US1956396A - Trigger tube - Google Patents

Description

April 24, 1934. w G, M'QRANl v 1,956,396

TRIGGER TUBE Filed April 29, 1935 z3 29 ATroRNEY PateniedvAvpr'. l24, 1934 UNITED STATES PATENT OFFICE TBIGGER TUBE viliuianrl c. Moran, Bloomfield, N. J., signor to Westinghouse Lamp Company, a corporation of Pennsylvania Application April 2991933, Serial No. 668,528l

s claims. (o1. 25o-27.5)

ages is relatively high in the X-ray field where this device finds especial application.

My invention nds the same application and may be used in the same places and for the same purposes as is the trigger device or electronic switch of Montford Morrison described in his patent application filed March 5, 1932, bearing Serial No. 596,948 and assigned to the same assignee as the present invention. The mode and principle of operation of my device is in essence the same as those of the trigger tube of said Morrison application. As a matter of fact, my invention is an improvement over the trigger device disclosed by Morrison.

Briefly, my invention has been made for the purposes of providing a more rugged trigger tube and one which shall have the additional advantage of improved electrical characteristics.

These advantages, which are substantially the broad objects of my invention, and the more specific objects of my invention will be readily apparent from the following description and drawing wherein,

Figure 1 represents a longitudinal sectional view with some of the parts in elevation and some parts shortened;

' Figure 2 represents a plan view taken on line II-II of Figure 1 in the direction of the arrows; Figure 3 represents a cross sectional View taken on line III--III of Figure 1 in the directionof the alIOWS.

As shown in Figure 1, an improved trigger tube embodying my invention comprises an evacuated gas-tight envelope of a di-electric material such as glass or the like, in the form of a cylinder 10 and a plurality of oppositely disposed arms 11 and 12 extending outwardly therefrom. Within said arm 11 is a re-entrant d-electric stem 13 having a press 14 at the free end thereof. Sealed in said press and extending interiorly and exteriorly of said envelope isa rigid conductor 15 of tungsten. Electrically secured to one end of said leading-in and supporting conductor 15 is a conductor 16 having its other end electrically secured to a contact cap or terminal 17. The contact cap or terminal 17 rests upcn and surrounds the outer end of the arm 11. The other end of said rod 15- is in the form of a small diameter discV 18 to which a plate 19 is secured by suitable mechanical means as for example rivets 19', as shown.

The plate 19, which is the anode, may be composed of refractory metal such asmolybdenum or the like and comprises aplane smooth surfaced disc having a rounded circumferential outer portion thereof curled upwardly and inwardly to- .wards the anode end ofthe envelope and away from the other electrodes hereinafter described. The portion of the anode which faces the cathode may have an area greater, and preferably about fifty percent greater, than that of the cathode hereinafter more fully described. Secured to said rod 15 near the seal or press 14 and within the envelope is a refractory metal cup-shaped member 20 extending towards the outer end of said envelope and surrounding said seal 14.. The cup 20 protects the seal from the heat generated at 75 the anode and from stray electron bombardment during operation of the device.

Extending within the arm 12 is a re-entrant tube 21 whose upper limit is Within the body section 10 of the envelope. At-about the midlength of said re-entrant tube 21 and fusedly ring sealed to the inner periphery thereof is another re-entrant stem 22 whose diam-.ter is substantially less than the corresponding dimension of the stem 21. The upper end of said stem 22 is in the form of a pinch or press 23 of substantially cruciform configuration, with the upper end of said press being located a substantial distance below the free end of the tube 2l.

Forming a, hermetic seal with said press and extending therethrough is a pair of spaced rigid supports or standards 24 and 25 of tungsten or other'seal-forming material. These supports or standards are in line with each other and are located in opposite arms of said press. The supports or standards 24 and 25 sealed in said press extend interiorly and exteriorly of said envelope. The outer ends of said rods 24 and 25 are electrically connected to respective conductors 26 and 27 secured to spaced contact termi- 100 nals 28 and 29.` The contact terminals 28 and y 29 are insulated from each other and are carried by a contact cap 30 secured to and surround- Those portions of the rods 24 and 25 extending within the envelope are parallel to each other and to the longitudinal axis of the tube. Substantial lengths of the upper free ends of rods 24 and 25 are bent outwardly and away from each other and at about right angles tothe longitudinal axis of the envelope. Between said supporting Wires and sealed in said press 23 are a plurality of and, as illustrated, six supporting wires 31, 32, 33, 34, and 36 composed of molybdenum or the like and at their lower ends insulated from each other at the press 23. The upper portions of these wires are bent away from the longitudinal axis of the tube, with the upper free ends of the wires 31, 32 and 33 bent in a direction generally opposite to the direction of bend of the wires 34, 35 and 36. The rods 31 and 36 have the longitudinally extending portions thereof in line with the standards 24 and 25 and the rods 32, 33, 34 and 35 have the longitudinally extending portions thereof in line with each other and at right angles to a vertical line connecting the longitudinal portion of the standards 24 and 25.

