Smoke alarm

• US 4,021,792 A
• Filed: 06/23/1975
• Issued: 05/03/1977
• Est. Priority Date: 06/23/1975
• Status: Expired due to Term

• Current Assignee: Wellen Industries
• Original Assignee: Wellen Industries
• Inventors: Eggert, Carl A., Skarman, John, Ludt, Roy R.
• Primary Examiner(s): Caldwell, John W.
• Assistant Examiner(s): Myer, Daniel
• Application Number:
  US05/589,420
• Time in Patent Office: 680 Days
• Field of Search: 340/237, 340/251, 250/564, 250/565, 250/574, 250/575, 250/552, 250/573, 356/207
• US Class Current: 340/630
• CPC Class Codes: G08B 17/103 using a light emitting and receiving device
• CPC Class Codes: G08B 17/107 for detecting light-scattering due to smoke
• CPC Class Codes: G08B 17/113 Constructional details

Abstract

A smoke alarm having a smoke chamber with at least two inlet ports together with an array of louvered apertures and flue means to provide free access to the smoke chamber for smoke flowing in any direction within a hemispherical zone. A circuit employing photocells to measure smoke obscuration and reflection by means of an improved wheatstone bridge to sound a loud audible alarm. A relaxation oscillator coupled to a light source which is used for the optical portion of the smoke alarm. The oscillator produces an alarm to indicate failure of the light source, which alarm is distinguishable from the smoke alarm. A heat sink thermally coupled to the light source to induce filament vapors to condense on non-critical portions of the light source.

Claims

1. A smoke alarm for detecting smoke in air comprising:

a light shielded smoke chamber defining a generally closed space having a longitudinal axis with a first and second port provided in said chamber at each end of said longitudinal axis, and having a third port disposed on an axis substantially perpendicular to said longitudinal axis, each of said ports having a baffling means for preventing the entry of light without substantially interfering with the entry of smoke through each of said ports into said chamber, at least one of said baffling means being a reticulated foam layer disposed across one of said ports, said reticulated layer having a nonporous plate disposed thereon whereby light is substantially prevented from penetrating said layer while smoke is permitted to enter said layer and aperture through the sides of said layer;

an array of louvered apertures proximately disposed to said third aperture, said array of apertures having louvers oriented with opposite inclinations whereby smoke flowing perpendicular to said longitudinal axis of said chamber is directed toward said third aperture regardless of direction of flow;

a flue means for directing smoke flowing parallel to said longitudinal axis of said chamber into said first and second ports;

an incandescant bulb and lens assembly to provide a beam of collimated light said bulb thermally coupled to a heat sink at selected portions of said bulb whereby vaporized matter within said incandescant bulb is induced to condense on said selected portions of said bulb thermally coupled to said heat sink and light produced by said bulb and directed into said collimated beam is substantially unattenuated by condensation of said vaporized matter;

a first photoelectric cell to provide an electrical response upon the irradiation by light scattered from said collimated beam, said scattered light beam scattered by smoke dispersed into said chamber;

a second photoelectric cell to produce an electrical response upon the radiation by light from said beam;

a power supply to provide a source of electrical power;

a wheatstone bridge having four circuit segments coupled to said power supply and grouped in a first and second series pair said first and second series pairs being coupled in parallel, said first series pair being said first and second photoelectric cell and said second series pair being low impedance electrical resistors, one of said resistors being a low impedance variable resistor, whereby said wheatstone bridge is substantially unaffected by changes in relative humidity;

an alarm means coupled to said wheatstone bridge for producing an alarm signal when said first photoelectric cell responds to a measured increase of light scattered from smoke within said chamber and for silencing said alarm signal when said first photoelectric cell responds to a measured decrease of light scattered from smoke within said chamber;

a relaxation oscillator coupled to said incandescant bulb, said relaxation oscillator being triggered when said incandescant bulb becomes open circuited, whereby a fail-safe signal is produced which is distinguishable from said alarm signal; and

a coated wire having a predetermined optical scattering coefficient to simulate the scattering of light from smoke within said chamber, said wire removably disposed in said beam by a spring means and a shaft coupled to said wire, said shaft extending from said smoke alarm to allow manual depression to dispose said wire into said beam, said spring means for encouraging said wire from said beam when said shaft is not depressed.

2. A smoke alarm for detecting smoke comprising:

a light shielded smoke chamber having at least two ports provided therein to permit smoke dispersed in air to flow through a space defined by said chamber;

a light source means for providing a beam of collimated light, said beam propagating through at least a portion of said space defined by said chamber, wherein said light source means includes an incandescant bulb thermally coupled to a heat sink at portions of said bulb propagating light in directions other than the direction of said collimated beam, whereby vaporized matter within said incandescant bulb is induced to condense on portions of said bulb thermally coupled to said heat sink and light produced by said bulb and directed into said collimated beam is substantially unattenuated by condensation of said vaporized matter;

a first light detection means for producing an electrical response upon irradiation by light scattered from said beam, said scattered light being scattered by smoke dispersed in said portion of said chamber having said beam propagating therethrough;

a second light detection means for producing an electrical response upon irradiation by light from said beam; and

a circuit means for comparing said electrical responses from said first and second light detection means to produce at least one alarm signal in response to light scattered from smoke within said chamber.

3. In a smoke alarm having a light source, a power supply, a sensing circuit with an output detection signal, a gate controlled rectifier, and an alarm transducer wherein said light source, sensing circuit and alarm transducer are coupled to said power supply, the anode of said gate controlled rectifier is coupled to said alarm transducer and is gated by a control signal from an alarm trigger means, said alarm trigger means being coupled to said sensing circuit and said alarm trigger means for responding to said output detection signal by generating said control signal, a relaxation oscillator for generating a distinct lamp failure alarm comprising:

a passive network having a chargeable node, said chargeable node being coupled to the input of said alarm trigger means;

a diode having its anode coupled to said chargeable node of said passive network and its cathode coupled to said anode of said gate controlled rectifier; and

relaxation trigger means having an input coupled to said light source and an output coupled to said chargeable node for maintaining said chargeable node in a substantially discharged condition when the impedance of said light source is less than a predetermined value.

4. The relaxation oscillator to claim 3 wherein said passive network is a series RC circuit, said relaxation trigger means includes a semiconductor transistor having its base coupled to said light source, its collector coupled to said chargeable node and its emitter coupled to ground.

5. A smoke alarm comprising:

a light shielded smoke chamber having at least two ports provided therein to permit smoke dispersed in air to flow through a space defined by said chamber;

light source means for providing a beam of light through at least a portion of said space defined by said chamber;

means for detecting light scattered by smoke from said beam for light and for generating at least one alarm signal; and

a heat sink thermally coupled to said light source at portions of said light source propagating light in directions other than the direction of said beam of light so that vaporized matter within said light source is induced to condense on portions of said light coupled to said heat sink and light produced by said light source and directed into said beam is substantially unattenuated by condensation of said vaporized matter.