US2094848A - Gaseous and vapor electric discharge device - Google Patents

Description

Oct. 5, 1937. w. A. ROBERTS GASEOUS AND VAPOR ELECTRIC DISCHARGE DEVICE Filed Sept. 20; 1954 I-nve'ncov: willon d A. R0 er'ts',

Hi Attorney.

Patented Oct. 5, 1937 UNITED STATES PATENT" OFFICE GASEOUS AND VAPOR ELECTRIC ms- CHARGE DEVICE Willard A. Roberts. Cleveland Heights, Ohio, assignor to General Electric Company, a corporation of New York Application September 20, 1934, Serial No. 744,797 Q 8- Claims. (01. 176-122) My invention relates to gaseous and vapor electric discharge devices containing some working substance providing an ionizable atmosphere during'operation, and particularly to discharge is around l or' 2 to 7 mm.), to assist in starting the sodiumor othervapor discharge: i. e., the lamp st a rts as a gas lamp, and as it heats up operates more and more as a sodium vapor lamp. My jinvention is especially concernedwiththe .starting of positive column devices, and is very useful in reducing or minimizing the starting voltages of such devices, and in starting relatively long tubular devices, with gaps between their terminal electrodes approaching and even very much exceeding what has heretofore appeared to be the limit for easy starting, especially in the case of low-pressure positive column alternating current glow discharge devices having "hot or separately heated electron-emissive thermi- .onic electrodes. Devices with so-called cold electrodes, heated only by the discharge, are even more diflicult to start than devices with hot electrodes.

Various other features and advantages of the invention will appear from the following description of species thereof, and from the drawing.

In the drawing, Fig. 1 is a side view (with wiring diagram) of one form of tubularglow discharge lamp embodying my invention, adapted for operation on alternating current; Fig. 2 shows an axial mid-section through an electrode, ona larger scale than Fig;- 1; Fig. 3 is a side view of a somewhat difierent lamp, adaptable to a greater over-all length than the lamp shown in Fig. 1; and Fig. 4 is a side view of still another form oflampr The lamp shown'in Fig. 1 has a U-bent tubular glass envelope or bulb I .0, although neither a U-tube nor' a tubular form, even, is essential to the invention in its broaderaspects. The envelope I contains a series of (three) rather widely spaced glow discharge electrodes I I, I2, II and is provided with'current supply leads I3,

I3 sealed into its ends- The terminal; or end ielectroiies II, I I, which-are the main discharge electrodes, maybe axially arranged in the oppotrode I2, which is an auxiliary electrode, is shown midway between the main electrodes II, II. this particular instance, this intermediate electrode I2 extends transversely of the tube III in the U-bend, and parallel with the main electrodes I I, II, although this is not essential in all cases. The electrodes II, I2, II are of the heated electron-emissive (thermionic) type; and in the present instance, they are all indirectly heated unipotential electrodes-each having associated with its emissive portion a heating resistance I5,

connectedbetween suitable current leads. Most simply, the current supply lead I3 to each main electrode I I is connected to one end of its heating resistance I5 as one of the leads for the latter,

as well as to the emissive portion of the. electrode; and another lead It is connected to the other end of the resistance I5. In like manner,

the intermediate electrode I2 has its heating resistance I5 connected between leads I6, I6 one of which is also connected to the electron-emissive portion of electrode I2. The lead I6 of each electrode u is connected (or identical) with one lead I6 of the electrode I2. In the present instance/ the leads I6, I6 extend outside the envelope II) from left-hand electrode -II to electrode I2, and

from the latter to right-hand electrode I I, being The emissive portions of the electrodes II, I2, II

are connected to this circuit C at points whose differences of potential are determined by theamounts of intermediate (heating) resistance (15). Also, the circuit C as a whole is in parallel main or terminal electrodes II, II, and likewise in parallel with the series of shorter, intermediate 1 with the main long discharge gap between the discharge gaps between successive electrodes in the series II, I2, II. I

Whilethe details of electrode construction aa'e unessential, yet for the sake of clearness it may be pointed out that each of the electrodes I I, .Ili,

II here shown (see Fig. 2) comprises a metal,

(nickel) base tube H with an external coating I8- of emissive material suchas barium oxide,

3 and shouldered insulative refractory (lava) plugs I9, I9 in'the en-ds of the 'tube,centrally bored .for passage of the current leads I3, I6 (orv I6, I6) to the helically coiled (tungsten) heating wire or filament I 5, extending axially in the tube II. The tube I1 is shown connected to the lead I3 or It by a metal (nickel) strip 20. Preferably the connection 20 of each lead I3 or I6 to the tube I1 is at the end of each electrode that is farthest from the others, as shown in Fig. 1.

