US2152985A - Electric gaseous discharge device - Google Patents

Description

April 1939- H. ALTERTHUM ET AL 2,152,985

ELECTRIC GASEOUS DISCHARGE DEVICE Filed Nov. 4, 1938 Fig.4

{xi @TQ INVENTOR H (m 6 AH; er chwm Arv ed Lo'm pe BY 50 M44 ZZORNEY mas-.1 Apr. 4, "1939 UNITED STATES ELECTRIC GASEOUS DISCHARGE DEVICE Hans Alterthnm, Berlin-Wilmcrsdori', and Arved Lompe, Berlin, Germany, assignors to General Electric Company, York a' corporation of New 3 Application November 4, 1938, Serial No. 238,866 In Germany November 10, 1937 '6 Claims. 176-126) The present invention relates to electric gaseous discharge devices, and particularly to cathodes of the so-called cold type for use in these devices.

A particular object of the invention is to provide a discharge device containing a rare gas, such as neon, at low pressure which will have a long useful life. Another object of the invention is to provide a discharge device having a high 1o luminous eificiency. A further object of the invention is to provide an improved cathode of the so-called cold type. Still further objects and advantages of the invention will appear from the following detailed description or from an inspec- 5 tion of the accompanying drawing.

The invention consists in the new and novel structure and combination of elements hereinafter set forth and claimed.

Where electric gaseous discharge tubes of the type having cold cathodes and producing light radiation by means of the positive column are filled with neon or with mercury and neon, the neon pressure, in practice, has always been in excess of 4 mm. The reason for this is the fact that at lower pressures than 4 mm. the neon is rapidly consumed, whereby the tube becomes hard, that is it no longer ignites nor burns at the applied voltage. While it was known that one could greatly improve the light yield of the tubes and also achieve other advantages with filling pressures below 4 mm., such tubes, although they have often been made in the laboratory and also described in the literature, could not be placed on the market because, for the reasons given above, they did not have a sufiicient life span and.were incapable of lasting 2000 hours and more, as do the tubes with filling pressures above Many proposals have been made heretofore as to means to retard the consumption of the rare gas. Almost all these proposals were based upon the idea that the cathode spattering which is caused by the discharge is the cause of the gas consumption, namely that the rare gas ions 5 which strike the cathode fly away with the spattered cathode particles and are-built by the latter' into the coating which is formed on the glass wall of the tube. Thus for the purpose of avoiding this undesired condition it has been proposed to make the electrodes in the form of grids, wire netting, and slitted or perforated hollow sheet metal bodies of such metals as iron, tungsten, aluminum, copper or molybdenum. With these structures the rare gas ions, without influencing the electrodes, were expected to pass freely through the intermediate spaces which exist between the wires or in the sheet metal'grids. The hitherto known electrodes of this kind have, however, actually not fulfilled this task; especially with neon filling pressures below 4 mm., there occurred a rapid spattering of the electrodes up to a complete disintegration of the latter, together with a consumption of the gas filling which was negligibly retarded as compared with hollow, cylindrical electrodes made of solid sheet metal. As a result it has been impossible to reduce the neon filling pressure below 4 mm. and still attain a satisfactory life span in devices using these electrodes.

We have now discovered that this undesired gas consumption or clean-uphis not caused by the spattering, as heretofore believed, but that on the contrary even a considerable amount of spattering of the electrode does not result in appreciable gas consumption, even in electric high voltage luminous tubes filled with neon or neonmercury of less than 4 mm., provided a novel cathode of our invention is employed. According to our invention these tubes are provided with hollow electrodes of wire or sheet metal which are open in the direction of the discharge path, and which in their wall have uniformly distributed slits or slots of 0.3-0.7 mm. width, with these slots in their entirety amounting to 40-60% of the ideal electrode-surface. Under the heading of ideal electrode-surface we here understand the surface which completely covers the electrode including the slits or slots contained in it.

As for the rest,the form and length of the slits or slots can be as desired. The electrodes are, for instance, made of hollow, sheet metal bodies in which slots of the above given width are stamped out, or alternatively the electrode consists of a wire wound into a helix, or of equally large wire rings arranged above each other with space between them, or of wire rods which are arranged beside each other in a circle like a grid and which run in the longitudinal direction of the discharge, while the distance between the helical windings or between the wire parts which run parallel in a longitudinal or transverse direction, all of which consist preferably of iron wire of 0.5 mm. thickness, expediently amounts to 0.5 mm.

