US2098679A - Gaseous discharge device - Google Patents

Description

Nov. 9, 1937. R. M. soMx-:Rs n 2,093,679

GASEOUS DISCHARGE DEVICE I Filed March 2o, 1935 2 sheets-sheet 1 INVENTOR Ric-bard M. Somers ATTORNEY v Nov. 9, 1937. R. M. soMERs 2,093,679

GASEOUS DIS CHARG E DEVICE Filed March 20, 1935 2 Sheets-Sheet 2 [N VENTOR BY Pfc/5am M Somer;

ATTORNEY Patented Nov. 9, 1937 UNITED STATES PATENT lori-Ice 2,098,679 GASEOUS DISCHARGE DEVICE Application March 2o, 1935, serial No. 11,919 s' o1aims. `(o1. "17e- 122) Further the invention relates to such devices wherein are employed a plurality or anodes relatively near to each other and relatively distant from the cathode' as is common practise in posil tive column devices when the discharge is to be maintained by an alternating current supply.

The operation of such devices is usually such that large potential diierences exist between the anodes. -In the absence o1 any preventive measl ure, these potential diierences may cause arcbacks between the anodes--ie., disruptivel discharges from one anode or its connecting lead to the other anode or lead, which discharges impair the operation of the device and usually com- .,0 pletely ruin it. customarily these arc-backs are vprevented by arranging the anodes in individual stems, constrictions, or the like, or by suitably interposing between the anodes shields of metal or of glass or other refractory material. These preventive measures function by increasing the length and/or the circuitousness of the anodeto-anode path within the device. While they are eiective ii appropriately carried out', they obviously materially increase the structural complexity and cost of the device. v It is an object oi my inventionto provide simplified device of the class described wherein arc-backs are elciently prevented.

It is another object to provide a device of lthe class described, characterized in operation by freedom from arc-backs, wherein the anodes are placed very close to one another' Vwithout the interposition of shields or the like between the anodes. Another object is the provision of improved means for preventing arc-backs in devices of the class described. v

Still another object is the vprovision .of improved anode supporting and connecting struci5 tures and arrangements appropriate to the prevention of arc-backs Yet another object is the provision of improved methods oi assembling `the anodesy'stem in a device of the class described. 5o Other andallied objects will more iully appear from the .following description and the appended claims.

In the description reference is had to the accompanying drawings, oi which: Figure 1 is a partly cross-sectional and partly schematic view of a discharge deviceaccording to my invention, together with a typical associated circuit; 4

Figure 1a is an enlarged cross-sectional view of the anode portion of Figure 1, which com- 5 prises one embodiment of the rst species of my invention;

Figures 2 and 3 are cross-sectional views of two variations of the portion oi' Figure 1 which is shown as Figure 1a, illustrating as many al.- l0 ternative embcdiments of the rst species, Figure 3 illustrating the preferred among the three illustrated embodiments of this species;

Figure 4 is a cross-sectional view, of similar scope as to contents to the three preceding gl5 ures, but illustrating a second species of my in vention;V and Figures 5 and 6 are cross-sectional views of two embodiments of the third species ci my invention, Figure 6 illustrating the preferred be- 20 tween the embodiments of this third species.

It is well understood that the prevention of arc-backs in any case is facilitated by the use of anodes of carbon or other high work function material. l have found that with such anodes, 25 close together and unshielded from each otheri. e., mutually exposed--arc-backs will be confined to those occurring between an anode and the electrical connecting means for the other anode; and further, that arc-backs'will vnot oc- 30 cur at all below a critical anode-to-anode voltage, provided the means for making electrical connection to the anodes are suitably 'constructed and arranged. The critical voltage abovemen tioned will vary according to .various parameters 35 of the device, particularly with the gas pres sure, tending to lower as the pressure is raised.

I have found, however, that llor typical low pressure tubes, e.v g., containing gas at a pressure of 10 millimeters of mercury or less--the critical 40 voltage may be established at a value well in excess of 300 volts A. C. (420 volts peak or D. C.);

for a typical tube with a gas pressure of 4 millimeters of mercury it may be of the order oi 500 volts A. C. (700 volts peak or D. C.). Either vof 45 these figures is obviously well in' excess -of the voltage required to exist betweenanodes in emcient devices adapted for various uses, among which may'be particularly mentioned that o! illumination. 50

Brcadly and principally, the structure and arrangement .which I employ in association with the connecting means for the anodes is one wherein each of these means is surrounded, at all points longitudinally thereof between the envelope and a point intermediate the extremities ofthe respective anode, by one or more tubes formed of refractory insulating material. These tubes are so disposed as to lengthen the shortest arcing paths, from the anodes to the connecting means for the respectively opposite anodes, by annular passages oi' negligible thicknesses, or of thicknesses which are at most very small fractions of their lengths. 'I'hese passages are formed between the refractory insulating tubes and portions ofthe anodes and/or between portions of different tubes. Their eihcacy in suppressing arc-backs probably results from the development of space charges on the passage walls.

