Abstract:
A clamp type digital multimeter has one or more digital displays mounted so as to permit at least one of the displays to be read even when attachment of the clamp jaws about a conductor forces the display into an orientation that renders it inaccessible. The meter either has a single display that can be pivoted to an orientation convenient for viewing, or it has dual displays mounted on separate surfaces of the meter&#39;s housing. A protective flap may cover one or both of the displays when it is not needed for viewing.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     This invention relates generally to electronic test instruments, particularly digital multimeters having a current sensing clamp. Digital multimeters, or DMM&#39;s, are used to measure a variety of electrical parameters, such as AC voltage, DC voltage, resistance and current. Clamp-type DMMs, also known simply as clamp meters, can measure current without interfering with the current carrying conductor. One such clamp meter is described in U.S. patent application Ser. No. 09/774,526, the disclosure of which is hereby incorporated by reference. In addition, clamp meters have the ability to measure fairly high levels of current.  
         [0002]     Clamp meters measure current flow in a conductor without having to make electrical connection with the conductors forming the circuit. Instead two clamp jaws having electrical coils embedded therein encircle the conductor and sense the magnetic field created by the current flow in order to measure the current. However, the physical arrangement of the measured conductor in relation to the clamp jaws, housing and display dictates the orientation in which the clamp meter must be used. This can make it difficult to read the display in certain situations.  
         [0003]     Typically, clamp meters have an elongated rectangular housing designed to be held in one hand. A pair of clamp jaws extends from the top of the housing. The jaws are situated in a fixed plane that is generally parallel to the plane of the front face of the housing. The meter&#39;s display is normally also disposed in the front face of the housing. Accordingly, when the clamp jaws are placed around a conductor the display can be forced into a position which may make reading the display difficult, if not impossible. This occurs most often when the current-carrying conductor is overhead or disposed in tight physical spaces such as an electrical cabinet.  
         [0004]     It has been determined that adding a display to the side of a multimeter housing disposed on a plane generally perpendicular to the plane formed by the clamp jaws facilitates the reading of measurements even when the clamp meter is in an awkward position dictated by the need to surround a current-carrying conductor.  
       SUMMARY OF THE INVENTION  
       [0005]     A primary object of the present invention is a clamp meter having multiple displays mounted in separate planes. At least one of the displays will be readily visible regardless of the orientation of the meter. The clamp meter has a housing having at least first, second and third faces. A pair of rigid jaws extends from the first face of the housing. The jaws define a jaw plane with at least one rigid jaw being pivotally movable in the jaw plane. A first display is disposed on the second face of the housing in a plane approximately parallel to the jaw plane. A second display is disposed on the third face of the housing in a plane approximately perpendicular to the jaw plane. One of the displays may be selectably covered by a pivotable flap.  
         [0006]     In an alternate embodiment a single display is pivotally mounted in the housing so it can be tilted to a suitable viewing position. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0007]      FIG. 1  is a front elevation view of a clamp meter of the present invention, with the clamp jaws closed to encircle a conductor shown in phantom lines.  
         [0008]      FIG. 2  is a front elevation view of a clamp meter of the present invention, with the clamp jaws open.  
         [0009]      FIG. 3  is a bottom plan view of the clamp meter of the present invention, showing a protective flap in a closed position for covering a display.  
         [0010]      FIG. 4  is a bottom plan view of the clamp meter of the present invention, showing the protective flap in an open position to expose a display.  
         [0011]      FIG. 5  is a front elevation view of a second embodiment of a clamp meter according to the present invention, with the clamp jaws open to receive a conductor shown in phantom lines and the display shown in a retracted position.  
         [0012]      FIG. 6  is a bottom plan view of the clamp meter of  FIG. 5 , with the display shown in a raised position. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0013]      FIGS. 1-4  illustrate a clamp meter  10  according to the present invention. The clamp meter has an elongated housing  12  that mounts a first digital display  14 . The display is mounted such that its outer surface is generally contiguous with the front face  16  of the housing. Two input jacks  18 ,  20  are provided for receiving test leads (not shown). The housing  12  is made from a hard, durable, lightweight plastic material. Also included on the front face  16  is a series of pushbuttons  22 A- 22 D for selecting one or more of the testing functions of the meter. A selector knob or dial  24  is disposed on the front face  16  for choosing an electrical measurement mode.  
         [0014]     Extending from the top of the housing is a pair of rigid clamp jaws  26 ,  28 . Typically one of the jaws is pivotally mounted in the housing. In the embodiment shown jaw  26  is movable. Jaw  26  is spring-biased to a closed position against fixed jaw  28 . The jaws  26 ,  28  have an arcuate shape to present outer convex surfaces  30  and inner concave surfaces  32 . The ends of the outer surfaces are slightly offset to form a tip  34  at the end of fixed jaw  28 . Tip  34  permits manipulation of electrical wires. Inside the jaws are electrical coils (not shown) which are connected to appropriate circuitry in the housing for detecting electrical properties of a conductor placed within the clamp jaws. These coils and circuitry are conventional. The internal circuitry displays the selected parameter on the displays.  
