SMOKE SENSING CIRCUIT WITH BATTERY STANDBY
United States Patent 3750123
A fire and gas alarm system utilizing a four-terminal sensing device positioned in the environmental region to be monitored. The sensing device includes a pair of resistance heating wires spaced apart by a conducting core and encompassed by an outer metallic shell. A transformer powers a pair of rectifiers which supply current to both a normally operated standby relay and the four-terminal smoke and gas sensing device. When hydrocarbon vapors or smoke impinges upon the metallic shell of the sensing device, the resistance between the pair of heater wires drops to operate a relay and produce an alarm indication. Upon failure of a.c. power, the standby relay is released to connect battery power to the circuit and insure continued operation in response to an alarm condition.
US Patent References:
METHODS AND APPARATUS FOR MEASURING THE CONTENT OF HYDROGEN OR REDUCING GASES IN AN ATMOSPHERE
Shaver - November 1969 - 3479257
GAS RESPONSIVE SWITCHING DEVICE
Kasahara - September 1971 - 3609732
Alarm system
Gerber - November 1956 - 2771598
Electrical alarm system
Watts - July 1959 - 2895125
METHODS AND APPARATUS FOR MEASURING THE CONTENT OF HYDROGEN OR REDUCING GASES IN AN ATMOSPHERE
Shaver - November 1969 - 3479257
GAS RESPONSIVE SWITCHING DEVICE
Kasahara - September 1971 - 3609732
Alarm system
Gerber - November 1956 - 2771598
Electrical alarm system
Watts - July 1959 - 2895125
Application Number:
05/194679
Publication Date:
07/31/1973
Filing Date:
11/01/1971
View Patent Images:
Export Citation:
Assignee:
T. J. Connelly Construction Company, Inc. (Dallas, TX)
Primary Class:
Other Classes:
340/634, 307/64, 340/333, 340/632
International Classes:
G08B17/117; G08B17/10; G08B21/00
Field of Search:
340/237R,276,409,333 23/232E,254E,255E
Primary Examiner:
Caldwell, John W.
Assistant Examiner:
Myer, Daniel
Claims:
What is claimed is
1. A fire and gas alarm system comprising:
2. A fire and gas alarm system comprising:
3. A fire and gas alarm system comprising:
1. A fire and gas alarm system comprising:
2. A fire and gas alarm system comprising:
3. A fire and gas alarm system comprising:
Description:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to alarm systems and, more particularly, relates to fire and gas alarm systems.
2. History of the Prior Art
A wide variety of fire alarm systems have heretofore been devised. Certain of such prior systems have included devices for detecting the presence of smoke or gas in order to actuate alarms, such as a light or a noise source. However, many of the previously developed alarm systems have not provided a sufficiently economical and reliable alarm function. Moreover, previously developed fire and smoke alarm systems have not been completely satisfactory in that they rely exclusively on either commercial a.c. power or upon self-contained battery power. The a.c. powered devices are inoperative to detect a fire or gas alarm condition in the event of commercial power failure. The battery powered devices are inherently expensive and somewhat unreliable because the batteries must be replaced periodically to insure continuous operability. The present invention combines the desirable features of both a.c. and battery power by providing battery power utilized automatically only in the event of a power failure.
SUMMARY OF THE INVENTION
In accordance with the present invention, an alarm system is provided which eliminates or tends to reduce the problems and deficiencies of previously developed systems. The present alarm system requires a relatively simple d.c. power supply and a single gas or smoke detector. The detector of the present invention is small and inconspicuous and requires only low voltage so that special installation structure and techniques are not required.
In accordance with the present invention, an alarm system is provided with includes a detector operable to generate electrical signals in response to the presence of vaporous hydrocarbons. A low voltage power supply is connected to energize the detector, with an electronic switch operable in response to the electrical signals generated thereby. An alarm device is operable by the electronic switch to generate an alarm indication.
In accordance with a more specific aspect of the invention, a fire and gas alarm system includes a four-terminal sensing device adapted to be positioned in an environmental region to be monitored. The sensing device includes first and second resistance heating wires spaced apart by a conducting core and encompassed by an outer metallic shell. An a.c. source is rectified to supply a low voltage which is connected to heat the first resistance heating wire. The terminals of the second heating wire are connected for generation of electrical alarm signals upon the impingement of hydrocarbon vapors upon the outer metallic shell. A standby battery relay is operated from the a.c. power and provides current to the resistance heating wire in the event of power failure. An alarm structure is operable in response to the electrical alarm signals for generating alarm indications with or without a.c. power.
