US2217939A

US2217939A - X-ray apparatus

Info

Publication number: US2217939A
Application number: US167696A
Authority: US
Inventors: Bischoff Kurt; Silbermann Karl
Original assignee: Siemens Reiniger Werke AG
Current assignee: Siemens Reiniger Werke AG
Priority date: 1936-10-19
Filing date: 1937-10-07
Publication date: 1940-10-15
Anticipated expiration: 1957-10-15
Also published as: GB484281A; AT156238B; NL48602C

Description

Oct. 15, 1940. K, B|$HQFF HAL 2,217,939 I X-RAY APPARATUS Filed Oct. 7. 1957 2 sheets-Snead Patented Oct. 15, 1940 UNITED" STATES X-RAY APPARATUS Kurt Bischofl' and Karl Silbermann, Erlangen,

Germany, assignors to the firm Siemens- Reiniger -We rke Aktiengesellschaft, Berlin,

Germany Application October 7, 1937, Serial No. 167,696

In Germany October 19, 1936 18 Claims. (01. 250103) The present invention relates to Roentgen or X-ray apparatus, and is particularly concerned with arrangements for preventing overloading the Roentgen tube. These arrangements lend themselves advantageously to a new method of operating such tubes, with better results than have been attained heretofore,

The temperature of the focal spot of a Roentgen tube must not exceed a certain value, in

' order to avoid danger of destroying the anode, or at least doing it serious damage. Devices andcontrol means have been suggested in-the past which attempt to avoid the overloading of a Roentgen tube either by disconnecting the tube when the highest possible temperature of the anode is exceeded, or by regulating the tube current in such a manner that the temperature of the anode is maintained approximately at the highest permissible value during the entire operation of the apparatus. However, such devices have been found unsatisfactory and objectionable in several respects, since they do not provide either for a disconnection of the tube which a is free of delay, or for a substantially continuous be used and installed in Roentgen apparatus.

which is already in operation and may be grounded in apparatus where the anode of the tube is connected to a high tension current source. That is, in the case of a Roentgen tube having an anode operating at high potential, which is arranged within a high tension insulating and radiation- .protecting housing with groundedwalLthe ar- 45-rangement according to the invention may be carried out in such a'manner that the optical system and .the light-sensitive device are at ground potential, with the light rays emanating from the focal spot of the Roentgen tube di- 50 rected through an aperture or opening in the housing.

invention is useful for disconnecting the Roentgen tube when a certain permissible maximum focal spot temperature is reached or exceeded, and has the particular advantaf'e that the control of the tube current for the purpose of using a photoelectric cell" or other light-sensitive connection and disconnection of the Roentgen tube current may be obtained by means of a grid-controlled valve provided either in the primary or the secondary circuit of the high tension transformer. The substantially instantane- 5 ous disconnection of the Roentgen tube .can be accomplished in such a case by the use of relay means which operate without delayand which is actuated when the load limit is reached.- Permanent interruption or disconnection of the 10 Roentgen tube current may be obtained upon operative actuation of the lightfsensitive device by using suitable switching means, for example, of the stay-put or locking type, and corresponding circuits.

It is of importance for the practical realization of the invention to provide means for separating the Roentgen rays emanating from the focal spot 'of the X-ray tube from the light-sensitive device or preventing such rays from reaching the 20 device. The lenses used in the optical system may for this purpose be made of lead glass, for example, "or a mirror may be arranged in the path of therays from the focal spot, which deflects the light rays to the light-sensitive means, or photoelectric cell, the latter being properly located at the side of the apparatus.

Instead of disconnecting the Roentgen tube at the moment'when the highest permissible focal spot temperature is reached or exceeded, the invention may be used as previously intimated, so as to maintain the focal spot temperature substantially constant at a desirable value. This object may be accomplished by regulating the Roentgen tube current directly and substantially without delay in dependence on or as a function of the focal spot temperature. The Roentgen tube is equipped in this case with a control grid by means of which the light-sensitive device regulates the current flowing through the Roentgen I tube in such a manner that the temperature of the focal spot cannot exceed a certain predetermined value.

- Particularly advantageous is an arrangement whereby the light sensitive device regulates the 5 heating of the Roentgen tube so that the luminosity of thefocal spot remains substantially constant. This may be accomplished by disconnecting or diminishing the heating of the Roent-- gen tube under the control of the light sensitive device when the focal spot reaches a certain degree of luminosity, the re-connection or increased heating taking place upon decrease of luminosity 'of the focal spot below an adjustable value or after the lapse of a certain adjustable time period.

