Abstract:
A digital multimeter includes a display for displaying a measured parameter, a selector for selecting the measured parameter, at least one jack configured to receive a test lead plug, and a housing assembly including the display, the selector and the jack. The selector includes a push button, a rotary selector switch, a knob coupled to the rotary selector switch, and a cover molded over the knob. The cover includes a relatively soft material compared to the knob. The housing assembly includes a first and second housing portions coupled together, a gasket sealing the first and second housing portions, and a jacket overlying parts of the first and second housing portions and the gasket. The housing assembly defines an internal cavity and is configured to absorb impact energy in response to dropping the digital multimeter up to approximately one meter and protect against water and dust ingress into the cavity.

Description:
TECHNICAL FIELD 
     The present disclosure relates generally to ruggedized digital multimeters. More particularly, the present disclosure relates to a digital multimeter including a ruggedized jacket. 
     BACKGROUND 
     Digital multimeters or “DMMs” are adapted for measuring a number of parameters generally needed for service, troubleshooting, and maintenance applications. Such parameters typically include alternating current (a.c.) voltage and current, direct current (d.c.) voltage and current, and resistance or continuity. Other parameters including frequency, capacitance, and temperature may also be measured to meet the requirements of the particular application. 
     Conventional DMMs include a hard plastic housing or case. These housings support various electrical components for measuring the parameters and electrically insulate these components from an operator. 
     DMMs are frequently used in environments that may damage a conventional DMM. For example, a conventional DMM may be dropped distances of one meter or less onto a hard surface, e.g., concrete, steel, etc. Such drops may fracture the housings of conventional DMMs. In addition to possibly rendering the conventional DMM inoperable, such drops may compromise the electrical insulation and potentially make it unsafe for the operator to use. DMMs may also be used above liquids such as water. Fluid ingress as a result of being immersed in a liquid may cause irreparable damage to the internal components a conventional DMM. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is front elevation view of a ruggedized digital multimeter (DMM) according to an embodiment of the present disclosure. 
         FIG. 2  is a left-side elevation view of the ruggedized DMM shown in  FIG. 1 . 
         FIG. 3  is a right-side elevation view of the ruggedized DMM shown in  FIG. 1 . 
         FIG. 4  is a top plan view of the ruggedized DMM shown in  FIG. 1 . 
         FIG. 5  is a bottom view of the ruggedized DMM shown in  FIG. 1 . 
         FIG. 6  is a back elevation view of the ruggedized DMM shown in  FIG. 1 . 
         FIG. 7  is a first perspective view of the ruggedized DMM shown in  FIG. 1 . 
         FIG. 8  is a second perspective view of the ruggedized DMM shown in  FIG. 1 . 
         FIG. 9  is front elevation view of a DMM according to an embodiment of the present disclosure. 
         FIG. 10  is a left-side elevation view of the DMM shown in  FIG. 9 . 
         FIG. 11  is a right-side elevation view of the DMM shown in  FIG. 9 . 
         FIG. 12  is a top plan view of the DMM shown in  FIG. 9 . 
         FIG. 13  is a bottom view of the DMM shown in  FIG. 9 . 
         FIG. 14  is a back elevation view of the DMM shown in  FIG. 9 . 
         FIG. 15  is a first perspective view of the DMM shown in  FIG. 9 . 
         FIG. 16  is a second perspective view of the DMM shown in  FIG. 9 . 
         FIG. 17  is an exploded perspective view of the DMM shown in  FIG. 9 . 
         FIG. 18  is front elevation view of a jacket according to an embodiment of the present disclosure. 
         FIG. 19  is a left-side elevation view of the jacket shown in  FIG. 18 . 
         FIG. 20  is a right-side elevation view of the jacket shown in  FIG. 18 . 
         FIG. 21  is a top plan view of the jacket shown in  FIG. 18 . 
         FIG. 22  is a bottom view of the jacket shown in  FIG. 18 . 
         FIG. 23  is a back elevation view of the jacket shown in  FIG. 18 . 
         FIG. 24  is a first perspective view of the jacket shown in  FIG. 18 . 
