High performance current shunt

• US 5,214,407 A
• Filed: 11/06/1991
• Issued: 05/25/1993
• Est. Priority Date: 11/06/1991
• Status: Expired due to Term

• Current Assignee: Agilent Technologies, Inc.
• Original Assignee: Hewlett-Packard Company (HP Inc.)
• Inventors: Pickel, William H., Myers, Richard S., Peck, Robert D., Cudworth, Alan W., McKim, James B. Jr.
• Primary Examiner(s): Lateef, Marvin M.
• Application Number:
  US07/788,404
• Time in Patent Office: 566 Days
• Field of Search: 338/49, 338/120, 338/195, 324/126
• US Class Current: 338/49
• CPC Class Codes: G01R 1/203 Resistors used for electric measuring, e.g. decade resistors standards, resistors for comparators, series resistors, shunts resistors in general H01C; microwave or radiowave terminations H01P1/26; coupling devices H01R
• CPC Class Codes: H01C 17/24 by removing or adding resistive material H01C17/23, H01C17/232, H01C17/235 take precedence
• CPC Class Codes: H01C 3/00 Non-adjustable metal resistors made of wire or ribbon, e.g. coiled, woven or formed as grids

Abstract

A current shunt for converting a current to a voltage. The current shunt of the invention is made from a conductive material such as a high performance resistance alloy in sheet form which is sheared, punched, and bent to produce a highly stable current shunt with respect to time and temperature. Contact pins of current and potential connections are welded to the material using a fusion welding process, and techniques are also provided for isolating the potential contacts from the current contacts so as to improve stability. Trimming slits of the type used for thin film or foil resistors are also extended to bulk materials in accordance with the invention such that highly accurate resistances may be obtained. An integral heat sink and strain relief mechanism is also provided so as to minimize the adverse effects of temperature on the resistance of the material. The resulting current shunt has an extremely stable resistance value with respect to time and temperature at a minimal cost.

Claims

1. A high-performance current shunt for converting a current applied thereto into a potential which is precisely proportional to the current flow through said current shunt, the proportionality between said current and said potential being substantially independent of changes in ambient temperature and the magnitude of current flow through said current shunt, said current shunt comprising:

first and second current connections responsive to said input current;

first and second potential connections for providing said output potential, said first and second potential connections being spaced so as to define an effective resistance value for said current shunt; and

a resistive element formed of a sheet of material having a known temperature coefficient of resistance, said resistive element having said current connections and potential connections disposed thereon so as to define a current path between said first and second current connections whereby a proportion of a potential drop between said first and second current connections may be sensed at said first and second potential connections, said resistive element further including a first slit between said first and second current connections for diverting the current flow in said current path around said first slit so as to control the location of heat dissipation and to thereby prevent localized heating of said resistive element and the resultant temperature induced changes in said effective resistance and in the sensed proportion of said potential drop between said first and second current connections in said current path, and a second slit for electrically isolating said first and second potential connections from that portion of said current path between said first and second current connections at which said proportion of said potential drop is sensed, thereby eliminating variation in said temperature coefficient of resistance of said material in said current path as a result of material impurities introduced by connection of said first and second potential connections to said resistive element.

2. A current shunt as in claim 1, wherein said first and second current and potential connections are fusion welded to respective ends of said resistive element.

3. A current shunt as in claim 1, wherein said resistive element is a composition comprising by weight approximately 72% nickel, 20% chromium, 3% aluminum, 4% manganese, and 1% silicon.

4. A current shunt as in claim 1, wherein said resistive element further comprises an integral heat sink into which the current flow is diverted by said first slit for purposes of heat dissipation via said integral heat sink.

5. A current shunt as in claim 4, wherein said resistive element further comprises means for relieving strain caused by thermal expansion of said material.

6. A current shunt as in claim 5, wherein said strain relieving means comprises a third slit in said integral heat sink which extends in a direction substantially perpendicular to an axis through mounting points of said resistive element.

7. A current shunt as in claim 5, wherein said strain relieving means comprises at least one bend in a transverse direction of said resistive element between mounting points of said resistive element.

8. A current shunt as in claim 1, wherein said first slit has a size adjustable in accordance with the error tolerance of said resistive element.

9. A current shunt as in claim 1, wherein said resistive element has a thickness such that it is self-supporting.

10. A current shunt as in claim 9, wherein said resistive element has a thickness of approximately 0.020 inch.