Abstract:
An aspirated smoke detector includes at least one ambient atmosphere inflow collection pipe with a plurality of inflow ports arranged along the pipe. The ports of the pipe are defined at least in part by temperature sensitive materials which alter the area of the respective inflow port in response to physical and/or chemical changes. As the temperature increases the area increases, thereby drawing more of the local ambient air and airborne particulate matter into the flow pipe, and then onto the smoke sensing chamber. This increased flow off-sets the dilution present due to other air in the respective pipe from other inflow ports which might not be near the developing fire condition.

Description:
FIELD 
     The invention pertains to aspirated smoke detectors. More particularly, the invention pertains to such detectors which respond to local physical and or chemical environment parameter changes, such as, for example, temperature increases, by increasing inflowing local ambient atmosphere from the region where the modified environment parameter has been sensed. 
     BACKGROUND 
     Various types of aspirated smoke detectors are known. One example is disclosed in U.S. Pat. No. 7,493,816 entitled, “Smoke Detectors” which issued Feb. 24, 2009. Another is disclosed in published US Patent Application 2009/0025453 entitled “Apparatus and Method of Smoke Detection” published Jan. 29, 2009. Both the &#39;816 patent and the published &#39;453 application are assigned to the assignee hereof and incorporated herein by reference. 
     Aspirated smoke detectors usually need a careful balance between sensitivity and nuisance rejection. Such detectors usually supervise a pretty wide area: in case of a fire, only a few holes in the aspirating pipe will be exposed to smoke/gas whilst most of the pipe still sucks clean air. So a large and unpredictable dilution effect will occur. Since the system must take in account the high dilution effect, high sensitivity—usually laser based—optical systems, are employed to maintain early fire detection in such conditions. This tends to limit the suitability of aspirated systems to clean environments such as computer rooms, telecommunication rooms or the like. 
     There is a need for aspirated detectors which might be usable in a broader range of environments. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram of an aspirated detector in accordance with the invention; 
         FIG. 1A  illustrates an enlarged section of a prior art ambient air inflow pipe; 
         FIGS. 2A-2D  illustrate aspects of one embodiment of a detector in accordance with the invention; and 
         FIGS. 3A ,  3 B illustrate aspects of another embodiment of a detector in accordance with the invention. 
     
    
    
