US3510717A

US3510717A - Electric glow discharge device with telescoped electrodes

Info

Publication number: US3510717A
Application number: US657881A
Authority: US
Inventors: Ted E Foulke
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1967-08-02
Filing date: 1967-08-02
Publication date: 1970-05-05
Anticipated expiration: 1987-05-05
Also published as: DE6604889U; DE1764745A1

Description

- May 5, 1970 TVC. E.II='OULKE ELECTRIC GLOW DISCHARGE DEVICE WITH TELESCOPE-1D ELECTRODES Filed Aug. 2. 1967 lnvervtor: Ted E. Foutke b9 1s A how-neg United States Patent US. Cl. 313210 9 Claims ABSTRACT OF THE DISCLOSURE A crater-type electric glow discharge device having an envelope containing a rare gas and comprised of a pair of cold electrodes consisting of telescoped outer and inner metal tubes with a glass seal hermetically joining the inner electrode tube to one end of the outer electrode tube and supporting them in spaced concentric relation with the inner tube terminating short of a glass window hermetically sealing oif the other end of the outer electrode tube. The outer end of the inner electrode tube is also hermetically sealed 01f.

BACKGROUND OF THE INVENTION Field of the invention This invention relates in general to gaseous electric discharge devices and more particularly to such devices of the cathode or negative glow type.

Description of the prior art Glow lamps, as generally known in the art, usually comprise a sealed envelope containing one or more rare gases such as neon or argon at a suitable pressure and, in some cases, for dark adaptation of the device,,also containing a radioactive element to facilitate rapid response in starting of the discharge. Within the envelope, and properly spaced from each other, an anode and a cathode are so disposed that a comparatively low voltage applied thereacross will produce a discharge within the envelope causing the cathode to become enveloped in a glow.

Where it is desired to obtain a very concentrated light source in such glow lamps, the cathode or negative electrode thereof is formed with a cavity or deep recess and the gas pressure is so chosen with relation to the dimensions of the recess and the voltage of the supply circuit that substantially all the discharge occurs in the recess or crater in the electrode, thereby producing a spot of intense light or glow the size of the cross section of the recess, and variable in luminosity with variations of current in the supply circuit. Such crater-type glow lamps are useful as a light source in apparatus for transmitting facsimiles, photographs and motion pictures by wire or by radio, and as the light source of the receiver or reproducer in television apparatus and for many other purposes where a very concentrated light source is required.

The concentrated glow discharge produced by such crater-type glow discharge lamps is also well adapted for use in lighting arrays or groupings thereof to form an illuminated readout or other display device such as, for example, a numeric or alpha-numeric readout device. However, in the prior crater-type glow discharge lamps, the lamp electrodes and associated supporting structures generally have been mounted Within a separate enclosing envelope the additional size of which therefore adds to the overall size of the lamp. As a result, lighting arrays composed of such prior crater-type glow discharge lamps mounted alongside one another are characterized by comparatively poor delineation and readability of the illumi- 3,510,717 Patented May 5, 1970 nated characters produced by the lighting array owing to the fact that, because of the dimensional size of the lamp envelope, the crater glow discharges produced within the individual lamps making up the lighting array necessarily are spaced an inordinate distance apart. The dimensional size of the enclosing envelopes of such prior crater-type glow discharge devices also places a limitation on the minimum overall size of lighting array which can be obtained therewith.

Summary of the invention It is an object of the invention, therefore, to provide a crater-type glow discharge device of the end-on light emission type which is of appreciably smaller width dimension than that of prior crater-type glow discharge devices.

Another object of the invention is to provide a cratertype glow discharge device comprised of an enclosing envelope formed principally by the cathode and anode electrodes of the device.

Still another object of the invention is to provide a crater-type glow discharge device which is of simplified construction such as lends itself to fabrication by a simplified manufacturing procedure.

A further object of the invention is to provide a cratertype glow discharge device of the end-on light emission type which is of minimal width dimension such as permits the mounting of a large number of the devices sideby-side in a relatively close space to thereby form a lighting array readout capable of producing lighted characters of greatly improved delineation and readability as compared to that obtained heretofore with prior type glow discharge devices.

Briefly stated, in accordance with one aspect of the invention, a crater-type glow discharge device is made of minimum width dimension or size by having the envelope of the device formed principally by the metal cathode and anode electrodes thereof, for which purpose the electrodes are constituted by telescoped inner and outer metal tubes the outer one of which is hermetically sealed at one end by a glass window and at its other end to the inner electrode tube by a glass seal which serves to support the electrode tubes in spaced concentric relation. The device is evacuated, and filled with one or more rare gases at a low pressure, through the outer end of the inner metal tube which is then hermetically sealed off in a suitable manner.

