Abstract:
A repeater case for high density subscriber lines includes a repeater base and a repeater housing forming a sealed enclosure and having interior walls. A plurality of module slots receive HDSL-4 circuit board modules. A heat conductive material in the housing contacts HDSL-4 modules in the slots and the housing to form a heat escape path to ambient. The HDSL-4 modules are cooled through thermal conductivity with thermally conductive contact with the interior wall of the repeater housing. The heat conductive material is not required for structural support of the modules or their electrical functioning.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to improvements in repeater cases and design thereof for high density subscriber lines. Repeater cases have been known for years and the technology was well developed for T1 telecommunication lines. The cases are designed to hold sensitive telecommunications equipment in relatively unfavorable environments. In particularly, they are designed for installation in manholes or on telephone poles exposed to the weather. Accordingly, in order to protect the contents, the housing of the cases provide environmental protection and seal the contents from the impact of the environmental elements such as water, insects, and the like. 
     The repeater cases, which were originally designed to hold T1 line cards, have been used to hold HDSL modules. The HDSL modules work well in the T1 repeater case, except that it has been found that the modules prematurely fail due to excessive heat build up in the case. Premature failure adds considerably to the cost in having to replace the modules. The modules are fairly expensive in the first instance and replacement, of course, creates additional expense. There is also a problem of loss of reliability and performance arising from the premature failure. Obviously, when a module fails, it needs to be replaced and there is a cessation of service. If there are several module failures, the maintenance costs will also rise in addition to the cost of the module itself. There is a need in the art for a solution to the heat build-up problem in the HDSL cases. 
     In addition to the heat causing the electronics to fail, applicant has found another failure mode arising from high heats in the repeater case. The material of the connectors to which the cards are mounted fatigue, causing dimensional instability, warping and cracking. This, in turn can cause a loss of connection between the module and the connector, leading to performance failures. 
     SUMMARY OF THE INVENTION 
     The present invention fulfills one or more of these needs in the art by providing a repealer case for high density subscriber lines including a repeater base, a repeater housing having interior walls forming a sealed enclosure with the base, a plurality of module slots wherein the module slots are configured to receive HDSL-4 circuit board modules and wherein the HDSL-4 circuit board modules are cooled through thermal conductivity with thermally conductive contact with certain of the interior walls of the repeater housing. The thermally conductive material is not being required for structural support of the modules or their electrical functioning. 
     The apparatus may further include a cable inlet in the repeater case which has the capability to receive high density subscriber lines. The sections of the repeater case are made from a high temperature plastic. The repealer housing has a lid with an interior wall and typically includes a layer of thermally conductive material attached to the interior wall of the repeater housing lid. This layer of thermally conductive material preferably includes an exterior layer of aluminum foil on the top and bottom of the layer of thermally conductive material. A preferred thermal conductive material is G974 Therm-A-Gap material. 
     The repeater base of the repeater case can have up to twenty-five module slots to receive the HDSL-4 circuit board modules. The HDSL-4 circuit board modules further include connectors which are mounted to a circuit boards. These connectors are preferably made of a high temperature plastic, and the circuit board is preferably made of phenolic. The connectors, which receive the HDSL-4 circuit board modules are electrically connected to the cable inlet in the repeater housing case in conventional fashion through the phenolic board. The repeater case is typically comprised of three different sections, the repeater case, the repeater housing, and the repeater base. 
     After the HDSL-4 circuit board modules are mounted in the module slots and the connectors are connected to the high density subscriber lines via the cable inlet, the sections of the repeater case may be closed. A rubber gasket is placed between the repeater base and the repeater housing, and the repeater housing is bolted to the repeater base. Then, a rubber gasket is placed between the repeater case and the repeater housing lid, and the repeater housing lid is bolted to the repeater housing. When the repeater housing parts are connected, the repeater case is sealed and protects the HDSL-4 circuit board modules within from the environment. The interior of the housing may be pressurized in conventional fashion. 
     When the repeater housing lid is put in place, the thermally conductive material and the aluminum foil layer comes into contact with the tops of the HDSL-4 circuit board modules. When the lid is closed and tightened, the thermally conductive material compresses sufficiently against the HDSL-4 circuit board modules to make a good thermal transfer contact. The layer of thermally conductive material receives the heat generated by the HDSL-4 circuit board modules, and the heat is then distributed through the thermally conductive material layer. From there, the heat is radiated through the repeater housing lid to the outside, thereby keeping the heat build-up within the repeater case to a level which permits the HDSL-4 circuit board modules to operate and function without failure. 
     Preferably, the modules are mounted in high temperature connectors. The connectors are made of a plastic that can withstand the temperatures expected in the housing without fatiguing or deforming, and are, in turn, mounted to a phenolic circuit board. 
     The invention also provides a method of converting a repeater case so as to dissipate thermal energy from high-density subscriber lines including providing repeater case including a base, housing and lid; and installing a thermally conductive material in the lid sized so as to come into contact with the tops of HDSL modules mounted in the repeater case when the lid is mounted on the case. The method may include installing connectors for the HDSL modules in the case that are made of a plastic selected to withstand the expected operating conditions of the repeater case without warping. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a front perspective view of a repeater case according to a preferred embodiment of the invention; 