The envelope I0 may contain a charge of sodium or other metal, and also a small amount of easily ionized gas like neon, argon, etc. And. it will be understood that in practice the device may be operated with such usual sodium vapor lamp accessories as an enclosing vacuum jacket (not shown); a ballast resistance R (preferably of positive temperature-resistance coeflicient, like the tungsten filament of an incandescent lamp), connected in series with the device to control the current rise as the device heats up after starting; or a compensating resistance, reactor, or transformer (not shown), if necessary, to allow the device to be used on ordinary A. C. lighting circuits of 110 to 120 volts or the like, etc.

When the current is turned on to start the device, there are definite potential diiferences between the adjacent electrodes II, I2, II, whose relative magnitudes depend on the resistance between them in the heating circuit C. By using a suitable supply voltage, the difierence of potential across all the intermediate electrode gaps can 'be made greater than the ionization voltage of the starting gas used (which is 21.5 volts for neon, or 15.7 volts for argon). Supposing that the eflective distance or gap (around the bend of the U-tube IIl) between the terminal electrodes II, II materially exceeds the limit for easy starting as mentioned above, then it'follows that in the absence of the auxiliary electrode I2, an ionization discharge would not start in thedevice even after the electrodes II, II had heated up and begun to emit electrons freely,--un1ess, pos sibly, under an extreme initial voltage, materially exceeding that of ordinary lighting circuits. However, if the intermediate electrode gaps III2 and I2-II are each well within the limit of easy starting, then separate intermediate gas glow discharges will start in these intermediate gaps as soon as the electrodes II, I2, II heat up sufllciently,first in the gap with the greater difference of potential across it (which for the connections of the electrodeemissive/portions to the circuit C shown in Fig. 1 would naturally be the right-hand gap I 2-H), and then, after the first glow discharge has started, in the other.

These intermediate discharges ionize the'gas more or less throughout the length of the tube I0, thus creating much more favorableconditions than at the outset for a glow discharge bridging the longer gap between the main electrodes I I, II,which, of course, also have a greater potential diiference between them than can obtain across any intermediate gap. When, moreover, the intermediate glow discharges have started in all the intermediate gaps, and the discharge current increases; the current in the parallel heating resistance circuit C greatly diminishes; and so, likewise, the temperature and electron emission of the intermediate electrode I2. Accord-.

ingly, a glow discharge starts directly between ,the main electrodes II, II under their higher potential difference; the intermediate discharges die away; and the auxiliary electrode I2 becomes too cold to emit effectively, and ceases to operate. This change tends to go on cumulatively, b cause the main electrodes II, II are heated by the entire glow discharge current in the device, while the intermediate electrode I2 is heated mainly by the diminishing currents in circuit C and in vaporizes suflicient'sodium to participate in the glow discharge, the conditions become still more favorable for the discharge between the main electrodes II, II, owing to .the low ionization po tential (5.1 volts) of sodium as compared with that of neon (21.5 volts) or argon (15.7 volts).

' Ordinarily, however, theintermediate electrode I2 virtually ceases to Operate before the characteristic sodium yellow becomes prominent in the glow discharge luminosity.

