US2843805A - Electric discharge apparatus - Google Patents

Description

July 15, 1958 R. K. BRQDERSEN 2,843,805 ELECTRIC DISCHARGE APPARATUS Filed Aug. l2, 1957 :zrF-'g-r 1.

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Ma-amavi- Eff- '55- United States Patent C ELECTRIC DISCHARGE APPARATUS Rolf K. Brodersen, Orange, N. J., assigner to Westiughouse Electric Corporation, East Pittsburgh, Pa., a cor-l poration of Pennsylvania This invention relates generally to an electric discharge apparatus, `and more particularly to lan A. C.operable 'ilu-crescent lighting system wherein the radio-interference normally ygenerated fduring operation is suppressed to a minimum and maintained at an unobjectionable level for a substantially greater portion of the lamp life than was heretofore possible.

As is well known, when a gaseous discharge device such -as a fluorescent lamp is operated from an A. C. power supply high-frequency electromagnetic radiations are generated which, unless proper preventive measures are taken, emanate from the lamp or its supply line or are -fed back into the latter creat-ing a disturbance -which interferes with radio reception or the reliable operation of other apparatus, such as radiation-sensitive instruments Ior the like.

The phenomenon of radio-interference generation is not as yet perfectly understood but is a fault common to hot cathode gaseous discharge devices of all types and manufactures and, because of the inconvenience and expense involved in minimizing `the deleterious effects of the radiations by indirect methods after the device has been installed, constitutes a major problem in the `fluorescent` lamp industry. While the noise-generative process is a` very complex one it has been ldetermined Ithat the cathode is the primary source of these undesirable radiations which apparently evolve when the ionization efficiency 'abruptly changesduring the transition ofthe cathode fall voltage within the A. C. half cycie. `In the copending U. S. application Serial No. 677,623 of il. J. Mason entitled Electric -Discharge Apparatus and-Method, 'led concurrently herewith and which 'is assigned to the instant assignee, there is disclosed a means for substantially eliminating the most pronounced components of radio interferencenoise, i. e. the so-called ignition `and extinction components, by sequentially effecting an yauX- iliary discharge from the cathode 'to an Iauxiliary electrode which, in conjunction with the main discharge, keeps the `net cathode current unidirectional and above a predetermined value thereby maintaining `at all times a normal cathode `fall land producing "the desired stabilizing effect on the cathode. In U. S. Patent No. 2,714,681 to R. L. Ke'ifer et al. a `different approach to the problem is y,disclosed iwherein it is proposed to minimize the generation of these undesirable electromagnetic radiations -by utilizing, in addition to the mercury vapor and argon normally employed in vfluorescent lamps, a gas mixture of Xenon and krypton to provide a gradation of ionizing potentials suchthat sudden changes in the ionization process during `the transition from low to high current conditions are avoided.

`Neither of `the foregoing arrangements have proven entirelysatisiactory insofar as the radio-interference is frequently only temporarily suppressed, in many cases lasting only during the first -lOO to 300 hours of lamp life. It has been theorized that perhaps lthe reason for this` reoccurrence of R. F. noise is `that lwhile the most prevalent of the transitional noise components are supfice pressed a D. C. type noise subsequently appears or becomes more pronounced Ias the operating lconditions of the cathode change with lamp life until the intensity of the radio-interference again reaches an objectionable level.

It is accordinglythe general object of the present invention to provide an electric discharge apparatus vrwhich may be operated from an alternating voltage source-Without generating objectionable amounts of radio-interference even after prolonged periods of operation.

A more specific object of the invention is the provision of a fluorescent lighting system adapted for A. C. operation wherein the suppression of radio-frequency noise is sustained over a greater portion of the lamp life than heretofore.

Another object of the invention is the provision of alluorescent lamp and circuit wherein the generation of radio-interference is not only effectively suppressed but accomplishedwith a minimum `dissipation of electrical energy.