It may here be noted that I employ the term "passage as denoting the space, between two mutually adjacent members, through which an arc-back might travel; and that this term is still employed although the members may be in actual contact with each other and the space therefore vanishingly small,.since such a space may still under certain circumstances provide an arcing path or passage. It will further be understood that the term tube and its derivatives are intended to denote broadly cross-sectional continuity, and not necessarily true circularity, and

that the term "annular as employed herein is likewise not intended to be limited to'true circularity. The circular formation is usually most convenient, however, and has been employedin illustration herein.

The particular features which are characteristic of my invention are set forth in detail hereinafter. Reference is first invited, however, to Figure 1, wherein I illustrate a typical device and associated circuit.

In the figure will be seen the tube I having the glass or other refractory envelope 2, the space 2 within the envelope having been evacuated of -air and containing an inert gas, or combination of gases, and/or if desired a small quantity of metal adapted for 4vaporization upon heating of the device. The elements of the tube are the cathode 3, the anodes la and 4b (hereinafter more fully referred to), and the auxiliary starting electrode l5. The cathode 3 is of the thermionic type, and by way ci' example has been illustrated as) a folded filament which may be coated with suitable oxides r the like to increase its emission. The anodes/4a and 4b are located near the opposite end of the tube from the cath- 'f ode 3. The starting electrode 5 may be a conductive ring surrounding and in slight spaced relationship to the cathode 3.

'I'he discharge current for the device may be terminal 6p of the transformer, while the other side of the line is connected selectively to the primary terminals 6p', 6p" and Gp'" through the selecting switch 9". 'I'he transformer may have the extreme secondary terminals 6a and 6b and the secondary center-tap 6c; the first two are connected respectively to the anodes la and 4b through the ballast resistances or lamps 8a and 8b, while the center-tap 6c is connected to the cathode 3 through the inductance coil or choke I0. A tertiary winding 1 forming a part of the transformer B may be connected across the extremities of the filament or cathode 3 for heating the same.

ni a system such as I .have liuustratdi 1t 1s usually necessary to initiate the gas discharge by a momentary discharge at relatively high voltage. While a variety of means for producing sucha transient discharge may be employed, I -have by way of illustration shown a system certain features oi' which have been described and claimed in my copending application Serial No. 716,038, filed March 17, 1934, and on which Letters Patent No. 2,013,974 were issued on September 10, 1935. Briey this system may be constructed by connecting the starting electrode 5 through a circuit-breaking switch I2 to a tap 6d located on the transformer secondary to one side of the center-tap 6c. The switch I2 comprises a spring arm l2 carrying the armature I2 and the contact I2a, the arm being biased normally to press the contact l2a against a stationary contact I2b-i. e., to maintain the switch closed.' The armature I2" is positioned in the field of attraction of the core I0' of choke I0, and is adapted to be moved toward the core I0', and thus to open the switch I2, when the attraction ofthe core I0' exceeds a certain minimum. As soon as the primary/on-oif switch 9' is closed heating of the cathode 3 is initiated and the terminals 6a and 6b are invested with alternatingl potential differences from the center-tap 6c. As soon as the cathode has been slightly heated a small gaseous discharge will take place every a1- ternate half-cycle from the starting electrode 5 to the'cathode. As the temperature of the cathode rises the magnitude of this discharge increases; and when the discharge attains a. magnitude correspondent to substantially normal cathode operating temperature the attendant current through the choke I0 causes the core IIJ' to attract the armature I2" and open the switch I2, which has been adjusted to this end. The sudden breaking of current flow through the choke causes the appearance across the choke of charge by virtue of the potentials from the sec- 1 ondary terminals. If vaporizable metal such as mercury is included in the device in addition to an inert gas such as krypton, the gaseous discharge Will serve to vaporize the metal, whereupon the normal discharge may transfer itself from the gas to the vapor as a medium.

Y It will of course be understood that throughout the normal discharge in this system the positive end of the discharge column will shift'fback and forth between the two anodes 4a and 4b, each anode being inoperative during alternate substantial half cycles. It will further be apprec'iated that at the peak of each half cycle the .potential difference between the anodelsfriscs` to almost the peak voltage diierence'between the secondary terminals 6a and 6b; this voltage rise is that which tends to produce arc-backs.