, it should sufiiciently exceed the ionization potential of the atmosphere in the envelope II), at or during starting, to cause a preliminary local discharge across a relatively short gap in parallel with the resistance I5,as' between the emissive surface I8 of the electrode II and an adjacent part of or connected to the heating current lead I6,so as to ionize enough of the atmosphere in. the device to facilitate starting of the longer intermediate disoharge(s).- A suitably high (but not excessive) value of the heating resistance I5 is of course required, in proportion to the totalresistance of the heating circuit C, to take a voltage drop sufficiently exceeding the ionization potential to produce the local discharge. Undesirable persistence of the local discharge after starting of intermediate discharge(s)or even after starting of the main discharge-is prevented or minimized by the reduction of the over-all voltage on the device, by its ballast resistance R, as the total discharge current passing between the main electrodes II, II increases. This, however, does not necessarily require reducing the voltage along the resistance I5 actually below the ionization potential of the atmosphere in the device, after starting of the intermediate discharge(s), or even of the main discharge, but only requires reducing the voltage along resistance IE to a point. where the local discharge gap is too great for such voltage to maintain an appreciable local discharge. As the operating voltage of the .device is considerably lower than the starting voltage, no difliculty in operation is to be apprehended if the starting voltage on each resistance I5 is kept within proper limits.

Fig. 3 illustrates an extension of the same principles in a longer series of (five) electrodes, by interposing an additional auxiliary electrode I2a between each of the main terminal electrodes II, I I and the middle electrode I2. -In this instance, the electrode I2 is arranged to extend along (or tangent to) the axis of the envelope III at its U- bend, like the electrodes II, II and I2a,- I2a. The current leads I6, I6, I6, I 6 serially interconnecting the electrbde heating resistances I5, I5, I5, I5, I5 also extend axially of the tube ID, instead of being outside it as in Fig. 1. As shown, starting anode pieces 24, 24, 24, 24 are provided on the leads I6, I6, IS, IS closely adjacent electrodes H, II and IZa, I2a: They may consist of short (tungsten) wire cross-pieces welded to the (molybdenum) leads I 6, IS, IS, I 6. Each of these pieces 24- serves as an anode for a local starting discharge to the corresponding electrode II, II or I 2a, I2a functioning as cathode, to ionize I6, I6, I6, I6 are enclosed in insulative refractory (alumina) tubes 25, 25, 25, 25. After starting of the intermediate glow discharges between adjacent electrodes of the series II, I2a, I2, I2a, II

and also after supercession of these by the main discharge between electrodes I I, I I, the'insulative coverings 25 on the leads I6 serve to minimize the persistence of local discharges.

With the connections shown, the greatest 'potential difference is between the electrode I2 and the right-hand electrode I2a, so that the first intermediate glowdischarge tends to start between them, to be followed by the other intermediate glow discharges. These may be followed by a secondary intermediate glow discharge between electrode I2 and the right-hand electrode .II, bridging past right-hand electrode In and throwing it out of operation, before the main discharge starts directly between electrodes II,

tween the main, terminal electrodes II, II by (molybdenum) current leads I6, I6, l6. Two such intermediate electrodes I2b, I2b are shown, though obviously a greater or less number could be used. This particular lamp has a straight tubular envelope Illb, with electrodes II, I21), I21),

II and their leads I6, I6, I6 all axially arranged therein. Next to the main electrodes II, II,

starting points 24, 24 are attached to the leads.

I6, I6, as in Fig. 3, and the leads I6, I6, I6 have insulative refractory (alumina) tubular coverings 25, 25, 25. The filaments I2b, I2b may either be bare tungsten filaments of such resistanceas to be electron-emissive by incand'escencewhen the device is being started, and afterward to cool down below emissive temperature as the glowdischarge grows; or they may be coated with barium oxide to render them emissive at lower temperatures .and may afterward cool down below such lower emissive temperature. Their resistances need not be the same as those of the llieating filaments I5, I of the main electrodes I, II.

The operation of this device is substantially like that of those shown in Figs. 1 and 3, except that the markedly greater'diiference of potential across certain electrode gaps may be either more or less pronounced, owing to variation of potential along the filaments I21), I21; themselves.

In Figs. 3 and 4, various parts and features are marked with the same reference numbers as in Figs. 1 and 2 (with added letters, where such distinction appears necessary), as a means of dis-- What I claim as new and desire to secure by Letters Patent of the United States is:

1. A positive column electric discharge device comprising an elongated, tubular envelope containing working substance providing a vaporous, ionizable atmosphere therein during operation; and a series of .widely spaced electron-emissive electrodes axially mounted in said envelope each electrode having a heating resistance, the intermediate discharge gaps between said electrodes being electrically in series, said heating resistances being connected inseries with one another, and in parallel with the seriesof discharge gaps, the connections to the respective resistances beinginsulated from the discharge gaps.

