Abstract:
A flame detector includes a sensor module, which carries a plurality of pyroelectric sensors, and a filter module which carries a plurality of replaceable filters with one filter being associated with each sensor. The modules are coupled together and carried in an exterior housing. A cover can overlay the filters to retain them in predetermined positions relative to the respective sensors.

Description:
FIELD 
     The invention pertains to flame detectors. More particularly, the invention pertains to modular flame detectors which include interchangeable filter modules. 
     BACKGROUND 
     Known flame detectors of a type used in oil refineries and chemical plants often include triple band infrared sensing structures. Such flame detectors currently available in the marketplace are usually sold in fixed configurations. Customers order flame detectors that are either tuned to detect hydrocarbon fires (petroleum products) or non-hydrocarbon fires (hydrogen). 
     The detectors are tuned to either of these two fire types by the selection of particular wavelength filters that are placed in front of an infrared radiation sensor, such as, for example, a pyroelectric sensor. In known detectors, the filters are permanently affixed to the detectors. Infrared filters usually pass wavelengths of 2-6 microns. Known flame detectors often use three or four channels. 
     It would be advantageous to be able to easily change the sensing characteristics or, personality of the detector by quickly changing the set of filters in the product. The filters could be factory installable, or field installable. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1A-1B  are various views of a first embodiment of a detector which embodies the invention; 
         FIGS. 2A-2B  are various views of a second embodiment of a detector which embodies the invention; and 
         FIGS. 3A-3B  are various views of another embodiment of a detector which embodies 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, a filter module holds a set of filters that establish the detector&#39;s personality, that is, which fires it is optimized to detect. The module can be fitted over broadband infrared or UV detectors that are mounted on a circuit board or any other component mounting member. 
     The set of filters, or, personality module, could either be changed by a customer or by a manufacturer (in order to be able to offer fewer SKU&#39;s). In another aspect of the invention, the filter module can be designed to hold up to six filters. It will be understood that the number of filters is not a limitation of the invention. 
     The filters can pass infrared or ultraviolet radiation, for example, based on the types of fires of interest. For example, a spectral range of 2-6 microns might be selected for multi-channel IR detectors having changeable filter modules. 
     In another aspect, and without limitation, two pieces of thin material, metal or plastic, can be used to sandwich the filters. The filters can be any size, but would, preferably be about 0.25 inches in diameter or along an edge. The material could be formed with a pocket or recess to hold the filter in the proper position relative to the respective infrared sensor. The filter-holder, or module, can then be keyed so that it can be plugged into the flame detector. 
     In a disclosed embodiment, the various modules can be coupled together by using fasteners, by providing threads and a screw-type attachment feature, or, by means of a snap-fit fastener structure. The modules can be installed in an external housing. Depending on the environment, an explosion proof housing can be used. 
     Control circuits could be mounted on a planar member, such as a printed circuit board along with the sensors. The filter module can overlay the printed circuit board and sensor module, and be attached thereto as discussed above. Such modular detectors could be coupled wirelessly or by cables to a monitoring system. 
       FIGS. 1A ,  1 B illustrate an embodiment of a flame detector  10  which embodies the invention. Detector  10  includes a mounting element  12 , which could be a printed circuit board, a filter module  14  and a cover  16 . 
     A plurality of pyroelectric sensors  18  is carried on the member  12 . It will be understood that any appropriate type of radiant energy sensor could be used in the detector  10 , without limitation. The type of sensor chosen is not a limitation of the invention. 
     Control Circuits  20  also carried on element  12  are coupled to members of the plurality  18 , such as  18   a, b c  . . . . The control circuits  20  carry out processing of signals from the sensors  18  to determine the presence of fire. The control circuits  20  can also communicate wirelessly, or wired, as indicated at  20   a  with a displaced monitoring system S. 
     The filter module  14  includes a plurality of shaped openings, or recesses,  22  which can receive the various filters  24 . The filters  24  are retained in position relative to optical inputs of sensors  18 , such as  18 - 1 , by a portion  22   a  of respective ones of the recesses  22 . An optical path, such as  22   b  extends through each of the members of the plurality  22  to enable incoming radiant energy R, perhaps from a fire, which has passed through the various filters  24 , to pass through the member  14  and be incident on the optical inputs  18 - 1  of the sensors  18 . 
     As would be understood by those of skill in the art, the filters of plurality  24  would be selected to have optical characteristics consistent with the particular incident radiant energy R which is indicative of a type of fire, or fires of interest. Neither the composition, nor the shapes of the filters  24  are limitations of the invention. The members of the plurality  24  can be the same or different depending on the type of fire of interest as well as signal processing by circuits  20 . 
     The cover  16  protects the filters  24  and retains them in position in the openings  22 , in the recesses  22   a.  Openings  26  through the cover  16  provide a plurality of optical paths for incident radiant energy R to enter detector  10 , pass through he filters  24 , and the module  14  so as to be incident on the optical inputs of the sensors  18 . 
     Elements  12 ,  14 ,  16  can be coupled together via fasteners, such as  28 - 1 ,  28 - 1 , snap-fit members  28 - 2  as in embodiment  30 , or snap-fit elements  38 - 2  of embodiment  50 , all without limitation. 
     Alternately, threads can be formed on the members, such as  14 ,  16  which can be threadably coupled together without needing separate fasteners, such as  28 - 1 ,  28 - 2 . It will be understood that the exact form of coupling of the elements  12 ,  14 ,  16  together is not a limitation of the invention. 
     The detector  10  can be carried in an explosion proof container  10   a . As would be understood by those of skill in the art, connectors could be carried by the housing  10   a  to provide wired communication  20   a  to/from the monitoring system S. 
     In the embodiment  30  of  FIGS. 2A ,  2 B snap lock-type connectors  38 - 2  which engage slots  14   b  have been provided to lock the filter module  14 - 1  to the cover  16 - 1 . In the embodiment  50  of  FIGS. 3A ,  3 B filter module  14 - 2  is illustrated coupled to mounting member  12 - 1  by snap fit-type connectors  14   c  which engages slots  12   b  in the mounting plate  12 - 1 . Other elements, as described above that appear in embodiments  30  and  50  have been assigned the same numerals in  FIGS. 2A ,  2 B,  3 A and  3 B as in embodiment  10  of  FIGS. 1A ,  1 B. 
     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.