The free ends of these wires are all approximately in the same general plane normal to the longitudinal axis of the envelope. A plurality of 4short rods are welded near each end of said six rods 31-36. Secured by welding or other convenient means to ,the bent portions of the supporting standards 24 and 25 and to the upper ends of the short rods and in a. generally zig-zag fashion, as shown with each of its segments being in the same general plane, is a filamentary cathode 37. The cathode 37 may comprise a filament composed of tungsten or the like and has its respective ends secured near the extremities of the bent portions of the standards 24 and 25.

The composition, length and diameter of the cathode is so chosen that, upon being energized by means of a suitable source of potential, it will provide a thermionic emission therefrom of suflcient magnitude to supply a comparatively large anode current of about 1,000 milliamperes more or less when a potential of about 22 volts is applied between the terminals thereof. This emission is effectively secured at the temperature attained by the filament without substantial vaporization of said filament.

Spaced from and closely surrounding the cathode 37 is an open-ended molybdenum cup 38 consisting essentially of a unitary single structure including a cylindrical portion integral with a base portion. The upper edge of the cylindrical portion has a curled or rounded upper end with its edge located away from the anode for the purpose of preventing cold emission therefrom. The base portion of the cup has a circular opening therein adapted to accommodate the standards and supporting rods that pass therethrough without contacting the same. The cup is so mounted that its cylindrical portion and base portion are spaced a small distance from the standards and rods. The cup is supported by an elongated cylindrical member 40 of molybdenum or the like having a flange at one end thereof secured by rivets to thebase portion. The upper edge of the cup is located a small distance above the lamentary cathode. The member 40 extends downwardly from the base of the cup, surrounds the cathode supporting rods and standards, the pinch 23 and a portion of the stem 22.

At the lower end of the cylinder 40 are a plurality of spaced spring fingers 41 bearing against the outer surface of the stem 22. The cup 38 is maintained at the same potential as the cathode by virtue of an angle bar 42 welded to both the cup and the standard 24. Besides serving as an electrical conductive means for the purpose heretofore set forth, said element 42 also serves to support the cup 38. The cup 38 serves to confine the electrons emanating at the cathode and so limits their direction of travel that no appreciable percentage thereof strikes the bulb'immediately opposite the same. It also prevents the electrons from striking that portion of the grid below the cathode.

A third or control electrode 45 has a portion thereof located between said anode 19 and cathode cup 38 and serves, when a suitable negative potential is applied thereto, to prevent electrons, emanating. at the cathode, from reaching the anode and thus maintains 'a zero plate current when the cathode is energized and a potential of about seventy thousand volts is applied between the anode and the cathode. When said potential at the grid is changed to a suitable positive value, it allows the establishment of the desired plate current which may be a high X-ra-y value. By high X-ray value current, I mean a current which is regarded as high in the X-ray field and more particularly when it passes through an X- ray tube.

The control electrode or grid element 45 comprises a plurality of spaced inverted U-shaped lrods 46 secured together near their respective ends. The rods 46 have no sharp points or bends and are of appreciable diameter to prevent cold emission therefrom. They are preferably composed of a refractory material such as pure tungsten and are arranged in spaced relationship, with the legs and cross piece of each rod being respectively parallel to the corresponding parts of the other rods. A retaining member in the form of a collar 47 has an inwardly directed annular flange 48 supporting all of the inverted U-shaped members and maintains them in their proper spaced relationship. So mounted, the cross pieces of the rods 46 are all located in the same general plane of substantially circular form. A pair of said round rods 46 have the legs 46' thereof extending below the lower limit of the collar 47 of the retaining member to provide means for securing the control electrode to a supporting member 50. The ratio of the diameter of the rods 46 to the space between some of them is one to four.

As shown, the control electrode in the form of a squirrel cage is mounted so that the upper extremity of the collar 47 is located an appreciable distance below the cup 38 and with the members 46 having their cross pieces substantially parallel to the plane of the cathode and the legs 46 of said rods 46 extending downwardly therefrom an appreciable length and a substantial distance below the base of the cup to prevent the building-up of a large control electrode or grid current. With this construction it is possible to prevent the flow of electrons from the cathode to the anode and, when desired, at an appointed time to allow the ow of electrons between said two electrodes.

Wrapped around the re-entrant tube 21 is a resilientv band 50 of appreciable width. 'I'his band, composed of molybdenum or the like, may be secured to the re-entrant tube 21 by adjusting a nut and bolt arrangement 51. Secured to the band 50, as by welding, are four spaced rigid support rods 52 secured also to those legs 46' of 3. An electric switch comprising a di-electric the members 46 projecting below the ring 47. The control electrode is electrically connected to a contact terminal 53 by a flexible lead l54 electrically connected thereto and to the band 50. The lead 54 is electrically secured to a conductor hermetically sealed to the envelope at about the mid-length of the arm 12 and it, together with said conductor, is located below the electric ileld between the anodev and the grid so as to eliminate distortion of said field.