Thorough measurements have shown that observance of the limits of 0.3-0.7 mm. given for the 'slot width is of decisive significance for the gas consumption, especially in tubes with neon below 4 mm. pressure. Thus with tubes of this pressure, a pronounced minimum value of the gas conhitherto customary solid, sheet metal electrodes is a about eight times as large. The thickness of the wire, which expediently is likewise 0.5 mm., is so proportioned in the new electrodes that, on the one hand, the slots amount to the largest possible portion of the ideal electrode-surface, but that, on the other hand, the wire is not rapidly eaten through by the spattering, which otherwise occurs easily at an essentially smaller wire diameter than 0.5 mm.

While the electrodes of the tubes according to the invention spatter somewhat in operation, the gas consumption is not in any way influenced thereby, nor is the life span decreased below the values useful in commercial practice, for instance 2000 hours. However, in order to avoid any possibility of rapid mechanical destruction of the uppermost and lowermost edges of the electrodes, which are especially subject to the spattering, these edges of the electrode are each thickened by a ring which has a larger cross section than the wire or sheet metal used for making the electrode, in a preferred form of the invention. The spattered particles which fly all all the electrode parts are also prevented from reaching the vessel wall, where desired, by means of a sheet metal mantle which is concentrically placed around the hollow electrode with space between them, but which is not electrically connected with the electrode, so that no blackening occurs on the vessel wall.

The appearance and the behavior of the electrodes during operation is practically the same as that of hollow cylindrical electrodes made of imperforate sheet metal, that is the cathode glow light afiixes itself inside of the hollow space and does not penetrate for instance through the individual slits or envelope them, as is the case with cathode glow light lamps having a wireshaped or net-shaped electrode. Therefore, only a cohesive glow-film is formed inside of the electrode, and the electrode therefore also has the same low cathode fall as an electrode of imperforate sheet metal. The fact that the gas consumption is surprisingly so much smaller evidently is due to the fact that the rare gas ions, which are accelerated in the cathode fall and which therefore easily succumb to consumption, in part do not strike the metallic parts of the electrode but pass through the intermediate spaces of the latter, after they have been discharged in the glow layer. The increase in the gas consumption which occurs upon enlargement of the intermediate spaces is due in all probability to the fact that, even though the glow-film is then still cohesively present to the eye, the electric field in the glow-film has a preferential direction toward the metallic parts of the electrode, so that also a larger part of the arriving rare gas ions again strike these metallic parts.

High voltage luminous tubes according to the invention are filled, for instance, with neon of 3 mm. pressure; they then have a larger light yield and burn more steadily than tubes with, for instance, neon of 6 mm. of the hitherto customary filling. With a neon pressure of 2 mm. a still further increase in the light yield with a more uniform filling-out of the tube cross section by the light of the positive column is achieved. For

such low filling pressure, it is, however, especially advantageous according to the invention, if the electrodes of the above mentioned construction have a diameter of about 20 mm. and a length of about 90 mm. Thereby the current density in the cathode is reduced, which fact contributes to a further reduction of the gas consumption.

Luminous tubes of 20 mm. inside diameter and 50 cm. and more between the electrodes, filled with neon or neon-mercury at a pressure of 2 mm., and having electrodes constructed in this manner, reach life spans of over 2500 hours when operated with a discharge current of 50 milliamperes.

The electrode of a high voltage luminous tube according to the invention is shown schematically in front view in Fig. 1.

As shown in this figure the pinch stem I oarries the three electrode supports 2, 2 and 2", of which only the middle one 2' is carried through the stem and serves for actual current feeding. All three electrode supports continue in the props 3, 3' and 3" which carry the helix 4 which is wound from 0.5 mm. thick wire with an intermediate space of 0.5 mm., and which props, for instance are welded to the helix at three places. The uppermost winding 5 and the lowermost winding 6 of the wire helix 4 are thickened or consist of special rings of thicker wire.

