US1804467A - Electric discharge device - Google Patents

Description

y 1931. w. HENDRY 1,804,467

ELECTRIC DISCHARGE DEVICE Filed Nov. 9, 1926 lnvemor 14/5 A/rj 25 can occur.

Patented; May 12, 193 l UNITED STATES PATENT. OFFICE WILLIAM I. HENDRY, OF OSSINING, NEW YORK, ASSIGNOR, BY MESNE ASSIGNMENTS, TO MANHATTAN ,ELECTRICAL SUPPLY COMPANY, INC., OF JERSEY CITY, NEW JERSEY, A CORPORATION OF NEW JERSEY ELECTRIC DISCHARGE DEVICE v Application filed November 9, 1926.. Serial No.'147,298.

devices such as neon sign tubes or lamps, electrodes provided within the lass vessel must be carefully designed as to size, material and shape, and then skillfully treated to remove, as far as practicable, all occluded gases. The

5 size is important because the current densitymust be kept below a certain maximum value for a given tube in order to reduce to the minimum objectionalsputtering; and yet the larger the size the more diflicult it is to remove occluded gases. A material must be selected which will sputter. a minimum amount and yet can be commercially em-,

ployed, and the shape must be such that no concentrated points of high current density Tubes with internal electrodes, even when carefully treated for removal of impurities, give trouble owing to continued sputtering of electrodes and to the high temperature of the tube, which causes expansion 0 and contraction resulting eventually in minute cracks.

In order to counteract the former it has been suggested to provide means for increasing from time to time the rare gas content of the tube, but owing to their expensiveness and unreliability, such arrangements have not found reat favor. The manufacture of this type 0 sign or illuminating device under commercial conditions where continual tech-- nical supervision is not always practical is qulte troublesome, because "procedure in one direction to avoid one kind of difliculty if carelectrodes and-to guard against the ever pres-- ent danger of excessive sputtering andocclusion of neon or other noble gas,, it has been suggested to provide such electrodes on the outside of discharge tubes. However, in the operation of such devices new defects arise. Water vapor and gases in the glass wall of the vessel become liberated, the pressure increases,.whereby the relative neon or other rare gas content of the tubeis reduced to a point where the color of the discharge r changesor the tube ceases to, operate. When the pressure rises or the percentage of impurities increases to thepoint where the color changes or the resistance increasessufiiciently to stop the discharge, there being no metal in the tube to sputter, it is impossible to do anything to bring it back to operating. condition.

An important advantage of'external electrodes resides 'in the possibility of operating two or more independent tubes in parallel from the secondary of a transformer irrespective (within practical limits) of the lengths of such tubes. An advertising sign may be made up of separate and interchangeable letters and the latter operated in parallel from a common source of current supply withoutthe necessity of providing separate transformers or condensers for the individual letters. With internal electrodes, a short'tube,

e. g., one representing the lettter I, would tend to short-circuit a long tube, e. g., S, if the two were connected in parallel to the secondary of a transformer. p

However, for the above mentioned reasons, the art generally adhered to the use of inside electrodes which, if of proper size or supplemented by' auxiliary electrodes, could be relied upon to eliminate the impurities and operate for awhile (2-4 thousand hours). This-necessitated the forming of entire words or groups of letters of a single tube and the obvious advantages of an interchangeable letter sign could not be availed of.

In accordance with the present invention an electric discharge device is so constructed .that the advantages of external electrodes are obtained without any of the attendant disadvantages. Tubes constructed in accordance with the present invention can be operated in parallel on the secondary of a transformer for very long periods of time without the necessity of repairs or other attendtest was abandoned solely because no further proof as to life was thought necessary. The probable reason for this seems to be that in normal use the gases, water vapor, etc., which may be driven out of the Walls of the vessel are forced by the discharge to combine with the particles of metal sputtered from the internal electrode which may be a line copper wire. Current indicating instruments inserted in the branch circuits of a mature tube (one that has operated two thousand hours) show that the current at 60 cycles divides so that less current flows through the condenser electrode (external) than through the internal electrode. The proportional current flow is affected by the relative dimensions of the external and internal electrodes and also by the frequency of applied current; During the life of the tube most of the current flows continuously through the internal electrode. Prior to curing, maximum current flows through the external and minimum current through the internal electrode. In a cured tube, maximum current flows through the internal and minimum current through the external electrode. Furthermore, the currents flowing through these electrodes seem to be displaced in phase. At.a frequency of 60 cycles the displacement was found to be of 180. The phase of the current flowing through the external electrode lead the impressed E. M. F. A tube constructed in accordance with the description to follow may be heated with a gas flame so that gases are driven out of the glass walls until the neon color is changed to a. thin yellow or pink, in fact the glass may be heated hot enough to bend it, and the tube will appear spoiled, yet in from ten minutes to an hour of normal operation, the original color will be entirely restored. I have even found that a leak, if not too bad, may be counteracted by this arrangement; The q nestion immediately arises as to why the tube does not go hard as the ordinary type of internal electrocle'tube does. The answer may be that while impurities such as oxygen, hydrogen, etc., unite chemically with the molecules, atoms or ionized particles knocked loose from the internal electrode, the noble or inert gases, helium, neon, argon, krypton and xenon, are only entangled mechanically and carried over to the wall of the glass envelope. In normal operation the current that flows through the external electrode to and from the metallic or conducting coating which is formed on the inside wall of the vessel in the initial curing of the tube, very possibly causes breaking down of the metallic part of this coating which has entangled the neon and consequently liberates the neon as fast as the sputtering of the internal (wire) electrode entangles it. Whether this is the correct theory or not, the external electrode functions to aid the gas regulation in some manner, because if it is omitted the tube will go hard in a short time. The fact that the current through the external electrode is displaced in phasemay be important.

