US1961754A - Method of and apparatus for operating gaseous electric discharge devices - Google Patents

Description

June 5,1934. Y J FQRNEY 1,961,754"

METHOD OF AND APPARATUS FOR PERATING GASEOUS ELECTRIC DISCHARGE DEVICES Filed Jan. 31, 1931 INVENTOR 1| I U BY ATTORNEY Patented June 5, 1934 UNITED STATES PATENT OFFICE METHOD OF AND APPARATUS FOR. OPERAT- ING GASEOUS ELECTRIC DISCHARGE DEVICES Application January 31,

9 Claims.

The present invention relates to electric discharge devices, and more particularly to gas or vapor discharge devices which operate with a hot cathode.

A particular object of the invention is to provide an improved method of and apparatus for starting and operating such devices. Another object of my invention is to provide a method of and apparatus for preventing operation of the- 10 said starting and operating apparatus if and when the discharge device has been damaged. Other objects and advantages of the invention will appear from the following detailed specification, or from an inspection of the accompanying drawing.

The invention consists in the new apparatus and in the new and novel methods of operation, as hereinafter set forth and claimed.

A well known type of electric gaseous discharge device utilizes a so-called hot cathode, which is usually coated with an active thermionic material such as barium, strontium, or compounds thereof, or mixtures of the aforesaid, to increase the thermionic emission therefrom, in order to eliminate the relatively high cathode fall which is characteristic of the ordinary gaseous discharge device. Due to the thermal capacity of these electrodes an appreciable interval, of say to 45 seconds, is required at starting before the heating means usually provided can bring these cathodes to a temperature at which the thermionic emission therefrom will be suflicient to support the normal discharge current. The operating potential of thesedevices being ordinarily insuificient to initiate the discharge therein, an auxiliary starting means is commonly employed for this purpose. Experience has taught that actuation of this starting means must be delayed until the cathode has 40 reached substantially operating temperature, for if the discharge is initiated before the cathode temperature is such as to provide sufiicient electron emission the discharge will form a hot spot thereon which will seriously injure, if not destroy, the cathode. Various means of providing this delay have been suggested heretofore, but all have been based on the related functions of cathode temperature or time, rather than on the fundamental characteristic of electron emis- 5 sion. I have now discovered that the electron emission from the cathode may be directly availed of to actuate the discharge initiating means at precisely the right time regardless of -ambient temperature, deterioration of the ac- 5 tive surface, or variation in other factors which 1931, Serial No. 512,678

have adversely aifected the operation of the delay means heretofore provided. According to my new invention an axuiliary anode is provided adjacent to the cathode. A potential which is suflicient to collect at least part of the electrons which are emitted from the cathode, but which is at the same time insufficient to disintegrate the cathode by bombardment thereof, or to cause a destructive localized discharge or hot spot thereon, is applied between said auxiliary anode and said cathode. The thermionic emission from the cathode is infinitesimal while the cathode is cold, but rapidly increases as said cathode approaches operating temperature, as is well known. Hence the current flowing from said anode, which is a direct function of said emission, likewise rapidly increases as the oathode approaches operating temperature. I have discovered that this current, which is thus a measure of the thermionic emission, can be utilized to actuate the means by which the main arc is initiated. Thus, if this means is so adjusted as to operate when the current flowing from the auxiliary anode equals the normal discharge current no damage can be done to the cathode, provided that the auxiliary anode is simultaneously disconnected. I have also discovered that it is not necessary to delay the initiation of the are for so long a period, since I have also found that the main discharge may be safely initiated as soon as the current from the auxiliary anode is appreciable, say a sixth of the value of the normal discharge current. While it is probable that the initiation of the main discharge at this time momentarily results in an increased cathode fall, which assists in the heating of the cathode, it is an observed fact that no hot spot is formed thereby, hence this mode of operation is not only entirely satisfactory, but extremely desirable, since it results in cutting the delay period to the minimum. A further advantage of my new invention is found in the fact that if the discharge device is damaged in any way which seriously reduces the thermionic emission, as by breakage of the envelope, the discharge initiating means is rendered inoperative, thus avoiding the production of electrical strains on the associated auxiliary apparatus. In order to reduce the demands on the cathode, and to increase the efiiciency of the discharge device, the auxiliary anode is preferably disconnected at the same time that the main discharge is initiated, a simple means being provided therefor.

For the purpose of illustration I have shown in 11 the accompanying drawing a diagrammatic representation, in part section, of a preferred embodiment of my invention.