The general operation of the typical system having been thus outlined, particular attention may be directed to the anodes la and lb and their supporting and' connecting means, a particular structure and .arrangement of which is illustrated in `Figure 1, and in enlarged crosssectional form in Figure 1a, with variations in succeeding figures. l.,ln general all the structures are adapted for manufacture by automatic machines and do not require laborious and costly hand-work. Y

In Figure 1a the anodes la and Ib are seen in the form of short round rods of carbon having axes mutually parallel and in line with the direction of the discharge column. Illustratively the anodes may be approximately M4 -inch in diameter, 1 inch long, and spaced apart by slightly more than 11; inch (i. e., having slightly greater than a '1% inch center separation). As the length of the positive discharge column may be considered to be 5 inches or greater, it will be seen that the anodes are relatively closely adjacent each other and the cathode relatively distant therefrom. The anodes are supported and electrically contacted by the rods 42a and 2b. These rods are of conductive material-desirably of tungsten-and are held in appropriate mutually spaced and lsubstantially parallel relationship in the stem or press 2 of the envelope I. sembling the illustrated anode system there are rst formed around intermediate portions of the rods 42a and 42h the elongated glass or other refractory insulating beads a and Mb; the thus beaded rods are then sealed into the stem 2 so that upon assembly of the stem to the envelope the beads 44a and Mb will extend inwardly of the envelope. The anodes are next assembled on the. rods Ma and Mb, as below more fullydescribed, and the stem 2'* finally sealed in its place at the end of the envelope, as along the line 2"' of Figure l.

For assembling the anodes on the rods 42a and 42h the anodes are provided with the axial holes lia and Mb, which may extend inwardly from one end of each for a maior fraction of the anode length. These holes are adapted frictionally to engage the extrennties of i, the rods 42a and 42h, these extremities 42 having been peripherally roughened-for example as a result of having been cut oif by pliers-as clearly illustrated for example in Figure 2. In Figure la the .anodes are also shown as provided with the central apertures 43a and 43h of larger diameter than the holes Ma and Mb but extending a shorter distance inwardly from the same end; in assembling the anodes on the rods the anodes are pushed onto the rods until the bases of the apertures'43a and 13b have bottomed against the extremities of the beads Ma and Mb. These aperture bases are preferably slightly rounded or bevelled so as to tend to fit the ends of the beads.

In this structure it will be seen that the rods 42a and 42D are completely surrounded with the tubular beads 44a and 44h from the stem 2" to the bases of the apertures 43a and 43h, so that the only portion of either rod which is connected by any form of passage with the space 2' within the envelope is the very small or ininitesimal portion between the respective aperture base and the end of the respective bead.

nected with the space 2' is principally the .very

thin annular passage 45a formed between the bead 44a and the wall of the aperture 43a, or the like passage formed between the bead Mb and the wall of the aperture 63h, as the case may be. (Additionally, of course, each passage includes the short, cross-'sectionally rounded or bevelled, thin space between the baseV of the respective aperture and the end of the respective bead.) These passages become included in the arcing paths to the respective rods from the respectively opposite anodes, which paths are thus lelgthencd by these passages.

Inas- Generally speakingthe emca'cy of the thin annular passages upon which I largely rely in suppressing arc-backs vis a function of the passagelength and an inverse function of the passage thickness; thus for example in the particular embodiment of Figure 1a it is desirable that at least the end portions of the beads 44a' and Mb be always as Vnearly perfectly circular as practicable, and thatv the diameter of the apertures 43a and 43h be as small as may be depended upon in production to admit the bead end portions. A furthercharacteristic of these annular passages, as illustrated not only'in the passages of Figure la but also in all the other annular passages of negligible thickness in all of the embodiments, is that .their length is at least of the order of the residual length oi' the shortest arcing path, or of the minimum spacing of either anode from the opposite rod. 'While I consider this characteristic advantageous, I do not wish to limit my invention thereby excepting as so specically claimed.

In succeeding figures I show several variations of'the anode assembly. 42a and 42h may be provided with the roughened end peripheries 42' to provide frictional engagement with the holes Ila and 4| b in the anodes; but the apertures 43a and 43h inthe anodes, and the beading a and Mb on therods, are retained, eliminated or replaced as specically described for each variation.

