US2617047A

US2617047A - X-ray apparatus

Info

Publication number: US2617047A
Application number: US115408A
Authority: US
Inventors: Kuntke Alfred
Original assignee: Hartford National Bank and Trust Co
Current assignee: Hartford National Bank and Trust Co
Priority date: 1948-09-30
Filing date: 1949-09-13
Publication date: 1952-11-04
Anticipated expiration: 1969-11-04
Also published as: CH281880A; NL72521C; GB677145A; BE491389A; FR996351A; DE803178C

Description

Nov. 4, 1952 A. KQNTKE 2,617,047

x-RAY APPARATUS 20g'- Zl l.

Zoff' u' I l@ 2 INTOR.

KUN

- Nov. 4, 1952 K -nQKunrrKE y 2,617,047`

-x-RAY APPARATUS Filed sept. 15, 1949 Mx/W A.y KUNTKE X-RAY APPARATUS Nov. 4, 1952 Filed sept. 15, 1949 4 Sheets-Sheet 5 INVENTOR. zmKmK/F Nov. 4,` "1952 A. KUNTKE v 2,617,047

X-'RAY APPARATUS Filed Sept. 13, 1949 4 Sheets-Sheet 4 k AAAAI l n 'Vllvli n l i foo ' INVENToR. ALFRED KUN/KE AGENT Patented Nov. 4, 1952 UNITEDV STATES PATENT OFFICE X-RAY APPARATUS (Cl. Z50-103)' Claims.

This invention relates to X-ray apparatus pro-V vided with automatic control.

The maximum permissible load (number of kw.) of X-ray tubes for diagnostic plu-poses VariesY with different factors.V such as the size of the focal spot, lthe manner in which the heat of the focal spotis withdrawn-the thermal capacity of the anode and the substance of which the anode is made. The maximum permissible load is smaller according as its duration is longer. If a given X-ray tube may be loaded for one sec-` ond with a, maximum power ofv Nikw., a load of one tenth of a second duration may-be, `for example, 1.4 N kw. but-a load of, say, 5 secs. duration must not be in excess of 0.6 N kw.' The number of N may vary widely forA different types of tubes; as a rule itlliesgbetween 5 and 20 but even the factors Varying with time (in the said example 1.4 for 0.1 sec. and 0.6 for'5 sec.) vary considerably for the varioustyp'esof tubes.

Modern X-ray apparatus comprise a controldevice for the load quantities of the tube, which automatically adapts the load on the tube to the load characteristic curve, the current -being adjusted as a, function ofY the duration of loading and of the voltage across the tube.' which* is generally variable between 50 and 100 kv.A

The requirements of the control can be better visualized with the aid ofv Fig. 1 and Fig. 2 of the accompanying drawings whichA are perspective' Views o1" three-dimensional graphs'ofthe load capacity of an X-ray tube. f

In Fig. 1, the ordinate of each point of an arcuate surface ABCD is a measureof the maximum current intensity which is permissible at a Voltage and for a, length ofgtime, the values of which are determined by the distances from the two vertical coordinateA planes. It is desirable that with the use of the current intensity which is adjustedby the automatic contrlde'vice, the values determined by this plane should be approximated to the greatest possible extent. is carried out in practice byusing a variable resistance included in the. primaryv circuit of the filament-supply transformer or by connecting into the circuit'a voltage source which contributes to or counteracts the effect of thelament-sup-A ply transformer. The controlemember of this resistance or the switches by which this voltage' is connected into the circuit are coupled with the voltage control-member orvl with the load duration control member or with both.

As a rule, the control of the current intensity is carried out stepwise. Fig. 1 shows how in the latter case the steps may be chosen,f-;namely in This' 2 three steps in accordance with the voltage chosenv and in three step's'in' accordance' Withthe time interval chosen', so` that thecurrent vintensity may be'adjusted to` nine values' in all.

The eie'ct of the X-rays Ona photographic lm, that'is to say' the blackenhg' 0f the' ln'h'is approximately prp'o'rtionalV to" 'Lt-U4, whereV I is tle'nthsty 'of' the tube Current, 't thedurae tion of the loading arid U the voltage across the X-ray' tube. The factors I t` (expressed in mA'mpsQ/sec.) andUKexpie'ssed' in kv.) are, con` sequently, thel quantities" which determine" the optimum exposure of the film.