         [0015]     A trigger  36  extends from the side of the housing  12  and is attached to the movable jaw. Preferably, as shown in  FIG. 2 , the trigger  36  is integrally formed with the movable jaw  26 . Depressing the trigger  36  toward the housing causes the movable jaw  26  to pivot away from the fixed jaw  28  and move to the open position, as shown in  FIG. 2 . Once the clamp jaw  26  is in the open position, the multimeter  10  can be positioned to pass the jaws  26 ,  28  around a conductor. This is illustrated schematically in  FIG. 2  where the conductor C is shown in two different positions; one just as it clears the opening between the jaws  26 ,  28  and one where it is seated against the top of the housing  12 . When the trigger  36  is released, movable clamp jaw  26  closes around the conductor C, as shown in  FIG. 1 , to permit a current measurement to be taken. The clamp jaws  26 ,  28  can be designed to accommodate a number of different conductor diameters. Although conductor C is shown contacting the inner surfaces  32  of jaws  26 ,  28  in  FIG. 1 , it is not necessary that they do so. However, in order to measure the current carried by a conductor, the clamp jaws  26 ,  28  must surround the conductor as shown in  FIG. 1 .  
         [0016]     A protective flap  38  is included on the bottom face  40  of the housing, as shown in  FIGS. 3 and 4 . Flap  38  is connected to the housing by a hinge  42 . A second digital display  44  is mounted in the housing on the bottom face. When the flap  38  is closed it protects the second display  44 . Two flexible beads  46  engage indentations  48  in the bottom face  40  to frictionally retain the flap in the closed position.  
         [0017]     Second display  44  lies in a plane approximately perpendicular to the plane defined by the clamp jaws and to the plane defined by the front face  16  of the housing. Accordingly, the second display  44  is generally perpendicular to the plane of the first display  14 . This arrangement of first display  14  and second display  44  permits a measurement to be read even when the clamp meter is forced into an awkward or difficult viewing position by the necessary placement of the clamp jaws. If the position of the clamp meter affords the user a decent view of the first display  14 , the flap  38  may remain closed. However, if the location of a conductor requires placement of the clamp meter housing in a position where the first display  14  is obscured or otherwise unavailable for viewing, the flap  38  may be opened to expose the second display  44 . Second display  44  provides a readout of the same data as in first display  14 . Thus, regardless of the orientation of the clamp meter housing, one of the displays will be readily visually accessible.  
         [0018]     A second embodiment of a multimeter  50  according to the present invention is shown in  FIGS. 5 and 6 . Multimeter  50  has a housing  52  with clamp jaws  54  and  56  extending from one end. The jaws  54 ,  56  are the same as jaws  26 ,  28 . The knob, jacks and buttons of the housing  52  are the same as those described above. Housing  52  itself is similar to housing  12  except that instead of two displays lying in perpendicular planes, multimeter  50  has a single pivoting display  58  connected to the housing  52  by a hinge  60 . Preferably the display  58  when in a retracted position is disposed in a recess  62  of the front face  64  of the housing  52 . The display  58  is shown in  FIG. 5  in a retracted position so that the display defines a plane that is substantially parallel to the plane defined by the clamp arms  54 ,  56 . In  FIG. 6 , the display  58  is shown in a fully raised position such that the plane defined by the display is substantially perpendicular to the clamp arm plane. A depression  66  is provided in the housing to permit a user&#39;s thumb or finger to access the display  58  so that it can be raised out of the recess  62 .  
         [0019]     A flexible electrical connection to the display is provided. The electrical connection is arranged to accommodate the pivoting motion of the display. A flexible polyester film with printed electrodes thereon would be suitable for this purpose.  
         [0020]     Preferably, hinge  60  has sufficient friction or stiffness to hold or retain the display  58  in a multitude of positions relative to the clamp plane, from fully upright and perpendicular to the clamp plane to fully recessed and parallel to the clamp plane and every angle in between. In other words, the hinge is loose enough to permit a user to tilt the display from one angle to another but stiff enough to prevent the display from moving out of position by gravity or normal movement of the multimeter. As shown in  FIG. 6 , the display  58  may also include protruding detents  68  on both sides of the display. The housing recess  62  includes complementary notches (not shown) that are engaged by the detents to frictionally retain the display in the recess.  
         [0021]     Alternatively, a torsion spring (not shown) could be used to bias the display  58  to an upright or raised position as shown in  FIG. 6 . In that case a catch or latch would be formed on or in the housing. The latch could be released by a trigger mechanism on the side of the housing. When engaged the latch would hold the display in the retracted position against the biasing force of the torsion spring. A further alternate would be to hold the display in an upright position by means of a releasable support arm. In addition, although a piano-type hinge is shown, the hinge could have other configurations and the display may be pivotally attached to the housing in any number of ways known to those skilled in the art. Yet another alternate would be to pivotally attach the display  58  to the bottom face of the housing.  
         [0022]     Although the invention has been described with reference to certain preferred embodiments, the invention is not meant to be limited to those preferred embodiments. Alterations to the preferred embodiments described are possible without departing from the spirit of the invention. Rather the scope of the invention is defined by reference to the appended claims.