In this drawing there is shown a gaseous discharge device 1 of the Cooper Hewitt type, containing a suitable gas or vapor, such as neon or mercury vapor, at a pressure of say 0.5 to 4.0 millimeters of mercury, and employing a hot cathode 2 and anode 3 of iron, graphite or the like. Said cathode, which is of nickel or other suitable material, is in the shape of a hollow truncated cone and is entirely closed except for the opening 4 in the larger end thereof, which faces away from said anodes 3. The interior of said cathode is. preferably coated with a substance which will readily emit electrons when heated, such as barium or strontium or compounds thereof, or mixtures of the aforesaid. Said cathode is suitably supported at some distance from the pinch seal by a nickel wire 5 which is welded thereto, the other end of said wire connecting with the inlead 6 at a point near said seal. A tube 7 of thoria or other suitable refractory material which extends into said cathode 2 through the smaller end thereof has a heater 8 of tungsten or the like wound thereon, one end of said heater being connected to said cathode while the other end thereof is connected to a wire 9 of molybdenum or other metal having a high melting point which passes through said tube '7. Said wire 9 is in turn connected in a suitable manner to the inlead 10. A third inlead 11 terminates in a coiled tungsten electrode 12 which serves as an auxiliary anode during the starting of the device, said electrode 12 being located near the opening 4 in the oathode 2. The inlead 11 is preferably enclosed within a glass sheath extending from the pinch seal to a point near the electrode 12, in order to prevent any possible connection thereof to the other inleads by sputtered metal or the like.

An autotransformer 14 which is connected to a suitable source of alternating current through a. ballast resistance 15, has the ends thereof connected to the anodes 3 in the usual manner. The midpoint on said autotransformer 14 is connected through an inductance 16 to the inlead 6. Said inlead is also connected to one terminal of a low voltage secondary which is in inductive relation to the autotransformer 14, the other end of said secondary being connected to the inlead 10. A connection is likewise made from the inlead 11 through a mercury switch 18 of the type commonly called a. shifter, and a resistance 19 to a point of suitable potential on the autotransformer 14. Said switch 18, which is -normally in a closed circuit position, has an armature connected thereto which is in magnetic relation to the inductance 16, whereby said switch is opened whenever a current of a desired value traverses said inductance. Where the normal arc current is 3.5 amperes this switch is usually set to open at 0.75 amperes.

In the use and operation of this device a suitable alternating current potential is first applied to the autotransformer 14. The secondary 17 is thereby energized, causing a current of several amperes to flow from said secondary 1'? through inlead 10, wire 9, heater 8, cathode 2, support wire 5, and inlead 6 back to said secondary. The gaseous content of the lamp 1 not being ionized, a discharge will not be produced between the anodes 3 and the cathode 2 at the relatively low potential available from the autotransformer 14, as is well known. Since the cathode 2 is cold the thermionic emission therefrom is inflnitesi mal, hence the discharge permitted thereby from the auxiliary anode, which is at a potential of say 70-100 volts higher than that of the cathode 2, will not exceed a few microamperes. To this there may be added a possible cathode glow discharge current of a few milliamperes. The inductance 16, which is in series with both the main and auxiliary discharge paths, will not, therefore, be traversed by any appreciable current at this time. As the cathode temperature rises under the influence of the heater 8 the thermionic emission therefrom will increase more and more rapidly, according to a well known law. The half-wave current flowing from the autotransformer 14 through resistance 19, shifter 18 and inlead 11 to the auxiliary anode 12, through the gaseous atmosphere of the discharge device 1 to the oathode 2, and thence through inlead 6, and inductance 16 back to said autotransformer 14, being determined by said emission, varies in a like manner. After an interval of say 15 seconds this current may equal 0.75 amperes in a device connected as shown and having a normal arc current of 3.5 amperes. The armature of the shifter 18 is thereupon attracted by the-inductance 16, causing said shifter to open the circuit therethrough. Not only is the auxiliary anode 12 thereby disconnected, but the circuit through the inductance 16 is interrupted. As the magnetic field about said inductance 16 collapses a high potential surge is generated therein which momentarily so depresses the potential of the cathode 2 that the main discharge is initiated from an anode 3 to said cathode 2, due to the abnormally high potential therebetween. This discharge is then continued at the normal impressed potential in a well known manner. Current thereupon flows from the autotransformer 14 through one or the other of the anodes 3, the arc space of the discharge device 1, cathode 2, support wire 5, inlead 6 and inductance 16 back to said autotransformer. The inductance 16 thus maintains the shifter 18 in an open circuit position so long as the are continues to operate. In case the arc is not initiated by the first kick of the shifter the circuit is again closed through said shifter 18, energizing said inductance 16 and thus again opening said shifter, with the attendant voltage surge as before, this cycle being automatically repeated until the main discharge has been initiated.

