Abstract:
An electronic device having one or more contact posts is disclosed having a sleeve slidably mounted around the contact post and lockable by a push-push latching system in a retracted position in which the sleeve is below an upper end of the contact post and an extended position in which the sleeve extends around and covers the upper end of the contact post. The sleeve and contact post may have respective apertures extending transversely therethrough, which are aligned when the sleeve is slightly retracted to receive a probe. Alternatively, an ECG electrode clip may engage an end of the contact post when it is exposed by the sleeve being in the retracted position.

Description:
TECHNICAL FIELD 
   This invention relates to electrical testing equipment, and, more particularly to an apparatus and method for preventing accidental electric shock in testing equipment having exposed contact posts. 
   BACKGROUND OF THE INVENTION 
   Medical equipment must be carefully tested and calibrated in order to ensure that it will function properly in critical situations. Electrocardiogram (ECG) testers are an example of such test equipment. As shown in  FIG. 1 , an ECG tester  10  typically includes a number of contact posts  12  that may be coupled to electrode leads of an ECG monitor by means of clips  14 . The ECG tester  10  must be able to test ECG monitors having a wide variety of electrode lead clips. Some of these lead clips normally clip to electrodes having exposed terminals. Therefore, the contact posts  12 , like the electrode terminals, must be exposed rather than insulated from external contact by an insulating structure. 
   Hospital equipment, including ECG monitors, must be tested to ensure that they do not pose a shock hazard resulting from short circuits to an AC line power lead. The ECG leads, as well as cases of ECG monitors, are normally isolated from AC line voltage by suitable insulation, which can become damaged. ECG testers check electrical isolation of ECG monitors by applying line voltage to the contact posts  12 . The exposed contact posts  12  in prior art systems can be hazardous inasmuch as they can be inadvertently touched and cause electrocution. Accordingly, it would be an advancement in the art to provide a conveniently used apparatus and method for shielding the contact posts of ECG testers and like equipment when they are not covered by an electrode clip. 
   SUMMARY OF THE INVENTION 
   In one aspect of the invention, an electronic device, such as an ECG tester, includes a contact post having first and second ends mounted on a housing having the first end exposed and the second end electrically coupled to a circuit board operable to apply signals to and receive signals from the contact post. An insulative sleeve is slidably mounted on the contact post and engages a latching mechanism that secures the sleeve in either of two positions, an extended position in which the sleeve is positioned over the contact post in order to protect and insulate the post and a retracted position in which the first end of the contact post is exposed. 
   In another aspect of the invention the latching mechanism is a push-push latch. An engagement member may be secured to the sleeve to enable a user to push the sleeve into the retracted and extended positions. 
   In another aspect of the invention, the sleeve has an aperture extending transversely through a wall thereof such that a clip, such as a banana plug, may engage the first end of the contact post when the sleeve is in the extended position. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is an isometric view of an ECG tester in accordance with the prior art. 
       FIGS. 2A-2B  are isometric views of an ECG tester having contact post shields in accordance with an embodiment of the invention. 
       FIG. 3  is an exploded view of a contact post shield in accordance with an embodiment of the present invention. 
       FIG. 4  is a cutaway isometric view of a contact post shield mounted within an ECG tester in accordance with an embodiment of the present invention. 
       FIG. 5  is an isometric view of a housing suitable for mounting a contact post shield in accordance with an embodiment of the present invention. 
       FIGS. 6A-6C  are bottom plan views of a latching mechanism in accordance with an embodiment of the present invention. 
