US2036069A - Electric switch - Google Patents

Description

M. MORRISON ELECTRIC SWITCH Filed March 5, 1932 2 Sheets-Sheet l ATTORNEY EM, QSG.

3l, 1936, M. MORRISON zg@ ELECTRIC SWITCH Filed March 5, 1932 2 Sheets-Sheet 2 lil Mu. 31., 193e i c im@ il ai Hennepin p opany, a cotation nlication il, lilith, um 'ini No.. tutti@ "ilus invention relates to electrical suites rl more particularly to switches oi the character adapted to maite and hreali an electrical cireuit ci predeterniinm voltage and current values. ln more speciilc aspect the invention le rilrented to a thernilonic switching or trigger device adapted to operate without deental arcing in an electrical circuit vvhere the voltageapplied to the thermlonic device is oi the order ci about iorty thousand volts or more and the current passing through said device may he ahout one thousand nnlianiperes more or lese.

iin sonne ci the electrical coercial arts it is sometimes essential that electrical energy oi predetermined voltage and current chars-.icterictics he applied to a pair oi conductors ior a prerleteed length ci t. One ci the heide where the shove factors are oi importance is the K-ray photographic field where antane-l ons ee radiographic plat@ are 1- i 'lhese so-called instantaneous enposin'e radiographie plates may be prepared hy subjecting the object to he K-rayed to a beam of X-radiatlon oi" appropriate intensity and neve lengths ier a limited period of time, which is oi the order oi a fraction oi a second.

in order that an instantaneous e iii-ray plate or film may he produced in such n short period of time, it is essentiel that the wave lengths or the X-radiation oi the Krait heani and the intensity ol the K-ray henne ww on the object to he X-rayed he oi at least certain magnitudes so that the plate or may receive and he properly anected by a comparatively large i auantity ci K-rays ci selective wave lengths.

in. the :course oi my enperimentatlons with lit-rey tunes in general in the radiographic art, l have observed that good X-ray photographic plates o! the instantaneous exposure type may be produced providing the electrical energy supplied to an X-ray tube has certain characteristics. Some of the salient characteristics of the electrical energy employed for this purpose which. must be taken into consideration are, the magnitude of the applied tube voltage, the time dura.- tion of said applied tube voltage, and the magnitude of the tube current. To obtain good lnstantaneous" exposure radiographic plates I have found that the time of X-ray exposure should be very short and of the order of a small fraction of a second, both the applied tube voltage and the tube current should be relatively high and o! the order of about forty thousand volts and upwardly and about one thousand millinmperes more or less respectively. the latter ot which is an exceedingly high tune current iler ll-ray vvorlt. luy virtue oi the emplont oi this type oi electrical energy, the intensity and wave lengths ci the lt-ray beam produced are oi s-rl cient magnitude to permit the production oi a p superior instantaneous X-ray plate in a all traction oi n second.

hriey stated, my invention comprises a three electrode tube which is adapted to prevent end allow the instantaneous discharge oi a conin denser at a high potential alter it is charged., The tube consists primarily ol a gas-tight dim electric envelope having an anode and a caode appropriately spaced from each other and a grid of novel design appropriately spaced between le the cathode and the anode. With a tuloe oi this general construction embodying my invention, it is practical to block the discharge of a creed condenser ior a period of time and at an ap pointed time to allow the discharge oi said con gp denser therethrough, which discharge may he as high as one thousand mllliamperes or more at iorty thousand volts or upward.

@ne ci the objects oi invention is to pro1 vide me whereby electrical energy oi high volt- 2li nee values may he applied to an X-ray tute for a relatively snort period oi time, without detri mental areing or current discharge.

.Another object of my invention is to provide a thermionlc tube capable of edectively'prevent- 3@ lng and allowing the instantaneous passage therethrough of electric energy which is oi n paratively high potential and high current values for X-ray use.

Another object oi my invention is to provide e. new method oi preventing and allowing the passage of electrical energy from e. source oi electrical supply to a. load,

Another object of my invention is to provide 40 s. new method of preventing and allowing the passage of electrical energy of high voltage and high current values from a. source of electrical supply to a. load.

