US3052862A - Fixed resistor - Google Patents

Description

P 1962 J. G. RUCKELSHAUS 3,052,862

FIXED RESISTOR Original Filed June 7, 1952 INVENTOR. JOHN G. RUCK ELS H ADS ATTORNEY United. States Patent and this application July 17, 1959, Ser. No. 827,935

2 Claims. (Cl. 338258) This invention relates to a resistor. More particularly, this invention relates to a metallic film resistor of the sealed type, and having improved characteristics.

This application is a division and continuation-in-part of my copending application, Serial No. 292,367, filed June 7, 1952, now issued as US. Patent No. 2,917,814, dated December 22, 1959.

An object of my invention is to provide a metal film resistance unit that is stable and has a low temperature coefficient of resistance.

A further object of my invention is to provide a simple, low cost, sealed, precision metal film resistor.

One further object of my invention is to provide a sealed resistor comprising an insulating tube whose interior is glazed with a metalliferous surface and has terminal conductors at sealed ends thereof.

An object of this invention is the provision of an improved resistor comprising an insulating tube carrying metallic terminals at each end, a metallic resistance material on the inner wall of the tube and at least partially overlying each of the said metallic terminals, and end caps alfixed to the tube and making individual contact with the metallic terminals such that the metallic terminals act as electrical conductors between the resistance material and the end caps.

Other objects and features of my invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a longitudinal sectional view of one embodiment of my invention,

FIG. 2 shows a transverse section view of another embodiment of the invention,

FIG. 3 is a longitudinal section takenon line 33 of FIG. 2,

FIG. 4 is a fragmentary, exploded, longitudinal sectional view showing a modified sealing means and a different form of the metallic resistance film.

Similar reference numbers refer to like parts throughout. Referring now to FIG. 1, there is shown an insulator cylinder or tube 14 which may be made of glass, ceramic or other suitable material adapted to hold a metallic film thereon and which is made of dielectric material. Said tube is provided with recessed or undercut end portions 15 and thread 16, said thread extending from one to the other of the recessed portions. Prior to forming the resistance film on the inner wall of the tube, the recessed end portions 15 are coated with a silver, or platinum or other metal paste or frit and baked or fired or heat treated thereby forming terminal bands 17 which are interfused with the dielectric material forming the substrate. The terminal bands then may be masked off with any suitable paste, but leaving a portion exposed for contacting with :a film to be formed.

The cylinder or tube 14 is then treated as described in the parent application whereby the helical thread 16 is formed and then coated with a metallic resistance film 18, such as Nichrome, preferably by an evaporation process as disclosed in the parent application. It is a well known physical law that when a filament such as Nichrome or some other alloy is heated or lighted in a container encasing a high vacuum, the metal will evaporate or sublimate and deposit either on the inner walls of the container or onto other objects which may be in said r 3,052,862 Patented Sept. 4, 1962 vacuum. The amount of material evaporated or sublimated is in proportion to the heat of the filament and the length of time that the filament is heated or lighted.

The tops 19 of the film 18 are removed by reaming, this, forming a helical ribbon of resistance material that overlies or spans each of the terminal bands 17. It is to be noted that the amount of reaming depends upon the resistance value desired in the finished product or unit. Furthermore, in forming the helical metallic resistance film, the terminal bands are in good contact therewith.

After the interior of tube 14 has been prepared, metal end caps 20 are tightly fitted into the recesses 15, as shown, so that there is good contact between the thread or film 18, the band 17 and the cap 20. Said end caps are then peripherally soldered to the terminal bands 17 as indicated by numeral 21. It is to be noted that there is provided a good soldered joint, since the outer portion of the terminal band was masked which mask is removed prior to the installation and attachment of ends caps 20.

It is apparent that such construction results in a sealed unit wherein the terminal bands 17 and 17 serve as good electrical connections between the associated metal caps 20 and the resistance film 16.

Connection leads 22 are provided for each end cap 20, being soldered thereto or otherwise being firmly con nected to each end capfor connecting the resistor into an electrical circuit.

In FIGS. 2 and 3, it will be seen that the cylinder or tube 14a has longitudinal splines 23. Said splines when coated as described in my parent application provide a desired ohmage or resistance. The ends of the tube 14a are shown as not being recessed although they may be as shown in FIG. 1. The terminal portions 24 and 25 may be initially treated with a silver or platinum or other metal paste and fired or baked, and then coated with a resistance film according to my invention described hereinabove. The resistance of the splined tube is determined and end caps 20 are connected and soldered at 21 as shown. Furthermore, the end caps 20 are each provided with connection leads 22.