In the perspective Figure 2, the product'IX't is plotted as a function'pf the tubfe' Voltage U and the time interval' t. In thisigu're the'surface EFGH corresponds to the load characteristic' curve of the X-ray tube. It'niay' be seen from this ligure that the' stepwisecont'rol is assumed to be such that, inacc'rdan'ce' with the shape 'of the surfaceV EFGrH, on an increase in time interval, the prdu'ctIXtis not'i'r'l'creasedat' the points of current variation but' instead is decreased and hence also-the photographic effect of the X-'r'ays emitted by the tube. On an increase'in voltage the product 1X1?, atthe points ofcurret varia-v tion, falls to a lower' v'ali'fe,"so"that in spite of this increase the blackei'ir'ig initially diminishes.

Apart from thesedeiciencie's thereis a fur-l ther one which is duetot evoltag'eloss v6c'curring in the high-voltage geeratr'and" in the supply mains. Even if the v"autorriatic control' werecaried out completely in accrdance with thesurface ABCD of Fig. l or the surface EFGHof Fig. 2.J the voltage loss 1.111 th' apparatus results; in a decrease in tube voltage, and this aiiects the blackening materially, since the latter is deter` mined by the Vfmuth' power 0f U- In order to transfer the load guantitiesofV oneA X-ray apparatus to another it is necessary to know the *tube voltages? actually occurring and their Vcorrect adjustment. However, as a Irule, they can .b e deter ith thelu's'eioyf" calibrartion characteristic curves only. Attempts) have* oi the resistance. leads to break'tlov'v'n"ofA the tube therein. Y but if disturbances .toy operation oc it is ineii'icient when the supply mains has a high resistance.

It1 has flirtMarmor@r .beensugeested to rrovd an indicating device ypelfrrnftt xinethe vralirls .of Y the tube voltage -iactually occurring, fibydeducting 3 from the value of the no-load voltage an amount which is proportional to the intensity of the tube current. The results thus obtained can only be correct so long as one is concerned with a voltage loss which is proportional with the current intensity. With a mains supply having an appreciable resistance, such as the ,mains supplies usually available in practice, this is not the case.

For the same reason compensation of the voltage loss by applying to the primary circuit a correction voltage which is proportional with the current does not yield satisfactory results. As may be seen from Fig. l, this correction voltage must otherwise be chosen to vary in accordance with the voltage and time interval chosen. With any known measure of compensating or indicating the voltage loss based on the intensity of the tube current, it was invariably assumed that the resistance of the mains was negligible. In practice, however, this is not so and therefore the solutions hitherto proposed are not successful.

` The present invention provides a control of improved operation which can be provided at low cost. The voltage loss is taken into account and the invention is based on recognition of the fact that at a given ratio between the resistance lying (as viewed from the mains) in front of the autotransformer controlling the voltage and that following this transformer, the voltage loss is constant throughout the voltage control-range if the load on the tube is kept constant, It has been found possible thus to compensate the voltage loss throughout the range of voltage-control by increasing the primary voltage of the highvoltage transformer by an amountvarying with the load.

In order that the invention may be more clearly understood and readily carried into effect, it will now be described more fully with reference to Figures 3 to 8 of the accompanying drawings.

The principle of such voltage compensation is set out more fully hereafter.

Fig. 3 shows the greatly simplified circuit-diagram of an X-ray apparatus, in which T1 is an autotransformer and T2 a high-voltage transformer. UN designates the mains voltage and RN the resistance of the mains as far as the autotransformer, RA designatesrthe resistance of the autotransformer transferred to the output side and RH the resistance of the high-voltage transformer, including that of any rectifying tubes used, transferred to the high-voltage side of the said transformer.

XA=U1/UN represents the ratio of the autotransformer and XH=U2/U1 the ratio -of the high-voltage transformer. v Y

The total resistance of the circuit appearing at the high-voltage side of the transformer T2 is calculated as follows:

If 2R is' plotted as a function of U1 or U2, this gives the sum of a constant component and a quadratic component RN.X2A.X2H, as shown in Fig. 4a. Y

Fig. 4a. shows the control-range which extends, for example, from 50 to 100 kv. for U2 and in which the voltage loss'isrequired to be constant at a definite load (kw.). The limit values of this range are I and II. Since the load is required to be constant, the current intensity varies in this range by a factor 2, as indicated in Fig. 4b.