The 'foregoing objects and others which will become obvious to those skilled'in the art as the description proceeds are achieved by utilizing as a lill `gas a mixture of gases of such character that a suitable gradation of ionization potentials is obtained, `as disclosed in U. S. Patent No. 2,714,681, and providing an auxiliary electrode and circuit adapted to maintain a normal cathode fall at all times in the manner disclosed in `the aforementioned copending U. S. application of I. l. Mason. yAccording to 'the preferred form of `the invention these features are incorporated in a rectifying type iluorescent lamp system thus not only increasing the longevity of the noise-suppression but materially reducing fthe amount of auxiliary discharge current required -to maintain the net cathode current above the preselected minimum value and effecting `a` proportionate increase in lamp efficiency. lt Ihas ybeen foundthat the synthesis of these two modes of radiointerference suppression maintains y the noise intensity below an objectionable level `for a greater length of `time than that heretofore obtained from either of the modes aloneor expected on `the basis of ltheir mere additive effect. In addition, by incorporating 1these modes into a `device `which 4is operated in accordance with the principlesyof full-wave rectification the power `consumption necessitated by `the D C. operated type cathode arrangement is reduced to la minimum.

A` better understanding of the invention may be obtained by referring totheaccompanying drawing wherein:

Fig. l is an elevational View of a rectifying type lluorescent llamp and schematic diagram of an A. C. energizing circuit Atherefor according to the present invention;

Figs. 2a, b, c and d are graphical representations of the line current, the main and auxiliary discharge currents and the ne't cathodecurrent, respectively, of the 'lamp shown in Fig. 1` during the A. C. yoperation thereof according tothe invention;

yFig. 3 is an elevational View of a conventional dualcathode fluorescent lamp and schematic diagram of an instant start A. C.energizing circuit, therefor according to an alternative embodiment of the .present invention;

Fig. 4 is an enlarged viewl of an electrode mount employed in the lamp shown in Figs. l and 3.

While the invention may 'be utilized in conjunction With any A; y@operated electric discharge device which pro- -duces R. F. noise, it is especially adapted `for use with a `fluorescent lighting system and hence has been so illustrated and will beso described.

Turning now` to the drawing, particularly Fig. 1, the invention maybe incorporated into a rectifying type fluorescent lamp 10 which, briefly stated, comprises a tubular light-transmissive `envelope 12 sealed at both la ends by mounts 14 and 15 and containing an ionizable medium such as a droplet of mercury 34 and an inert gas mixture of argon, krypton and Xenon at substantially equal partial pressures, as for example, 1.17 mm. of mercury to provide a total pressure of about 3.5 mm. of mercury. The total gas pressure within the lamp may vary over a rather wide range depending upon the starting voltage and eiciency desired, as pointed out in the previously-mentioned U. S. Patent No. 2,714,681, thereby providing an ionizable medium having graded ionization potentials of such character that the rate of change of the cathode current is controlled and the amount of R. F. noise generated by fluctuations in the cathode fall and current is minimized in accordance with the principles disclosed in the patent. A quantity of phosphor material is distributed over the inner surface of the envelope 12 to form a coating 32 as is well known in the art. The mount 14, as shown more particularly in Fig. 4, may be of conventional glass stem construction wherein three lead wires 16, 18 and 20 are hermetically sealed through a press formed at the end of a flared section of glass tubing. A thermionic electrode, as for example a coil of tungsten wire which has been impregnated with suitable electron-emissive material such as the conventional alkaline earth compounds, is transversely connected to the ends of the lead wires 16 and 18 and serves as a cathode 24 which axially protrudes into the envelope 12 when the mount 14 is sealed therein. The end section of the remaining lead wire 20 is bent in the shape of a hook having a straight end which is disposed in adjacent and generally parallel relation with the cathode 24 to thus form an auxiliary electrode 22. Inasmuch as the auxiliary electrode 22 is formed from the lead wire or other non-activated material it is less electron-emissive than the cathode 24 and hence always functions as an anode with respect thereto.

At the opposite end of the lamp a pair of axiallyextending tubular electrodes depend from the mount into the lamp envelope 12 to serve as a pair of anodes 26 and 2S. In order to minimize sputtering the anodes 26 and 2S are preferably fabricated from carbon or other suitable material. An insulated shield 30 separates the anodes 26 and 28 from each other thereby preventing arcs therebetween during the operation of the lamp. Base members 36 and 37 attached to opposite ends of the lamp envelope 12 enclose the sealed-in portions of the envelope 12 and carry contacts 38, 40, 42 and 39 and 41, respectively, which serve to facilitate the connection of the lamp to a source of electrical energy. The lead wires 16 and 18 connect with the contacts 38 and 4t), respectively, whereas the lead wire 20 is connected to the remaining contact 42 that protrudes from the base member 36. In a similar fashion the anodes 26 and 28 at the opposite end of the lamp 10 exteriorily connect with the contacts 39 and 41, respectively, carried by the base member 37.

