Abstract:
A thermal imaging instrument and method is disclosed for viewing hot spots within a normally enclosed cabinet, for example, a high voltage electrical power distribution cabinet. Large and expensive thermal viewing windows normally required for thermal examination of these cabinets utilizing standard thermal imaging cameras is obviated by the use of an accessory lens assembly. The unique combination and methodology of using the lens assembly, standard thermal imaging camera and small access opening in the cabinet face allows for the retention of the safety rating of the cabinet. Further adding to the accuracy, convenience and safety of the approach, an infrared view port, together with cap and ring chain assembly, is permanently affixed to the cabinet face in relation to the small access hole.  
     The unique combination of the instrument portion of the invention can be integrally combined in a single unit for exclusive use in detecting hot spots within a cabinet.

Description:
[0001]    This invention claims the benefit of U.S. Provisional Application No. 60/362,743, filed Mar. 8, 2002. This invention relates generally to a thermal imaging combination and method for measuring hot spots. 
     
    
     
       BACKGROUND  
         [0002]    Specifically the invention includes an assembly combination and methodology for monitoring the thermal profile of an interior panel of a shut cabinet, for example, a power distribution box.  
           [0003]    There are important applications in electrical power distribution that involve measurement of hot spots within electrical high voltage cabinets without compromising the safety of working personnel. One way is to open the cabinet door and make a quick thermal image of electrical panel. However, for a high voltage electrical cabinet, the door of the cabinet can only be opened if the power is first shut-off. As a safety precaution, the cabinet door is interlocked with the incoming power circuit breaker. The fact the power is turned off results in a cooling of electrical circuit breakers. This can result in the rapid redistribution of accumulated heat, precluding the identifications of the true hot spots. Also shutting off the power may not be desirable to the operation of down stream users.  
           [0004]    An alternative, albeit expensive, method employed today involves installing one or more infrared transmitting windows in the cabinet door. This allows the direct thermal “viewing” of the interior of an electrical panel, without opening the cabinet door. The diameter of these windows is large in order to accommodate the large aperture of a thermal imaging camera&#39;s objective lens. The typical window diameter is  3 ″ (75 mm). To maintain the NEMA (National Electrical Manufacturing Association) safety rating, such as 1, 2, 3, 4, or 12, of the cabinet, qualified personnel should perform the installation of this window(s); or they should be installed at the time the electrical cabinet is assembled. This involves the customization of the electrical cabinet. It is to these problems that the present invention is directed.  
           [0005]    It is therefore a primary object of the present invention to provide a method and means for evaluating the thermal profile of the interior of an enclosure without degrading the integrity of the enclosure.  
           [0006]    It is still another object of the present invention to provide a method and means for evaluating the thermal profile of the interior of the enclosure without opening any access door.  
           [0007]    It is yet another object of the present invention to expand the breadth of applications for thermal imaging equipment by facilitating their use with enclosures containing heat generating equipment which needs to be monitored.  
           [0008]    Still another object is to provide a means and method for surveying a broad internal area of an enclosure, again without violating the integrity thereof or accessing the interior through the opening of an enclosure door.  
           [0009]    A still further object is to provide a means and method for making accurate thermal profiles of the interior of an enclosure even though the heat source within the enclosure may be positioned at various depths from the evaluating means.  
         SUMMARY  
         [0010]    These and other objects are obtained with the thermal imaging combination and method of the present invention. It occurred to the applicant that an innovative lens assembly design (designated a “fisheye” assembly by the applicant) could simplify this costly and difficult measurement. Rather than placing a large diameter window(s) in the face of the cabinet door, a ⅝″ (16 mm) hole is drilled in the center of the cabinet door. A ⅝″ hole is permitted without compromising the safety issues. The hole can be effectively sealed while not in use. As such, the door is still able to maintain its NEMA rating. The fisheye lens assembly with a 66° diagonally wide angle field of view, can image a broad section of the cabinet interior for hot spots through this hole, in one exercise. The small objective lens of the fisheye assembly provides very wide angle viewing, at different depths, without compromising the quality of the received thermal image and the NEDT (Noise Equivalent Differential temperature) of the thermal imaging system.  
           [0011]    In the preferred embodiment the design of the fisheye lens assembly includes multi-element, infrared transmitting optical material consistent with the spectral transmission characteristics of the thermal imager camera, for example, Model #s 7102, 7200 and 7515, manufactured by Mikron Instrument Company, Inc. of Oakland, N.J., (hereinafter “Mikron”), connected to the fisheye assembly. The lenses are placed inside a precision housing with appropriate spacing between the various lenses. A mechanism for manual focusing allows the best image quality for various depths of field, typically between 4″ to 45″ distance. Therefore the user has the advantage of expanding the capabilities of the thermal imager, to cover practically all preventative maintenance applications. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]    [0012]FIG. 1 is a perspective view of one version of the combination thermal camera-fisheye lens assembly portion of the present invention.  