The heating of the Roentgen tube is, in this form of practicing the invention, preferably considerably increased or accelerated for the purpose of quickly reaching the load limit. If this greatly accelerated heating of the Roentgen tube would take place prior to connecting the high tension, the focal spot would be initially overloaded because the filament temperature would not drop quickly enough to the permissible value due to the inertia of the filament. The arrangement is for this reason operated so that the heating current is connected to the Roentgen tube upon starting the exposure simulaneously with connecting the high tension. so that the filament temperature is rising at that moment.

Inasmuch as the light sensitive device takes care that the filament temperature can never exceed the highest permissible value (since the focal spot luminosity would otherwise also rise to an impermissible value), it follows that the heating current can be increased-as desired, so that the speed with which the cathode and, therefore, also the focal spot reach the highest permissible temperatures can be accelerated at will. It is therefore entirely possible to heat a cathode intermittently with a current of, for example, 12 or more amperes, whose maximum permissible permanent heating current is about 8 amperes.

A milliampere-second relay is preferably provided, which disconnects the high tension connected to the Roentgen tube as soon as a milliampere-second product is reached which has previously been adjusted on this relay. The use of a known device for disconnecting the Roentgen tube as soon as a sufliclent blackening of the fllm is accomplished incident to the exposure, is also very advantageous.

The heating of the Roentgen tube takes place preferably from a direct current source, or from an alternating current source of high frequency, in order to avoid the oscillations of the emission caused by the use of an alternating current of, for example, 50 cycles, thereby accomplishing more accurate work.

In order to protect the Roentgen tube, the light sensitive cell is generally adjusted to a value which lies below the load limit. In order to prevent destruction of the Roentgen tube due to failure of the equipment, a second light sensitive device, e. g., a photoelectric cell, may be, provided which disconnects the Roentgen tube when the highest permissible luminosity of the focal spot is exceeded. v

The above stated and other objects and features of the invention will appear from the detailed description presented below with reference to the accompanying drawings. In these drawmgs,

Figs. 1, 2 and 3 show three diiferent embodiments of the invention, wherein the Roentgen tube is disconnected at the instant when the focal spot temperature reaches a predetermined va ue;

Fig. 4 shows by means oftwo curves the variation of the temperature of the focal spot in relation to the load time;

Fig. 5 shows a practical structure wherein the Roentgen or X-ray tube is enclosed in a high tension insulating and radiation protecting grounded housing with means for transmitting the light rays from the focal spot through an optical system to the light-sensitive device.

The apparatus is represented in the drawings, except Fig. 5, in a conventional and more or less schematic manner. The general structure and operation of individual devices, such as photoelectric cells, electronic valves, gaseous discharge tubes, and others, as used in connection with the various structures herein described, is well known and will not be dwelled upon in detail except when necessary for an understanding of the invention.

Referring now to the embodiment shown in Fig. 1. the Roentgen tube is indicated at I. It receives current from the high tension transformer 2 which may be connected to the current source 4 by means of a switch 3. The light rays emanating from the focal spot of the Roentgen tube l are directed over an optical system 5 to a photoelectric cell 6 which is located in a circuit of the relay 1; this circuit being provided with a battery, as indicated. The lens or lenses used in the optical system may be made of lead glass. Relay 'I-is provided with an armature adapted to close the circuit for the relay I which operates the switch 8. In other words, when the contact of relay 1 is closed, relay 8 is energized and the switch 3 opens its contacts, disconnecting the current source 4 from the primary winding of the transformer 2. Current for the Roentgen tube I is thus disconnected. The actuation of relay 1 is dependent, on the activation of the light-sensitive device 6 which is energized by the light rays from the focal spot of the Roentgen tube through the medium of the optical system 5. at the instant when the focal spot temperature reaches a critical value and produces light rays of suflicient intensity to activate the light-sensitive device 6. The high tension transformer 2 is thus disconnected from the current source and the Roentgen tube ceases to operate for a short interval, or until the focal spot has cooled off enough to reduce the light reaching photo cell 8 sufliciently to allow relay I to deenergize.

