Abstract:
A multimeter includes a case having a rotary selector knob for selecting a multimeter function. A circuit board defining multiple switching terminals thereon is located in the case. A rotary switch assembly is operatively coupled to the selector knob. The rotary switch assembly has a plurality of contact pairs which selectively complete a galvanic connection across predetermined pairs of switching terminals. The rotary switch assembly further includes first and second switch members located in opposition on respective sides of the circuit board. Each of the switch members has at least one of the contact pairs.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The present invention relates generally to digital multimeters. More particularly, the invention relates to a digital multimeter having an improved rotary switch assembly. 
         [0002]    Digital multimeters (DMMs) function to measure a number of electrical parameters as needed for service, troubleshooting and maintenance. Such parameters may include AC voltage and current, DC voltage and current, resistance and continuity. In some cases, a DMM may measure other parameters such as capacitance and temperature. 
         [0003]    A DMM will often be configured as a hand-held unit having a rotary knob by which various functions are selected. A plurality of lead jacks are provided in the case (i.e., housing) of the unit for connection of test leads. The specific jack used may depend on the function that has been selected. An LCD display provides a reading of the tested parameter. 
         [0004]    Various electronic components are mounted to a printed circuit board located inside the case of the DMM. A rotary switch having multiple contact pairs may be mounted to the printed circuit board. When the selector knob is rotated by a user, the contact pairs are moved into or out of engagement with pairs of contact terminals located on the surface of the printed circuit board itself. As a result, a galvanic connection between the terminal pairs will be made as necessary for the selected function. The terminal pairs are formed through suitable printed circuit technology as conductive pads on the printed circuit board. 
         [0005]    Details regarding the construction and operation of multimeters may be discerned from U.S. Pat. Nos. 7,034,517, 6,466,003 and 6,043,640, incorporated herein by reference. 
       SUMMARY OF THE INVENTION 
       [0006]    According to one aspect, the present invention provides a multimeter comprising a case having a rotary selector knob for selecting a multimeter function. A circuit board defining multiple switching terminals thereon is located in the case. A rotary switch assembly is operatively coupled to the selector knob. The rotary switch assembly has a plurality of contact pairs which selectively complete a galvanic connection across predetermined pairs of switching terminals. The rotary switch assembly further includes first and second switch members located in opposition to one another on respective sides of the circuit board. Each of the switch members has at least one of the contact pairs. 
         [0007]    In presently preferred embodiments, the rotary switch assembly includes a shaft interconnecting the first and second switch members. The shaft is configured such that the first switch member and the second switch member are interconnected in a predetermined angular orientation. 
         [0008]    Often, it will be desirable for the first switch member to include at least four contact pairs. Similarly, the second switch member may include at least three contact pairs. In addition, the second switch member may also have a nonfunctional sweeper operative to facilitate balance during rotation. For example, the nonfunctional sweeper may include a pair of parallel sweeper members. 
         [0009]    Exemplary embodiments may include a detent disc located on an inside surface of the case. In such embodiments, the detent disc may interconnect the selector knob and first switch member for rotation about a common rotational axis. In this regard, the selector knob may include a coupling structure engaging the detent disc such that the selector knob and detent disc rotate together. The detent disc and first switch member may be interconnected via a plurality of drive pins offset from but parallel to the common rotational axis. Preferably, the detent disc and first switch member may each include a visual alignment feature to facilitate assembly. 
         [0010]    According to exemplary embodiments, each of the first and second switch members may comprise a support disc in which the contact pairs are carried. The support disc in such embodiments may be formed of a polymeric material. A least one punch-out aperture may be provided in the support disc at which adjacent contact pairs are disconnected. 
         [0011]    According to an additional aspect, the present invention provides a method of forming a rotary switch member for use in a multimeter. One step of the method involves providing a unitary metallic element defining a plurality of contact pairs wherein adjacent contact pairs are interconnected by a strip. At least two of the contact pairs are oriented in different directions. Another step involves encapsulating portions of the unitary metallic element with a polymeric material such that end portions of the contact pairs and at least part of each strip remain exposed. A further step of the method involves removing a portion of each strip to prevent galvanic connection between adjacent contact pairs. 
