Abstract:
A photo-electric smoke detector includes a source of radiant energy and a closed loop control circuit which responds to a radiant energy feedback signal to adjust an output characteristic of the emitted radiant energy and which evaluates a quality characteristic of the emitted radiant energy. The feedback circuit and the source can be intermittently activated. Emitted radiant energy is directed toward a lens. The feedback signal is proportional to radiant energy reflected or scattered off of the lens.

Description:
FIELD 
       [0001]    The invention pertains to smoke detectors. More particularly, the invention pertains to aspirated smoke detectors where the source which injects radiant energy into the detector&#39;s smoke chamber can be monitored and controlled. 
       BACKGROUND 
       [0002]    Photoelectric smoke detectors often include a mechanism to monitor an optical source which injects radiant energy into a smoke chamber of the detector. Photoelectric scattering smoke detectors often rely on a background quiescent level of optical measurement from the chamber to determine if source is operational. This is the result of light reflecting off many surfaces with the chamber and detected by a smoke sensing photo sensor. However, a very high sensitivity device, such as one having an aspirated smoke sensing chamber, may have little or no quiescent level at the respective photo sensor. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         [0003]      FIG. 1  is a block diagram of a detector which embodies the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0004]    While embodiments of this invention can take many different forms, specific embodiments thereof are shown in the drawings and will be described herein in detail with the understanding that the present disclosure is to be considered as an exemplification of the principles of the invention, as well as the best mode of practicing same, and is not intended to limit the invention to the specific embodiment illustrated. 
         [0005]    In an embodiment of the invention, monitoring of output of a source light emitting diode (LED) can be implemented by measuring reflected or scattered light from a lens that is used to focus the LED light into a smoke chamber. The reflected light can be used to both control the optical intensity of the LED and to provide feedback as to the LED&#39;s optical output intensity. 
         [0006]    In one aspect, the drive circuit for the LED employs a photo diode to provide feedback. Some of the light from the LED is reflected off the lens. An optical sensor, such as a photo diode detects the reflected light. The current produced by the photo diode can be used to provide feedback to a driver amplifier for the LED to maintain the optical output power at a predetermined level. 
         [0007]    In another aspect of the invention, the feedback circuit that is connected to the photo diode can also include a detection circuit. When feedback signal establishes that the LED amplifier is in its linear region of operation, the detection circuit provides an output indicative of the LED operating properly. When the feedback is no longer enough to maintain the LED amplifier within its linear region, the detection circuit provides an output indicative of the LED not working correctly (for example, burned out, degraded excessively). In response thereto, a maintenance or trouble signal can be generated. 
         [0008]    In another aspect of the invention, an aspiration unit, a fan or blower for example, can be coupled to the detector&#39;s smoke chamber to inject fluid into or draw fluid from that chamber. That aspiration unit can be local to or remote the detector. 
         [0009]    Control circuits can be coupled to the amplifier for the optical source, a sensor of reflected radiant energy therefrom and a smoke sensor associated with a sensing chamber of the respective detector. Such circuits could be implemented with one or more programmable processors and associated control software pre-stored on a computer storage medium. 
         [0010]      FIG. 1  illustrates an embodiment  10  of the present invention. Detector  10  includes a housing  12  which carries a smoke chamber  14 . Control circuits, generally indicated at  16  can also be carried by housing  12 . It will be understood that the circuitry configuration of  FIG. 1  is exemplary only. Other circuit configurations come within the spirit and scope of the invention. 
         [0011]    Circuitry  16  includes an optical amplifier  16   a  which is coupled to a source light emitting diode  16   b.  Radiant energy  16   c  emitted by LED  16   b  is directed toward a lens  18 . A focused portion  18   a  is directed into the smoke chamber  14  and used to detect a smoke concentration therein. 
         [0012]    Various configurations of smoke chambers are known to those of skill in the art and do not represent a limitation of the present invention. An optical smoke sensor  14   a,  for example, a photo sensor, is coupled to chamber  14  and produces an electrical signal, on line  14   b  indicative of smoke concentration in chamber  14 . 
         [0013]    Radiant energy  18   b  reflected off of lens  18  is indicative of radiant energy output from LED  16   b  and is received by photo sensor  16   d.  Sensor  16   d  is coupled in parallel to a resistor  16   e.  A voltage generated across the sensor/resistor combination  16   d,e  can be fed back to amplifier  16   a  so as to adjust an electrical input parameter of source LED  16   b  and to maintain the source  16   b  operating in its linear range, assuming normal operation. That same voltage can be evaluated in a threshold establishing amplifier  16   f  to generate a binary output status signal. 
         [0014]    A buffer amplifier  16   g  can be used to intermittently activate source  16   b  and sensor  16   d.  It will also be understood that at least some of the above noted circuit elements could be incorporated into additional control circuitry  16 - 1 . 
         [0015]    Control circuitry  16 - 1  could be implemented, at least in part, with one or more programmed processors  16 - 2  which execute control programs  16 - 3  pre-stored on a computer readable storage medium, for example EEPROM. Control circuitry  16 - 1  can also include a wired or wireless interface to communicate with a displaced monitoring system M via a medium  22 . 
         [0016]    Smoke indicating signals, on the line  14   b  can also be coupled to control circuits  16 - 1  for evaluation and transmission of indicia thereof to the monitoring system M. An aspirator  24  can be coupled to the smoke chamber  14 , to inject ambient air into the chamber or to draw it from the chamber, all without limitation. 
         [0017]    The aspirator  24  can operate under the control of circuits  16 - 1 . It will be understood that aspirator  24  can be carried by housing  12 , or, displaced from housing  12  all without limitation. Neither the exact characteristics of the aspirator  24  nor its location are limitations of the invention. 
         [0018]    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.