Operation of the lamp 10 is effected by connecting the contacts 39 and 41 to opposite ends of a center-tapped secondary winding 46 of a transformer 44 through suitable conductors 50 and 52, respectively, and by connecting the contacts 38 and 40 to each other and by means of a suitable conductor 54 to the center-tap 48 of the secondary winding 46 through a suitable ballast 56 and electrical-energy storage element 58 arranged in series. Thus, the anode 26 is connected to one end of the secondary winding 46 and the other anode 2S to the opposite end of said winding whereas the cathode 24 is connected to the center-tap 48 thereby constituting a main energizing circuit and permitting the lamp 10 when operated from single-phase A. C. power source to function as a full-wave rectifier. Upon the energization of the transformer 44 the anodes 26 and 28 alternately become positive with respect to the cathode 24 causing a predetermined voltage to be impressed across the lamp 10 such that a gaseous discharge occurs between the cathode 24 and the anodes 26 and 28, the discharge alternating between the latter on each half cycle of applied voltage and terminating at whichever one is positive.

The .lead wire 20 connects the auxiliary electrode 22 with the line side of the electrical-energy storage element S8 by means of the base contact 42 and a suitable conductor 60. This provides a branch circuit at the cathode end of the lamp 10 which circuit comprises the auxiliary electrode 22, lead wire 20, base contact 42, conductor 6l) and (in common with the main energizing circuit) the electrical-energy storage element 58, contacts 38 and 40, lead wires 16 and 18 and the cathode 24. The electrical-energy storage element 58 is preferably a choke of such inductance that it stores suicient energy during the rising-current portion of each half cycle that an auxiliary discharge of the desired intensity and duration will occur between the cathode 24 and auxiliary electrode 22 during the falling-current portion of the sarne half cycle and leading part of the succeeding half cycle. In this manner the branch circuit serves as an auxiliary D. C. circuit which, while including a part of the main energizing or lamp operating circuit, does not form a part thereof nor interfere with the normal A. C. operation of the lamp 10 in accordance with the principles disclosed in the aforementioned copending application of I. I. Mason.

Hence, although the wave-form of the alternating line current I applied to the lamp 10 through the transformer 44 is generally sinusoidal as shown in Fig. 2a, the main cathode current ic is unidirectional and pulsating in nature as illustrated in Fig. 2b. The cathode 24 during the operation of the lamp 10 accordingly supplies a D. C. current which reaches a peak and falls to zero twice during each cycle of the applied A. C. voltage. When the main cathode current z'c reaches a peak and begins to fall off, the electricalenergy stored in the choke 58 during the rising-current portion of the halfcycle is progressively released and causes an auxiliary discharge to occur between the cathode 24 and the adjacent auxiliary electrode 22, which discharge continues during the falling-current portion of the half cycle and the beginning of the rising-current portion of the succeeding half-cycle. This cyclic storing and release of electrical energy produces an intermittent auxiliary discharge current id of sharply-peaked character which ows in the previously-described auxiliary circuit at the cathode end of the lamp 10 bridging the gaps between successive pulses of the main discharge current ic as illustrated in Fig. 2c.

Insofar as both the main cathode current ic and the auxiliary discharge current z'd are supplied by the cathode 24, the Inet cathode current imm) which flows is equal to the sum of the aforesaid currents and will undulate above a predetermined minimum value femm.) in the manner indicated by the solid-line portion 62 of the cornposite wave-form diagram of the currents shown in Fig. 2d. The unshaded area under the solid-line portion 62 of the diagram represents the main discharge current ic and the shaded area the auxiliary discharge current id, as is indicated in the drawing. It will be evident, therefore, that the net cathode current imm) reaches a maximum immun) during each half cycle and thereafter expotentially decays to a minimum value femm.) during the time interval when it would normally fall to zero and subsequently rise to the latter value. Thus, the current drawn from the cathode 24 is at all times maintained above a predetermined critical value cnm.) assuring a normal cathode fall voltage and substantially eliminating the most pronounced co-mponents of radio-interference noise incident with subcritical current values in the manner disclosed in the aforementioned copending application of Mason. It should be particularly noted that in this embodiment of the invention the amount of power `dissipated in the auxiliary discharge and the size of the electrical-energy storage component 58 are reduced to a minimum since only sufficient auxiliary discharge current z'd must be supplied to fill in the relatively small gaps between adjacent pulses of the main discharge current ic as compared to the comparatively large blocks of current required to lill in the voids between the intermittent main current pulses when a non-rectifyi-ng type energizing system such as that disclosed in the above-noted copending application of I. I. Mason is employed.-

