US2147445A - Combination starting electrode - Google Patents

Description

Feb; 14, 1939. D, KNOWLES I. 2,147,445

COMBINATION STARTING ELECTRODE Filed Oct. 21, 1936 WITNESSES; INVENTOR fi I De we D. Know/ks.

F. BY

I ATTOR EY Patented Feb. 14, 1939 UNITED STATES PATENT OFFICE COMBINATION STARTING ELECTRODE.

Pennsylvania Application October 21, 1936, Serial No. 106,791

6 Claims.

My invention relates to gaseous discharge devices, and especially a pool type of device in which an auxiliary electrode is utilized to establish an are between the pool and a main anode.

An object of my invention is to produce an arc discharge type of device having the sensitive starting characteristic of a glow discharge type of device.

Another object of my invention is to eliminate the requirement for glow tubes or other auxiliary means that have hitherto been necessary to fire the arc type of device.

Other objects and advantages of the invention will become apparent from the following description in which the figure is a view, partly in cross section of a tube incorporating my invention, and 1partly of diagrammatic circuit connections there- The are type of tube has been utilized where high peaks of current and long life are necessary. The common forms of such a device is a container having a vaporizable constructing material therein such as mercury or its amalgams that will vaporize and then recondense into its liquid pool. Such a type of device requires auxiliary electrodes for initiating an are between the pool and the one or more other main electrodes.

The prior art contains several types of these starting devices. The most recent and most successful of these auxiliary electrodes is the make-alive type in which a high resistance material such as carborundum or a composite or alloy of boron and carbide has its tip immersed in the pool of mercury. This type of device is designated by the registered mark of "Ignitron. Make-alive is a term designating a material, generally of the high resistance material referred to, which is in contact with the cathode and causes a cathode spot at the beginning of each conducting half cycle. While this type of device is especially adapted to have a very high surge capacity and rugged construction, yet it has the disadvantage that it is not as sensitive as might be desired for some uses.

Heretofore auxiliary tubes have been utilized to ignite this tube having the make-alive electrode therein. In firing the tube through the make-alive, these auxiliary tubes have to withstand for a few micro-seconds a peak current of 25 amperes under 100 volts or more pressure. Because of this high peak current, these tubes have to be constructed in large sizes, although the average current they carry is very small. Another difficulty with this pool type of device is that it is not very sensitive in cool weather because, due to its construction, no appreciable amount of heat is put into the device when it is started and the arc does not readily start with cold metallic vapor.

My invention, therefore, concerns with utilizing a very sensitive auxiliary starting electrode or grid in combination with the make-alive electrode to provide this are type discharge device with the sensitivity of the grid-glow type of tube.

In the figure of the drawing, a preferred type of tube is disclosed in which certain parts are enlarged for the sake of understanding clearly the invention. The tube, as illustrated, has a container wall ll] of glass with a pool II preferably of mercury and an upper chamber portion l2 containing the anode I3. Other types of container and the plurality and changed position of anodes may be utilized as disclosed in the prior art. 7

A control grid 14 may also be present, if desired. A starting electrode is placed adjacent the pool of mercury and this type of starting electrode is preferably of the make-alive type l5 of a high resistance material which is more particularly described in Patent No. 2,069,283 granted on the application of Joseph Slepian et al., Serial No. 626,866, filed July 30, 1932.

Heretofore it was necessary to provide a surge of current through this auxiliary electrode IE to establish the arc discharge between the pool I i and the anode l3. Inasmuch as the construction did not utilize any appreciable heating current, the tube had very low sensitivity in cold Weather.

My invention contemplates utilizing another sensitive auxiliary starting device in combination with the make-alive I5. I also desire to utilize such a device that will supply a certain amount of heat to the interior of the device in order that there may be little diificulty in establishing the are very quickly in the device. I have accordingly selected a hot cathode type of device for an auxiliary electrode and in particular the type of device which is described as a cathode in the copending application of Erwin F. Lowry, Serial No. 97,978, filed August 26, 1936.