In order that the voltage loss may become con- 4 stant throughout the control-range, the product I XR for point I must first of all be equal to that obtaining for point II. This is ensured at a definite ratio, as is found by calculation, if

R11-Hui@ =15 eiiiozljl (1) Under this condition, if vthe load-is looked upon as the parameter, a parallel shift of the tube voltages is obtained, as is shown in Fig. 5.

Fig. 6 shows the variation of the auxiliary voltage U as a function of the load for a denite, adequately chosen mains constant which is such that most mains connections exhibit this constant or else, may be brought in accordance therewith by use of a ballast resistance. In practice the desired result may be obtained by a mains constant of, for example, l/3802 (ohm/volt2) (l ohm for a 380 volts mains and 0.33 ohm for a 220 volts mains). The characteristic impedances of the apparatus are purposely chosen to be such that the Equation 1 is fulfilled.

If these conditions are fulfilled, the voltage loss can be compensated in a simple manner.

Since the load on the X-ray tube is required to vary with the duration of the load, it is only necessary to couple the time adjusting member with a corresponding member for controlling the auxiliary voltage. This may be seen from Fig. 6. By way of example. the load Nk at the minimum time of loading to be chosen is such that for compensating the voltage loss the amount dUk must be added. With increase in time the load drops to that which is associated with the longest time interval and is designated N1.. at which the voltage dUL is required to be added for compensation. .A I

In order that the technical means for carrying out the control may -be reduced in size and the load to be switched may be kept small, the compensating voltage is resolved into a constant component A and a component varying with time between Band +B. This is particularly advantageous if two or more tubes of diiferent power are required to be connected to the supply device. This is set out more fully with reference to Fig. 7. IIt is assumed that for two tubes of different load capacity the voltage loss is required to be compensated. Without introducing a great error, the component B, which varies with time, may be kept constant and the component A or Az may alone be chosen to correspond to the tube which is brought into operay tion.

An even more simple explanation will -be given to show that it is possible for the voltage loss to be kept substantially constant throughout the control-range. The resistance in front of the autotransformer is assumedto be R1 the mains resistance being` consequently included and the Whole of the resistance following this transformer, reduced to the primary side of the highvoltage transformer,r to be R2. If the mains voltage is furthermore'designated by E and the secondary voltage of the control-transformer by E2, and the primary and secondary current intensities of the control transformer I1 and I2, respectively, the total voltage loss dEz'can be assumed to be approximately equal to 75;?. where a=E12.Ra/Rr. 1

mamon-'z u When Eil Ais variedfbetweenEis-incanti. Eix';

Ez-I-a/Ez will be` substantially 'f constant; if a=Emm.Em`aX, and consequently if f RZ/REmaEmax/Ea 2)V Not only for Emln but also for Enix the voltage loss dE2=NR1/E12(Emin-l-Emax). Between Een and Emax, at E2=\/Emin.'Emax, @E2 haSva minimum Vahle Of NRl/E12.2\/Emln.'Emax. t

For the case considered above thatfEmln'-/2Emax (control between 50. and..1(lfkv.);the ratio between the maximum and minimum-valuesmf; dEz is 3:2\/2. Consequently there is only V`a difference of '7% between these-values.- Therfac-tor 15 30.108 which appears in' Formula1 -is substituted forEmmXEmaxinfForml-ila 2.-'l If the tube voltage is varied'from'sto /100 lsv-j, maximum value,` which corresponds -with`--35"to'70 kV.eff, Emin Emax=25X1B; Between" 45:and '90 kv. this becomes 20X 108. Y

By way of example, a simplied" ycircuit-diagram of an X-ra-y apparatus''according tothe invention is shown in Fig.-8, itbeing assumed that this apparatus comprises two ltubes of different load capacity.

Firstly provision must be made that theL tube current as a function ofthe lOading-'timeand of the tube voltage exhibits a variation as represented, for example, in Fig. 1 'bythe' surface ABCD. For this purpose both the shaft I for voltage-control andthe shaft'2 for-time control are provided with variable 'resistances 3 and 4, the variation of which is chosen'so as to'fulll this condition.

