US3413475A

US3413475A - X-ray tube power supply for producing a series of selected numbers of consecutive alternating current voltage cycles

Info

Publication number: US3413475A
Application number: US517281A
Authority: US
Inventors: George H Russ; Jr Robert L Wright
Original assignee: Westinghouse Electric Corp
Current assignee: CBS Corp
Priority date: 1965-12-29
Filing date: 1965-12-29
Publication date: 1968-11-26
Anticipated expiration: 1985-11-26

Description

1968 G. H. RUSS ETAL 3,

X-RAY TUBE POWER SUPPLY FOR PRODUCING A SERIES OF SELECTED NUMBERS OF CONSECUTIVE ALTERNATING CURRENT VOLTAGE CYCLES Filed Dec. 29, 1965 X-RAY TUBE ENERGIZATION CONTROL CIRCUIT MEANS VOLTAGE AT A mam MEANS 3|2 VOLTAGE AT PRIMARY OF HIGH TENSION TRANSFORMER l5 I \f U WITNESSES INVENTORS @Waa-AQ Q. 6' George H Russ and Robert L. Wright,dn

I miw United States Patent 3,413,475 X-RAY TUBE POWER SUPPLY FOR PRODUCING A SERIES OF SELECTED NUMBERS 0F CON- SECUTIVE ALTERNATING CURRENT VOLT- AGE CYCLES George H. Russ, Baltimore, and Robert L. Wright, Jr.,

North Linthicum, Md., assignors to Westinghouse Electric Corporation, Pittsburgh, Pa., a corporation of Pennsylvania Filed Dec. 29, 1965, Ser. No. 517,281 2 Claims. (Cl. 250100) ABSTRACT OF THE DISCLOSURE Described is an X-ray apparatus which includes the usual X-ray tube, full-wave rectifier and high tension transformer secondary in series together with a wellknown energization control circuit means that produces a series of selected numbers of consecutive alternating current voltage cycles to the transformers primary. A selector switch is operable to cut in an impedance means for damping the first half cycle pulse of any given series of voltage cycles from the control circuit means, and a diode and relay arrangement automatically inetfectuates the impedance means during all succeeding half cycle pulses of such series.

The electronic control circuits to which the present invention relate utilize an electronic contactor which is operable to produce selected numbers of alternating current full-cycle voltage pulses which always commence with a particular polarity and end with the opposite polarity for corresponding energization of the X-ray tube through a rectifier bridge circuit. Such operation of a contactor to produce full-cycle A.C. voltage pulses which always commence with a particular polarity and end with the opposite polarity takes care of residual magnetism in the core of the high tension transformer in such a manner as assures that the current supplied to the X-ray tube will be substantially uniform for each successive exposure period of the same selected time. Such operation, however, tends to limit the number of exposure times available for selection, inasmuch as the available exposure times are determined by the number of full cycles of energization of the primary winding of the high tension transformer. An X-ray tube energization control circuit means of this type is shown and described in US. Patent 2,785,343. In the apparatus disclosed in such patent, a half-cycle exposure, second, however, can be obtained by deactivating half of the rectifier bridge via which the X-ray tube is energized from the secondary of the high tension transformer. This technique, however, is not satisfactory for obtaining other multiples of halfcycle periods, such as three half-cycle periods to obtain an exposure of 4 of a second, or five half-cycle periods to obtain an exposure time of of a second, for example.

In view of the foregoing remarks it becomes the prime object of the present invention to provide an X-ray apparatus which embodies X-ray tube energization control circuit means which produces selected numbers of alternating current full-cycle high-tension-transformer-energization pulses which always commence with a particular polarity and end with the opposite polarity together with means for controlling energization of the high tension transformer by such pulses in a manner which enables selection of multiples of half-wave pulses to obtain corre sponding X-ray exposure periods.

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The above objects is obtained in accord with an illustrative embodiment of the present invention by interposing a pulse-damping impedance means in series with the primary winding of the high tension transformer to ineffectuate the first half-wave pulse with respect to energization of the X-ray tube, while permitting sufficient current to pass through the primary winding during such first half-wave pulse as will maintain the desired residual magnetismconditions in the core of such transformer.

The apparatus further comprises means for ineifectuating the pulse-damping impedance means during any half-wave pulses from the contactor following such first half-wave pulse.

Other objects, features and advantages of the invention will. become apparent from the following detailed description of an illustrative embodiment thereof, when taken in connection with the accompanying drawings, in which:

FIGURE 1 is a circuit diagram, partially in block diagram form, showing details of the illustrative embodiment of the present invention; and

FIG. 2 shows contactor output voltage waves.

