US3925672A

US3925672A - X-ray diagnosis apparatus with a directly heated X-ray tube

Info

Publication number: US3925672A
Application number: US468640A
Authority: US
Inventors: Eickhardt Soder; Ulrich Grassme
Original assignee: Siemens AG
Current assignee: Siemens AG
Priority date: 1972-12-06
Filing date: 1974-05-10
Publication date: 1975-12-09
Anticipated expiration: 1992-12-09

Abstract

An X-ray diagnosis apparatus wherein the filament of the X-ray tube is connected to a tapping point of the secondary winding of the high-voltage transformer and provided with a time switch for determining the exposure time, is particularly characterized by a blocking circuit connected with the time switch and releasing it when the X-ray tube current, after the switching on of the X-ray tube, exceeds a predetermined amount. The blocking circuit contains a device for determining the change in the phase displacement between the primary current of the high-voltage transformer and the line voltage during the rise of the X-ray tube current.

Description

States Patent Seder et a].

X-RAY DIAGNOSIS APPARATUS WITH A DIRECTLY HEATED X-RAY TUBE Inventors: Eickhardt Soder, Uttenreuth; Ulrich Grassme, Numberg, both of Germany Assignee: Siemens Aktiengesellschaft, Munich,

Germany Filed: May 10, 1974 App]. No.: 468,640

Related U.S. Application Data Continuation-impart of Ser. No. 313,094, Dec. 6, I972, abandoned.

U.S. Cl, 250/402; 250/421 Int. Cl. H05G 1/10 Field of Search 250/402, 408, 413, 415,

References Cited UNITED STATES PATENTS 7/1939 Scaife 250/413 Dec. 9, 1975 Primary Examiner-Craig E. Church Attorney, Agent, or FirmRichards & Geier [57] ABSTRACT An X-ray diagnosis apparatus wherein the filament of the X-ray tube is connected to a tapping point of the secondary winding of the high-voltage transformer and provided with a time switch for determining the exposure time, is particularly characterized by a blocking circuit connected with the time switch and releasing it when the X-ray tube current, after the switching on of the X-ray tube, exceeds a predetermined amount. The blocking circuit contains a device for determining the change in the phase displacement between the primary current of the high-voltage transformer and the line voltage during the rise of the X-ray tube current.

5 Claims, 8 Drawing Figures Sheet 1 of i US. Patent Dec. 9, 1975 N Fi .1.

AAA ANNNW'M US. Patent Dec. 9, 1975 Sheet 2 of 2 3,925,672

X-RAY DIAGNOSIS APPARATUS WITH A DIRECTLY HEATED X-RAY TUBE This application is a continuation-in-part of a US. Pat. application filed Dec. 6, 1972, Ser. No. 313,094, now abandoned.

This invention relates to an X-ray diagnosis apparatus wherein the filament ofthe X-ray tube is connected to a tapping point of the secondary winding of the highvoltage transformer, and wherein a time switch is pro 1 vided for determining the time of exposure.

X-ray diagnosis apparatuses of this type generally contain small X-ray generators, and are used particularly for making exposures of teeth. When high voltage is applied, there is a great heating of the heating wire of the X-ray tube. The X-ray tube is therefore described as directly heated. There is the drawback that the image-producing X-rays appear only after a certain delay, namely, after the reaching of a certain cathode temperature and thus a certain X-ray tube current, thus, after the passing of a certain preliminary time. The time switch must, therefore, switch on an exposure time, which is composed of this preliminary time and the actual exposure time desired for the highly heated 2 X-ray tube. Since the preliminary time period depends strongly upon the net voltage, it'is difficult to consider it, and it cannot be determined precisely. The result is that, in many cases, the best film darkening is not produced, particularly for short exposures. The preliminary time period depends not only upon the net voltage, but also upon the shape and thickness of the filament, so that these factors mustalso be taken into consideration.

An object of the present invention is to provide an X-ray diagnosis apparatus of the described type wherein the preliminary time period is automatically taken into consideration, so that only the actual desired exposure time must be set in the time switch. Thus, the actually desired exposure time will be maintained more precisely than in known X-ray diagnosis apparatuses.

Other objects will become apparent in the course of the following specification.

