Abstract:
Providing strain relief for a test lead comprises passing the test lead through a housing that includes a generally elongate tubular member having a longitudinal cavity therein for retaining the test lead and maintaining a connection between the test lead and an electrical probe. A plurality of slots is formed in sidewall portions of the tubular member near an end thereof to provide flexibility, thereby providing strain relief for the test lead.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    This invention relates generally to electrical leads for connecting a test probe to an electrical instrument and particularly to strain relief devices for preventing flexible test leads from breaking near their connections to a rigid probe or connector.  
           [0002]    Prior art strain relief devices for test leads are either ineffective or expensive to manufacture.  
         SUMMARY OF THE INVENTION  
         [0003]    This invention overcomes difficulties associated with prior art strain relief devices for test leads. A method according to the invention for providing strain relief for a test lead, comprises the steps of passing the test lead through a housing that includes a generally elongate tubular member having a longitudinal cavity therein for retaining the test lead and maintaining a connection between the test lead and an electrical probe, and forming a plurality of slots in sidewall portions of the tubular member near an end thereof to provide flexibility, thereby providing strain relief for the test lead.  
           [0004]    The method according to the invention preferably includes the step of arranging the slots in linearly separated pairs. Adjacent pairs of the slots preferably are arranged to be angularly displaced from one another in the tubular member. In a preferred embodiment of the invention adjacent pairs of the slots are displaced  900  from one another.  
           [0005]    The tubular member preferably is arranged to have a flared end where the slots are formed.  
           [0006]    The structure and function of the invention may be best understood by referring to the accompanying drawings, which are not to scale, and to the following detailed description. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0007]    [0007]FIG. 1 is a side elevation view of a pair of strain relief devices according to the invention used to interface a test lead with a test probe and with an electrical connector;  
         [0008]    [0008]FIG. 2 is an end elevation view of an electrical connector that may be used with the strain relief device of FIG. 1;  
         [0009]    [0009]FIG. 3 is a cross sectional view of the invention as shown in FIG. 1;  
         [0010]    [0010]FIG. 4 is a top plan view of a strain relief device according to the invention enlarged to show structural features thereof;  
         [0011]    [0011]FIG. 5 is an enlarged side elevation view of one of the strain relief devices of FIG. 1;  
         [0012]    [0012]FIG. 6 is a cross sectional view of the strain relief device of FIG. 5;  
         [0013]    [0013]FIG. 7 is a cross sectional view of the strain relief device as shown in FIG. 4;  
         [0014]    [0014]FIG. 8 shows the strain relief device of FIG. 4 with the test lead bent about 90°; and  
         [0015]    [0015]FIG. 9 shows the strain relief device of FIG. 6 with the test lead bent about 90°. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0016]    The following description is intended to describe an exemplary preferred embodiment of the invention. Specific structural details are described to explain how to make and use the invention. It should be recognized that modifications could be made to the specifically described structure without departing from the spirit and scope of the invention.  
         [0017]    Referring to FIGS. 1-3 a test lead  10  extends between a test probe  12  and an electrical connector  14 . The test lead  10  is connected to a flared end portion  16  of the test probe  12 . The test probe  12  is formed as an elongate molded plastic tube having a central longitudinal cavity  13  therein. The test lead  10  extends through the central cavity  13  and is connected to a metal probe  17 . The test lead  10  is also connected to a flared end portion  18  of the electrical connector  14 .  