         [0013]    [0013]FIG. 2 is a perspective view of an operator using one version of the thermal camera-fisheye lens assembly-access hole combination of the invention.  
         [0014]    [0014]FIG. 3 is a partially sectional view of one version of the combination thermal camera-fisheye lens assembly portion of the present invention.  
         [0015]    [0015]FIG. 4 is a schematic representation of the lensing system employed in one version of the fisheye lens assembly of the invention.  
         [0016]    [0016]FIG. 5A is a front, elevation view of the nose portion of one version of the fisheye lens assembly of the invention.  
         [0017]    [0017]FIG. 5B is a side, elevation view of the nose portion of one version of the invention similar to the view of FIG. 5A.  
         [0018]    [0018]FIG. 5C is a side, sectional view of the nose portion of one version of the invention, taken along the lines  5 C- 5 C of FIG. 5A.  
         [0019]    [0019]FIG. 6 is a perspective view of a portion of the cabinet face including the access opening portion of the present invention required for thermal viewing of a shut cabinet and including an exploded view of one version of a safety closure for the opening.  
         [0020]    [0020]FIG. 7 is a side, elevation, partially sectional view of a shut cabinet in the process of being thermally examined by one version of the combination thermal camera-fisheye lens assembly portion of the invention.  
         [0021]    [0021]FIG. 7A is a schematic representation of a typical area of a shut cabinet accessible to thermal viewing by one version of the combination of the invention.  
         [0022]    [0022]FIG. 8 is a graphic representation of a typical radiometric thermal image of a desired target produced by the thermal camera component of the combination of the invention. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0023]    Turning now to the drawings, in FIG. 1 a version of the thermal imaging instrument portion  10  of the invention is depicted. The instrument  10  is a combination of a standard thermal imager camera  14  (such as the Mikron model no. 7102, 7200, or 7515, and similar cameras), and a lens assembly  12 , designated as a fisheye lens assembly  12 .  
         [0024]    [0024]FIG. 2 illustrates an operator  18  utilizing the combination of the thermal imaging camera  14  and fisheye lens assembly  12 , making use of the strap  16  on the camera and the opening  92  in a cabinet closure  74  to view the interior of the cabinet for hot spots. The fisheye lens assembly  12  permits the use of thermal imagining cameras to see hot spots occurring over a relatively large area through a small access opening. Means are disclosed hereinafter for effectively sealing the opening so as to not violate the electrical rating of the cabinet.  
         [0025]    As best seen in FIGS. 3, 4 and  5  the fisheye lens assembly employs a four (4) lens element, reversed telescope design with the eye position or exit pupil located at the small opening of the nose  20 . The conical shape of the nose  20 , allows the entire ray bundle entering the small opening  21  of the nose  20 , which has a very wide angle to reach lens  22 . The lenses  22 ,  28 ,  36 , and  64  (FIG. 4,) are configured and disposed within the lens assembly such that the angles of the ray bundles when the bundles exit from the last lens  64 , is consistent with a given thermal imager optical system such as those employed in Mikron models 7102, 7200, 7515, and similar thermal cameras. This way a thermal imager can be used in addition to its conventional application, for the purposes of thermal profiling and hot spot detection in closed-door, high voltage cabinets.  
         [0026]    The following itemized description refers to the referenced items in FIGS.  3 - 5 .  
         [0027]    Nose portion  20  (FIG. 5) of the lens housing  13 : This has a few important functions. It defines the minimum required hole diameter (for example, 0.625″ (16 mm)) for the access opening,  92  in the face of the cabinet forming the enclosure. It allows for an easy and precise alignment when used in conjunction with the fisheye view port ring  86  (FIGS. 6 and 7) which will be more fully described below. Nose portion  20  typically is made from plastic material to insure that an extra level of electrical insulation exists between the instrument and electrical cabinet door in the unlikely event that a high voltage condition may exist in the vicinity of the opening  92  in the cabinet face  74 . The diameter of the nose opening  21  in the preferred embodiment is 12 mm. The half angle  23 , between the side forming the cone and the optical axis  25 , in the preferred embodiment is 33° or a total angle of 66°.  
