Abstract:
A method and apparatus for achieving electrical conductivity that can, for instance, obviate the need for the use of two hands to make a measurement of electrical properties across two contacts that do not lend themselves to the acceptance of clip-on leads, or across contacts that are located where access is difficult. Probes constructed partially with ferromagnetic materials and small permanent magnets provide the connectivity and conductivity of the present invention.

Description:
[0001]     This application claims priority from provisional application 60/581,614 filed Jun. 21, 2004 
     
    
     FIELD OF THE INVENTION  
       [0002]     The present invention pertains to the field of electronics, specifically to the fields of electronic measurement, calibration, and instrumentation.  
       BACKGROUND OF THE INVENTION  
       [0003]     All uses of electricity eventually require voltage measurements. Residential and commercial wiring installations, air conditioning systems, vehicle electrical systems, computer repair, and monitoring of laboratory experiments all require voltage measurements. One type of voltage probe common in the industry is a set of two spikes, each having an insulated holding portion and a pointed end that is forced into contact with an electrical conductor by an operator gripping the insulated portion. The spikes typically conduct current through flexible insulated wire leads attached to the ends of the spikes opposite the points. The leads are attached to the measurement device, typically a meter that senses the voltage drop between the two conductors in contact with the two spike points. Of the many other available probes, some take the shape of alligator clips, L-shaped clips, or hook-shaped clips.  
         [0004]     Because a measurement with spike probes generally requires two hands, holding or adjusting the meter or holding another tool while simultaneously making a measurement, is almost impossible, particularly where the contacts are not easily accessible. Also, alligator clips and other clip-on probes are only capable of attachment to contacts that have features small enough to be gripped by the clips. Contacts such as the heads of countersunk or round, oval, or pan-head screws, for example, are extremely difficult to grip with clip-on probes. For such contacts, hand-held spike probes are used.  
       SUMMARY OF THE INVENTION  
       [0005]     By interposing at least one magnet between the probe or the lead of a measurement device, and a contact at which the measurement of an electrical property is desired, the present invention overcomes most of the problems of typical probes. In one embodiment of the present invention, the inventor discloses a method and apparatus for making electrically conductive, nonmechanical connections with ferromagnetic contacts. Such connections facilitate the measurement and monitoring of current, voltage, power, impedance, resistance, and other electrical properties. The electrical connections of the present invention can also be used with circuit tracing devices such as the commonly understood Fox and Hound tracer. The electrical connections of the present invention can also be used as charging devices and jumpers. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0006]      FIG. 1  is an exploded schematic of one embodiment of the present invention.  
         [0007]      FIG. 2  is a cross sectional view of one embodiment of a permanent magnet used in one embodiment of the present invention.  
         [0008]      FIG. 3  is a cross sectional view of an alternate embodiment of the attachment of a permanent magnet to a lead cable.  
         [0009]      FIG. 4  is a cross sectional view of an alternate embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0010]      FIG. 1  is an exploded view of one embodiment of the present invention, spike probe  100  that consists of the probe housing  16  and the lead  19 . When assembled, probe  100  conducts current from a magnetizable contact  18  to a meter (not shown) to which connector  10  is attached. An operator holds the nonconductive surface of probe housing  16  in or to which the electrically conducting tip  17  is embedded, molded, threaded, or otherwise attached. The operator presses tip  17  against contact  18 , and current flows through tip  17 , permanent magnet  13 , the screw  15  that attaches magnet  13  to tip  17 , and solder ball or wire crimp  14  on one end of lead cable  12 . Lead cable  12  is insulated with conformal coating or sleeve  11 . The end of lead cable  12  opposite the end attached to magnet  13  terminates in connector  10  that makes ultimate contact with a meter conductor (not shown). An identical probe can be used on a second contact, identical or similar to  18 , to measure the voltage differential, impedance, resistance, or current between the two contacts.  
         [0011]     The novel feature of the present invention that is illustrated in  FIG. 1  is the electrically conducting, magnetic connection made between the two permanent magnets  13  inside the probe housing  16 . That magnetic connection enables simultaneous and concurrent magnetic physical connectivity between contact  18  and tip  17  and electrical continuity between contact  18  and a conductor on a sampling device such as a meter that measures or monitors electrical or thermal properties.  