Another object of my invention is to provide 45 a, new method of preventing and allowing the instantaneous" passage of electrical energy from a source of electrical supply to a load.

Other objects and advantages of my invention will be readily apparent from the following specl- 50 cation and appended drawings wherein,

Figure l represents a. shortened longitudinal cross sectional view, with some of the parts in elevation of a device embodying my invention;

Figure 2 represents a cross sectional view taken 55 along line II-II of Figure 1 in the direction o! the arrows;

Figure 3 represents a cross sectional view taken along line III-III of Figure 1 in the direction of the arrows;

Figure 4 represents a modification oi' Figure 3:

Figure 5 represents a cross sectional view along line IV--IV of Figure 4.

As shown in Figure l, one embodiment of my invention is the illustrated trigger tube A comprising an evacuated enclosing gas tight dielectric elongated envelope I0, composed of glass or the like, in the form of a bulbous mld-portion with a pair of diametrically opposed elongated tubular arms I2 and I3. Extending within said tubular arms I2 and I3 respectively, are a plurality of reentrant dielectric tubes I4 and I5 having presses IB and II at their respective ends, located in proximity of the respective limits of the bulbous portion Located within the envelope I0 and with the effective portions thereof in the approximate center of the bulbous portion of the envelope are a plurality of spaced parallelly arranged electrodes I8, I9 and 2l. 'I'he presure of the residual gas within the tube is preferably as low as possible and may be of the order of about 10-5 to 10-4 mm. of mercury.

The electrode I8 is the plate or anode in the form of a plane smooth surface disc, having the circumferential outer portion thereof curled upwardly and inwardly towards the anode end of the envelope, and away from the electrodes I! and 20 to provide a surface of large radii of curvature so as to minimize cold electron emission between the electrodes.

This anode or plate I8 may be about 25 mils thick and composed of a refractory metal, as for example, molybdenum and is supported by an electrical conductor 2| of molybdenum or the like having one end secured thereto and its outer end secured to the conductor 22. The eective anode area is preferably greater and about ilfty percent greater than the overall area of the cathode 2U, hereinafter more specifically described. Between the anode or plate I 8 and the conductor 22, a portion of the supporting conductor 2| forms an air-tight seal and supporting means with the vitreous press Ii. Secured to a face of the anode or plate I8, within the periphery of the curled edge thereof by means of welded right angle supports or other mechanical means, is a metallic tubular section 2l composed of molybdenum or the like.

This tubular section 23 extends away from the effective anode I8, surrounds that portion of the anode support and conductor 2| within the envelope, the seal and press I6, and a substantial portion of the reentrant tube Il beyond the press. On the inner surface of that portion of the tube 23 surrounding the reentrant tube are secured a plurality of spring fingers 24 whose outer surfaces bear against theouter surface of the reentrant tube I4. 'I'his metallic tubular section 23, due to this peculiar assembly and design, serves as a heat distributor and a shock-absorbing and distributing means to aid in the prevention of anode over-heating, seal impairment due to heat and/or stray electron bombardment thereof and seal fracture.

Moreover this particular construction aids in the prevention of general tube fracture caused by mechanical shocks to which tubes of this character might normally be subjected in the course of practical commercial manufacture, manipulationoroperation. Italsoservestoassistinsupporting the anode I8.

At the cathode side of the tube and forming an air-tight seal with the press Il are a plurality of cathode lead-in and rigid supporting wires 2i and 26 having portions thereof extending exteriorly of the envelope and portions thereoi' extending within said envelope. Substantial lengths of the upper free endsv 21 and 2l of the support wires 25 and 28 are bent outwardly and away from each other and are at about right angles to the longitudinal axis of the tube. Between said supporting wires and sealed in the press I'l are a plurality of, and as illustrated six, rigid supporting wires 2l, Il, 3|, 32, 33 and 3l composed of molybdenum or the like, and insulated from each other at the press I1. The upper portions of these wires are bent away from the longitudinal axis of the tube, with upper portions of the wires 28, Il and 3| bent in a direction generally opposite to the direction of bend of the wires 32, I3 and u.