       FIG. 7  is bottom isometric view of an alternative embodiment of a shield having a truncated indexing member in accordance with an embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
   Referring to  FIGS. 2A and 2B , in one embodiment of the invention, an ECG tester  16  includes a plurality of insulating shields  18  positioned around respective contact posts  20 . The shields  18  are in the form of cylindrical sleeves  30  that are slidably positioned around respective contact posts  20 , but other configurations can be used. The shields  18  are positionable in a retracted position leaving an upper end  22  of the contact post  20  extending from the shield  18  and an extended position in which the upper end  22  is positioned within the shield  18 . The upper end  22  of the contact post  20  is shaped to be engaged by conventional ECG electrode clips. In some embodiments, in the extended position, the shield  18  extends beyond the top of the contact post  20  a substantial distance, such as a distance about equal or greater than the extent the top of the shield  18  is below the top of the contact post  20  in the retracted position. The shield  18  may be coupled to the housing  24  by means of a push-push latching system such that an operator may push a retracted shield  18  to cause it to spring back to the extended position and push an extended shield  18  to lock it in the retracted position. 
   In some embodiments, the shield  18  includes an aperture  26  that extends through a wall of the shield  18 . When the shield  18  is retracted slightly, but not enough to expose the upper end  22  of the contact post  20 , the aperture  26  is aligned with an aperture  27  formed in the contact post  20 . As shown in  FIG. 2B , when the shield  18  is retracted slightly further from the position shown in  FIG. 2A , a banana plug  14   b  may be inserted through the aperture  26  in the shield  18  and the aperture  27  in the contact post  20 . The contact post  20  may include a narrowed upper portion  28  sized to receive a connector, such as an ECG clip  14   a  when the shield  18  is in the fully retracted position. 
   An engagement member  32  may be secured to the sleeve  30  and provide an area for a user to safely press to move the sleeve  30  into the extended and retracted positions of  FIGS. 2A and 2B . In the illustrated embodiment, the engagement member  32  has a cross section that is constant for a portion of its length along a direction of movement  34  of the shield  18  as it moves between the retracted and extended positions. For example, the engagement member  32  is substantially cylindrical in the illustrated embodiment, however many other cross sectional shapes may be used such as rectangular, hexagonal, I- or H-shaped, or some other shape having a keyway, or any polygon offering sufficient structural shape. The engagement member  32  may be secured to the sleeve  30  by a web  36  of material, which may serve to increase the separation between the engagement member  32  and the contact post  20  to reduce the risk of accidental electrical shocks to an operator. 
   Referring to  FIGS. 3 and 4 , a latching mechanism  38 , such as a push-push latching mechanism, secures the shield  18  in either the extended or retracted position. The latching mechanism may be any push-push type latching mechanism or other latching mechanism known in the art. In the illustrated embodiment, the latching mechanism  38  includes indexing members  40  secured to the sleeve  30 . The indexing members  40  may include pointed ends formed by intersecting sloped surfaces  42 . The indexing members  40  are distributed evenly around the sleeve  30  and may be positioned slightly radially outwardly from the sleeve  30  with a gap between each adjacent members  40 . 
   The indexing members  40  engage arms  44  formed on a ratchet  46 . The arms  44  include sloped surfaces  48 , such that pressing the indexing members  40  against the arms  44  causes the ratchet to rotate in direction  50  ( FIG. 4 ). In the illustrated embodiment, there are twice as many indexing members  40  as arms  44 , that is, eight indexing members  40  and four arms  44 . The arms  44  may bear another sloped surface  52  sloping in the opposite direction from the sloped surface  48  such that the sloped surfaces  48 ,  52  form a point. The surface  52  is preferably substantially narrower than the surface  48 , however they may also be of equal width. The arms  44  secure to a ratchet hub  54  having an aperture  56  for receiving the contact post  20 . A biasing member  58 , such as a spring or other resilient member, engages the ratchet hub  54  and urges the sloped surfaces  48  against the indexing members  40 . In the illustrated embodiment, the biasing member  58  extends between the arms  44  of the ratchet hub  54  and a printed circuit board  60  ( FIG. 4 ) to which the contact post  20  is mounted. The circuit board  60  may be an ECG tester control circuit for applying line voltages to the contact posts  20  and receiving signals from the contact posts  20 . The engagement member  32  may slide within a channel  62 . Slidable engagement of the engagement member  32  within the channel  62  may advantageously fix the rotational position of the indexing members  40  relative to the ratchet  46 . 