. Figure 2 illustrates an alternative embodiment of the same species of my invention as Figure la. In Figure 2 the rods 42a and 42h are surrounded for part of their length by the small glass or other refractory insulating tubes 46a and 4Gb; these tubes may have an internal diameter just large enough to slip over the rodsi The rods are assembled into the stern 2" with the tubes 46a and -tlb partially extending. into the stem material, so that both rod and tube are sealed into In each case the rods the stem. Instead oi' the apertures fia'and 43h fto that of Figure la, but the annular passages,

herein designated as 68a and 60h, are more easily held to a. negligible Ithickness, by virtue of the naturally more perfect periphery of a separately formed tube than of a bead formed on the rod. An additional small distinction is found in vthe nature of the space between the aperture base and the end of the insulating tube; this is nowv a thin, short, washer-like passage in series with and at complete right angles4 to the respective annular passage Gitta or Elib. This right angular relationship aiords a measure of additional security against arc-backs, which may in general .be considered reluctant to follow a sharply angled passage.

Figure 3 I have termed the preferred embodiment of the iirst species oi` my invention because it adds at the outer extremity of each annular passage a thin, washer-like passage in series with and at right angles to the annular passage. This washer-like passage is formed between the end of each anode and an adjacent refractory insulating member. and may comprise an addition to either of the thus-far illustrated embodiments. I have illustrated it in Figure 3 as the. structure of Figure la with the addition of glass or other refactory insulating tubes 31a and 31h sealed into the stem 2" around and at the same time as the beads a and Mb. These tubes may be of slightly larger internal diameter than will dependably admit the beads, though of course of smaller external diameter than the anodes; they are of a length appropriate to come into substantial abutment against the anodes when the latter are assembled on the rods as set forth in the description of Figure laiabove. Thus the thin, washer-like passages are formed between the anodes and the respective extremities of tubes 31a and 31h, and have been designated in Figure 3 as Sla and SIb.

In Figure 4 I have illustrated a structure which I term the second species of my invention. I again surround the rods with tubes of refractory insulating material sealed into the stem ,coincidentally with the rods and extending to points intermediate the extremities of the anodes; but in this instance I employ tubes 48a and 48h which are of aninternal diameter appropriate to be fairly snugly tted by thev periphery of the anodes, which are slipped onto the Vrods suillciently to extend for a distance within the tubes. Annular passages 62a and 62h of negligible thickness are thus formed between the outer walls of the anodes and the inner walls of the respective tubes.

The arrangement of Figure 4 provides no sharp angles to be turned by an arc-back, but offers, in addition to the annular passages of negligible thickness, a diierent impediment to arc-backs. 'I'his may be best understood by noting that in each of the embodiments of the'first species the path of an arc-back, between one anode an'd its terminal point on the rod of the respectively opposite anode, traverses a space between the two anode structures which is removed from the vcathode (and hence from the Apositive discharge the refractory insulating material, such strains` are sometimes setup in the structures above described, and these strains tend to be augmented by the great heating of the anodes .which is a necessary incident to evacuation of the complete discharge device. For this reason I believe A most advantageous the third species of my invention, which I have illustrated in two embodiments, neither involving tight holding of a refractory insulating tube at more than one extremity. The surrounding of the rods with tubular refractory insulating means from stem to points intermediate the anode extremities is of course maintained, but in a slightly more elaborate form.

In the embodiment of Figure the anodes, adapted to be held onthe rods in the usual Vmanner, are provided with apertures 50a and 50h, generally similar to apertures 41a and 41h of Figure 2 butpreferably extending for a relatively greater distance into the anodes. Into the stem 2" are sealed the rods 42a and 42h and therearound the glass or other refractory insulating tubes Sla and Sib, having an internal diameter equal to or slightly exceeding the diameter of the apertures 50a and 50h, and extending inwardly from the stem by a length preferably still greater than the length of apertures 50a and 50h. Glass or other refractory insulating tubes 49a and 49h of internal diameter to fit somewhat loosely over the rods 42a and 42h and of external diameter slightly less than that of apertures 50a and 50h, are slipped over the rods. Finally the anodes are assembled on the rods in longitudinal position ai.'- fording a substantially snug longitudinal iit for the tubes 49a and 49h between the stem 2" and the bases of the anode apertures 50a and Elib; preferably the lengths are so apportioned that the anodes are then but slightly spaced from the tubes Sla and 5ib.

In this embodiment two thin annular passages exist in each anode vassembly through which an arc-back might pass to the rod-e. g., the passage 63a between the tube 49a and the anode 4a, and the passage 64a betweenthe same tube and the tube Sia, each in series with a respective thin, washer-like passage formed'at the respective end of the tube 49a. In addition there is a common thin washer-like passage 65a in series with both of the annular passages 63a and 64a. The finite, though small, mean thickness of passage 63a is compensated for by somewhat greater length than previously illustrated annular passages, and the still greater mean thickness of passage Bla by still greater length.

