Abstract:
A modular smoke detector has a sensing electrode carried by an insulator module. The insulator module also carries an ionization source and a field effect transistor. The insulator module lockingly engages a printed circuit board. A conical smoke deflector and exterior electrode are assembled to the insulator module. The deflector and exterior electrode are spaced apart providing a space for inflow and outflow of airborne particles of combustion.

Description:
The benefit of a Jun. 27, 2002 filing date for Provisional Patent Application Ser. No. 60/392,123 is hereby claimed. 

   FIELD OF THE INVENTION 
   The invention pertains to ionization-type smoke detectors. More particularly, the invention pertains to such detectors which have a modular substructure which carries the sensing electrode and ionization source. 
   BACKGROUND OF THE INVENTION 
   Known ionization-type smoke detectors include spaced apart ionization source, sensing electrode, active chamber closed by an exterior electrode. Spaces or openings are usually provided to facilitate the inflow and outflow of airborne smoke which can be detected in the active chamber. A high impedance circuit is usually coupled to the sensing electrode. 
   While known detectors are effective for sensing airborne smoke, they require a number of manufacturing steps given the number of required parts. It would be preferable if the parts of the detector could be configured such that the number of manufacturing steps could be reduced. This will in turn improve manufacturability and reduce cost. Additionally, it would be desirable if at least some of the parts could be snap-fit together to reduce the number of soldering steps needed to assemble a detector. 
   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 an enlarged perspective view partly cut away of a detector in accordance with the invention; 
       FIG. 2  is an exploded view of the detector of  FIG. 1 ; 
       FIGS. 3A-3D  are alternate views of portions of the detector of  FIG. 1 ; 
       FIG. 4  is a side sectional schematic view illustrating relative dimensions of structural elements of the detector of  FIG. 1 ; 
       FIGS. 5A-5E  illustrate alternate configurations of a sensing electrode usable with the detector of FIG.  1 . 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   While embodiments 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 and is not intended to limit the invention to the specific embodiments illustrated. 
   An ionization type smoke sensing chamber exhibits improved stability to environmental conditions. More specifically, the chamber maintains a stable reference value and smoke characteristics under the influence of air velocity currents not containing smoke particles. The configuration allows for the opening for smoke entry into the chamber to be much larger than known ionization smoke sensing chambers. These larger openings enable more smoke particles to enter the chamber. 
   The detector includes three electrodes. The inner or source electrode carries the radioactive source. A sensing electrode contains an opening for the radiation to pass through to the sensing chamber or volume. An outer electrode closes the chamber. 
   The outer electrode is separated from the sensing electrode by a slit or window that allows smoke to enter the sensing volume. The opening in the sensing electrode is configured so as to block some of the radiation of the radioactive source from entering the sensing volume. Blocking is achieved by partly filling the opening with inwardly extending features such as tabs of various shapes. Representative shapes include rectangles, squares, triangles, semi-circles, or semi-ellipses. 
   The details that block some of the radioactive particles from entering the sensing volume are preferably symmetrical about a central axis. The blocking details will improve detector performance at higher ambient air/smoke velocities. 
   The outer electrode is configured such that it has a large cylindrical slit or window opening to allow smoke to enter the sensing volume or chamber. In one embodiment, the slit or window has a height on the order of one-quarter inch. The shape of the opening is modified by an interior cone that directs smoke entering the chamber toward and across the interior top surface of the outer electrode inside the sensing volume. 
   As the velocity of incident smoke increases, the cone forces the smoke closer to the interior top surface of the outer electrode. As described subsequently, a majority of recombination will occur at the interior top surface of the outer electrode. Thus, making this region of the chamber the most sensitive to smoke particles. 
   The configuration of the electrodes also provides a simplified assembly method. An insulator carries the inner and sensing electrodes spaced apart from one another. The insulator that separates the electrodes is also configured to carry a semiconductor buffer. The impedance of the center electrode is transformed by the buffer so that standard electrical circuits may be used to measure the voltage of the sensing electrode and thus, the amount of smoke present. 
   The insulator is configured so that the inner electrode, which carries the radioactive source, the sensing electrode, the buffer and a series resistor or diode can all be assembled to the insulator. The buffer and series resistor or diode are encapsulated in a protective coating that minimizes the effects of contamination of the chamber operation. 
   The insulator assembly can be mechanically attached to a printed circuit board that contains the remaining circuitry necessary for the detector. The source and the drain leads of the buffer can then be soldered to the printed circuit board. The outer electrode is then also mechanically attached to the printed circuit board, completing the assembly of the smoke sensing chamber. 
   The assembly of the chamber is simplified since the entire leakage sensitive portion for the chamber can be assembled independently of the remaining detector circuitry thereby minimizing the chances of contamination of one or more of the chamber electrodes. The last assembly step, attaching the outer electrode to the printed circuit board, also effectively seals the chamber from foreign debris normally associated with the manufacturing processes. 
   Another advantage of the above described insulator is that the source electrode does not need to be soldered to the detector printed circuit board. It is electrically coupled to the printed circuit board by a pressure contact. The source electrode can be configured with one or multiple spring contacts. As it is inserted into the insulator, the source electrode spring contact(s) will make a pressure contact with pads on the detector printed circuit to establish an electrical connection. 