2. A positive column electric discharge device comprising an elongated, tubular envelope containing working substance-providing a vaporous, ionizable atmosphere therein during operation; and a series of widely spaced, indirectly heated, unipotential, electron-emissive electrodes axially mounted in said envelope, the intermediate discharge gaps between said electrodes being electric'ally in series, said heatingresistances being connected in series with one another, and in parallel with the series of discharge gaps, the connections tothe respective resistances being insu lated from the discharge gaps.

3. A positive column electric discharge device comprising an elongated, tubular envelope containing working substance providing a vaporous, ionizable atmosphere therein during operation; a series of widely spaced, indirectly heated, unipotential, electron-emissive electrodes axially mounted in said envelope, the discharge gaps between said electrodes being electrically in series, the heating resistances for said electrodes being in series with one another, and in parallel with the series of discharge gaps; and means connecting the electron-emissive portions of said electrodes to the circuit of the heating resistances with approximately equal resistance intervening between successive points of connection in every instance but one, and with substantially greater resistance so intervening in that instance.

4. A positive column electricdischarge device comprising an elongated, tubular envelope containing working substance providing a vaporous, ionizable atmosphere therein during operation; a

series of widely spaced, indirectly heated; unipotential,

electron-emissive electrodes axially mounted in said envelope, the discharge gaps of said electrodes to the circuit of the heating resistances with a heating resistance intervening between successive points ofconnection in every instance, and with an additional heating resistance so intervening in one instance.

5. A positive column electric dischargedevice comprising an elongated, tubular envelope containing working substance providing a vaporous, ionizable atmosphere therein during operation; a series of widely spaced electron-emissive electrodes ranged along the axis of said envelope, a

heating resistance for each of said electrodes, the

intermediate'discharge gaps between said electrodes being. electrically in series, and current sistances in series with one another, and in parallel with the series of discharge gaps, and a body of insulating material on said current leads.

6. A positive column electric discharge device comprising an elongated, U-tube envelope containing working substance providing a vaporous, ionizable atmosphere therein during operation; a series of widely spaced electron-emissive electrodes axially mounted in said envelope, intermediate discharge gaps between said electrodes being electrically in series, two of said electrodes being mounted in the tube ends and an intermediate electrode being mounted in at the U- bend'of said tube, and means electrically connecting the heating resistances of said electrodes in series with one another and in parallel with the series of discharge gaps, said means being insulated from the discharge gaps.

7. A positive column electric discharge device comprising an elongated, tubular envelope containing working substance providing a vaporous,

ionizable atmosphere therein during operation; a

series of Widelyspaced electron-emissive electrodes axially mounted in said envelope and having their intermediate discharge gaps electrically in series, a heating resistance for each of said electrodes, a heating circuit including said heating resistances and means for connecting said heating circuit in parallel with said discharge gaps, said heating circuit having a discharge supporting surface adjacent each of said electrodes, the short discharge gaps between said surface and said electrodes being in parallel with said re sistances, respectively; the parts of said heater circuit other than said discharge supporting surfaces and said resistances being insulated from.

the discharge in said device, said resistances being so proportioned to the total resistance of said heating circuit as to take voltages suificiently exceeding the ionization potential of the atmosphere in the envelope, during starting, to produce local discharges across said short gaps and thus start discharges across the aforesaid intermediate gaps, and thereafter to take reduced voltages preventing objectionable persistence of such local discharges.

circuit having parts in such close proximityto the emissive surfaces of said electrodes as to provide relatively short discharge gaps in parallel with the resistances, respectively; the parts of said heater circuit other than said discharge supporting surfaces and said resistances being insulated from the discharge in said device, said resistances being so proportioned to the total resistance of said heating circuit as to take voltages sufficiently exceeding the ionization potential of the atmosphere in the envelope, during starting, to produce local discharges across said short gaps and thus start discharges across the aforesaid intermediate gaps, and thereafter to take reduced voltages preventing objectionable persistence of such local discharges.

' WILLARD A. ROBERTS.

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