US1943846A - Alternating current electrical discharge device - Google Patents

Description

ALTERNATING CURRENT ELECTRICAL DISCHARGE DEVICE Filed March 7, 1930 HARL S SPRGZ'VH Smventoz Patented Jan. 16, 1934 ALTERNATING CURRENT ELECTRICAL DISCHARGE DEVICE Charles Spaeth, Flushing, N. Y., assignor to Ne-Arga Corporation, New York, N. Y., a corporation of New York Application March '7, 1930. Serial No. 433,967

7 Claims.

This invention relates to electrical discharge devices of the alternating current type.

It is an object of my invention to provide a full wave electrical discharge device which is adapted to operate efficiently for long periods of time at high current density.

Another object is the provision of an electrical discharge device which is so arranged and operated that an alkali metal electrode may be used 0 at high current density without destructive sputtering effects.

In accordance with my invention an electrical discharge illuminating tube is constructed with an elongated light transmitting gas filled envelope having at one end a pair of electrode chambers and at the other end a single cooperating electrode chamber. The electrodes of said pair of chambers are so arranged to be connected to a source of potential such as a secondary of a trans former and are adapted to produce electrons under the influence of normal exciting current. A connection is made from an intermediate point of said source of potential, e. g., an intermediate point of the secondary to the single electrode which cooperates with said pair of electrodes. This single electrode may be of alkali metal in order to reduce the potential drop thereof. In operation the potential of the supply source is so selected that the pair of electrodes are ex cited by the currents passing between them, sufficiently to eject electrons. This insures that each of these electrodes in turn will act as a cathode in cooperation with the single electrode which then must necessarily be the anode. As

the anode fall of potential of all metallic materials is low the sputtering of the single electrode will be slight. However, an alkali metal, which has a very small fall to potential when being used as an anode, may form the single electrode.

Where an alkali metal is so used, the sputtering is not suflicient to coat the main light emitting portion of the envelope. For this reason, even when using an alkali metal in order to reduce the necessary operating potential of such an electrical discharge device, a normal discharge current may be passed through the device many times as great as that which may normally be successfully used with it, when the alkali metal serves as a cathode. This is due to the fact that an anode fall of potential is only a small fraction of a cathode fall of potential of a metal.

The above mentioned and other objects and advantages of the device and manner of obtaining them will be made clear in the following description and accompanying drawing.

In the drawing, the figure illustrates a tube constructed in accordance with my invention, and the operating circuit therefor.

Reference numeral 1 indicates an envelope or 69 tube of glass, quartz or other light transmitting material having a filling of rare gas, such as neon, at a pressure of a few millimeters of mercury. This envelope has at one end a pair of electrode chambers 2 and 3 containing electrodes 4 and 5 respectively. At the other end of the tube is a chamber 6 containing an electrode '7 which is preferably of an alkali metal or alloy thereof, but which may be of any other ordinary material. The electrodes 4 and 5 preferably comprise a relatively thin sheet of tungsten which is adapted to be heated to incandescence by passage of normal discharge current therethrough. These electrode are of low thermal capacity. Other electrode materials may be used in place thereof, provided they are adapted to produce electrons in normal operating conditions. Connected to the envelope 1 at some suitable point, for example, adjacent the electrode chambers 2 and 3, is a reservoir 8 containing a quantity of mercury 9. A tube 10 which projects within the reservoir prevents the mercury from entering the main portion of the envelope 1. Connected to the envelope 1 and projecting within the electrode chamber 6 is a tube 11 of restricted diameter, the object of which is to prevent particles sputtered from the surface of the electrode 7 from entering the light emitting portion of the envelope 1. Adjacent to the pointof junction to this tube and the envelope 1 a plurality of small openings or breather holes 12 are made in the wall of the tube.

The circuit connections for the device comprise a transformer 13 having its primary connected to a suitable source of potential 14 and having its secondary 15 connected to the electrodes 4 and 5 through the usual lead-in wires.

A connectlon 16 is made from the mid point of the transformer secondary through a choke coil 17 and the lead-in wire to the electrode 7, and another connection is made between one of the pair of electrodes, for example, 5 and a lead-in wire of the mercury electrode 9. This connection includes a variable resistance 18.

In operation the current supply source 14 is caused to energize the primary of the transformer whereupon a potential is applied to the electrodes 4 and 5 which causes a gaseous discharge current to pass therebetween. This discharge is sufiicient, because of the proper proportioning of the potential of the transformer secondary with respect to the spacing between the electrodes and the pressure of the gas within the envelope, to cause electrodes 4 and 5 to become heated to the point of incandescence. As soon as this point is reached the electrodes start radiating electrons. These electrodes are therefore thermionic. A discharge is now caused to pass through the main portion of the tube between electrodes 4 and 5 and the single electrode '7. The potential which is applied between either of the electrodes 4 and 5 and electrode 7 is normally insufiicient to create a discharge therebetween but is great enough to maintain such a discharge when it is initiated by auxiliary means. Any means well known to the art may be used, such as a high frequency generator or other device for creating an instantaneous high potential between the two electrodes. Because the electrodes 4 and 5 are heated to the point of producing electrons they will of necessity each act as a cathode with respect to the electrode '7. The device therefore operates in full wave manner utilizing both alternations of the supply current cycle, the current passing alternately from the electrode 7 to the electrodes 4 and 5. The choke coil 17 functions in the usual manner to smooth out the flow of current from the tube.

