US3027460A

US3027460A - X-ray device

Info

Publication number: US3027460A
Application number: US796925A
Authority: US
Inventors: Boldingh Willem Hondius
Original assignee: US Philips Corp
Current assignee: US Philips Corp; North American Philips Co Inc
Priority date: 1958-03-11
Filing date: 1959-03-03
Publication date: 1962-03-27
Anticipated expiration: 1979-03-27
Also published as: CH373476A; DE1126526B; NL97148C; GB908535A; FR1221302A

Description

March 27, 1962 w. H. BOLDINGH 3,027,460

X-RAY DEVICE Filed March 3, 1959 2 Sheets-Sheet 1 FICA mi L

INVENTOR WI LLEM HON DIUS BOLDINGH M e. AGEN March 27, 1962 w. H. BOLDINGH X-RAY DEVICE Filed March 5, 1959 2 Sheets-Sheet 2 FIG. 2

FIG. 3

INVENTOR W I LLEM HONDIUS BOLDINGH AGEN - voltage upon the blackening is fairly considerable.

United States Patent The present invention relates to voltage regulating circuit arrangements for X-ray tubes.

X-ray tube circuit arrangements usually comprise means for regulating the voltage between the anode and the cathode of the X-ray tube, i.e. the tube voltage. However, some X-ray devices are known in which the effective tube voltage always retains the same mean value, but these are usually small-size devices for certain uses,

such as dentistry, in which the objects or specimens contemplated to be examined are substantially of the same ilk. The use of voltage-regulating means, permits, however, diflt'erent medical examinations to be performed by means of one and the same X-ray device where different kinds of objects or specimens are to be examined.

Means for regulating the voltage is necessary in taking X-ray photographs, if the required tube voltage differs for each kind of object to be photographed. For example, the tube voltage required for fat patients is higher than that for thin patients. Furthermore, in choosing the voltage, allowance is made for the different X-ray absorption characteristics ofthe various parts of the body.

When the desired tube voltage has been determined, it is customary to determine also the product of the tube current and the exposure time, and hence the load, in order to obtain a given blackening of the photographic plate. An X-ray device is usually provided with tables or graphs from which the adjustment of the load values may be derived for most examinations occurring in practice in which an X-ray photograph is to be taken.

Such a graph or table does not supply all the details which may affect the absorption of rays of an object. Composing all the data for each individual object would become too expensive besides leading to an expedient which is not particularly surveyable and hence diflicult to handle. In view thereof, the indications supplied by the graphs or tables are limited to the cases of most frequent occurrence. It is possible to distinguish a plurality of groups of objects for which the energy required for obtaining a given blackening of the photographic plate and the optimum tube voltage at which the photographs are taken differ considerably. Examples of objects arranged in different groups or categories are the skull, the limbs, the thorax and the trunk.

It is known that the blackening obtained with a given value of the tube voltage kilovolts (kv.) and load mil- ].iampere seconds (ma/S.) remains constant if it is ensured that the product kv. rna./s. is constant. In this product, the exponent p has a value which is dependent upon the X-ray photographing technique, for example direct photograph or screen image photography, and varies between 5 and 3. The influence of a variation in In the case of direct photography, for which the higher values apply, it appears that a 1% voltage increase must be compensated by a 5% ma./s. decrease in order to obtain the same blackening. As a result of the incompleteness of a graph or table which does not specify the optimum combination of tube voltage, tube current and exposure time for all possible cases which may occur there is no certainty that the desired blackening is always obtained.

Making use of the influence of voltage variations upon the blackening, the disadvantage of false adjustment may be reduced by causing the tube voltage, during exposure,

to vary from a minimum value to a maximum value which are, respectively, lower and higher than the optimum value derived from a table or determined in another way.

