Smoke, fire and gas alarm with remote sensing, back-up emergency power, and system self monitoring

• US 4,088,986 A
• Filed: 10/01/1976
• Issued: 05/09/1978
• Est. Priority Date: 10/01/1976
• Status: Expired due to Term

• Current Assignee: Charles E. Boucher
• Original Assignee: Charles E. Boucher
• Inventors: Boucher, Charles E.
• Primary Examiner(s): Caldwell, Sr., John W.
• Application Number:
  US05/728,813
• Time in Patent Office: 585 Days
• Field of Search: 340/237 S, 340/237 R, 340/249, 324/71 SN
• US Class Current: 340/521
• CPC Class Codes: G08B 17/06 Electric actuation of the alarm, e.g. using a thermally-operated switch
• CPC Class Codes: G08B 17/117 by using a detection device for specific gases, e.g. combustion products, produced by the fire G08B17/103, G08B17/11 take precedence
• CPC Class Codes: G08B 29/043 of fire detection circuits
• CPC Class Codes: G08B 29/06 Monitoring of the line circuits, e.g. signalling of line faults
• CPC Class Codes: G08B 29/181 due to failing power supply

Abstract

A system for sensing smoke and fire, primarily through the sensing of associated carbon monoixide and optionally with supplementary heat sensing, and for sensing hazardous gases and vapors. The system senses the presence of carbon monoxide, even in the absence of fire and is capable of sensing the presence of hydrogen and hydrocarbon vapors such as methane and propane. Additionally, the volatile vapors of paints, varnishes and other household and industrial substances are detectable. The system also includes circuitry and equipment for notification and warning of such detection, together with circuitry and equipment for providing emergency operation in the event of normal power failure. Further circuitry and equipment for self-monitoring of system remote wiring and sensor integrity, and associated notification means for such integrity checks is included. The system provides for the use of a suitable multitude of sensor devices located remotely from a main control unit, so that sensor device locations may be chosen to maximize the possibility of detecting the presence of smoke, fire or the gases and vapors previously described. The system also includes a novel form of sounding device, of the type wherein an electro-magnet causes a hammer to strike a sounding apparatus with such sounding devices being suitable for use in flammable, combustible or otherwise reactive atmospheres.

Claims

1. A smoke, fire and gas alarm characterized by a plurality of remote sensors and a central control and alarm unit, comprising:

A. a plurality of remote gas sensing means which respond to the presence of carbon monoxide and the like by a lowered electrical resistance; and

B. a centralized power supply operable for generating a D.C. supply voltage to each of said remote sensors, and for generating further distinct voltage levels VL1 and VL2, said power supply being characterized by a normal supply source and an alternate supply source, and including automatic means to switch therebetween; and

C. centralized threshold circuits for each of said remote sensors, each threshold circuit being adapted to compare said voltage level VL2 with a voltage from its associated sensor to produce a sensor output voltage; and

D. a centralized processing unit for receiving a sensor output voltage from each of said threshold circuits, said processing unit comprising logic element means for comparing each of said plurality of sensor output voltages with said voltage levels VL1 and VL2, said logic means further being adapted for generating an enabling processing unit output signal in response to either increase or a decrease of any of said sensor output voltages; and

E. a centralized alarm power drive for receiving said processing unit output signal, said alarm drive comprising a oscillator for generating a variable alarm signal; and

F. a centralized alarm, responsive to said alarm signal, and further comprising an interruptor device having means to prevent ignition of an explosive gas in the vicinity of said alarm.

2. An alarm system as in claim 1 wherein at least one of said plurality of remote sensors comprises a doped semiconductor resistance with a heater for maintaining said semiconductor at an elevated temperature, said heater being supplied with said supply voltage through a remotely mounted zener diode to maintain proper heater voltage irrespective of supply voltage variations.

3. An alarm system as in claim 2 wherein at least one of said plurality of remote sensors includes a thermostatic switch operable to short circuit said electrical resistance in response to an elevated temperature.

