US2117794A - Ionic discharge tube - Google Patents

Description

May l?, 1938- D. M. DUINKER E1- AL 2,117,794

` 10u10 DISCHARGE TUBE Filed 001;. 3, 1935 h yf lll

MSS. .af

Waff/Vix Patented May 17,1938

IoNIc DISCHARGE TUBE Danil Marie Duinker and. Johannes Gijsbertus Wilhelm Mulder, Eindhoven, Netherlands, assignors to N. V. Philips Gloeilampenfabrieken, Eindhoven, Netherlands Application October `3, 1935, Serial No. 43,428 In Germany October 9, 1934 11 Claims.

Our invention relates to ionic discharge tubes having an envelope at least; partly of vitreous 4material and electrodes provided in a common discharge space, and in which one or more elec- 5 trostatic screens are provided to separate a plurality of electrodes.

Our invention has special reference to a novel construction of such electrostatic screens, and to a novel method of assembling the screens and the anodes.

'I'he term ionic discharge tube as used herein and in the claims is to be understood to mean a discharge tube Whose filling consists of one or more gases or vapors, or a mixture of gases and vapor, and has a pressure from several microns to several centimeters of mercury.

Electrostatic screens are frequently used in discharge tubes in which the anodes operate on high alternating voltages and more particularly in discharge tubes in which a plurality of anodes operate on polyphase anode currents. Such screens, which at least partly surround the individual electrodes, and in some cases surround both each individual anode and also surround the entire group of anodes, are usually made of metal.

Although the use of metal for this purpose has several advantages it has, however, several disadvantages, namely; due to the comparatively high electron emissivity of metal, there is the danger that the screen itself permits a back discharge between one of the anodes and the cathode, or a direct arc discharge between two of the anodes. Such discharges`may be brought about by the fact that the screen acts as a 35 cathode with respect to one of the anodes, and also with regard tothe cathode', and thus the cathode, in respect to .the screen, acts as an anode. 'Ihus such a metal screen defeats its own purpose, i. e., the prevention of such discharges.

Furthermore, such metal screens, particularly when they are used in high-power tubes, may become heated to very high temperatures, which may even reach the melting point of the partic- 45 ular metal used notwithstanding the use of high melting point metals such as molybdenum.

In accordance with the present invention the above-mentioned disadvantages of metal screens are overcome by using as the material of the 50 screen a carbonaceous material.

The term carbonaceous material is meant to include carbon, graphite, and also articial carbons consisting of these materials, together with additional substances, such as silica or oxide.

As such carbonaceous materials have good elec- (CL Z50-27.5)

trical and thermal conductivity and their surfaces, without further treatment, have good heatradiating properties, excellent cooling conditions are insured. Y

In addition, the melting point of such carbonaceous materials is the same, or at least of the same order, as that of the material used for the anodethus greatly in excess of the usual cathode temperatures-and there is no danger of melting as might occur with metal screens.

Furthermore the electron-emissivity of such carbonaceous materials is very low, which greatly reduces the possibility of back discharges occurring while the screen acts as a cathode.

'I'he screens according to the invention are particularly useful in connection with oxide cathodes the low working temperature of which permits them to be located in the immediate vicinity of the anodes, whereby the close spacing of the electrodes provides for a vry compact arrangement.

With such a compact arrangement of the electrodes it is preferable to make the screen from a single piece or block of carbonaceous material provided with cavities which are preferably arranged symmetrically and parallel to each other, and to place the anodes in these cavities. The block may also be provided with a cavity for the incandescible cathode, this cavity being preferably arranged normal to the anode cavities. Such a block can be easily made and at the same time provides a compact construction of the anodes and screens.

In a particular construction of the screen the anode cavities do not pass through the block, but only partly extend therein, the closed end being provided with a bore which closely embraces an insulated support for the anode. Such a construction improves the mechanical construction of the screen and anode system and also the electrical characteristics thereof.

To improve the cooling conditions we prefer to provide the block` with apertures or slots in order to facilitate thermal radiation, and means may also be provided whereby an electric potential may be applied thereto to ignite the discharge, or to aid in the suppression of back discharges. y if Constructions in which the anodes and the cathode are located close to each other and are surrounded by a common block acting as a screen, constitute a compact system which can be housed within a substantially tubular envelope whereby the anodes are located near one end and the cathode is located near the other end of the envelope with their terminals located at the corresponding ends of the tube.

When a discharge tube according to the invention is used in various apparatus a considerable saving in space is obtained, and in addition the location of the terminals clearly indicates the correct manner of making the necessary connections thereto.

'I'he screen and anode assembly according to the invention must be assembled in a particular manner in order to insure the proper results, and a novel method of assembling same will be described hereinafter.

In order that the invention may be more clearly understood and readily carried into eiect, it will be more fully described in connection with the accompanying drawing, in which:

Figure 1 is a sectionized side view of a discharge tube according to the invention;

Fig. 2 is a sectionized view taken on the line II-II of Fig. 1;

Figs. 3 to 6 are sectionized views used in connection with describing the method of assembling;

Fig. '1 is a sectionized side view of a discharge tube according to another embodiment of the invention; and

Fig. 8 is a sectional view along line 8 8 of Fig. 7.