The present invention relates to an X-ray circuit arrangement comprising means for regulating the voltage between the anode and the cathode of the X-ray tube, in which the tube voltage automatically increases during the exposure time for taking a photograph. A single control range in which the voltage can traverse all values which may be used for taking photographs, affords the advantage that the choosing of the voltage value may be omited. However, in this case, it is necessary for the highest and lowest voltages to be chosen for objects which differ most as to their kind and thickness. If then, the patient is exposed to X-rays which slightly contribute to obtaining the required blackening, such as in the case where a photograph is taken of a part of the body which is sufficiently permeable only for rays produced at the higher voltages, or in the case where a short exposure time is necessary to avoid lack of definition due to movements of the object to be photographed, a disadvantage is that the quantity of rays supplied to the patient is increased to an unnecessary extent. According to the invention, this disadvantage is substantially avoided by the use of means for regulating the tube voltage, which allows, inter alia, the tube voltage upon switching on the X-ray tube to be adjusted, as well as the value of the voltage variation, i.e., the range through which the tube voltage varies, and the rate at which the voltage varies. The addition of one or more of these possibilities of adjustment is not harmful to the simple operation of the device, since the adjustments to be performed are less critical than determining the correct photographing voltage by the con- 7 ventional methods. The adjustments are not intended for individual cases but each combination of adjustments, owing to the rising voltage, is contended for 'a plurality of cases within the domains of application. For all cases classified in one group, the same variation of the tube voltage is used, a prescribed value being chosen for the milliamp.-second product.

The above-mentioned and other features and objects of this invention will become apparent by reference to the following description taken in conjunction with the ac companying drawings, in which:

FIG. 1 is a schematic diagram of an embodiment of the circuit arrangement of this invention comprising electro-mechanical voltage regulating means;

FIG. 2 is a schematic diagram of still another embodiment of the circuit arrangement of this invention; and

FIG. 3 is a partial sectional view of part of a component which may be utilized in the embodiment of FIG. 2.

In the diagram of FIG. 1, the X-ray tube 1 is connected to a high-voltage transformer 2; anode 3 being connected to one terminal of secondary winding 4 of transformer 2 and cathode 5 being connected to the other terminal thereof. The cathode 5 is also connected to a secondary winding 6 of a transformer 7 which supplies the heating current for the cathode 5.

The voltage for the primary winding 8 of high-voltage transformer 2 is supplied by a regulating transformer 9. The transformer 9 is connected to voltage mains terminals 10 and 11 via a main switch 12.

The diagram of FIG. 1 contains only the necessary elements to illustrate the principle of this invention and which also include a time-switching device. This may be an electronically operating time switch which may be mechanically adjusted to a given exposure time. It is alternatively possible to employ a device having automatic limitation of time. A device of the last-mentioned kind is shown in FIG. 1. It comprises a photo-electric 8 cell 13, which is sensitive to X-rays or which comprises a fluorescent screen for converting X-rays into visible light. A current source 14 and a resistor 15 are connected in series with the photo-electric cell 13. The current traversing the resistor 15 is determined by the internal resistance of the photo-electric cell, which is high at a low intensity of the incident radiation and decreases upon increasing intensity of the rays. The voltage across the resistor 15 varies in the reverse sense and serves to charge a capacitor 16. The charging voltage of capacitor. is proportional to the quantity of rays and serves as a measure of the blackening of the photographic plate, which, in taking photographs by means of an X-ray tube, is positioned, together with the object, between the photo-electric cell and'the X-ray tube. The voltage on the capacitor 16 is applied to a control grid 17 of an electron discharge tube -18 and acts upon the intensity of the electron current produced between an anode 19 and a cathode 20. The anode circuit includes a coil 21 of an electro-rnagnetic relay and a voltage source 22. The anode circuit includes a switch, illustrated, by way of example, as a pressbutton switch 23.

Before the photographing process starts, the capacitor 16 is without voltage. The grid 17 has cathode potential so that, after pressing the press-button switch 23, an anode current flows, which energizes coil 21'of the electromagnetic relay, so that a switch 24 is closed. Before operating the press-button switch 23, themain switch 12 is closed and voltage is applied to a primary winding 25 of heating-current transformer 7. The thermionic cathode 5 ofthe X-ray tube 1 is thus heated. Due to the closure of switch 24, the high-voltage transformer 2 receives voltage and the X-ray tube 1 is made operative. The voltage source 14 charges capacitor 1:6, so'that the potential on grid 17 of the discharge tube 18 varies in a negative-sense with respect to the cathode '20 and, after a certain period, the anode current decreases to so low a value that the relay coil 21 releases the switch 24. The opening of switch 24 causes the supply of current to the X-ray tube to be interrupted and the photographing process to be terminated.