         [0028]    Lens  22  (FIG. 4): The ray bundles emanate from a target, located at a distance, from 4″ (10 cm) to 45″ (115 cm), from the nose opening  21 . They enter the nose opening  21  and are re-directed by lens  22 , which is called an eye lens, towards the other lenses in the assembly. The material of this and all lenses must have a spectral transmissivity in the infrared range compatible with the infrared transmission characteristics of the particular thermal imager used.  
         [0029]    Retainer  24  (FIG. 3): This is a metallic retaining ring that holds the eye lens  22  firmly in position and concentric to the system optical axis.  
         [0030]    Front Cell  26  (FIG. 3): This portion of the housing  13  is precision machined from light metal. It houses and provides a seat for the eye lens  22  and lens  28 .  
         [0031]    Lenses  28  &amp;  36  (FIG. 4): The ray bundles from the target which have passed through lens  22  are focused onto the combination of lenses  28  and  36 . The combination of lens  28  and  36  allows for the optics within the lens assembly to focus, for different enclosure, interior distances, by varying the space between them. Lens  28  is stationary and lens  36  moves to allow an optimum image quality for a given interior distance. They form an intermediate image between lens  36  and lens  64 .  
         [0032]    Clamp  30  (FIG. 3): This clamp is made from metal and, together with the retainer  32 , holds the lens  36  secure and concentric to the system optical axis.  
         [0033]    Retainer  32  (FIG. 3): This retainer is made from metal and in combination with clamp  30  hold the lens  36  in place.  
         [0034]    Lens  36  (FIG. 4): The cooperative relationship between lens  36  and  28  allows the optical assembly to focus optimally for different enclosure, interior distances. Lens  28  is stationary and lens  36  moves relative thereto.  
         [0035]    Focus Slide  38  (FIG. 3): The focus slide provides a housing and seating for lens  36 . It also allows sliding of lens  36 , left and right as viewed in FIG. 3, for optimum focusing. A gentle pressure exerted by a plurality (eight, typically) of springs  56  circumferentially disposed around its perimeter, provides the necessary force to keep the focus slide  38  in position once the desired focusing is achieved.  
         [0036]    Spacer Tube  40  (FIG. 3): A precision machined metallic part that guides the focus slide  38  in a concentric manner.  
         [0037]    Scale Tube  44  (FIG. 3): A precision machined metallic part, with the focusing distance marking  45  engraved in inches and/or metric scale. Four setscrews  46  circumferentially disposed around the perimeter of tube  44 , hold the scale tube  44  to actuator nut  50  after an optimum focusing is achieved for a given, cabinet interior distance.  
         [0038]    Pin  48  (FIG. 3): This pin restricts the motion of focus slide  38  to only horizontal movement. It prevents the lens  36  from rotating. It assists in maintaining the precision of the optical axis.  
         [0039]    Actuator nut  50  (FIG. 3): This is a precision machined metallic part that holds the guide pin  48  loosely. As the actuator nut  50  rotates, it forces the guide pin  48  to slide forward or backward forcing the focus slide to change the spacing between lens  28  and  36  for optimum image quality. It also provides a mounting thread to seal retainer  54 .  
         [0040]    Seal Retainer  54  (FIG. 3): A precision machined metallic part that seals the sensitive and exposed parts of the assembly from dust and dirt and also gives a finished look to the assembly.  
         [0041]    Springs  56  (FIG. 3): As noted above, these springs (eight are used in the assembly of FIG. 3) provide a constant, necessary force to urge the focus slide  38  forward, to insure that the spacing between lens  28  and  36  will not change, once set, during actual usage of the lens assembly in the field.  
         [0042]    Retainer  58  (FIG. 3): The retainer is a precision machined metallic part that forces the spacer  62  against the objective lens  64 .  
         [0043]    Rear Cell  60  (FIG. 3): A precision-machined metallic part that houses and provides a seat for the objective lens  64  and ensures its concentricity to the entire optical assembly. In addition, it provides a secure platform for a precision coupling to the front end of a given thermal imager, optical system.  
         [0044]    Spacer  62  (FIG. 38): A precision machined metallic part that holds the objective lens  64 , in place, concentric to the optical assembly.  
         [0045]    Lens  64  (FIG. 4): The objective lens  64  takes the intermediate image produced by lens  22 ,  28  and  36  and produces near parallel ray bundles coming from a desired target and projects these rays into the optical system of a given thermal imager camera  14  (FIG. 1).  
         [0046]    Setscrews  66  (FIG. 3): A set (four) of dog tail setscrews that allow the connector  68  to freely rotate on rear cell  60 .  
