ULTRA-SHORT WAVELENGTH PHOTOELECTRIC SMOKE DETECTOR

Abstract: A photoelectric smoke detector incorporates a short wavelength radiant energy emitter (14). The emitter, an LED or laser diode, emits frequencies in a range of 430 to 450 nanometers. The emitted frequencies can be further shortened by directing them to impinge on a non-linear crystalline material (22). Radiant energy emitted from the material will have a wavelength on the order of sixty percent that of incident radiant energy (14'). The short wavelength energy will be scattered by airborn particulate matter characteristic of relatively fast, flaming fires. The emitter, an LED or laser diode can include an 880 or 940 nm wavelength coupled with shorter wavelength ranges (190-450 nm) with associated detection. It also has the capability of detecting slow burning smoldering-type fires. A control circuit and an audible output device provide a local audible alarm of a detected fire.

Description: U TRA-SHORT WAVELENGTH PHOTOELECTRIC SMOKE DETECTOR This application claims the benefit of the earlier filing date of Provisional Application Ser. No. 60/122,981, filed March 5, 1999. Field of the Invention: The invention pertains to photoelectric smoke detectors. More particularly, the invention pertains to such detectors with short wavelength radiant energy injected into a scattering region. Background of the Invention: A variety of fire detectors are known for both residential and commercial applications. Known detector technology includes heat detectors, smoke responsive detectors such as photoelectric detectors, ionization detectors or combinations of both types, flame detectors and detectors based on gas detection. Heat detectors respond to rising ambient temperatures. Photoelectric detectors are based on light scattering or light obscuration. Ionization detectors incorporate a radioactive source which ionizes the air in the vicinity of an electrode. Ions generated attached to airborne smoke aerosols which in turn reduces the ionization current. This reduction triggers an alarm at a predetermined threshold. It is known that the size distribution of smoke aerosols covers a spectrum from approximately 0.05 micrometers to 3.0 micrometers. Photoelectric smoke detectors ,tend to be more responsive to larger particles, associated with smoldering fires. Ionization-type detectors tend to be more responsive to smaller particles associated with faster flaming fires. Summary of the Invention: In accordance with the present invention, a photoelectric smoke detector injects a relatively short wavelength radiant energy into a scattering region. With the aid of a non-linear crystal, the injected beam can have even shorter wavelength. The radiation is in turn scattered by airborne particulate matter, such as smoke aerosols, in the sensing region. The scattered radiant energy can then be sensed at a sensor responsive to the relatively short wavelength scattered radiant energy. In one aspect of the invention, a blue light-emitting diode or laser diode which emits light at a wavelength on the order of 450 nanometers can be used as a source of radiant energy. That radiant energy can be injected directly into a scattering region. In another aspect of the invention, a non-linear crystalline material can be positioned in the path of the emitted radiant energy. The crystalline material is selected so as to emit, in response to incident radiant energy, radiant energy having a wavelength on the order of 60 percent of the incident radiant energy. This shorter wavelength radiant energy can in turn be injected into the scattering region. If the source emits radiant energy in a range of 430 to 470 nanometers, output from the nonlinear optical material could be expected to fall within a range of 190 nanometers to 350 nanometers depending on the input frequencies and the material selected. In yet another aspect of the invention, a photoelectric smoke detector incorporates a source of infrared radiant energy, such as a light emitting diode or laser diode with an emitted range of wavelengths on the order of 880 nanometers to 940 nanometers. A second source emitting radiant energy in the 430 to 470 nanometer range can be incorporated into the detector spaced from the first source. Alternately, a single source which might be switchable from one frequency range to the other could be used. A single sensor having a broad enough frequency response range or two different sensors could be incorporated into the detector so as to detect scattered light in two different frequency bands. In yet another aspect of the invention, a non-linear optical material can be positioned in the pathway of energy-emitted in the 430 to 470 nanometer wavelength range so as to make available shorter wavelength 190 to 350 nanometer radiant energy in the scattering region. The non-linear crystalline optical materials could be selected from a class which includes beta barium borate, lithium triborate, lithium tantalate or lithium niobate. The non-linear optical material may be selected from other optical crystal that can down convert wavelengths at various ranges. In accordance with the invention, control circuitry can be coupled to the emitter or emitters in the detector as well as the sensor or sensors therein. If desired, the