In the accomplishment of the objectives of the present invention, it was found advisable to provide a blocking circuit connected with the time switch and releasing it when the current of the X-ray tube exceeds a predetermined amount after the X-ray tube has been switched on. The blocking circuit contains a device for determining the change in the phase displacement between the primary current of the high-voltage transformer and the line voltage during the increase of the X-ray tube current. Thus, in the apparatus of the present invention, the exposure time set at the time switch begins to run only after the X-ray tube current and thus the ray intensity have reached a predetermined value. The preliminary time period, which corresponds to the highest heating time of the heating wire, is considered automatically.

The invention will appear more clearly from the following detailed description when taken in connection with the accompanying drawing, showing, by way of example only, a preferred embodiment of the inventive idea.

IN THE DRAWING FIG. 1 is a circuit diagram of the X-ray diagnosis apparatus of the present invention.

FIGS. 2 to 7 are curves showing the voltage conditions at different locations of the X-ray diagnosis apparatus of FIG. 1.

FIG. 8 is a circuit diagram showing the switching connections of the parts shown in FIG. 1.

The X-ray diagnosis apparatus of the present invention shown in FIG. 1 includes a high-voltage transformer 1 having a primary wiring 2 which can be connected to a line and a secondary winding 3. The sec- 0 ondary winding has a part 4 transmitting the anodecathode voltage and a part 5 serving as the heating voltage of an X-ray tube 6. For connection of the primary winding 2 to the line serves an exposure relay 7, which can actuate a switch 8. The relay 7 is operated by an exposure releaser 9 and a switch 10 constituting a part of a time switch 11. A resistance 12 is connected in series in the primary circuit of the high-voltage transformer l.

The resistance 12 provides a signal which corresponds to the current in the primary circuit of the highvoltage transformer 1. This signal is transmitted to a pulse shaper 13. The outlet of the pulse shaper 13 is connected to an inlet of a comparator 14. The other inlet of the comparator 14 receives a signal from a pulse shaper 15, which corresponds to the running of the net voltage. To produce this signal, a phase shifter 16 is connected in front of the pulse shaper 15.

The outgoing signal of the comparator l4 actuates an integrator 19, which operates through a threshold value switch 20 upon the time switch 11 so as to block it or to release it.

The operation of the X-ray diagnosis apparatus of the present invention shown in FIG. 1 is described hereinafter with reference to curves shown in FIGS. 2 to 7.

FIG. 2 shows the time course of the current in the primary circuit of the high-voltage transformer 1, and thus also the ingoing signal of the pulse shaper 13 after the closing of the exposure releaser 9 and when the switch 10 is closed. Up to the time period t1, the high-voltage transformer 1 is operated practically idle, since, up to that point, there is no flow of X-ray tube current. After the time period :1, the cathode of the X-ray tube 6 is heated to such an extent that the X-ray tube current begins to flow. Up to the time period t1, the positive and the negative half waves of a period of the primary current are equal in covering, while, after the time period t1, the positive half wave assumes a different form relatively to the negative half wave due to the valve action of the X-ray tube 6. The pulse shaper 13 supplies rectangular impulses of constant amplitude, the duration of which is equal to the duration of the positive half waves of the primary current. The voltage at the inlet 17 of the comparator 14 thus runs in accordance with FIG. 3.

FIG. 4 shows the extent of the outgoing voltage of the phase displacer 16. This outgoing voltage corresponds to the network voltage as far as the amplitude is concerned, while its phase location is so set that its positive half waves and its negative half waves coincide in time with the positive and negative half waves of the primary current when the high-voltage transformer 1 is operated idly. The pulse shaper 15 forms, out of its incoming signal, rectangular impulses, the amplitude of which is equal to the amplitude of impulses shown in FIG. 3, and which coincide in time with the positive half waves of the outgoing voltage of the phase shifter 16. These impulses are shown in FIG. 5.

The comparator 14 compares the impulses shown in FIG. 3 at its inlet 17 with the outgoing impulses of the pulse shaper 15 at its inlet 18, i.e., it compares the impulses of FIG. 3 with the impulses of FIG. 5. It produces an outgoing signal, while the voltage at the inlet 17 differs from the voltage at the inlet 18. Until the time period t1, the impulses fall together precisely, so that there is no outgoing signal at the outlet of the comparator 14. After the X-ray tube current begins to flow, there is a phase displacement between the impulses of FIG. 3, which correspond to the primary current of the highvoltage transformer 1, and the impulses of FIG. 5, which correspond to the line voltage. Then the outgoing voltage of the comparator 14 runs as indicated in FIG. 6.

