US3418620A - High voltage low temperature resistance device - Google Patents

Description

Dec. 24, 1968 M. OHANIAN 3,418,620

HIGH VOLTAGE LOW TEMPERATURE RESISTANCE DEVICE Filed May 19, 1966 Michael Ohoni INVENT My? VW W WZ Zyef United States Patent 3,418,620 HIGH VOLTAGE LQW TEMPERATURE RESISTANCE DEVICE Michael Ohanian, Methuen, Mass., assignor, by mesne assignments, to the United States of America as represented by the Secretary of the Army Filed May 19, 1966, Ser. No. 551,864 2 Claims. (Cl. 338-57) ABSTRACT OF THE DISCLOSURE A compact high voltage, high wattage and low temperature coeflicient resistor that is made by depositing a metallic film or smoke on a piece of glass tubing. The tubing is surrounded by a dielectric and is centrally positioned inside an epoxy glass tube by two end caps that have a series of holes for passing a high heat transfer and high dielectric strength fluid.

This invention relates to a resistance device and more specifically to a compact high voltage, high wattage and low temperature coeflicient resistor.

Very high values of resistance are made by depositing a metallic film or smoke on a piece of glass tubing and attaching suitable terminals to the end of the tube. Also, various forms of carbon are used quite extensively. However, the watt-dissipating capacity of a compact resistor of this type is rather limited, and the value of resistance changes considerably with the temperature and with impressed voltage.

It is, therefore, an object of this invention to provide a compact high-wattage dissipating resistor.

It is another object of this invention to provide an extremely stable resistor for high voltage applications.

Other objects and many of the attendant advantages of this invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in conjunction with the accompanying drawing in which the single figure is a perspective view partially in section of a resistance device according to the present invention.

Referring now to the figure, there is shown a resistor blank which is a standard metallic film resistor similar to the RN80 series which has been calibrated to the desired ohmic value by selectively cutting a spiral in the film leaving a spiral metallic film 7 about a glass tube 9. Electrical connection leads 11 and 13 are fused to the ends of the resistor in a normal manner, and a thick coating of dielectric 15 is applied over the entire body of the resistor which protects the resistive film from outside elements and still allows satisfactory heat transfer. One example of a suitable dielectric is a one-mil thick epoxy coating per Raytheon specifications S296MS471, paragraph 4.3.2 which has a dielectric strength of 1500 VDC-per-mil. The resistor is inserted in a tube 17 made of epoxy glass and inclosed at each end by caps 19 and 21 bonded to tube 17 and the ends of the resistor through which leads 11 and 13 extend respectively supporting the resistor symmetrically within tube 17 forming a passageway for fluid communication about the resistor. Each of the caps 19 and 21 have a plurality of apertures 23 disposed in a circular pattern in said caps 19 and 21 coincident with the fluid passageway inside tube 17 to allow free passage of a suitable high heat transfer and high dielectric strength fluid. Fluids such as FC- and Freon 114 have these characteristics and, therefore, are suitable for use in the resistor described above.

An RN resistor which is rated at two watts in military specifications was able to dissipate thirty-eight watts of power with no ill-effects after prolonged periods. Higher voltages resulting in more power dissipation are possible by increasing the distance between spiral turns, resulting in a higher volts per turn rating.

The use of the present resistance device in conjunction with Freon 114 or equivalent allows the design of a compact high voltage power supply or extremely stable resistive load boxes, and the use of epoxy glass for tube 17 allows the resistor to be clip mounted.

It is, therefore, obvious from the above disclosure that the resistance device of the instant disclosure is capable of dissipating abnormally high wattage at high voltages using presently available types of resistor blanks.

While the invention has been described with reference to a preferred embodiment thereof, it will be apparent that various modifications and other embodiments thereof will occur to those skilled in the art within the scope of the invention. Accordingly, it is desired that the scope of the invention be limited only by the appended claims.

What is claimed is:

1. A high voltage, low temperature resistance device comprising: a resistor blank having electrical connections fused to each end; an inner glass tube; said resistor blank being a metallic film resistor wound around said inner glass tube and calibrated to a desired ohmic value, said metallic film resistor having a dielectric coating disposed over the entire outer portion thereof to protect said resistor; a cylindrical housing comprising a glass tube, said glass tube having end caps bonded to each end thereof through which said electrical connections extend outward therefrom, said end caps further being bonded to said resistor blank for spacing said resistor blank symmetrically within said glass tube and providing a passageway for a cooling fluid, said end caps each having a plurality of apertures disposed in a circular pattern therein and coincident with said fluid passageway for allowing free passage of a high heat transfer, high dielectric strength fluid.

2. A high voltage, low temperature resistance device as set forth in claim 1 wherein said glass tube of said cylindrical housing is made of an epoxy glass for reinforcing said tube whereby said resistance device may be clip mounted.

References Cited UNITED STATES PATENTS 1,694,178 12/1928 Hudson 338-57 1,841,332 1/1932 Kranz 33857 2,338,531 1/1944 Naumann et al. 338-53 2,381,724 8/1945 Crosby 33857 2,423,021 6/ 1947 Henckler et al. 33857 CARL D. QUARFORTH, Primary Examiner. R. L. GRUDZIECKI, Assistant Examiner.

US. Cl. X.R. 33853

Images