         [0012]    Additional aspects of the present invention are provided by a rotary switch assembly for use in an electronic metering device. The assembly comprises a selector knob and a generally planar substrate board having conductive pads thereon defining multiple switching terminals. First and second switch members are located on respective sides of the substrate board. The switch members are operatively connected to the selector knob for rotation about a common rotational axis. Each of the switch members is configured having a support disc formed of a polymeric material in which a plurality of contact pairs are carried. The contact pairs are operative to complete a galvanic connection across predetermined pairs of the switching terminals. 
         [0013]    In presently preferred embodiments, the first and second switch members are interconnected via a shaft extending through the substrate board along the common rotational axis. Preferably, the shaft is configured such that the first and second switch members are interconnected in a predetermined angular orientation. 
         [0014]    Additional aspects of the present invention are achieved by a rotary switch assembly for use in an electronic metering device. The assembly comprises a selector knob and a generally planar substrate board having conductive pads thereon defining multiple switching terminals. A first switch member, located on the substrate board, has a support disc formed of a polymeric material in which a plurality of contact pairs are carried. The contact pairs of the first switch member are operative to complete a galvanic connection across predetermined pairs of switching terminals. A detent disc interconnects the selector knob and first switch member for rotation about a common rotational axis. The detent disc and first switch member each include a visual alignment feature to facilitate assembly. 
         [0015]    Other objects, features and aspects of the present invention are provided by various combinations and subcombinations of the disclosed elements, as well as methods of practicing same, which are discussed in greater detail below. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]    A full and enabling disclosure of the present invention, including the best mode thereof, to one of ordinary skill in the art, is set forth more particularly in the remainder of the specification, including reference to the accompanying drawings, in which: 
           [0017]      FIG. 1  is a perspective view of a digital multimeter constructed in accordance with the present invention; 
           [0018]      FIG. 2  is an exploded view showing various components of the multimeter of  FIG. 1 ; 
           [0019]      FIG. 3  is an enlarged exploded view of various components of a rotary switch assembly utilized in the multimeter of  FIG. 1 ; 
           [0020]      FIG. 4  is a side elevation showing first and second rotary switch members of the rotary switch assembly as mounted to a circuit board; 
           [0021]      FIG. 5  is a plan view of a portion of the circuit board showing various terminal pairs thereon; 
           [0022]      FIG. 6  is a plan view of the second rotary switch member showing an outer side thereof (i.e., the side away from the circuit board); 
           [0023]      FIG. 7  is a perspective view of the second rotary switch member showing an inner side thereof (i.e., the side mounted toward the circuit board); 
           [0024]      FIG. 8  is a perspective view of a unitary metallic element used in producing the second rotary switch member; 
           [0025]      FIG. 9  is a plan view of the first rotary switch member showing an outer side thereof; 
           [0026]      FIG. 10  is a perspective view of the first rotary switch member showing an inner side thereof; 
           [0027]      FIG. 11  is a perspective view of a unitary metallic element used in producing the first rotary switch member; 
           [0028]      FIGS. 12-14  are diagrammatic illustrations showing various molding steps that may be used in producing a rotary switch member in accordance with the present invention; and 
           [0029]      FIG. 15  is a perspective view showing the rotary switch member as it emerges from the mold in  FIG. 14 . 
       
    
    
       [0030]    Repeat use of reference characters in the present specification and drawings is intended to represent same or analogous features or elements of the invention. 
       DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0031]    It is to be understood by one of ordinary skill in the art that the present discussion is a description of exemplary embodiments only, and is not intended as limiting the broader aspects of the present invention, which broader aspects are embodied in the exemplary constructions. 
         [0032]      FIG. 1  illustrates a digital multimeter (DMM)  10  constructed in accordance with the present invention. Multimeter  10  comprises a housing in the form of a case  12  defining an interior cavity in which various internal components are located. A suitable display, such as a liquid crystal display (LCD), can be viewed through a transparent window  14  located in the top surface of case  12 . A plurality of keys (collectively indicated at  16 ) provide a user interface. As shown, these keys may include directional navigation buttons as indicated at  18 . A plurality of jacks for connection of respective test leads are also provided, as collectively indicated at  20 . 