The discharge tube shown in Figure 1 has a substantially cylindrically-shaped envelope I 'of vitreous material enclosing an incandescible cathode 9 and three anodes 2 (only one of which is visible). Hermetically sealed in the envelope I are two discs I5, three discs 5 (only one being visible), and a disc I3. The discs 5, I5, and I3 may be oi chrome iron, and the method of sealing same into the envelope has been set forth in the U. S. Patent #1,627,780 to Jonas, dated May 10, 1927.

'Ihe incandescible cathode 9 is supported and electrically connected by rods I4 of conductive material to each of the discs I5, to which are secured leads I5 for making the external connections to the cathode supply.

Provided in the central portion of the tube are the three anodes 2, which are of similar construction and are supported in a similar manner from discs 5. The anode 2 visible in Figure 1 is secured, for instance, by a screwed connection to the lower end of a rod 3 of conductive material, which rod is mechanically secured and electrically connected to the disc 5, provided with a screw terminal 6 for making the external anode connection. Surrounding rod 3 and slightly extending therewith into a cooperating bore vin the anode 2, is a sleeve 4 of insulating material, .for instance porcelain. The upper portion of sleeve 4 is closely embraced by a tubular protuberance 20 of envelope I, which aids in its support.

Insulatingly supported from a protuberance 25 of the envelope I by means of rods I and Il of conductive material is a cylindrically-shaped block 1 of carbonaceous material, for instance of carbon or graphite, which acts as a screen.

The rod Il is fused into the protuberance 25, whereas the rod I0 is attached to the block 1 by means of a screw connector 22.

The rod I0 is electrically connected to a terminal 21 secured to disc I3 by means of a rod 36, a exible lead I2, and rod 26, whereby a suitable potential can be applied to the block 1 for the purpose of igniting the discharge or of lsuppressing back discharges.

The block 1 is provided with three symmetrically arranged and parallelcylindrical cavities 23 in each of which is disposed one of the anodes 2. Each of the cavities is provided on its closed end with a bore 24 adapted to receive one of the insulating tubes 4 with a snug fit.

To facilitate the cooling, the wall of each of the cavities 23 is provided with a slot l1. The slots I1 should be so placed and dimensioned as to prevent lines of force of high intensity from forming between adjacent anodes and rendering the mutual screening of the latter inoperative. Such would be the case if the slots had sucient width so that adjacent anodes could see each other, i. e., so that a straight line between any two points on adjacent anodes would not be intercepted by the block. Therefore portions of the block 1 should always slightly project from between the anodes, not only at the sides but also at the ends.

Supported from the bottom of block 1 and electrically connected thereto, forA instance by means of a screw connector 2l, is a. tubular screen 8 of graphite or carbon, which screen surrounds the cathode 9 and overlaps the ends thereof.

It will be noted that the above construction affords a simple and eiective support for the block 1 and the anodes 2. The insulating tubes 4, due to the fact that they closely t into the protuberance 20 and bore 24, prevent any lateral movement of the block 1 and at the same time prevent any movement of the anodes with respect to the inner surfaces of the cavities 23. Furthermore, the block 1 is supported axially in a simple manner by means of rods I0 and II which are secured together at 3|, for instance by welding, during the assembling of the tube.

The construction shown must be assembled in a denite manner in order to secure the best results, and a novel method of assembling also forms part of our invention.

The obvious method of assembling such a construction would be to rst secure the rods 3 to the discs and then slip the insulating tubes 4 over the rods 3. The block 1 would then be moved upwardly so that the insulating tubes pass through the apertures 23 after which the anodes would be secured to the ends of rods 3 and the connection made between rods l0 and II.

However, such a method of assembling has the following drawback: As the insulating tubes 4 tightly t into the apertures 23, the movement of the block 1 upwardly over the tubes 4 results in the surfaces of the tubes receiving a coating of the conductive material of which the block is made. As, in the nal position of the parts, the distance along the surface of the insulating tube between the anodes and the block is relatively short, such a. conductive coating on this surface portion would deleteriously affect the insulation between the anodes and block.

In accordance with the invention such assembling diculties are eliminated by assembling the parts in the following novel manner, which will be described in connection with Figs. 3 to 6. Although the Figures 3 to 6 show a two-anode construction the method of assembling is the same irrespective of the number of anodes used.

As indicated by the arrows in Fig'. 3, the insulating sleeves 4 are rst moved in the direction of the arrows through the cavities and partly into the cavities 23. It should be noted that the insulating tubes 4 are inserted into the aperture only to about halt their length, whereby the lower ends do not come into contact with the block 1.

The sleeves 4, with the block 1 attached in the position shown in Fig. 3, are then slipped over the rods 3-which have been previously secured to discs 5-and the block 1 is moved slightly upwardly along the sleeves 4 into the position shown in Fig. 4; the rod being bent to allow such movement. It will be noted that the lower ends of rods 3 protrude from the cavities 23.