   The printed circuit board&#39;s pads may be made of copper that is covered by solder or another material to reduce corrosion potential. The use of two spring contacts provides duplicate connections for reliability. 
   It will be understood that the exact details of the spring contact(s) is/are not a limitation of the invention. Deflectable or compressible contacts all come within the spirit and scope of the invention. 
     FIG. 1  illustrates various aspects of a detector  10  in accordance with the present invention. The detector  10  can be assembled on a printed circuit board  12  as a modular self-contained unit. The detector  10  includes an outer electrode  16 , a sensing electrode  18  and a reference or inner electrode generally indicated at  20 . 
   The outer electrode  16  has a generally cylindrical shape with side walls such as  16 - 1  which define a plurality of elongated rectangular slits or windows  16 - 2  which enable smoke to enter into an interior sensing volume indicated generally at  22 . 
   The sensing volume  22  is defined in part by a tapered or partially conical surface  24 - 1  which is carried by a vertical cylindrical side wall  24 - 2 . The side wall  16 - 1  extends along and outside of the side wall  24 - 2  relative to the sensing region  22 . It slidably engages a circular mounting region  24 - 3  at an annular region  24 - 3   a.    
   The circular mounting region  24 - 3  is in turn mechanically attached to the printed circuit board  12 . It will be understood that a gasket could be interposed between a lower edge  24 - 5  and the printed circuit board  12 . An additional gasket could be located between surface  24 - 6  and the printed circuit board  12 . 
   As described in more detail subsequently, the slits or windows  16 - 2  in combination with tapered annular surface  24 - 1  facilitate the ingress and egress of smoke from the adjacent ambient atmosphere into the sensing region or chamber  22 . The surface  24 - 1  facilitates and improves performance of the detector  10  at higher flow velocities such that the openings  16 - 2  can be larger thereby providing improved performance at lower flow velocities. 
   Electrodes  18  and  20  are carried on and locked to a cylindrical insulating structure generally indicated at  30  and can be processed as a modular sub-assembly of the detector  10 . Additionally, the insulator  30  carries those electrical components which directly interface with sensing electrode  18 , a very high impedance output. These components include a resistor or a diode  32   a  which is coupled in series between electrode  18  and a gate input of a semiconductor buffer  32   b.    
   The buffer  32   b  could be implemented, for example, as a field effect transistor with a high impedance input gate as would be understood by those of skill in the art. Source and drain connections indicated generally at  32   c  can in turn be electrically coupled to conductor traces on printed circuit board  12  and in turn electrically coupled to control circuitry  32   d  carried on printed circuit board  12 . 
   The insulating assembly  30  can be mechanically attached to printed circuit board  12  via a plurality of spaced apart deflectable connector legs such as the leg  30 - 1 , best seen in  FIGS. 3A ,  3 B. Legs such as the leg  30 - 1  extend from the assembly  30  and are radially deflectable so as to slidably engage lock to slots in the printed circuit board  12 . It will be understood that the exact nature and configuration of the locking mechanism of the legs  30 - 1  with the printed circuit board  12  is not a limitation of the present invention. 
   As described in more detail subsequently, the assembly  30  including electrodes  18 ,  20  and components  32   a, b  can be assembled as a modular sub-unit of the detector  10  and connected mechanically to printed circuit board  12  via legs  30 - 1 . As a result, the high impedance electrode/component sub-assembly  18 ,  31   a ,  32   b  can be isolated from other manufacturing operations involving either the printed circuit board  12 , control circuitry  32   d  or outer electrode  16  and exterior assembly or housing  24 - 3 . 
   Also as explained in more detail subsequently, the inner electrode  20  can be electrically coupled to conductors or traces on printed circuit board  12  and subsequently to control circuitry  32   d  via one or more deflectable electrical connector elements  20 - 1 . The connector elements  20 - 1  resiliently engage metal pads on the printed circuit board  12  thereby electrically coupling the electrode  20  to the control circuitry  32   d.    
   It will be understood that the electrode  20  can carry a selected ionization source  20   a  adjacent to an opening  20 - 2  formed therein as part of the modular assembly provided by the assembly  30 . 
     FIG. 2  is an exploded view illustrating various components of the detector  10 . The detector  10  can be assembled on a base  36  of a generally cylindrical shape which mechanically carries and supports the printed circuit board  12  and other components thereon as discussed previously relative to FIG.  1 . As will be understood by those of skill in the art, the control circuitry  32 - d  can be an electrical communication via a bi-directional communication link generally indicated at  40  with other detectors, control elements, or circuitry without limitation. The detector  10  can be enclosed by an exterior cover  36 - 2 . 
     FIGS. 3A , B, C and D illustrate additional details of the sub-assembly  30 . The sensing electrode  18  is mechanically attached to insulator  30  by spaced apart deflectable integrally formed latching members  18 - 1  which slidably engage slots in insulator  30 . 