Referring to FIG. 1 in the drawing, the X-ray apparatus of the present invention comprises an X-ray tube energization control circuit means 300 which is operable to produce selected numbers of consecutive alternating current full cycles which always commence with a particular polarity and end with the opposite polarity. Such circuit means 300 is shown herein in block diagram form in behalf of simplifying the description of the present invention, For a detailed showing and explanation of such a circuit means reference may be had to the aforementioned US. Patent 2,785,343. Any reference numerals employed in the present description below the numeral 300 can 'be correlated with the showing and description in such patent. The circuit means 300 is operable to energize the primary winding 19 of the high tension transformer means 15 through the medium of output leads 301 and 302, a switch 303 and a lead 304. As will be apparent by reference to Patent 2,785,343, with the primary winding 19 of high tension transformer 15 connected to the output leads 301 and 302 of the circuit means 300 by way of the switch 303 when closed, a selected number of alternating current voltage cycles will appear at such winding to produce a corresponding number of high voltage half-wave direct current pulses across the X-ray tube 11 for effective energization of same of a duration equal to the length of timesuch voltage pulses are in existence at the primary of transformer 15. Such X-ray tube energization, as is well known, determines the length of an X-ray exposure. Each voltage cycle occurring at the primary winding 19 of the high tension transformer 15 represents an exposure time equal to that required for the alternating current reference voltage to complete a full cycle. In the aforementioned patent, such reference voltage is at the sixty cycle per second frequency, so that each voltage cycle appearing at the primary winding 19 represents an exposure period of 4 of a second. The X-ray tube energization control circuit means 300 is capable of effecting selected numbers of such cycles, hence of effecting X-ray exposures of durations which are multiples of of a second. Although unnecessary in the presence of the present invention as will be described subsequently, the apparatus of Patent 2,785,343 also provides for effecting a half-cycle exposure, or of a second, by opening a switch 294 to disable

rectifiers

51 and 47 by disrupting their filament supply, when the circuit means 300 was set to select and produce a single alternating current voltage cycle at the output leads 301 and 302. With the switch 294 open and the

rectifiers

47 and 51 ineffectuated, the

rectifiers

47 and 53 of the rectifier bridge 13 then operate to conduct only onehalf of the full-wave cycle produced in the high tension transformer 15 through the X-ray tube 11.

In accord with the present invention, an impedance means 306 is provided for insertion in the energizing circuit for the primary winding 19 of the high tension transformer 15 to damp the first half cycle voltage pulse produced by the circuit means 300 to the extent that the corresponding voltage appearing at the X-ray tube 11 produces X-ray radiation of little, if any, penetrating power, while at the same time providing for sufiicient flow of current through the primary winding 19 to properly magnetize the iron core of such transformer. Such impedance means in the form of a selected one of a plurality of

resistors

307, 308 and 309, the choice of which depends upon the expected load on the X-ray apparatus, is automatically .ineffectuated by a diode 310 which shorts out the impedance 306 during the next successive half-wave pulse of alternating current voltage from the circuit means 300. Presuming the first pulse emanating from the circuit means 300 to be positive, for example, cur-rent will be forced to pass through the selected one of the resistors 307 to 309 to experience a voltage drop therein while enroute to the primary winding 19 of the high voltage transformer, while the next successive pulse from the circuit means 300 of opposite polarity, negative, for example, will be short-circuited through the diode 310 without such voltage drop enroute to the primary winding 19. Thus, it will be seen that the first pulse leaving the circuit means 300 will be ineffectuated with respect to causing significant production of X-rays by the X-ray tube 11 during such first half-wave period. If the circuit means 300 has been set to produce a single cycle at its output, then the ineffectuation of the first half-cycle by the damping means 306 obtains half-cycle production of effective X-rays by the X-ray tube 11 for an exposure of of a second, for example, when the alternating current reference voltage is at a frequency of 60 cycles per second. Thus, it will be apparent that where an exposure of a single half-cycle duration, of a second, for example, is desired, the switch 294 afiiliated with the apparatus of Patent 2,785,343 can be dispensed with.

