US1653102A - Electron-discharge apparatus - Google Patents

Description

Dec. 20', 1927.

MILL! AMP.

W. K. KEARSLEY. JR

ELEGTRCN DISCHARGE APPARATUS Filed Sept. 2, 1924 Fig. 1.

2 Sheets-Sheet l Fig. 2.

so WITHOUT 67$45lL/ZER Inventor: William K. KearsIe Ar Hi6 Attorn e15.

Deaf-20, 1927. I '1;$53,102

Y W. K. KEAfRSLEYpJR- Y ELECTRON VQIIISGHARGE APPARKTUS Fig. 5.

Inventor 1 William K. KeorslegJr.

His Attorneg.

Patented Dec. 2a, 1927.

wires l star wrermm- K. KEARsLE i', 33,0? s'crrnri'noranif, l ili'iiii'" roiaaj ss eeea To ELECTRIC COMPANY, A conrojrterlloiv on NEW YORK.

ELECTRON-Disclaimer: Arman-Ares.

Application filed. September 2, 19242. Serial no'lt'saaee.

charge produced independently of gaseous.

ionization. It is the object of my invention lo to provide a method and means for automatically regulating the electron emission of the cathode of a thermionic device to give a desired operatlng characterist c.

My invention is particularly applicable to the operation of an X ray tube of the in cande'scent cathode type, and is embodied in an apparatus whereby a constant" X-ray output may be secured even though the source of cathode heating current varies in voltage.

The novel features of my invention will be pointed out with greater particularity in the appended claims. For a better understanding of my invention, reference may be had to the following description taken 1n connection with the accompanying drawings in which Fig. 1 is a diagram of an X-ray system embodying my lnvention; Fig. 2 is a graph-of electrical characteristics of a? de-.

vice equipped with a stabilizer, as compared In) with the same device not so equipped 3 is adetail view of a vibrator 'used'm my tube 1 of the type now known as the self rectifying Coolidge tube, is shown connected to the high tension secondary winding of I 4o'tlie transformer 2, having the low tension primary circuit connected to a suitable source of current represented by mains 8, 4, carrying alternating current. The X-ray tube 1 contains a cathode shown'in detailin Fig;

taining an inset 7 of refractory metal, pref erably tungsten. The anode is preferably i i in good thermal relation to a radiator 8, but auxiliary devices such as this radiator, are

merely shown in thecdrawing as illustrating one complete embodiment of my invention. My invention is not confined inits function toan X-ray tube,-but is applicable to other ustable;

. tacts 15,16 to'reducesparking.

r '4: consisting of a heated filament 5 surrounds ed by a focusing device 6 and an anode 7 consisting preferably of a. rodof coppcr.con-' forms of electron-discharge devices, diife'riiig in function and structural details from an X ray tube. 7 I 1 I The cathode 5 of the X-ray tube is connectod by the conductors '9, 10 to the secondary winding of a transformer 11, .the

primary of which is connected in series with a suitable adjustable resistance 12 to thesup ply ma ns 3, a. r-Xresis-tancelel' is included, 111' the auxiliary heating circuit 9, .10 111 series with the secondary winding of the transformer 11. In a shunt circuit to the re sistance 14 are vibrating or make-and- break contacts 15, 16, one at .leastof which is adlliese contacts 15, 16 are caused to open and close at a rapid rate during the, operatioirof the tube, the relative durations of periods of make as compared withthe periods of break being determined by the strength of the current flowing through an electromagne-t 17, the winding of which is included in the circuit 18 carrying the cur rent flowing from cathode to anode through the. X-ray tube. One embodiment of a vibrator magnet is shown in Fig; -Inv the apparatus illustrated in this figure the vibrating armature- 19 of the magiietiopposes in its downward motion a springQO, the tensionof whichmay be adjusted by ascrew "21. Preferably the vibrator is adjustedtoi operatesubstantially in synchronism with the I alternating current supply. A condenser 22 may 'beprovided connected across the con- Before.describing-the operation or fund tion of the apparatus illust-ratediby. Fig. 1, 1

attention is directed to the graph shownin' Fig; 2. In a system similar to tliefsystem shown in Fig". 1'. but in which the resistance 14c and the shunt connected vibrating contacts 15, 16, are omitted, and in which the i i cathodezofgan electron dischargedevice is heated w thout: any regulation .by current from a transformerv supplied from a source varying'in potential, the load current flowing from cathode to anode throughthe electron discharge device varies with the variations, I

of potential [of the cathode heating-current.