   The inner or source electrode  20  is mechanically attached to insulator  30  along a common center line with the electrode  18  by outwardly extending frictional locking members indicated generally at  20 - 3  which slidably engage locking surfaces of the insulator  30 . Hence, the insulator  30  carries both sensing and inner electrodes  18 ,  20 . Additionally, as illustrated in  FIGS. 3A-3D , diode or resistor  32   a  and buffer semi-conductor  32   b  are carried in a bounded region generally indicated at  42 , best seen in FIG.  3 C. One contact of resistor  32   a  is electrically and mechanically attached to sensing electrode  18 . The other contact of resistor  32   a  is mechanically and electrically attached to gate input  32   b - 1  of buffer  32   b  to form a series connection. 
   The region  42  can be filled with an encapsulating compound so as to mechanically enclose the components  32   a ,  32   b  therein. The inner electrode  20 , noted above, carries an ionization radioactive source  20   a  of a type known to those of skill in the art to provide a source of charged particles and a current which can be altered by smoke in the sensing region  22  as would be known and understood by those of skill in the art. 
   Each of the legs  30 - 1  of the insulator  30  has an integrally formed elongated deflectable portion  30 - 2  which extends generally axially relative to the insulator  30 . The deflecting member  30 - 2  terminates in a locking element  30 - 3  which in combination with the deflection of the members  30 - 2  slidably engages the printed circuit board  12  and locks the insulator  30 , along with electrodes  18 ,  20  and components  32   a, b  thereto as a unit. 
   As illustrated in  FIGS. 3A-3D , the inner electrode  20  carries at least one and preferably a plurality of spring biased conductors  20 - 1 , illustrated herein as deflectable members with an end region  20   b  that slidably engages an electrical contact on the printed circuit board  12 . It will be understood that as the insulating member  30  moves toward the printed circuit board  12  slidably engaging same via latching elements  30 - 3 , the deflectable conducting members  20 - 1 , and surfaces  20 - b  slidably engage respective electrical contacts on the printed circuit board  12  thereby placing the electrode  20  in electrical communication with the control circuitry  32   d.    
   It will be understood that the exact details of the spring members  20 - 1  are not a limitation of the present invention. Alternately, instead of being deflectable spring members, they could be compressible spring members without departing from the spirit and scope of the present invention. Similarly, the electrodes  18 ,  20  can be fixedly connected to the insulator  30  by a variety of structures. The connecting structures  18 - 1  and  20 - 3  are exemplary only and not limitations of the present invention. 
     FIG. 4  illustrates additional details of the relationship between the slits or windows  16 - 2  and the tapered surface  24 - 1 . As noted previously, the conical structure  24 - 1  improves stability of the detector  10  at higher fluid velocities of several hundred feet per minute and above. The effect of the conical structure  24 - 1  is to permit the slits or windows  16 - 2  to have a greater height dimension, thereby improving performance at lower velocities without degrading higher velocity performance. 
   The height dimension D 1  can be maximized for low velocity performance. For example, the dimension D 1  can be on the order of 0.25 inches or greater. 
   Preferably, dimension D 2  will be in a range of 50% to 120% of dimension D 1 . The dimension D 3 , the opening between the top surface  24   a  of the conical structure  24 - 1  and interior surface  16   a  of outer electrode  16  preferably will fall in a range of 50 to 100% of the dimension D 1 . Preferably, dimension D 3  will be about 75% of dimension D 1 . The conical structure  24 - 1  directs incoming smoke particles toward surface  16   a  at higher flow velocities where particle recombination will be strongest. 
     FIG. 5A  illustrates sensing electrode  18 . The electrode  18  defines an interior opening  44  which permits a flow of ionized particles from source  20   a  to flow into sensing region  22  as will be understood by those of skill in the art. 
   The performance of detector  10  can be improved at higher velocities by providing a plurality of protrusions, such as exemplary protrusions  46   a, b, c  which extend into and reduce the area of the opening  44 . Preferably the protrusions will reduce the area of the opening  44  on the order of 10 to 30%. By increasing the reduction of the area of the opening  44 , variations in the output signal from electrode  18  can be minimized at higher velocities. 
     FIGS. 5B , C, D, and E illustrate alternate configurations of the opening  44  and protrusions  46   a, b  and  c . Electrodes  18   a-d  have an exterior periphery different than the periphery of the electrode  18 . Other such variations come within the spirit and scope of the invention. 
   In  FIG. 5B , the area of opening  44 - 1  can be reduced by V-shaped members  46 - 1  which extend into and extend through opening  44 - 1 . In  FIG. 5C , the area of opening  44 - 2  can be reduced by a plurality of four inwardly extending tabs  46 - 2 . In  FIG. 5D , electrode  18   c , has an interior opening  44 - 3  whose area is reduced by a plurality of inwardly extending protrusions or tabs  46 - 3 . Finally,  FIG. 5E  illustrates a sensing electrode having a central opening  44 - 4  whose area is reduced by a plurality of V-shaped tabs  46 - 4  which interrupt the perimeter of the opening  44 - 4 . Other shapes which alter the periphery of a respective opening such as  44 ,  44 - 1  . . . - 4  come within the spirit and scope of the 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.