The anodes are now screwed onto the lower ends of rods 3, as indicated in Figure 5, which at the same time clamps the tubes 4 between the anodes and the discs 5. As the ends of rods 3 protrude from the cavities 23, the attachment of the anode may be readily effected with the use of standard tools.

The block 1 is then slipped downwardly, as indicated by the arrow in Fig. 6, into its proper position with respect to the anodes, after which the rod is bent back into its proper position and the rod l is secured to both the block 1 and to the rod The lead I2 is then secured to rod I0 and the parts are completely assembled, as shown in Fig. 6.

In accordance with the above-described method the outer surface of the lower part of sleeves 4 at no time comes in contact with the block 1 and the possibilities of this surface receiving a coating of conductive material is completely i eliminated.

The discharge tube schematically shown in Figures 7 and 8 has an envelope 40 supporting a single block 44 of carbonaceous material provided with two parallel cylindrical cavities 50 and and a third cavity 52 arranged perpendlcularly to cavities 50 and 5|. Arranged within cavities 50 and 5| are cylindrical anodes 4| and 42 respectively, of carbonaceous material, whereas an vincandescible cathode 43 is disposed within cavity 52. It will be noted that, also in this construction, a straight line between any point on one of the electrodes and any point on any one of the other electrodes is intercepted by block 44. Such a single block construction is simple, inexpensive, and mechanically strong.

While we have described our invention in connection with specic examples and in specific applications, we do not Wish to be limited thereto, but desire the appended claims to be construed as broadly as permissible in View of the prior art.

l. An ionic discharge tube comprising an envelope partly of vitreous material, a plurality of anodes and a cathode adjacently disposed in a common discharge space, and a single block of carbonaceous material provided with a plurality of inwardly-extending cavities connected only with the discharge space surrounding said block, said anodes being individually disposed in said cavities and separated by the walls of said block.

2. An ionic discharge tube comprising an envelope partly of vitreous material, a plurality of anodes and an incandescible cathode adjacently disposed in a common discharge space and a block of carbonaceous material provided with a plurality of separated cavities connected only with the discharge space surrounding the block, said anodes and cathode being individually disposed in said cavities.

3. An ionic discharge ltube comprising an envelope partly of vitreous material, a plurality of anodes and an incandescible cathode adjacently disposed in a common discharge space and a block of carbonaceous material provided with a plurality of symmetrical and parallel cavities each containing one of said anodes and connected only with the discharge space surrounding said block, said block also. being provided with a cavity extending normal to said par'allel cavities and containing said cathode.

4. An ionic discharge tube comprising an envelope partly of vitreous material, a plurality of anodes and a cathode adjacently disposed in a common discharge space, and a block of carbonaceous material provided with a plurality of cavities each containing one of said anodes, the wall of each of said cavities being provided with a slot to facilitate thermal radiation, said block intercepting Vall straight lines between points on one of said anodes and points on another or said anodes.

5. An ionic discharge tube comprising an envelope partly of vitreous material, a plurality of anodes and a cathode adjacently disposed in a -common discharge space, and a block of carbonaceous material provided with a plurality of substantially parallel cavities each housing one of said anodes, the cylindrical delimiting surface of each cavity extending tothe outer surface of the block to form an opening for the free radiation of heat from the anode and through the vitreous envelope portion to the outside of the tube, said block intercepting straight lines from any point on one anode to any point on any other of the anodes.

6. An ionic discharge tube comprising electrostatic screen formed of a block of carbonaceous material provided with a plurality of symmetric and parallel cavities extending partly into the block and adapted to receive the anodes, said block also being provided with-bores connecting the bottom of the cavities to the outside of the block, said bores being adapted to receive anode supports with a snug fit which is free from play.

7. A method of assembling anodes in a screen comprising the steps, passing insulating tubes through cavities of the screenand to part of their length through bores connected to the closed end of the cavities, placing the insulating tubes over supports for the anodes, displacing the screen along the tubes sothat the supports project from the cavities, securing an anode to the end of each support, and moving the screen along the tubes so that the anodes are located within the cavities.

8. An ionic discharge tube comprising, an envelope partly of vitreous material, a plurality of anodes and a cathode adjacently disposed in a common discharge path, a single block of carbonaceous material provided with a plurality of cavities connected only with the discharge space surrounding said block, said anodes being individually disposed Within said cavities and separated by the walls of said block, and a screen partly surrounding said cathode.

9. An ionic discharge tube comprising, an envelope partly of vitreous material, a plurality of anodes and a cathode adjacently disposed in a common discharge path, a single block of carbonaceous material provided with a plurality of cavities connected only with the discharge space surrounding said block, said anodes being individually disposed within said cavities and separated bythe walls of said block. and a screen of carbonaceous material secured to said block and partly surrounding said cathode.

10. An ionic discharge tube comprising an envelope partly of vitreous material, electrodes adjacently disposed in a common discharge space,

of carbonaceous material partly surrounding each of a plurality of said electrodes while placing each electrode in individual communication with only the discharge space surrounding the screen, said screen being insulated from said electrodes and intercepting straight lines between any point on one of said electrodes and any point on any other of said electrodes.

DANIEL MARIE DUINKER. JOHANNES GIJSBERTUS WILHELM MULDER.

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