Furthermore a variable 'resistance-'Beets to connect into the filament-supply circuit'a-resistance suitable for each o fv the twoL tubes; The filament-supply current forY 'each v`of* the `X-ray tubes I1 and I8 `is supplied from the filamentsupply transformer I9. Thelatter is fed in a conventional manner through a voltage stabilizing device 6 from an autotransformer 'I. It is eicient to load the two tubes and-any further tube that may be provided)v in accordance with geometrically identical characteristic curves, which'is to be understood to rneanthat withboth tubes the tube currentis'controlld by the automatic device such that at eachloading time the ratio between the loads (kw.) .remainsconstant This is advantageous since it permits of the product It (mAmp.sec.) beingl indicated on a single logarithmic scale. Differences inload'capacy between the tubes are allowed for by shifting .the scale or the pointer through va distance -thevalu'e of which varies with the ratio betweenthelloads;

The autotransformer 1 is connected to the mains 8. A resistance 9 serves to adjust the mains resistance to the desired value. A controlley II] has the function of supplying the correct Voltage to the autotransformer in the event of voltage fluctuations in the mains. The correct voltage may be read from a voltmeter I I.

The high-voltage generator comprises a transformer I2, the secondary alternating current of which is converted into direct current by rectifying tubes I3 and supplied at will through arms Ill and I of a switch to either of the two X-ray tubes I1 and I8.

The auxiliary voltage dU for compensatingthe voltage loss is added as follows: The component A is taken directly from an auxiliary winding 2U, which is provided on the control transformer. The component B is taken from a. winding 22 with. the. use lof;- a control-member :2Iz,xwhich.ris coupled to' .the :time selector.; The..winding.:2.2 isuconnected to the rcontrol-transformer..` The component B. isf added through a .transformer 23 to.A the voltagewhichlacts on the primary winding of the' high-voltage.transformer. I2.: Thecur.- rent is switched onrand off ;by anelectromagnetizcally controlled switch .24', Vtheenergizing current of whichis controlled. by a time switch V25.'

WhatI claimi-s;

1. A: circuit arrangement.; for. energizing;y an X-ray tube. with automatic `control of tube.- cur.- rent. 'comprising .a low-tension circuit; 'for ,-enere gizing the cathode. of the X-ray tube...'includng means tofadjust the loading time of..the.tube:for a predetermined time.A interval, a separatehighfv tension circuit. having :a given electrical resist.- ance for energizing thel anode ofthe Xl-ray. tube, means to-couple the highandflow-tensionrcircuits to a sourcev of electrical 'power havingan electrical resistance proportional to the electrical resistance of the high-tension circuit =for which the voltage loss across the tube is' proportional to the input-"power-to the tube, and means;-in eluded inthe high-tension circuit for compensating for the voltage loss f resulting ywithcurrent flow in the high-tensionrcircuit and-from the source comprising `means to.` derive a relatively constant voltage 'component .proportional tothe voltage appliedfrom the source, Vmeans 'to add the voltage thus derived .to the voltage applied from the source to thehi-gh-tension circuit, means to derive a voltage proportional to the adjusted loading time ofthe tube, andmeansto add-the Voltage proportionall to the adjusted loading. time to the sum of the applied voltageandthe voltage proportional to .the applied voltage tothereby adjust theA voltage applied to the ytube tov-the 1=;,^ quivalent no-load voltage without compensa- 2.A.fcircuitl arrangementior energizingan X-raytube with automatic control. of tube currentr. comprising ar low-tension circuit forenergizing thecathode of the X-ray tube-including means to adjust the. loading `time of the tubefor a predetermined time interval, a separate hightensionV circuit includinga high-tensiontransformer and having a vgiven electricalI resistance for. energizing 'the anode-of the X`rayVV tube, means .to couple'thefhighand low-tension circuits to a source of electricalpowe-rhaving -a given-.electrical resistance proportionall to the electrical resistance of the high-tensionvcircuit for which the voltage loss across the tube is proportional to thel input power-to the tube,4 and means included-in the high-tension circuit for compensating for the voltage-lossresulting/with current ow in the'high-tensioncircuit and from the source comprising means to derive a relatively constant voltage component proportional to the voltage applied from the source. means to add the voltage thus derived to the voltage applied from the source to the high-tension circuit, an adjustable inductor responsive to the adjustment of said tube timing means coupled to the source of electrical power for deriving a voltage proportional to the adjusted loading time of the tube, and means to add the voltage proportional to the adjusted loading time to the sum of the applied voltage and the voltage proportional to the applied voltage to thereby adjust the Voltage applied to the tube to the equivalent no-load voltage without compensation.

