US2056662A - Electric gaseous discharge device - Google Patents

Description

@6151, 6, 1936 E FOULKE 2,6,fi

ELECTRIC GASEOUS DISCHARGE DEVICE Filed Feb. 8, 1955 ALKALINE EARTH fiffifizi Patented Oct. 6, 1936 UNITED STATES PATENT OFFICE ELECTRIC GASEOUS DISCHARGE DEVICE Application February 8, 1935, Serial No. 5,671

1 Claim.

The present invention relates to electric gaseous discharge devices generally and. in particular to devices of this type which are used to regulate the potential of the system to which they are connected.

A particular object of the invention is to provide a gaseous discharge device whose discharge maintaining potential varies only slightly with the discharge current. A further object of the invention is to provide a device whose discharge maintaining potential for any given current is always the same. Another object of my invention is to provide a device having both a relatively low discharge maintaining potential, and a low breakdown potential. Another object of my invention is to provide a device of this type which will have a long useful life. Still other objects and advantages of my invention will appear from the following detailed specification or from an inspection of the accompanying drawing.

The invention consists in the novel structure hereinafter set forth and claimed.

Electric gaseous discharge devices of the cathode glow type have been used heretofore in various types of electrical circuits as voltage regulators. This field of use has been decidedly restricted, however, by the fact that the minimum breakdown and discharge maintaining potential of the devices heretofore produced has been relatively high. In an effort to reduce these potentials applicant tried adding to the principal gas within the device a small quantity of a gas whose ionizing potential is less than a metastable potential of the principal gas. This gave the desired reduction in the breakdown potential, but applicant soon discovered that it also introduced a new and serious difiiculty, in that the discharge maintaining potential now varied erratically between two widely difierent values; Such a variation, of course, rendered these devices entirely unsuitable for use as voltage regulators. Upon further research applicant discovered that this variation in the maintaining potential was due to variations in the location of the cathode glow, and that if the relation of this glow to the anode were kept constant the maintaining potential was also maintained constant. Applicant furthermore found that the maintaining potential is much less when the anode is exposed to the radiations from the cathode glow than when it is shielded therefrom, and that the apparent internal resistance of the device is also less under this condition, both of these features, of course, being extremely desirable in a voltage regulator.

As a result of these discoveries applicant has devised a novel structure using a mixture of gases of the type hereinbefore described, such as neon containing a small quantity of argon, in which the anode is continuously subjected to strong radiations from the cathode glow whenever there is a discharge within the device. The resonance radiations which are produced by this discharge are characteristic of the principal gas and hence these radiations produce excited atoms of this gas in the vicinity of the anode. These excited atoms, or the metastable atoms into which they are changed as the result of energy lost or gained in collisions with other particles, have sufficient energy to ionize an atom of the added gas upon collision therewith, with the result that the gas is maintained in a highly ionized condition close to the anode. This eliminates the usual anode fall, as is indicated by the absence of anode glow, and thus accounts not only for the lower maintaining potential, but also for the unusually slow rate at which this potential increases with current flow. This novel and unexpected result is attained by locating the anode and cathode parallel and in proximity to each other, with the cathode glow permanently confined to the face of the electrode which is toward said anode by any suitable means. In practicexthe glow supporting face of my electrodes is preferably coated with barium and strontium in the manner described in my Patent 1,965,589, granted July 10,

1934, while the remaining surface is coated with finely divided aluminum or the like as disclosed in my Patent 1,965,586, granted July 10, 1934, since this has been found to produce the desired result of confining the glow, and at the same time to reduce the break-down and maintaining potentials. As a further unexpected result of this novel structure, I have found that the electrode spacing is no longer especially critical, so that the usual manufacturing tolerances do not produce objectionable variations in the electrical constants of the device. As a result these devices are easily reproducible without special precautions which otherwise would have to be observed.

For the purpose of illustrating my invention I have shown a preferred embodiment thereof in the accompanying drawing, in which Fig. 1 is an elevational view of an electric gaseous discharge device which is especially intended for use as a voltage regulator, and

Fig. 2 is a sectional view of the electrodes of the device of Fig. 1.

As shown in the drawing my novel device has a sealed envelope I of glass or any other suitable material having a reentrant stem 2 through which is sealed a pair of inleads 3 and 4. The inlead 3 extends within said envelope and is welded to a downturned lip on the electrode 5. A second lip on said electrode is also preferably welded to a support wire 3' which is also fused into the stem 2 in order to give said electrode additional support. An insulator 6 of any suitable refractory material extends through a central opening in the electrode 5 which it closely fits for purposes of support, and through said insulator there in turn extends a support wire 1 for the electrode 8, the lower end of said wire being welded to the inlead 4 and a similar supporting wire I.