DESCRIPTION OF THE DRAWING
For a more complete understanding of the present invention and for further objects and advantages thereof, reference is now made to the following description taken in conjunction with the accompanying drawing, in which:
FIG. 1 is a schematic diagram of the preferred embodiment system; and
FIG. 2 is a somewhat diagrammatic illustration of a sensor constructed in accordance with the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring to FIG. 1, a power plug 10 is adapted to be plugged into a 220 volt, 50 H z a.c. power outlet. The present embodiment of the invention is especially intended for operation with the conventional commercial power most commonly found in European countries. The plug 10 is connected across the primary winding 11 of a power transformer 12. A dropping resistor 13 and a neon indicator lamp 14 are connected in series across the primary transformer winding 11 to provide a visual indication of whether or not the a.c. power source is operating. The transformer 12 also includes first and second secondary winding 15 and 16, respectively. The turns ratio of the primary winding 11 to the first secondary winding 15 is designed to produce an output on the order of 1 volt and deliver current on the order of 500 milliamperes. The winding 15 is connected across a first heating filament 21 of a smoke and hydrocarbon gas sensing unit 20 to be described in further detail below.
The second secondary winding 16 is connected in series with a pair of diodes 31 and 32 forming a first half-wave rectifier 17. The output of the diodes 31 and 32 is connected across a capacitor 33 and a resistor 34 which together form a ripple filter for the rectifier. A dropping resistor 35 is connected across the output of the RC filter formed by capacitor 33 and resistor 34 and to one end of a second heating filament 22 of the sensing unit 20.
A second pair of diodes 36 and 37 are also connected across the secondary winding 16 to form a second half-wave rectifier 18. A capacitor 39 is connected across the two diodes 36 and 37 to form a ripple filter. The diode 37 is connected in series with a resistor 38 and the winding 41 of a standby power relay 40. The standby relay 40 includes a first and second pair of contacts 42 and 43, respectively, which are both open when the relay 40 is operated. One contact 42a of the first set 42 is connected to the collector electrode of a transistor 44 through the winding 45 of an alarm relay 46. The other contact 42b of the set 42 is connected to the positive electrode of a 6-volt emergency battery 47 and through an isolation diode 48 to a contact 43a of the other contact set 43. The negative electrode of the battery 47 is grounded. The contact 43a is also connected to the negative electrode of a 1.5 volt emergency battery 49, the positive electrode of which is connected to one terminal of the second heating filament 22 of the sensing device 20. The contact 43b of the set 43 is connected to the other terminal of the filament 22. A blocking diode 51 is connected between the second rectifier and the winding 45 of the relay 46 to isolate the standby d.c. power from the rectified a.c. power.
The alarm relay 46 includes one pair of normally open contacts 52 which are connected from the negative terminal of the blocking diode 51 to an alarm buzzer 53.
The transistor 44 is connected in the grounded emitter configuration through a resistor 54. The base electrode of the transistor 44 is connected through a base resistor 55 to one side of the secondary transformer winding 15. A potentiometer 56 has one terminal connected to the secondary winding 15 with the wiper contact 57 grounded.
FIG. 2 illustrates the partial cutaway view of a typical sensor 20 showing four terminals 23 - 26 which extend from a ceramic base 27. A 400-gauge mesh screen 28 provides a cylindrical container which is topped off by a steel cap 29. The mesh screen 28 allows hydrocarbon vapors to penetrate within the sensor and impinge upon a sensing pod 30 which comprises an outer shell of Corundum, a natural aluminum oxide. Paladium heating elements are exposed within the Corundum outer shell and are spaced apart by an alpha alumina inner spacer core. Although the operation of the sensing pod is not absolutely understood, it is believed that the electrical heating wires heat the pod up such that the pod generates a predetermined electrical signal from the output terminal thereof. When hydrocarbons from smoke or gas strike the Corundum, the resistance between the two resistance heating wires decreases to cause the electrical output of the device to rise to indicate the presence of hydrocarbon vapors.