In order more clearly to explain the nature of the present invention, I have schematically illustrated one embodiment in the drawmg.

l is a tubular glass vessel representing the letter S and having bulging ends 2 and 3 provided with the usual tips. 4 and 5 are the external electrodes in the form of tinfoil wrappers around the bulging ends and 6 is a fine copper (or other sputterable material) wire projecting through the tip of the end 3 within the vessel. The outside end of the wire 6 is bent back after curing and maintained in contact with the external electrode 5. The external electrodes must be spaced from the tips and particularly from the tip through which the electrode 6 passes. The vessel is exhausted through the tip of the bulging end 2. The tube is filled with neon and is operated from a high frequency current source '7 which is bridged across the electrodes 4 and 5. For the curing of the tube any well known getter may be used to accelerate, the process and high frequency source 7 is connected between the electrode 4 and the copper wire 6 until the water vapor or gases have been eliminated, whichi is indicated by a deep orange color in the case of neon, by the sputtering of the wire 6. During this curing process a dark film or coating is formed on the inside of the wall of the vessel opposite the wire 6. This coating is conductive, showing that some copper, magnesium or whatever metal is-used for electrode 6, has been detached from this electrode and driven away from it by the action of the ap lied electric stress. The metal in this pecu ia-r ionized or unstable state probably combines chemically with any gases or vapors in the tube that have an uncompleted ring of electrons in the outer shell and the resultant particle which finally impinges against the wall of the vessel may be, for example, copper oxide, although many particles of the metal alone reach the surface of the lass walL T e noble gases, such as neon, etc., which are believed to have 8,electrons in the outer shell, and thus age not readily susceptible to chemical union, may be to some extent entangled or occluded by the flying particles,

but the combination is perhaps not permanent and are probably broken upv if again-subjected to electric stress. i

In the construction of such tubes care must be exercised in establishing sufiiciently high neon pressures.- In large tubes, pressure may be of the order of two mm. mercury, but in small tubes, the pressure must often be 'ca rried as high as four mm. mercury.

The tube 1 may be formed 'nto anydesired shape-such as letters, numerals or figures, and will operate in parallel 'as.indicated at 10. The tube 10 represents the letter S-and is providedwith two external and an internal electrode like tube 1. As

nection to said container, one of said discharge meansconslstmg' of electrically connected and substantially concentrically ar-,

rangedinternal and external electrodes and the other of said discharge means consisting solely ofan external electrode.

In testimony whereof, I have signed my name to this specification; this Sth-day of November-1926. v 1 WILLIAM F.-HENDRY.

clearly shown in the. drawing, the individual letters may be readily connected in circuit by pushing the electrodes into socket openings where they maybe suitably held by means of spring contacts or the like. The

a construction of such sockets is inore'fully described in my copending application Serial No. 139,223, filed October 2, 1926.

p I have found that best results are obtained 7 by having external electrodes of. a large area.

Instead of the copper wire',6,' other material may also be used for the internal electrode and the high frequency source may be re-- placed by a lowfrequency current generator, Other variations and adaptations'of the invention will be apparent/to those skilled in the art.

.What I-claiin is: Y

1. In combination, a glass tube having tipped bulging ends and filled with neongas, a separate sheet of conducting material wrapped around each of said bulging ends respectively but spaced from the tips, a; thin copper wire projecting through the tip within a single one of said bulging ends, the out-.

wardly projecting end of the'wire being bent back and v contacting with the surrounding conducting wrapper and a source of current bridged across the conducting wrappers.

' 2." The'methodiof making and operating gas filled luminous signs which'comprises 'providin an; external and an nternal-electrode, bridging a source of current acrossv f said electrodes until the sign is..cured, then connecting said internal electrode with a second external electrode,- and br1dg1n a current source across said external electr es.

- neon filled luminous signs which comprises.

.3. The method .of making and operating vessel, and two relatively'spaced electrical discharge means providing forelectrical con l in combination, a: hermetically sealed

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