During photographing, the voltage between the anode 3 and the cathode 5 of X-ray tube 1 is increased by means of a variable resistor 26. The resistor 26 comprises an annular body on 'which resistance wire is wound. Its sliding contact 27 is moved by means of a continuously rotating shaft 28 which is driven by an electric motor 29 switched onby the closure of main switch 12. Rotary shaft 30 of sliding contact 27 and the shaft 28-of the electric motor are connected by meansof a friction coupling 31.

Alongthe periphery of the variable resistor 26 there are arranged two

abutments

32 and 33 which can check the sliding contact 27 but which may also be removed from the path of the sliding contact. The abutment 32, at the beginning of the path of the resistor is a pin which may be removed from the vicinity of resistor 26 by energization of' a magnet winding 34. The winding 34 is energized when the magnetic switch Holmes and hence when the X-ray' tube is switched on. Due to the withdrawal of the pin," the- 'sliding contact 27 is rotated by the continuously-rotating shaft 28 via the coupling 31 and displaces itself along the resistor 26 to the other extremity. The resistance in the primary circuit of the high-voltage transformer -2 is thus successively reduced and finally completely short-'circuited.

The second abutment 33'is situated at the area where the resistor 26 terminates. It is operated dififerently from the first-mentioned abutment 32. When a coil 35 is ener- 'gized, the movement of sliding contact 27 is blocked by the'iabutment '33 and when the energization disappears,

the movement ofthe sliding contact is resumed. The coils of the two

abutments

32 and 33 are connected in parallel. 'W-ith the X-ray' tube switched on, when the sliding contact'l g s its m veme t al g the resistance P reached, the tube voltage hasits maximum value.

the tube voltage is low. The X-ray tube voltageincreases moves past the second abutment '33, which has been with drawn due to the de-energization of coil 35, and comes to rest against the first abutment 32, so that the initial'condition is restored and a new photograph can be taken.

An X-raytube circuit arrangement designed as above described fundamentally permits taking of any arbitrary photograph in which no other manipulations are per formed other than closing .the press-button switch 23 and keeping it closed. The time of exposureis controlled automatically.

For thin objects and objects with small X-ray absorbing characteristics, the quantity of rays required for producing the desired blackening of the photographic plate requires a shorter exposure period than for a photograph which is taken of a thicker object or one which has a greater X-ray absorbing characteristic. In the last-mentioned case, the radiation obtained at the lower voltage is valueless for obtaining a given blackening. This radiation thus unnecessarily increases the skin dose and it is therefore desirable to avoid it. For this purpose, the circuit arrangement of theinvention has the feature that thevoltage between the anode 3 and the cathode 5 of the X-ray tube 1, at which the photographing process begins, is adjustable. To this end, the abutment 32 which checks the slide ing contact 27 in the initial'position, is displaceable along the periphery of the variable resistor .26 in the direction of the sliding contact 27 as indicated by arrow 36. When a new adjustment of the abutment has been'chosen, the sliding contact 27, after the driving motor 29 has been switched on and hence as soon as the main switch '12 is closed, moves towards the position of the abutment 32,. whereby the portion of the resistor located between the connection of the current supply wire and the abutment 32 is short-cir'cuited. The portion of the resistor which remains switched on is then smallerso that operation of the circuit arrangement is started with a higher initial voltage.

Furthermore, the boundary of the displacement of the sliding contact 27 is adjust-able in order to limit the increase in tube voltage to a value lower th-anthe peak value. For thispurpose, the abutment 3-3, at the end of resistor 26, is displaceable along the periphery of resistor 26 in the opposite sense to the direction of rotation of sliding contact 27 as indicated by arrow 37. The abutment 33 then stops the sliding contact 27 before the latter has performedthe complete rotation, a portion of the resistor 26 remaining switched into thecircuit. v

In the foregoing, the current strength with which the X-ray tube is loaded has not been considered. Since the current strength also determines the time of exposure,

' it may in certain cases be important to regulate the rate of the increasing voltage. This is effected by varying the speed of rotation of the electric motor 29 which drives the sliding contact 27 In the embodiment shown in FIG. 2, the rotary potentiometer is also designed as a switching element for terminating the exposure time. The resistor 26 isconnected in series with the primary winding 8 of high-voltage transformer 2, the secondary winding 4 f which is connected'to the anode 3 and the cathode 5 of the X-ray tube 1.

