Single tip Kelvin probe

• US 6,384,614 B1
• Filed: 02/05/2000
• Issued: 05/07/2002
• Est. Priority Date: 02/05/2000
• Status: Expired due to Fees

• Current Assignee: Fluke Corporation (Fortive Corp.)
• Original Assignee: Fluke Corporation (Fortive Corp.)
• Inventors: Hager, Edward J., Harmon, Rondal K. Jr.
• Primary Examiner(s): Metjahic, Safet
• Assistant Examiner(s): LEROUX, ETIENNE PIERRE
• Application Number:
  US09/497,415
• Time in Patent Office: 822 Days
• Field of Search: 324/754, 324/72.5, 324/758, 439/82, 439/264, 439/482, 439/736, 335/03, 335/59, 338/32
• US Class Current: 324/754.05
• CPC Class Codes: G01R 1/06738 related to tip portion
• CPC Class Codes: G01R 1/06788 Hand-held or hand-manipulated probes, e.g. for oscilloscopes or for portable test instruments end pieces terminating in a probe H01R11/18

Abstract

A Kelvin probe system is described for measuring resistance between two locations on an electrical device, by the use of two probe assemblies that each includes two wires, wherein each probe assembly is of simplified construction, easier to use, and more reliable. Each probe assembly (110, 112) includes a single point probe tip (12) with a pointed proximal end (102) for engaging a device contact and with a distal end (106). A cable (110) with voltage and current conductors (114, 116) has distal ends (120, 122) connected to contacts of a connector, and proximal ends (130, 132) each connected to the distal end of the probe tip. Although a large current passes through the current conductor (116) and through the length of the probe tip, the resistance-caused voltage drop across the probe tip is very small and therefore does not significantly affect accuracy of a resistance measurement.

Claims

1. Kelvin probe apparatus comprising:

a manually-moveable dielectric handle;

a rigid electrically conductive probe tip fixed to said handle, said probe tip having a single point proximal end and having a distal end with a bore;

a connector with first and second electrically independent connector terminals;

a cable with first and second conductors with said cable extending from said handle, said conductors each having a conductor distal end connected to a different one of said connector terminals, and said conductors each having a conductor proximal end;

at least one of said conductor proximal ends lies in said bore and said conductor proximal ends are electrically connected together.

2. The apparatus described in claim 1 including:

a Kelvin resistance measuring circuit that includes first and second pairs of circuit terminals with said first pair of circuit terminals having current and voltage circuit terminals that are connectable to said connector terminals, and with said second pair of circuit terminals having current and voltage circuit terminals;

said circuit having a current source of constant voltage connected between said circuit current terminals and said circuit having a subcircuit that indicates voltage and that is connected between said circuit voltage terminals;

a second Kelvin probe device which has a handle device, connector device, single point probe tip device, and cable device that are substantially identical to said handle, connector, probe tip and cable, with said connector device connected to said second set of circuit terminals.

3. The Kelvin probe apparatus describe in claim 1 wherein:

said conductor proximal ends are in contact with each other at said probe tip and are out of contact with each other at a separation point that is spaced from said probe tip;

said probe tip proximal end has a contact point, and the distance that current travels between said contact point and each of connector terminals is at least 0.5 meters;

the distance that current travels between said contact point and said separation point is less than 10% of said distance that current travels between said probe tip contact point and said current conductor distal end.

4. The apparatus described in claim 1 wherein:

said probe tip comprises a single piece of metal with a pointed proximal end for engaging a first contact location of a pair of contact locations of an electrical device whose resistance between said location is to be measured;

said cable comprises a coaxial cable having inner and outer conductors forming said first and second conductors, with said conductor proximal ends both lying in said bore and with said probe tip distal end crimped to said conductor proximal ends.

5. A Kelvin probe system for measuring resistance or impedance between a pair of location on an electrical device which includes a Kelvin resistance measuring circuit device that includes first voltage and current circuit terminals and second voltage and current circuit terminals, and a resistance-measuring subcircuit connected to said circuit terminals, said circuit device including a source that flows a current between said first and second current terminals and through the electrical device, comprising:

first and second Kelvin probe assemblies including a first Kelvin probe assembly engaged with said first circuit terminals, and a second Kelvin probe assembly engaged with said second circuit terminals;

said first Kelvin probe assembly including an elongated voltage conductor and an elongated current conductor with each conductor having a distal end connected to one of said first voltage and current circuit terminals, respectively, a handle which can be manually grasped, and a rigid probe tip fixed to said handle, with said probe tip having a proximal end for engaging one of said locations on the electrical device and having a distal location spaced from said proximal end;

said voltage and current conductors being arranged with said current conductor having a proximal end connected to said probe tip distal location to establish a current flow path of predetermined length that extends from said probe tip proximal end and through at least part of said probe tip and through said current conductor to said first current circuit terminal and along which flows all current passing through said current conductor, and with said voltage conductor having a proximal end connected to said current flow path, said voltage conductor separating from connection to said current flow path at a location that is spaced from said probe tip proximal end by no more than 10% of said length of said current flow path.

6. The Kelvin probe system described in claim 5, wherein:

said probe tip has a bore extending into said probe tip from said distal location;

said proximal ends of said voltage and current conductors each extends into said bore of said probe tip and is connected to said probe tip thereat.

7. The Kelvin probe described in claim 5 wherein:

said probe tip has a bore extending into said probe tip of said distal location;

said Kelvin probe system includes a cable that includes said voltage and current conductors, with said proximal ends of said conductors wrapped one about the other and with the wrapped ends projecting into said bore and with said probe tip being crimped around said wrapped ends.

8. The Kelvin probe system described in claim 5 wherein:

said probe tip is rigid and said voltage and current conductors are each flexible and each has a length of at least 0.5 meter, and the distance between said probe tip proximal location and voltage conductor proximal end is no more than 10% of said voltage conductor length.

9. A Kelvin probe for use with another similar probe device and a Kelvin resistance impedance measuring circuit to measure resistance or impedance comprising:

a cable that includes two conductors that each have proximal and distal ends;

a handle (160);

a rigid probe tip (12) fixed said handle, said probe tip having a proximal end that is pointed, and said probe tip having a distal end that has a bore (162);

said proximal ends of said two conductors both lying in said bore of said probe tip and fixed thereat to said probe tip.

10. A Kelvin probe comprising:

a cable that includes two conductors that each has proximal and distal ends;

a handle;

a rigid probe tip fixed to said handle, said probe tip having a proximal end that is pointed, and said probe tip having a distal end that has a bore;

the proximal end of a first of said conductors lying in said bore and the proximal end of the second of said conductors being in electrical engagement with said first conductor immediately outside said bore.

11. A Kelvin probe comprising:

a cable that includes two conductors that each has proximal and distal ends;

a handle;

a rigid probe tip fixed to said handle, said probe tip having a proximal end that is pointed, and said probe tip having a distal end that has a bore with a distal end;

the proximal end of a first of said conductors lying in said bore and the proximal end of the second of said conductors being connected to said probe tip at a location closer to said probe tip than said bore.