The embodiment shown in Fig. 2 comprises a Roentgen tube II, the high tension transformer l1, and a current source It However, in the primary circuit of the transformer there is pro vided a valve or tube 9 which takes the place of the switch 3 used in the previous embodiment. The grid of this valve 9 is controlled from the valve I 0, the latter being connected in a closed. circuit, as shown in the drawings, and governed in its operation by the "light-sensitive device It,

which may again be a photoelectric cell or the like. Current flowing in the cell i6 (depending, of course, on the light rays striking the cell according to the intensity of the temperature of the focal spot of the Roentgen tube) changes the potential of the upper terminal of the resistance ii. The potential at thispoint becomes less negative with an increase in the current flow through the cell, and when the current reaches a certain value the normal negative grid bias at the valve I0 is reduced enough so that the valve becomes conductive. This in turn causes a current flow in the plate circuit of valve Ill, including the resistance l2, and the grid of the valve 8 changes from positive to negative, whereupon the discharge through the valve ceases. Since this tube is in the primary circuit of the transformer 2, the Roentgen tube It connected in the secondary circuit is deprived of current and ceases to operate. As in the previous case, operation is resumed as soon as the focal spot in the Roentgen tube has cooled off somewhat.

The manner of transmitting the light rays from the focal spot of the Roentgen tube II to the photoelectric cell I6 is apparent from the drawing Fig. 2. The light rays first strikethe mirror i3 from striking the cell It.

and are reflected laterally toward the photoelecr "the quality of the Roentgen picture and without trio cell I6 through the optical system IS. The

Roentgen rays emanating from the Roentgen tube M are not reflected and are thus prevented Thearrangement disclosed in Fig. 3 comprises the Roentgen tube 20 connected to the secondary winding of the transformer 2|, the primary of which is connected to the current source 29. The

connection and disconnection of the Roentgen tube are taken care of in this case by the gridcontrolled switching valve 22 connected in series with the Roentgen tube in the circuit of the secondary winding of the transformer 2|. The light rays from the focal spot of the Roentgen tube 20 strike the mirror 26, which reflects them through the optical system 21 and a suitable shutter, as indicated, to the light-sensitive device 28. As in the previous embodiments, the light rays, varying in intensity, cause a current flow through the photoelectric cell in accordance with the temperature of the focal spot. In the present case, however, when current flows through the photo cell, the grid of the tube 25 becomes more negative,

which reducesor prevents current flow in the plate circuit of the tube andcauses the grid of the tube 24 to become positive with respect to its cathode. As a result, the tube 24 is rendered conductive, and a suitable control or transmitting device 23 is operated to place a negative potential on the grid of the tube 22. Any known arrangement for effecting this purpose may be used and accordingly the same has not been shown in detail, being represented in the drawings merely by a rectangle. The negative potential on the grid of the switching valve 22 renders the tube non-conductive and thus cuts off the current to the Roentgen tube 20. The switching actions described herein are substantially without any delay, once the critical temperature is reached.

In Fig. 4 two curves a and b are shown, which illustrate how the temperature T of the focal spot rises as a function of the load time t. 'Curve a. shows what happens when the input to the Roentgen tube is such that a moderately rapid rise in temperature occurs. When the highest permissible temperature T1 is reached, the current to the Roentgen tube will be interrupted, whereupon the temperature of the focal spot will drop quickly in accordance with the curve a. When the temperature of the focal spot reaches a certain adjustable value T2, the relay orvalve which is used vre-establishes the current flow through the Roentgen tube and the temperature again rises to the maximum allowed. The relay or valve thus disconnects and connects current to the tube periodically and maintains the temperature of the focalspotbetween the values T1 and T2. Curve 1; is similar to curve a, but corresponds to a higher input to the Roentgen tube and a more rapid heating. By comparing the curves, it will be seen that in the'second case the maximum temperature T1 is reached inless than half the time required in the first case. The cooling rate, shown by curve b, is of course the same as the cooling rate indicated by a.

It is particularly advantageous to repeat the disconnection and reconnection of the current through the Roentgen tube until a predetermined milliampere-second product is obtained which has been previously adjusted on a suitable milliampere-second relay. This furnishes the possibility of adjusting the values which determine the load of the Roentgen tube, namely, voltage, current and exposure time, solely with respect to any danger of overloading the Roentgen tube. It is also possible, as indicated in Fig. 4, curve b,

to accelerate the heating of the Roentgen tube so much that the temperature of the focal spot rises very quickly without danger of overloading the Roentgen tube. Such a rapid heating is of advantage in making an exposure, because the transition period from the starting-up of the Roentgen tube to penetration of the object and actual exposure is considerably shortened, and a definite milliampere-second product is reached in a shorter time.

In Fig. 5 is shown a practical embodiment of the invention wherein the Roentgen tube, the tube M in Fig. 2, for example, is provided with a high tension insulating and radiation-protecting housing 50.v the outer wall of which-is grounded. The light rays emanating from the Roentgen tube .are transmitted through an opening 5| of the housing to the outside and strike the mirror III which is located within the grounded shutter housing 52. The light rays are then conducted through the optical system l5 to the removably mounted light-sensitive cell It. The optical system l5 and the light-sensitive cell l6 are therefore at ground potential, as they are mounted on the grounded housing 50.