After the main switch 12 has beenclosed, the autotransformer 9 is energized. The current supply {to the primary winding 8 of high voltage transformer 2 remains inter-- rupted as long as the electromagnetic switch 59 is open. Switch 59 is operated by an energizing winding 64.. The supplycurrent for the relay winding 64 passes via two

contact devices

63 and 65, which are connected in series and which serve to'switch bu and. switch otiithe. energizing current, respectively. The rotary contact 27, which is also designed as a switching arm, is seated on the shaft of the resistor 26.

At the initial position, at which the whole resistor 26 is switched in, the rotary contact 27 keeps the

contacts

61 and 62 of the contact device 63 open, so that the circuit of the relay winding 64 is interrupted. The X-ray tube 1 is made operative by switching on the electric motor 66, which drives a shaft 60 of the rotary contact 27. The motor 66 starts running when a push button switch 67 is closed. The contact 27, which is also a switching arm is rotated by the rotary shaft 60, resulting in the

contacts

61 and 62 of the contact device 63 being closed and the relay winding 64 being energized. The latter closes the switch 59 and hence connects the supply current to the Xray tube 1.

After contact 27 has traversed the whole resistor 26, the contacts 68 and 69 of the contact device 65 are opened and the current through the winding 64 is interrupted causing switch 59 to open, so that the X-ray tube 1 is switched off. A regulation of the speed of rotation of the electric motor 66, for example, a three-stage regulation, serves to match the exposure time to the various groups of objects, the contact 27 moving from the beginning to the end of the resistor 26 within 0.3, 1.5 and seconds. The shaft 60 of the current collector is therefore driven by the electric motor 66 via a speed regulator 70.

Another possibility of controlling the exposure time consists in positioning the terminal contact device 65 to be displaceable along the periphery of the resistor 26. This may be combined with the use of speed stages, so that during each of these stages exposure times may be chosen shorter than those required for traversing the whole resistor. This also results in a decrease of the voltage rise at the X-ray tube 1. In order to obtain the same blackening of the photographic plate when utilizing a shorter exposure time and a voltage which rises to a lesser value so that the mean X-ray tube voltage is lower, it is necessary to increase the X-ray tube current. Automatic regulation of the X-ray tube current may be obtained by coupling the movable contact device 65 to a device 71 which adjusts the heating current of the X-ray tube.

If the rotary contact is not also operative as a switching arm, but a separate arm 72 operates the

contact devices

63 and 65, it is possible to regulate the increase in tube voltage and exposure time individually.

Referring now to FIG. 3, the switching arm 72 is arranged as a separate rotary arm on the shaft 60 of potentiometer 26. The potentiometer body 26 is supported by a carrier 73 of insulating material. Also secured thereto, by means of a support 74, is the contact device 63. The shaft also carries the rotary contact 27. The contact 27 and the switching arm 72 are pinched in position between small press plates 75 so as to be moved due to friction when the shaft 60 rotates, but they may alternatively be checked while the shaft keeps rotating. The rotary contact 27 is stopped by an abutment 76, which is rotatably secured to the support 73 for the resistor body 26. The point Where the movement of the rotary contact terminates is thus adjustable. If the switching arm 72 then has not reached the switch ing-ofif contact 65, it continues its movement and a constant tube voltage is supplied to the X-ray tube during'the portion of the path described by the switching arm 72 after the movement of the contact 27 has been blocked. To enable displacement of the contact device 65, it is rotatably secured to the support 73 by means of a supporting member 77.

After a photograph has been taken, the contact 27 and the switching arm 72 are turned back to their initial positions. The support 74 for the contact device 63 may be secured to be displaceable along the periphery of the support 73 so as to permit adjustment of the tube voltage at which the photographing process begins.

While I have described the principles of my invention in connection with specific apparatus, it is to be clearly understood that this description is made only by way of example and not as a limitation to the scope of my invention as set forth in the objects thereof and in the accompanying claims.

I claim:

1. A voltage regulating circuit arrangement for an X-ray tube having an anode and a cathode, said X-ray tube being adapted to operate at a desired operating voltage dependent upon the characteristics of an object to be X-ray-photographed during the time of exposure required for the X-ray photograph, said desired operating voltage having a value in a range of voltages from a minimum voltage magnitude to a maximum voltage magnitude, comprising means for applying a voltage across said X-ray tube, means for automatically varying the voltage across said X-ray tube from said minimum magnitude to said maximum magnitude during said time of exposure comprising voltage regulating means having a movable adjustment member, and means for varying said minimum and maximum magnitudes comprising first and second adjustable abutment members engaging said movable adjustment member at predetermined locations in the path thereof.