Referring again to FIG. 1, when a.c. power is aplied to the terminals of the plug 10, the diodes 31 and 36 together with the capacitor 33 and the resistor 34 produce a d.c. potential at point 60 on the order of a positive 6 volts. The output of the secondary winding 15 is connected across the terminals 23 and 24 of the sensor 20 to deliver a voltage on the order of 1 volt to the first heating filament 21. When one of the filaments of a sensor 20 is heated, the resistance between the filaments 21 and 22 is fairly high, for example, on the order of several thousand ohms. The voltage at the base of the transistor 44 is normally maintained at a level below the turn-on potential due to the adjustment of the wiper arm 57 of the potentiometer 56 and the relatively high resistance between the filaments 21 and 22, the latter being connected to the positive 6 volt potential at point 60. While the transistor 44 is in a nonconductive state, the alarm relay 46 remains unoperated.
As long as the a.c. power source is operating, the second rectifier 18 comprising the diodes 36 and 37 together with the filter capacitor 39 produce d.c. current flow through the resistor 38 and the winding 41 of the standby relay 40 to hold the relay operated and the contact sets 42 and 43 open.
In the event the sensor 20 is subjected to smoke or hydrocarbon vapors, the resistance between the heated filament 21 and the other filament 22 falls to a much lower value, for example, less than 100 ohms. The positive voltage on the base of the transistor 44 rises to a value sufficient to initiate conduction through the collector-emitter path and operate the alarm relay 46 to close the contacts 52 and energize the alarm buzzer 53. Once energized, the buzzer 53 will continue to operate and produce an alarm indication until the smoke or hydrocarbon vapor clears and the resistance between the filaments 21 and 22 rises to stop conduction in the transistor 44.
In the event of an a.c. power failure, the second rectifier 18 comprised of the diodes 36 and 37 and the capacitor 38 ceases producing a d.c. output voltage to energize the winding 41 and the standby relay 40 releases to close the contact sets 42 and 43. Closure of the contacts 42 connects the positive terminal of the 6 volt standby battery 47 to the collector electrode of the transistor 44 through the winding 45 of the alarm relay 46. Closure of contacts 43 connects the 1.5 volt standby battery 49 across the other filament 22 of the sensor 20 to heat the filament so that the sensor 20 remains sensitive to detection of smoke or hydrocarbon vapors. The positive 6 volt potential of the standby battery 47 is also connected through the isolation diode 48 and the contacts 43 to produce a positive 6 volt potential at the point 60.
Upon exposure of the sensor 20 to smoke or hydrocarbon vapors, the resistance between the two filaments 21 and 22 is reduced so that the transistor 44 is biased into conduction to operate the alarm relay 46 through its emitter-collector path and energize the alarm buzzer 53.
When a.c. power is reestablished, current again flows through the second rectifier 18 formed by the diodes 36 and 37 to reenergize the coil 41 of the standby relay 40 and disconnect the emergency batteries 47 and 49 from the circuit. Current is drawn from the batteries 47 and 49 only during a period of a.c. power failure, thereby extending their useful lives.
From the foregoing, it will be understood that the present invention provides an alarm system which detects a fire or gas emergency. The present system is relatively simple in construction and maintenance-free. The gas sensing detector utilized is small and may be operated with only a low voltage requirement. The system of the present invention functions to automatically change from a.c. to standby battery upon the occurrence of a power failure and again returns to a.c. power upon reestablishment thereof. The circuit functions in generally the same manner whether being operated by a.c. power or standby batteries.
Having described the invention in connection with certain specific embodiments thereof, it is to be understood that further modifications may now suggest themselves to those skilled in the art and it is intended to cover such modifications as fall within the scope of the appended claims.
1. Field of the Invention
This invention relates to alarm systems and, more particularly, relates to fire and gas alarm systems.
2. History of the Prior Art
A wide variety of fire alarm systems have heretofore been devised. Certain of such prior systems have included devices for detecting the presence of smoke or gas in order to actuate alarms, such as a light or a noise source. However, many of the previously developed alarm systems have not provided a sufficiently economical and reliable alarm function. Moreover, previously developed fire and smoke alarm systems have not been completely satisfactory in that they rely exclusively on either commercial a.c. power or upon self-contained battery power. The a.c. powered devices are inoperative to detect a fire or gas alarm condition in the event of commercial power failure. The battery powered devices are inherently expensive and somewhat unreliable because the batteries must be replaced periodically to insure continuous operability. The present invention combines the desirable features of both a.c. and battery power by providing battery power utilized automatically only in the event of a power failure.