As illustrated, the anode 19, grid 45 and cathode 37 are all substantially parallel to' each other, and at right angles to the longitudinal axis of the envelope which passes through the approximate center of each of these elements. 'I'he effective area of the grid is larger than that of the cathode and the eiective area of the anode is greater and about 25% to 50% greaterthan that of either the grid or the cathode.

In operation the cathode is incandesced and a suitable negative potential is applied to the grid. A suitable potential, depending on the X-rays to be produced in an X-ray tube not shown, is applied between the terminals of the anode and cathode. Because of the properpotential having been applied to the grid, no plate current is established because substantially all the electrons emanating from the cathode are prevented from reaching the anode. At an appointed time, the potential at the control electrode is changed from negative to a suitable positive value and the electrons immediately travel to the anode to establish the desired plate current.

In the course of my experimentation, I have found that effective tube action may be realized Without danger of cold emission and without high power losses by having the spacing between the -cathode and grid and that between the upper face of the grid and the anode in the ratio of about one to three. The total area of the spaces between the cross pieces of the rods 46 is about three times the total projected area of the cross pieces of said rods 46. The projected area of each cross rod is equal to its diameter times its length. A tube designed as above set forth nds especial utility in the X-ray field where a voltage of about eighty or ninety thousand volts and a current of about one thousand milliamperes more or less is required.

Although I have described and illustrated my invention with particularity, it is to be limited only by the prior art.

What is claimed is:

l. An electric switch comprising an enclosing envelope, an anode, a cathode, a control electrode therein, means surrounding said cathode for limiting the direction of ow of electrons emanated from said cathode, said control electrode having a portion thereof located between said anode and cathode and including a plurality of spaced rods secured to a retaining member, the upper limit of said retaining member being located appreciably below the upper edge of said means.

2. An electric switch comprising an enclosing envelope, an anode, a cathode and a control electrode therein, said electrodes being spaced from each other with a portion of the control clectrode being located between said anode and cathode, means surrounding said cathode for limiting the direction of ow of electrons emanated from said cathode, said control electrode including a plurality of spaced inverted U-shaped rods, a retaining member located appreciably below said means and being secured to the legs o'f said rods.

ing-in conductors sealed in said press and connected to said cathode, means surrounding said cathode for limiting the direction of ow of electrons emitted by said cathode, said control electrode including a plurality of spaced rods having no sharp bends, a retaining member secured to said rods, said retaining member having its upper edgelocated appreciably below the upper edge of said means, the elective areas of said three electrodes being located substantially parallel to each other.

4. An electric switch comprising a di-electric envelope, an anode, a cathode and a control electrode therein, the body portion of said envelope having a re-entrant di-electric stem extending therein, another di-electric stem secured to said lrst mentioned di-electric stem and having a press at one end thereof, leading-in conductors sealed in said press and electrically connected to said cathode, said control electrode having a portion thereof located between said anode and cathode, means carried by said/first mentioned stem supporting said control electrode and a conductor electrically connected to said means and hermetically sealed through said envelope.

5. An electric switch comprising a di-electric envelope having a ,plurality of arms, an anode, a cathode and a control electrode therein, said electrodes being spaced from each other, means surrounding said cathode for limiting the direction of ow of electrons emanated therefrom, a di-electric re-entrant stem extending in one of said arms, another di-electric stem secured to said first mentioned stem and h'aving a pinch at one end thereof, means carried by said first mentioned stem supporting said control electrode, said control electrode including a plurality of spaced U-shaped rods, a retaining member secured to said U-shaped rods and having its upper edge located appreciably below the upper edge of said rst mentioned means.

6. An electric switch comprising an envelope having a plurality of arms, an anode, a cathode and control electrode therein, means surrounding said cathode for limiting the direction of ow of electrons emanated therefrom, said control electrode including a plurality of U-shaped rods having the cross pieces thereof located between said anode and cathode, a retaining member secured to the legs of said rods, the upper edge of said retaining member being located appreciably below the upper edge of said means, a re-entrant stem extending into one of said arms, a second re-entrant stem secured to said rst mentioned re-entrant stem and extending therein, a resilient band carried by said rst mentioned re-entrant stem and secured to said control electrode for supporting the same.

7. An electric switch comprising an envelope having a plurality of arms, an anode, a cathode and a control electrode therein, means surrounding said cathode for limiting the direction of flow of electrons emanated therefrom, a di-electric stem extending within one of said arms, another di-electric stem extending within and secured to said first mentioned stem, said second mentioned stem having a press, a plurality of spaced standards sealed in said press, one of said standards being connected to said means for supporting the same, said control electrode for limiting the direction of flow of electrons emanated from said cathode, said control electrode having a portion thereof located between said anode and cathode and including a plurality of spaced rods, a retaining member, said rods secured to said retaining member the upper limit of said retaining member being located appreciably below the upper edge of said means, said rods including cross pieces, the total area oi the spaces between the cross pieces oi' said rods as compared to the total projected area of said cross pieces being in the ratio of about three to one.

WILLIAM G. MORAN.

Images