         [0033]    A rotary selector knob  22  allows the user to select a particular multimeter function. In this case, ten such functions are provided, indicated by respective stop positions in the knob rotation. As one skilled in the art will appreciate, suitable graphics will typically be printed on the top surface of case  12  to indicate the respective function. 
         [0034]    Certain additional details about the construction of multimeter  10  can be most easily explained with reference to  FIG. 2 . In this embodiment, case  12  is preferably formed having top and bottom case members  12   a  and  12   b  which together define the interior cavity. Preferably, each of the case members  12   a  and  12   b  may be formed of a molded shell of high impact rigid plastic which is at least partially overmolded with a softer polymeric material. The softer material provides a desirable gripping surface. The molded shell of the bottom case member may be opaque, whereas embodiments are contemplated in which the molded shell of the top case member is transparent. An opaque “skin” may be applied to the top case member to cover areas not already covered by the overmold that should not be transparent. 
         [0035]    Various electronic components necessary for operation of multimeter  10  are mounted to a circuit board  24  within the interior cavity. Portions of circuit board  24  are covered by a bottom shield  26  and a top shield  28  to reduce the effects of interference on the operation of multimeter  10 . 
         [0036]    Multimeter  10  includes a rotary switch assembly by which circuit board  24  “knows” the position of selector knob  22 . Referring now to  FIGS. 2-4 , switch assembly  30  in this embodiment includes a first switch member  32  and a second switch member  34  opposed to one another on the top and bottom sides, respectively, of circuit board  24 . In this case, switch member  34  includes a shaft  36  extending through an aperture  38  defined in circuit board  24 . Shaft  36  is received in a corresponding bore  40  defined in the center of switch element  32 . 
         [0037]    Preferably, shaft  36  includes a key received in a corresponding keyway defined in bore  40 . As a result, switch members  32  and  34  will be situated in the correct angular orientation during the assembly process. In addition, shaft  36  and bore  40  may define a series of flats which further prevent relative rotation between switch members  32  and  34 . An appropriate locking feature may be provided having a tendency to maintain the interconnection between switch members  32  and  34  after they are connected together. 
         [0038]    A detent mechanism is used to divide rotation of selector knob  22  into discrete increments. As a result, selector knob  22  will remain in the selected position until the user intentionally moves the knob to a new position. In this embodiment, the detent mechanism comprises a detent disc  42  located in a recess  44  defined on the inside surface of case member  12   a . Recess  44  defines a series of “teeth”  46  around its circumference. The teeth  46  are engaged by protuberances located at the end of respective springs (such as spring  48  and its protuberance  50 ) formed as an integral extension of detent disc  42 . As one skilled in the art will recognize, the springs urge the respective protuberance into the valley between adjacent teeth  46 . 
         [0039]    A stop feature is preferably provided to limit rotation of knob  22  in both clockwise and counterclockwise directions. In this case, the stop feature comprises an arcuate groove  52  ( FIG. 2 ) defined in the housing. Groove  52  receives a protrusion  54  ( FIG. 3 ) located on the bottom of selector knob  22 . When protrusion  54  gets to the end faces of groove  52 , further rotation is prevented. 
         [0040]    As shown in  FIG. 3 , selector knob  22  includes a depending shaft  56  that extends through an aperture  58  defined in case member  12   a . Shaft  56  couples selector knob  22  to detent disc  42  such that they rotate together. In addition, detent disc  42  includes a pair of drive pins  60  received in respective drive holes  62  defined in the top of first switch member  32 . As a result of this arrangement, rotation of selector knob  22  by a user will rotate detent disc  42 , which in turn rotates switch assembly  30 . In this embodiment, all of the components rotate around a common rotational axis A. Depending on the configuration of shield  28 , an opening, such as circular opening  64 , may be necessary to accommodate drive pins  60 . 
         [0041]    Detent disc  42  and switch member  32  may include visual indicators to ensure proper orientation during assembly. In this case, respective arrows  66  and  68  are provided for this purpose (see  FIG. 3 ). The assembler knows that if the arrows are pointed in a particular direction, all of the rotational components will be oriented correctly with respect to one another. 