Where it is desired to obtain energization of the X-ray tube 11 for exposure of an odd number of half-cycle periods greater than one, the present apparatus includes a relay means 312 having a switch 313 which closes some time during the second half-cycle period of the output from the circuit means 300 to bypass the impedance means 306 as Well as the diode 310 and enable at least one full-Wave cycle, in other words, two subsequent consecutive half-wave pulses from the circuit means 300 to reach the transformer 19 without modification by such impedance means. For example, if the X-ray tube energization control circuit means 300 is set to produce an exposure corresponding to duration of a certain number of complete cycles, and it is desired to produce an exposure corresponding to an odd number of half-cycle periods, the first half-cycle voltage will be dropped by the impedance means 306 to ineffectuate output from the X-ray tube, the diode 310 will permit the second halfcycle to pass to the primary winding 19 at full voltage for effective X-ray production, and closure of the relay switch 313 within the second half-cycle period will enable subsequent numbers of full cycles to pass to such winding without voltage drop until energization of the X-ray tube is terminated by such circuit means. For example, if an exposure corresponding to three half-cycle periods are desired, with the switch 303 closed, the circuit means 300 will be set for an exposure time corresponding to two complete voltage cycles, and the first half-cycle introduced to the impedance means 306 inelfectuates the X-ray production for such period, with resultant effective production of X-rays for three of the four half-cycle periods called for by circuit means 300. For a five halfcycle-period exposure, the circuit means 300 will be set to produce six half-cycles, or three full cycles, and the damping provided by the impedance means 306 will result in a net period of etfective X-ray generation corresponding to the duration of five half-cycles, etc.

If the relay means 312 is capable of closing within a half-cycle period of energization precisely at the end of such half-cycle period, then the diode 310 might be dispensed with. Under these circumstances energization of the winding 315 of the relay means can be operated responsively to the output of circuit means 300 through the medium of output leads 301 and 302 and the transformer 316 as well as

leads

318 and 319 which may be connected directly to such Winding. The presence of the diode 310, however, eliminates need for a precise operation of the relay means 312 by enabling it to establish closure of its switch 313 any time within the second halfcycle period. To this end a rectifier bridge 321 is interposed between the relay winding 315 and the transformer 316 to enable unidirectional cur-rent flow through such winding for the entire full-cycle period. With this arrangement the relay means 312 need only be capable of closing Within A of a second and after a lapse of a first halfcycle period of of a second.

From the foregoing it will be apparent that there has been provided an X-ray apparatus wherein the high tension transformer is energized for selected numbers of consecutive alternating current voltage cycles Which always commence with a particular polarity and end with the opposite polarity and in which selected energization of the X-ray tube can be obtained in terms of selected numbers of consecutive half-cycle periods. When even numbers of half-cycle X-ray exposure periods are desired, the first-half-cycle-expostire-eliminating circuitry will be disabled by such as closure of the manual switch 303, which shorts out the impedance means 306, diode 310 and switch 313 to permit circuit means 300 to have full control of X-ray tube energization.

Since numerous changes may be made in the abovedescribed apparatus and different embodiments of the invention may be made without departing from the spirit thereof, it is intended that all matter contained in the foregoing description or shown in the accompanying drawings, shall be interpreted as illustrative and not necessarily in a limiting sense.

We claim as our invention:

1. X-ray apparatus comprising an X-ray tube, full-wave rectifier means in series with such tube, a high tension transformer having a secondary winding means connected in series with said rectifier means and having a primary winding, X-ray tube energization control circuit means operable to produce a series of selected numbers of consecutive alternating current voltage cycles which always commences with the same polarity and ends with the opposite polarity, and selectively operable means including impedance means and pulse-damping-control means controlling electrical communication between said circuit means and said primary winding operable to reduce primary winding current during the first half-cycle voltage pulse produced by said circiut means to substantially inetfectuate generation of X-rays while preserving production of a residual flux polarity condition in said trans former and thereafter permitting full primary winding current during subsequent consecutive half-cycle voltage pulses produced by such circuit means.

2. The X-ray apparatus as set forth in claim 1, wherein the impedance means is paralleled by a diode which permits the second half-cycle voltage pulse from the circuit means to reach the primary winding of the high tension transformer in bypass of such impedance means for effective X-ray generation by the X-ray tube, and said pulsetlamping-control means establishes connection of the out- 5 6 put of the aforesaid circuit means with the primary wind- References Cited ing of the high tension transformer in bypass of both the UNITED STATES PATENTS diode means and the impedance means during the second consecutive half-cycle voltage pulse from said circuit g g g g means and maintains Such pass connection during all 5 3079506 2/1963 Gages subsequent consecutive half-cycle voltage pulses.

RALPH G. N ILSON, Primary Examiner.

A. L. BIRCH, Assistant Examiner.