         FIG. 25  is a second perspective view of the jacket shown in  FIG. 18 . 
     
    
    
     DETAILED DESCRIPTION 
     Specific details of embodiments according to the present disclosure are described below with reference to a ruggedized digital multimeter. Other embodiments of the disclosure can have configurations, components, features or procedures different than those described in this section. A person of ordinary skill in the art, therefore, will accordingly understand that the disclosure may have other embodiments with additional elements, or the disclosure may have other embodiments without several of the elements shown and described below with reference to  FIGS. 1-25 . 
       FIGS. 1-8  are views of a ruggedized DMM  10  including a DMM  100  and a jacket  200  according to an embodiment of the present disclosure.  FIGS. 9-17  are views of the DMM  100  per se and  FIGS. 18-25  are views of the jacket  200  per se. 
       FIG. 1  is a front elevation view showing a front face  12  of the ruggedized DMM  10 . In particular, the front  12  includes a front face  102  of the DMM  100  surrounded by the jacket  200 . As will be discussed in greater detail with respect to  FIG. 9 , the face  102  includes a display  120 , a rotary selector  130 , a plurality of push buttons  140 , and a plurality of jacks  150 . 
     The jacket  200  includes an upstanding ridge or brow  210  that projects outward from the front face  102  and is positioned adjacent to the display  120 . Another upstanding ridge or chin  212  can project outward from the front face  102  and is positioned adjacent to the jacks  150 . According to certain embodiments of the present disclosure, the brow  210  and/or the chin  212  may prevent or eliminate contact with the display  120 , the rotary selector  130 , the push buttons  140 , and/or the jacks  150  if the ruggedized DMM  10  falls with the front face  12  oriented downward. 
     Referring additionally to  FIGS. 2 and 3 , grips  220  (four grips  220   a - 220   d  are shown in  FIG. 1 ) project laterally outward from the DMM  100 . According to certain embodiments of the present disclosure, the grips  220  may initially contact the ground if the ruggedized DMM  10  falls with its left-side  14  ( FIG. 2 ) or its right-side  16  ( FIG. 3 ) oriented downward. Depression  222  (two depressions  222   a  and  222   b  are shown in  FIG. 1 ) between each pair of the grips  220  on the left-side  14  or the right-side  16  may facilitate grasping the ruggedized DMM  10  between the fingers and thumb of an operator&#39;s hand (not shown). Accordingly, the grips  220  that project above the depressions  222  may provide ledges that deter the ruggedized DMM from sliding through the operator&#39;s hand. 
     Referring additionally to  FIGS. 4-6 , a back side  18  of the ruggedized DMM  10  may include various fittings and features for supporting the ruggedized DMM  10  or accessories for the ruggedized DMM  10 . For example, an aperture  224  in the jacket  200  may provide a receptacle for a mounting bracket (not shown) to support the ruggedized DMM  10 . The jacket  200  may include a stand  230  for supporting the ruggedized DMM  10  in a generally upright orientation on a support surface, e.g., a table (not shown). The stand  230  may also include a cable manager  232 . The cable manager  232  may include a keyhole shaped opening  234  for passing cords of test leads (not shown). Test lead holders  240  (two test lead holders  240   a  and  240   b  are shown in  FIGS. 4-6 ) may be provided for releasably retaining the probes of test leads (not shown) on the ruggedized DMM  10 . Slots  242  (slots  242   a  and  242   b  are shown in  FIG. 6 ) may accommodate cross guard flares on the test leads (not shown).  FIGS. 4 and 5  show the top  20  and bottom  22 , respectively, of the ruggedized DMM  10 . 
       FIGS. 7 and 8  provide perspective views of the ruggedized DMM  10 . In particular,  FIG. 7  shows a perspective view including the front side  12 , the right-side  16 , and the bottom  22 .  FIG. 8  shows a perspective view including the left-side  16 , the back  18 , and the bottom  22 . 