         [0042]    Referring to  FIG. 5 , circuit board  24  includes a plurality of switching terminals that are either open (nonconducting) or closed (conducting) depending on the position of switch members  32  and  34 . The switching terminals are formed as conductive pads on both planar surfaces of circuit board  24 . For example, one position of selector knob  22  may provide a galvanic connection across terminals  70   a  and  70   b . Another position of selector knob  22  may provide a galvanic connection across terminals  72   a  and  72   b . As a result, the function to be performed by multimeter  10  is selected. 
         [0043]    Additional details regarding the construction of second switch member  34  can be most easily explained with reference to  FIGS. 6 and 7 . As shown, switch member  34  comprises a support disc  74  in which a plurality of contact pairs  76   a ,  76   b  and  76   c  are carried. Support disc  74  is preferably formed of a suitable polymeric material such as an acceptable ABS/PC blend. 
         [0044]    Contact pairs  78   a - c  are preferably formed from a suitable metal having the desired conductive and spring-like qualities. For example, presently preferred embodiments of the invention utilize beryllium copper which has been plated with nickel. As shown, each of the contact pairs  78   a - c  includes a pair of spring-like “fingers,” such as fingers  78   a  and  b , that are connected together at their proximal ends (as indicated at  80 ). The fingers will contact a respective terminal pad as the switch member is rotated. 
         [0045]    In this embodiment, switch member  34  also includes a “nonfunctional” sweeper  82 . Sweeper  82  is “nonfunctional” in the sense that it does not serve as a switch armature, but instead functions to provide balance to switch member  34  during rotation. Specifically, sweeper  82  counteracts the upward spring force of contact pair  76   a  which might otherwise cause switch member  34  to tilt. As will be described in more detail below, contact pairs  76   a - c  and nonfunctional sweeper  82  may be advantageously formed from a unitary metallic element  84  ( FIG. 8 ). 
         [0046]    Referring now to  FIGS. 9 and 10 , first switch member  32  is also preferably formed having a support disc  86  in which a plurality of contact pairs  88   a - d  are carried. Like support disc  74 , support disc  86  may be formed of a ABS/PC blend, or other suitable polymeric material. Contact pairs  88   a - d  are preferably produced from nickel-plated beryllium copper or other suitable conductive material. Contact pairs  88   a - d  may be formed from a unitary metallic element  90  ( FIG. 11 ). 
         [0047]    One exemplary process for producing a switch member according to the present invention will now be described with reference to the remaining figures. 
         [0048]    In this regard,  FIGS. 12-14  diagrammatically illustrate a mold in which the support disc may be formed. In this case, the mold is configured to form support disc  74  of first switch member  32 . Referring now to  FIG. 12 , unitary metallic element  84  is placed into a base  92  of the mold. Base  92  will include a suitable fixture ensuring the correct orientation of element  84 . For example, element  84  may define a plurality of holes, such as hole  94 , that receive aligning pins located in the mold. 
         [0049]    After element  84  is placed in the correct orientation, the mold is closed, as shown in  FIG. 13 . The polymeric material is injected into the mold so as to surround selected regions of unitary metallic element  84  and thereby form support disc  86 . Once the polymeric material is suitably hardened, it can be removed from the mold as indicated in  FIG. 14 . 
         [0050]    Referring now to  FIG. 15 , one skilled in the art will appreciate that all of the contact pairs are connected to one another when the switch member is removed from the mold. To interrupt a galvanic connection between the respective contact pairs, the support discs are provided with a number of punch-out apertures, such as punch-out aperture  96 . These apertures expose the connecting strips between adjacent contact pairs so that at least a portion  98  of the strip can be removed. As a result, each of the contact pairs functions as an individual armature in the switch arrangement. 
         [0051]    It can thus be seen that the present invention provides a digital multimeter having an improved rotary switch assembly. While preferred embodiments of the invention have been shown and described, modifications and variations may be made thereto by those of ordinary skill in the art without departing from the spirit and scope of the present invention. In addition, it should be understood that aspects of the various embodiments may be interchanged both in whole or in part. Furthermore, those of ordinary skill in the art will appreciate that the foregoing description is by way of example only, and is not intended to be limitative of the invention as further described in the appended claims.