With this arrangement it is obvious that the discharge will be initiated with a minimum delay regardless of ambient temperature. Likewise, if the are should be interrupted by momentary power failure it is apparent that'the shifter 18 will be actuated immediately upon restoration of the line potential, provided the cathode 2 has not unduly cooled in the interval; and that even if it has appreciably cooled the delay will be only that necessary to restore the necessary emission. Furthermore, in case the active substance is partially destroyed, decreasing the emissivity of the cathode, it is obvious that my new apparatus provides proper compensation therefor. In case of breakage of the discharge device, or other accident which seriously impairs the emissivity of the cathode 2, so that it would be impossible to start the main discharge, my device automatically prevents the application of the repeated high voltage surges thereto, thereby saving the auxiliary apparatus the electrical strain to which it would otherwise be subjected.

While I have described my invention by reference to a discharge device of a particular type,

and designed for alternating currents, it is to be understood that it is not limited thereto. It is also to be understood that various changes, omissions and substitutions, within the scope of the appended claims, may be made therein, without departing from the spirit of my invention.

I claim as my invention:

1. In combination, an electric gaseous discharge device having a cathode adapted to emit electrons when heated and an anode, means for heating said cathode, and means responsive to the thermionic emission from said cathode to impress an abnormal potential upon said device to initiate a discharge in said device.

2. In combination, an electric gaseous discharge device having a cathode adapted to emit electrons when heated and an anode, means for heating said cathode, and means responsive to the thermionic emission from said cathode to impress an abnormal potential upon said device to initiate a discharge in said device when said emission is of such a value that it will support the normal discharge current without formation of a hot spot thereon.

3. In combination, an electric gaseous discharge device having a cathode adapted to emit electrons when heated and an anode, means for heating said cathode, and means to impress a voltage surge upon said device to initiate a discharge therein, said last mentioned means being responsive to the thermionic emission from said cathode.

4. In combination, an electric gaseous discharge device having a cathode adapted to emit electrons when heated and an anode, means forheating said cathode, an auxiliary anode adjacent to said cathode, means to maintain said auxiliary anode at a potential sufiicient to collect a portion of the free electron emission from said cathode, and means responsive to the resulting current to said auxiliary anode to impress an abnormal potential upon said devi'ce tov initiate a discharge from said anode to said cathode.

5. In combination. an electric gaseous discharge device having a cathode adapted to emit electrons when heated and an anode, means to heat said cathode, an auxiliary anode adjacent -to said cathode, means to maintain said auxiliary anode at such a potential that it collects the free electron emission from said cathode, and means responsive to the resulting current flow to said auxiliary anode to initiate a discharge from said anode to said cathode and to disconnect said auxiliary anode.

6. In combination, an electric gaseous discharge device having a cathode adapted to emit electrons when heated and an anode, means to heat said cathode, an auxiliary anode adjacent to said cathode. means to maintain said auxiliary anode at a potential sufficient to collect the free electron emission from said cathode, an inductance in series with said cathode and a shifter in the lead to said auxiliary anode and in electromagnetic relation to said inductance, and means to open said shifter when the current to said auxiliary anode reaches a predetermined value whereby said auxiliary anode is disconnected and a voltage surge is impressed upon said device to initiate the main discharge therein.

7. The method of operating an electric gaseous discharge device of the type having a cathode adapted to emit electrons when heated which comprises heating said cathode, collecting and measuring the free electron emission from said cathode, and applying an abnormal potential to said device to initiate a discharge therein when said free electron emission has reached a predetermined value.

8. The method of operating an electric gaseous discharge device of the type having a cathode adapted to emit electrons when heated which comprises collecting the free electron emission from said cathode passing the resulting current through an inductance, and opening the circuit through said inductance to produce a voltage surge to initiate a discharge in said device when said free electron emission has reached a predetermined value.

9. The method of operating an electric gaseous discharge device of the type having a cathode adapted to emit electrons when heated which comprises'collecting the free electron emission from said cathode at an auxiliary anode, passing of the resulting current to said anode through an

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