In Fig 2 an electrode is shown which is constructed like that of Fig. 1, except for the addition of a bottom plate 1 of insulating material which expediently consists of mica, quartz, glass or a ceramic material, in order to be able to withstand the temperatures which occur during degassing of the electrode. This bottom plate of insulating material closes the end of the electrode and serves, according to the invention, to shield the lower metallic parts of the electrode which are otherwise especially exposed to spattering, that is the electrode supports 2, 2' and 2", from bombardment by the discharge.

In Fig. 3, finally, an electrode for a mercury high voltage luminous tube with a neon filling is shown, which electrode, at its rear end, has a vessel which subsequently delivers mercury and which serves in the same manner as the plate I of Fig. 2 to close the electrode body. The vessel consists of a sheet metal hollow body 8 which is closed on all sides except for an opening 9 toward the side of the discharge path, which opening is lengthened into the inside of the sheet metal hollow body 8 by means of a sheet metal capillary ID. This sheet metal hollow body contains a small amount of mercury II which, upon heating of the sheet metal hollow body by means of the discharge, provides the mercury vapor which serves for subsequently feeding the tube filling. An electrode for mercury luminous tubes with a low rare gas filling pressure, which electrode according to the invention is constructed in this manner and does not consume gas, avoids discoloration at winter temperatures. That part of the sheet metal hollow body 8 which faces the electrode can moreover be covered, where desired, with an insulating plate 1, as in Fig. 2,

' which is bored through at the opening 9 of the small capillary tube l0, whereby any increase in the gas consumption, such as might otherwise result from the presence of the imperforate metal body 8 is prevented.

In Fig. 4 there is shown an elevational view of a discharge device having our novel electrodes incorporated therein.

High voltage luminous tubes according to the aioaoas gon, krypton or xenon is added where desired to the neon filling, in order either to reduce the igni tion voltage of the tube, or in the co-presence of mercury vapor to prevent a red coloration of the tube at low outside temperatures. It is likewise to be understood that various other changes, omissions and substitutions, within the scope of the appended claims, may be made in the structure illustrated and described without departing from the spirit of our invention.

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

1. An electric gaseous discharge device comprising an elongated sealed envelope having an electrode at each end thereof, at least one of said electrodes consisting of a hollow metal body which is open in the direction of the discharge path to the other electrode and having uniformly distributed slits in the wall thereof of a width of from 0.3 to 0.7 mm., said slits in their entirety occupying -60% of the area of the inner surface which said electrode would have if imperforate, and a filling of neon at low pressure within said envelope.

2. An electric gaseous discharge device comprising an elongated sealed envelope having an electrode at each end thereof, at least one of said electrodes consisting of a hollow metal body which is open in the direction of the discharge path to the other electrode and having its surface uniformly perforated with slits 0.5 mm. wide separated by metal portions of the same width,

and a filling of neon at low pressure within said envelope.

3. A cathode for an electric gaseous discharge device comprising a hollow metal body having an open end, said body having uniformly distributed slits in the wall thereof of a width of from 0.3 to 0.7 mm., said slits in their entirety occupying 40-60% of the area of the inner surface said electrode would have if imperforate.

4. A cathode for an electric gaseous discharge device comprising a hollow metal body having open ends, a second metal body having a capillary opening and containing a vaporizable material located adjacent one of said ends, said first mentioned metal body .,having uniformly distributed slits in the wall thereof of a width of from. 0.3 to 0.7 mm., said slits in their entirety occupying 40-60%of the area of the inner surface said electrode would have if imperforate.

5. A cathode for an electric gaseous discharge device comprising a hollow metal body having open ends, a second metal body having a capillary opening and containing mercury located adjacent one of said ends, said first mentioned metal body having uniformly distributed slits in the wall thereof of a width of from 0.3 to 0.7 mm., said slits in their entirety occupying 40-60% of the area of the inner surface said electrode would have if imperforate.

6. A cathode for an electric gaseous discharge device comprising a hollow metal body having open ends. one of said ends being closed by a sheet of insulating material, said body having uniformly distributed slits in the wall thereof of a width of from 0.3 to 0.7 mm., said slits in their entirety occupying 40-60% of the area of the inner surface said electrode would have if imperforate.

HANS ALTERTHUM. ARVED LOMPE.

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