2. A voltage regulating circuit arrangement for an X-ray tube having an anode and a cathode, said X-ray tube being adapted to operate at a desired operating voltage dependent upon the characteristics of an object to be X-ray-photographed during the time of exposure required for the X-ray photograph, said desired operating voltage having a value in a range of voltages from a minimum voltage magnitude to a maximum voltage magnitude, comprising means for applying a voltage across said X-ray tube, said voltage applying means comprising a high voltage transformer having a primary winding and a secondary winding connected between the anode and cathode of said X-ray tube, first switch means and means for applying a voltage across said primary winding through said first switch means, means for automatically varying the voltage across said X-ray tube from said minimum magnitude to said maximum magnitude during said time of exposure, said voltage varying means comprising a rotary type resistor having a resistance interposed between said primary winding and said first switch means, a rotary contact and means electrically connecting said resistance between said primary winding and said first switch means through said rotary contact in a manner whereby when said first switch means is closed and the said rotary contact is at the beginning of its cycle of rotation a maximum value "of said resistance is connected between the said primary winding and the said first switch means and rotation of the said rotary contact reduces said resistance value to a minimum upon termination of the cycle of rotation, means for varying said minimum and maximum magnitudes of voltage comprising first and second adjustable abutment members engaging said rotary contact at predetermined locations in the path thereof, and means actuated by closure of said first switch means for rotating said rotary contact through the cycle of rotation from said maximum resistance value to said minimum resistance value.

3. A voltage regulating circuit arrangement for an X-ray tube having an anode and a cathode, said X-ray tube being adapted to operate at a desired operating voltage dependent upon the characteristics of an object to be X-ray-photographed during the time of exposure required for the X-ray photograph, said desired operating voltage having a value in a range of voltages from a minimum voltage magnitude to a maximum voltage magnitude, comprising means for applying a voltage across said X-ray tube, said voltage applying means comprising a high voltage transformer having a primary winding and a secondary winding connected between the anode timeof exposure, said voltage varying means comp-rising a rotary type resistor having a resistance interposed'between lsaidprimary winding and said first switch means, a rotary contact and means electrically connecting said resistance between said primary winding and said first switch means through said rotary contact in a manner whereby when said first switch means is closed and the said rotary contact is at the beginning of its cycle of rotation a maximumvalue of said resistance is connected between the said primary winding and the said first switch means and rotation of the said rotary contact reduces said resistance value to a minimum upon termination of the cycle of rotation, means for varying said minimum and maximum magnitudes of voltage comprising a first movable abutment positioned at the beginning of the cycleof rotation and means actuated by the start of said time of exposure for moving said abutmentrout of the path of rotation ofsaid rotary contact in a manner whereby the said rotary contact is permitted to initiate the cycle of'rotation at'said start of said time of exposure and a second movable abument positioned at the end of the cycle of rotation and means actuated by the end of said time "of exposure for moving said second abutment into the path of rotation'of the said rotary contact in a manner whereby the said rotary contact isstopped at said end of said'time of exposure, a'slip coupling and a motor actuated byrclosure of said first switch means for rotating said'rota ry contact through the cycle of rotation from said maximum resistance value to said minim-um resistance value.

4. A voltage regulating circuit arrangement for an X- ray tube having an anode and a cathode, said X-ray tube being adapted to operate at a desired operating voltage dependent upon the characteristics of an object to be Xeray -photographed during the time of exposure required for the X-ray'photograph, said desired operating voltage having a value in :a range of voltages from a minimum voltage magnitude to a maximum voltage magnitude, comprising means for applying a voltage across said X ray tube, said voltage applying means comprising a high voltage transformer having a primary winding and a secondary winding connected between the anode and cathode of said X-ray tube, first switch means and means for applying a'voltage across said primary winding through said first switch "means, means for automatically varying the voltage across said X-ray tube from said minimum magnitude to said maximum magnitude during said time of exposure, said voltage varying means comprising a rotary type resistor having a resistance interposed between said primary winding and said first switch means,