     DETAILED DESCRIPTION 
     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. 
     In embodiments of the invention, an environmental stimulus, for example temperature, can be used to alter the size of aspirating ports, to increase ambient atmosphere inflow, or nozzle cross section. Since this process will occur only at the inflow ports closest to the fire/combustion phenomena, it will dramatically impact the amount of smoke/particulate/gas that is sucked or drawn into the collection pipe or conduit and will thus minimize the dilution effect. This would allow a prompt response, even with a lower sensitivity, thus reducing the occurrence of false alarm in normal or even in harsh environments. 
     All flaming fires release radiation energy. As a result, the ambient air in the vicinity is subjected to a measurable temperature increase. One embodiment of the invention employs bi-metallic or memory shaped alloy nozzles to adapt ambient air inflow hole size to ambient temperature. The higher the local temperature, the larger the inflow port becomes. 
     Embodiments of the invention can be sensitive to absolute temperature, rate of raise of temperature, or even differential temperature (compared to the air temperature sucked in the pipe). Most smoldering fires (i.e. negligible thermal contribution) will release high amounts of carbon monoxide (smoldering combustion is an oxygen poor-type of combustion so almost all organic fuels will led to a carbon monoxide rich gas compound release). 
     In order to increase a nozzle&#39;s active area that is responsive to such combustion, a layer of suitable catalyst could be deposited over the thermally sensitive element. Preferred catalyst materials are hopcalites, which are commercially available as carbon monoxide oxidants and sorbents. There are two main formulations of hopcalite: one is a mixture of about 50% MnO2, about 30% CuO, about 15% Co2O3, and about 5% Ag2O whilst the other contains about 60% MnO2 and about 40% CuO (David R. Merrill and Charles C. Scalione, J. Am. Chem. Soc., 43, 1921, p. 1982). Carbon monoxide hopcalite induced oxidation is highly exothermic (approx 60 Kcal/mol) so the detector will be fairly sensitive even to small amounts of CO (and consequently to smoldering combustion). CO dependant-hopcalite induced heat release has been used to implement a CO detector as described in expired U.S. Pat. No. 3,895,912 entitled, “Carbon Monoxide Monitor”. 
     Another embodiment could employ an inflow pipe design with built in thermally sensitive material. The pipe might be co-molded as a bi-material arrangement: most of the pipe will be made of cheap standard ABS plastic blend and just a partial area of the pipe will present thermally sensitive material ready to be punched during system commissioning. 
       FIG. 1  illustrates an aspirated smoke detector  10 , in accordance with the invention, monitoring a region R. Detector  10  is in wired or wireless communication with a monitoring system  12 . Components of detector  10  can be carried by housing  14 . 
     Detector  10  includes a smoke sensing chamber  20 , for example a photo-electric type of sensor as would be understood by those of skill in the art. The details of chamber  20  are not limitations of the invention. Aspirated air and smoke flow in at inflow port  20   a  and out at port  20   b.    
     An aspirating unit, fan or blower  22  draws or injects ambient atmosphere, and associated airborne particulate matter, smoke particles, into the chamber  20  where a concentration thereof can be sensed. Control circuits  24  coupled to chamber  20  and perhaps aspiration unit  22  evaluate a degree of smoke sensed in the chamber  24  as would be understood by those of skill in the art and need not discussed further. Control circuits  24  couple smoke concentration indicia to the monitoring system  12 . Unit  22  could also be installed upstream of chamber  20  without departing from the spirit and scope of the invention. 
     Ambient atmosphere, including airborne particulate matter and gases, can be acquired from a plurality of different locations in the region R by use of a plurality of inflow conduits or pipes  30 ,  30 - 1  . . .  30 - n  which are coupled to the chamber  20 . Each of the pipes, such as  30  is positioned in advance to provide smoke related information as to specific locations in the region R. A discussion of inflow conduit  30  also applies to  30 - 1  . . .  30 - n.    
     Inflow conduit or pipe  30  is hollow with a distal end  30   a  (which might be open to receive ambient air and smoke or, most likely, present a suitable termination calibrated based on overall pipe design) into which local ambient air, or atmosphere, can be drawn by the aspirating unit  22 . In addition, pipe  30  can be perforated at a plurality of displaced locations, such as  30   b ,  30   c  . . .  30   n . These inflow ports or openings provide additional, location specific access points into region R for acquiring samples of the ambient air for analysis in chamber  20 . If desired, inflow port  30   a  could be sealed with all samples coming from  30   b  . . .  30   n  without limitation. Other inflow pipes  30 - 1  . . .  30 - n  are formed similarly. 
     By way of explanation,  FIG. 1A  illustrates a section of prior art aspiration, atmospheric, inflow pipe  40 . Pipe  40  illustrates a distal end  40   a , which might be open or sealed, and an inflow port  40   b  through which ambient air at a location in a region R′ being monitored could be drawn and directed, as at  40   c  to a sensing chamber of an aspirated detector. As explained above, air and smoke particulate matter inflowing via port  40   b  to be drawn into the respective smoke sensing chamber would become diluted by the much larger volume of air in pipe  40  which is being drawn thereinto from a variety of other points in the region R′. 
       FIGS. 2A-2D  illustrate aspects of one embodiment of the invention. The inflow ports formed in the respective pipe  30 , such as port  30   b , are formed with a larger area than port  40   b  of  FIG. 1A . All such ports are covered by a temperature responsive cover, or nozzle such as nozzle  32  of  FIGS. 2B-2D . 
     Nozzle  32  includes a bi-metallic element  34  with an opening  34   a  therethrough. Opening  34   a  is comparable to opening  40   b  of  FIG. 1A . 
     Nozzle  32  has a first, inactive state as in  FIG. 2C  and a second active state as in  FIG. 2D . Nozzle  32  goes from the inactive position or state,  FIG. 2C , to the active position or state,  FIG. 2D , in response to the ambient air heating the element  32  due to a locally developing fire condition. As the element  32  moves to the active state, the amount of inflowing air increases into the pipe  30 , thereby increasing the inflowing particulate matter and off-setting the above noted dilution effect due to being mixed with air in the main flow to the intake port  20   a . As noted above, some or all of the nozzle  32  could be coated with an exothermic material or catalyst to increase the amount of local heat, thereby providing a larger air, and particulate matter, inflow area into the associated flow or collection pipe. Nozzle  32  provides a retrofit solution to be added to previously installed aspirated detectors. 
     Thermally sensitive nozzle designs could be optimized to maximize both convective (heat exchange radiators) and irradiated heat transfer (opaque dark color) from the ambient air towards the heat sensitive elements, i.e. to maximize temperature difference between the pipe (which will be kept at a fairly constant temperature form the air circulating inside) and the local environment. 
       FIGS. 3A ,  3 B illustrate another embodiment of the present invention. In the embodiment of  FIGS. 3A ,  3 B a thermally sensitive or responsive material  52  can be formed on a section of inflow or collector pipe  50 . An opening  54  can be provided into the pipe  50 , through the material  52 . 
     In the absence of heat, the inflow port  54  has a first inflow area. In the presence of heat, due to heated air in the region R adjacent to the opening  54 , the thermally responsive material  52  expands, thereby increasing the opening of the inflow port  54  so that an increased inflow from that part of the region R results. This, in turn, significantly increases the flow of airborne particulate matter from that portion of the region R adjacent to the opening  54  into the inflow port  20   a  of the smoke sensing chamber  20 . A faster smoke or fire determination can then be made by the control circuits  24 . 
     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.