In Figure 5 the inner insulating tube-e. g., 49a-is not held at either of its extremities. No objection obtains against holding such an inner tube at one extremity; and in Figure 6 I show a preferred embodiment of this third species in which an inner tube is so held. The anodes in this figure are provided with the apertures 41a and 41h (as in Figure 2), and into these holes are respectively fitted, as snugly as practicable, glass or other refractory insulating tubes 52a and B2b of internal diameter well exceeding the diameter of rods 42a and 42h, Glass or other refractory insulating tubes 53a and 5317, of slightly greaterinternal diameter than the apertures 41a and G'lb, are sealed into the stem'2" as were the tubes 5Ia and Sib of Figure 5; the tubes 53a and 53h extend inwardly from the stem 2" by a length desirably greater than that of apertures 41a and llb. While the rods 42a and 42h may be sealed into the stem 2"-as in Figure 5, I prefer iirst to provide them with short beads 54a and 54h which after sealing extend somewhat inwardly from the stem. The anodes, with tubes 52a and 52h respectively secured therein, are assembled on the rods so that the outer extremities of the tubes 52a and 52h extend into the annular spacings between the beads 54a and 54h and the tubes 53a and 53h; these extremities may be slightly spaced, however, from the stem 2f, and are not in contact any more than loosely with the beads 54a and 54h. While the tubes 53a and 53h need only extend from the stem by the extent above mentioned, they may if desired extend to a very slight spacing from the anodes, and have been so illustrated.

In this embodiment the annular passages between the inner tubes (52a and 52h) and the anodes are of course of negligible thickness, being similar to the passages 60a and 60h of Figure 2 and having been designated as 60a' and 80b; they are of course in series with the washer-like passages of negligible thickness formed at the inward extremities of the inner tubes. 'I'he annular passages between inner and outer tubes, desigaoeaeve nated as 66a, and 66h, are of nite thickness but of greater length than passages 66a' and eb'; furthermore these passages 66a and 66h are respectively in series with the short, thin annular passages 61a and 61h formed between the inner tubes and the respective beads 54a and 54h, the mutual arrangement of vpassages 66a and 61a (or 66h and 61h) being such as to force a possible arc-back therethrough to execute a complete reversal of direction in the very small space at the end of thefinner tube. Finally, if the outer tubes 53a and 53h are extended, as illustrated, into very slight spacing from the anodes, they form with the anodes the thin, Washer-like passages 65a' and 65h', in series with both the passages 60a' and 66a (or both 60h and 66h) and at right angles thereto. It will be understood that in the appended claims, some of them generic to the three species of my invention and others specific to individual species, I intend to claim my invention as broadly as the state of the art will permit.

The term gas and its derivatives, as used in the following claims and in broader contexts in the description, are intended to referA to one or more gases and/or one or more metal vapors. Also the term refractory insulating as used in the specification and claims, is intended to refer to materials such as glasses, alumina, magnesium oxide, natural rocks, etc.

I claim:-

1. In a gaseous'discharge device having an eni velope, a conductive rod passing through said a refractory insulating bead about said rod, sealed to said envelope and entering said first means.

3. In a gaseous discharge device, an envelope having a stem; a conductive rod passing through said stem and extending therefrom inwardly of said envelope; an anode entered by said rod, an aperture being provided inthe outward extremity of said anode about said rod; tubular refractory insulating means spacedly surrounding said rod and extending from adjacent'the base of said aperture toward said stem; a further tubular refractory insulating meanssurrounding said first mentioned tubular means, with at most'relatively small spacing therefrom, sealed into said stem, and extending therefrom inwardly by a substantial distance; and a refractory insulating bead about said rod, sealed into said stem, and extending therefrom for a dlstance'inwardly of said rst mentioned tubular means.

4. In a gaseous discharge device, an envelope and therein a pair of mutually exposed and closely adjacent anodes; conductive rods entering said anodes respectively and passing through said envelope; and refractory insulating means, surrounding each of said rods at all points longitudinally thereof between said envelope and a point intermediate the extremities of the respeca point intermediate the extremities of the respective said anode, the portions of said means co-extensive' with said anodes forming therewith very thin, annular arcing passages each having a length at least of the order of the shortest path from its exposed extremity to the respectively opposite anode.

- RICHARD M. SOMERS.

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