   Referring to  FIG. 5 , the sleeve  30  and ratchet  46  may mount within a channel  64  having vertical guides  66  formed therein. The vertical guides  66  may be equal in number to the arms  44  of the ratchet  46  and sized to slidably receive the arms  44 . The vertical guides  66  constrain the ratchet to movement in the vertical direction when the arms  44  are positioned therein. Stops  68  are positioned between the vertical guides  66  and likewise may be equal in number to the arms  44  of the ratchet  46 . The stops  68  prevent upward movement of the arms  44  when the arms  44  are aligned therewith. The stops  68  may have a sloped surface such that when the arms  44  are urged against the stops  68 , they are urged against a raised area  70  that prevents further rotation until the arms  44  are pushed away from the stops  68 . Grooves  72  may be formed in the stops  68  to receive the indexing members  40 . In the illustrated embodiments, the vertical guides  66  are formed by gaps between the stops  68 . 
   Referring to  FIGS. 6A-6C , while referring generally to  FIGS. 4 and 5 , the function of the illustrated latching mechanism  38  will be more particularly pointed out. When the shield  18  is in the extended position, the arms  44  are positioned within the vertical guides  66 , as shown in  FIG. 6A , such that the biasing member  58  is able to urge the shield  18  upwardly. To move the shield  18  into the retracted position, the operator pushes downwardly on the engagement member  32 , which causes the indexing members  40  to press against the sloped upper surface  48  of the ratchet  46 , causing the arms  44  rotate over the edges of vertical guide  66 , as shown in  FIG. 6B . Upon release of the engagement member  32 , the biasing member  58  urges the sloped upper surface  48  against the sloped surface of stop  68 , causing the ratchet and arms  44  to rotate and move into alignment with another of the indexing members  40 , stopping against the raised portion of  70 , as shown in  FIG. 6C . As is apparent in  FIG. 6C , the arms  44  are positioned over the stops  68  such that they are constrained from moving upwardly. To move from the retracted position to the extended position, the operator pushes downwardly on the engagement member  32 , the indexing members  40  are again urged against the sloped upper surfaces  48 , causing the arms  44  to rotate over the raised portion of  70  and into alignment with the vertical guides  66 , as shown in  FIG. 6A , where they are allowed to move vertically upward upon release of the engagement member  32 . 
   Referring to  FIG. 7 , in embodiments where the engagement member  32  is secured to the shield  18 , pressing on the engagement member may result in a rotational moment  74  being exerted on the shield  18  inasmuch as the engagement member  32  is offset from the shield  18 . As a result, the indexing members  40  may tend to become misaligned from the sloped upper surfaces  48 . In particular, indexing member  76  that is located about 90 degrees from the engagement member moving along the direction of rotation  78  may tend to move over the surface  52  such that it will exert a force on the surface  52  opposite the direction of rotation  78  of the ratchet  46 . Accordingly, the indexing member  76  may be truncated such that it does not have sloped surfaces  42 . The indexing member  76  may have instead a flat upper surface  80  that is offset from the pointed ends of the other indexing members  40  along the direction  82  of movement of the sleeve  18  such that the flat upper surface  80  does not contact the sloped surfaces  48 ,  52  of the ratchet  46 . In the illustrated embodiment, a portion of the indexing member  76  remains and aids in registering the shield  18  within a vertical guide  66  or groove  72 . In an alternative embodiment, there is no indexing member located in the position of indexing member  76 . In yet another alternative embodiment, the sloped surfaces  42  of the indexing member  76  may be of different lengths such that the point formed by the surfaces  42  is shifted opposite the direction of rotation  78  in order to compensate for shifting caused by the rotational moment  74 . 
   Although the present invention has been described with reference to the disclosed embodiments, persons skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention. Such modifications are well within the skill of those ordinarily skilled in the art. Accordingly, the invention is not limited except as by the appended claims.