US2301237A - Electric arc device - Google Patents

Description

Filed March 30, 1940 (Ittorneg Patented Nov. 10, 1942 ELEOTRIC ARC DEVICE James R. Alburger, Merion, Pa., assignor to Radio Corporation of America,

Delaware a corporation of Application March 30, 1940, Serial No. 326,833

6 Claims.

This invention relates to mercury vapor lamps, rectifiers and like electric are devices of the type requiring the use of an auxiliary electrode for lighting or starting the arc.

It has previously been proposed to employ a bimetallic element or strip as a movable support for a starting electrode in a mercury arc device. The bimetallic element in such cases is arranged to be deformed when a heating current is passed through it and the mercury anode in which it is immersed when the device is unenergized. The heating current serves to vaporize some of the mercury and, as the starting electrode is moved by the bimetallic element through this conductive vapor, an arc is started which, when extended and transferred to the main cathode, lights up or otherwise starts the device. Since the vaporized mercury comprises a conductive medium which permeates the interior of the envelope, it is apparent that the heating-current may continue to flow through the device even when the bimetallic element operates, by its deformation, to withdraw the starting electrode from the liquid mercury.

The heating current in devices of the general character described is usefully employed only during the starting period. If the heating current continues to flow during the normal operating periods, it may adversely affect both the operating characteristics and the life of the device. It is, therefore, usual to employ an extemal relay in the heating circuit between the heating current source and the auxiliary electrode lead of the tube and to open this relay either manually or automatically when the arc has been started.

Even where the use of the heretofore necessary separate electrode terminal (for the starting electrode), auxiliary heating circuit, and auxiliary relay can be tolterated, their use fails to afford a satisfactory solution of the problem principally because in the tubes of the prior art the practice has been to so dispose the starting electrode that it remains in the path of the main arc irrespective of whether or not it is connected to the heating circuit. This results in excessive heating of the bimetallic element upon which the starting electrode is supported and in any event augments the tendency of the mercury to form an amalgam with the nickel and other thermal responsive metals of which the bimetallic element is constituted.

Accordingly, the principal object of the present invention is to obviate the above-described and other less apparent objections to electric arc devices of the general character described.

Another and related object of the invention is to provide a reliable and flickerless mercury arc lamp and one characterized by its economy of parts and absence of troublesome auxiliary starting apparatus.

Another and more specific object of the invention is to provide a mercury vapor device wherein the starting electrode is movable out of the path of the are between the anode and cathode whereby the dangers of destructive heating of this electrode and its support are substantially obviated.

Other objects and advantages will be apparent and the invention itself will be best understood by reference to the following specification and to the accompanying drawing wherein,

Figure 1 is a longitudinal view in perspective of a mercury arc lamp constructed in accordance with the principle of the invention and showing, schematically, one manner in which it may be energized, and

Figure 2 is a longitudinal sectional view of another embodiment of the invention.

Referring now to the drawing, and particularly to the mercury arc lamp shown in Fig. l; the lamp bulb comprises a hermetically sealed evacuated transparent envelope 1 and has a reentrant press 2 through which but two conductors 3 and 4, which are preferably constituted of tungsten, are sealed. Lead 3 which is shown in the drawing as connected to the negative terminal of the electric source, exemplified by the battery B, will occasionally hereinafter be referred to as the cathode lead, and the lead 4, which is connected to the terminal of the said source, will be designated the anode sad. The cathode lead of the device of Fig. 1 comprises a rod-like element which terminates at a point 3b immediately above (say, .25" above) the surface of a pool of mercury 5.

In the usual mercury arc device wherein the necessary electrical connection to the mercury pool comprises a short-lead which extends from the bottom of the pool directly through the wall of the envelope, the are under normal operating conditions extends between the surface of the mercury (anode) and the cathode electrode. An'

arc to the surface of an unbroken pool of mercury is relatively unstable, probably because the temperature of they arc sets up turbulations in the pool which cause the arc to dance about and to flicker. This, of course, is especially objectionable in the case of a lamp for use, by way of example, in ultraviolet sound recording apparatus.

To obviate such flickering the anode lead 4 extends into the mercury pool 5 and is provided with a return bend portion 4a which terminates at a point 42) adjacent the surface of the mercury pool and in line with the terminal of the cathode lead 3. With this arrangement, the main arc in the device is confined to the area of the surface of the pool immediately surrounding the point or terminal 4b of the anode lead and is substantially free from flicker.