ata rate indicated by thecurve 28. The,

voltage across the terminals of the primary winding of the filament heating transformer have been plotted in- Fig; 2' as abscissee through'a range of voltages :from 70 to 87.

ivolts, the corresponding current ,values be:

Lil

crease of about 5.1% the space current in creases from to milliamperes, an increase of about When a system such as above described having no regulator is connected to an ordi nary commercial transmission line, incidental voltage variations in these lines, espe' cially when commercial devices such as elevator motors, are supplied by the same lines,

is suflicient to produce such wide variations in output of an electron device, such as an X-ray tube, as to make it difficult to deter mine a proper X-ray exposure.

When, in accordance with my invention, a device havinga cathode which emits elec trons independently of ionization efiects and from which hence a saturation current may be obtained, such for example as a hot cathode X-ray tube, is supplied with a stabilizer responsive in its operation to the load current passing through the device, the transmitted current becomes substantially con stant with wide variations of voltage. As shown, for example in the curve 24., an increase of voltage from 82 to 87 volts produces no, appreciable change of current, and

in fact, even an extreme increase of line voltage to 120 volts causes an increase of current of only slightly more than one milliampere or anincrease of about 10% of current change with a voltage change of 46%.

- In commercial operation the filament heating transformer of an X-ray tube probably.

would not be subjected in its primary voltage to :this wide variation. In practice,

therefore, over an operating range of say,;10

volts, the current through the tube is maintained substantially constant. This action occurs by reason of the variations in magnetic attraction of the core of the stabilizer magnet 17 upon the armature 19 of the vibrator, as already indicated. The magnet 17 for any particular current setting varies the effective length of the cyclic impulses ofv the current fed to the cathode, the impulse of current depending in duration on the conditions governing electron emission, thus heating the cathode to'the temperature required to maintain the desired current value.

' By effective length of current impulses, I mean the length of the current wave before it is reduced to a low value, as'when a resistance is inserted in the circuit. For example, if the current has atendency to in-' crease the time required for the magnet 17 to build up to a strength required to open the contacts 15, 16' each wave of current is reduced. Hence, the contacts 15, 16 are open longer and the resistance 14 is included in series with the circuit 9, 10 for relatively longer periods, thereby weakening the cathode heating current sufficiently to oppose any further increase of thecathode temperature. Similarly, a slight decrease of current will result in weakening the magnet 17, thereby increasing the relative durations of the periods of closure of "the short-circuiting contacts and thereby strengthening the oathode heating current. As the electron emissivity of the cathode varies at a rapid rate directly with the temperature, this control of cathode ten'iperature by the vibrating stabilizer in the cathode heating circuit controls the electron'en'iission and hence the currentcarrying capacity of the X-ray tube. The stabilizer consequently maintains the current reaching the anode at a predetermined value, I

as the described X-ray tube. isv operated at voltages at which substantially all of the electrons emitted from the cathode'are utioccur in the electron emissivity of the cathode. 1 In some cases my invention may be "used advantageously in an 7 X-ray apparatus which has a resistance in series with the primary of the high voltage transformer in order to limit the current which may be drawn from this transforn'ler. F or example, in X- ray devices operating at exceedingly high voltages, say, for therapeutic purposes, such a resistance can be used to limit the current to a value not fatal to life. My invention in such a system can be used to give a substantially constant current through the X-ray tube instead of a. variable current as would otherwise be the case. p

In Fig. 5 l have illustrated an X-ray system suitable for operation with a regulable resistance 26 in series with the primary winding of. a high potential transformer 27. The X-iay tube 28 in this case is con ected to the secondary windings of the transformer 27in series with a mechanical rectifier 29 driven by a synchronous electric motor 30.