The auxiliary circuit connection between the transformer and the mercury electrode 9 causes a quantity of this mercury to be vaporized and diffused through the gas within the main portion of the envelope 1. By adjusting the value of the resistance, the amount of mercury vapor may be controlled. This general principle is more fully set forth in my copending application Serial No. 343,873, filed March 2, 1929. This vapor, as stated before, passes down into the main bed of the envelope, and is energized by the passage of the main discharge current therethrough, with the result that the light emitted by the tube is a combination of that characteristic of the gas filling plus that characteristic of mercury vapor. Where the gas used is neon the resultant light will be a combination of neon red and mercury blue. By adjusting the resistance the color of the emitted. light may be varied between the pure neon red and the substantially pure mercury blue. In the latter case, the mercury may be made entirely to mask the light produced by the neon. By properly adjusting the resistance 18 the produced light may be made white in appearance. I have found that where a tube is used at 11 of relatively small size and great length that an even diffusion of the mercury vapor through the discharge path of the electrodes 4 and 5 and cooperating electrodes 7 is not had. This effect may be overcome by providing small apertures or breather holes 12 which in some manner permit the mercury vapor to permeate the entire length of the gaseous discharge path so that light of even color is produced the entire length of the tube.

I find that successful results may be obtained by utilizing at 1 an envelope having a length of approximately 52" and a bore in the neighborhood of 18 mm., the distance between the electrodes 4 and 5 being about 6" and the tube being filled with neon gas at a pressure of about 1 /2 mm. of mercury. With these dimensions the electrodes 4 and 5, may be of tungsten about five thousandths of an inch thick and having an area of approximately one square inch. An alkali metal anode is used at 7. The tube 11 may be 1 /2" long and have a bore of about 11 mm.

A tube thus designed will produce excellent results when the potential of the transformer secondary 15 is approximately 600 volts, in which case the current through the main discharge path of the tube will be of the order of 10 amperes. when the resistance 18 is so regulated that I: the light produced is between neon red and mercury blue in color. While the'pressure of neon gas within a tube of this length may be as low as 1 /2 mm., when a shorter tube is used higher pressures are necessary for best results. As stated above, I prefer to use thin tungsten electrodes which are so proportioned as to be heated to incandescence upon application of normal discharge current, but other electrodes may be used. For example, tungsten, or other metal, may be coated with some of the well known electron emitting materials in which case they could be arranged to operate at much lower temperatures and still produce the necessary electron fiow.

What I claim is:

1. In an alternating current electrical discharge device, a gas filled envelope containing a pair of tungsten electrodes and an associated alkali metal electrode, means for applying a potential between said tungsten electrodes sufiicient to beat them to incandescence and for causing a current to flow between said alkali electrode and said pair of electrodes.

2. In an alternating current arrangement comprising an electrical discharge device, a gas filled envelope, a pair of metallic electrodes of low thermal capacity within one end of said envelope and spaced apart, a third electrode containing alkali metal within said envelope, said electrode being of relatively high thermal capacity and spaced from said pair of electrodes a distance greater than the spacing of the electrodes constituting said pair, a mercury pool, said mercury being adapted to be vaporized in small quantities and said vapor being adapted to be mixed with said gas to modify the color of the light radiated therefrom.

3. An arrangement in accordance with claim 2 wherein means is provided for passing a current between said pair of electrodes, and between each of said pair of electrodes and said third electrode.

a. In an electrical discharge device, an envelope containing a rare gas and a quantity of mercury, an electrode chamber at one end of said envelope, a tube of smaller diameter than said envelope sealed to said envelope and projecting within said chamber, and a plurality of breather holes in said tube adjacent to its point of juncture with said envelope.

5. In an alternating current electrical discharge arrangement, a gas filled envelope, 2. pair of thermionic electrodes within said envelope and spaced apart, a third electrode within said envelope and spaced from said pair of electrodes a greater distance than the spacing of the electrodes constituting said pair, a transformer having its secondary terminals connected to said pair of electrodes and a connection from a point between said terminals to said third electrode, the potential of said transformer being suificient to cause said thermionic electrodes to emit electrons.

6. In an alternating current electrical discharge arrangement, a gas filled envelope, a pair of thermionic electrodes within said envelope and spaced apart, a third electrode of alkali metal within said envelope and spaced apart from said pair of electrodes a greater distance than the spacing of the electrodes constituting said pair.

'I. An alternating current electrical discharge arrangement comprising an envelope filled with neon gas, means for adding a quantity of mercury vapor thereto, a pair of thermionic electrodes within said envelope and spaced apart, a third electrode within said envelope and spaced from said pair of electrodes a greater distance than the spacing of the electrodes constituting said pair.

CHARLES SPAETH.

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