3. A circuit arrangement for energizing an X-ray tube with automatic control of tube current comprising a low-tension circuit for energizing the cathode of the X-ray tube including means to adjust the loading time of the tube for a predetermined time interval. a separate hightension supply circuit having a given electrical resistance for energizing the anode of the X-ray tube, a common transformer for coupling the highand low-tension circuits to a source of electrical power having an electrical resistance proportional to the electrical resistance of the high-tension circuit for which the voltage loss across the tube is proportional to the input power to the tube, and means included in the hightension circuit for compensating for the voltage loss resulting with current flow in the hightension circuit and from the source comprising a transformer winding coupled to said common transformer for deriving a relativelyconstant voltage component proportional to the voltage applied from the source through said common transformer in series with said high-tension supply circuit, an adjustable inductor responsive to the adjustment of said tube timing means coupled to said common transformer for vderiving a voltage proportional to the adjusted loading time of the tube, and a control transformer in the high-tension supply for adding the voltage proportional to the adjusted loading time to the sum of the applied voltage and the voltage proportional to the applied voltage to thereby adjust` the voltage applied to the tube to the equivalent no-load voltage without compensation.

4. A circuit arrangement for energizing an X-ray tube with automatic control of tube current comprising a low-tension circuit for energizing the cathode of the X-ray tube including means to adjust the loading time of the tube for aipredetermined time interval, a separate high-tension circuit having a given electrical resistance for energizing the anode of the X-ray tube, means to couple the high-,and low-tension circuits to a source of electrical power including an electrical resistance for adjusting the resistance of said source to a value proportionaluto the electrical resistance of the high-tension circuit for which the voltage loss across ,the tube is proportional to the input power to the tube, and means included in the high-tension circuit for compensating for the voltage loss resulting with current flow inthe high-tension circuit and from the source comprising means to derive a relatively constant voltage component proportional to the voltage applied from` the source, means to add the voltage thus derivedto the voltage applied from the source to the hightension circuit, means to derive a voltage vproportional to they adjusted loading time of the tube. and means to add the voltage proportional to the adjusted loading time to the sum of the applied voltage and the voltage proportional to the applied voltage to thereby adjust the voltage applied to the tube to the equivalent no-load voltage without compensation.

5.1K circuit arrangement for energizing an X-ray tube with automatic control of tube current comprising a low-tension circuit for energizing the cathode of the X-ray tube including means to adjust the loading time of the tube for a predetermined time interval and means to control the current to the cathode proportional to the adjusted voltage applied to the tube, a separate high-tension circuit having a given electrical resistance for energizing the anode of the X-ray tube, means to couple the highand low-tension circuits to a source of electrical power including an electrical resistance for adjusting the resistance of said source to a value proportional to the electrical resistance of the high-tensionvcircuit for which the voltage loss across the tube is proportional to the input power to the tube, and means included in the high-tension circuit for compensating for the voltage loss resulting with current ow in the high-tension circuit and from the source comprising means to derive a relatively constant voltage component proportional to the voltage applied from the source, means to add the voltage thus derived to' the voltage applied from the source to the high-tension circuit, means to derive a voltage proportional to the adjusted loading time of the tube, and means to add the voltage proportional to the adjusted loading time to the sum of the applied voltage and the voltage proportional to the applied voltage to thereby adjust the voltage applied to the tube to the equivalent no-load Vvoltage without compensation.

ALFRED KUNTKE.

REFERENCES CITED The following references are of record in the file of this zpatent:

UNITED STATES PATENTS Number Name Date 2,137,647 Graves Nov. 22, 1938 2,351,486 Constable et al. June 13, 1944 2,379,125 Weisglass June 26, 1945 2,512,193 Zavales June 20, 1950 OTHER REFERENCES A Diagnostic X-Ray Apparatus With Exposure Technique Indication and Overload Protection by A. Nemet et al., Philips Technical Review, August 1948, pp 37-45.