     FIG. 2 is a perspective view of the circuit board connectors according to the preferred embodiment of the invention; 
     FIG. 3 is a top schematic drawing of the inside of the repeater case looking downward, showing the module slots with HDSL-4 circuit boards according to the preferred embodiment of the invention; and 
     FIG. 4 is a partial sectional view of the repeater housing lid and housing showing placement of the thermally conductive material and HDSL-4 circuit modules within the repeater case according to the preferred embodiment of the invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In the following description like reference characters designate like or corresponding parts throughout the several views. Also, in the following description it is to be understood that such terms as “forward”, “rearward”, “left”, “right”, “upwardly”, “downwardly” and the like are words of convenience and are not to be construed as limiting terms. Referring now to the drawings in general, and FIG. 1 in particular it will be understood that the illustrations are for the purpose of describing a preferred embodiment of the invention and are not intended to limit the invention thereto. 
     As best seen in FIG. 1, the repeater case  10  includes a repeater base  12 , a repeater case housing  14 , and a repeater housing lid  26 . In the embodiment shown in FIG. 1, the lid  26  is in two sections. When closed as shown in FIG. 1, the repeater case housing  14  is secured closed with bolts  36  to the repeater base  12 . A gasket  34  placed between the repeater case housing  14  and the repeater base  12  before it is bolted closed provides a sealed container. The repeater housing lid  26  is bolted with bolts  36  to the repeater case housing  14 . A gasket  34  is placed between the repeater housing lid  26  and the repeater case housing  14  before it is bolted. Once all of the parts of the repeater case  10  are bolted together, the entire unit provides a sealed enclosure. 
     The repeater case  10  further includes a cable inlet  22  (see FIG.  3 ), which receives a stub for high density subscriber lines. The repeater base  12 , the repeater case housing  14 , and the repeater housing lid  26  which comprise the exterior parts of the repeater case  10  are constructed of a conventional repeater case material such as high temperature plastic. This high temperature plastic assists with radiating the heat from within the repeater case  10  including through the repeater housing lid  26  to the outside of the housing. 
     FIG. 3 shows that the repeater case  10  has a plurality of module slots  16  which have been configured to receive HDSL-4 circuit board modules  20 . The repeater base  12  is designed to have up to 25 module slots  16 . These features are conventional. The module slots  16  provide space to hold the HDSL-4 circuit board modules  20 . A phenolic circuit board  21 , seen in FIG. 2 has connections to the cable inlet  22  and has mounted on it connectors  32 . The connectors  32  are shown in FIG.  2  and made of a high temperature plastic. The preferred plastic of the connectors  32  is ABS D-150, which does not prematurely fatigue at the expected operating temperatures and maintains its dimensional stability at the elevated operating temperatures. This improvement prevents loosening of connections to the HDSL-4 modules. 
     Referring now to FIG. 4, the repeater case housing  14  and the repeater housing lid  26  are depicted. FIG. 4 depicts a cross-sectional view of the repeater housing lid  26  and the repeater case housing  14  sealed with a gasket  34  and a bolt  36 . The repeater housing lid  26  has nested within it a layer of thermally conductive material  30 . If desired, an adhesive material may be used to secure the material  30  to the lid. In the preferred embodiment, this layer of thermally conductive material  30  is G974 Therm-A-Gap material available from Chromerics, a Division of Parker Hannifin Corp., 77 Dragon Court, Woburn Mass. 01888-4014. Therm-A-Gap is described as an electrically non-conductive, boron-nitride-filled silicone elastomer best suited for applications with pressures from 5 to 100 psi. A thermally conductive foil such as aluminum foil  40  is layered on both sides of the thermally conductive material  30 . In the sealed position shown in FIG. 4, the repeater housing lid  26  with the thermally conductive material  30  is in slight compression with the HDSL-4 circuit board modules  20 . 
     In operation, the heat generated by the HDSL-4 circuit board modules  20  conducts to the thermally conductive material  30 . The thermally conductive material  30  in the repeater housing lid  26  distributes the heat throughout the layer of thermally conductive material  30  and the repeater housing lid  26  with which it is in intimate contact. The heat is thereafter radiated through the repeater housing lid  26  to the outside. 
     A laboratory test was conducted to determine the effectiveness of the repeater case  10  with the thermally conductive material  30  in the repeater housing lid  26  as compared to a repeater housing lid  26  containing just high temperature plastic. The repeater case  10  was loaded with twenty-five HDSL-4 circuit board modules  20  in the module slots  16 . A 30 watt cartridge heater at 120 volts was used for the heat source for each of the twenty-five modules. A 30 watt cartridge heater created a heat effect of 5.25 watts per module. Both units were placed under electrical load for four hours. The temperature readings of the modules were recorded after four hours of the electrical load. In addition, a solar load was applied to determine the effect of a sun bake with equal amounts at 100% on the left side of the top and right side of the repeater case  10 . The solar load provided a simulation of an ambient temperature of 145° F. Sensors were placed at various locations in the repeater case  10  with the plain top, and sensors were placed in the same locations in the repeater case  10  of the lid with the thermally conductive material  30 . Sensor numbers 1L and 2L were placed at the top and bottom of the repeater housing lid  26 . Sensors 1T, 2T, and 3T were placed on the HDSL-4 circuit board modules  20 . Sensor  5  was placed on the side of the HDSL-4 circuit board module  20  near a connector. 
     