According to a further aspect of the invention, the in ner end of the inner electrode tube or cathode is located adjacent the glass window of the device so that the glow discharge which forms within the hollow interior or crater of the inner electrode tube will, in turn, be correspondingly located adjacent the glass window of the device to thereby afford a good end-on lighted appearance to the device during operation.

According to a still further aspect of the invention, the outer side of that portion of the inner electrode tube or cathode extending into the outer electrode tube or anode from the glass seal therebetween is coated with an anti-glow material to thereby positively assure the confinement of the glow discharge to the hollow interior space or crater of the inner electrode tube.

Further objects and advantages of the invention will appear from the following detailed description of species thereof and from the accompanying drawing.

Brief description of the drawing In the drawing:

FIG. 1 is a sectional view of a gaseous electric glow discharge device according to the invention;

FIG. 2 is a fragmentary perspective view, partly in section, of the glow discharge device shown in FIG. 1;

FIG. 3 is a fragmentary sectional view of the outer end of the inner electrode tube of the glow discharge device according to the invention illustrating a modified manner of hermetically sealing off the said inner electrode tube, and

FIG. 4 is an elevational view showing a number of individual glow discharge devices according to the invention arranged in side-by-side relation to form a representative lighting array or readout device.

Description of the preferred embodiments Referring to the drawing, the glow discharge device according to the invention comprises an envelope 1 containing a gaseous filling of a rare gas such as neon, argon, helium or krypton, or mixtures thereof, at a relatively low pressure within the range of, for example from 20 to 100 torr., to give the desired breakdown potential for the device. The envelope 1 is comprised of inner and

outer metal tubes

2 and 3 which constitute the cold cathode electrode and anode electrode, respectively, of the discharge device and are hermetically sealed together and supported in spaced concentric relation by a glass collar 4 fusion-sealed to the inner electrode tube 2 and to one end 5 of the outer electrode tube 3 to form a glass seal therebetween. The glass collar or seal 4 is made of a suitable glass, preferably any of the low expansion heat-resisting glasses such as are customarily referred to as hard glasses and are commonly employed in the lamp art for glass-to-metal seals. The

electrode tubes

2 and 3 may be made of any suitable metal having a coefficient of expansion approximately matching that of the glass of the seal 4 and which will wet and adhere thereto. A preferred material for the

cold electrodes

2 and 3 is an alloy of iron, nickel and cobalt such as, for example, that commercially known as Kovar and consisting essentially of, by weight, 54% iron, 29% nickel and 17% cobalt. As shown, the outer metal tube or anode 3 has an inside diameter somewhat greater than, but less than twice the outside diameter of the inner metal tube or cathode 2 so that the spacial distance between the walls of the telescoped portions of the

metal tubes

2 and 3 is considerably smaller than the inside diameter of the inner metal tube 2. A very closely compacted arrangement of the

telescoped tubes

2 and 3, and thus an optimum minimal outside dimension for the glow discharge device is thereby afforded, among other things.

The other end 6 of the outer electrode tube 3 is hermetically sealed off by a glass window 7 through which is emitted the light from the glow discharge which forms within the hollow interior of the inner electrode tube or cathode 2 during the operation of the glow discharge device. The glass of which the window 7 is made may be similar to that employed for the glass seal 4.

As shown, the inner electrode tube or cathode 2 preferably extends into the outer metal tube 3 from the glass seal 4 therebetween to a point adjacent the glass window 7 so as to locate its inner end 8, and thus the glow discharge which forms therewithin during the operation of the device, as near as possible to the glass window 7, thereby affording maximum emission of the light from the glow discharge within the cathode tube 2. The outer end of the inner electrode tube or cathode 2 is hermetically sealed off in a suitable manner, as by means of the tippedoif residue or glass tip 9 of a glass exhaust tube which is fusion-sealed to the end of the inner electrode tube 2 and through which the gas filling is introduced into the envelope 1.

If desired, the inside wall of the inner electrode tube 2 may be coated with a suitable electron emissive material of low work function such as is commonly employed in glow discharge devices to reduce the operating voltage of the device. A suitable electron emissive material for such purpose may be barium oxide.

While there is a strong tendency for the glow discharge to concentrate within the inner electrode tube 2 during the operation of the glow discharge device, it is advisable to coat the outer side of that portion of the inner electrode tube 2 which extends into the outer tube from the glass seal 4 therebetween with a suitable anti-glow material, as indicated at 10, in order to thereby assure the confinement of the glow discharge within the interior of the inner electrode tube 2 at all times during the operation of the device. Finely powdered aluminum is preferably used for the anti-glow coating 10, since it has been found to be extremely elfective for this purpose, but any other substance which has the like property of resisting the creeping of the cathode glow discharge, such as insulating materials like aluminum oxide, may be used if desired.

