US2330248A - Electrode for gaseous discharge devices - Google Patents

Description

Sept. 28, 1943. I w. v. SMITH 2,330,248

ELECTRODE FOR GASEOUS DISCHARGE DEVICES Filed Jan. 50, 1942 William mithINVENTOR.

r A TTORNEY Patented'Sept. 28, 1943 William v. Smith, Salem, Mass, assignor to Sylvania Electric Products Inc., a corporatio of Massachusetts Application January 30, 1942, Serial No. 428,887 4 Claims. (Cl. its-12c) This invention relates to electric gaseous discharge lamps and-more particularly to cathodes therefon,

An object of this invention is to provide a cathode of such a structure that the lamp in which it is used will have a relatively long life.

Another object is to provide a cathode capable of being readily adapted to cold starting conditions with a minimum of deleterious eflects.

A further object is to provide a cathode of such a structure that such conditions as sputter will be greatly eliminated.

Further objects; advantages and features will be apparent from the following specification taken in conjunction with the accompanying drawing in which:

Figure 1 is a side elevational view partly cut away to show the cathode structure.

Figure 2 is an end view showing the coiledcoiled filamentary wire within the coiled wire.

In the manufacture of electric gaseous discharge lamps of the type with one or more electrodes having electron emissive materialit has been found that one of the factors which affect the life of the lamp is the disintegration of the electron-emissive material. I have therefore devised a cathode capable of carrying a large quantity of electron emissive material considerably shielded and protected from the path of the discharge.

The lead-in wires l and 2 extending up through the glass mount 3 have the outer coil 4 mounted between the ends thereof. The coiled-coiled wire 5 is located within the turn of the outer coil 4 as shown in the cut-away portion of Figure 1 and in the end view of Figure 2.

If the inner coil 5 is of considerably higher resistance than the outer coil 4, it is immaterial whether they are connected at their ends or not for the difference in resistances plus the dinerence in pitch of the two coils will prevent any substantial short-circuiting from taking place. If the innercoil is of about the same resistance as the outer coil it is preferable to join the ends of the inner coil to the outer coil. In either case if the inner coil touches the outer at several points along their longitudinal axis the practical result will be a series of parallel resistors having the same eifective resistance as the parallel resistance of the two coils. 1

The electron-emissive material may be applied to the coiled-coiled wire before it is inserted within the outer coil and then a second application of electron-emissive material be made. However, I have found it more advantageous to locat the coiled-coiled wire within the outer coil first and then apply the electron-emissive material thereto. This may be done in the manner described in U. S. Patent No. 2,258,158 issued October 7, 1941, whereby the material is closely held in a uniform manner.

A structure of this type provides considerable protection of the electron-emissive material from the positive ion bombardment. The outer coil, being closely wound, shields the inner coiledcoiled wire and the main body of the electronemissive material. Thus sputtering of the coating is cut down considerably. This shielding not only p fevents the flying ofi of particles of the electron-emissive material and the collection thereof on the walls of the lamp but it also protects the electron-emissive material from the discharge under cold starting conditions.

It may be noted that if coils 4 and 5 are both connected to the lead-in wires, the discharge may go to either coil, depending, at least in part, on which coil retains the most active cathode coating. With the outer coil closely wound the inner coil and the electron-emissive material is shielded and .thus no substantial amount of sputtering takes place. Such sputtering as might take place is not sufficient to discolor the walls of the lamp and is just about enough to keep the outer coil active.

What I claim is:

1. An electrode assembly for an electric gaseous discharge device comprising: a pair of leading each end connected to one of said lead-in wires; an inner, coiled-coiled filamentary wire having a major and a minor coil and located within the coils of said outer wire; and a filling of electronemissive material within and between the turns of said major and minor coils and within the turns of said outer coil.

2. An electrode assembly for an electric gaseous discharge device comprising: a coiled filamentary wire, a second coiled filamentary wire of a difierent degree of pitch than said first wire, said second wire being located within the coils of said firstwire and disposed along the longitudinal axis thereof; and a filling of electronemissive material within the turns of said first wire, and within and between the turns of aid second wire in such manner as to fill the space within the turns of, and to envelop, said second wire.

3. An electrode assembly for an electric gaseous discharge device comprising: a coiled filamentary wire; a second coiled filamentary wire a different pitch than said first wire, said second wire being located within the coils 01. said first wire and disposed along the longitudinal axis thereof; and a filling of electron-emissivematerial within the turns of said first wire, within the turns of said second wire and enveloping said second wire; said second wire having a resistance substantially higher than the resistance of the first wire.

WILLIAM V. SMITH.

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