The electrodes 5 and 8 are each in the form of a disc having a plane surface, in the device illustrated, three quarters of an inch in diameter with the edge turned over on a one eighth inch radius, the edges of said electrodes extending toward each other as shown, with a gap of the order of 1 or 2 millimeters therebetween. These electrodes are preferably formed of nickel. The opposed faces of these electrodes are coated with a substance having a'low work function, while the outer surface of each of these electrodes is preferably coated with a substance which resists the formation of such a coating thereon by sputtering or the'like, in order to permanently confine the cathode glow to the opposed faces of these electrodes. In practice these opposed faces are coated with a mixture of barium and strontium carbonates while the remaining surface is coated with finely powdered aluminum, a suitable binder, such as nitrocellulose, being employed where desired. The electrodes are then heated sufficiently in a vacuum, as by means of an induction furnace, to decompose the binder and to reduce the carbonates to the oxide.

The envelope I is thereupon filled with the desired gaseous atmosphere, such as neon containing say .8% of argon, at a pressure of the order of 42.5 m. m. of mercury, and sealed off. The pressure of the gas and the percentage of argon may, of course, be varied if desired, to control the breakdown and discharge maintaining potentials and the apparent intemai resistance of the device, but the values given have been found by exhaustive experiment to give by far the best results where low potential operation is desired. Likewise other gas mixtures may be employed, so long as the principal gas has a metastable potential in excess of the ionizing potential of the minor gas. Thus a small quantity of krypton may be used with neon, or a trace of argon may be used with helium, the same results being produced with any such combination. For low voltage operation, however, the neon argon mixture described is preferred.

After the device is sealed-ofl a steep wave front discharge is produced between the electrodes 5 and 8, in accordance with the disclosure of my Patent 1,965,589, hereinbefore referred to, with the result that the oxide is reduced, an extremely tenacious coating containing barium and strontium being thus produced, as described in that patent. The device is then preferably operated for a few hours with the rated current flowing therethrough, in order to bring the electrode surfaces to a condition which will remain constant throughout the life of the device.

A conventional base 9 is then affixed to the envelope I, the inleads 3 and 4 being connected to two of the prongs thereof in the usual manner, as indicated by dotted lines.

I have found that a device constructed as hereinbefore described has many unique properties which render it especially desirable for use as a voltage regulator. Thus the breakdown potential of such a device is less than volts, while its maintaining voltage with minimum stable current flow is less than 55 volts, as compared with the 65 or 70 volt devices now in use. Even more important, however, this latter voltage is reproducible and remains constant throughout the life of the device, as contrasted to the erratic variation heretofore encountered with devices having a mixture of gases such as is here employed. Furthermore the apparent internal resistance of this novel device is extremely low, being less than'75 ohms, with the result that the discharge maintaining potential increases less than a volt and a half when the full load current of 20 milliamperes flows therethrough.

This low resistance, which permits exceptionally. 10

close voltage control, is to be contrasted with that of devices using the same gas mixture and same type of electrodes, but with the electrodes differently arranged, as in the same plane for example, where the lowest apparent internal resistance obtainable is of the order of at least ohms.

All of these new and unexpected results are due to the elimination of the usual potential fall at the anode, as a result of the ionization produced close to the anode by the intense radiations from the cathode glow to which the gas in that vicinity is subjected. As hereinbefore described this resonance radiation, of neon in the case described, produces metastable neon atoms close to the anode, and these atoms upon collision with an argon atom ionize the latter in a goodly number of cases, with intense ionization thus resulting in the neighborhood of the anode. This concentration of ions eliminates the anode fall, as evidenced both by the low maintaining voltage and internal resistance, and by the absence of visible anode glow.

To fully obtain this result it is essential, of course, that the radiation ould be as intense as possible at the anode, an that the maximum possible area of the anode should be subjected to these radiations. The novel structure illustrated has been found to be especially effective in this respect, since the anode is not only in registry with the cathode, but is also close thereto, so that the radiations from the cathode are used to great advantage. The rolled edges of these electrodes not only facilitate the initiation of the discharge, due to their proximity, but also serve to entrap any particles sputtered from the electrodes, and thus to prolong the useful life of the device.

For use on direct current the electrode 8 is preferably made negative, since it has a slightly larger area than the electrode 5. Likewise for direct current use only one of the electrodes needs to be coated. In general, however, I prefer to coat both electrodes.

While I have described my invention by reference to a specific embodiment thereof it is to be understood that it is not to be limited thereto, but that various changes, substitutions and omissions. within the scope of the appended claim can be made therein without departing from the spirit of the invention.

I claim as my invention:-

An electric gaseous discharge device comprising a sealed envelope containing neon intermixed with .8% argon at a pressure of the order of 42.5 m. m. of mercury, a pair of electrodes sealed within said envelope, said electrodes consisting of disc shaped members with turned over rims which closely approach each other, a low work function coating containing an alkaline earth metal on the opposed faces of said electrodes, and a coating of finely divided aluminum on the remaining surface of said electrodes, whereby a cathode glow discharge between said electrodes is confined to the space enclosed by said electrodes.

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