SUMMARY OF THE INVENTION
In accordance with the present invention, an alarm system is provided which eliminates or tends to reduce the problems and deficiencies of previously developed systems. The present alarm system requires a relatively simple d.c. power supply and a single gas or smoke detector. The detector of the present invention is small and inconspicuous and requires only low voltage so that special installation structure and techniques are not required.
In accordance with the present invention, an alarm system is provided with includes a detector operable to generate electrical signals in response to the presence of vaporous hydrocarbons. A low voltage power supply is connected to energize the detector, with an electronic switch operable in response to the electrical signals generated thereby. An alarm device is operable by the electronic switch to generate an alarm indication.
In accordance with a more specific aspect of the invention, a fire and gas alarm system includes a four-terminal sensing device adapted to be positioned in an environmental region to be monitored. The sensing device includes first and second resistance heating wires spaced apart by a conducting core and encompassed by an outer metallic shell. An a.c. source is rectified to supply a low voltage which is connected to heat the first resistance heating wire. The terminals of the second heating wire are connected for generation of electrical alarm signals upon the impingement of hydrocarbon vapors upon the outer metallic shell. A standby battery relay is operated from the a.c. power and provides current to the resistance heating wire in the event of power failure. An alarm structure is operable in response to the electrical alarm signals for generating alarm indications with or without a.c. power.
DESCRIPTION OF THE DRAWING
For a more complete understanding of the present invention and for further objects and advantages thereof, reference is now made to the following description taken in conjunction with the accompanying drawing, in which:
FIG. 1 is a schematic diagram of the preferred embodiment system; and
FIG. 2 is a somewhat diagrammatic illustration of a sensor constructed in accordance with the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring to FIG. 1, a power plug 10 is adapted to be plugged into a 220 volt, 50 H z a.c. power outlet. The present embodiment of the invention is especially intended for operation with the conventional commercial power most commonly found in European countries. The plug 10 is connected across the primary winding 11 of a power transformer 12. A dropping resistor 13 and a neon indicator lamp 14 are connected in series across the primary transformer winding 11 to provide a visual indication of whether or not the a.c. power source is operating. The transformer 12 also includes first and second secondary winding 15 and 16, respectively. The turns ratio of the primary winding 11 to the first secondary winding 15 is designed to produce an output on the order of 1 volt and deliver current on the order of 500 milliamperes. The winding 15 is connected across a first heating filament 21 of a smoke and hydrocarbon gas sensing unit 20 to be described in further detail below.
The second secondary winding 16 is connected in series with a pair of diodes 31 and 32 forming a first half-wave rectifier 17. The output of the diodes 31 and 32 is connected across a capacitor 33 and a resistor 34 which together form a ripple filter for the rectifier. A dropping resistor 35 is connected across the output of the RC filter formed by capacitor 33 and resistor 34 and to one end of a second heating filament 22 of the sensing unit 20.
A second pair of diodes 36 and 37 are also connected across the secondary winding 16 to form a second half-wave rectifier 18. A capacitor 39 is connected across the two diodes 36 and 37 to form a ripple filter. The diode 37 is connected in series with a resistor 38 and the winding 41 of a standby power relay 40. The standby relay 40 includes a first and second pair of contacts 42 and 43, respectively, which are both open when the relay 40 is operated. One contact 42a of the first set 42 is connected to the collector electrode of a transistor 44 through the winding 45 of an alarm relay 46. The other contact 42b of the set 42 is connected to the positive electrode of a 6-volt emergency battery 47 and through an isolation diode 48 to a contact 43a of the other contact set 43. The negative electrode of the battery 47 is grounded. The contact 43a is also connected to the negative electrode of a 1.5 volt emergency battery 49, the positive electrode of which is connected to one terminal of the second heating filament 22 of the sensing device 20. The contact 43b of the set 43 is connected to the other terminal of the filament 22. A blocking diode 51 is connected between the second rectifier and the winding 45 of the relay 46 to isolate the standby d.c. power from the rectified a.c. power.
The alarm relay 46 includes one pair of normally open contacts 52 which are connected from the negative terminal of the blocking diode 51 to an alarm buzzer 53.
The transistor 44 is connected in the grounded emitter configuration through a resistor 54. The base electrode of the transistor 44 is connected through a base resistor 55 to one side of the secondary transformer winding 15. A potentiometer 56 has one terminal connected to the secondary winding 15 with the wiper contact 57 grounded.