         [0012]      FIG. 2  shows the internal construction of one embodiment of magnet  13  that permits attachment, with screw  15 , of one magnet to a tapped hole in probe tip  17  and attachment, with solder, swaging, or press fit, of an identical or similar magnet  13  to one end  14  of lead cable  12 . During assembly the end of cable  12  opposite connector  10  is led through the small diameter center hole  20  and into the larger diameter center hole  21  of a magnet  13 . The cable end is then soldered, swaged, press fit, or otherwise tightly attached inside the cavity formed by center hole  21  so that it does not protrude from the hole  21  at the end of the magnet opposite hole  20 . The lead insulation  11  is then snugged against the hole  20  end of magnet  13 , and the connector  10  end of the lead made up for completion of lead  19 .  
         [0013]     The magnets can be any of the small rare-earth permanent magnets such as the neodymium iron boron or samarium cobalt magnets that can be sintered in various shapes and purchased from Magnetic Component Engineering, Inc. of Torrance, Calif. The two magnets are attached in orientations that assure that ends of opposite polarity contact each other when the magnet end of lead  19  is inserted into probe housing  16 . The magnets of the present invention could also be electromagnets, which, while requiring power input, generally provide more holding power and longevity than permanent magnets.  
         [0014]     The magnetic attachment feature illustrated in  FIG. 1  permits probes of all types to be easily interchanged with the spike probe shown. Clips and other types of probes can be attached to lead  19  by detaching housing  16  and replacing it with housings holding various other types of probes and a properly oriented magnet. Clips, threaded tips, or other types of mechanical (nonmagnetic) lead attachments can augment the magnetic connection depicted in  FIG. 1 . Also, in monitoring two contacts, one or both of the probes can be magnetic.  
         [0015]     The probe construction discussed above is one of many embodiments of the present invention that can be used where contact  18  is either magnetizable or nonmagnetizable. Where a contact is nonmagnetizable, a mechanical attachment type of tip or operator force is required to maintain continuity. Where a contact is magnetizable, the present invention&#39;s preferred embodiment dispenses with the need for probe housing  16  and probe tip  17  or other types of mechanical attachment such as clips. Electrical continuity required for measurements of electrical properties at a contact  18  can be established through the magnetic attachment to that contact of the magnet  13  that is integral to lead  19 . For example, if the contact  18  of  FIG. 1  were made of or coated with a ferrous material, an operator could attach lead  19  directly to it without the need for probe housing  16  or tip  17 . In circumstances where direct attachment is made difficult by the flexible nature of lead  19 , for example where the contact to be monitored is recessed in a deep receptacle, tube, or box, a loose spike probe can be used to hold and guide the magnet  13  into position on contact  18  and then removed. The same guidance could be achieved with the use of a lightweight straw slipped over the magnet end of a lead  19 . The straw would add temporary stiffness to the lead sufficient for the user to guide the magnet into position on a deeply recessed contact.  
         [0016]     Another embodiment of the present invention is an adapter constructed of a flexible or rigid connector that has a magnet attached on one end and an industry-standard male or female banana plug on the other end. With the adapter&#39;s magnet properly oriented, it could be attached to the magnet  13  on the end of the lead  19  of  FIG. 1 . The banana plug could then be used for connection of various contacts and probes that utilize the industry standard banana configuration. Adapters using other connector types such as BNC could be constructed within the scope of the present invention.  
         [0017]     Another embodiment of the present invention is a conducting lead made of a wire having magnets attached to both ends. Such a device can be used for establishing electrical continuity between two contacts capable of being magnetized. Such a device is sometimes called a “jumper” or a “shunt.” Where there is a need for joining multiple contacts into a common shunt, the present invention can take the form of a multi-armed jumper with a magnet at the end of each arm and all arms electrically joined.  
         [0018]     Another embodiment of the present invention uses magnetic connections to charge devices such as capacitors and batteries.  
         [0019]     In any of the embodiments of the present invention electrical continuity can be achieved by contact between two magnets, between one magnet and a conductive means of attachment of a second magnet, between the conductive means of attachment of two magnets, between one magnet and a conductive contact, or between the conductive means of attachment of one magnet and a conductive contact. For example, when probe housing  16  and lead  19  of  FIG. 1  are joined to form probe  100 , electrical continuity can be achieved with contact between the two magnets  13 , or continuity can be achieved with contact between the conductive end  14  of lead cable  12  and the head of screw  15  or the magnet  13  attached to tip  17 . Magnets  13  of  FIG. 1  can therefore perform as part of an electrical circuit, or can perform as mere conductor holding means.  
         [0020]     In the latter case, for breakdown protection of a magnet  13 , or for minimization of extraneous measurement effects, it may be desirable to isolate the magnet or magnets  13  from the electrical circuit created between the measurement device and a contact being monitored. One embodiment of the present invention utilizes a nonconductive conformal coating dipped, sprayed, painted, electroplated, molded, or otherwise applied to part or all of the exterior surface of magnet  13 . The coating is sufficiently thin such that the magnetic strength of magnet  13  is not significantly diminished.  