As `shown in Fig. 3, the inventionmay also be applied to the more commonly used' dual-cathode lamp 10a wherein a pair of electrodes 24a` and 64 are disposed at opposite ends of a light-transmissive envelope 12a which includes a quantity of mercury 34a, the usual phosphor `coating 32a and an inert gas composition consisting of argon, krypton and xenon at predetermined partial pressures and a total pressure selected as discussed in connection with the preferred embodiment. The cathodes 24a and 64, at least one of which is thermionic, are connected by means of suitable lead wires to the contacts 66 and 67, respectively, which depend from the bases 36a and 37a attached'to the ends of the lamp envelope 12a and by means of suitable electrical-energy storage components 74. and 7S and conductors 72 and 73 to an energizing source such as an auto-transformer 76 for example. Auxiliary electrodes 22a and 63 of less electronemissivity than the` adjacent cathodes 24ay and 64 are connected to the remaining base pins 68 and 69, respectively, and by means of suitable conductors 70 and 71 to the line side of the aforementioned electrical- energy storage components 74 and 75, respectively, thus providing a D. C. cathode lamp, an auxiliary circuit, and an instant-start energizing circuit of the` type described in detail in the aforesaid copending application of J. J. Mason. While the foregoing circuit components and arrangement are identical to those disclosed by Mason, the inclusion of krypton and xenon within the lamp in accordance with the present invention renders the lamp operation dilferent in kind as regards R. F. noise generation from that achieved in accordance with the teachings of Mason or Keiffer et al. resulting in the unexpected advantageous effect hereinafter disclosed.

Actual test data have indicated that the magnitude of radio-interference produced by lamps incorporating both the D. C. cathode and multiple gas composition having graded ionization potentials is not only reduced to a negligible level but effectively suppressed for a longer period of time than that heretofore possible with lamps separately incorporating the foregoing elements or contemplated on the basis of their additive effect alone. Experience has shown that lamps constructed and operated in accordance with the principles disclosed in the aforementioned application to Mason and patent to Keiffer et al. were not entirely satisfactory in that the expected degree of noise suppression would not always be achieved and when it was elfected would only last for about the lirst 100 to 300 hours of lamp life at which time a D. C. or other type of noise component would become suiciently pronounced to cause the overall noise intensity to reach an objectionable level. Thus, on the basis of the mere additive effect of these two modes of noise-suppression one would expect that at lbest a lamp incorporating both modes would, under ideal conditions, operate twice as long or for about 200 to 600 hours before generating an objectionable amount of noise. It was discovered, however, that when the two modes of noise-suppression were combined in the same lamp in accordance with the present invention the R. F. noise would be maintained at a level comparable to that described by Mason and Keiifer et al. for approximately the first 900 hours of lamp life thereby effecting at least a 300% increase in the longevity of the noise-suppressive effect. Moreover, this disideratum is advantageously accomplished according to the preferred embodiment of the invention with a minimum amount of electrical power through the utilization of a rectifying type energizing circuit.

It will be obvious that the` objects of the invention have been achieved by providing a gaseous discharge apparatus ofsuch character that through the synthesis of two basically different cathode-stabilizing means conveniently and economically fabricated not only are the most pronounced components `of Vradio-interference incident with the A. C. operationof such devices substantially eliminated but the suppression of these and` other components of R. F. noise is sustained below an objectionable level for a greater portion of the` lamp life than was heretofore possible.

While in accordance with the` patent statutes one best known and one alternative. embodiment of the invention has been illustrated and described in detail, it is to be particularly understood that various modifications may be made without departing from the spirit and scope ofthe invention.

Iclaim:

l. Electric discharge apparatus comprising a gaseous discharge` device, an energizing circuit, and an auxiliary discharge circuit; said device comprising an envelope containing a plurality of main electrodes, one of which is thermionic and serves as a cathode during the operation of said device, ani auxiliary electrode adjacent to and havinglesselectron-emissivity than said cathode, and an ionizable medium including a gaseous atmosphere consisting of argon, krypton and xenon; said `energizing circuit-comprising `a transformer connected to said cathode and the other of said main` electrodes and operable when energizedto initiateandsustain a controlled gaseous dischargeftherebetween, and an electrical-energy storage means connected-1in series -with'fand between said cathode and transformer; and said auxiliary discharge circuit cornprising conductor means connecting said auxiliary electrode to said energizing circuit and said cathode through the electrical-energy storage means; said electrical-energy storage means being operable to sustain during the operation of said device an intermittent D. C. auxiliary discharge between said cathode and auxiliary electrode of such magnitude and duration that the current from said cathode is maintained above a predetermined value, which condition in conjunction with the additional stabilizing effect produced by the said ionizable medium reduces to a minimum the radio-frequency noise generated by said device over a substantial portion of its life.