4. An alarm system as in claim 1 wherein said centralized processing unit logic means further comprises a NAND gate having a plurality of inputs, one for connection to each of the plurality of sensor output voltages, and an OR gate having a plurality of inputs, one for connection to each of said plurality of sensor output voltages, said NAND gate and said OR gate being thereby in parallel input connection to each of said plurality of sensor output voltages, the outputs of said NAND and OR gates comprising inputs to further logic means being adapted for generating said enabling processing unit output signal in response to a change in either gate, wherein each of said threshold circuits is adapted to decrease its sensor output voltage in response to a decrease in resistance of said sensor resistance, and thereby change said NAND gate, and said each threshold circuits is adapted to increase said sensor output voltage in response to an open circuit between its remote sensor and said threshold circuit, and thereby change said OR gate.

9. An alarm system as in claim 1 wherein at least one of said plurality of remote sensors includes a thermostatic switch operable to short circuit said electrical resistance in response to an elevated temperature.

10. An alarm system as in claim 9 wherein said alternate source further comprises a condition monitoring circuit means adapted to sound said alarm if the voltage of said alternate source drops below a predetermined level.

11. An alarm system as in claim 1 wherein said centralized alarm comprises an electromagnet adapted to be selectively energized for urging a hammer against a sound making element, a spring adapted to return said hammer from said sound making element during non-energization of said electromagnet, wherein an interrupting signal from said oscillator is operable to energize said electromagnet and produce an audible interrupting sound.

12. An alarm system as in claim 1 wherein said centralized alarm comprises an interrupting-contact sound device enclosed within a wire mesh enclosure, wherein said mesh is adapted to prevent propagation of a flame from the vicinity of arcing contacts within said sound device through said mesh.

13. An alarm system as in claim 1 wherein said alternate power supply source comprises a rechargeable battery in parallel with a normal D.C. power supply, a battery charger activated by said normal supply for maintaining said rechargeable battery, and a diode between said rechargeable battery and said normal supply to prevent power from said battery from flowing towards said normal supply in the event of failure of the same.

14. An alarm system as in claim 1 wherein said normal power supply includes means to furnish said voltages through a diode, with a relay between said alternate source and the output voltage of said diode, wherein said relay is de-energized upon failure of said normal supply and adapted to switch to said alternate source.

15. An alarm system as in claim 14 wherein said alternate source further comprises a condition monitoring circuit means adapted to sound said alarm if the voltage of said alternate source drops below a predetermined level.

16. An alarm system as in claim 15, wherein said condition monitoring circuit means further comprises a relay means adapted to be periodically energized by a pulse from a timer means, whereupon said relay means is adapted to momentarily connect said replaceable battery to ground through a resistance, a battery voltage threshold means adpated to momentarily sound said alarm upon sensing a less than predetermined level of voltage from said replaceable battery when it is so momentarily connected to ground.

5. An alarm system as in clsaim 4 wherein said voltage level VL2 is less than said voltage level VL1, said voltage level Vl2 being a reference to said NAND gate and said voltage level VL1 being a reference to said OR gate.

6. An alarm system as in claim 5 wherein said processing unit further includes sensor self-monitoring circuitry means comprising a resistance connected to the output of said OR gate, said resistance being connected to a first input of a NOR gate, a second zener diode connected between a relatively zero level of said D.C. supply voltage and said same first input of said NOR gate, wherein the output of said NAND gate is connected to a second input of said NOR gate, said NOR gate being referenced to said voltage level VL2, and said second zener diode having a zener value equal to VL2.

7. An alarm system as in claim 6 wherein the output of said NOR gate is connected to one input of a second OR gate, said second OR gate being referenced to said voltage level VL2, the second input of said second OR gate being connected to a source of said voltage level VL2 through a capacitor, whereby the output of said second OR gate is said processing unit output signal, and which is maintained disabled during an initial stabilization period for said remote sensors.

8. An alarm system as in claim 6 wherein said alternate source further comprises a condition monitoring circuit means adapted to sound said alarm if the voltage of said alternate source drops below a predetermined level.