US3719914A

US3719914A - Resistance standard

Info

Publication number: US3719914A
Application number: US00213940A
Authority: US
Inventors: C Scharle
Original assignee: BIDDLE CO J
Current assignee: BIDDLE CO J; BIDDLE J CO US
Priority date: 1971-12-30
Filing date: 1971-12-30
Publication date: 1973-03-06
Anticipated expiration: 1990-03-06

Abstract

A zig-zag pattern is formed from a sheet of resistance material, such as manganin or a nickel chrome alloy, preferably by providing parallel slots alternately extending from opposite edges of the sheet and evenly spaced from one another and the patterned sheet is folded back upon itself and separated by sheets of insulating material so that the patterned areas of the opposed folded portions are superimposed upon one another and current flowing through the resistance pattern will be flowing in opposite directions on opposite sides of the insulating material, thus cancelling out inductive effects and providing a resistance standard with an essentially pure resistance characteristic.

Description

United States Patent [191 Scharle 1 RESISTANCE STANDARD [75] Inventor: Carl R. Scharle, Glenside, Pa.

[58] Field of Search ..338/61, 49; 219/538, 543, 544, 219/548, 549, 553; 174/32 [56] References Cited UNITED STATES PATENTS 2,487,695 11/1949 Cloud ..338/6l 3,296,415 1/1967 Eisler ..2 19/549 X March 6, 1973 Primary Examiner-C. L. Albritton Attorney-John C. Dorfman [57] ABSTRACT A zig-zag pattern is formed from a sheet of resistance material, such as manganin or a nickel chrome alloy, preferably by providing parallel slots alternately extending from opposite edges of the sheet and evenly spaced from one another and the patterned sheet is folded back upon itself and separated by sheets of insulating material so that the patterned areas of the opposed folded portions are superimposed upon one another and current flowing through the resistance pattern will be flowing in opposite directions on opposite sides of the insulating material, thus cancelling out inductive effects and providing a resistance standard with an essentially pure resistance characteristic.

14 Claims, 5 Drawing Figures PATENTEUHAR 6l975 3,719,914

FIG. 2. I6

. standard.

RESISTANCE STANDARD This invention relates to a resistance standard, and more specifically, relates to a standard resistance element which has a novel construction and which is particularly useful as a standard shunt.

In the prior art commercial standard low resistance shunts have offered some serious problems from the standpoint of stability and unwanted inductive effects. The present invention is directed to a novel structure for a resistance standard wherein a current path of sufficiently large cross-section is provided to eliminate unwanted heating effects, particularly by providing large flat radiating surfaces, while at the same time providing a construction which is essentially non-inductive. The novel structure provides a highly reliable resistance standard capable of use over a long period of time and producing essentially constant response with a minimum of unwanted inductive effect. Nevertheless, the structure employs a simple construction which lends itself to ease in manufacture and adjustment without sacrificing accuracy or stability.

More specifically, the present invention concerns a resistance standard employing a standard resistance element, connected at each end to a current terminal and to a potential terminal, connections on the resistance standard to the potential terminals being inside of the high current path defined between connections to the current terminals. The improvement comprises a standard resistance element formed from a sheet of resistance material, such as manganin, or a nickel chrome alloy in a symmetrical pattern and folded and the halves secured together face-to-face with sheet insulation or coating of very high resistivity interposed such that the patterns and theelectrically connected symmetrical halves fit close together and the current flowing in opposite directions in opposed parts of the pattern tends to cancel the inductive effect in each part of the pattern and therefore throughout the resistance Preferably a symmetrical zig-zag pattern is formed in a rectangular sheet of resistance material by making slots across the sheet, alternating from opposite sides with the slots parallel to one another and the spacing between the adjacent slots uniform and so that the slots from each side terminate a'distance from the other edge approximately equal to the spacing between the slots. Also, preferably laces are woven in and out through the slots to hold the folded halves of the standard resistance close together. The opposite edges through which the slots extend are preferably engaged in edge engaging insulating supports; the insulating supports, in turn, are preferably separated by spacer columns located on each side of the standard resistance to provide fixed separation of said insulating supports. The current and potential terminals may be supported on one of said supports.