This auxiliary electrode I6 preferably comprises two leads II and I8 for the heating current extending through a wall or press l9 in the casing to the interior thereof. A filament 2|] is connected to these leads in order to provide the heating energy. As disclosed, one end of this filament has a connection 2| extending through the insulating supporting base 22 to the filament lead [8. The filament is preferably enclosed within a cylindrical casing or enclosure 23 having a top cover 24 with a restricted opening 25 therein. If desired, a second cylindrical tube 26 preferably surrounds the inner casing 23 for the purpose of utilizing the heat most efficiently within the container 23.

The container 23 and the radiation of the heat shield 26, if used, are preferably connected electrically together such as at 21. The make-alive I5 is most conveniently connected to the auxiliary cathode 16 by the connection 28 to the exterior casing. The filament 20 or the interior walls of the enclosure 23, or both, are preferably covered with an electron emitting coating such as the oxides of barium and strontium.

The cathode connection 30 and the anode connection 3| are connected to a load 32 and the exterior source of anode-cathode power 33 which may be of any suitable primary or secondary type of electrical energy.

In starting the device, a heating current is put through the leads I! and I8 to produce electrons emitting from the interior of the enclosure 23 through the opening 25 to produce a glow discharge to the anode l3. The heating current and this glow discharge will raise the temperature of the mercury vapor in case the ambient temperature of the tube is cold. This glow discharge will take place at a very low current. The glow discharge will create a passage of current from the anode l3 to the auxiliary cathode IE to the connection 28 and the make-alive l5 to establish a cathode spot on the pool II that will create, in turn, an arc discharge from the anode l3 to this cathode spot on the mercury pool II. It will be noted that the make-alive l5 has a high resistance and this will contribute to cause a higher voltage drop in the path including the auxiliary electrode l6 and the make-alive l5 than in the path directly from the anode I3 to the surface of the mercury pool II.

I have utilized the particular type of auxiliary electrode IS in order to ensure that the discharge will very quickly change to the direct discharge between the anode l3 and the surface of the mercury pool II. The electrons emitted from the oxide coating within the container 23 will very soon saturate the opening 25. In order to increase the current flowing through this opening 25, a higher electrical pressure will be necessarily applied to create a larger current through this opening. Stated in other words, this means that the discharge current will be readily established up to a certain value, depending upon the size of the opening 25, and that thereafter any rise of current will be accompanied by a rise in the voltage drop between the anode l3 and the auxiliary electrode l6. This rise in voltage ensures that the discharge will transfer to the lower voltage drop path from the anode to the mercury pool.

As an example, I prefer to design the opening 25 so that the voltage drop rises when the current is approximately 10 to 20% greater than the firing current necessary for the firing current of the make-alive l5. This value gives the gradient necessary to transfer the discharge to the pool.

While I have disclosed a preferred embodiment of my invention, it is obvious that many modifications thereof are possible Within the spirit of my invention. I accordingly desire that the following claims should have only such limitations as are necessitated by the prior art.

I claim as my invention:

1. A discharge device comprising a container, a plurality of electrodes including a pool of vaporizable material therein, a make-alive in contact with said pool, an enclosure having an electron emissive coating connected to said makealive, said enclosure having a limited area for egress of electrons therefrom.

2. A discharge device comprising a container, a plurality of electrodes including a pool of vaporizable material therein, a make-alive in contact with said pool and a casing connected to said make-alive having a filament and an electron emitting coating therein.

3. A discharge device comprising a container, a plurality of electrodes including a pool of vaporizable material therein, a make-alive in contact with said pool and a casing connected to said make-alive having a heater and an electron emitting coating therein, said casing having a limited area for egress of electrons therefrom.

4. A discharge device comprising a container, a plurality of electrodes including a pool of vaporizable material therein, a starting electrode in contact with said pool, an enclosure having an electron emissive coating connected to said starting electrode, said enclosure having a limited area for egress of electrons therefrom.

5. A discharge device comprising a container, a plurality of electrodes including a pool of vaporizable material therein, a starting electrode in contact with said pool and a casing connected to said starting electrode having a filament and an electron emitting coating therein.

6. A discharge device comprising a container, a plurality of electrodes including a pool of vaporizable material therein, a starting electrode in contact with said pool and a casing connected to said starting electrode having a filament and an electron emitting coating therein, said casing having a limited area for egress of electrons therefrom.

DEWEY D. KNOWLES.

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