,a rotary'contact'and means electrically connecting said resistance between said primary winding and said first switch means through said rotary contact in a manner whereby when said-first switch means is closed and the said rotary contact is at the beginning of its cycle of rotation a maximum value of said resistance is connected between the said primary winding and the said first switch means and rotation of the said rotary contact .reducespsaid resistance value to a minimum upon termination of the cycle of rotation, means for varying said minimum andmaximum magnitudes of voltage comprising a first movable pin abutment positioned at the beginning of the cycle of rotation and electromagnetic means actuated by the start of said time of exposure for moving said first pin out of the path of rotation of said rotary contact in a manner whereby the said rotary contact is per-mitted'to' initiate the cycle of rotation at said start of said time of exposure and a second movable-pin abutmentpositioned 'at the end of the cycle of rotation andrelectrornagnetic means actuated by the end o't'said time of exposure formoving said second pin into thepath of rotation of the said rotary contact in a manner whereby the said rotary contact is stopped at said end of said time of exposure and rotation of the said rotary contact is prevented until the start of the next succeeding time of exposure, a slip coupling and a motor actuated by closure of said first switch means for rotating said rotary contact through the cycle of rotation from said maximum resistance value to said minimum resistance value.

5. A voltage regulating circuit arrangement for an X- ray tube having an anode and a cathode, said X-ray tube being adapted to operate at a desired operating voltage dependent upon the characteristics of an object .to be X-ray-photographed during the time of exposure required for the X-ray photograph, said desired operating voltage having a value in a range of voltages from a minimum voltage magnitude to a maximum voltage magnitude,.comprising means for applying a voltage .across 'said X-ray tube, said voltage applying means comprisingra high voltage transformer having a primary winding and a secondary winding connected between the anode and cathode ofsaid X-ray tube, first switch vmeans and means for applying a voltage across said primary winding through said first switch means, means .for automatically varying thevoltage across said X-ray tube from said minimum magnitude to said maximum magnitude during said time of exposure, said voltage varying means comprising arotary type :resistor having a resistance interposed betweensaid primary winding and said first switch means, a rotary 'contact'and means electrically connecting said resistance'between said primary winding and :said first switch means through said rotary contact in a maner whereby when said first-switch means is closed and the said rotary contact is at the beginning of its cycle of rotation a maximum value of said resistance is connected between the said primary winding and the said first switch means and rotation of the said rotary contact reduces said resistance value to a minimum upon termination of the cycle of rotation, means for varying said minimum and maximum :magnitudes of voltage, means actuated by closure of said first switch means for rotating said rotary contact through the cycle of rotation from saidmaximum resistance value to said minimum resistance value, .a first movable circuit breaking device positioned at the beginning of the cycle of rotation in a manner whereby when said rotary contact initiates said cycle of rotation the said rotary contact closes said first circuit breaking device, means connecting said first circuit breaking device between said primary windingzand SElid'fiISt switch means in armanner whereby energization of said X-ray tube is permitted when said first circuit breaking device is closed, a second rnov: able circuit breaking device positioned at theend of the cycle of rotation in a manner whereby when the ;said rotary contact terminates said cycle of rotation the said rotary contact=openssaidsecond circuit breaking device, and means connecting said second circuit breaking device between the said primary winding and the said first switch means in a manner whereby said X-ray tube is deenergized when said second circuit breaking device is open,