         [0047]    Connector  68  (FIG. 3): This is a precision machined metallic ring. It connects the entire fisheye optical assembly firmly and concentrically to the host thermal imager (camera) optical system. It also maintains the proper distance between the lens  67  of the camera and the objective lens  64  of the fisheye optical assembly. The outside diameter of the rear connector  68  is knurled to provide a firm grip during attachment of the fisheye assembly to the camera.  
         [0048]    Camera  14  (FIG. 1): The thermal imager camera  14 , for example Mikron&#39;s thermal imagers model 7102, 7200 and 7515, includes an optical system which produces a thermal image of the target on a detector focal plane array  72  (FIG. 3). Software internal to the Mikron cameras mentioned above, produces various graphic portrayals of the received, infrared data. For example, a full radiometric thermal image of the desired target (see FIG. 8) can be immediately viewed through the eye piece view finder  73  of the camera and/or stored on a digital media for subsequent use or processing outside of the camera.  
         [0049]    Cement  34  (FIG. 31): A cement such as Locktite® adhesive # 495, or equivalent, is used, as required, for permanent binding of some metallic parts.  
         [0050]    A lens cap (not shown) protects the fisheye lens during storage from dust and dirt settling on optical surfaces.  
         [0051]    Teflon® type tape  42  and  52 , with exact thickness, is placed, as required, between metallic parts to reduce the friction between moving parts such as between the focus slide  38  and the spacer tube  40 .  
         [0052]    For the fisheye lens-camera assembly portion of the invention to be able to create thermal images of the interior of a high voltage electrical cabinet  94  so as to locate possible hot spots, an infrared viewing, access opening  92  (FIG. 6) is needed. This opening must allow inspection, but at the same time not be of such size as to degrade the NEMA safety rating of the electrical cabinet. The opening  92  is located in the cabinet face  74 , at a position, in relation to the electrical power distribution blocks  96  (see FIG. 7), that optimizes the field of view for the lens assembly-imaging camera combination. Most high voltage electrical cabinets used are NEMA 1, 2, 3, 4 or 12 rated. The infrared viewing opening designed for the present invention allows the cabinet to retain a NEMA 4 rating which is the most demanding and meets the most stringent requirements.  
         [0053]    Infrared View Port Alignment Ring  86  (FIG. 6): This part is machined or cast from metal or plastic and includes a central opening  87 . The diameter of the opening is slightly larger(0.65 inches, 16.5 mm) than the access opening  92 . Its primary function is to provide a nesting platform for the nose  20  of the fisheye lens assembly to rest and to axially align the optical axis  25  with the centerline axis of the hole  92  already drilled through the electrical cabinet face  74  for inspection purposes. The view port ring  86 , in combination with the frusto-conical shape of the nose portion  20  of the housing  13 , also provides approximately 10 degrees of freedom for the fisheye lens assembly to rotate, in any direction, in search of hot spots inside of the electrical cabinet  94  near the perimeter of the field of view. In addition, the port includes precision grooves for insertion of, two o-rings  84 ,  88 ,(FIG. 6) on both sides thereof for sealing out dirt and water, so that the NEMA 4 rating can be met and preserved.  
         [0054]    Cap  90  (FIG. 6): This cap is machined or cast from high strength plastic. The cap, when secured to the view port ring  86 , will seal the infrared viewing port by compressing the outside o-ring,  88 . This insures the integrity of the cabinet NEMA rating before and after infrared inspection.  
         [0055]    Ring and Chain Assembly  80 ,  81 ,  82  (FIG. 6): The chain-retaining ring  81  is made from thin metal either by stamping or laser cutting. Chain  80  is secured to the ring  81  at eyelet  79 . Screw  82  at the other end of the chain is threaded into opening  83  in cap  90 . Screws and Lock washers  76  &amp;  78  (FIG. 6) are needed for installation of the infrared viewing port to the cabinet face  74  via the mounting holes  85  as typically configured and shown in FIG. 6. Chain  80  is of sufficient length so that when the retaining ring  81  is secured to the cabinet door, the retaining ring  81  holds the chain  80  freely, allowing unscrewing of the cap with ease, while retaining the cap chained to the view port assembly. This serves as a constant reminder to inspection personnel that the cap should be screwed in place after completion of the monitoring function so as not to breach the NEMA rating requirements.  