'Ihe free ends of these wires are all approximately in the same general plane, which is substantially normal to the longitudinal axis of the envelope. Securely mounted by welding or other convenient means to the bent portions at or near the free ends thereof, in a generally zig-zag fashion as shown with each of its segments being in the same general approximate plane, is the fllamentary cathode 2l.

The cathode 2l may comprise a tungsten lament measuring about 20 cms. in length and 16.5 mils in diameter and has its respective ends secured to the bent portions 21 and 28 of the support wires 25 and 26. Because of such composition. length and diameter, the cathode 20 will provide a thermionic emission therefrom, of suiilcient magnitude to supply the desired comparatively large current of the order of about 1000 milliamperes, when a potential of about seventeen volts is applied between its terminals from the secondary winding of a low voltage transformer connected to lead in wires 25 and 26. Moreover, this comparatively large thermionic electron emission is effectively secured at the temperature to which the filament is raised without any substantial vaporization thereof at its maximum attained temperature due to said voltage being applied between its terminals.

Spaced from and closely surrounding the thermionic cathode 2l is an open ended cup 36 of molybdenum or the like, having an inwardly directed flange with adownwardly extending cylindrical portion integral with said flange and having a curled upper end whose edge is away from the face of the anode Il and in close proximity to the outer surface of the cup proper.

'Ihe cup 36 has a base 31 provided with an elongated slot 3l adapted to receive the rigid support wire 26 and the support wires 29, 3l, 3|, 32, Il and u. The other rigid support wire 25 passes through and is in contact with the base as shown in Figure 2. The support wire 25 may be welded to said base, although this is not necessary because it is suillciently in contact therewith as shown in Figure 2.

The inner wall of the cup 3i is in close proximity of the ends of the bent support portions. Its upper curled edge is above the plane of the cathode andthe flange portion extends inwardly and below the edges of the bent portions of the support and together with its base serves as a reecting surface for the electrons emitted at the cathode 2l. Telescoping the downwardly extending cylindrical portion integral with said flange is a metallic tubular section 40 having one end thereof secured to said cylindrical portion. This tubular section 40, composed of molybdenum or the like, supports the cup, surrounds all of the cathode supporting wires, the press and a substantial portion of the reentrant tube beyond the press.

On that portion of the inner wall of the tubular section 40, surrounding the reentrant tube i5, are secured a plurality of spring lingers adapted to frictionally engage and bear against the reentrant tube I5.

The cup 36, together with the cylindrical section t0, serves as a heat distributer and a shock absorbing and distributing means to aid in a prevention of seal impairment due to heat and/or stray electron bombardment thereof which may ultimately result in seal break down. Moreover, this particular construction aids in the prevention oi tube fracture caused by mechanical shocks to which a tube of this character might normally be subjected in the course of practical commercial manufacture, manipulationl or operation. It also serves to prevent the electrons emitted at the cathode from migrating over towards the walls of the envelope and acts to constrain the electrons in a limited ileld so that they may approach the anode in a preferred path upon excursion.

dt the respective ends of the vitreous bulb i0 are secured terminal caps 43 and d4 in electrical contact with the respective lead in wires 22 and tt, 2li. The vitreous envelope i0 is of appropriate length so that these caps t3 and t4 are remotely disposed from each other to prevent spark over therebetween when a potential of forty thousand volts or more is applied therebetween.

integral with the envelope l0 at about the midf length thereof and the bulbous portion il is a relatively short outwardly extending vitreous cup tt having a relatively short reentrant tube 39 forming an air tight seal. Within said reentrant tube 39 is a Y supporting molybdenum member iii secured to the third electrode It and sealed in the tube 39. The third electrode i9 is essentially a control electrode and, as shown in Figures ll and 3. may comprise a metallic cup whose internal diameter is substantially greater than the corresponding external dimension of the cup 36.