In the modification shown in FIG. 4, it will be noted that the inside wall or interior 26 of tube 27 is provided with a continuous film 28. Also, the terminal portions 29 of the tube are provided with a coating of silver or platinum or other metal on both the inside and outside of the ends of the tube. This can be done by dipping each end of the tube into a paste to the proper depth or the paste can be brushed on to form an annulus 30, preparatory to baking the tube. The tube may then be sealed, after having determined its ohmage, by using end caps 31 which are shown to pass over the periphery of the end of the tube to contact the silver or platinum or other metal end thereof. Said caps 31 are adapted to fit tightly over the ends 29 of the tube.

In addition to the above metals, I may employ pure metals or alloys thereof for coating the cylinders or helices above indicated. It has been found that a pure Nichrome alloy, free of impurities such as iron and/or aluminum, has produced a very stable unit or resistor.

It can readily be seen that many resistors can be prepared in batch form since many tubes can be strung onto one fixture, and coated so as to create several resistors at a time. These resistors can be removed and checked, thus economically forming stable metal film resistors of extremely low temperature co-eificient of resistance. In this case, the ends can be filled with a casting material, such as is shown in FIGS. 1, 3 and 4 in order to seal the resistance element. Furthermore, the ends of the cylinder 14 may be initially provided with end terminals baked thereon, namely on the inside, the ends and the outside so that an end cap can be readily added thereon.

Instead of accurately evaporating the metal, metal can be deposited to a value lower than required, then, by connecting the unit across a Wheatstone bridge or similar apparatus, careful adjustment of the unit can be made by the amount of material cut or reamed off. This unit can then have lug or wire terminals attached to each end and sealed, or a shaft carrying a moving contact can be inserted so that the unit can be used as a potentiometer or rheostat.

In accordance with my invention the resistor is made by first threading the interior of tube '14, and then may be undercut as shown in FIG. 1 to the depth of the thread. The cylinder is then glazed and fired, during which the undercuts are coated with silver, platinum or other metal paste up to and including the thread ends. If desired the platinum or other metal paste may extend over one or more of the adjacent threads to insure proper connection. The cylinders are then fired and baked. Next the alloy is then evaporated into the interior of the tube, first masking oil? the undercut with platinum so that the alloy film contacts platinum on first and last thread in the cylinder. The thread is cut or reamed to the desired resistance as shown, by a Wheatstone bridge or other suitable instrument. Once the desired ohmage has been obtained, caps carrying their respective lead wires, are forced into the respective undercuts or over the end and solder applied to the platinum to seal the unit.

Furthermore, it will be noted that, by my invention, I provide a resistor having a film of nickel-chrome alloy deposited on the inner wall of aglazed or unglazed ceramic, glass or similar type of tube on which a metal tenminal material has been baked or otherwise deposited at each end. Furthermore, there is provided a ceramic tube in which grooves have been cut either in the form of a helix or parallel splines having metal terminals deposited at each end of the tube so as to form a resistance path between the metal terminals. The metal film may be removed from the inside diameter of the grooves or threads so as to form threads of resistance material in 'one case and parallel resistance paths between the metal terminals in the second, said removal being dependent upon the amount of resistance desired or needed, but

approximately the same amount of material will always be removed from all parts.

It is to be noted that I may use any dielectric material suitable for the purpose intended such as ceramic, porcelain, glass, Alundum, all of which may be glazed or unglazed.

Also, a resistor is provided having metal end terminals forced into the ends of tubes and electrically connected to the terminal bands so as to form a hermetically sealed resistor unit inside of the tube.

While preferred emobdiments of my invention have been illustrated and described, it is to be understood that modifications as to form, arrangement of parts and use of materials may be made without departing from the spirit and scope of the invention as claimed herein.

I claim:

1. A resistor comprising an insulator tube, metallic terminals on each end of the tube interfused therewith, a helical, metallic resistance film on the inner wall of said tube and overlaying at least a portion of each terminal, said film consisting of a nickel chromium alloy bonded to said wall and terminals, and metallic end caps aflixed to said tube making electrical contact with said terminals and sealing said tube, said terminals acting as electrical connectors between the resistance film and the end caps.

2. A resistor acocrding to claim 1, in which said terminals are selected from the group consisting of platinum and silver.

References Cited in the file of this patent UNITED STATES PATENTS 1,739,256 Peuder et a1. Dec. 10, 1929 2,037,951 Thomson Apr. 21, 1936 2,547,405 Mitchell et a1. Apr. 3, 1951 2,557,983 Linder June 26, .1951 2,569,773 Orr Oct. 2, 1951 2,586,752 Weber et a1 Feb. 19, 1952 2,792,620 Kohring May 21, 1957 FOREIGN PATENTS 61 1,250 Great Britain Oct. 27, 1948

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