FIG. 2 illustrates the partial cutaway view of a typical sensor 20 showing four terminals 23 - 26 which extend from a ceramic base 27. A 400-gauge mesh screen 28 provides a cylindrical container which is topped off by a steel cap 29. The mesh screen 28 allows hydrocarbon vapors to penetrate within the sensor and impinge upon a sensing pod 30 which comprises an outer shell of Corundum, a natural aluminum oxide. Paladium heating elements are exposed within the Corundum outer shell and are spaced apart by an alpha alumina inner spacer core. Although the operation of the sensing pod is not absolutely understood, it is believed that the electrical heating wires heat the pod up such that the pod generates a predetermined electrical signal from the output terminal thereof. When hydrocarbons from smoke or gas strike the Corundum, the resistance between the two resistance heating wires decreases to cause the electrical output of the device to rise to indicate the presence of hydrocarbon vapors.
Referring again to FIG. 1, when a.c. power is aplied to the terminals of the plug 10, the diodes 31 and 36 together with the capacitor 33 and the resistor 34 produce a d.c. potential at point 60 on the order of a positive 6 volts. The output of the secondary winding 15 is connected across the terminals 23 and 24 of the sensor 20 to deliver a voltage on the order of 1 volt to the first heating filament 21. When one of the filaments of a sensor 20 is heated, the resistance between the filaments 21 and 22 is fairly high, for example, on the order of several thousand ohms. The voltage at the base of the transistor 44 is normally maintained at a level below the turn-on potential due to the adjustment of the wiper arm 57 of the potentiometer 56 and the relatively high resistance between the filaments 21 and 22, the latter being connected to the positive 6 volt potential at point 60. While the transistor 44 is in a nonconductive state, the alarm relay 46 remains unoperated.
As long as the a.c. power source is operating, the second rectifier 18 comprising the diodes 36 and 37 together with the filter capacitor 39 produce d.c. current flow through the resistor 38 and the winding 41 of the standby relay 40 to hold the relay operated and the contact sets 42 and 43 open.
In the event the sensor 20 is subjected to smoke or hydrocarbon vapors, the resistance between the heated filament 21 and the other filament 22 falls to a much lower value, for example, less than 100 ohms. The positive voltage on the base of the transistor 44 rises to a value sufficient to initiate conduction through the collector-emitter path and operate the alarm relay 46 to close the contacts 52 and energize the alarm buzzer 53. Once energized, the buzzer 53 will continue to operate and produce an alarm indication until the smoke or hydrocarbon vapor clears and the resistance between the filaments 21 and 22 rises to stop conduction in the transistor 44.
In the event of an a.c. power failure, the second rectifier 18 comprised of the diodes 36 and 37 and the capacitor 38 ceases producing a d.c. output voltage to energize the winding 41 and the standby relay 40 releases to close the contact sets 42 and 43. Closure of the contacts 42 connects the positive terminal of the 6 volt standby battery 47 to the collector electrode of the transistor 44 through the winding 45 of the alarm relay 46. Closure of contacts 43 connects the 1.5 volt standby battery 49 across the other filament 22 of the sensor 20 to heat the filament so that the sensor 20 remains sensitive to detection of smoke or hydrocarbon vapors. The positive 6 volt potential of the standby battery 47 is also connected through the isolation diode 48 and the contacts 43 to produce a positive 6 volt potential at the point 60.
Upon exposure of the sensor 20 to smoke or hydrocarbon vapors, the resistance between the two filaments 21 and 22 is reduced so that the transistor 44 is biased into conduction to operate the alarm relay 46 through its emitter-collector path and energize the alarm buzzer 53.
When a.c. power is reestablished, current again flows through the second rectifier 18 formed by the diodes 36 and 37 to reenergize the coil 41 of the standby relay 40 and disconnect the emergency batteries 47 and 49 from the circuit. Current is drawn from the batteries 47 and 49 only during a period of a.c. power failure, thereby extending their useful lives.
From the foregoing, it will be understood that the present invention provides an alarm system which detects a fire or gas emergency. The present system is relatively simple in construction and maintenance-free. The gas sensing detector utilized is small and may be operated with only a low voltage requirement. The system of the present invention functions to automatically change from a.c. to standby battery upon the occurrence of a power failure and again returns to a.c. power upon reestablishment thereof. The circuit functions in generally the same manner whether being operated by a.c. power or standby batteries.
Having described the invention in connection with certain specific embodiments thereof, it is to be understood that further modifications may now suggest themselves to those skilled in the art and it is intended to cover such modifications as fall within the scope of the appended claims.