The cup shaped control electrode l0 is of substantial depth and may have a perforated base t2 with the edge of the perforations being preferably rounded to prevent cold electron emission. The distances between the perforations are preferably less than the corresponding dimension of said opening. The control or grid electrode it, supported by the lead il l, is located between the anode it and the cathode cup 36 with its sides surroundlng the upper portion of the cup 30, extending downwardly appreciably below the upper edge of said cup 36 and appropriately spaced therefrom.

The perforated base of the cup is preferably disposed substantially parallel to the planes oi the anode and cathode, with the virtual longitudinal center line of the envelope passing through the approximate centers of the planes oi each of the electrodes it, i9 and 2li.

Closely adjacent the seal of the arm di and the reentrant tube 39 is a cup shaped member d3 of molybdenum or the like secured to said arm and shielding said seal from electron bombardment or radiated heat. In order that this novel tube may be operable in a circuit so as to efficiently and effectively prevent and allow the instan taneous discharge therethrough of electric energy having high potential and high current characteristics in the X-ray eld consideration must be given to the composition and size of each electrode, as well as to the relative positions of these electrodes to each other.

The anode and cathode are preferably so spaced from each other that any danger of filament distortion or other deleterious effects. such as arcing, may be prevented during the operation of the tube at the high voltages to which it may be normally subjected.

The cup-shaped grid i9 surrounding the cup 36 has its bottom t2 substantially parallel to each of said electrodes and is adapted when negatively biased to prevent electron ilow from said cathode to said anode when said cathode is at operable temperatures. Thus. a zero plate current may be maintained when the cathode is heated to its maximum temperature and a high voltage ls applied between the anode and the cathode terminals because the sides of the control electrode I9, together with the cup tt, which is electrically connected to and at approximately the same potential as the cathode 20, acts as a mechanical and electrical barrier to prevent the electrons from migrating outside of the sphere defined by the cup 36 and the control electrode i9.

Besides being amenable to said shielding or blocking action the grid is preferably of such composition and design that when it is positively biased it will instantaneously allow and aid the migration of electrons from the cathode to the anode to provide a high value plate current of the order of about 1000 milliamperes.

The controlv electrode i0 may be of any suitable design, as for example, as shown in Figures l and 2, merely set forth as illustrative embodiments. As illustrated in Figures l and 2 the control electrode -i9 may comprise a cup-shaped member having an overall area substantially greater than that of the cathode and about equal to that of the anode, and so positioned in the envelope that its sides may extend downwardly below the upper limit of the cup 36 and spaced from the sides thereof. By the term overall area" of the cathode I mean the area oi a plane whose perimeter is defined by the outermost points of the filament. l

The base of the cup located between the anode and the cathode is preferentially perforated so as to allow upon discharge the migration of a large number of electrons from the cathode to the anode to provide a large value plate current in the X-ray art without undue overheating oi the grid. Further the size and spacing of adjacent perfor-ations are of such a magnitude that a comparatively low negative potential may be applied to said grid to provide an electrostatic held suillcient to prevent, when the cathode is at its maximum temperature, the establishment of a continuous electrostatic held and an electron ow between the active surfaces of the cathode amperes at a relatively high voltage, the grid does not become unduly overheated and the grid current value during discharge is moderately low.

The control electrode I9, of predetermined composition and design, is so positioned between the anode I8 and the cathode 20 that when a high potential is applied between the cathode and the anode terminals and the grid having a negative bias sufficient to prevent electron flow from the active cathode to the anode, the intensity of the electrostatic eld between the cathode 20, the cup 36 and the grid I9 will be insufficient to cause any substantial distortion of either the rigid grid i9 or the cathode 20. The grid I 9 is also so spaced from the anode that there is no appreciable sparking therebetween and the electrostatic eld is insuicient to cause distortion of either or both of the component parts. The spacing of the grid I9 from the anode is important because if the spacing is not great enough, the potential gradient at the surface of the grid during the blocking action when the cathode is incandesced may be so high that cold emission or sparking takes place. If there is appreciable cold emission or sparking at the grid, the blocking action of the grid is obviated and the current will ow from the cathode to the anode at some time other than that appointed.

