US 2521894 A
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Description (OCR text may contain errors)
p 9 1950 R. J. s. BROWN 2,521,894
LOW INDUCTANCE RESISTOR Filed Feb. 8, 1950 WITNESSES INVENTOR.
I J Rober-Z' J- S. Brown I BY JW 6. %m JMM amp Patented Sept. 12, 1950 LOW INDUCT ANCE RESISTOR Robert J. S. Brown, St. Paul, Minn, aesignor to the United States of America as represented by the United States Atomic Energy Commission Application February a, 1950, Serial No. 143,011
2 Claims. (01. 201-73) value so as not to appreciably impede the current being measured. The resistor should also have an inductance value which is negligible compared to its resistance value in order that the observed voltage be directly proportional to the instantaneous value of the current rather than the time rate of change of the current. These characteristics are particularly important in the measurements of the current in a spark-gap where the time rate of current change may be of the order of 10 amperes per second.
Prior to this invention, resistors having low inductance have fallen in two categories. One comprises a carbon material while the second makes use of bifilar-wound metal conductor. In the first category a resistor comprising carbon material requires a large amount of carbon material and therefore is bulky, unhandy to use a and is unstable in characteristics.
' The second category of low inductance resistors requires a large diameter construction in order to withstand currents of a high value and thus is bulky and diflicult to use. In addition, the bifllar type resistor is susceptible to flash-over between separated portions thereof.
It is therefore an object of this invention to provide a low resistance, low inductance resistor.
Another object of this invention is to provide a low resistance, low inductance resistor which is compact and rugged.
A further object of this invention is to provide a low resistance, low inductance resistor capable of conducting currents of high value.
It is a further object of this invention to provide a resistor particularly adapted to the use of measuring the current in spark-gap switches where the time rate of current change may be of the order of 10 amperes per second.
Other objects and advantages of the presentinvention will become apparent to persons skilled in the art from the following description of the presently preferred embodiment taken in connection with the drawing made part of this specification.
jects can be accomplished and the enumerated diiiiculties overcome according to this invention by a resistor having low inductance, low resistance and the property of withstanding currents of high value. The resistor comprises essentially a single sheet of resistive material such as an alloy consisting of 80 per cent nickel and 20 per cent chromium folded in a U-shape having dielectric material between the folds and metallic conductors connected to its ends. The geometric configuration of a resistor so formed causes the magnetic field set up by the current in passing through one portion of the resistor to be in opposition to the magnetic field created by the adjacent portion, thereby resulting in negligible inductance.
One embodiment of the present invention is shown in the accompanying drawing made a part of this specification for the purpose of illustration only but in no way intended to limit the scope of the present invention.
The drawing is a per p ctive view of a resistor constructed in accordance with the present invention.
Referring now to the drawing, the resistive material II is a single sheet folded in a U-shape with enough separation between the folded parts to permit insulating material II to be inserted therein, the free ends of resistive material I. thus being separated suiiiciently to prevent areover within the range of currents to be measured.
' .Two plates l2 and I! of a suitable conductive material ll are two sheets of insulating material it and H.
In order that the resistor may be connected in a circuit that is to be tested, a pair of terminals it and I! are provided and are connected to the conducting plates l2 and i3. These terminals l8 and it which are connected to the outer edge of the conducting plates "and It may be soldered or otherwise fastened to make good electrical contact.
Although an alloy consisting of per cent nickel and 20 per cent chromium is employed as the resistance material and copper as the con- It has been found that the above and other obo5 ducting material in the illustrative embodiment 3 oi the invention, the invention is not restricted to the use oi these materials as other equivalent materials may be used. The insulating material used, however, must be 01' a type having high resistance and a high dielectric constant.
It will thus be seen that what has been described is a simple low resistance, low inductance resistor. Other variations will be apparent to those skilled in the art without departin from the principles of this invention. Therefore the present invention is to be considered limited only by the appended claims as interpreted in view of the prior art.
What is claimed is:
1. A resistance device comprising a sheet 0! material offering resistance to electric current, said sheet being continuous and being i'olded upon itself and having insulation between the folded portions, stiiimetallic conductors having 2. A resistance device comprising a U-shaped unbroken sheet of resistive material, abar 0! conductingmaterialsecuredtoeachoutcrwalio! said U-shaped sheet adjacent to and along its entire end and covering only a relatively small portion of said outer wall, conducting plates securedatoneendtotheentirelengthofsaid conducting bars and substantially covering the outer walls of said U-shaped sheet, sheets of dielectric material substantially filling the spaces between the inner walls or said U-shaped sheet and between the outer walls of said U-shaped sheet and said conducting plates, and terminals attached to the outer surfaces of said conducting plates adjacent their other ends, whereby the magnetic field set up by a current passing through one portion of said U-shaped sheet is in opposition to the magnetic iield created by the adjacent portion, thus aiving said device a' a width substantially equal to that of the sheet 20 umble inductance.
of material and of low resistivity enclosing said folded sheet and providing a current path, said tors, whereby the arrangement of said folded "sheet with said supporting metallic conductors cancels the inductive effect due to the current passing therethrough.
ROBERT J. 8. BROWN.
'25 ilie of this patent:
UNITED STATES PATENTS Nmaber Rams Date 2,487,895 Cloud Nov. 8, 1049