As previously set forth, the present invention contemplates the use of an auxiliary or arc-starting electrode which is movable out of the path which it starts between the main operating elements. To this end, referring still to Fig. 1, the starting electrode, here designated 6, is mounted on the free end of a bimetallic element or strip l which is fixed at its opposite end to a conductive supporting arm 3 which, in turn, is fixed as by a strap or weld 8 to the cathode lead 3. Inasmuch as the tube contains mercury, it is desirable to construct the bimetallic strip of material which will not appreciably amalgamate with mercury. Nickel and tungsten have proven satisfactory in the above respect and exhibit the necessary different coefiicients of linear expansion. In one successfully operated device, excellent result were obtained using a strip of nickel wide and 5 mils thick, and a tungsten 10 mil drawn wire, spot welded along the middle of the nickel strip. As indicated in Fig. 1 Where the tungsten Wire of the bimetallic element extends beyond the nickel the extended part may itself comprise the arc starting electrode 6, in which case its free end is bent over downwardly so that, when the device is at room temperature, it contacts the surface of the mercury pool 5.

The length of the bimetallic strip should preferably be made long enough to lift the tip of the starting electrode out of the mercury pool and move it beyond the point or terminal of the cathode 3 so that, when the arc which is initiated between the starting electrode and the surface of the mercury pool is transferred to the main electrodes, the starting electrode will be entirely out of the short path between the point of the cathode and the surface area of the mercury adjacent the point of the anode.

Another embodiment of the invention is shown in Fig 2 wherein the highly evacuated transparent envelope is designated it, a pool of mercury ii, and the necessary external leads are designated i2 and i3, respectively. These leads l2 and l 3 terminate above the surface of the pool H in inwardly directed spaced apart points l'3a and i311, respectively. To each lead there is at tached, preferably on the side nearer the wall of the envelope, a bimetallic element I i, l5, respectively, which, like the element 1 of the device of Fig. 1, may comprise a nickel strip and an elongated tungsten wire which extends beyond the nickel parts. In this case, the tungsten wires, which are designated l6 and H, respectively, are bent inwardly and touch each other, when the device is at room temperature, to provide a conductive path for the heating current which,.in this case, is supplied by an alternating current source indicated symbolically at 13. When the device is employed as a lamp, the source may comprise a -25 volt generator. The passage of current through the continuous path comprising the bimetallic elements and tungsten wires generates heat which serves to vaporize the mercury and thereby create a conductive path between the spaced apart points of the main operating electrodes l2 and i3. At the same time, the heat thus generated deforms or bends the bimetallic elements it and i5 outwardly beyond the terminals of the main operating electrodes [2 and 13.

Other modifications of the invention will suggest themselves to those skilled in the art. It is to be understood, therefore, that the foregoing should be interpreted as illustative and not in a limiting sense except as required by the prior art and by the spirit of the appended claims.

What is claimed is:

1. A gas-discharge device comprising a pair of spaced arc-maintaining electrodes, an auxiliary arc-starting electrode mounted upon an electrode of said pair, and means to move said startin electrode out of the path of the arc which it starts between said pair of arc-maintaining electrodes without altering the spacing therebetween.

2. A mercury vapor device comprising an envelope containing a pool of mercury, an electrode mounted above said pool for maintaining an arc therebetween, an auxiliary electrode for starting an are between said first-mentioned electrode and the surface of said pool, and means for concentrating said are adjacent the surface area of said pool which lies beneath said first-mentioned electrode.

3. The invention as set forth in claim 2 and wherein said last-mentioned means comprises a rod-like element within said pool and which terminates adjacent the surface of said pool in line with the terminal end of said first-mentioned electrode.

4. A mercury vapor device comprising an envelope containing a pool of mercury, an electrode having a terminal spaced from the surface of said pool for maintaining an are between it and the surface of said mercury, an arc-starting auxiliary electrode having a terminal immersed in said pool adjacent the area thereof beneath said firstmentioned electrode, and thermally actuated means for moving the terminal of said auxiliary electrode out of said pool to a point beyond the terminal of said first-mentioned electrode.

5. A mercury vapor device comprising an envelope containing a pool of mercury, an anode comprising a point projecting from said pool, a cathode comprising a conductor'having a terminal spaced from the surface of said pool in line with said anode point, a bimetallic element connected only at one end to said cathode conductor and an auxiliary arc-starting electrode fixed to the other end of said bimetallic element, said auxiliary electrode having a terminal which contacts the surface of said poocl of mercury when said bimetallic element is at rest.

6. A gas-discharge device comprising a pair of are maintaining electrodes mounted in spaced relation within a hermetically sealed envelope, a bimetallic element supported at one end by one of said arc-maintaining electrodes and an auxiliary arc-starting electrode. fixed to the other end of said bimetallic element and adapted to be moved by said bimetallic element out of the path of the are which it starts between said arc-maintaining electrodes and without disturbing the initial spacing between said pair of electrodes,

JAMES R. ALBURGER.

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