Instead of the inner electrode tube 2 being hermetically sealed off at its outer end by the glass exhaust tube tip 9, it may be sealed off by a plug 11 of a suitable fusible material filling the outer end of the inner electrode tube 2, as shown in FIG. 3. The sealing plug 11 may be formed of metal that will wet and adhere to the particular metal employed for the inner electrode tube 2. Thus, where the inner electrode tube 2 is made of an alloy of iron, nickel and cobalt such as Kovar, the sealing plug 11 may be formed of brass, for example.

In the operation of the electric glow discharge device according to the invention, when the anode 3 and cathode 2 are connected, respectively, to the positive and negative sides of a DC. power supply of sufficient potential to cause the breakdown of the device, a negative glow discharge is formed in, and is confined within the hollow interior or crater of the inner electrode tube 2. The concentrated light source thus formed by this glow discharge within the inner electrode tube 2 is then directed outwardly from the open inner end 8 thereof as a concentrated beam of light which then passes out through the glass window 7 in the end of the outer electrode tube 3. Because of the concentrated character of the light beam produced by the glow discharge device according to the invention, it is therefore well suited for use as a signal or indicator light, or in a lighting array composed of a grouping of such glow discharge devices mounted in side-by-side relation to form a numeric or other type readout device 12, as shown in FIG. 4. By selective operation of respective ones of the individual glow discharge devices making up such a lighting array or readout device 12, lighted numbers, letters or other characters of the desired selection may be made to appear at the viewing end of the readout device.

Since no enclosing envelope other than that formed by the

tubular electrodes

2, 3 themselves is necessary in the glow discharge device according to the invention, the discharge device therefore is of minimum width dimension or size, thus permitting the mounting of a large number of the devices side-by-side in a relatively close space to form a readout device 12. Thus, the glow discharge device according to the invention not only enables the formation of lighting array readouts 12 of considerably smaller size than that heretofore obtainable with prior type glow discharge devices, but also, and more importantly, assures greatly improved delineation and readability of the lighted characters produced by such readout devices because of the closer positioning of the light beams from the individual discharge devices in the lighting array 12.

By forming the envelope 1 of the glow discharge device essentially out of the cathode and

anode electrode elements

2, 3 thereof, in the manner according to the invention, the number of component parts required to form the discharge device is thereby reduced, thus resulting in a crater-type glow discharge device which is of greatly simplified construction and reduced cost and which can be fabricated by a simplified manufacturing procedure.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. An electric glow discharge device comprising an envelope comprised of a pair of cold electrodes consisting of outer and inner metal tubes telescoped with one another, the outer electrode tube having a straight cylindrical inner wall of uniform diameter throughout its entire length and spaced from the inner electrode tube, said outer electrode tube having an inside diameter less than twice the outside diameter of the inner electrode tube and the inner electrode tube extending into the outer electrode tube from one end thereof but terminating short of its other end, a glass seal hermetically joining the said one end of the outer electrode tube to the inner electrode tube and supporting them in spaced concentric relation, a glass window hermetically sealing off the said other end of the outer electrode tube, said inner electrode tube being hermetically sealed off at its outer end, and a filling of a rare gas in said envelope at a low pressure.

2. An electric glow discharge device as specified in claim 1 wherein the inner end of the said inner electrode tube is located adjacent the said glass window.

3. An electric glow discharge device as specified in claim 1 and having a coating of an anti-glow material on the exterior surface of the portion of said inner electrode tube extending into said outer electrode tube from the said glass seal.

4. An electric glow discharge device as specified in claim 3 wherein the said anti-glow material is comprised of powdered aluminum.

5. An electric glow discharge device as specified in claim 1 wherein the inner wall of the said inner electrode tube is coated with barium oxide.

6. An electric glow discharge device as specified in claim 1 wherein the said electrode tubes are composed of an alloy consisting essentially of iron, nickel, and cobalt.

7. An electric glow discharge device as specified in claim 1 wherein the said outer electrode tube is joined by said glass seal to a region of the said inner electrode tube between the ends thereof.

8. An electric glow discharge device as specified in claim 7 wherein the said inner electrode tube is hermetically sealed olf at its outer end by a tipped-off glass exhaust tube fusion-sealed thereto.

9. An electric glow discharge device as specified in claim 7 wherein the said inner electrode tube is hermetically sealed off at its outer end by a plug of fusible material therein consisting of a metal which will wet and adhere to the metal of said inner electrode tube.

References Cited UNITED STATES PATENTS 2,056,662 10/1936 Foulke 3l32l0 X 2,465,084 3/ 1949 Greiner 313-318 X 2,556,059 6/1951 Braunsdorif 3l3318 X 2,667,593 1/1954 Doolittle 3 133 18 X 2,802,130 8/1957 Engelman et a1. 313--210 X 2,876,385 3/1959 Landrey 313-210 X 3,020,437 2/ 1962 Horan 3133 l8 FOREIGN PATENTS 610,004 3/ 1935 Germany.

JAMES W. LAWRENCE, Primary Examiner P. C. DEMEO, Assistant Examiner US. Cl. X.R.