US2244070A - Electrode for gaseous discharge tubes - Google Patents

Description

June 3, 1941.

J. KURTZ ELECTRODE FOR cmsaous DISCHARGE TUBES Filed Dec. 21, 1940 Jae BYfi A ATTORNEY tion.

Patented June 3, 1941 ELECTRODE FOR GASEOUS DISCHARGE TUBES Jacob Kurtz, Teaneck, N. J., assignor to Callite Tungsten Corporation, Union City. N. J., a corporation of Delaware Application December 21, 1940, Serial No. 371,086

4 Claims.

The present invention relates to new and useful improvements in electrodes for gaseous discharge tubes, particularly for fluorescent discharge tubes starting at high voltages and operating in conjunction with constant current transformers of the usual type.

In discharge tubes, such as neon sign tubes, copper, nickel, or iron electrodes have been used on which current at relatively low density and high voltage was impressed. The customary voltage drop was approximately 200 volts per pair of electrodes. The object was to prolong the operating life of the tubes by keeping down the operating temperatures and thus to lower the sputtering of the electrodes. Therefore, relatively large surfaces areas were used.

It is the object of the present invention to provide for discharge tubes electrodes having relatively small surface areas, which are suitable for high voltage starting, 1. e., 3004000 volts, and low'voltage operation, 1. e., 75-300 volts, at reasonably low current densities. Values given are for tubes 4 ft. long. This is accomplished by providing a filamentary body having an electron emitting surface of the Wehnelt type and which is surrounded by a metal sheath insulated therefrom.

The drawing illustrates in side elevation, partly in section, an embodiment of the inven- The filamentary body is formed of a tungsten wire, nickel plated so that its diameter is increased by 15 and preferably about per cent. The nickel plated wire is formed into a coil l of suitable diameter and length. The coil I ismounted near the ends of two rods 4 and is surrounded by a cylinder or shell 2 of nickel, or iron or other metal having a low sputtering factor which rests on a mica disc 3 out of contact with said rods 4. The shell 2 is held in position by one or more of the supporting rods 4 welded thereto and projecting through holes in mica disc 3, but not the two rods 4 on which coil I is mounted. The rods 4 and 4' are anchored in and pass through press 1 which seals the end of glass tube 6.

According to a further feature of this invention the two posts or lead-in wires 4 on which electrode I is mounted have pointed upper extensions which may be refractory metal such as tungsten or molybdenum points welded to the rods. This will greatly facilitate the initial ionization of the gas insuring the starting and operation at substantially lower voltages tha would otherwise be possible.

The mica disc 3 serves as an insulating support for shell 2 and as a bafile to protect the lead-in wires 4 and the seal I against bombardment.

Oxide coated tungsten filaments which are not nickel plated disintegrate rapidly when used in fluorescent discharge tubes because the coating peels or chips off. The oxide coating will, however, stick -to nickel plated tungsten filament, particularly when in accordance with the present invention, it is built up of three or more strands. The standard wire is wound over a mandrel into the coil I, and the coil is coated with a mixture of alkaline-earth oxides, e. g., barium and strontium. The standard coil will have a. large surface which will firmly anchor the oxide coating.

The advantages of electrodes constructed in accordance with the present invention as compared to customary electrodes consisting of a nickel cylinder having a relatively large total surface area (e. g., two square inches) will now be quantitatively demonstrated with the aid of tables in which CT-3 designates the latter, and CT-I the preferred embodiment disclosed herein. In the CI'-I electrode the area (both sides) of shell 2 was one-half square inch, and the area of coil I was 0.03 square inch, or 6% of the shell 2.

TABLE I Comparison of volts per ft. and volts per pair of electrodes CT-3 and CT-7 operating at 6'0 ma.

12 mm. ave. volts per foot CT-3 electrodes 100.0 12 mm. ave. volts per foot CT-7 electrodes. 9%. 5 12 mm. ave. volts per pr. elec. (IT-3 electrodes. 192. 2 12 mm. ave. volts per pr. elec. CT-7 electrodes. 35.0 15 mm. ave. volts per foot (ET-3 electrodes.-. 87. 0 15 mm. ave. volts per foot CT-7 electrodes- 80. 0 15 mm. ave. volts per pr. elec. CT-3 electrodes 185.0 15 mm. ave. volts per pr. elec. Cl-7 electrodes. 31. 0

TABLE II Volts per ft. and volts per pair of electrodes CT-7 operating at 360 ma.

25 mm. average volts per foot CT-7 electrodes 3f 25 mm. average volts per pair of Cl-7 electrodes I trode for footage on a 3,000 volt ma. transformer T b 0 551g; 3 Tube Watts Electrode e tubes m) Watts er size rent tra Input D m len th series former g I have found that generally the starting voltage of fluorescent tubes equipped with CT-I electrodes was lower than those equipped with CT-3 electrodes.

The footage of fluorescent tubes equipped with CT-I electrodes can, therefore, be safely increased by 50% over tubes equipped with CT-S electrodes.

The voltage across a 4 ft. tube of 12 mm. diameter having CT-i electrodes was approximately 590 volts, and for a similar tube having CT-I electrodes only 390 volts.

The voltage drop across a pair of T4 electrodes was 192 and across CT-l electrodes it was 35. These values are for 12 mm. tubing operating trodes can, therefore, be adjusted for low voltage operation and high voltage starting and will function at maximum economy and efliciency for a long time. For this purpose the mass and area of the filamentary body must be proportioned with respect to the desired operative current of the tube. I have found that with increasing current the area of the coil i must also be increased.

In a discharge tube in which the electrode carried 350 ma. current, the area of the shell was sq. in. and the area of the filament was .15 sq. in. or approximately 20% of the shell 2.

What is claimed is:

1. In a fluorescent discharge device, a glass tube enclosing an electrode of stranded nickelplated tungsten filaments formed into a coil and coated with alkaline-earth oxides, metallic rods passing through the tube and near the free ends of which said coil is mounted, an insulating disc through which said rods project, a nickel shell seated on said disc and surrounding said coil out of contact with said coil and rods, and other rods sealed in said tube and passing through said disc and to which said shellis fastened.

2. In a fluorescent discharge device, a glass tube enclosing an electrode of stranded nickelplated tungsten filaments formed into a coil and tube and passing through said disc and to which i said shell is fastened, and refractory metal points welded to the ends of said first mentioned rods and projecting above said shell.

3. In a fluorescent discharge device, a glass tube enclosing an electrode of nickel-plated tungsten filament and coated with alkaline-earth oxides, metallic rods passing through the tube and near the free ends of which said coil is mounted, an insulating disc through which said rods project, a metal shell seated on said disc and surrounding said coil out of contact with said coil and rods, and another rod sealed in said tube and passing through said disc and to which said shell is fastened.

4. In a'fiuorescent discharge device, a glass tube enclosing an electrode of nickel-plated tungsten filament formed into a coil and coated with alkaline-earth oxides, metallic rods passing through the tube and near the free ends of which sail coil is mounted, an insulating disc through which said rods project, a metal shell seated on said disc and surrounding said coil out of contact with said coil and rods, another rod sealed in said tube and passing through said disc and to which said shell is fastened, and refractory metal points welded to the ends of said first-mentioned rods and projecting above said shell.

JACOB KURTZ.

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