Conveniently this motor is supplied with current by the conductors 31 connected to the supply mains 32 in common with the X-ray transformer 27. The cathode 5 of theX-iay tube is supplied with a heating current by a transformer 11 in the primary winding of which are vibrating contacts 15, '16, con-. trolled by a magnet 17 connected by the con-- ductors 33, 34, in series with the secondary coils 35, 36, of the X-ray transformer. A resistance 14 preferably is connected across the contacts 15, 16'.

The system shown in Fig. 5 is closely similar to'the system shown in Fig. 1 except that the use of a resistance in the primary or" the main transformer 27 renders the use of a special rectifier in series with the X ray tube desirable inorder to protect the tube from high potential during the periods of polarity reversal when a rectifying direct connected X-ray tube, as shown in Fig. l, is not taking current. V

In both the systems described, that is the systems shown in Fig. 1 and also in Fig. 5,

the regulator maintains in response to space current flowing through the X-ray tube, an Xray output which s constant in quantity.

.In. these systems the energy input 'to the cathode is regulated to maintain a constant em ssion of electrons regardless not only of voltage varlations of the cathode heatlng source but also of variations of conditions inthe X-ray tube-which affect the emissivity of the cathode, such for example, as the evointerior parts of the X-ray tube.

' 'stancy of electron emission at'the cathode and hence or quantity X-ray output, which of the Xray tube.

which the heating current is flowing.

is sutficient for some purposes, may be maintained "by keeping the temperature of the cathode substantially constant, regardless of line voltage changes. In that case the actuating coil of the regulator may be connected directly tothe heating source for the cathode Such an arrangement is illustrated by Fig. 6, in which the actuating coil 17 is connected by the conductors 38, 39 to the respective supply lines 3, 4E. The parts and electric connections otherwise correspond to the apparatus described inconriection with Fig. 1. An X ray tube such as shown in Fig. 5 may be used. Fluctuations oi supply voltage will advance or retard'the instant the circuit is broken each half wave, thus increasing or decreasing as required the. doles of current received by the cathode. For example, should the supply'voltage'rise, the 'coil 37 will cause the contact 16 to open sooner, thus decreasing the periods. during. y reason of the increased voltage the current rises at atast-e'r' rate and hence" energy delivered during these shorter periods remains unchanged. By reason of the heat storage capacity oi the cathode, this internnttent heat input" will produce continuously a substantially constant cathode temperature.

Conversely, a fall of voltage of the supply circuit will cause thejperiods of cathode excitation to increase but without substantially" altering the:cathode 'temper'ature and hence. the electron emission. As already stated, constancy of vacuum and other tube condi tions are assumed to secure a constant quantity of X-ray output from the apparatus illustrated by Fig. 6. Y r

, It is obvious that various modifications, such for exalnpleas the above described, may be made without departing from the spirit oi my invention. a

hat I claim as new and'desire to secure by Letters Patent of the United States, is: 1. An Xray apparatus comprising the combination of an Xray tube having main" electrodes including a cathode which is heat-' ed; by passage or current therethrough, .a main operating circuit connected to the main electrodes of said tube, an independent heating circuit connected to said cathode, a

source of alternating current subject to volt- I age variation for supplying both circuits, and means responsive to load current in said main circuit'for reducing the current in said heating circuit :durln'g each half wave for periods of suchlength that the load. current is maintained substantially constant.