The integrator 19 sums up, due to the rectifier 21, only the positive outgoing impulses of the comparator 14. Its outgoing voltage is shown in FIG. 7. When this outgoing voltage reaches a predetermined value, the sweep circuit 20 tips over and causes the release of the time switch 1 1, so that, from then on, the exposure time set at the time switch 11 begins to run. After the completion of the exposure time, the X-ray diagnosis apparatus is switched off by the switch 10.

The operation of the X-ray diagnosis is apparatus of the present invention shown in FIG. 1 can be summarized as follows:

The exposure time is set at the time switch 11. However, this time does not start to run as yet after the closing of the exposure releaser 9. The time switch 11 is freed, and the exposure time begins only when the phase shifting between the current in the primary circuit of the high-voltage transformer and the network voltage and thus the X-ray tube current have reached a predetermined value which is characteristic for the appearance of image-producing X-rays. The preliminary time which passes until the X-ray tube current has reached its predetermined value is variable, namely, it is automatically adapted to the prevailing network voltage and the prevailing heat wire data. Thus, only the actually desired exposure time needs to be set at the time switch 11.

A different embodiment of the subject matter of the present invention consists in that the phase displacements between the network voltage and the primary current are determined by a coincidence reel receiving impulses which characterize the zero passages of the primary current and the line voltage, and which are suitably shifted relatively to each other by a constant phase angle, so that they cover each other when the desired X-ray current flows. Then the time switch is released by the outgoing signal of the coincidence reel.

In the embodiment of the present invention shown in FIG. 1, the switch 30 is closed by the outgoing signal of the sweep circuit 20 when the time switch 11 is freed. At that time period, the relay 31 is excited, which bridges over with its contact 32 the resistance 12. Thus, the resistance required for X-ray apparatuses for damping the blow of the switched-in current can be identical with the series resistance 12, and the voltage at the resistance 12 does not lower the X-ray dose during the actual exposure time.

FIG. 8 shows that the pulse shaper 13 contains a transistor 35, which is connected by a resistance 36 to the feed voltage source. Voltage taken from the resistance 12 is supplied between its base and emitter. The transistor 35 is a switch transistor which is switched over into its conducting condition with a very small incoming voltage of the size of 0.6 v. and then supplies an impulse of 24 v. at the outlet 37 until the incoming voltage again drops below the threshold of 0.6 v. Thus, with the switch transistor, it is also possible to change the current signal according to FIG. 2 into rectangular impulses according to FIG 3. These rectangular impulses are transmitted to the inlet 17 of the comparator 14.

The phase shifter 16 includes a series connection consisting of a resistance 38 and a condenser 39, from which the outgoing voltage is taken. This outgoing voltage is supplied through a diode 40 to a switch transistor 41 in the pulse shaper 15. The switch transistor 41 is fed through a resistance 42. As shown in FIG. 4, the outgoing voltage of the phase shifter 16, when without lead, is in equal phase with the incoming voltage of the pulse shaper 13. The switch transistor 41 is also switched at a threshold voltage of 0.6 v. to its conducting condition, at which a 24 v. impulse is provided at the outlet 18. Thus, the outgoing voltage of the pulse shaper 15 extends according to FIG. 5, since the switch transistor 41 switches in the range of the zero passage of the incoming voltage, namely, at 0.6 v.

The comparator 14 includes an operation amplifier 43 having a minus inlet receiving the signal at inlet 17 through a coupling resistance 44, and a plus inlet receiving the signal at inlet 18 through a coupling resistance 45. The operation amplifier 43 is rearwardly coupled through a resistance 46 and strengthens the difference between the signals at the

inlets

17 and 18, namely, it supplies, through the diode 21 to the integrator 19, a signal which corresponds to the difference between the signals at the

inlets

17 and 18.

The integrator 19 consists of a resistance 47 and a condenser 48, at which the integrated outgoing voltage is taken according to FIG. 7. The incoming voltage of the integrator 19 runs according to FIG. 6 (positive impulses).