       
         
               
               
               
               
             
           
               
                   
                   
               
               
                   
                   
                   
                 Lid with Thermally 
               
               
                   
                 Sensor Location 
                 Plain 
                 Conductive Material 
               
               
                   
                   
               
             
             
               
                   
                 IL 
                 163.4° F. 
                 156.6° F. 
               
               
                   
                 2L 
                 162.3° F. 
                 152.6° F. 
               
               
                   
                 1T 
                 179.8° F. 
                 168.3° F. 
               
               
                   
                 2T 
                 182.4° F. 
                 169.9° F. 
               
               
                   
                 3T 
                 170.6° F. 
                 166.8° F. 
               
               
                   
                 5S 
                 178.3° F. 
                 170.1° F. 
               
               
                   
                   
               
             
          
         
       
     
     The test indicates that the repeater housing lids  26  with the thermally conductive material  30  maintained lower temperatures at the test sites in the cases. The sensor locations of the repeater case  10  with the thermally conductive material  30  in the repeater housing lid  26  averaged 8.5 degrees less than the repeater case  10  with the plain repeater housing lid  26 . 
     The thermally conductive material  30  assists in an efficient removal of heat from within a sealed atmosphere of the repeater case  10 . Excessive heat build up can produce a failure of the HDSL-4 circuit board modules  20  and failure of the connectors  32 . Excessive heat causes the connectors  32  from to disconnect from the HDSL-4 circuit board modules  20 , thereby causing failure of these modules. Making the connectors  32  of high temperature plastic assists in maintaining the electrical connection between the connectors  32  and the HDSL -4  circuit board modules  20 . The thermally conductive material  30  in the repeater housing  26  creates an efficient removal of heat buildup within the sealed atmosphere of the repeater case  10 , reducing heat buildup problems and HDSL-4 circuit board module  20  failure. 
     Certain modifications and improvements will occur to those skilled in the art upon reading of a foregoing description. It should be understood that all such modifications have been deleted herein for the sake of conciseness and readability but are properly within the scope of the following claims.