For a better understanding of the present invention, reference is made to the following figures in which FIG. 1 shows a preferred embodiment of the present invention viewed from one side, with part of the structure broken away for clarity;

FIG. 2 is a plan view from above showing the structure of FIG. 1, again with part of the structure broken away for clarity;

FIG. 3 is a further enlarged sectional view taken along line 3-3 of FIG. 1, further with some of the structure which would otherwise be shown in elevation broken away for clarity and to show structural details;

FIG. 4 is a partial sectional view taken along line 4 4 of FIG. 1 and on a scale similar to that of FIG. 3; and

FIG. 5 is a perspective constructional drawing showing how parts of the structure of the preferred embodiment of the other drawings are assembled.

Referring to the drawings, a preferred embodiment of a low resistance standard shunt in accordance with the present invention is illustrated. Looking first at FIGS. 1 and 2, a standard resistance element generally designated 10 is formed of a patterned and folded sheet of manganin, a nickel chrome alloy or other resistance material, the two symmetrical halves of which are separated by a thin insulating layer, preferably a sheet of insulating material 12, such as Mylar, Teflon or Kapton or mica. Alternatively a coating of very high resistivity, such as an appropriate varnish, silicone or epoxy coating, may be applied to at least one of the adjacent surfaces of the folded sheet. The opposite edges of the composite resistance element structure are engagedin opposed triangular grooves 14a and 16a of insulating supports 14 and 16. The insulating supports are, in turn, separated by eight identical spacer columns 18. As shown in FIG. 3, the spacer columns 18 and insulating supports 14 and 16 may be held together by screws 20, or any other suitable means, preferably in the positions shown. Also supported on insulating support 16, which serves as a standing base in the embodiment shown, are a pair of identical potential terminals 22 and a pair of identical current terminals 24. Conductors 26 to the current terminals 24 are shown connected toward the ends of the resistance element, using low resistance insulated wires which are kept close together until connected to their respective terminals. The insulated potential leads 28 are twisted together and connected to points inside the high current path defined between the connections to the current terminals. The potential leads need not be of as heavy conductors as the current leads.

In constructing the resistance standard of the present invention, preferably an elongated rectangle or strip of manganin a nickel chrome alloy or other sheet resistance material is used and is fabricated by punching, or slotting, to provide slots at evenly spaced terminals, alternately extending from opposite ones of the long edges of the strip to provide a current path of essentially uniform cross-sections along its length-The slots typically may extend approximately to a distance from the opposite edge equal to the distance between slots. If the slots are parallel and perpendicular to the edges and the spacing between the slots is uniform, as is the slot length distribution when the slotted strip is folded in half, as shown in FIG. 5, along one of the slots, the opposed halves should exactly overlie one another, as suming the slot and spacing dimensions to be standard. Before the sheet 10 is completely folded together, a sheet of insulating material 12 is inserted between the two halves, preferably so as to completely separate the two symmetrical halves from one another. Neverthesides of the thin sheet to cancel each other out, leaving at most, a negligible net inductance effect. The insulating material between the two halves of the resistance element may then be slit at the slots in order to permit the passage of waxed laces 30. Here two such laces are shown, but in other embodiments one or three or more might be used. The laces are woven in one slot and out the next throughout the length of the resistance element, preferably using a pair of laces at each level woven opposite to one another and tied together at their ends so that the lace will lie outside both sides of each opposed leg and cross through each slot, as shown in FIG. 4, thereby pulling the legs of the resistance element tightly down against the insulating material 12. The laces 30 provide means to hold intermediate portions of the resistance elements close together and into the insulation. Consequently the spacing between the opposed resistance legs at every location is determined by the thickness of the sheet of insulation 12. The slots 14a and 16a in the insulating supports 14 and 16 may be triangular grooves, as shown in FIG. 3, in order to further hold the halves of the resistance element close together at its opposed edges by a wedging action.

In a preferred embodiment of the present invention the resistance element was 0.2 ohm, rated at 5 amperes and 5 watts and designed for a voltage drop of 1.0 volt. The sheet manganin was .022 inch; the slot width was .062 inch; the strip width between the slots was .688 inch and the sheet was 6 inches wide with 42 strips formed by 40 slots. With this preferred embodiment the phase angle was observed to be $0.2 milliradian at a frequency of 60 Hertz and +1.4 milliradians at 400 Hertz.