       FIG. 9  is a front elevation view showing the front face  102  of the DMM  100  including the display  120 , the rotary selector  130 , the plurality of push buttons  140  (eight push buttons  140   a - 140   h  are shown in  FIG. 9 ), and the plurality of jacks  150  (four jacks  150   a - 150   d  are shown in  FIG. 9 ). The display  120  may show information such as the parameters that are measured by the DMM  100 , one or more settings selected by the operator for the DMM  100 , etc. The display  120  may include a liquid crystal display (LCD), a set of light emitting diodes (LEDs), or another device suitable for conveying information to the operator. 
     The rotary selector  130  may include a rotary selector switch  132  ( FIG. 17 ), a knob  134  ( FIG. 17 ) coupled to the rotary selector switch  132 , and a cover  136  molded over the knob  134 . Certain embodiments according to the present disclosure include a double molded knob  134  and cover  136 . Specifically, the knob  134  may be molded with a relatively hard plastic such as acrylonitrile butadiene styrene (ABS) and the cover  136  may be over molded on the knob  134  with a relatively soft plastic such as Santoprene®. Accordingly, the knob  134  provides a relatively rigid form and the cover  136  provides an impact energy absorbing over layer so that the cover  136  may prevent fracturing the knob  134  if the ruggedized DMM  10  falls with the front face  12  oriented downward. 
     The push buttons  140  may include “smart” buttons to select settings for the DMM  100  that may be identified in the display  120  immediately above a corresponding push button  140 . Accordingly, push buttons  140   a - 140   d  may select settings specific to a particular setting of the rotary selector switch  132 . The push buttons  140  may also be used in connection with selecting global settings for the DMM  100 . The push buttons  140   e - 140   h  may be used to activate or reset operation of the DMM  100 . 
     The jacks  150  provide connections for test leads (not shown) to different functions of the DMM  100 . For example, jack  150   a  may be for connecting a common test lead, i.e., used in conjunction with one or more the other jacks  150   b - 150   d , and the jacks  150   b - 150   d  may be for connecting a second test lead used in conjunction with measuring one of resistance, voltage, current, etc. 
       FIGS. 10-14  show a left-side  104  ( FIG. 10 ), a right-side  106  ( FIG. 11 ), a top  108  ( FIG. 12 ), a bottom  110  ( FIG. 13 ) and a back  112  ( FIG. 14 ) of the DMM  100 .  FIGS. 15 and 16  provide perspective views of the DMM  100 . In particular,  FIG. 15  shows a perspective view including the front side  102 , the right-side  106 , and the bottom  110 .  FIG. 16  shows a perspective view including the left-side  104 , the bottom  110 , and the back  112 . 
       FIG. 17  is an exploded perspective view of an embodiment of the DMM  100  according to the present disclosure. The DMM  100  includes a housing assembly  160  including a top case  162  and a bottom case  164 . The top case  162  may include the display  120 , the rotary selector knob  134  and cover  136 , a keypad  142  supporting the push buttons  140 , and the jacks  150 . Certain embodiments of the display  120  according to the present disclosure include an LCD mask  122 , an LCD  124 , and a backlight  126 . In addition to over molding the cover  136  on a front side of the knob  134 , a seal  138  may be over molded on a back side of the knob  134 . The seal  138  may provide a fluid tight barrier between the knob  134  and the top case  162 . The jacks  150  (only one is indicated in  FIG. 17 ) may be hermetically sealed with respect to the top case  162  and respective electrical contacts  152  may conveying an electric signal from an external test lead (not shown) to inside the cavity  180 . 
     The bottom case  164  may include a detachable door  166  through which operator replaceable components  168  (e.g.,  FIG. 17  shows batteries  168   a  and a fuse  168   b ) may be accessed. A secondary door  168   c  may cover the fuse  168   b.    
     A gasket  170  may make fluid tight an interface between the top and bottom cases  162  and  164 . Accordingly, the top case  162  (including, for example, the display  120 , the knob  134 , the seal  138 , the keypad  142 , and the jacks  150 ), the bottom case  164 , and the gasket  170  form the housing assembly  160  that defines an internal cavity  180 . The internal cavity  180  provides a buoyant chamber such that the DMM  100  may float toward the surface of a liquid such as water. Internal components  190  for measuring parameters may be disposed in the cavity  180 . Certain embodiments according to the present disclosure have internal components  190  including shields  192  (a top shield  192   a  and a bottom shield  192   b  are shown in  FIG. 17 ), a printed circuit board  194  supporting solid state circuitry  196 , and rotary selector couplings  198  (a spring detent  198   a  and a spacer  198   b  are shown in  FIG. 17 ). 