.2. The combination of an electron discharge tube having a cathode adapted to be heated by passage of current, an alternating current supply means for heatlng' sald cathode, and a. vibrating regulator responsive to load current in said tube and constructed to operate in synchronlsm with the current in said supply circuit for regulating V the heating'current to maintain the load current at a predetermined value. I I

3. The combination ofan X-ray tube haw ing a cathode adaptedto be independently. heated, a source of alternating currentsubject to variations of voltage connected to operate said tube, means for deriving current from said source toheat said cathode, and means responsive to currentthrough said tube for decreasing the heating current for said cathode to a low vaiueduring each cyclic change of current i'or a period or" suchlength that the current through said tube is maintained substantially constant.

4. An X-ray apparatus comprising the combination ofan X-ray tube hav ngv a cathode operable at incandescence, a main supply circuitftor said tube,a heating circuit for Sfi-lClCEltllOdQ,-l resistance in said heatingcircuit, a circuit containingmake and break contacts connected in shunt toisaid resistance,

and meansrespon'sive to an electrical condilac tion of the current in said maincircuitfor varying the relative duration of the periods of make and break of said contacts to control the heating current for said cathode.

X-ray tube having a cathode adapted tobe independently heated and an anode, 1621118 for heating said cathode,- a main operating circuit connected to the electrodes of said X-ray tube, and a vibrating regulator .arranged to maintain the electron emission 0]": said cathode at a predetermined relation to an electrical characteristic of said main circuit.

6. An X-ray apparatus comprising a source ct alternating currentsubject to variations of voltage, an X-ray tube operatively connected thereto, said tube having a cathode i supplied 7 with heating current from said sourceand means responsive to load current in said tube and operating in synchronism with said source for controlling the cathode heating current. I V ,7. An X-ray apparatus comprising an i tube having an incandescible cathoce and an anode, a main supply circuit connected to said electrodes, a circuit for supplyingheat ingf energy to said cathode, vibrating contacts in said heating circuit, and electromagnetic means responsive to current in said main circuit for regulating the relative duration of the periods of make and break off? said contacts thereby preventing departures oi current in said main circuit from a predeter mined value.

8; An X-ray apparatus adapted for opera tion ltrom a source of alternating current of fluctuating voltage con'iprising the combination of an X-ray tube of the Coolidge type operating substanti ally independently of impactionization, a main stcp-up transformer having a secondary winding connected to the.

main. electrodes of said tube, an auxiliary transformer having a whirling connected to supply heating current to the cathode oi? sa d tube, a resistance in circuit with said winding, electric make and break contacts connected in shunt to said refstance, and electromagnetic means in circuit *ith said X- ray tube tor operating said contacts in syntion from a source of variable voltage com- 7 prising an X-ray device having an electrode capable ofeinitting electrons When heated, a main load circuit, a'heating circuit for said electrode, a resistance in said heating circuit andelectromagnetic means responsive to the current in said main circuit having contacts arranged to insert and Withdraw said resistance intermittently, and means for controlling the relative durat on of the periods 0. An X-ray apparatus comprising an of insertion and withdrawal to maintain the load current at a predetermined value.

10. An X-ray apparatus comprising an.

X-ray tube having a cathode adapted to be heated by passage ot current and operating without substantial gas ionization, a source of alternating current subject to variations variable voltage con'iprising the combination or" an X-ray tube'having a cathode adapted to emit electrons when heatedby passage of current, means for deriving energy from the supply sourceto operate said tube, separate means for deriving energy fromthe supply source toheat said cathode, and means oper- I ated by current from said source for intermittently reducing said cathode current synchronously with the alternations of said source for periods varying in duration in such measure that the quantity of X-ray out put remains substantially constant When the voltage of said source varies.

12. The combination of an electron discharge device which" is constructed and evacuated to be capable of operation substantially independently of positive ionization, and having a cathode adapted to generate electrons independently of a load current in said device, means for energizing said cathode with alternating current, and means responsive to a load currentin said device for varying the el'l'ective duration of the i cyclic impulses of said alternating circuit in such measure that the load current is maintained substantially constant.