emitter or emitters could be operated in a pulsed mode as is known for use with photoelectric detectors. The control circuitry could be implemented as an application specific integrated circuit (ASIC) or in the form of a programmed processor. A plurality of pre-stored instructions can be extracted from a read-only memory, executed by the processor for the purpose of implementing detector functionality. The detector can be operated off of a self-contained battery and/or an AC/DC power supply energized with utility supplied power. Numerous other advantages and features of the present invention will become readily apparent from the following detailed description of the invention and the embodiments thereof, from the claims and from the accompanying drawings. Brief Description of the Drawings: Fig. 1 is a side sectional view, enlarged, of a sensing chamber in accordance with the present invention; Fig. 2 is a block diagram of control circuitry usable with the chamber of Fig. 1; Fig. 3 is a top, plan, schematic view of an alternate form of a sensing chamber in accordance with the present invention; Fig. 4 is a block diagram illustrating exemplary signal processing in accordance with the present invention; and Fig. 5 is a graph illustrating performance characteristics of the chamber of Fig. 1. Detailed Description of the Preferred Embodiments: While this invention is susceptible of embodiment in many different forms, there are shown in the drawing and will be described herein in detail specific embodiments thereof with the understanding that the present disclosure is to be considered as an exemplification of the principles of the invention and is not intended to limit the invention to the specific embodiments illustrated. Fig. 1 illustrates a side sectional view of a photoelectric sensing chamber 10. The chamber 10 includes a substantially closed housing 12 with spaced apart vanes or labyrinths for ingress and egress of airborne particulate matter while at the same time excluding exterior ambient light. The housing 12 carries an emitter 14 which could be implemented as a blue light emitting diode or laser diode. Such emitters are commercially available in the market place and would be known to those of skill in the art. The emitter 14 emits radiant energy with a wavelength on the order of 430 to 470 nanometers. Radiant energy 14' from emitter 14 could be directed into scattering region 16 without further processing. In this instance, radiant energy scattered by airborne combustible particulate matter in the region 16 could be sensed at photodiode or phototransistor 20. As those of skill in the art will understand, a variety of commercially available photosensors could be used without departing from the spirit and scope of the present invention provided they responded to the frequency of scattered radiant energy from the region 16. In an alternate embodiment, a non-linear crystalline optical material 22 can be positioned in the path of the radiant energy 14'. The optical material 22 is selected from a class which could include beta barium borate, lithium triborate, lithium tantalate and lithium niobate or any other equivalent non-linear crystalline material. The material 22 produces a shorter wavelength beam 14" having a wavelength on the order of 60 percent or less of the wavelength of the beam 14'. Where the source 14 emits radiant energy with a wavelength of 430 to 470 nanometers, the non-linear optical material 22 can reduce the wavelength in the beam 14" to a range of 190 to 350 nanometers. The shorter wavelengths in the beam 14" can be expected to effectively scatter off of smaller airborne combustible particles of a type associated with fast flaming fires. Fig. 5 is a graph illustrative of response of the detector 10 with a blue emitter 14 to increasing smoke obscuration plotted versus time. The sharply rising upper plot 100 is a measurement off of the sensor 20 versus a plot 102 taken off of a commercially available laboratory grade optical sensor. As illustrated in Fig. 5, the plot 100 has a sharper slope when compared to the plot 102 indicative of a more rapid response by the chamber 10. The plot 10 is not reflective of any performance improvement achievable with the use of the non-linear optical material 22. Fig. 2 illustrates an exemplary block diagram of control circuitry 40 usable with the chamber 10. Circuitry 40 includes a programmed processor 42 which is coupled via a pulsed current drive circuit 44 and power supply 46 to the emitter or emitters 14. Processor 42 receives feedback from sensor 20 via isolation/buffer amplifier circuitry 50. Output from the circuitry 50 is digitized in analog to digital converter 52. Processor 42 in turn is coupled to audible output device 54 which can be used to provide an audible alarm indicative of a sensed smoke condition. Those of skill in the art will understand that a variety of control programs can be executed by the processor 42 to carry out signal processing associated with scattered radiant energy received at sensor 20. Fig. 4 is a block diagram which illustrates exemplary processing steps for carrying out a smoke sensing function. In a step 100, the processor 42 is activated from its "sleep" condition. In a step 102, the processor's input/output ports are