6. A voltage regulating circuit arrangement for an X-ray tube having an anode and a cathode, said X-ray tube being adapted to operate at a desired operating voltagedepcndent upon the characteristics of an object to'be X'-ray-photographed during the time of exposure required for the X-ray photograph, said desired operating voltage having'a value in a range of voltages from a minimum voltage magnitude to a maximum voltage magnitude, comprising means for applying a voltage across said 'X-r-ay tube, said voltage applying means comprising ahighvoltage transformer having a primary. winding and a secondary winding connected between the anode and cathode of said X-ray tube, first switchmeans and means for applying a voltage across said primary winding through said first switch means, means for automatically varying the voltage across said X-ray tube from said 9 minimum magnitude to said maximum magnitude during said time of exposure, said voltage varying means comprising a rotary type resistor having a resistance interposed between said primary winding and said first switch means, a rotary contact and means electrically connecting said resistance between said primary winding and said first switch means through said rotary contact in a manner whereby when said first switch means is closed and the said rotary contact is at the beginning of its cycle of rotation a maximum value of said resistance is connected between the said primary winding and the said first switch means and rotation of the said rotary contact reduces said resistance value to a minimum upon termination of the cycle of rotation, means for varying said minimum and maximum magnitudes of voltage, means actuated by closure of said first switch means for rotating said rotary contact through the cycle of rotation from said maximum resistance value to said minimum resistance value, a switching arm coaxially positioned with said rotary contact in a manner whereby said switching arm rotates with the said rotary contact through its cycle of rotation, a first movable circuit breaking device positioned at the beginning of the cycle of rotation in a manner whereby when said switching arm initiates said cycle of rotation the said switching arm closes said first circuit breaking device, means connecting said first circuit breaking device between said primary winding and said first switch means in a manner whereby energization of said X-ray tube is permitted when said first circuit breakingdevice is closed, a second movable circuit breaking device positioned at the end of the cycle of rotation in a manner whereby when the said switching arm terminates said cycle of rotation the said switching arm opens said second circuit breaking device, means connecting said second circuit breaking device between the said primary winding and the said first switch means in a manner whereby said X-ray tube is deener-gized when said second circuit breaking device is open, and adjustable abutment means for stopping said switching arm before it reaches said second circuit breaking device.

7. A voltage regulating circuit arrangement for an X-ray tube having an anode and a cathode, said X-ray tube being adapted to operate at a desired operating voltage dependent upon the characteristics of an object to be X-ray-photographed during the time of exposure required for the X-ray photograph, said desired operating voltage having a value in a range of voltages cErom a minimum voltage magnitude to a maximum voltage magnitude, comprising means for applying a voltage across said X-ray tube, said voltage applying means comprising a high voltage transformer having a primary winding and a secondary winding connected between the anode and cathode of said X-ray tube, first switch means and means for applying a voltage across said primary winding through said first switch means, means for automatically varying the voltage across said X-ray tube from said minimum magnitude to said maximum magnitude during said time of exposure, said voltage varying means comprising a rotary type resistor having a resistance interposed between said primary winding and said first switch means, a rotary contact and means electrically connecting said resistance between said primary winding and said first switch means through said rotary contact in a manner whereby when said first switch means is closed and the said rotary contact is at the beginning of its cycle of rotation at maximum value of said resistance is connected between the said primary winding and the said first switch means and rotation of the said rotary contact reduces said resistance value to a minimum upon termination of the cycle of rotation, means for varying said minimum and maximum magnitudes of voltage, means actuated by closure of said first switch means for rotating said rotary contact through the cycle of rotation from said maximum resistance value to said minimum resistance value, a switching arm coaxially positioned with said rotary contact in a manner whereby said switching arm rotates with the said rotary contact through its cycle of rotation, a first movable circuit breaking device positioned at the beginning of the cycle of rotation in a manner whereby when said switching arm initiates said cycle of rotation the said switching arm closes said first circuit breaking device, means connecting said first circuit breaking device between said primary winding and said first switch means in a manner whereby energization of said X-ray tube is permitted when said first circuit breaking device is closed, a second movable circuit breaking device positioned at the end of the cycle of rotation in a manner whereby when the said switching arm terminates said cycle of rotation the said switching arm opens said second circuit breaking device, means connecting said second circuit breaking device between the said primary winding and the said first switch means in a manner whereby said X-ray tube is deenergized when said second circuit breaking device is open, means for regulating the current in the cathode of said X-ray tube, and means connecting said second circuit breaking device to said current regulating means in a manner whereby operation of the said current regulating means is determined by operation of the said second circuit breaking means.

References Cited in the file of this patent UNITED STATES PATENTS 2,036,072 Mutscheller Mar. 31, 1936 2,617,047 Kuntke Nov. 4, 1952 2,786,949 Boucher Mar. 26, 1957 2,883,554 Reed et al. Apr. 21, 1959 2,936,376 Hoekstra May 10, 1960 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,027,460 March 27, 1962 Willem Hondius Boldingh It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

In the heading to the printed specification, line 7, for "Nov. 14, 1958 read Mar. 11, 1958 Signed and sealed this 31st day of July 1962.

(SEA L) Attest:

ERNEST w. SWIDER DAVID LADD Attesting Officer Commissioner of Panama