Another type of grid or control electrode that I have found suitable for my purposes is illustrated in Figures 4 and 5 and comprises essentially a molybdenum wire mesh cup 45 of approximately the same general dimensions as the cup I9.

The openings in this screen and the spacing between each opening are preferably of the same approximate dimensions as the corresponding dimensions of the corresponding parts of the base 42. Surrounding the sides and lower edge of said foraminous cup and extending up to the base thereof is a substantially cylindrical thin sheet of molybdenum 46 of a U cross section.

It has been found that tubes embodying my invention and having electrical energy of high voltage, of the order of about sixty thousand volts between the terminals of the anode i8 and i-he hot cathode 20, may be completely prevented from discharging between these electrodes by virtue of the grid or control electrode I9 having a negative grid bias of about three thousand volts.

This tube also by virtue of its particular construction besides being able to prevent the passage therethrough of said electrical energy will by proper means allow the "instantaneous" passage of high currents of the order of about one thousand milliamperes at a voltage of about sixty thousand volts without any arcing or high power losses.

With the tube construction herein described a 1000 volt positive grid bias may be substituted for the 3000 volt negative grid bias so that the tube will allow the instantaneous passage therethrough of electrical energy of the order of about sixty thousand volts and one thousand milliamperes, without any fusion or undue overheating of the electrodes.

Although I have described one oi' the forms of my invention with minute particularity I do not wish to be limited thereby because it is sus- Aaccepts ceptible to a number of modifications and is to be limited only by the prior art.

What is claimed is:

l. A switch for effectively preventing the flow of current therethrough and allowing at an appointed time the passage of electrical energy therethrough, comprising an envelope, an anode, a thermionic cathode, a control electrode, and means surrounding said cathode for limiting the direction of movement of the electrons emanating from said cathode when said cathode is heated, said means having a portion thereof located beyond a. limit of said cathode, said means being electrically connected to said cathode, a portion of said control electrode being adjacent a portion of said means for the establishment of an electric eld when a potential is applied between said means and said control electrode to prevent electrons emanating at the cathode from passing between the space defined by said portions of said means and said control electrode, said control electrode having openings therein and being cupshaped, the concave side of said control electrode surrounding said means, with the side of said cup being opposite the side of said means along an appreciable length of said means.

2. An electric switch for effectively preventing the flow of current therethrough and allowing the flow of electrical energy comprising an envelope, an anode, a thermionic cathode and a control electrode therein, means for limiting the direction of movement of electrons emanating from said cathode when said cathode is heated, said means having a mouth facing said anode, said cathode being located in said means and below the upper limit of the mouth thereof, said control electrode surrounding the mouth of said means and having a portion thereof extending outside and below the mouth of said means, said portion bcing spaced from a portion of said means.

3. A switch for effectively preventing and allowing the passage therethrough of electrical energy comprising an envelope, a plurality of presses therein, conductors sealed in said presses, an anode and a cathode secured to said conductors means for limiting the direction of movement of the electrons emanating from said cathode, said means surrounding said cathode and having an opening facing said anode, said cathode being located below the upper limit of said means, said means having a rounded upper limit, a cupshaped control electrode surrounding the mouth of said means and extending an appreciable distance therebelow and shielding means for said presses.

4. An X-ray-clrcuit electric switch comprising a dielectric envelope having a plurality of presses therein, conductors sealed to said presses, an anode and a cathode electrically connected to said conductors, a cup-shaped means for limiting the direction of electrons emanating at said cathode, said means having an opening in the bottom thereof through which a plurality of said conductors extend, tubular shielding means surrounding one of said presses and extending upwardly to said means, a cup-shaped control electrode across the mouth of said means, the lower limit of the side of said control electrode being located appreciably below the upper limit of said means.

MONTFORD MORRISON.

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