         [0056]    [0056]FIGS. 7 and 7A depict schematically the application of the combined fisheye lens assembly  12  and thermal imager  70  for use in the thermal imaging of electrical power distribution blocks  96  in the interior of an enclosure or cabinet  94 . In FIG. 7A, the field of view  98  for the assembly is shown, for example, as 40° vertically and 53° horizontally, or 66° on the diagonal. The diagonal field of view of 66° stays constant regardless of the focusing distance. The camera-lens assembly can be moved up or down and/or side to side while the nose  20  of the assembly is nested in the view port ring  86 . This expands the field of view sufficiently to permit scanning of the interior of the enclosure. The operator can focus more directly on the perimeter areas of the field of view so as to double check for possible lens vignetting errors.  
         [0057]    Operational Procedure  
         [0058]    The following is a suggested procedure for utilizing the thermal imaging combination of the invention. First-of-all a standard camera  14  is selected. All Mikron thermal imagers such as model 7102, 7200 and 7515 are acceptable for this measurement. The camera is connected to the fisheye lens assembly  12 . The camera is then “set-up”; and, finally, the actual measurements made.  
         [0059]    Camera-Lens Assembly Procedure:  
         [0060]    First, the operator removes any existing lens ring on the imaging camera. He then secures the fisheye lens assembly  12  to the camera taking extra care to protect the camera&#39;s lens mounting threads, so as to avoid stripping the threads.  
         [0061]    The camera  14  should then be adjusted to compensate for attenuation through the wide-angle, lens assembly  12 . Thermal image cameras include this selection ability and internal frimware automatically adjusts for attenuation of the lens assembly  12 . The scale tube  44  is rotated to set the lens assembly for an average depth of the enclosure, if known.  
         [0062]    The level and sensitivity of the imaging camera is then adjusted according to the imager instruction manual. Usually 100° C. is the maximum temperature; while ambient is the minimum.  
         [0063]    Actual Measurement:  
         [0064]    [0064] 1 . The operator first supports the fisheye lens assembly with the left hand. The right hand is placed in the imager strap. (See FIG. 2)  
         [0065]    [0065] 2 . The lens cone  20  is then inserted flush into the view port ring  86 .  
         [0066]    [0066] 3 . While viewing through the eyepiece of the thermal imager, the operator, if required, is directed to move the imager up and down and sideways, to view larger regions inside the cabinet. He adjusts the focus to sharpen the image, as he does this, at each location, if required.  
         [0067]    [0067] 4 . One possible image available to the operator, as noted above, because of the software built into the Mikron Company&#39;s cameras, is as pictured in FIG. 8. As viewed through the camera and as may be reproduced in a photograph or stored on a digital medium, the image at  100  is, in fact, a colorized rendition of the temperature profile of the field of view of the lens assembly for a given axial placement in the view part ring  86 . The operator can select various points of interest and identify them on the image,  100 , such as points 1, 2, 3, etc. The internal software will produce and display the associated temperatures,  103 . The software can also provide a temperature scale, in color,  104 , which allows the operator to more critically evaluate the image  100  in real time.  
         [0068]    Thermal imaging cameras such as Mikron&#39;s model #s 7102, 7250 and 7515 store the images and data to PCMC1A cards. This allows subsequent analysis using a PC. Software is available which allows post image analysis. Also, more sophisticated software will permit computer enhancement of areas where distortions may occur, for example, the distortions attributable to fish-eye lens vignetting.  
         [0069]    Thus it can be seen that the wide angle fisheye lens assembly of the invention provides new conveniences, safety, and economy when used in conjunction with traditional thermal imaging equipment and a relatively small access hole in the cabinet defining the enclosure. The fisheye lens assembly of the invention has been described for use with the specific thermal imaging camera of the assignee. It is to be understood that the fisheye lens assembly may be reconfigured for operation with other thermal imagers and other applications without deviating from the basic concept of the present invention.  
         [0070]    While the present invention has been disclosed in connection with a preferred embodiment shown in detail, various modifications and improvements will become readily apparent to those skilled in the art.  
         [0071]    So for example, whereas the preferred embodiment discloses the use of a separate fish-eye lens assembly taken together with a standard, available thermal imager, to accomplish the purposes of the invention, the breadth of the invention envisions the inclusion of the fish-eye lens assembly within an overall housing which includes the thermal imaging aspects of a standard camera. A reduction in the number of lenses of course would be a consequence of this combination leading to a reduction in the expense of the unit.  
         [0072]    Further, even though a series of lenses are employed in the preferred embodiment of the fish-eye lens assembly, developments in optics suggest the use of aspherical lenses to compensate for distortions that presently require the use of a series of lenses to remedy. As such, a single wide-angle lens of appropriate design, should be able to accomplish the purposes of the series of lenses.  
         [0073]    Accordingly, the spirit and scope of the present invention is to be limited only by the following claims.