The sweep circuit switch 20 includes an operation amplifier 49, the plus inlet of which is subjected to a preliminary voltage U1 and is connected by a coupling resistance 50 with the outlet. Therefore, the signal tips over at the outlet of the operation amplifier 49 when the voltage U1 is reached by the voltage at the minus inlet. The minus inlet is coupled by a coupling resistance 51 to the outlet of the integrator 19. As soon as the sweep circuit switch 20 tips over, a charging of a condenser 52 in the time switch 11 takes place through a charging resistance 53 and a diode 54. A sweep circuit switch connected behind the condenser 52 in the time switch 11 consists similarly to the switch 20 of an operation amplifier 55 having a pre-voltage U2 at the plus inlet. Coupling

resistances

56 and 57 are provided for the operation amplifier 55.

After the voltage at the outlet of the operation amplifier 49 has tipped over, the set photographing time begins to run at the time switch 11 by means of the charging resistance. As soon as the voltage at the minus inlet of the operation amplifier 55 has reached the pre-voltage U2, a relay 58 is excited through a switch transistor 59 and actuates the contact 10.

It is thus apparent that the specific photographing time period is set at the charging resistance 53, and that this time period starts running only when the sweep circuit switch tips over, namely, when the phase shifting between the primary current and the network voltage has reached a predetermined value.

In the illustrated X-ray diagnosis apparatus, the heating current and the X-ray tube voltage at the X-ray tube 6 are switched on at the same time. This is important for the present invention since, only in that case, the X-ray tube current rises after the closing of the contact a, namely, after the switching of the high-voltage transformer 1, so that it is not immediately available in its full desired amount. X-rays are obviously produced immediately after the closing of the contact a 8. However, the photographing time set at the time switch 11 by means of the resistance 53 begins to run only when the X-ray tube current has reached a predetermined value. This takes into consideration that the time directly after the closing of the contact 8, during which the X-ray tube current still rises, and therefore, the X-rays are still very weak, is not considered as the photographing time by the time switch 1 1.

FIG. 1 does not show a high-voltage rectifier. The Xray tube 6 thus takes care by itself of the outgoing voltage of the high-voltage transformer. However, within the scope of the present invention, a high-voltage rectifier can be connected behind the winding member 4.

What is claimed is:

1. An X-ray diagnosis apparatus, comprising an X-ray tube of the directly heated type having a filament, a high-voltage transformer connected to a line and having a first secondary winding, connected to the anode and the cathode of the X-ray tube and a second secondary winding connected to said filament, a time switch, and a blocking circuit connected with said time switch and said transformer for releasing said time switch when the anode current of said X-ray tube has reached a predetermined value after the X-ray tube is switched on, said blocking circuit having means for detecting the change in phase displacement between the primary current of said transformer and the line voltage during a rise in the current of the X-ray tube.

2. An X-ray diagnosis apparatus according to claim 1, wherein the last-mentioned means comprise a comparator providing an outgoing signal corresponding to the difference between the prevailing phase displacement and the phase displacement when said transformer runs idle.

3. An X-ray diagnosis apparatus according to claim 2, wherein the last-mentioned means further comprise two pulse shapers, said comparator having two inputs connected to separate pulse shapers, said pulse shapers delivering to said inputs rectangular impulses of the same and constant size, the duration of which corresponds to the duration of a half wave of the primary current and the duration of the half period of the line voltage, the last-mentioned means further comprising means shifting said rectangular impulses relatively to each other by a phase angle which causes them to coincide in time when said transformer runs idle.

4. An X-ray diagnosis apparatus according to claim 3, wherein said comparator produces, during each period of the line voltage, an outgoing impulse according to the phase displacement between the rectangular imoutgoing signal has been reached.

Claims

4. An X-ray diagnosis apparatus according to claim 3, wherein said comparator produces, during each period of the line voltage, an outgoing impulse according to the phase displacement between the rectangular impulses at its two inputs.

5. An X-ray diagnosis apparatus according to claim 4, wherein said detecting means further comprise an integrator and a threshold switch connected in series with said comparator, said integrator receiving the outgoing signal of said comparator, said threshold switch releasing said time switch when a limiting value for the outgoing signal has been reached.