initialized. In a step 104, the processor measures a noise level, indicative of stray light in chamber 12, when source 14 is inactive. This base line noise signal can be stored for a later use when evaluating chamber outputs from sensor 20 in response to emitter 14 having been energized. In a step 106, the emitter or emitters 14 are energized with a current pulse which produces radiant energy 14' directed toward the scattering region 16. The energy 14', as discussed above, can be passed through non-linear optical material 22 to reduce the wavelength thereof prior to scattering. Scattered short wave length radiant energy is then sensed by detector 20 and processed in processor 42 in step 108. An alarm decision can be made in a step 110 based on the output or outputs from the sensor 20. In the event that an alarm is indicated in the step 112, the audible output device 54 can be energized in step 114. Otherwise, the processor returns to its low power, inactive, "sleep" state in step 116. It will be understood that control circuitry 40 could be implemented in a hardwired embodiment using an application specific integrated circuit without departing from the spirit and scope of the present invention. Other implementations such as programmable logic arrays and the like are also within the scope and spirit of the present invention. Fig. 3 illustrates a dual emitter chamber 10'. The chamber 10' includes a housing 12' which could be comparable to the housing 12 of Fig. 1. The chamber 10' includes a first emitter 60 which could emit radiant energy in the ultraviolet wavelengths discussed above. Those wavelengths can be shortened by directing the emitted radiant energy through a non-linear optical crystalline material 62 of a type discussed previously. The short wavelength radiant energy 60" is in turn projected into scattering region 66. Scattered short wavelength energy is in turn sensed at detector 68. Additionally, chamber 10' includes a second, infrared, emitter 70 which emits radiant energy in the 880 nanometer wavelength range. An associated sensor 72 senses scattered infrared radiant energy from scattering region 16. It will be understood that emitter 70 and sensor 72 could in turn be coupled to processor 42 as discussed previously whereupon processor 42 could carry out processing based on received scattered radiant energy at two different wavelengths. In this embodiment, the longer wavelength related signals from emitter 70 could be expected to respond to particulate matter associated with smoldering fires. On the other hand, the scattered radiant energy emitted from source 60, having a shorter wavelength can be expected to respond to particulate matter associated with fast flaming-type fires. It will also be understood that power supply 46 could be implemented as a replaceable or rechargeable battery alone or in combination with a AC/DC power supply which would be coupled to utility lines as a source of electrical energy. A single emitter or sensor could be used instead of separate emitters and sensors if desired without departing from the spirit and scope of the present invention. From the foregoing, it will be observed that numerous variations and modifications may be effected without departing from the spirit and scope of the invention. It is to be understood that no limitation with respect to the specific apparatus illustrated herein is intended or should be inferred. It is, of course, intended to cover by the appended claims all such modifications as fall within the scope of the claims.

Claims: What is Claimed: 1. A smoke detector comprising: an emitter of radiant energy having a wavelength substantially in a range of 430 to 470 nanometers; and a sensor responsive to at least some of the emitted radiant energy. 2. A detector as in claim 1 wherein the emitter and the sensor are carried in a common housing oriented at a selected angle relative to one another. 3. A detector as in claim 2 wherein the housing is aperture thereby providing for ingress and egress of ambient atmosphere. 4. A detector as in claim 2 wherein the angle falls in a range of 15 to 22° of the axial placement of the emitter and detector. 5. A detector as in claim 2 wherein the housing includes a conical reflective structure for dispersal of stray radiant energy within the housing. 6. A detector as in claim 2 which includes a control circuit, carried within the housing and an audible output device, carried within the housing and coupled to the control circuit. 7. A detector as in claim 6 wherein the control circuit comprises a programmed processor. 8. A detector as in claim 2 which includes an optical element through which the emitted radiant energy passes wherein the optical element substantially emits radiant energy with a wavelength in a range of 190 to 350 nanometers. 9. A detector as in claim 8 wherein the sensor is responsive to radiant energy in the 190 to 350 nanometer range. 10. A detector as in claim 2 which includes a second emitter of radiant energy having a wavelength in a range of 850 to 950 nanometers. 11. A detector as in claim 10 wherein the two emitters are offset from one another at an angle in a range of 30 to 60° . 12. A detector as in claim 10 which includes a second sensor responsive to radiant energy emitted by the second emitter. 