     The top and bottom cases  162  and  164  may include a relatively rigid material that resists deflection, e.g., having a hardness of at least approximately 65 Shore D. The top and bottom cases  162  and  164  may include, for example, ABS or another suitable thermoplastic resin. 
       FIGS. 18-25  show the jacket  200  separated from the DMM  100 . In general, the jacket  200  has a concave arrangement with a lip  202  surrounding an opening  204 . The lip  202  includes the brow  210  and the chin  212 . The grips  220  and the depression  222  are included on the left-side ( FIG. 19 ) and/or the right-side ( FIG. 20 ) of the jacket  200 . The aperture  224 , the stand  230 , the cable manager  232 , the test lead holders  240   a  and  240   b  are included on the back ( FIG. 23 ) of the jacket  200 . 
     As best seen in  FIGS. 18 and 24 , the jacket  200  includes a plurality of spaced ribs  250  that absorb impact energy that for protecting the housing assembly  160 . A skin  252  ( FIG. 25 ) connecting the ribs  250  may be disposed between the ribs  250  and the DMM  100  (not shown) or the ribs  250  may be disposed between the skin  252  and the DMM  100 . 
     The jacket  200  may include a relatively flexible material having that can be resiliently stretched over the DMM  100 , e.g., having a hardness range from approximately 35 Shore A to approximately 45 Shore D. The jacket  200  may include, for example, Santoprene®, a mixture of an in-situ cross linked ethylene propylene diene Monomer (EPDM) rubber with polypropylene, or another suitable thermoplastic vulcanizate (TPV). 
     Certain embodiments according to the present disclosure can absorb impact energy in response to dropping the ruggedized DMM  10  up to approximately one meter onto a hard surface. Moreover, the jacket  200  and/or the gasket  170  protect against water and dust ingress into the cavity. Certain embodiments according to the present disclosure prevent water ingress into the cavity  180  in response to submerging the ruggedized DMM  10  under approximately one meter of water, and prevent dust ingress into the cavity  180 . Certain embodiments of the jacket  200  according to the present disclosure may also be stable over a range of environmental conditions, are electrical insulators, and/or are liquid resistant. 
     Specific details of the embodiments of the present disclosure are set forth in the description and in the figures to provide a thorough understanding of these embodiments. A person skilled in the art, however, will understand that the invention may be practiced without several of these details or additional details can be added to the invention. Well-known structures and functions have not been shown or described in detail to avoid unnecessarily obscuring the description of the embodiments of the present disclosure. 
     Unless the context clearly requires otherwise, throughout the description and the claims, the words “comprise”, “comprising”, and the like are to be construed in an inclusive sense, as opposed to an exclusive or exhaustive sense; that is to say, in the sense of including, but not limited to. Additionally, the words “herein”, “above”, “below”, and words of similar connotation, when used in the present disclosure, shall refer to the present disclosure as a whole and not to any particular portions of the present disclosure. Where the context permits, words in the above Detailed Description using the singular or plural number may also include the plural or singular number respectively. The word “or”, in reference to a list of two or more items, covers all of the following interpretations of the word: any of the items in the list, all of the items in the list, and any combination of the items in the list. 
     The above detailed description of embodiments is not intended to be exhaustive or to limit the invention to the precise form disclosed above. While specific embodiments of, and examples for, the invention are described above for illustrative purposes, various equivalent modifications are possible within the scope of the invention, as those skilled in the relevant art will recognize. 
     While certain aspects of the invention are presented below in certain claim forms, the inventors contemplate the various aspects of the invention in any number of claim forms. Accordingly, the inventors reserve the right to add additional claims after filing the application to pursue such additional claim forms for other aspects of the invention.