2. Electric discharge apparatus comprising a gaseous discharge device having an envelope, arc-supporting means within said envelope between which a gaseous discharge occurs during the operation of said device, said arcsupporting means comprising three main electrodes one of which is thermionic and serves as a cathode in conjunction with the other two which function as anodes, an auxiliary electrode disposed adjacent said cathode, said auxiliary electrode being less electron-emissive than said cathode, means for operating said device from` an alternating voltage source including a ballast and. a transformer having a center-tapped secondary winding, conductor means connecting said anodes to opposite ends of said secondary winding and said cathode and auxiliary electrode to each other and to the center-tap of said secondary winding to thus provide a full-wave rectifying circuit, electrical-energy storage means in said circuit between said alternating voltage source and said cathode operable to sustain during the operation of said device a D. C. auxiliary discharge between said cathode and said auxiliary electrode such that the net current from said cathode is maintained above a predetermined value, and an ionizable medium within said envelope including a gaseous atmosphere consisting of argon, krypton and xenon which in conjunction with the said electrical-energy storage means produces an enhanced stabilizing effect on the cathode such that the radio-frequency noise generated by said device is reduced to a minimum, even after prolonged periods of operation thereof.

3.` A light-generating system comprising a low-pressure type iluorescent lamp and an energizing circuit for operating said lamp from an A. C. power source; said lamp cornprising a light-transmissive envelope containing three main electrodes one of which is thermionic and disposed at one end of said envelope to constitute a cathode and the other of said main electrodes being disposed at the opposite end of the envelope and serving as anodes, an auxiliary electrode adjacent said cathode, a coating of phosphor on the inner surface of said envelope, and an ionizable medium including mercury vapor and a gaseous atmosphere consisting of argon, krypton and xenon at substantially equal partial pressures and at a total pressure of approximately 3.5 mm. of mercury; said energizing circuit including a ballast and a transformer having a center tapped secondary winding, the endsofrsaid secondary winding being connected to said anodes and the centertap thereof to said cathode to thus constitute a full-wave rectifying circuit; conductor means connecting said auxiliary electrode with said cathode and said energizing circuit and in conjunction with a portion of said energizing circuit constituting an auxiliary circuit; and a choke in the said portion of the energizing circuit common to said auxiliary circuit; said choke being connected in a series with said cathode and the secondary winding of said transformer and operable in response to the decrease in the cathode current during the operation of said lamp to initiate and sustain an intermittent D. C. auxiliary discharge between said cathode and auxiliary electrode'of such magnitude and duration that the current from said cathode is maintained above a predetermined value during that portion of each half cycle when said cathode 5% current would normally drop below said value, which condition in conjunction with the additional stabilizing effect produced by said argon, krypton and xenon reduces to a minimum the radio-frequency noise generated by said lamp over a substantial portion of its life.

4. A fluorescent lighting system comprising a fluorescent lamp; an energizing circuit; and an auxiliary discharge circuit; said lamp comprising a phosphor-coated light-transmissive envelope containing an ionizable medium, three main electrodes, one of Which is thermionic and serves as a cathode in conjunction with the other of said main electrodes which function as anodes, and an auxiliary electrode adjacent to and less electronaemissive than said cathode; said energizing circuit comprising a transformer having a center-tapped secondary winding, conductor means connecting said anodes to opposite ends of said secondary winding and said cathode and auxiliary electrode to each other and to the center-tap of said secondary winding to thus provide a full-wave rectifying circuit, and an electrical-energy storage component connected in series with and between said cathode and transformer; and said auxiliary discharge circuit comprising conductor means connecting said auxiliary electrode to said energizing circuit and said cathode through the electrical-energy storage component; said electrical-energy storage component being operable to sustain during the operation of said lamp an intermittent D. C. auxiliary discharge between said cathode and auxiliary electrode such that the current from said cathode is maintained above a predetermined value with a minimum of auxiliary discharge current.

No references cited.

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