for receiving said modulated signal; means for amplifying and demodulating said modulated signal; and said alarm producing means produces an alarm in response to said demodulated signal. 5. A fire alarm system in accordance with claim 4 wherein said temperature sensing means comprises a bismuthtelluride element having hot and cold junctions, said hot junction extending into a temperature changing environment and said cold junction thermally connected to a heat sink; and said solid state circuit means comprises a tunnel diode circuit.
References Cited UNITED STATES PATENTS THOMAS B. HABECKER, Primary Examiner P. PALAN, Assistant Examiner US. Cl. X.R.