The various devices shown in Figs. 1 to 3 may, however, be mounted in any convenient and suitable manner so long as the relation of the equipment is maintained as indicated and described,

for the purpose of obtaining the desired explained 3 results. Fig. 5 merely shows one example of how the parts may be arranged.

What is desired to have protected by,Letters Patent of the United States is particularly pointed out in the appended claims.

We claim:

1. Apparatus for controlling the operation of a Roentgen tube, comprising means for controlling the supply of operating current to the tube, and means including a light-sensitive element responsive to light-emitted from the focal spot of the tube for controlling said first means.

2. Apparatus for controlling the operation of a Roentgen tube, comprising a switch for cutting oif the supply of operating current to the tube,

and means including a photoelectric cell responthe ' said tube, a mirror for reflecting light from the focal spot of the tube to said cell, and means controlled by said cell for controlling the current supply to said tube.

5. Apparatus for controlling the operation of a Roentgen tube, comprising a photoelectric cell located within the range of X-nays and light rays thrown off from the focal spot in said tube, an optical system impervious to X-rays for directing light rays to said cell, and means controlled by.

said cell for controlling the supply of power to said tube. I

6. Apparatu for controlling the operation of a Roentgen tube, comprising a photoelectric cell responsive to light emanated from the focal spot of said tube, and means controlled by said cell for maintaining the temperature of the focal spot between a maximum and minimum value by perif odically disconnecting and connecting the supply of power for the tube.

7. Apparatus for controlling the operation of a Roentgen tube, comprising a space discharge device having a control grid, means including a photoelectric cell responsive to light emanated from the focal spot in said tube for controllin the potential on said grid, and means controlled by said device for cutting off the supply of power to said tube when the focal spot temperature reaches a certain value and for re-connecting it when the temperature falls below a certain value.

8. Apparatus for controlling the operation of a Roentgen tube, comprising a light-sensitive device responsive to light emitted from the focal spot of said tube, and means controlled by said device for regulating the supply of power to said tube by reducing the power when the light emitted reaches a certain value and increasing the power when the amount of light drops below said value.

9. Apparatus for controlling the operation of a -Roentgen tube, comprising means for connecting and disconnecting the supply of power to said tube, and means dependent upon the intensity of light emitted from the focal spot of said tube for controlling said connecting and disconnecting means.

10. The combination, with a Roentgen tube,

A and a source of power therefor, of a protective housing for said tube having a grounded outer wall, an optical system and a photo cell mounted on said housing, said optical system being so positioned that it receives light through an opening in the housing from the focal spot of the tube and transmits said light to said photo cell, and means I controlled by said photo cell for governing the supply of power to said tube.

11. The method of operating a Roentgen tube, which consists in testing the' amount of light emitted from the focal spot while the tube is in operation, and shutting off the power supply to the tube when the light emitted reaches a certain predetermined value.

12. The method of operating a Roentgen tube, which consists in continuously testing the amount of light emitted from focal spot while the tube is in operation, reducing the power supplied to the tube when the light emitted exceeds a certain value and increasing the power supplied to the tube when the light emitted falls below said value.

- 13. The method of preventing the overloading of a Roentgen tube, which consists in separating the light rays generated at the focal point in said tube from the X-rays produced at said spot, directing said light rays to a photoelectric cell, and regulating the load on said tube in accordance with the resistance of said cell under the action of said light.

14. The combination, with a Roentgen tube and a switching device for controlling the supply of power thereto, of a photoelectric cell, an optical system for receiving visible light from the focal spot of said tube and for transmitting it to said cell, and means including said cell for controlling said switching device.

15. The combination, with a Roentgen tube and a source of power for operating it, of a photoelectric cell, an optical system having a selective said cell, and means including said cell for controlling said switching'device.

17. The combination, with a Roentgen tube and a circuit over which high tension operating potentials are supplied to'the anode thereof, of a space discharge device included in said circuit, a photoelectric cell, an optical system for transmitting light from the focal spot in said tube to said cell, and means including said cell acting under the influence of said transmitted light for rendering said discharge device non-conductive.

18. The method of operating a Roentgen tube, which consists in supplying an excess amount of power to the tube to enable the same to quickly reach an efficient operating condition, in testing the amount, of light emitted from the focal spot while the tube is in operation, and shutting oif the power supply to the tube when the light emitted reaches a certain predetermined value, thereby preventing the excess power from damaging the tube.

KURT BISCHOFF. KARL SILBERMANN.