         [0021]     Alternatively, if electrical isolation of magnet  13  is necessary, it can be achieved by mechanical design. For example, when probe housing  16  and lead  19  of  FIG. 1  are joined to form probe  100 , electrical continuity can be achieved with contact between the conductive end  14  of lead cable  12  and the head of screw  15  without involving magnets  13  in the circuit. Such isolation can be achieved by (1) proper design clearance or insulation between the threads of screw  15  and the inner diameter of an annular magnet  13 , (2) a nonconductive washer between magnet  13  and the underside of the head of screw  15 , (3) a nonconductive washer between magnet  13  and tip  17 , (4) proper design clearance or insulation between the portion of cable  12  that penetrates annular magnet  13  and the inner diameter of an annular magnet  13 , and (5) proper design clearance or insulation between magnet  13  and the cable end  14  that slightly protrudes from or is flush with the end of magnet  13  on lead  19 .  
         [0022]     For minimization of arcing that may occur between a contact and a magnetic probe when the probe is positioned in initial proximity to a contact, magnets  13  can be constructed in annular shapes fitted with centrally-mounted miniature spring-loaded needle probes that in their relaxed positions protrude slightly from the face of the magnet that is put into proximity with a contact to be monitored. In operation, such a needle probe is pushed against the contact, establishes electrical continuity with minimal arcing, and, when the magnet is fully seated on or around the contact, is pushed back into a position slightly protruding from or flush with the face of the magnet adjacent to the contact. In the event of minute debris particles on the face of a magnet or a contact, the needle probe of such a configuration will provide the best possible electrical contact.  
         [0023]     Some magnets may add resistance, or, in the case of an electromagnet, inductance, to an electrical circuit. Any such effects can be predicted or measured, and can be calibrated out of a measurement. Alternatively, such effects can be negated with the use of fixed or adjustable current, resistance, or voltage offsets built into the measuring device.  
         [0024]     One embodiment of the present invention includes means for attachment of magnets  13  such that the magnets are replaceable in the field. Such convenience can be realized with, for example, the use of screws  15  instead of solder or crimp joints  14 .  
         [0025]     In various embodiments of the present invention where mating magnets are used, for example the lead  19  and probe housing  16  of probe  100 , the two magnets in one model, say the red model, can be installed so that the North polarity end of one particular magnet, say magnet  13  in probe housing  16 , faces the South polarity end of the other magnet, say magnet  13  in the lead  19 . The two magnets in another model, say the black model, can be installed with polarities arranged opposite from those of the red model. Such a construction would prevent a red lead  19  from being mated with a black probe housing  16 , and vice versa.  
         [0026]     One embodiment of the present invention enables power leads or charging devices to be attached to terminals without the necessity for mechanical connections.  
         [0027]      FIG. 3  shows one method of attachment of magnet  13  to one end of a lead  19 . Annular magnet  13  is fixed to an end of lead  19  by threading female threaded post  31  onto male threaded post  33  that is crimped, soldered, or otherwise conductively attached to conductive wire lead  12  coated with insulation  11 . Post  31  is tightened with drive socket or slot  30 .  
         [0028]      FIG. 4  shows an alternate embodiment  400  of the present invention. Permanent magnet  13 , attached to wire lead  12  coated with insulation  11  is made integral with flexible stress relief feature  36  in a molding or press fit process. The concave front face of magnet  13  seats with magnetic force onto the convex rear face of magnetizable tip  17 . Tubular housing  44  slides along lead insulation  11  and is capable of a snug fit between its funnel-shaped front end and the mating funnel-shaped stress relief feature  36 . The snug fit enables an operator to use housing  44  as a guide or handle to position tip  17  on a contact from which a measurement is desired. When magnetic contact is made, the operator can pull housing  44  away from stress relief feature  36  and slide it away from the contact and tip area. This prevents the weight of the housing from imposing a torque on tip  17  that could force it off of the contact.  
         [0029]     It will be apparent to those with ordinary skill in the relevant art having the benefit of this disclosure that the present invention provides a method and apparatus for achieving electrical continuity. It is understood that the forms of the invention shown and described in the detailed description and the drawings are to be taken merely as presently preferred examples and that the invention is limited only by the language of the claims. While the present invention has been described in terms of one preferred embodiment and various variations thereof, it will be apparent to those skilled in the art that form and detail modifications may be made to those embodiments without departing from the spirit or scope of the invention.