         [0018]    Referring to FIGS. 1 and 3- 5 , the flared end portion  16  has a plurality of arcuate slots  20 - 27  formed therein to define a strain relief device  15 . The material between adjacent slots forms a ladder-like arrangement that has flexibility sufficient to deform as the test lead is displace laterally away from the outer end of the strain relief device  15 . The slots  20 - 27  extend through the sidewall  30  of the flared end portion  16  and are generally perpendicular to the longitudinal cavity  17 . The slots  20 - 27  are arranged on the flared end  16  in linearly spaced apart pairs whose members are diametrically opposed. The slots  20 - 27  each form arcs that preferably range about 90° to 150°. The slots  20  and  21  are diametrically opposed so that they are separated by small portions  32  and  34  of the plastic material that forms the flared end portion  16 . The slots  22  and  23  are separated lengthwise along the flared end  16  from the slots  20  and  21 . The slots  22  and  23  are diametrically opposed and have their centers rotated 90° from the centers of the slots  20  and  21 . The slots  24  and  25  are linearly spaced apart from the slots  22  and  23 . The centers of the slots  24  and  25  are angularly displaced from the centers of the slots  22  and  23 . The centers of the slots  24  and  25  are preferably aligned with the centers of the slots  21  and  22 . The slots  26  and  27  are linearly spaced apart from the slots  24  and  25  and are preferably angularly aligned with the slots  22  and  23 . The slots  21 - 27  preferably have widths that increase with proximity to the end  36  of the flared portion  16 .  
         [0019]    The electrical connector  14  includes a housing  38  that preferably is formed of molded plastic. The housing  14  includes a first tubular projection  40  that includes a central longitudinal cavity  42 . A second tubular projection  44  extends from the housing  38  in a direction perpendicular to the projection  40 . The test lead  10  extends through the cavity  42  and is connected to a terminal  46  that extends through the projection  44  for connection to an electrical test instrument (not shown).  
         [0020]    The projection  40  includes a flared end  50  that has a plurality of slots  52 - 57  formed therein to define a strain relief device  19 . The material between the slots  52 - 57  forms a ladder-like structure. The slots  52 - 57  are also arranged in linearly spaced apart pairs with the members of each pair being diametrically opposed in an arrangement that is similar to that of the slots  20 - 27 .  
         [0021]    The slots  56  and  57  preferably are wider than the slots  54  and  55 , which are in turn preferably wider than the slots  52  and  53 . The slots  21 - 27  preferably have widths that increase with proximity to the end  36  of the flared portion  16 . Forming the slots  20 - 27  and  52 - 57  in the flared end portions  16  and  18 , respectively, makes the flared end portions more flexible than the adjacent portions of the tube and the projection  40 , respectively. Having the slot widths increase toward the end  36  of the flared portions  16  makes the flared end portion have progressively increasing flexibility toward the end  36 . The increasing slot widths toward the end  60  of the flared end  18  provides similar progressively increasing flexibility toward the end  60   
         [0022]    Referring to FIG. 8, bending the test lead  10  through a 90° angle as it emerges from the strain relief device  15  deforms the strain relief device  15  so that the slots  23  and  23  (for the example shown) close and prevent additional bending of the test lead  10 . The sizes of the gaps and the widths of the ladder rungs are designed so that both slots end up closing at about the same time, thus providing the precise maximum radius on the bent wire.  
         [0023]    Bending the test lead  10  90° in the opposite direction would compress the sides of the slots  22  and  26  together to prevent further bending. Bending the test lead  10  out of the plane of the paper would similarly deform the slots  20  and  24 . Bending the test lead 90° into the plane of the paper of FIG. 8 would deform the slots  22  and  26  (shown in FIG. 4, not shown in FIG. 8).  
         [0024]    Referring to FIG. 9, bending the test lead  10  as it emerges from the strain relief device  19  deforms the sides of the slots  53  and  57 , which prevents further bending of the test lead  10 . The strain relief device  19  functions essentially the same as the strain relief device  15 .  
         [0025]    The strain relief devices  15  and  19  provide the largest bend radius possible (given the length of the strain relief) for a wire pulled at a 90° angle. The strain relief devices  15  and  19  accomplish this by making the size of the slots  20 - 27  and  52 - 57  and the size of the“ladder rungs” between them so that the slots enclosed in the arc through which the test lead  10  is bent close almost simultaneously as the wire is pulled at 90 degrees. The sides of the latter are just thin enough to bend well (the whole strain relief section flops in the direction of the lead pull), yet big enough to support the ladder rungs, and not fat enough to break.