The insulating supports were formed of phenolic material and the top insulating support had a dimension of 16 X 1441 X binches, while the bottom support, or base, had a dimension of 19% 4%X rinches. The spacer columns, of which there were eight in the positions shown were .344 inch diameter Delrin rods, tapped to receive the screws as illustrated and 5-9/16 inches long to allow enough room for the edge-engaging grooves to perform their function. The grooves in the insulating supports were 60 V-grooves.

The insulation between the folded halves of resistance material was provided by .003 inch Mylar tape and waxed cord laces were placed 2 inches from the top and 2 inches from the bottom of the resistance element to keep the halves in close contact. Current leads were made with No. 12 solid copper insulated with Teflon and potential leads were made with No. 14 solid copper insulated with Teflon and twisted together. The opposed potential points were carefully selected in connection with standard practice in the art.

It will be clear to those skilled in the art that many modifications and changes of the structure within the scope of the present invention is defined by the appended claims are possible. All such modifications are intended to be within the scope and spirit of the present invention.

lclaim:

1. In a resistance standard employing a standard resistance element connected at each end to a current terminal and to a potential terminal, connections on the resistance standard to the potential terminals being inside the high current paths defined between connectrons to the current terminals, the improvements comprising a standard resistance element formed from a sheet of resistance material cut in a symmetrical pattern and folded about its line of symmetry defining electrically connected parts and secured together face-to-face with a thin insulating layer interposed such that the patterns in said parts are super-imposed on one another and the current flowing in opposite directions in said opposed parts of the pattern tends to cancel the inductive effect in each portion of the pattern and there-fore throughout the resistance standard.

2. The resistance standard of claim 1 in which the symmetrical pattern is a zig-zag pattern formed in a rectangular sheet of resistance material by making slots across the sheet alternating from opposite ones of the long edges.

3. The resistance standard of claim 2 in which the slots are parallel to one another, the spacing between adjacent slots is uniform and the slots terminate a distance from an edge approximately equal to the spacing between the slots.

4. The resistance standard of claim 3 in which laces are woven in and out through the slots to hold the folded halves of the standard resistance together and the opposite edges of the folded standard resistance through which the slots extend are engaged in insulating supports.

5. The resistance standard of claim 4 in which the edge engaging insulating supports are separated by spacer columns located on each side of the resistance material to provide fixed separation of said insulating supports and current and potential terminals are supported on one of said supports.

6. The resistance standard of claim 4 in which the resistance material is manganin.

7. The resistance standard of claim 4 in which the resistance material is a nickel chrome alloy.

8. The resistance standard of claim 4 in which the insulation between the opposed parts is Mylar sheet and the laces are waxed cord.

9. The resistance standard of claim 4 in which the insulation between the opposed parts in Teflon sheet.

10. The resistance standard of claim 4 in which the insulating between the opposed parts is Kapton sheet.

11. The resistance standard of claim 4 in which the insulation between the opposed parts is a high resistivity coating of varnish.

12. The resistance standard of claim 4 in which the insulation between the opposed parts is a high resistivity coating of silicon.

13. The resistance standard of claim 4 in which the insulation between the opposed parts is a high resistivity coating of epoxy.'

14. The resistance standard of claim 4 in which the insulation between the opposed parts is mica.

i i i i

Claims

1. In a resistance standard employing a standard resistance element connected at each end to a current terminal and to a potential terminal, connections on the resistance standard to the potential terminals being inside the high current paths defined between connections to the current terminals, the improvements comprising a standard resistance element formed from a sheet of resistance material cut in a symmetrical pattern and folded about its line of symmetry defining electrically connected parts and secured together face-to-face with a thin insulating layer inteRposed such that the patterns in said parts are super-imposed on one another and the current flowing in opposite directions in said opposed parts of the pattern tends to cancel the inductive effect in each portion of the pattern and there-fore throughout the resistance standard.

13. The resistance standard of claim 4 in which the insulation between the opposed parts is a high resistivity coating of epoxy.