13. A detector as in claim 11 wherein both emitters are coupled to the control circuitry. 14. A detector as in claim 12 wherein both sensors and both emitters are coupled to the control circuitry. 15. A photoelectric smoke detector comprising: a perforated housing; a source of substantially blue radiant energy carried within the housing wherein the source emits a beam of radiant energy into a sensing region within the housing; a sensor, carried by the housing and spaced from the source wherein the source and sensor are oriented at a selected angle relative to one another such that scattered radiant energy from the source will impinge on the sensor; and a control circuit and an audible output device coupled thereto and carried by the housing wherein the circuit is coupled to the source and the sensor to detect the presence of scattered radiant energy due to airborn particulate matter indicative of a relatively fast, flaming-type of fire. 16. A detector as in claim 15 which includes an optical material located in the beam of radiant energy emitted by the LED or laser diode for receiving the substantially blue radiant energy and for emitting a beam having a wavelength on the order of one-half the wavelength of the received energy. 17. A detector as in claim 15 which includes an optical element located in the beam of radiant energy for receiving the emitted radiant energy and for emitting therefrom a beam having a frequency with a wavelength in a range of 60 percent or less of the received radiant energy. 18. A detector as in claim 16 wherein the optical element comprises a nonlinear crystalline material responsive to the incident radiant energy. 19. A detector as in claim 17 wherein the material is selected from a class which includes beta barium borate, lithium tri-borate, lithium tantalate and lithium violate. 20. A multi-element ambient condition detector comprising: first and second different sources of radiant energy spaced apart from one another in a housing wherein the sources each direct a beam of radiant energy toward a region of the housing; first and second sensors, carried in the housing and spaced so as to receive scattered energy emitted from a respective source; a control circuit carried by the housing and coupled to the sources and the sensors. 21. A detector as in claim 20 which includes an audible output device coupled to the control circuit. 22. A detector as in claim 21 wherein the control circuit comprises a programmed processor. 23. A detector as in claim 21 wherein one source of energy emits a substantially blue beam and the other source emits an infrared beam. 24. A detector as in claim 20 which includes an optical element located in one of the beams wherein the element emits radiant energy with a wavelength on the order of sixty percent or less of the incident wavelength. 25. A detector as in claim 20 wherein one source has a wavelength in a range of 430 nanometers to 470 nanometers. 26. A detector as in claim 25 wherein in the beam from the one source is incident on a nonlinear optical element which emits an output beam with a wavelength in a range of 190 nanometers to 350 nanometers. 27. A detector as in claim 20 which includes a replacable battery and an audible output device coupled to the control circuit. 28. A detector as in claim 27 wherein the control circuit comprises a programmed processor. 29. A photoelectric smoke detector comprising: a housing with an internal region and openings for the ingress and egress of airborne combustible particulate matter; an emitter of radiant energy in a selected wavelength range; a non-linear optical element, interposed in the emitted radiant energy, wherein the optical element emits radiant energy with a wavelength in a range of forty to sixty percent of the wavelength of incident radiant energy from the emitter; and a sensor responsive to radiant energy emitted by the optical element and scattered by particulate matter in the internal region. 30. A detector as in claim 29 wherein the radiant energy from the emitter has wavelengths substantially in a range of 430-470 nanometers. 31. A detector as in claim 29 wherein the radiant energy emitted by the non-linear optical element has wavelengths substantially in a range of 190-350 nanometers. 32. A detector as in claim 29 which includes a control circuit, coupled to the emitter and the sensor, for determining the presence of a predetermined degree of particulate matter in the internal region and for producing an audible alarm responsive thereto. 33. A detector as in claim 33 which includes at least a self-contained power supply. 34. A detector as in claim 33 which includes an AC power supply with a battery backup. 35. A detector as in claim 17 wherein the material comprises a non-linear material that can down convert visible and infrared radiation to shorter wavelengths. 36. A detector as in claim 21 wherein the control circuit comprises an application specific integrated circuit (ASIC).

Inventors: BROOKS FLOYD E, DURAN EDWARD C, JOHNSTON DEREK SCOTT, VENZANT KENNETH L, WATSON MARK A, BROOKS, FLOYD, E., DURAN, EDWARD, C., JOHNSTON, DEREK, SCOTT, VENZANT, KENNETH, L., WATSON, MARK, A.
Applicants: BRK BRANDS INC, BRK BRANDS, INC.
Application year: 2000
Main classification: G08B17
IPC codes: G08B17