13. An Ix-ray apparatus adapted for operation from an alternating current supply source of variable voltage comprising the combination of an X-ray tube provided with a cathode adapted to emit electrons When heated by passage of current, a main circuit coni cctedto the electrodes of said tube, a heating circuit for said cathode connected to derive current from said source, and arranged for operation at voltages at which current in the main circuit is limited by electron emission of the cathode, and regulating means responsive to current in said load circuit for decreasing the cathode heating current during each Wave of current flowing therein for periods of such duration that the cathode temperature and current in the main circuit will remain substantially constant. 1

14. An X-ray apparatus adapted for operation from a source of alternating current subject to variations of voltage comprising an X-ray tube of the Coolidge type having a cathode operable at incandescence, a high potential transformer connected v.to said source for supplying said tube with current,

circuit connected to said electrode,a-lternating current supply means subject to voltage variations for said heating circu t, and

electron'iagnetic means responsive to a load current in said tube and operating in synchronismwith said heating current for varying the effective resistance of said heating circuit during each wave of heating current for periods of such duration that the electron emission in said X-ray tube and consequently the output of X-rays aremaintained substantially constant.

16. The method of operating an electrical discharge device which consists in supplying energy to the cathode of said device at a rate which it continued would generate a greater supply of current carriers than is required to maintain a desired current through said device at a given voltage and intermittently reducing the supply of energy to said cathode below the value required to maintain the desired current, said reductions occurring during time intervals of the order of frequency per second of commercial alternating current and varying the duration of said intervals of energy reduction in such measure that a load current of desired value can be maintained at a chosen impressed voltage.

17. The method of operating a thermionic discharge device which is subject to changes of operating conditions which consists in supplying to the cathode of said device a heating current of materially higher value than is required to give a desired electron emission, intermittently reducing said current at intervals recurring per second with a frequency of the order of cyclic changes of commercial alternating current and varying the relative duration of the intervals of reduced current in such measure that-the load current in said device is maintained at a substantially predetermined value.

18. The method of operating a thermionic discharge device which is subject to changes electron emission of operating conditions which consist in supplying to the cathode of said device a cyclic current of higher value than requlred 'to heat said cathode'to a temperature giving desired electron emission, materially reducing said current during each cycle, and

varying the duration of the intervals of reduced current relative to intervals of-unreduced current in such measurethat the electron emission of said cathode is maintained at a predetermined value.

19. The combination ofan electron discharge device having a cathode adapted to be heated by passage of current, means for supplying a heating current to said cathode, means responsive to space current in said tube for reducing the heating current to a low value at rapidly recurring intervals of such variable duration relative to the periods of high current that a substantially uniform is obtained from said cathode. i

20. The combination of a thermionic X- ray device, a supply circuit therefor, means for supplying a heating current to said cathode, means for materially reducing said current at intervals recurring with a frequency of the order of commercial alternat ing current and means responsive to a space current in said device for varying the duration of said intervals of reduced heating current relative to the unreduced' heating current to produce a desired electron emission by said cathode, whereby the X-ray output is maintained substantially constant.

21. An X-ray apparatus comprising the combination of an X-ray. tube which is operable independently of positive ionization and is provided with a cathode rendered active by passage of current, means for supplying a cyclic heating current to said cathode, and

means for regulating the effective value of said heating current in such measure during the periods when said X-ray. apparatus is conducting current that a constant current carrying capacity 1s maintained in the X- ray tube when changes occur in the electron emissivity of said cathode or in the voltage of the cathode heating current.

22. In a system of theclass described, an

X-ray tube of the hot cathode type with a secondary of a step up' transfori'ner divided into two coils, a relay in'sai'd system with its magnet connected to said coils, a transformer for generating a hot cathode current and suitable connections including a resistance so that when the system is in use the resistancewill be thrown in and out of circuit accordingtov the action of the relay -magnet..

In witness whereof, I have hereunto set my hand this 29th day of August, 1924.

WILLIAM K. KEARsLErJR.

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